Beta-lactamase mediated resistance in Salmonella spp. at a tertiary hospital in KwaZulu-Natal.

Abstract

Extended spectrum (3-lactamases (ESBLs) were characterized in Salmonella spp. isolates from a pediatric ward of a hospital in Durban. Forty one Salmonella spp. were subjected to serotyping, antibiotic susceptibility testing, E-Tests for ESBL detection, iso-electric focusing, polymerase chain reaction for detection of genes and sequencing. Isolates were screened for the presence of WaTEM, WaSHV, WaCTX-M, WaOXA , WaCMY, WaDHA and WaACC genes. The most common serotype was Salmonella Typhimurium. Isolates were multi-drug resistant with 100% susceptibility only to meropenem and ciprofloxacin. Tazobactam was the most effective inhibitor. Forty-one percent of the isolates were resistant to ceftriaxone, thus limiting therapeutic options for Salmonella infections.TEM-1 was the most predominant (3-lactamase found in 51% of isolates while SHV-12 found in 39 % was the most common ESBL. TEM-63 was evident in 29 %, TEM-116 in 10 % and TEM-131 was found in one isolate. The high ceftazidime MICs of isolates expressing only TEM-63 were indicative of R164S substitution which widens the binding cavity to accommodate the bulky side chains of oxyiminoaminothiazolyl cephalosporins. The identification of TEM-131 which differs from TEM-63 by 1 amino acid reiterates the evolutionary potential of the TEM-type plactamase. Other ESBLs identified included SHV-2, CTX-M-3, CTX-M-15 and CTX-M-37. CMY-2 and the OXA-1 p-lactamase were also detected. This is the first report of TEM-116, CTX-M-3, -15 and -37 in Salmonella spp. in South Africa. All isolates with nalidixic acid MICs > 48 ug/ml had the mutation D87N, or D87G in the QRDR of the gyrA gene. This study showed that Salmonella spp. may be multi-drug resistant with the propensity to harbour p-lactamases in unique combinations. The diversity of ESBLs and the co-expression of quinolone resistance suggests that their incidence in salmonellae needs to be monitored.