Detection of Biofilm Formation and Biofilm-related Genes of Food-borne Methicillin-resistant Staphylococcus aureus
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Abstract:
In order to investigate understand the biofilm-forming ability and carried biofilm-associated genes of food-borne methicillin-resistant S. aureus (MRSA), the biofilm-forming abilities of twenty-two food-borne MRSA strains (including 4 isolated from raw milk, 6 from raw chicken, 6 from quick-frozen dumplings and 6 from ready-to-eat foods) were analyzed using the Congo red agar (CRA) method and 96-well plate method. In the meantime, fifteen biofilm-associated genes of the MRSA strains were detected by PCR. Among the 22 MRSA strains, 21 strains (95.45%) and 22 strains (100.00%) were found by the Congo red agar and 96-well plate methods to exhibit a biofilm-forming ability. The 96-well plate method showed that the detection rates of the strains with weak, medium and strong biofilm-forming abilities were 54.55%, 40.91% and 4.55%, respectively. The rates for the MRSA strain to carry the biofilm-related genes, clfA, fib and eno were found the highest (95.45%), followed by clfB (90.91%), fnbB (54.55%), icaBC and ebpS (both 45.45%), agr (27.27%), icaAD and cna (both 22.73%), fnbA (13.64%), and sar, bbp and sigB (all 4.55%). In addition, the MRSA strains from raw milk and ready-to-eat foods had stronger biofilm-forming abilities than those from raw chicken and quick-frozen dumplings (p<0.05). The results showed that the 96-well plate method can allow qualitative and quantitative detections of biofilm formation, while the Congo red agar method can only qualitatively detect the formation of biofilms. There were significant differences between the results of the qualitative tests obtained by the two methods. The results of the quantitative detection by the 96-well plate method showed that the food-borne MRSA strains can generally form biofilms, with some MRSA strains exhibiting strong biofilm-forming ability. Most MRSA strains did not rely on the ica pathway to form biofilms, suggesting that enterotoxin-producing MRSA strains can form a biofilm and colonize in the environments of food processing. Owing to the difficulty with their removal, the MRSA strains may become food safety hazards.
