engleski

Genotoxic sub-lethal injuries, filamentous growth and culturability of Salmonella typhimurium TA1535/pSK1002

Enteropathogenic and coliform indicator bacteria become damaged with exposure to sub-lethal doses of various biological, chemical and physical agents. Stressed bacteria can grow, increase biomass, stay viable, divide very slowly or not at all, which leads to filamentous growth as result of the bacterial SOS-response. This can caused false negative estimation of contamination and misinterpretation of results. To examine filamentous bacteriostatic growth, we treated Salmonella typhimurium TA1535/pSK1002 with model genotoxic agents (UV and 4-NQO). Dose related induction of bacterial SOS response was proved, measured as umuC'-'lacZ gene expression (error prone repair) and co-expression of beta -galactosidase activity. After UV and NQO treatment the optical density of incubation mixture at 600 nm, the number of bacteria, percent incidence of normal sized bacteria and the colony forming units decreased significantly comparing to control. The ability to form colonies on solid TGA media decreased rapidly and represented only a small fraction of total counts obtained by fluorescence microscopy analysis. Consequences of sub-lethal effects on detection of S. typhimurium and other coliform bacteria as indicator organisms of contamination by human and domestic wastes are discussed.

Salmonella typhimurium; UV; 4-Nitroquinoline-N-oxide; SOS response; cell division inhibition; filamentous growth; culturability

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