Aims: To investigate the presence of enterotoxigenic Staphylococcus aureus in bulk milk and in a selection of raw milk products. Methods and results: Samples of bovine (n ¼ 220) and caprine (n ¼ 213) bulk milk, and raw milk products (n ¼ 82) were analysed for S. aureus. Isolates were tested for staphylococcal enterotoxin (SE) production (SEA-SED) by reversed passive latex agglutination and for SE genes (sea-see, seg-sej) by multiplex PCR. Staphylococcus aureus was detected in 165 (75%) bovine and 205 (96AE2%) caprine bulk milk samples and in 31 (37AE8%) raw milk product samples. Enterotoxin production was observed in 22AE1% and 57AE3% of S. aureus isolates from bovine and caprine bulk milk, respectively, while SE genes were detected in 52AE5% of the bovine and 55AE8% of the caprine bulk milk isolates. SEC and sec were most commonly detected. A greater diversity of SE genes were observed in bovine vs caprine isolates. Conclusions: Staphylococcus aureus seems highly prevalent in Norwegian bulk milk and isolates frequently produce SEs and contain SE genes. Enterotoxigenic S. aureus were also found in raw milk products. Significance and Impact of the Study: Staphylococcus aureus in Norwegian bovine and caprine bulk milk may constitute a risk with respect to staphylococcal food poisoning from raw milk products.
Strains of Staphylococcus aureus obtained from bovine (n ؍ 117) and caprine (n ؍ 114) bulk milk were characterized and compared with S. aureus strains from raw-milk products (n ؍ 27), bovine mastitis specimens (n ؍ 9), and human blood cultures (n ؍ 39). All isolates were typed by pulsed-field gel electrophoresis (PFGE). In addition, subsets of isolates were characterized using multilocus sequence typing (MLST), multiplex PCR (m-PCR) for genes encoding nine of the staphylococcal enterotoxins (SE), and the cloverleaf method for penicillin resistance. A variety of genotypes were observed, and greater genetic diversity was found among bovine than caprine bulk milk isolates. Certain genotypes, with a wide geographic distribution, were common to bovine and caprine bulk milk and may represent ruminant-specialized S. aureus. Isolates with genotypes indistinguishable from those of strains from ruminant mastitis were frequently found in bulk milk, and strains with genotypes indistinguishable from those from bulk milk were observed in raw-milk products. This indicates that S. aureus from infected udders may contaminate bulk milk and, subsequently, raw-milk products. Human blood culture isolates were diverse and differed from isolates from other sources. Genotyping by PFGE, MLST, and m-PCR for SE genes largely corresponded. In general, isolates with indistinguishable PFGE banding patterns had the same SE gene profile and isolates with identical SE gene profiles were placed together in PFGE clusters. Phylogenetic analyses agreed with the division of MLST sequence types into clonal complexes, and isolates within the same clonal complex had the same SE gene profile. Furthermore, isolates within PFGE clusters generally belonged to the same clonal complex.
A 1-yr field investigation of clinical mastitis in heifers was carried out in 24 veterinary districts in Norway. Quarter lacteal secretions from cases that occurred prepartum or within 14 d postpartum were examined bacteriologically. The study included 1040 heifers with clinical mastitis, and the total number of quarters that were clinically affected was 1361. The organisms that were most frequently isolated from samples from these quarters were Staphylococcus aureus (44.3%), Streptococcus dysgalactiae (18.2%), Staph. aureus together with Strep. dysgalactiae (1.2%), coagulase-negative staphylococci (12.8%), Arcanobacterium pyogenes (3.5%), A. pyogenes together with Strep. dysgalactiae (0.5%) or Staph. aureus (0.4%), and Escherichia coli (6.4%). Of the coagulase-negative staphylococci, Staphylococcus simulans (53.7%), Staphylococcus hyicus (14.8%), and Staphylococcus chromogenes (14.8%) were the most prevalent species. Except for a higher relative percentage of A. pyogenes in cases that occurred before parturition (8.2%) than in cases that occurred after parturition (2.7%), no significant differences were observed in the distribution of the various organisms among prepartum and postpartum cases. Regional variations were observed in the distribution of organisms. The proportions of Staph. aureus and A. pyogenes were highest, and the proportion of coagulase-negative staphylococci was lowest, in late autumn and early winter. The proportion of E. coli was highest in summer. In heifers in which mastitis was associated with increased rectal temperature or other systemic signs, the proportion of clinically affected quarters that were infected with Staph. aureus was larger than that in heifers without systemic reaction.
In recent years, the small-scale production of raw milk products has increased in Norway, and there is some concern that such foods may pose a risk of staphylococcal food poisoning to consumers. The aim of the study was to evaluate potential sources of contamination of raw milk cheese with Staphylococcus aureus on a bovine dairy farm with small-scale production. Samples for bacteriological analyses (n = 144) were collected from the animals, the environment, processing equipments, from humans, and from cheeses at various stages of production. Staphylococcus aureus was isolated from 10 of 11 cows, the farmer, equipment, the environment, and the cheese. Seventy-five Staph. aureus isolates were genotyped by pulsed-field gel electrophoresis, tested for enterotoxin (SE) production by reversed passive latex agglutination, for SE genes by multiplex polymerase chain reaction, and for penicillin resistance by the cloverleaf method. Five different pulsotypes were identified and SE gene fragments were identified in 11 isolates, but no isolates produced SE or were penicillin resistant. Staphylococcus aureus was found throughout the farm, and appeared to be spread with the milk to the environment, equipment, and to products. One pulsotype dominated and was identified from most sample sites on the farm. Raw milk products are vulnerable to contamination with Staph. aureus. Strategies to reduce the occurrence of Staph. aureus in bulk milk are of particular importance on farms where milk is used for raw milk products.
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