Abstract
A total of 70 strains of enteroinvasive Escherichia coli (EIEC) belonging to 8 different O serogroups including O28ac O29, O121, O124, O136, O143, O144, and O164, was studied for their biochemical characteristics, growth on selective isolation agar, antimicrobial susceptibility, and diarrheagenic toxin production. Among the biochemical characteristics examined, all EIEC strains gave negative lysine decarboxylation and all but one belonging to O124 serogroup, were non-motile, regardless of their O serogroups. The one motile O124 strain had a H30 antigen. Some close correlations were also observed between their O serogroups and biochemicals such as utilization of sodium acetate and mucate, ornithine decarboxylation, arginine dihydrolation, gas production from glucose, and lactose fermentation. Among the selective isolation agars, MacConkey and Deoxycholate-hydrogen sulfide-lactose (DHL), and modified Shigella-Salmonella (SS) agars supported growth of the EIEC strains well, whereas SS agar was remarkably inhibitory for strains of some O serogroups. Antimicrobial susceptibility was tested for nine drugs including chloramphenicol (CP), tetracycline (TC), streptomycin (SM), kanamycin (KM), ampicillin (ABPC), sulfamethoxazole-trimethoprim (ST), nalidixic acid (NA), fosfomycin (FOM) and norfloxacin (NFLX). Forty-one of the 70 strains (58.6%) were found to be resistant to the 6 drugs, such as CP, TC, SM, KM, ABPC or ST. None of the strains were resistant to NA, FOM or NFLX. Among the resistant strains recognized, the strains which showed the resistant patterns of CP.TC.SM.ABPC, CP.TC.SM, TC.SM.ST, TC.SM, and SM appeared to be prevalent. None of the strains gave positive reactions for the production of diarrheagenic toxins of heat-labile enterotoxin, heat-stable enterotoxin, and verocytotoxins 1 and 2.
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