Introduction

The use of leeches to treat soft tissue with congestion in plastic surgery gained over the last decades a sort of renaissance even with the parallel further development of micro- and supermicro surgery. Main indications for this since 2004 FDA-approved medical device are often ring avulsion injuries, amputation of smaller parts, other mangled tissue with venous vessels too small to suture, or even soft tissue flaps with congestion. Leech therapy is further well known as a salvage option for tissue otherwise regarded impossible to save [1]. Despite the different potential complications with leech therapy like loss of blood and scaring, the main risk is still infection with a fatal outcome for congested tissue. The incidence of leech-born infections ranges from 2.4 to 36.2% with a delayed onset from 24 h to 26 days [2]. In a large systematic review of the efficacy of medicinal leeches in plastic and reconstructive surgery over a period from 1966 to 2009 with the inclusion of 67 papers, 79.05% of the included patients received antibiotics [3] to prevent or to treat infections of congested tissue. First report of a possible source of an infections by a leach-borne rod—identified as Aeromonas hydrophila—dated back until 1983 [4] and stated therefore the use of leeches as a contraindication. With the spreading of the benefits of leeches in the plastic surgery community, its use arose [5]. The first publication of a proven wound infection has been published in 1984 with Aeromonas hydrophila by using leeches to treat a congested flap [6]. Parallel to the slowly increasing number of reports of bacterial transmissions, more focus was placed on the source of infection [7, 8] and its resistance profile [9]. During the following decades, a growing numbers of reports of leech borne bacterial transmission and infections raised the question if there is an increase in drug resistance against common standard antibiotics and therefore do we have to adjust common treatment regimens like single use of gyrase inhibitors? The aim of this review is therefore to optimize the antibiotic treatment algorithm for leech borne infections in plastic surgery patients.

Methods

This review adheres to the PRISMA 2020 guidelines [10]. Prospero database was checked prior search for still existing reviews, but this protocol was refused to register because of overload by COVID-19 pandemic.

Search strategy and selection criteria

A systematic search through three different public databases, PubMed, Scopus, and Web of Science, was conducted from 1973, and the first data were extracted by search queries in June 2021 (Fig. 1). First search terms were “Aeromonas” AND “leech” OR “hirudo” AND “antibiotic resistance”. Because of the limited number of results, we performed a second search query with extended search items. Second search term queries were “Resistance” AND “hirudo” OR “resistance” AND “leech” OR “resistant” AND “hirudo” OR “resistant” AND “leech” OR “infection” AND “leech” OR “infection” AND “hirudo” OR “infection” AND “aeromonas” OR “resistance” AND “aeromonas” OR “resistant” AND “aeromonas” OR “treatment” AND “hirudo” OR “treatment” AND “leech”. Additional publications found by manually screening references and citations were also included in this publication. An additional repetitive search for recently published papers with the same search query was performed in September 2023 to be included in this review before publication. Additional studies found were also reviewed same way by the two independent reviewers. No language restrictions were included in the initial search, but by testing for inclusion, we discarded all studies other than written in English. Data extraction was guided by the previously prepared protocol conducted by the authors. Case reports or case series with low a number of patients were also included. No study was excluded based on the initial search by quality. A search for unpublished publications was not performed. We included studies which met the following criteria:

  1. 1.

    Medical leech gut samples or homogenates with bacterial identification and sensitivity or resistance testing

  2. 2.

    Wound infections samples caused by usage of a leech for medicinal treatment with bacterial rod identification of Aeromonas spp. and antibiotic treatment or resistance information

Fig. 1
figure 1

Flow diagram of the study selection process

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Two independent reviewers screened titles and abstracts to be sufficient for inclusion in this review. Disagreement was resolved by consensus with full text screening. Studies only available as abstracts or in a language other than English were not included in this review.

Quality of studies

Two independent reviewers assessed the quality of the included studies, and every study was overall rated in poor, fair, good, or not applicable. Disagreement was solved by consensus. The quality was assessed by the JBI critical appraisal tool for case series studies, the JBI critical appraisal checklist for case report, and Bias by the ROBIS tool.

Data extraction

The extraction protocol was based on data estimated as relevant for this review. Data were extracted based on the date of publication, title of the study, abstract, full text available in English, bacterial prevalence in leech gut or leech homogenates or wounds, and type of antibiotics tested and sensitivity/resistance.

Data analysis

For each included study, we calculated the presence of Aeromonas sup. percentage and the resistance of gut-born bacteria found against typically commonly used antibiotics. Data were collected in Microsoft Excel, and results were presented in tabular form.

Results

Flow of included studies

With the fist search strategy, we found 23 publications on Pubmed from 1973, 35 on Scopus, and 18 on Web of Science (both not earlier than 1988). Pubmed revealed with the second search query 1978 publications from 1973, Scopus 29 from 1988 (no earlier results), and Web of Science 9782 publications limited from 1973. A total of 12,037 publications could be found. After removing duplicates and screening titles, most of the studies we found were not appropriate in terms of inclusion. One hundred twenty-one studies remained for further processing. Of these studies, 3 were lacking an abstract and 26 were inappropriate after screening the abstract. Of the 92 publications, we found 12 were missing full text, six were written in a language other than English, and 31 had insufficient data. The remaining 43 publications were included in our survey.

Study characteristics

Study characteristics are summarized in Table 1. The studies—we included—were published between 1983 and 2022 (see Fig. 2). None of the studies was a randomized double-blinded control trial; only one was a retrospective multicenter cohort study. Most of the publications were case series or even case reports without controls. Inclusion criteria were the presence of Aeromonas spp. found in leech gut or leech homogenates and not in water samples with further determining of antibiotic sensitivity/resistance. Inclusion criteria of patients enrolled in case reports/case series were clinical signs of infection during leech therapy after surgical interventions.

Table 1 Study characteristics
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Fig. 2
figure 2

Distribution per year after removing duplicates from Scopus/Pubmed/Web of Science of the relevant publications. Increase after 2010

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Quality assessment

Quality assessment of the case series were based on the JBI critical appraisal tool [11] for case series and for case reports. Case series were rated by the JBI critical appraisal tool for case series (see Table 1) and for case reports with JBI critical appraisal checklist for case reports. Case series which were based on leech gut samples and were processed in a microbiological lab were rate good (13/43); case series based on different patient samples were rated poor (1/43) or rated fair (1/43). Case reports were most often rated good (24/28), fair (2/28), and poor (2/28) according to the JBI checklist. The poor and fair rated studies were also included in this review because of sufficient information related to the aim of the review. The only retrospective patient multicenter cohort study was rated in comparison to the case series good. Furthermore, most of the studies reported often a very limited number of patients or samples. Statistical analysis was therefore not performed even as meta-analysis caused by lack of RCT. Bias assessment was carried out by using the ROBIS tool [12]. We estimated the risk of selection bias low because of the high number of publications we found searching the most common public databases in the first instance and therefore the representativeness of the included paper is estimated high. Publication bias has been estimated high because of the fact of only published papers with stating increasing anti-microbiological resistance of Aeromonas spp. were included. The studies themselves were heterogenous, and therefor the risk of bias in the synthesis of findings was rated high.

Outcomes

Outcomes of the studies were included by percentage of Aeromonas spp. and anti-microbiological resistance. First study showing possible upcoming issues by using leeches for solving surgical problems was in 1983 by Whitlock et al. [4] with showing Aeromonas as the dominant rod in leech guts (see Table 1). First report of a confirmed surgical site infection was by Dickson et al. [6] in 1984.

Addressing the issue of resistance of leech gut-borne infections included in our review was of Hermansdorfer et al. in 1988 [8]. He dissected 20 leech guts and found in 16 of 20 specimen Aeromonas hydrophila (80%), which were all resistant to ampicillin (100%). In one of the 20 specimen, authors found Pseudomonas species other than aeruginosa, which also might have been a water-borne organism that was resistant to ampicillin and chloramphenicol. Lucht et al. reported a case of surgical site infection with loss of a free flap by Aeromonas, which was sensitive to cefotaxime and netilmicin without further resistance reporting [13]. Snower et al. [14] demonstrated a case of infection with flap failure caused by Aeromonas hydrophila which was susceptible to all common antibiotics. Further, water tank and leech sampling showed predominantly five different strains of Aeromonas spp. whereas three of five were resistant to ampicillin. Evans et al. [15] published a case of septicemia during leech therapy in an attempt to salvage a replanted arm by Aeromonas. In the patient sample, 50% of Aeromonas was resistant to cephradine and metronidazole but sensitive to gentamicin. Dabb et al. [16] presented a surgical site infection (SSI) in a 48-year-old women with breast reconstruction with Aeromonas without reporting any resistance. Lineaweaver et al. [17] demonstrated seven cases with SSI caused by Aeromonas with resistance to cephalosporins and in most cases loss of replants (5/7). Wilken et al. [18] did leech gut sampling of the potential Southern African leech and revealed 82% positivity for Aeromonas and resistance to penicillin, ampicillin, vancomycin, and clindamycin. Varghese et al. [19] reported a case of Vibrio fluvialis infection after leech therapy, which was treated with 10 days of doxycycline. Most probably was this a misclassification caused by unproperly bacterial culture testing [20, 21]. Nonomura et al. [22] tested homogenates of five leaches Hirudo medicinalis all positive for Aeromonas (four strains A. sobria and three strains A. hydrophila/caviae) and less susceptible for ampicillin and first-generation cephalosporins. Mackay et al. [23] found in 70% of leech gut samples Aeromonas spp., which were resistant to ampicillin, oxacillin, and chloramphenicol but sensitive to Co-trimoxacol. Eroglu et al. [24] found in leech gut samples from 16 leeches (Hirudo medicinalis) besides 81.25% Aeromonas spp. (13 × Aeromonas hydrophila, one Aeromonas sobria) also Ochrobacter anthropi, Serratia sp., Proteus sp. and Vibrio sp. All were sensitive to ciprofloxacin, trimethoprim/sulfamethoxazole, and resistant to ampicillin. Aydin et al. [25] reported in a case series of leech gut samples a percentage of 90% of Aeromonas of which all were resistant to ampicillin/sulbactam or amoxicillin/clavulanate and 66% resistant to cefalozin. Ouderkirk et al. [26] published a case of SSI in combination with meningitis caused by Aeromonas. Treated in first instance with gatifloxacin and aztreonam and secondary with ceftriaxone and cefipime and tobramycin for a total of 21 days, this might be the first documented resistant strain of Aeromonas to gyrase inhibitors at all. Ardehali et al. presented a case of SSI after usage of leeches for venous congestion caused by Aeromonas hydrophila, which was resistant to imipenem and gentamicin but sensitive to ciprofloxacin. Bauters et al. [27] found in a retrospective analysis of 47 patients treated with leeches during their clinical course 17 cultures were suspected of postoperative wound infection. Of these 47 patients, four (8.51%) tested positive for Aeromonas spp. (two Aeromonas hydrophila, one Aeromonas sobria and one with both strains). All were susceptible to ofloxacin and partially resistant to trimethoprim/sulfamethoxazole (three out of four). During sample testing from postoperative wound infections, multiple other strains like Morganella morganii, Escherichia coli, Klebsiella pneumonii, Staphylococci spp., Pseudomonas aeruginosa, Proteus spp., and Serratia spp. were found, but these samples were not specifically sampled directly from leeches. Mumcuoglu et al. [28] did leech gut sampling, showing 71.25% positive for Aeromonas in the control group and 0% in the test group after ciprofloxacin feeding. Schnabl et al. [29] presented five cases of SSI with Aeromonas spp. after using leeches for venous congestion, which where all sensitive to ciprofloxacin. Whitaker et al. [30] published a case series of SSI after the use of leeches whereas 14.2% of the specimen was positive for Aeromonas, but all strains were sensitive to ciprofloxacin (5/%). Wang [31] reported the first proven case of ciprofloxacin-resistant Aeromonas infection which was also resistant to trimethoprim/sulfamethoxazole. Investigation revealed most likely resistance before arriving at the institution of use. Maetz et al. [32] reported two cases of infection with Aeromonas veronii biovar sobria which were only resistant to amoxicillin/clavulanic acid. Sartor et al. [33] reported two cases of Aeromonas hydrophila infection, which where resistant to ciprofloxacin and sensitive to trimethoprim/sulfamethoxazole. Next was Patel et al. [34] who described a patient treated with Hirudo medicinalis, which was positive for ciprofloxacin-resistant Aeromonas hydrophila infection and treated with aztreonam. Giltner et al. published [35] a case report of Aeromonas hydrophila strain in a 9-year-old patient, which found to be resistant to ciprofloxacin and sensitive to trimethoprim/sulfamethoxazole. Bibbo et al. [36] presented a case of wound infection caused by an Aeromonas hydrophila strain non-susceptible to fluoroquinolones but sensitive to trimethoprim/sulfamethoxazole. Wilmer et al. [37] also reported a case of A. hydrophila infection which was resistant to ciprofloxacin but susceptible to gentamicin and trimethoprim/sulfamethoxazole. Further leech water sampling revealed Aeromonas spp. which were 100% sensitive to trimethoprim/sulfamethoxazole, 61.9% to gentamicin, and 71.4% to ciprofloxacin. Litwinowicz et al. [38] presented a case series of leech gut samples (ten) from the control group which were 100% positive for Aeromonas as well 100% of the study group (seven). All samples of the test group were sensitive to ciprofloxacin and co-trimoxazol. Whitaker et al. [39] processed seven Hirudo orientalis and noted the type of strains and resistant patterns. All Aeromonas spp. he found were sensitive to ciprofloxacin and resistant to amoxicillin, but also different other species were found not otherwise described. Van Alphen et al. [40] described two cases, whereas case one showed an infection after leech therapy with an Aeromonas strain resistant to ciprofloxacin, levofloxacin, ampicillin/sulbactam and prior administered ertapenem, but sensitive to trimethoprim/sulfamethoxazole. Case two revealed resistance to trimethoprim/sulfamethoxazole and moderate sensitivity to ciprofloxacin/levofloxacin. Kruer et al. [41] published a retrospective multicenter cohort study which showed 57.1% of Aeromonas in all SSI samples. Of the tested strains were 75% resistant to ciprofloxacin, 25% resistant to piperacillin-tazobactam, but 75% sensitive to co-trimoxazol. Verriere et al. [2] reported case series over a period of 24 months with three infections out of 28 patients treated with leeches, whereas only one showed resistance to fluroquinolones. Further, leech water tank sampling revealed similar bacterial strains of Aeromonas spp. between crushed leeches and simple water tank samples. All of them showed 100% sensitivity (21/21) to fluroquinolone and trimethoprim/sulfamethoxazole. Berger et al. [42] published a case of SSI with Aeromonas veronii complex, whereas all tested strains were sensitive to fluroquinolones and cefuroxime, but 60% were resistant to co-trimoxazol. Ruppe et al. [43] were the first to report a case of multidrug resistance Aeromonas salmonicida after medicinal leech therapy, whereas the primary Aeromonas veronii strain showed wildtype sensitivity (susceptible to ciprofloxacin and trimethoprim/sulfamethoxazole). This case was rated as colonization. Beka et al. [44] was the first who could link the rise in ciprofloxacin-resistant Aeromonas strains to low levels of ciprofloxacin concentrations in environment after 1999. Bykowski et al. [45] reported the first case of ceftriaxone-resistant Aeromonas hydrophila infection following postoperative leech therapy. This strain was resistant to trimethoprim/sulfamethoxazole, intermediate to ciprofloxacine and also resistant to 3rd generation cephalosporins. Next was Floug et al. [46], who presented a case of ESBL and extensively drug-resistant Aeromonas hydrophila infection after the use of leech therapy. This strain was also resistant to ciprofloxacin and trimethoprim/sulfamethoxazole. Mokhtar et al. [47] reported three cases of post-medical leech therapy infection with Aeromonas hydrophila (two patients) and one with Aeromonas veronii (one patient). Aeromonas hydrophila was resistant to trimethoprim/sulfamethoxazole and cipro/levofloxacin whereas Aeromonas veronii was resistant to ciprofloxacin but sensitive to trimethoprim/sulfamethoxazole. Barraud [48] presented a case report of infection with two distinct strains of Aeromonas veronii in one patient, one ESBL positive, resistant to fluoroquinolones and aminoglycosides, and the other resistant to fluoroquinolones only. Segatore et al. [49] found in samples of Dina lineata (leeches) from environment in Italy in nine out of ten samples of multidrug resistance of Aeromonas hydrophila and A. veronii. Masters et al. [50] reported recently also a case of multidrug-resistant Aeromonas species, which was resistant to ciprofloxacin, ceftriaxone, and trimethoprim/sulfamethoxazole. McCracken et al. [51] recently showed a case of Aeromonas infection after the use of medical leech therapy after surgical functional flap reconstruction with a relative broad spectrum of resistance to fluroquinolones, co-trimoxazole, tetracycline, and cefazolin. Most recently, Sproll et al. [52] most recently reported a case of a lethal Aeromonas veronii sepsis after the surgical use of medical leeches with a strain only resistant to ampicillin/sulbactam and amoxicillin, but sensitive to fluoroquinolone, co-trimoxazol, piperacillin, cefuroxime, ceftzidime, ertapenem, and gentamicin.

Discussion

This systemic review is the first to answer the question of growing drug resistance during leech therapy. During reviewing process, we were confronted with several limitations, most of them were inherent to the studies themselves like a small number of samples, different sample materials or included patients, publishing bias with overreporting of case reports, or possible underestimating of the problem by underreporting this issue or incoherent antibiotic testing. We most often found only case reports which were impossible to rate in means of quality, but they show well an increasing percentage of quinolone resistance or even multidrug resistance in leeches, especially over the last two decades. But this conclusion is influenced by publication bias. Thus, clear advice on how to treat patients during leech therapy is not possible to give based on the studies we found, even the overview of different regimes published recently by McCracken is inconclusive [51]. Brambullo et al. [53] still advise ciprofloxacin or in case of allergies or increased risk of resistance Co-timoxazol. Conclusively in the late 1980s and early 1990s of the twentieth century, first descriptions of leech-associated infections by Aeromonas spp. were published. During this period, almost all samples were susceptibly to common antibiotics like ciprofloxacin [24], tetracycline, and trimethoprim/sulfamethoxazole [54], or gentamicin, chloramphenicol, or 3rd generation cephalosporins [8]. Resistance to ciprofloxacin—of other quinolone—derived gyrase inhibitors was virtually absent [4, 8, 16, 18, 55] whilst intrinsic resistance to ampicillin or amoxicillin was well known by Aeromonas spp. With increasing use—especially of the easy-to-handle quinolone-derived antibiotics—the number of reported resistant strains rose [47]. One of the most putative reason is the misusage of quinolone antibiotics and others in large scale farm industry, especially in the feeding of poultry whose blood is use to feed medical leeches before inset instead of cattle blood caused by putative risk of prion transmission [56] or even in fish farm industries [57]. With the increasing awareness of potential infection risks with Aeromonas spp. and other species, which often have to be treated with potent antibiotics, the number of cases reported rose within the last two decades. Aeromonas species are nowadays susceptible in different degrees to second and third degree cephalosporins, fluoroquinolones, sulfamethoxazole-trimethoprim, tetracycline, and aminoglycosides [8, 58] and resistant to penicillin and derivates [35]. More up-to-date publications show a further expanding multidrug resistance for 3rd generation cephalosporin-like ceftriaxone [45] or even ESBL resistance [46]; thus, microbiological leech gut testing—regularly of every batch used—seems to get more important than ever, and the whole delivery pathway from supplier to the patient should be assessed. In most recent publications, there is also a growing number of reports regarding ciprofloxacin-resistant or 3rd degree cephalosporin-resistant (ceftriaxone) Aeromonas infections following leech therapy [34, 35, 37, 40, 45]. Taking the growing numbers of resistant strains of Aeromonas spp. into account and the misusage of quinolone-derived anti-microbiological drugs in the past, blind administration of a single antibiotic seems to be nowadays most probably insufficient, even because of the increasing numbers of other bacterial species found in the digestive tracts of leeches. Thus, it is recommendable to start antibiotics at least before leech therapy with a combination of ciprofloxacin and sulfamethoxazole-trimethoprim [35, 59, 60] because most of the Aeromonas samples were still susceptible to at least one of them, whilst constantly adjusting antibiotic therapy based on resistance testing. The advantage of both types of antibiotics is sufficient oral uptake and soft tissue penetration thus iv-antibiotics as 3rd generation cephalosporin, or others are not necessary and therefore potentially less hospitalization and costs [61].