Molecular Characterization of Microbial Quality of Ready-to-eat Salads using Multi-locus Sequence Typing

Abstract

Uncertainty persists concerning the role of ready-to-eat (RTE) salad as a bacterial reservoir. The attention paid to food safety by international agencies and international regulations has not improved food safety despite technological advancements, RTE salad’s microbiological quality and safety still seems challenging. The present study’s objective was to detect any microorganism in the RTE salads sold in supermarkets of Riyadh, Saudi Arabia, and to interpret the susceptibility pattern of isolated bacteria to a set of antimicrobials. Phenotypic methods and biochemical analysis were used to identify the isolated bacterium from each salad sample. Antibiograms of the isolated bacteria was determined by VITEK system 2. Multi-locus sequence typing (MLST) was performed for 15 Escherichia coli isolates for investigating evolutionary relationship and genetic analysis. The culture-based technique showed that the major species identified in samples were Aeromonas spp., Acinetobacter spp., E. coli, Roultella ornithinolytica, Citrobacter koseri, Luciferciaadec arboxylata, Klebsiella oxytoca, and Aerococcus viridians. Remarkably, Acinetobacter spp. showed the highest antibiotic resistance to erythromycin, nitrofurantoin and co-trimoxazole. ST 1887 was the most common one traced in 3 E. coli isolates, when total of 12 STs (sequence types) were specified to 15 isolates. A total of three clonal complexes (CC); CC-12, CC-14 & CC-23 were reported in this study. Implementing an accurate, rapid, and easy microbiological analysis method could be valuable for providing higher quality products. Based on the obtained results, dedicated regular RTE salad quality monitoring is recommended, and hand hygiene should be maintained while handling and packaging of RTE.

Keywords

• antibiotic resistance
• vitek system 2
• mlst
• microbial contamination
• rte salad
• supermarkets