Abstract
Antibiotic- and heat-resistant bacteria in camel milk is a potential public health problem. Staphylococcus aureus (S. aureus) is an opportunistic pathogen in humans, dairy cattle and camels. We characterized the phenotype and genotype of methicillin-resistant staphylococcal strains recovered from pasteurized and raw camel milk (as control) distributed in the retail markets of Saudi Arabia. Of the 100 samples assessed between March and May 2016, 20 S. aureus isolates were recovered from pasteurized milk, 10 of which were resistant to cefoxitin, and as such, were methicillin-resistant. However, raw camel milk did not contain methicillin-resistant S. aureus (MRSA). Antimicrobial susceptibility tests showed that the resistance ratio for other antibiotics was 60%. We performed a polymerase chain reaction (PCR) assay using primers for the methicillin-resistant gene mecA and nucleotide sequencing to detect and verify the methicillin-resistant strains. Basic local alignment search tool (BLAST) analysis of the gene sequences showed a 96–100% similarity between the resistant isolates and the S. aureus CS100 strain’s mecA gene. Ten of the methicillin-resistant isolates were heat-resistant and were stable at temperatures up to 85°C for 60 s, and three of these were resistant at 90°C for 60 or 90 s. The mean decimal reduction time (D85-value) was 111 s for the ten isolates. Sodium dodecyl sulfate (SDS)/polyacrylamide gel electrophoresis (PAGE) showed that there was no difference in the total protein profiles for the ten methicillin heat-resistant S. aureus (MHRSA) isolates and for S. aureus ATCC 29737. In conclusion, a relatively high percentage of the tested pasteurized camel milk samples contained S. aureus (20%) and MHRSA (10%).
Highlights
The foodborne pathogen Staphylococcus aureus (S. aureus), belonging to the Staphylococcus genus, is an opportunistic, nosocomial bacteria that has been previously reported in community-associated (CA) outbreaks worldwide [1,2]
The aims of the present study were to (1) isolate and identify methicillin heat-resistant S. aureus (MHRSA) from pasteurized camel milk samples collected from Riyadh markets in Saudi Arabia, (2) determine antibiotic resistance in these isolates and (3) compare the thermal death time (decimal reduction value (D-value)) for methicillin-resistant S. aureus (MRSA) and MHRSA strains at temperatures higher than that used for pasteurization to explain the latter’s presence in pasteurized milk
Results from the Analytical profile index (API) STAPH-IDENT system test have been shown in Table 1, which revealed that all ten MRSA isolates presented seven-digit profile numbers that were consistent with an S. aureus identity
Summary
The foodborne pathogen Staphylococcus aureus (S. aureus), belonging to the Staphylococcus genus, is an opportunistic, nosocomial bacteria that has been previously reported in community-associated (CA) outbreaks worldwide [1,2]. A number of S. aureus strains are resistant to multiple antibiotics, including methicillin. These methicillin-resistant S. aureus (MRSA) strains harbor the penicillin-binding protein (PBP) 2a (PBP2a)-encoding gene mecA and its analog mecC. Both genes confer resistance to methicillin and other beta (β)-lactam antibiotics, and their presence in food is a global health concern and a threat to public health [3]. The widespread distribution of these strains may be likely a result of the overuse of antibiotics in human medicine and veterinary medicine.
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