Characterization of Staphylococcus aureus isolates from raw milk sources in Victoria, Australia

Abstract

BackgroundHighly pathogenic strains of Staphylococcus aureus can cause disease in both humans and animals. In animal species, including ruminants, S. aureus may cause severe or sub-clinical mastitis. Dairy animals with mastitis frequently shed S. aureus into the milk supply which can lead to food poisoning in humans. The aim of this study was to use genotypic and immunological methods to characterize S. aureus isolates from milk-related samples collected from 7 dairy farms across Victoria.ResultsA total of 30 S. aureus isolates were collected from milk and milk filter samples from 3 bovine, 3 caprine and 1 ovine dairy farms across Victoria, Australia. Pulsed Field Gel Electrophoresis (PFGE) identified 11 distinct pulsotypes among isolates; all caprine and ovine isolates shared greater than 80 % similarity regardless of source. Conversely, bovine isolates showed higher diversity. Multi-Locus Sequence Typing (MLST) identified 5 different sequence types (STs) among bovine isolates, associated with human or ruminant lineages. All caprine and ovine isolates were ST133, or a single allele variant of ST133. Two new novel STs were identified among isolates in this study (ST3183 and ST3184). With the exception of these 2 new STs, eBURST analysis predicted all other STs to be founding members of their associated clonal complexes (CCs). Analysis of genetic markers revealed a diverse range of classical staphylococcal enterotoxins (SE) among isolates, with 11 different SEs identified among bovine isolates, compared with just 2 among caprine and ovine isolates. None of the isolates contained mecA, or were resistant to oxacillin. The only antibiotic resistance identified was that of a single isolate resistant to penicillin; this isolate also contained the penicillin resistance gene blaZ. Production of SE was observed at 16 °C and/or 37 °C in milk, however no SE production was detected at 12 °C.ConclusionAlthough this study characterized a limited number of isolates, bovine-associated isolates showed higher genetic diversity than their caprine or ovine counterparts. This was also reflected in a more diverse SE repertoire among bovine isolates. Very little antibiotic resistance was identified among isolates in this study. These results suggest maintaining the milk cold chain will minimise any risk from SE production and highlights the need to prevent temperature abuse.

Characterization of Enterotoxigenic Bacillus cereus sensu lato and Staphylococcus aureus Isolates and Associated Enterotoxin Production Dynamics in Milk or Meat-Based Broth

“…In contrast to this, the sed -containing isolate Sa14-003 produced detectable SED after 72 h in both milk and meat, suggesting that although 16 °C poses a risk for SED intoxication, it requires prolonged temperature abuse to achieve this. Taken together, these results support the assertion that maintaining the cold chain is an effective control to prevent SEC or SED intoxication [ 24 , 32 ].…”

“…Understanding toxin production together with cell density under temperature abuse conditions is critical to informing food safety. To this end, previous studies may be limited as a result of using laboratory broth rather than a food matrix [ 31 ], not providing adequate consideration for cell density [ 26 , 27 ], only examining relatively high temperatures [ 25 ], or not considering variable behaviour in different food matrices [ 32 ]. With the globalization of food supply chains, increasingly complex logistics presents an increasing opportunity for temperature abuse.…”

Phenotypic and genotypic characterization of Staphylococcus aureus isolates in milk from flocks diagnosed with subclinical mastitis

“…In farms, pathogenic strains of microorganisms may originate from a variety of sources, including the animal itself. These strains can easily pass from one source to another through different routes of transmission, which include: contact between animals, stalls, milking equipment, and the milkers' hands (McMillan et al, 2016). Genotypic methods may be employed to obtain information regarding the potential infection sources and routes of diseases transmission.…”

“…Among the typing methods based on fingerprint, PCR-RFLP, RAPD-PCR, ERIC-PCR, BOX-PCR, and REP-PCR have been described as simple and quick techniques for taxonomic and epidemiological analyses of several species of the genus Staphylococcus (Bergonier et al, 2014;Idil and Bilkay, 2014;Rahman et al, 2016;Ławniczek-Wałczyk et al, 2017). Epidemiological molecular studies have contributed significantly to the understanding of the sources, routes of transmission and prognosis for many pathogens that cause bovine mastitis, as well as to understand the mechanisms of adaptation to the host and the causes of the disease (Supré et al, 2011;McMillan et al, 2016).…”

Draft Genome Sequences of 15 Staphylococcus aureus Isolates Recovered from Raw Milk and Associated Milk Filters from Victoria, Australia

“…Seven sequence types (STs) were identified, including two novel STs (ST3183 and ST3184) (3). All ovine and caprine isolates were ST133 or a highly related variant (ST3184), whereas bovine isolate STs were diverse (ST1, ST5, ST8, ST705, and ST3183).…”