Survival, physiological response and recovery of enteric bacteria exposed to a polar marine environment

Abstract

Survival, sublethal injury, and recoverability of Escherichia coli, Enterococcus faecalis, SalmoneUla typhimurium, and Yersinia enterocolitica were investigated by using diffusion chambers over 54 to 56 days of in situ exposure to a polar marine environment (-1.8°C; salinity, 34.5 ppt) at McMurdo Station, Antarctica. Plate counts were used to assess recoverability and injury, whereas direct viable counts (DVCs) and 5-cyano-2,3ditolyl tetrazolium chloride (CTC) reduction were utilized to determine substrate responsiveness and respiratory activity, respectively. T%, values (times for 10-fold decreases in numbers of recoverable cells) on nonselective medium were ca. 216 to 259 h for E. coli, S. typhimurium, and Y. enterocolitica and 432 h for E. faecalis. Sublethal injury was greater in populations of indicator bacteria than in pathogens. DVCs, CTC reduction, and plate counts indicated progressive increases in viable but nonculturable cells in E. coli, S. typhimurium, and Y. enterocolitica cultures throughout the 54-day exposure. Forty-eight-day exposure of E. coli, S. typhimurium, and Y. enterocolitica resulted in decreased optimal incubation temperatures for colony formation and inability to form colonies at 37rC. The detection of responsive E. coli, S. typhimurium, and Y. enterocolitica by the DVC and CTC methods remained within 1% of inoculum values during 54 days of exposure, indicating some long-term persistence in the viable-but-nonculturable state. Percentages of respiring E. coli and S. typhimurium increased significantly upon addition of nutrients at all temperatures tested, indicating that nutrient availability rather than temperature limited enteric bacterial activity in this very cold environment. Large nutrient inputs to low-temperature marine environments may thus allow for the long-term persistence of enteric bacteria in a nonrecoverable state.

Resuscitation of Escherichia coli VBNC cells depends on a variety of environmental or chemical stimuli

“…Induction of the VBNC state in E. coli, a gram-negative bacterium often associated with foodborne illness, was already reported under low pH (Zhao and Matthews 2000), UV radiation in combination with high salinity (Pommepuy et al 1996), starvation conditions (Smith et al 1994), low water availability (Artz et al 2006), high salinity (Roth et al 1988) and high copper concentrations (Grey and Steck 2001). A food bacterium can encounter all these unfavourable environments because they are the base of most food preservation conditions used, alone or in different combinations and can also be part of the food composition.…”

Crude oil-induced structural shift of coastal bacterial communities of rod bay (Terra Nova Bay, Ross Sea, Antarctica) and characterization of cultured cold-adapted hydrocarbonoclastic bacteria

“…) is found to reduce rates of bacteriovory and resulted in prolonged survival of enteric bacteria in Antarctic seawater [56]. Fig.…”

Survival of enteric bacteria in seawater

“…In similar experiments conducted by Smith et al [21] at the polar environment of McMurdo station in Antarctica, the survival of four stationary phase enteric bacteria (E. coli, S. typhimurium, Yersinia enterocolitica and E. faecalis) in di¡usion chambers (31.8³C) was measured by several methods (TC, DVC, CTC, CFU) for 54^56 days. All strains retained stable TC, but colony formation ability (CFU), CTC reduction and DVC were decreased; the decay was gradual for the ¢rst three strains and rapid for E. faecalis (CTC reduction capability loss within 10 days).…”