(February 21st, 2012) Is an E. coli outbreak impending in the Antarctic? Maybe not (yet) but certain human-associated bacteria shouldn’t even be there...
There aren't many places left in this world that are still untouched by man. The Antarctic, however, is one of those rare sanctuaries – here, Nature is mostly left to her own devices. So in theory, there shouldn’t be anything that doesn’t belong there, right? Not quite. In 2010, Argentinian researchers detected the human-associated enterobacterium Salmonella enterica in faecal samples from Antarctic animals including the Southern Giant Petrel (Macronectes giganteus), the Adelie Penguin (Pygoscelis adeliae), the Skua (Stercorarius sp.), the Kelp Gull (Larus dominicanus) and the Weddell Seal (Leptonychotes weddelli). So how did these man-derived bugs manage to conquer that “unmanned land”?
Well, it's not totally free of men, of course. There are a few manned research stations (and possibly one or the other adventurous tourist) that lead, what must be, a pretty lonely existence at the South Pole. Some precautions have been taken, though, to keep the contact between these two worlds as low as possible, especially when it comes to wastewater treatment. Jorge Hernández from Uppsala University, Sweden reports, “All the Chilean stations practise treatment by decanting, filtration, chemical and biological processing in closed systems; and modern facilities are available for enzymatic and biological destruction of residues. The Chilean Antarctic Institute maintains a constant preoccupation for compliance with standards of protection to the Antarctic environment, and Chile has provided permanent bases with modern equipment for wastewater treatment that is constantly improving. Despite this, there are still filtrations of human bacteria in low levels toward the seawater.”
And that's exactly what Hernández and his colleagues from Sweden and Chile recently discovered. They didn’t find more Salmonella but a similar, maybe even worse, bug – E. coli. And not just your garden variety E. coli. Among the isolates collected from wastewater close to research stations on the Antarctic Peninsula, King George Island and Greenwich Island (South Shetlands), the scientists also found E. coli producing extended spectrum β-lactamases (ESBL). Synthesising these enzymes expands a bacterium's resistance against several β-lactam antibiotics like penicillin and various cephalosporins.
ESBLs come in different classes, including TEM, SHV and the “most widespread” CTX-M - “each with a different evolutionary origin”. All analysed isolates from the vicinity of the research stations were “positive for the CTX-M ESBL but negative for TEM and SHV”, Hernández et al. note in their publication. Further analysis of ten samples revealed that four isolates carried the blaCTX-M-1 gene, six (from different research stations) sported the blaCTX-M-15 gene. These two genes are indeed both human-associated ESBL genotypes, found in the human gastrointestinal biota and “belonging to widespread disease-associated genotypes”.
So, obviously, even though precautions have been taken at the research stations, they seem “inadequate”. But what can be done in the future to prevent bacteria escaping? “Improve the installations and submit treated water to a rigorous quality control prior to disposal into the sea”, is what Hernández has in mind. If that doesn’t happen any time soon, then, “The human bacteria could be incorporated into the intestinal bacterial flora of the penguin with results difficult to calculate.” He adds, “If these bacteria colonise the penguins, they can become disseminators and reinfect humans and other wildlife.”
During their studies, they, luckily, only found one E. coli isolate with a resistant phenotype (to chloramphenicol) in Gentoo Penguin (Pygoscelis papua) droppings but “penguins are but one part of the ecosystem, and compared to more opportunistic feeders, such as Kelp Gulls, Skuas and Snowy Sheathbills (Chionis albus), they may be less exposed to human-associated bacteria”. Therefore, future studies on Kelp Gulls promise more revealing insights.
“The presence of anthropogenic bacteria in the Antarctic environment is worrisome in itself and indicative of how widespread the global antibiotic resistance situation has become”, write Hernández et al. Let's hope there's still time to prevent worse.
Kathleen Gransalke
Photo: Jorge Hernández