Ready-to-eat vegetable salads served in Nigerian restaurants: a potential source of multidrug-resistant bacteria

Public health promotion of fruit and vegetables as healthier sources of nutrition in Nigeria has led to an increase in consumption of fruit and vegetables, particularly in the form of ready-to-eat (RTE) salads. However, the continual association of drug-resistant bacteria with fruit and vegetables creates an additional challenge for consumer safety. Hence this study was carried out to determine the prevalence of multidrug-resistant bacteria (MRB) in, and characterization of MRB isolated from, RTE salads.

RTE vegetable salad samples were randomly selected for bacterial analysis with Wei's Urn iterative randomization technique and a One Way Analysis of Variance performed with Kruskal-Wallis test. Total viable bacteria count (TVC) was performed with pour-plate technique. Bacterial colonies from Petri plates were tested for multidrug resistance with Kirby Bauer disc diffusion test and prevalence/counts of MRB, as well as multiple antibiotic resistance indices (MAR), was/were subsequently deduced. Mean prevalence of MRB in all RTE salad samples was estimated at 54·38% while mean counts of MRB were estimated at 6·83 ± 6·42 log₁₀ CFU per g. Prevalence of bacterial resistance to all antibiotics tested ranged from 5·92 to 100·00%. Mean MAR obtained for all RTE salad samples was estimated at 0·51 (recommended limit = 0·20) indicating that RTE salads were a potential source of MRB, with significant health risk. MRB isolated from RTE salads included Proteus vulgaris strain ATU 243, Bacillus thuringiensis strain AND 236, Citrobacter freundii strain ABC 2 and Serratia marcescens strain ADJ 212.

This study showed that MRB constitute a significant proportion of the bacterial community present in RTE salads served in Nigerian restaurants.

Our study provided empirical evidence which showed that RTE salads served in Nigerian restaurants were a potential source of MRB, with significant health risk.