Prevalence of methicillin-resistant (mecA gene) and heat-resistant Staphylococcus aureus strains in pasteurized camel milk

摘要

Staphylococcus aureus is a significant opportunisticpathogen in humans, dairy cattle, and camels. Thepresence of antibiotic-resistant and heat-resistant bacteriain camel milk has become a potential public healthissue. The phenotypic and molecular characterizationof methicillin-resistant staphylococcal strains recoveredfrom pasteurized camel milk distributed in retailmarkets of Saudi Arabia was assessed. A total of 100samples were collected between March and May 2017.Out of the 20 S. aureus isolates that were recoveredfrom the pasteurized camel milk, 10 were found to beresistant to cefoxitin (30 μg) and, thus, were designatedas methicillin-resistant strains. The resistance ratio ofmethicillin-resistant S. aureus isolates for a differentclass of antibiotics was determined by performing theantimicrobial susceptibility test and was estimated tobe approximately 60%. Polymerase chain reaction assaywas performed to amplify the methicillin-resistantgene mecA, and furthermore, nucleotide sequencing wasperformed to detect and verify the presence of methicillin-resistant strains. Upon sequencing the putativeS. aureus methicillin-resistant strains, we obtained 96to 100% similarity to the penicillin-binding protein 2agene (mecA) of the S. aureus strain CS100. Moreover,the 10 methicillin-resistant S. aureus isolates were alsoidentified to be heat resistant and were stable at temperaturesup to 85°C for 60 s, with 3 isolates being heatresistant even at 90°C for 60 or 90 s. The mean decimalreduction time (D_(85) value) was 111 s for all the 10 isolates.No difference was observed in the profile of totalprotein between the 10 methicillin- and heat-resistantS. aureus isolates and the S. aureus strain ATCC 29737,which was determined by sodium dodecyl sulfate-PAGEanalyses. Therefore, we could conclude that a relativelyhigh percentage of the tested pasteurized camel milksamples were contaminated with S. aureus (20%) andmethicillin- and heat-resistant S. aureus (10%).