1: Water Sci Technol. 1986;18(10):227-31. Links
Health significance and occurrence of injured bacteria in drinking water.
Department of Microbiology, Montana State University, Bozeman 59717, USA.
Enteropathogenic and indicator bacteria become injured in drinking water with exposure to sublethal
levels of various biological, chemical and physical factors. One manifestation of this injury is the inability to grow
and form colonies on selective media containing surfactants. The resulting underestimation of indicator bacteria can
lead to a false estimation of water potability. m-T7 medium was developed specifically for the recovery of injured
coliforms (both "total" and fecal) in drinking water. The m-T7 method was used to survey operating drinking water
treatment and distribution systems for the presence of injured coliforms that were undetected with currently used media.
The mean recovery with m-Endo LES medium was less than 1/100 ml while it ranged between 6 and 68/100ml with m-T7
agar. The majority of samples giving positive results with m-T7 medium yielded no detectable coliforms with m-Endo LES
agar. Over 95% of the coliform bacteria in these samples were injured. Laboratory experiments were also done to
ascribe the virulence of injured waterborne pathogens. Enteropathogens including Salmonella typhimurium, Yersinia
enterocolitica and Shigella spp. required up to 20 times the chlorine levels to produce the same injury in enterotoxigenic
Escherichia coli (ETEC) and nonpathogenic coliforms. Similar results were seen with Y. enterocolitica exposed to
copper. The recovery of ETEC was followed by delayed enterotoxin production, both in vitro and in the gut of
experimental animals. This indicates that injured waterborne enteropathogenic bacteria can be virulent.