Bovine Staphylococcus aureus: Subtyping, evolution, and zoonotic transfer.

Staphylococcus aureus is globally one of the most important pathogens causing contagious mastitis in cattle. Previous studies using ribosomal spacer (RS)-PCR, however, demonstrated in Swiss cows that Staph. aureus isolated from bovine intramammary infections are genetically heterogeneous, with Staph. aureus genotype B (GTB) and GTC being the most prominent genotypes. Furthermore, Staph. aureus GTB was found to be contagious, whereas Staph. aureus GTC and all the remaining genotypes were involved in individual cow disease. In addition to RS-PCR, other methods for subtyping Staph. aureus are known, including spa typing and multilocus sequence typing (MLST). They are based on sequencing the spa and various housekeeping genes, respectively. The aim of the present study was to compare the 3 analytic methods using 456 strains of Staph. aureus isolated from milk of bovine intramammary infections and bulk tanks obtained from 12 European countries. Furthermore, the phylogeny of animal Staph. aureus was inferred and the zoonotic transfer of Staph. aureus between cattle and humans was studied. The analyzed strains could be grouped into 6 genotypic clusters, with CLB, CLC, and CLR being the most prominent ones. Comparing the 3 subtyping methods, RS-PCR showed the highest resolution, followed by spa typing and MLST. We found associations among the methods but in many cases they were unsatisfactory except for CLB and CLC. Cluster CLB was positive for clonal complex (CC)8 in 99% of the cases and typically positive for t2953; it is the cattle-adapted form of CC8. Cluster CLC was always positive for tbl 2645 and typically positive for CC705. For CLR and the remaining subtypes, links among the 3 methods were generally poor. Bovine Staph. aureus is highly clonal and a few clones predominate. Animal Staph. aureus always evolve from human strains, such that every human strain may be the ancestor of a novel animal-adapted strain. The zoonotic transfer of IMI- and milk-associated strains of Staph. aureus between cattle and humans seems to be very limited and different hosts are not considered as a source for mutual, spontaneous infections. Spillover events, however, may happen.

Boss R ，Cosandey A ，Luini M ，Artursson K ，Bardiau M ，Breitenwieser F ，Hehenberger E ，Lam T ，Mansfeld M ，Michel A ，Mösslacher G ，Naskova J ，Nelson S ，Podpečan O ，Raemy A ，Ryan E ，Salat O ，Zangerl P ，Steiner A ，Graber HU ... -  《-》

Staphylococcus aureus genotype B and other genotypes isolated from cow milk in European countries.

Staphylococcus aureus is globally one of the most important pathogens causing contagious mastitis in cattle. Previous studies, however, have demonstrated in Swiss cows that Staph. aureus isolated from bovine intramammary infection is genetically heterogeneous, with Staph. aureus genotype B (GTB) and GTC being the most prominent genotypes. In addition, Staph. aureus GTB was found to be contagious, whereas Staph. aureus GTC and all the remaining genotypes were involved in individual cow disease. The aim of this study was to subtype strains of Staph. aureus isolated from bovine mastitic milk and bulk tank milk to obtain a unified view of the presence of bovine staphylococcal subtypes in 12 European countries. A total of 456 strains of Staph. aureus were subjected to different typing methods: ribosomal spacer PCR, detection of enterotoxin genes, and detection of gene polymorphisms (lukE, coa). Major genotypes with their variants were combined into genotypic clusters (CL). This study revealed 5 major CL representing 76% of all strains and comprised CLB, CLC, CLF, CLI, and CLR. The clusters were characterized by the same genetic properties as the Swiss isolates, demonstrating high clonality of bovine Staph. aureus. Interestingly, CLB was situated in central Europe whereas the other CL were widely disseminated. The remaining 24% of the strains comprised 41 genotypes and variants, some of which (GTAM, GTBG) were restricted to certain countries; many others, however, were observed only once.

Cosandey A ，Boss R ，Luini M ，Artursson K ，Bardiau M ，Breitenwieser F ，Hehenberger E ，Lam T ，Mansfeld M ，Michel A ，Mösslacher G ，Naskova J ，Nelson S ，Podpečan O ，Raemy A ，Ryan E ，Salat O ，Zangerl P ，Steiner A ，Graber HU ... -  《-》

Short communication: Characterization of Staphylococcus aureus from bulk tank milk of dairy cattle in Lombardy (northern Italy).

Staphylococcus aureus is one of the most important pathogens causing mastitis in cattle, and it is responsible for economic losses in dairy herds worldwide. The PCR amplification of the 16S-23S rRNA intergenic spacer (ribosomal spacer PCR, RS-PCR) allows a rapid classification of the strains in genotypes and genotypic clusters (CL), which are characterized by different epidemiological and clinical properties. Both RS-PCR and multi-locus sequence typing (MLST) were performed on strains isolated from bovine bulk tank milk (BTM) collected from dairy herds located in the Lombardy region (northern Italy), to outline the distribution of Staph. aureus genotypes in this geographical area. Out of 844 examined samples, 398 were positive for Staph. aureus, with a variable count (cfu/mL) Up to 8 colonies from each sample were genotyped. A total of 1,101 Staph. aureus strains were analyzed with RS-PCR, and only a selection of them (n = 86), in relation to their frequency and geographical origin, underwent MLST. This study revealed 8 major genotypic clusters (CLB, CLC, CLR, CLS, CLI, CLF, CLAO, and CLZ), of which Staph. aureus CLB (29.3%) was the most common. Samples of BTM positive for CLB had a Staph. aureus cfu/mL count significantly higher than the non-CLB positive ones. Our MLST analysis showed genotypes already known as bovine-associated in literature, such as clonal complexes CC8, CC97, and CC151. The same selection of 86 strains was also analyzed for the presence of the adlb gene, which was recently proposed as a possible marker of contagiousness. Most Staph. aureus belonging to CLB or CC8 carried the adlb gene (85%), whereas this gene was detected in only 9% of non-CLB strains (CLAA, CLBI, CLBJ, CLS). In conclusion, the present study confirms that Staph. aureus CLB, which is recognized as a contagious genotype, is a particularly relevant agent of intramammary infection in dairy cows in Lombardy, and indirectly supports the idea that adlb can be a possible marker of contagiousness of isolates.

Gazzola A ，Maisano AM ，Bianchini V ，Vezzoli F ，Romanò A ，Graber HU ，Cremonesi P ，Zanardi G ，Cappa V ，Luini M ... -  《-》

Genotypes of Staphylococcus aureus: On-farm epidemiology and the consequences for prevention of intramammary infections.

Staphylococcus aureus is a highly contagious mastitis-causing pathogen infecting dairy cattle worldwide. Previous studies have shown the presence of different genotypes (GT) on farms. In Switzerland, Staph. aureus genotype B (GTB) is contagious, whereas GTC and other genotypes cause sporadic, noncontagious mastitis. In this study, we evaluated the epidemiological properties of Staph. aureus, together with its genotypes and spa types, on Swiss dairy farms. A total of 21 dairy farms were sampled throughout Switzerland; 10 farms were positive for the contagious Staph. aureus GTB and 11 farms were negative for GTB. Samples were taken from milk, body surfaces of dairy cattle and other animals, milkers, milking equipment, and environmental sites (e.g., parlor, washing room, stall floor, manger, and bedding). The epidemiology of Staph. aureus depended markedly on the genotype. Staphylococcus aureus GTB was associated with mammary gland, intramammary infections (IMI), and milking clusters, whereas GTC and other genotypes were related to cow and other animal surfaces and occasionally to environment. Genotype C was by far the most common subtype in cattle and was found on GTB-negative and GTB-positive farms. Each farm had a predominant genotype, such as GTB, GTC, GTA, or GTF, but a few farms were almost free from Staph. aureus. The genotypes and spa types of Staph. aureus detected in the noses of milkers clearly differed from those found in dairy cattle, other animals, milking equipment, and the environment. Exceptions were GTS (spa type t034) and GTF (t899), which crossed the species barrier. In most cases, however, the species barrier was maintained because Staph. aureus is adapted to a particular host and even to particular body sites. As biological properties differ among the genotypes, new guidelines to prevent IMI caused by different genotypes were established: classical measures to prevent IMI caused by contagious pathogens still hold for GTB but not for Staph. aureus genotypes that are opportunistic colonizers of bovine skin (e.g., GTC and GTA). For those genotypes, protection of the skin from minor lesions and wounds, particularly on the hocks, is essential.

Leuenberger A ，Sartori C ，Boss R ，Resch G ，Oechslin F ，Steiner A ，Moreillon P ，Graber HU ... -  《-》

Genomic characteristics of Staphylococcus aureus strains associated with high within-herd prevalence of intramammary infections in dairy cows.

Staphylococcus aureus is one of the most important causes of mastitis in dairy cattle. Based on previous research, Staph. aureus genotypes with different pathogenic and contagious properties can cause intramammary infection (IMI) and coexist in the same herd. Our study aimed to compare Staph. aureus strains from herds that differed in IMI prevalence using different molecular approaches such as ribosomal spacer (RS)-PCR, multilocus sequence typing (MLST), spa typing, ribotyping, pulsed-field gel electrophoresis (PFGE), and multiplex PCR. For this purpose, 31 dairy herds with Staph. aureus IMI were selected, and 16 of these were chosen for a comparison study: the 8 high-prevalence (HP) herds had Staph. aureus IMI prevalence >28% and the 8 low-prevalence (LP) herds had an IMI prevalence <4%. A total of 650 isolates of Staph. aureus from mammary quarters of all positive cows were genotyped with RS-PCR, a technique based on amplification of a portion of the intergenic spacer 16S-23S rRNA, and a subset of 54 strains was also analyzed by multiplex PCR, ribotyping, PFGE, MLST, and spa typing. The RS-PCR analysis revealed 12 different profiles. Staphylococcus aureus strains isolated from 5 out of 8 HP herds showed a profile identical to the genotype B (GTB), described in previous studies as being strongly associated with high within-herd prevalence of Staph. aureus mastitis and the presence of the genes coding for enterotoxins sea, sed, and sej, a long x-region of spa gene, and 3 lukE fragments. Moreover, all strains isolated in the HP herds possessed genes coding for staphylococcal enterotoxins. In LP herds, a limited number of strains of 6 genotypes, different from those isolated in HP herds, were identified and GTB was not found. Within these genotypes, 4 strains were positive for the mecA gene. Preliminary results and comparison with other genotyping methods confirmed that genotyping by RS-PCR is an accurate, rapid, and inexpensive tool for future field studies on Staph. aureus mastitis strains and generates clinically relevant results.

Cremonesi P ，Pozzi F ，Raschetti M ，Bignoli G ，Capra E ，Graber HU ，Vezzoli F ，Piccinini R ，Bertasi B ，Biffani S ，Castiglioni B ，Luini M ... -  《-》