Survivability of Salmonella typhimurium L1388 and Salmonella enteritidis L1225 under stressful growth conditions
Ngwai, Y.B.; Wambebe, C. and Adachi, Y. (2007) Survivability of Salmonella typhimurium L1388 and Salmonella enteritidis L1225 under stressful growth conditions. Online Journal of Health and Allied Sciences, 6 (2). ISSN 0972-5997
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In an earlier study with Salmonella typhimurium L1388 (ST) and Salmonella enteritidis L1225 (SE) isolated from diseased chickens, we found that SE formed more biofilm than ST on abiotic surfaces in a time-dependent manner. Since the ability of salmonellae to survive extreme environment is related to their virulence, the present study examined the survival of Salmonella typhimurium L1388 and Salmonella nteritidis L1225 under the usual stresses that salmonellae encounter during their life cycle. This is with a view to understanding the strains’ stress tolerance that could be used to explain their virulence. Incubation at 37oC for various time periods was done for: i) stationary phase (SP) cells at pH 2.6; ii) log-phase (LP) cells at pH 4.0; log-phase or stationary phase cells in broth containing iii) hydrogen peroxide, iv) sodium chloride and v) ethanol; vi) stationary phase cells in Hank’s balanced salt solution (single strength) containing 10% human serum; and vii) prolong stationary phase cells. Stationary phase cells were also incubated at 52oC for 15 min. Surviving cells at the various incubation times were counted on trypticase soy agar (TSA) after appropriate dilution in saline and overnight incubation at 37oC. Growth iron-poor medium was determined by growing a single bacterial colony in Medium A with shaking at 37oC or 40oC for 24 h. Statistics was done by one-way analysis-of-variance (ANOVA) at P = 0.05. Differences in the survival of ST and SE were insignificant (p>0.05) in acid pH at both pH 4.0 (p = 0.3783) and pH 2.6 (p = 0.4711); at high salinity for log-phase (p = 0.1416) and stationary phase (p = 0.1816) cells; in ethanol (p = 0.5984), human serum (p = 0.8139), prolonged stationary phase (p = 0.3506); and under heat (p = 0.5766). SE was significantly (p<0.05; p = 0.0031) more tolerant to oxidative-killing by hydrogen peroxide. Culturable growth of the ST and SE in an iron-poor medium A revealed insignificant differences at 37oC (p = 0.8381) but marginally significant at 40oC (p = 0.0508). Thus, with the exception of survival in hydrogen peroxide, SE had similar response pattern with ST to the usual stresses that salmonellae encounter during their life cycle, despite the former’s preferential ability to form biofilm on abiotic surfaces. The relationship between the observed enhanced ability of SE to survive in hydrogen peroxide and virulence need to be investigated in subsequent study.
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