Introduction

Social theories of practice have been gaining ground across the social sciences and in the area of health and medicine. As a result, there is a growing body of work on topics such as smoking, drinking, gambling, obesity and oral health that is informed by this tradition (Blue et al., 2016; Cohn 2014; Maller 2015; Blue et al. 2021; Durey et al. 2021; Nyemcsok et al. 2023). For many authors, the use of a ‘practice lens’ involves little more than a focus on contextual factors that shape routinised behaviour but for others, practice theory represents a distinctive and powerful method of framing and conceptualising the doings and sayings of which social life is made.

According to Hui et al. (2017), strong interpretations of practice theory depend on positioning social practices, rather than individual agents or social structures, at the centre of analysis and enquiry. Despite differences of emphasis, those who subscribe to this view conclude that practices constitute the ‘site of the social’ (Schatzki 2002) and that they represent the ‘basic domain of study of the social sciences’ (Giddens 1984: p. 2). This goes hand in hand with a series of related commitments.

One is that practices consist of interwoven sayings and doings that exist across space and time and that have something of a life of their own. Whilst practices are reproduced and also transformed by those who ‘carry’ them (Reckwitz 2002), one feature that sets practice theories apart from others is that practices, and not practitioners are the object of study.

Second, proponents of practice theory generally agree ‘that practices link to form wider complexes and constellations’ (Hui et al. 2017: p. 1). In describing cross-cutting processes like those of merger, hybridisation and circulation (Shove 2023) and in analysing the formation of ‘large’ social phenomena (Schatzki 2016), practice theorists have begun to identify some of the connections involved. This is important work in that it demonstrates the relevance of practice theories for conceptualising and understanding spatially and temporally situated interactions and potentially global trends.

Third, and since practices do not exist in isolation, developments in any one domain are bound up with the emergent and interwoven dynamics of the total ‘nexus’ of practices. A further related conclusion is that past and present complexes of practice ‘prefigure’ the future, making some trajectories more likely than others (Schatzki 2010). More concretely, current combinations of infrastructures, material arrangements, competencies and ideas (Watson and Shove 2022) have a bearing on what happens next.

These few paragraphs capture some of the defining features of practice theory, but they do not, of themselves, reveal much about the role of non-humans, or about the part that microbes play in constituting, reproducing and transforming practices across space and time. One way forward is to revisit ideas about the material aspects of practice, broadly defined. According to Reckwitz (2002) and Shove et al. (2012) social practices depend on the active integration of diverse elements, including materials, meanings and forms of competence. In theory, materials might include bacteria and viruses—the distribution and extent of which clearly figure, recursively, in the lives of individual practices and combinations of them. This interpretation has much in common with Schatzki’s suggestion that ‘Practices and bundles arise, persist, and dissolve principally through human activity, though not only this: actions of nonhumans, as well as events and processes that befall nonhumans, also contribute to the development of practices and bundles.’ (Schatzki 2012: p. 9). Although they have different ideas about the status of material elements and arrangements, Reckwitz (2002), Shove et al. (2012) and Schatzki (2012) agree that non-human interactions, processes and patterns of development and change are folded into the dynamics of social practice.

More abstractly, practice theories, post-humanist materialist studies and multi-species ethnographies decentre human agency and in so doing open the way for conceptualising more-than human contributions to the reproduction and transformation of daily life (Maller and Strengers 2019). In taking up this idea, Wakefield-Rann et al. argue that social practices (including, for example, of building design, domestic cleaning, and urban life) engender and are intwined with human-microbial relations (e.g. the ‘microbiome’ of the home) (2019, 2020a, 2020b, 2021a; b). Maller (2023) has also called for new approaches to ‘reset’ negative discourse and research and to understand the prevalence and role of microbes in environments on and within human bodies.

In this paper we build on these approaches, elaborating on what we take to be the central features of practice theory in order to describe and investigate the emergence of human-microbial relations and what Ingold and Pálsson refer to as ‘biosocial becomings’ (2013).

In the introduction to an edited collection entitled Biosocial Becomings, Ingold (2013) writes about the always changing configuration of the biosocial world. Having dissolved traditional interpretations of the biological on the one hand and the social on the other, he contends that the social is biological just as the biological is social. In his words:

That life unfolds as a tapestry of mutually conditioning relations may be summed up in a single word, social. All life, in this sense, is social. Yet all life, too, is biological, in the sense that it entails processes of organic growth and decomposition, metabolism and respiration, brought about through fluxes and exchanges of materials across the membranous surfaces of its emergent forms. It follows that every trajectory of becoming issues forth within a field that is intrinsically social and biological, or in short, biosocial. (Ingold 2013: p. 9).

In essence, Ingold argues that we need ‘to think of humans, and indeed of creatures of all other kinds, in terms not of what they are, but of what they do.’ (Ingold 2013: p. 8) This is a crucial move in that it prompts further questions about how fluxes, exchanges and mutually conditioning relations are constituted in practice.

These are not entirely new topics and as outlined below, there are different ways of thinking about the intersection, or unity, of biological and social processes. Three examples give a sense of this diversity.

In the area of urban ecology, it is common to discuss the relation between ‘human-made’ phenomena, such as cities, road networks, sewerage systems, buildings and related flows of energy, waste and water. According to Hård and Misa (2008), urban networks constitute the conditions of modernity, enabling interconnected sets of practices on which contemporary ways of life depend. As is obvious, these same arrangements configure the environments in which non-humans (from animals through to plants and microbes) also exist, and the settings in which multiple species encounter each other.

Some go further, suggesting that practices, such as plants, change the ‘soil in which they live and sometimes even the climate’ (Odling-Smee et al. 1996: p. 642). In her book The Mushroom at the End of the World: On the Possibility of Life in Capitalist Ruins, Tsing (2017) takes up this theme, arguing that interactions between humans and non-humans are marked by and are also constitutive of the development of a particular form of capitalist society, and of related fungal (and other) ecologies. Tsing’s account of the very specific conditions in which matsutake mushrooms live and the commercial and economic practices that have grown up around them is not just a story of how and where fungi and people interact. It is also a tale of mutual adaptation (of mushrooms and of encounters with them) and of far-from accidental exposure mediated through social practices of consumption, marketing, distribution and exchange as these unfold on a global scale.

Multispecies ethnographers like Kirksey and Helmreich (2010) point out that the tendency towards ‘human exceptionalism’ obscures important aspects of interchange within the complex and unbounded ecologies in which organisms and microbes evolve. In focusing on different types of exchange, authors like Atchison (2018), Brives et al. (2021), Helmreich (2009) and Yong (2017) bring questions of power into view, arguing that deliberate efforts to manage the lives of plants and animals through cultivation and breeding are expressions and outcomes of unequal relations between human and non-human beings. This is, of course, only part of the story in that plants, microbes and other living non-humans respond and react, creating new problems and opportunities locally and sometimes on a global scale.

These are all useful contributions but, with the exception of Tsing, they tend to reproduce rather than overcome the biological-social divide. One response, and one way of escaping this trap, is to develop a strong version of practice theory capable of explaining and accounting for the details of biosocial becoming. This depends on making three related moves. The first is to show how doings and sayings combine and how categories and forms of knowledge are enacted in practice. The second is to show how these enactments combine and in combination, shape the social and material worlds that we, and a host of other living beings constitute and share. The third is to situate human and non-human interactions within and as part of a changing nexus of practices.

In working through these steps with the help of two worked examples we argue that social practices, and complexes of them (past and present) are woven into the lives of all manner of creatures (and vice versa). As already mentioned, practices consist of sayings and doings, but they are not simply or uniquely defined by people. The types of interaction that we describe are thus not between humans (as bounded organisms) on the one hand, and microbes, on the other. Instead, our point is that social practices engender and are outcomes of multiple habitats and microbiomes the dynamics of which, constitute processes on which forms of biosocial becoming depend.

For some practice theorists, engaging with the microbial and animal world and with the biological aspects of human life might appear to undercut the ‘social’ and historical analysis of culture and organisation, and open the way for a form of natural determinism. For others, including biologists, new materialists and multi-species ethnographers, our emphasis on the layering of categorisation and cohabitation, and our focus on the integrative role of social practice might seem to privilege aspects of human life over and above the biological and material processes of the living world. Rather than falling into one or another of these positions our contention is that focusing on practices themselves, rather than on the actions of practitioners or microorganisms, provides a way of describing the biological and the social in a single frame and of analysing moments and processes of biosocial development, as these vary and change across space and time.

In the following section, “Categories and their consequences”, we describe the recent history of gastric ulcer disease as a means of demonstrating how one particularly significant distinction—between communicable and non-communicable disease—is inscribed in treatments and responses, the details of which are important for the distribution and flourishing of Helicobacter Pylori (H. Pylori), and for where, when and how bacteria and practices evolve together.

In the next section, on “Cohabiting and mutual conditioning”, we take this analysis further, showing how categories-and-related-practices constitute habitats and interactions around which recursive processes of mutual adaptation (between microbes and organisms) unfold and extend across space and time. In this part of the paper, we suggest that strong versions of practice theory allow us to show how categories and discursive distinctions are reproduced in forms of doing and being, the details of which are crucial for the distribution and development of microbial and other forms of life.

Finally, in the section on “Practices as sites of biosocial becoming: implications for research and policy”, we elaborate on the theoretical and practical significance of conceptualising practices (and complexes of them) as sites of biosocial becoming.

As promised, our first step is to consider the close-coupled relation between sayings and doings on the grounds that every day and professional practices depend on both, and on the basis that histories of ideas (in biology, medicine, and public health) are enacted and in various ways, reproduced and materialised in multiple forms of human and microbial cohabitation.

Categories and their consequences

The conclusion that medical, political, and everyday languages constitute the world they describe is well established in science and technology studies and social theory (e.g. Bowker and Star 2000; Goodwin 1997; Hanson, 1965). It is also important in the medical field, and amongst those who cite Foucault’s earlier work (e.g. [1961; 1964] 2001 and [1963; 1973] 2012) on the power of ‘medical discourse’ and on how interpretations of the body ‘shaped the way it was seen, described and acted upon’ (Petersen and Bunton 1997: p. 5). As O’Malley and colleagues point out (O’Malley 2007; Hooks and O’Malley 2020), concepts and categories do not develop aside from dominant ideas and agendas within the biological sciences. In this field, as in others, judgements about method, observation and analysis mirror ideas about causality, explanation and change. By implication, lines of enquiry are products of their time, as are what come to be pressing debates, for example, about the origins and distribution of disease and/or the efficacy of treatment. To give just one example, Meloni describes what amounts to a paradigm shift in how the body has been understood. When ideas about humors held sway, the body was seen as a ‘porous’ entity, connected to and in part defined by fluxes and material flows, including those relating to diet and climate. Subsequent interpretations, many of which remain important today, view the body as a discrete organism, bounded by the skin. Ideas developed in what Meloni refers to as the ‘post-genomic’ era challenge some of these certainties, identifying new ways in which bodies and environments interact (Meloni 2018).

It is undoubtedly important to track what amount to paradigm shifts within histories of biology, but we need to go further if we are to show how categories are reproduced in the lives of microbes, bacteria, and complex organisms. Worboys’ (2000) Spreading Germs is an intriguing illustration of what this might involve. In this book, Worboys documents the practical implications of changing ideas about bacteria and germs, in the household, in the details of having a bath, and in the structure of professional and medical life as well. As he explains, germ-based theories challenged previously dominant notions of permeability, humoral balance and flow and introduced new distinctions between the body and its environment. In effect the world beyond the body was treated as a separate sphere. Rather than being viewed as something that was in continuous interaction with human biology, ‘the environment’ occupied a new role in the background, and as the place in which distal risk factors or remote triggers (like stressors or wider determinants of health like poverty and disadvantage) reside. As Meloni (2019) confirms, this way of thinking is now deeply embedded in contemporary science, medicine and public health, in the design of clinical pathways, in training programmes, in the difference between public health and environmental health and in the pervasive and powerful divide between what are classed as non-communicable diseases (that arise within the body but that extend beyond it by virtue of being linked to lifestyle, genetics, etc.), and those that are carried from the environment into the body by contagious viruses or bacteria. Although some authors question this split, arguing that non-communicable diseases spread through processes of ‘social contagion’ and that lifestyles and patterns of exposure are often linked (for example, Seeberg et al. 2020) these categories remain hugely important—governing the terms in which heath and illness are understood and infusing practices of treatment and prevention.

This is relevant in that ‘the sayings involved…’ in the conduct of social practices and in relations between them should ‘… be resolutely treated as components of… bundles and that these bundles be taken as the entities in which social phenomena consist.’ (Schatzki 2017: p. 136). In effect, categories and distinctions are integral to the lives of practices, and thus to the configuration of coexisting microbial communities. There are many instances of how concepts of the body and related interpretations of illness have effect, but the history of gastric ulcer disease and its treatment is an excellent example of how sayings and doings combine in practice, and of how practices and microbial relations interact.

For many years ‘it was a long-standing belief in medical teaching and practice that stress and lifestyle factors were the major causes of peptic ulcer disease.’ (Ahmed 2005: p. 1). This began to change in the early 1980s when Marshall and Warren, two Australian researchers, identified Helicobacter Pylori (H. Pyori—a bacterium that colonises the human stomach) as a cause of gastritis, peptic ulcer disease and gastric cancer. Even though Marshall and Warren’s research appeared to show that H. Pylori was responsible for 90% of duodenal ulcers and up to 80% of gastric ulcers, ‘the clinical community… met their findings with scepticism and a lot of criticism and that’s why it took quite a remarkable length of time for their discovery to become widely accepted.’ (Ahmed 2005: p. 1). In 1985, Marshall went so far as to experiment on himself, undergoing a gastric biopsy to demonstrate that he did not have ulcers or the bacterium, before deliberately infecting himself in an attempt to prove the connection between H. Pylori and gastric illness. In 2005, over twenty years later, Marshall and Warren were awarded the Nobel Prize in Physiology or Medicine for their work, which has led to changes to therapeutic regimes and a steep decline in all H. Pylori-related diseases.

There is still some debate about whether H. Pylori, alone, really does cause gastric disease (Lynch et al. 2019) but there is no question about the fact that gastric ulcers switched sides: first being defined as manifestations of non-communicable disease and then as an outcome of bacterial infection (i.e. as a communicable disease). There is also no doubt that this re-designation was hugely significant for research and treatment. Attention turned from the patient’s lifestyle to the life of H. Pylori and, more specifically, to longer-term interactions between bacteria, human activity, and human biology as that is shaped by diet, longevity, and sanitation. Following what amounts to an about turn in categorisation, clinical discourse, and treatment, H. Pylori has become one of the best-studied instances of pathogen biology, even resulting in a dedicated journal, Helicobacter.

Amongst other things, studies have shown that H. Pylori does not thrive just anywhere. According to Graham (2014), there is some evidence that it has only recently declined in some south-east Asian countries ‘where rapid development, improved sanitation, diet and methods of food preservation have occurred.’ (5198–5199). In addition, and as hinted at above, there is further evidence to suggest that it is misleading to focus on H. Pylori in isolation. What matters is how this bacterium has effect within a wider ecology and how its effects are mediated by a multitude of other social-material and biosocial relations. This points to a more subtle and also more complex process in which changes in that wider ecology matter for the manifestation and prevalence of disease. In Graham’s words: ‘Overall, the current data support the concept that the pattern of gastritis is most related to changes in host, bacteria, and environmental interaction, which is dominated by environmental changes likely diet.’ (2014, p. 5199).

There are two points to take from this. One is that categories and discourses are crucial for treatments and interventions, and for the reproduction of settings in which bacteria do and do not thrive. Over time, shifts in the sort of environmental interaction that Graham describes matter for the life of H. Pylori and for the settings in which it does, and does not, interact with co-existing microbes and organisms. Second, the re-designation of gastric ulcers as outcomes of H. Pylori and as a communicable rather than a non-communicable disease opened new lines of enquiry about how ‘communication’ happens with and alongside practices that have a bearing on populations and concentrations of microbes within the human body and beyond. Not surprisingly the course of scientific and medical research into gastric ulcers changed as paradigms shifted. This is important not just because it shows that biological knowledge has a social and political history. That is so, but as Landecker observes, such histories also matter for how living beings interact and co-evolve. Landecker does not write about H. Pylori and gastric ulcers but in her 2016 article, ‘Antibiotic Resistance and the Biology of History’ she describes the global development of antibiotic resistance as part of an also global explosion in the production and use of antibiotics from the 1940s onwards. This example underlines the broader point that there is a ‘physical registration of human history in bacterial life’ (2016: p. 19). In other words, human histories, including histories of scientific knowledge and categorisation are inscribed in ‘bacterial life’, including the life of H. Pylori.

As outlined above, the re-designation of what had been thought of as a non-communicable disease reconfigured methods of treatment and sites of encounter, adding to a host of parallel developments (for instance in diet and longevity) that reconfigured the distribution of H. Pylori and its part in human health/disease. To reiterate, interventions that framed H. Pylori as a causal agent modified the ecology of the bacterium and the sites in which it did and did not persist. As such they modified the ‘career’ of H. Pylori. In taking stock of these developments, it is important to remember that categories, distinctions, and attributions of responsibility, are products of an ongoing history of expert and lay discourses that are, of necessity, embedded in, and reproduced through everyday and professional practices. In other words, it is because sayings and doings hang together that they are real in their effects, and real in their impact on the biosocial world.

This far we have used the example of H. Pylori to show how discursive structures and distinctions are embedded in practices, the histories of which have an impact on the lives of the bacteria involved. To go further, and to show how histories of practice are inscribed in biological relations and trajectories we need to elaborate on the recursive ‘dance’ between microbes and practices, not in the abstract but as mediated by organising categories and forms of knowing and understanding. In the next part of the paper, we make use of contemporary examples of antibacterial resistance in order to illustrate relevant and related processes of cohabiting and mutual conditioning.

Cohabiting and mutual conditioning

We start this section with the very well-known story of Penicillin. In 1928 Alexander Fleming returned from holiday to find that the growth of mould on his petri dishes had killed off the bacteria that he had been studying. He published his findings on the properties and effects of Penicillin in the Journal of Experimental Pathology in 1929. His work was taken up by two chemists, Ernst Chain and Howard Florey in the late 1930s. They demonstrated the clinical value of Penicillin and pressed for it to be mass-produced, which it was in 1944. In 1945, Fleming, Chain, and Florey won the same Nobel Prize in Physiology or Medicine that Marshall and Warren would win in 2005 for their work on H. Pylori. At the time, Alexander Fleming knew and noted the potential ramifications of the mass-use of this new antibacterial response. He was particularly concerned about ‘mistreatment’, inadequate doses and misuses. He said, in his Nobel Lecture:

The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant. Here is a hypothetical illustration. Mr X has a sore throat. He buys some penicillin and gives himself, not enough to kill the streptococci but enough to educate them to resist penicillin. He then infects his wife. Mrs X gets pneumonia and is treated with penicillin. As the streptococci are now resistant to penicillin the treatment fails. Mrs X dies. Who is primarily responsible for Mrs X’s death? (Flemming in Davies et al. 2013: p. 23).

In the early 1940s, relatively little was known about exactly how bacteria mutate (now thought to be in three ways: from ‘mother’ to ‘daughter’, sharing DNA by contact with other bacteria and acquiring new genetic material from their environment—Davies et al. 2013: pp. 32–33). However, Fleming recognised that the rate of replication and capacity for mutation meant that bacteria would adapt to protect themselves against anti-microbial treatment. Antibiotics are notfreely available in shops in the UK.Footnote 1 Instead, and as Landecker observes (2016), their prevalence and use varies by country and by region, and changes over time.

Increasingly stringent guidelines about when to prescribe antibiotics tap into an ongoing debate about when medical professionals should prioritise the health of a given patient or the health of future populations (see Gröndal & Holmberg 2021). Beyond inadequate doses (that fail to eradicate harmful bacteria), the repeated use of antibiotic treatment can also reduce the commensal and healthy bacteria that live on bodies (especially in the gut and on the skin), leaving more space for other harmful bacteria to take their place. For example, the (‘over- ‘) use of broad-spectrum anti-microbials is regarded as a major factor in the rise of gut infections like clostridium difficile (Davies et al. 2013: p. 19) and related deaths.

These are generic trends, but it is important to remember that patterns of microbial interaction vary from one setting to another, and that local ecologies are crucial. For example, and as is well known, hospitals are home to distinctive combinations of bacteria and to specialized practices of treatment and infection control. This is relevant in that what become widespread trends arise from and are outcomes of spatially and temporally specific encounters and exchanges, aspects of which are (or become) shared across diverse locations.

These spatial dynamics form part of the interwoven lives of practices and microbes as illustrated by the history of the ‘super-bug’ Methicillin-resistant Staphylococcus aureus (MRSA). Staphylococcus aureus, the bacteria Fleming was investigating when he discovered Penicillin, became Penicillin resistant in the 1950s. In response, Methicillin was developed, but some bacteria became resistant to that as well. Cases of infection ‘peaked’ in UK hospitals in the early 2000s and as Davis et al. (2013: p. 34) explain, efforts to manage this problem varied. Some focused on the search for drugs capable of overcoming the resistant bacteria. Others took a different approach, introducing measures to reduce hospital acquired infection, including reporting regimes and methods of ‘deep cleaning’. Neither of these responses can be seen in isolation, nor can they be detached from national and international restrictions on the use of antibiotics (controls on prescription) and situated practices of cleaning and hand washing, the combination of which has reduced the number of hospital-acquired MRSA infections and transformed the habitats in which they develop, hospital by hospital and across the sector as a whole.

As this example reminds us, interactions between microbes vary depending on infrastructures and institutions and the settings within and through which social practices are configured, distributed and combined. In his ‘History of Helicobacter Pylori, Duodenal Ulcer, Gastric Ulcer and Gastric Cancer’, Graham (2014) arrives at much the same conclusion. He argues that sanitation infrastructures and generic ideas about germs and patterns of food consumption and production, have had reconfigured ‘local’ cleaning practices and the distribution of potentially harmful bacteria within and beyond the human body. This has ‘resulted in changes in the pattern of gastritis producing a change in the manifestation of H. Pylori infections’ and a rapid decline in all H. Pylori related diseases (5191).

In sum, the complexities of cohabitation and mutual conditioning—understood as outcomes of inherently dynamic combinations of practice, always situated in space and time—are such that microbial interactions are marked by unexpected trends and encounters. These are not random, nor can they be separated from dominant understandings and categories, not only of communicable and non-communicable disease, but also of cleanliness, health, risk and contamination.

In elaborating on these interdependences, Wakefield-Rann and colleagues argue that positive and negative interpretations of human-microbial exchange are always in flux, and that trends in production, consumption and practice are such that this flux sometimes occurs on a global scale. In explaining how chemicals and anti-microbials, introduced to homes after the Second World War (for instance, in the form of cleaning products), combine with micro-organisms and human biology to produce adverse health outcomes (2020a, 2020b), Wakefield-Rann contends that ‘the ecology makes the poison’. In her words, modern sanitation and reliance on antibiotics and anti-microbials ‘… have contributed to anti-microbial resistance, inflammatory disease, and the accumulation of pollutants in bodies and ecologies around the world.’ (2021b: p. 123—our emphasis).

Taking a long view, it is obvious that shifts in diet, agriculture and medicine have converged and combined and that people are, on average, living longer than ever before. These same trends and timescales are important for bacterial infections and their effects and for the details of microbial cohabitation. For example, in the nineteenth century the most common consequence of H. Pylori infection (as it is now known) was chronic atropic gastritis. As human lifespans extended, new problems arose, including gastric ulcers, and gastric cancer. The ageing of the population as a whole is part of this dynamic, and thus part of the changing relation between H. Pylori and the human body. It is easy to overlook the historical and geographical specificity of developments like these, but in our view, it is important to recognise that biosocial interactions are defined by practices that unfold across different spatial and temporal scales (Shove 2023).

This far, we have used the examples of H. Pylori and of antibacterial resistance to give a sense of how histories of biology, including the distribution and evolution of bacteria map on to histories of social practice (and vice versa). Along the way, we have shown how categories and forms of knowing are associated with responses and forms of treatment and how related practices, and combinations of them, generate distinctive and spatially uneven interactions between microbes and other organisms, including humans. In making these connections and in putting social practices centre stage we have described some of the processes on which biosocial becomings (Ingold and Pálsson 2013) depend. This is an important theoretical contribution in that it provides a means of bridging between social, biological and medical science and of understanding how public health policy relates to the interactions we have described.

Practices as sites of biosocial becoming: implications for research and policy

It is obvious that microbes (bacteria, viruses) matter for what people do, and vice versa. Within the home, germ theories and related practices have influenced the distribution of infection and the creation of habitats in which microbial communities do and do not survive (Tomes 1999). Habitats are also configured on a larger scale: for example, a recent review by Wegner et al. (2022) in The Lancet, suggests that major alterations in human disease have resulted from demographic and socio-economic changes. That paper shows how ‘zoonoses’ (infections caused by pathogens transmitted from animals to humans) are linked to food production and supply chains, hunting and trade in animals and meat, deforestation and climate change. In these and other such accounts, the ‘birth’ and transmission of viruses and bacteria depends on (malleable) characteristics and modes of communication (airborne, waterborne, sexually transmitted, and so on). Patterns of exposure are important, but as is also widely recognised, the entities involved (microbes, organisms, practices) are not fixed: instead, and as Meloni et al. note, the ‘plasticity’ of microorganisms is such that nothing stays the same (2021).

The strategy of taking social practices to be the central unit of conceptualisation and analysis allows us to go further. It does so in that it positions past and present practies as sites not only of cohabitation and encounter, but of hybridisation, mutual conditioning and transformation. From this perspective, practice theories provide a means of analysing the evolution of the entire ‘holobiont’ (Haraway 2008), and of capturing the recursive relation between multiple sayings and doings and also multiple forms of biosocial flux.

The result is an account that connects what are usually separate theories about the making of scientific and everyday practice (including the categories and concepts involved) and the dynamics of microbial life. As we know, humans are home to billions of viruses and bacteria, the populations of which vary and interact. The suggestion that these interactions are outcomes of social practice dissolves what have become classic distinctions between the body and its environment, and between microbes and the humans with, and within which, they live. This same move generates further lines of enquiry about how past and present practices constitute and transform the holobiont. To go back to the examples discussed above, we used the case of H. Pylori to show how the discursive shift from non-communicable to communicable disease transformed treatments and the ecology of the bacterium itself. Similarly, efforts to manage antibiotic resistance (hand washing, etc.) formed part of an ongoing ‘dance’ between the total plenum of practice and also changing populations of microbes. We used these two examples to show how processes of biosocial becoming are enacted on the ground. In taking up this challenge we drew attention to the interweaving of knowledge and practice and to related patterns of human and microbial cohabitation, all of which change over time. In our view, enquiries of this kind show how biosocial becomings are rooted in the historically and geographically specific dynamics of social practice.

These ideas have the potential to inspire new research at the interface of the social and biological sciences, and to bring practice theories into the realm of microbiology. These are important contributions, but the approach we have described is of more than academic interest. Although this article is not primarily aimed at public health practitioners, the focus on social practice is relevant for understanding when, where and how policy making figures in the exchanges and fluxes we have described.

It is usual to think of policy as something that exists aside from the world it is designed to influence. By contrast, we argue that rather than being beyond the realm of the biosocial, policies like those designed to limit the risks of antibiotic resistance form part of the ongoing flow of doings and sayings. As Canguilhem (1966) notes, medical and public health interventions reproduce understandings of well-being and pathology that are of their time. In this respect they mirror prevalent distinctions—such as that between communicable and non-communicable disease—and dominant interpretations, for instance of whether the body is thought to be essentially permeable or whether the environment is treated as an external ‘factor’. Ideas about bodies and microbes continue to change and as Meloni (2019) suggests, contemporary developments in microbiology and in epigenetics are eroding previously powerful paradigms (O’Malley, 2014; Warin et al. 2016; Meloni 2019).

Who knows how dominant theories will develop but at any one moment public health policies and interventions mirror ideas about disease and about social change. The relation between models of individual behaviour, and the those that attribute responsibility to ‘the environment’ or to a single bacterium is complicated but it is in this space that weak versions of practice theory have found their way into public health policy. As in other sectors including energy (Hampton 2018), water (Kadibadiba et al. 2018) (Pullinger et al. 2013)Footnote 2 and even forestry (Dandy 2016), the language of practice is used as a means of acknowledging the relevance of social norms, environmental factors and cultural contexts, and their impact on what people do. When framed like this, social theories, including practice theories, are readily absorbed into models of behaviour change (Spurling 2014).

Moves of this kind may modify the types of intervention that are proposed but the underlying logic remains one in which public health policies are designed to persuade individuals to make ‘better’ choices for themselves with respect to the spread of contagious and non-contagious disease. In other words, the goal is not that of reconfiguring the entire holobiont or of radically modifying the circumstances in which people and microbes encounter each other.

In our view, stronger theories and interpretations of practice make it possible to see how policy makers do and do not contribute to such encounters, and thus to the flux of biosocial becoming. As Schatzki points out, practices cannot be modified single handedly or by act of will. Instead ‘The best that designers of lives and institutions can do is to create contexts that, as experience and thought show, make certain activities very or more likely’ (Schatzki 2012: p. 22). This argues for a modest view of policy, and for an understanding of the unavoidable indeterminacy of practices and connections between them. Whilst binary categories and distinctions are real in their effects, and whilst behaviour change models matter for patterns of treatment and intervention and for related forms of exposure and cohabitation, their impact is channelled through the already interwoven lives of social practices. Put differently, policy makers can and do make a difference in that they figure in the complex and multidimensional lives of the interconnected practices to which they relate. Although this is not how public health professionals generally see their role, our point is that they – together with those involved in domains like those of transport, energy, education, labour etc. – contribute to the ongoing dynamics of practice, and thus to the sites in which microbes and other living entities interact.

The conclusion that public policies and related discourses, categories and forms of knowledge figure in the lives of social practices, and how they combine and connect, points to a much broader and more central role for social theory. It does so in that it brings many processes and relations into view, beyond the remit of behaviour change, narrowly defined. In describing how sayings and doings combine and how they define and constitute related patterns of human and non-human cohabitation this paper gives a sense of that potential, and of the value of treating practices as central sites of biosocial becoming.