食源性耐甲氧西林金黄色葡萄球菌生物被膜的形成及相关基因的检测

为了解食源性耐甲氧西林金黄色葡萄球菌（methicillin-resistant S. aureus，MRSA）生物被膜形成能力及其相关基因携带情况。采用刚果红琼脂法和96孔板法测定22株食源性MRSA菌株（包括：原料乳分离株4株，鸡肉、速冻水饺和即食食品分离株各6株）的生物被膜形成能力，同时通过PCR方法对MRSA菌株生物被膜形成相关的15个基因进行检测分析。22株MRSA菌株中，刚果红琼脂法和96孔板法分别检测出21株（95.45%）和22株（100.00%）有生物被膜形成能力。96孔板法测定菌株生物被膜形成能力弱、中等和强的检出率分别为54.55%、40.91%和4.55%。MRSA菌株生物被膜相关基因clfA、fib和eno的携带率最高均为95.45%，其次是clfB（90.91%）、fnbB（54.55%）、icaBC和ebpS（都为45.45%）、agr（27.27%）、icaAD和cna（都为22.73%）、fnbA（13.64%），sar，bbp和sigB（都为4.55%）。此外，来自原料乳和即食食品的MRSA菌株较生鸡肉和速冻水饺MRSA菌株生物被膜形成能力强（p<0.05）。结果表明，96孔板法能够进行定性和定量检测生物膜的形成，而刚果红琼脂法只能定性检测生物被膜的形成，两者的定性检测结果存在一定的差异。通过96孔板法定量检测的结果表明食源性MRSA菌株普遍能形成生物被膜，其中存在一些生物被膜形成能力强的MRSA菌株，同时大部分MRSA菌株不依赖ica途径形成生物被膜，提示产肠毒素MRSA菌株形成生物被膜定植在食品加工过程的环境中，不易清除，成为食品安全中的潜在隐患。

Detection of Biofilm Formation and Biofilm-related Genes of Food-borne Methicillin-resistant Staphylococcus aureus

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.