Detection of Carbapenem Resistance in Salmonella Species from a Tertiary Hospital in Eastern Cape, South Africa

Aims: Broad-spectrum carbapenem group is the current therapy for strains of Enterobacteriaceae that express extended spectrum beta-lactamases (ESBLs). However, recent reports of therapeutic failures of carbapenems with strains that produce multiple β-lactamases are being documented. This study profiled antibiotic resistance in clinical isolates of Salmonella species in a tertiary hospital in the Eastern Cape of South Africa with the aim of identifying the status of Salmonella therapy in the region.

Study Design: This is an analytical study.

Place and Duration of Study: Salmonella isolates (119) from 96 blood and 23 stool specimens of patients attending Nelson Mandela Academic Hospital Complex (NMAHC) and surrounding clinics, Eastern Cape, South Africa collected for surveillance purposes over a period of 3 years (2006 – 2009) were obtained from National Institute of Communicable Diseases, (NICD), for analysis between 2010 and 2011.

Methodology: Preliminary identification and serotyping were done at the NICD. The identification and antimicrobial susceptibility profile of isolates were confirmed with an Autoscan-4 antimicrobial susceptibility system. The MIC of ertapenem and imipenem tested for all Salmonella spp. were ≥2 mg/L and ≥4 mg/L respectively.

Results: A considerable portion of the isolates 59/119 (49.6%) showed pentavalent resistance to some antibiotics including ampicillin and amoxicillin. Of the 59 multiply resistant isolates, 14 (23.7%) were resistant to 1 or more of the carbapenems examined. The phenotypic determination of ESBLs resulted in 25 (21.0%) ESBL-positive Salmonella isolates. Using Fisher's exact test, the proportion of carbapenem resistance isolates was significant at P value 0.032.

Conclusion: The growing resistance of Salmonella isolates to carbapenem drugs in this setting call for caution in usage since this is a pointer to fewer options in the choice of drugs for ESBL’s therapy. Contact precautions should be put in place to forestall further transmission.