Generic Salmonella in Asymptomatic Adult Volunteers: Occurrence, Antibiogram, Extended-Spectrum β-Lactamase Production and Carbapenem Resistance

Abstract

This study was conducted to isolate generic Salmonella from stool of apparently-healthy/asymptomatic adult volunteers in Ankpa North-central Nigeria, and to determine antibacterial susceptibility, extended-spectrum β-lactamase production and carbapenem resistance. About a gram of stool was collected from 295 randomly-selected apparently-healthy/asymptomatic adult volunteers in Ankpa Kogi State, North-central Nigeria. Isolation of Salmonella was done by pre-enrichment with buffered peptone water, enrichment with Rapapport-Vassiliadis and sub-culturing on Salmonella-Shigella and MacConkey agar. Identification of the isolates to genus level was done using standard biochemical tests. Resistance of the isolates was determined by disc diffusion method. Production of ESBL was assessed by combination disc method while carbapenem resistance was determined using meropenem disc screening method. Nine (3.1%) out of 295 samples, gave positive growth of Salmonella. Of these 9 isolates, all were carbapenem (meropenem)-resistant and 1 (11.1%) was ESBL-producer. Among the isolates, all were resistant to ciprofloxacin, ofloxacin, norfloxacin, ampicillin, cefotaxime, ceftazidime, gentamicin and streptomycin, 5 (55.6%) to sulphamethoxazole-trimethoprim, 7 (77.8%) to amoxicillin-clavulanic acid and aztreonam, 6 (66.7%) to nitrofurantoin and 8 (88.9%) to tetracycline. All the isolates were resistant to ≥ 5 classes of antibacterial agents. Mean multiple antibacterial indexes of the isolates were 0.68 (range 0.79 - 1.00). Apparently-healthy/asymptomatic adults in Ankpa North-central Nigeria, are potential reservoirs and disseminators of multi- and extensive-drug resistant salmonellae.

Keywords

• asymptomatic adult; carbapenem resistance; extended-spectrum β-lactamase production; extensive drug resistance; Salmonella