Detection of bla-CTXM and bla-TEM Genes, and Biofilm Forming Ability of Esherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa Isolated From Salad Sold at a Private University

Abstract

Food poisoning can be caused by a wide range of substances including but not limited to the presence of pathogenic microorganisms in food e.g. salads. However, there is no report on the occurrence of pathogenic microorganisms in the salads sold in a private University campus and as such the research was performed in order to determine the food safety levels as well as probable sources of contaminants of the salads in the university. The purpose of this research, was to determine the frequency of occurrence of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus in salads sold in the cafeteria on the campus. A total number of 13 samples of salad were obtained and screened for the possible presence of pathogenic bacteria. Identified bacteria isolates were then tested for virulence traits such as antibiotic resistance, motility, biofilm and possession of blaTEM and blaCTX-M genes. All the sought for organisms were found in all collected samples. The total heterotrophic count ranged from 0.74 ± 1.3 ×103cfu/g to 28.2 ± 1.75 × 103cfu/g. The frequency of occurrence of these microorganisms in the salads from the cafeteria stalls ranged from 0(0%) to 5(41%). S. aureus and E. coli had the highest occurrence at 34%. The result of the antibiotic susceptibility test showed complete resistance of all isolates to amoxicillin clavulanate and cefotaxime and complete sensitivity to gentamycin and ofloxacin. Pseudomonas aeruginosa and S. aureus isolates showed multi-drug resistance. Multiple antibiotic resistance (MAR) index ranged from 0.16 to 0.83. Out of all the isolates, only one E. coli of all the E. coli isolates showed the ability to produce biofilm. Amplification of the ESBL genes (blaTEM and blaCTX-M genes) in S. aureus, E. coli and P. aeruginosa isolates showed that they possess the gene which encodes for their resistance to cefotaxime, ceftriaxone, penicillin and cephalosporins. The presence of these organisms in ready to eat salads is a cause for concern as these organisms have been associated with serious foodborne infections.