Abstract
Milk pasteurization eliminates vegetative pathogenic microorganisms and reduces microorganisms associated with spoilage. Camel milk is a well-accepted, traditionally consumed food in Arab countries. The present study aimed to investigate the microflora of pasteurized camel milk sold in Riyadh City, Saudi Arabia. The heat resistance of the microflora was tested in culture medium and lab-sterilized milk, and its composition was verified by multiplex polymerase chain reaction (PCR) using specific primers. Further verification was performed by using separate specific primers. The identified strain survived heat treatment at 65, 72, 80, 85, and 90°C for 30, 15, 10, 5, and 2 min, respectively. An unanticipated result was obtained when an enterotoxin producing strain of Staphylococcus aureus showed abnormal resistance to heat treatment. The enterotoxin gene within the PCR fragment was identified as enterotoxin C by DNA sequencing. During Basic Local Alignment Search Tool (BLAST) analysis, the isolated enterotoxin C genes showed >99% similarity to published database sequences of the Staphylococcus aureus strain SAI48 staphylococcal enterotoxin C variant v4 (sec) gene. The decimal reduction value (D-value) at 90°C (D90) was determined after 10 s. This is the first time to report this abnormally heat resistant and enterotoxin-producing strain of Staphylococcus aureus. The use of ultra-high temperatures (UHTs) is preferable for reducing or killing bacteria in camel milk, especially if this problem is encountered in many camel milk factories.
Highlights
Toxin producing strains of Staphylococcus aureus can cause diseases in humans and animals
Colonies of the Staphylococcus isolates were surrounded by clear zones on sheep blood agar, similar to that observed for the β-haemolysis of the reference S. aureus ATCC 29737 strain
Coagulase production was considered evidence that our isolates were toxin-producing organisms. These results corresponded to those obtained by Di Salvo (1958) [20], who confirmed that there is a correlation between coagulase activity and DNase activity because of the incorporation of DNA into the medium along with calcium chloride, which
Summary
Toxin producing strains of Staphylococcus aureus can cause diseases in humans and animals. Their pathogenicity is attributable to toxin production and the antibiotic-resistant nature of these strains [1]. S. aureus strains that are foodborne pathogens are referred to as toxin producing strains [2]. The enterotoxins produced by S. aureus (SEs) have been classified into five types based on serology, including sea, seb, sec, sed, and see [1]. Enterotoxins B (seb) and C (sec), as well as toxic shock syndrome toxin 1 (TSST-1), are located on the chromosome [5,6], while enterotoxins D (sed) and J (sej) are carried by plasmids [5]
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