The ability of foodborne pathogens to gain entry into food supply systems remains an ongoing concern. In dairy products, raw milk acts as a major vehicle for this transfer; however, the sources of pathogenic bacteria that contaminate raw milk are often not clear, and environmental sources of contamination or the animals themselves may contribute to the transfer. This survey examined the occurrence of 9 foodborne pathogens in raw milk and environments of 7 dairy farms (3 bovine, 3 caprine, and 1 ovine farm) in summer and autumn, in Victoria, Australia. A total of 120 samples were taken from sampling points common to dairy farms, including pasture, soil, feed, water sources, animal feces, raw milk, and milk filters. The prevalence of the Bacillus cereus group, Campylobacter, Clostridium perfringens, Cronobacter, Shiga-toxigenic Escherichia coli, Listeria, Salmonella, coagulase-positive staphylococci (CPS), and Yersinia enterocolitica across the farms was investigated. The 2 most prevalent bacteria, which were detected on all farms, were the B. cereus group, isolated from 41% of samples, followed by Cl. perfringens, which was isolated from 38% of samples. The highest occurrence of any pathogen was the B. cereus group in soil, present in 93% of samples tested. Fecal samples showed the highest diversity of pathogens, containing 7 of the 9 pathogens tested. Salmonella was isolated from 1 bovine farm, although it was found in multiple samples on both visits. Out of the 14 occurrences where any pathogen was detected in milk filters, only 5 (36%) of the corresponding raw milk samples collected at the same time were positive for the same pathogen. All of the CPS were Staphylococcus aureus, and were found in raw milk or milk filter samples from 6 of the 7 farms, but not in other sample types. Pathogenic Listeria species were detected on 3 of the 7 farms, and included 4 L. ivanovii-positive samples, and 1 L. monocytogenes-positive water sample. Shiga-toxigenic Escherichia coli were identified in fecal samples from 3 of the 7 farms and in a single raw milk sample. Cronobacter species were identified on 4 of the 7 farms, predominantly in feed samples. No Y. enterocolitica was detected. Results of this study demonstrate high standards of pathogen safety across the 7 farms, with a low incidence of pathogens detected in raw milk samples. Monitoring feed contamination levels may help control the spread of bacterial species such as Cl. perfringens and B. cereus through the farm environment, which is a natural reservoir for these organisms.

Highly 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. A 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. Although 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.