Sunday, March 27, 2011

Growth Inhibition of Three Strains of E. Coli Via Certain Probiotic Strains of Lactobacillus

Most of us probably recognize E. Coli as the culprit of many outbreaks resulting from food borne contamination.  Perhaps one would recall a 1996 outbreak in Japan in which over 6000 primary school children were infected with E. Coli 0157, 1000 of whom were hospitalized for anything from hemorrhagic colitis (bloody diarrhea), to hemolytic uremic syndrome (kidney failure); or a 2002 outbreak in the U.S. associated with contamination of ground beef.  Currently, there is no vaccine for the particular strain of E. Coli 0157:H7, however, aside from following basic steps of hygenic prevention of the diseases caused by enterovirulent strains of E.Coli, alternatives are being explored.

One such investigation conducted in 2009 by researchers, Erin L. Piper and Kathryn J. Leyva explored a keen, yet perhaps seemingly simple alternative to counteracting the serious effects of two virulent strains of E. Coli: 0157:H7 and Entertoxigenic E. coli.  Piper and Leyva experimented with the growth inhibition of these strains of E. coli, (and another non-pathogenic strain, E. Coli 25922), by exposing the pathogenic bacteria to probiotic species of Lactobacillus: L. acidophilus, L. casei, L. fermentum, and L. rhamnosus.  Previous investigations had demonstrated that certain Lactobacilli produce by-products called bacteriosins and adhesive factors which provided a noticeable degree of protection from enteric pathogens.  Based on this premise, the four strains of Lactobacilli were cultured on Man-Rogosa-Sharpe broths, and introduced to the three strands of E. Coli (cultured in Tryptic Soy Broth) to "determine the inhibitory activity of Lactobaccilus spp. against each of the three strains of E. coli." 

Three separate experiments were performed, the first two of which utilized live lactobacilli inoculated with each strain of E.coli. and the third of which utilized supernatant gathered from the lactobacilli. 

None of the experiments demonstrated complete growth inhibition of any of the E.coli strains, however the degree of inhibition varied based on the method used. "Our experimental findings suggest that Entertoxigenic E. coli was strongly inhibited when exposed to live lactobacilli cells, but only partially inhibited when exposed to supernatant alone."  On the other hand, Enterohemorrhagic (0157) E. coli was "equally inhibited by exposure to live cells or supernatant."  Needless to say, while this experiment was helpful, solutions to completely avoid such diseases have yet to come to fruition and the difficulty of finding a means to eradicate such diesase serves as a continued testament to the potency of bacterial resistance to scientific defenses.

Growth Inhibition of Gastrointestinal Strains of Eschericia coli by Lactobaccilus Species; Erin L. Piper and Kathryn J. Leyva. Journal of the Arizona-Nevada Academy of Science 2009

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