Molecular epidemiology of invasive isolates of Salmonella enterica serovar Typhimurium in Gauteng, South Africa, 2006-2008

The clonality of 840 invasive human Salmonella enterica serotype Typhimurium isolates isolated in Gauteng Province during January 2006 to May 2008 was investigated. PFGE analysis revealed 38 clusters: three (clusters 3, 5 and 11) were primary clusters. Most isolates originated from Hospital 2 and were isolated from patients in the age-range of 15-64 years. Ninety-two percent (256/277) of patients with known HIV status were HIV-positive. Antibiotic susceptibility testing showed the most commonly expressed antibiotic resistance profiles were ACSSuNa (13%; 90/671) and ACSSuTNa (12%; 82/671). Thirty-five nosocomial isolates were identified in 12 clusters, of which most isolates came from two of our three major clusters: cluster 3 (31%; 11/35) and cluster 5 (23%; 8/35). In South Africa, Salmonella Typhimurium remains an important opportunistic infection of HIVpositive patients and may circulate as a nosocomial pathogen over prolonged periods within the hospital environment. The study included characterization of 47 Salmonella isolates recovered from a 150 chicken specimens purchased in Gauteng Province during September 2007 to April 2008. Salmonella Heidelberg (34%; 16/47) and Salmonella Infantis (34%; 16/47) were the most common serotypes isolated from chickens. PFGE analysis showed Salmonella Heidelberg and Salmonella Hadar isolates were similar in PFGE profile to equivalent human serotypes, indicating that for these two serotypes some chicken and human isolates may be related. PFGE analysis and MLVA showed that some chicken and human Salmonella Typhimurium isolates were similar in molecular profile, indicating a relationship between these isolates. An epidemiological relationship between chicken and human isolates could not be confirmed; however results suggest that Salmonella strains with similar molecular profiles circulate in the animal and human communities, supporting the suggestion of animal-to-human transmission or possibly human-to-animal transmission. Further work is required to confirm this theory