Vancomycin and oxacillin co-resistance of commensal staphylococci.

Background: Many disease conditions including Staphylococcal infections are becoming increasingly difficult to treat in South Africa due to the surge of vancomycin-oxacillin resistant strains. How widespread this phenomenon is in commensal isolates in the Nkonkobe municipality in the Eastern Cape Province of South Africa is not known, and considering the high level of immunocompromised individuals in the province, this study couldn't have come at a better time.

Objectives: The objective of this study is to evaluate the prevalence of vancomycin and oxacillin co-resistance in methicillin-resistant commensal staphylococci in Nkonkobe municipality, South Africa as part of our larger study on the surveillance of reservoirs of antibiotic resistance in South Africa.

Materials And Methods: Staphylococcus species were isolated from domestic animals of Nkonkobe municipality, in the Eastern Cape Province of South Africa. The isolates were evaluated for antibiotic susceptibility against a panel of several relevant antibiotics. Specific primer sets were also used for the polymerase chain reaction assay to detect the presence of mecA gene as well as vanA and vanB genes in the genome of resistant Staphylococcus species.

Results: A total of 120 Staphylococcus isolates were screened, out of which, 32 (26%) were susceptible to both methicillin and vancomycin, while 12 (10%) had co-resistance to the antibiotics, which is still on the high side, both clinically and epidemiologically. Gentamicin (an aminoglycoside) had a relatively high potency against the isolates with 107 (89.17%) of the bacteria being susceptible to it, while 10 (8.33%) were resistant. On the other hand, erythromycin (a macrolide) was active against 72 (60%) of the isolates, while 5 (4.17%) and 74 (61.67%) of them yielded intermediate and resistant responses, respectively. Similarly, 51 (42.5%) of the isolates were susceptible to rifampicin, while 1 (0.83%) and 17 (14.17%) were intermediate and resistant, respectively.

Conclusions: Ten percent of the isolates were positive for mecA gene among the vancomycin-oxacillin resistant strains, while van gene was not detected in any of the isolates. The data obtained would be useful in clinical control of resistant staphylococcal strains.