Abstract:
BACKGROUND: Apart from localized gastrointestinal infections, Escherichia coli and Salmonella species are major
causes of systemic disease in both humans and animals. Salmonella spp. cause invasive infections such as enteric
fever, septicemia, osteomyelitis and meningitis while certain types of E. coli can cause systemic infections, including
pyelonephritis, meningitis and septicemia. These characteristic requires the involvement of a myriad of virulence
factors.
METHODS: This study investigated the virulence factors of Escherichia coli and Salmonella 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.
RESULTS: Out of a total of 315 samples screened, Salmonella isolates were obtained in 119 (37.8%) of cases and
these comprised: S. choleraesuis (6%), S. enteritidis (4%), S. eppendorf (1%), S. hadar (1%), S. isangi (8%), S. panama
(1%), S. typhi (52%), S. typhimurium (25%) and untyped Salmonella spp. (2%). Among the Salmonella species 87
(73.1%) were invasive. Using molecular diagnostic methods, diarrheagenic E. coli were detected in 90 cases (28.6%):
the greater proportion of this were enteroaggregative E. coli (EAEC) 37 (41.1%), enteropathogenic E. coli (EPEC) 21
(23.3%) and enterohemorrhagic E. coli (EHEC) 21 (23.3%). The predominant virulence gene among the
diarrheagenic E. coli was EAEC heat-stable enterotoxin astA genes while the virulence genes identified in the
Salmonella 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.
CONCLUSIONS: This study showed the diversity of virulence gene expression in two major enteric pathogens. S. typhi
and enteroaggregative E. coli 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 E. coli
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.
