| Summary: | <p>Abstract</p> <p>Background</p> <p>Apart from localized gastrointestinal infections, <it>Escherichia coli </it>and <it>Salmonella </it>species are major causes of systemic disease in both humans and animals. <it>Salmonella </it>spp. cause invasive infections such as enteric fever, septicemia, osteomyelitis and meningitis while certain types of <it>E. coli </it>can cause systemic infections, including</p> <p>pyelonephritis, meningitis and septicemia. These characteristic requires the involvement of a myriad of virulence factors.</p> <p>Methods</p> <p>This study investigated the virulence factors of <it>Escherichia coli </it>and <it>Salmonella </it>species in clinical specimens from patients with diarrhoea presenting to health care centres in Oliver R. Tambo District Municipality, Eastern Cape Province, Republic of South Africa. Microbiology analysis involved the use of cultural and molecular techniques.</p> <p>Results</p> <p>Out of a total of 315 samples screened, <it>Salmonella </it>isolates were obtained in 119 (37.8%) of cases and these comprised: <it>S. choleraesuis </it>(6%), <it>S. enteritidis </it>(4%), <it>S. eppendorf </it>(1%), <it>S. hadar </it>(1%), <it>S. isangi </it>(8%), <it>S. panama </it>(1%), <it>S. typhi </it>(52%), <it>S. typhimurium </it>(25%) and untyped <it>Salmonella </it>spp. (2%). Among the <it>Salmonella </it>species 87 (73.1%) were invasive. Using molecular diagnostic methods, diarrheagenic <it>E. coli </it>were detected in 90 cases (28.6%): the greater proportion of this were enteroaggregative <it>E. coli </it>(EAEC) 37 (41.1%), enteropathogenic <it>E. coli </it>(EPEC) 21 (23.3%) and enterohemorrhagic <it>E. coli </it>(EHEC) 21 (23.3%). The predominant virulence gene among the diarrheagenic <it>E. coli </it>was EAEC heat-stable enterotoxin <it>astA </it>genes while the virulence genes identified in the <it>Salmonella </it>strains were 15 (12.6%) flic and 105 (88.2%) inv genes. The amino acid identity of the representative genes showed 95-100% similarity to corresponding blast searched sequence.</p> <p>Conclusions</p> <p>This study showed the diversity of virulence gene expression in two major enteric pathogens. <it>S. typhi </it>and enteroaggregative <it>E. coli </it>were the predominant enteropathogens in our study area with an indication that EAEC is endemic within our study population. It was observed among other things that some diarrheagenic <it>E. coli </it>isolated from apparently asymptomatic subjects expressed some virulence genes at frequency as high as seen in diarrheagenic cases. This study underlines the importance of understanding the virulence composition and diversity of pathogens for enhanced clinico-epidemiological monitoring and health care delivery.</p>
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