Antimicrobial resistance pattern of enterococci isolated from stool samples in a tertiary hospital in Nigeria

Background: Enterococci cause infections both in and out of the hospital setting and have demonstrated resistance to almost all classes of drugs. A combination of cell wall acting agents and high-level aminoglycosides is a commonly used regimen for serious infections, but resistance to either renders the synergism ineffective. Vancomycin is the drug of choice for life-threatening infections, but there have been increasing reports of resistance to the drug. Vancomycin-resistant enterococci (VRE) infection is usually preceded by gastrointestinal colonization. Aim: This study was carried out to determine the antimicrobial resistance profile of Enterococcus species isolated from stool and the prevalence of VRE. Materials and Methods: Enterococci were identified from stool samples based on characteristic growth patterns on Bile Esculin Agar and MacConkey agar and growth in 6.5% sodium chloride broth. Speciation was by conventional biochemical identification. Antibiotic susceptibility testing and screening for high-level aminoglycoside resistance (HLAR) were done by modified Kirby–Bauer disk diffusion technique. Susceptibility of isolates to linezolid, penicillin, nitrofurantoin, high-level gentamicin and streptomycin, tetracycline, ciprofloxacin, vancomycin, and teicoplanin was tested. VRE screening was done using a chromogenic agar. The polymerase chain reaction was used for confirmation. Results: Nine species of Enterococcus were identified from 561 isolates. The most common species were Enterococcus faecium (46.0%), Enterococcus faecalis (21.6%), Enterococcus gallinarum (18.5%), and Enterococcus casseliflavus (5.2%). Resistance was highest to ciprofloxacin, tetracycline, and nitrofurantoin. Lowest resistance was to vancomycin, teicoplanin, gentamicin, and linezolid. VRE prevalence rate was 1.1% and that of HLAR was 20.7%. All VRE had vanA gene. Conclusion: Overall, E. faecium was the predominant species. Highest resistance was to ciprofloxacin and tetracycline.