Antarctica is the last continent to receive some considerations to limit the human activity and avoid introducing pathogen microorganisms to Antarctic animals. There are no measures planned to limit the dissemination of diseases in case of infectious outbreaks. Furthermore, there is evidence that introduced diseases can cause the declination of autochthonous population. One example frequently cited is the effect caused by the introduction of avian smallpox and avian malaria in Hawaiian birds (Warner 1968; Van Riper et al. 1986).
Several studies have been carried out in the Antarctic fauna with the purpose of assessing S. enterica presence. Between 1957 and 1996 in the Antarctic region, samples were taken from different animals, penguin species, skuas, seals, and the following serovars of Salmonella enterica were identified, S.
johannesburg, S. typhimurium, S. panama, and S. infantis (Soucek and Mushin 1970; Oelke and Steiniger 1973; Sieburth 1979). In 1995–1996, S. Enteritidis was isolated from gentoo penguins at Bird Island, South Georgia, and sub-Antarctica (Olsen et al. 1996). In addition, in sub-Antarctica S.
havana, S. Enteritidis, and S. Newport were isolated from gentoo penguins, black-browed albatrosses (Diodema melanophrys), and Antarctic fur seals (Palmgren et al. 2000). In the present study, S. Newport was isolated from southern giant petrels, and S. Enteritidis was isolated from Adelie penguins, skuas, kelp gulls, and Weddell seals. This is the first time that S. enterica was isolated from southern giant petrel, kelp gulls, and Weddell seals in the Antarctic region. In conclusion, very few S. enterica serovars appear to be circulating in the Antarctic area. If the bacterium is endemic in the region or was recently introduced is a question without answer yet.
S. Newport and S. Enteritidis are human pathogens, especially the latter serovar that is one of the most common causes of human salmonellosis (Rodrigue et al. 1990; Le Bacq et al. 1994). S. Newport was reported to cause disease in captive penguins (Cockburn 1947). Also, it is commonly isolated from seals without signs of salmonellosis and from ill animals (Gilmartin et al. 1979; Baker et al. 1995), and it is endemic in pinnipeds according to studies performed in the sub-Antarctic region and other places (Fenwick et al. 2004). None of the animals sampled in this study showed clinical signs of salmonellosis, so apparently, the studied Antarctic animals would be the healthy carriers.
One of the most possible routes of introduction of S. enterica to Antarctica is by migratory birds (Olsen et al. 1996). Many of Antarctic birds have long routes of migration, and along their routes, they pass over waste disposal tips, polluted rivers and lakes, and fields manured with feces; therefore, in these places, they could acquire the microorganism. Unfortunately, neither in this study nor in other previous investigations performed in the Antarctic region was it possible to determine the source of the bacterium.
In recent years, studies on antimicrobial resistance of S. enterica from different sources (human, animal, feed and environment) were carried out, and owing to the antimicrobial misuse and abuse, S. enterica resistant strains are being frequently found around the world (Levy et al. 1988; Poppe et al. 2001; Molla et al. 2006). All Antarctic isolates from this study were susceptible to all the antimicrobial agents tested. This would indicate that Antarctic isolates were not exposed to antimicrobial selection pressure and neither acquired resistance from other microorganisms circulating in the Antarctic ecosystem.
There is scarce knowledge about S. enterica epidemiology in Antarctic animals. To define control strategies, it is essential to know about the biological cycle of infectious agents. For that, it is necessary to investigate the reservoirs and transmission ways, as well as the ecological conditions that allow the pathogen’s survival. In addition, very few studies including the analysis of Salmonella enterica using molecular epidemiology were carried out in Antarctica. In the present study, S. Newport was only isolated from southern giant petrels in summer 2000 in Potter Peninsula, and all isolates showed an identical genomic profile by PFGE and RAPD-PCR. Therefore, the infections were caused by the same S. Newport subtype. Unfortunately, we could not determine whether the pathogen was transmitted from bird to bird or was acquired from exposure to the same infection source. S. Enteritidis was isolated from one southern giant petrel in summer 2000 in Potter Peninsula, and in summer 2003 in Hope Bay, the pathogen was isolated from three different bird species and from Weddell seals; all the isolates showed an identical genomic profile by PFGE and RAPD-PCR. Therefore, the infection was caused by the same S. Enteritidis subtype. Unfortunately, we could not determine whether the pathogen persisted in Antarctic animals or in the Antarctic environment.
Comparing the results obtained by PFGE of Antarctic S. Newport and S. Enteritidis within each serovar with the isolates from Argentina, we concluded that there is no relationship among them.
There are few reports of molecular epidemiology carried out with bacteria isolated from Antarctica: Pasteurella multocida subspecies gallicida type A:1 isolates were associated with two avian cholera outbreaks occurred with a difference of 1 year, and all strains showed identical genomic profiles by PFGE (Leotta et al. 2006a). In this study, S. Newport and S. Enteritidis showed identical genomic profile by PFGE and RAPD-PCR within each serovar. Therefore, this could be indicating that these Antarctic bacteria were either subjected to low pressure from the environment or recently introduced to the area.
We demonstrated previously that Antarctic seabirds carried bacterial pathogens in their intestines (Leotta et al. 2006b). Human activity in Antarctica has been identified as a possible source of infectious agents (SCAR 2001). Birds carrying S. Newport and S. Enteritidis in their guts settled around lakes which are used to supply with fresh water for human; therefore, this could be a possible way of S. enterica transmission to the inhabitants. However, to our knowledge, there are no reports about zoonotic enteropathogens causing diseases in humans that live in the Antarctic region. S. enterica epidemiology in the Antarctic fauna and its possible transmission to humans and vice versa needs to be further investigated.