District-Wide Herd Sanitation and Eradication of Intramammary Staphylococcus aureus Genotype B Infection in Dairy Herds in Ticino, Switzerland

The present study demonstrates successful herd sanitation and eradication of contagious mastitis caused by Staphylococcus aureus genotype B (S. aureus GTB) in an entire Swiss district (Ticino) including 3,364 dairy cows from 168 farms. Herd sanitation included testing of all cows using a highly GTB specific and sensitive qPCR assay, implementation of related on-farm measures, appropriate antibiotic therapy of GTB-positive cows and culling of therapy-resistant animals, respectively. A treatment index was used as an objective criterion to select GTB-positive cows eligible for culling and replacement payment. 62 herds (37%) were initially GTB-positive with a cow prevalence between 10% and 100% and were submitted to sanitation. Twenty mo after the start of the campaign, all these herds were free from S. aureus GTB, whereby 73% of them were sanitized during the first 7 mo. At the cow level, a total of 343 animals were infected. 50 of them were immediately culled and financially compensated based on their treatment index value. The remaining 293 cows were intramammarily treated with antibiotics either during lactation using the combination of cephalexin-kanamycin or penicillin-gentamicin or at dry-off using cloxacillin. Out of these cows, 275 (93.9%) were treated successfully meaning that their milk was twice GTB-negative by qPCR after therapy. For lactational treatment, control samples were taken ≥10 and ≥20 d after treatment, for dry off treatment ≥14 and ≥24 d after parturition. Neither lactation number nor SCC before treatment of the cow nor the type of therapy were associated with therapeutic cure. Using data of 30 GTB-positive and 71 GTB-negative herds (1855 observations), the impact of GTB sanitation on bulk tank milk SCC (BTSCC) was evaluated applying a linear mixed statistical model. In the year before sanitation, BTSCC was always higher in GTB positive than in GTB negative herds. After the start of the campaign, BTSCC declined rapidly in the herds under GTB sanitation and achieved values that no longer differed statistically from those of GTB-free herds after only 2 mo, remaining very similar for the rest of the campaign. The farmers were very satisfied with the outcome of the campaign as all GTB positive herds could be sanitized rapidly, sanitation was sustainable, and milk quality increased.

Pathogen group-specific risk factors for intramammary infection in water buffalo

A cross-sectional study was conducted to estimate the prevalence of intramammary infection (IMI) associated bacteria and to identify risk factors for pathogen group-specific IMI in water buffalo in Bangladesh. A California Mastitis Test (CMT) and bacteriological cultures were performed on 1,374 quarter milk samples collected from 763 water buffalo from 244 buffalo farms in nine districts in Bangladesh. Quarter, buffalo, and farm-related data were obtained through questionnaires and visual observations. A total of 618 quarter samples were found to be culture positive. Non-aureus staphylococci were the predominant IMI-associated bacterial species, and Staphylococcus (S.) chromogenes, S. hyicus, and S. epidermidis were the most common bacteria found. The proportion of non-aureus staphylococci or Mammaliicoccus sciuri (NASM), S. aureus, and other bacterial species identified in the buffalo quarter samples varied between buffalo farms. Therefore, different management practices, buffalo breeding factors, and nutrition were considered and further analyzed when estimating the IMI odds ratio (OR). The odds of IMI by any pathogen (OR: 1.8) or by NASM (OR: 2.2) was high in buffalo herds with poor milking hygiene. Poor cleanliness of the hind quarters had a high odds of IMI caused by any pathogen (OR: 2.0) or NASM (OR: 1.9). Twice daily milking (OR: 3.1) and farms with buffalo purchased from another herd (OR: 2.0) were associated with IMI by any pathogen. Asymmetrical udders were associated with IMI-caused by any bacteria (OR: 1.7). A poor body condition score showed higher odds of IMI by any pathogen (OR: 1.4) or by NASM (OR: 1.7). This study shows that the prevalence of IMI in water buffalo was high and varied between farms. In accordance with the literature, our data highlight that IMI can be partly controlled through better farm management, primarily by improving hygiene, milking management, breeding, and nutrition.

Staphylococcus aureus and biofilms: transmission, threats, and promising strategies in animal husbandry

Staphylococcus aureus (S. aureus) is a common pathogenic bacterium in animal husbandry that can cause diseases such as mastitis, skin infections, arthritis, and other ailments. The formation of biofilms threatens and exacerbates S. aureus infection by allowing the bacteria to adhere to pathological areas and livestock product surfaces, thus triggering animal health crises and safety issues with livestock products. To solve this problem, in this review, we provide a brief overview of the harm caused by S. aureus and its biofilms on livestock and animal byproducts (meat and dairy products). We also describe the ways in which S. aureus spreads in animals and the threats it poses to the livestock industry. The processes and molecular mechanisms involved in biofilm formation are then explained. Finally, we discuss strategies for the removal and eradication of S. aureus and biofilms in animal husbandry, including the use of antimicrobial peptides, plant extracts, nanoparticles, phages, and antibodies. These strategies to reduce the spread of S. aureus in animal husbandry help maintain livestock health and improve productivity to ensure the ecologically sustainable development of animal husbandry and the safety of livestock products.

The risk of multiple sclerosis on the Orkney islands. A review of the search for distinctively Orcadian risks, with a hypothesis for further investigations

The most extensive and meticulous epidemiological study yet to be published on the frequency of multiple sclerosis (MS) across the regions of Scotland has confirmed that the high incidence of MS on the Orcadian islands is unique and is most probably the highest in the world. Environmental and genetic studies of Orcadian MS have been carried out over many years but the results have been discouragingly inconclusive; no convincing explanation of the distinctively high Orcadian MS risks has come to light. However, studies of both prevalence and incidence of MS over a time line of approximately five decades, show that Orcadian MS has steadily increased to significantly exceed the neighbouring genetically related populations including North Eastern Scotland and the Shetland islands. Over this period the islands have progressively expanded occupations related to agriculture and have simultaneously acquired the highest concentration of cattle in Europe. Coinciding high and increasing Orcadian MS risk with increasing agricultural activities including bovine density and dairying, points towards a potential but unexpected causal risk. Raised incidence of MS with farming and in particular with dairy farming have been documented in Australia, Denmark, and more recently in Norway, further pointing to a possible MS risk associated with agricultural activities. A clue to the cause of this curious association has unexpectedly emerged from laboratory studies. Using very rarely available tissues from patients coming to autopsy during an MS attack, a toxin known as beta-haemolysin (sphingomyelinase), which is produced by the bacterium Staphylococcus aureus, has been identified in the affected tissues. Staph aureus is a common inhabitant of the mucosal linings of the human nasal sinuses and sinus mucosal inflammations have been shown to be closely associated with attacks of MS and optic neuritis. Irrespective of origin, human or animal, all strains of Staph aureus carry the beta haemolysin gene. However, the toxin is only sporadically expressed by the strains most commonly isolated from human carriers. Strains carried by bovines nearly always express toxin. Has the increasing high risk of MS in Orcadians been promoted by the nasal transmission and subsequent establishment of the high secreting bovine genotypes of Staph aureus in the Orcadian population? To demonstrate that bovine associated strains of Staph aureus are carried more frequently in the Orcadian population (or even specifically in Orcadian MS cases), would not of itself necessarily explain the high prevalence of Orcadian MS. It would however clearly justify an in-depth exploration of the nasal bacterial microbiome of MS cases. This should include the incidence of beta-toxin secreting Staph aureus genotypes. If MS cases are shown to have a distinctive nasal bacterial microbiome, including beta-toxin secretors, this finding would open up an almost entirely new range of investigations and approaches to the understanding of the pathogenesis of MS.

Phenotypic and genotypic assessment of iron acquisition in diverse bovine-associated non-aureus staphylococcal strains

Although the role of iron in bacterial infections has been well described for Staphylococcus (S.) aureus, iron acquisition in (bovine-associated) non-aureus staphylococci and mammaliicocci (NASM) remains insufficiently mapped. This study aimed at elucidating differences between four diverse bovine NASM field strains from two species, namely S. chromogenes and S. equorum, in regards to iron uptake (with ferritin and lactoferrin as an iron source) and siderophore production (staphyloferrin A and staphyloferrin B) by investigating the relationship between the genetic basis of iron acquisition through whole genome sequencing (WGS) with their observed phenotypic behavior. The four field strains were isolated in a previous study from composite cow milk (CCM) and bulk tank milk (BTM) in a Flemish dairy herd. Additionally, two well-studied S. chromogenes isolates originating from a persistent intramammary infection and from a teat apex were included for comparative purpose in all assays. Significant differences between species and strains were identified. In our phenotypical iron acquisition assay, while lactoferrin had no effect on growth recovery for all strains in iron deficient media, we found that ferritin served as an effective source for growth recovery in iron-deficient media for S. chromogenes CCM and BTM strains. This finding was further corroborated by analyzing potential ferritin iron acquisition genes using whole-genome sequencing data, which showed that all S. chromogenes strains contained hits for all three proposed ferritin reductive pathway genes. Furthermore, a qualitative assay indicated siderophore production by all strains, except for S. equorum. This lack of siderophore production in S. equorum was supported by a quantitative assay, which revealed significantly lower or negligible siderophore amounts compared to S. aureus and S. chromogenes. The WGS analysis showed that all tested strains, except for S. equorum, possessed complete staphyloferrin A (SA)-synthesis and export operons, which likely explains the phenotypic absence of siderophore production in S. equorum strains. While analyzing the staphyloferrin A and staphyloferrin B operon landscapes for all strains, we noticed some differences in the proteins responsible for iron acquisition between different species. However, within strains of the same species, the siderophore-related proteins remained conserved. Our findings contribute valuable insights into the genetic elements associated with bovine NASM pathogenesis.

Genotypes and virulence factors in Staphylococcus aureus isolated from dairy cows with subclinical mastitis in Serbia

This study aimed to determine the prevalence of Staphylococcus aureus subclinical mastitis and to genotype the S. aureus isolates using the 16S-23S rRNA intergenic spacer (RS-PCR) method. In addition, the genes responsible for adherence, biofilm formation, host evasion, tissue necrosis, methicillin resistance, and enterotoxin production of S. aureus were investigated. The overall prevalence of S. aureus subclinical mastitis in lactating cows was 5.4% (95% confidence interval, CI=4.7-6.1%). An increased risk of S. aureus intramammary infection was observed on small family farms (odds ratio, OR=4.2, 95% CI=2.6-6.6, P < 0.001) and medium-sized farms (OR=3.5, 95% CI=2.2-5.7, P < 0.001). The RS-PCR analysis revealed 44 genotypes and genotype variants, of which 15 new genotypes and five new variants were detected within small and medium-sized farms. S. aureus isolates of new genotypes and genotype variants carried the clfA gene responsible for adherence at a lower frequency (64.8%) and enterotoxin-producing genes sea (20.4%), seb (14.8%) and sec (14.8%) at a higher frequency than the other known genotypes (P < 0.001), and were confirmed to carry the sej and sep genes. The spa gene was detected in all S. aureus isolates, whereas none harbored bap, ser, or tsst-1 genes. Methicillin-resistant strains of S. aureus (MRSA) were also detected, with a higher prevalence (19.2%) on large farms with more than 50 cows (P < 0.001). Using molecular techniques as diagnostic tools provides a better understanding of intramammary staphylococcal infections' occurrence, spread, and eradication.

Elucidation of the Bovine Intramammary Bacteriome and Resistome from healthy cows of Swiss dairy farms in the Canton Tessin

Healthy, untreated cows of nine dairy herds from the Swiss Canton Tessin were analyzed three times within one year to identify the most abundant species of the intramammary bacteriome. Aseptically collected milk samples were cultured and bacteria identified using MALDI-TOF. Of 256 cows analyzed, 96% were bacteriologically positive and 80% of the 1,024 quarters were positive for at least one bacterial species. 84.5% of the quarters were healthy with somatic cell counts (SCC) < 200,000 cells/mL, whereas 15.5% of the quarters showed a subclinical mastitis (SCC ≥ 200,000 cells/mL). We could assign 1,288 isolates to 104 different bacterial species including 23 predominant species. Non-aureus staphylococci and mammaliicocci (NASM) were most prevalent (14 different species; 73.5% quarters). Staphylococcus xylosus and Mammaliicoccus sciuri accounted for 74.7% of all NASM isolates. To describe the intramammary resistome, 350 isolates of the predominant species were selected and subjected to short-read whole genome sequencing (WGS) and phenotypic antibiotic resistance profiling. While complete genomes of eight type strains were available, the remaining 15 were de novo assembled with long reads as a resource for the community. The 23 complete genomes served for reference-based assembly of the Illumina WGS data. Both chromosomes and mobile genetic elements were examined for antibiotic resistance genes (ARGs) using in-house and online software tools. ARGs were then correlated with phenotypic antibiotic resistance data from minimum inhibitory concentration (MIC). Phenotypic and genomic antimicrobial resistance was isolate-specific. Resistance to clindamycin and oxacillin was most frequently observed (65 and 30%) in Staphylococcus xylosus but could not be linked to chromosomal or plasmid-borne ARGs. However, in several cases, the observed antimicrobial resistance could be explained by the presence of mobile genetic elements like tetK carried on small plasmids. This represents a possible mechanism of transfer between non-pathogenic bacteria and pathogens of the mammary gland within and between herds. The-to our knowledge-most extensive bacteriome reported and the first attempt to link it with the resistome promise to profoundly affect veterinary bacteriology in the future and are highly relevant in a One Health context, in particular for mastitis, the treatment of which still heavily relies on antibiotics.

Colonization of Extramammary Sites with Mastitis-Associated S. aureus Strains in Dairy Goats

Staphylococcus aureus (S. aureus), a major mastitis pathogen in dairy goats, is classified as a contagious pathogen. Although previous research has shown that extramammary body sites can be colonized with S. aureus, it is unknown whether these sites are reservoirs for intramammary infections. The aim of this research was to determine whether extramammary sites can be colonized with mastitis-associated S. aureus strains in dairy goats. Milk samples were collected from 207 primiparous goats and from 120 of these goats, extramammary site samples (hock, groin, nares, vulva and udder) were collected from a large commercial dairy goat herd in the Netherlands during four sampling visits. Extramammary site swabs and milk samples were (selectively) cultured and S. aureus isolates were spa genotyped. The prevalence of colonization of the extramammary sites at goat level was 51.7% and the prevalence of S. aureus intramammary infections was 7.2%. The nares were colonized most frequently (45%), while the groin area was colonized the least (2.5%). Six spa genotypes were identified in this herd and there was no significant difference in the distribution of spa genotypes between the milk or the extramammary sites (p = 0.141). Both in the extramammary sites and in the milk, spa genotypes t544 (82.3% and 53.3%) and t1236 (22.6% and 33.3%) were the dominant genotypes. These results show that in goats, extramammary sites, particularly the nares, are frequently colonized with mastitis-associated S. aureus strains. Extramammary sites may, thus, be a source of S. aureus intramammary infections that are not targeted by the intervention measures aimed at preventing transmission from infected udder glands.

Staphylococcus aureus adlb gene is associated with high prevalence of intramammary infection in dairy herds of northern Italy: A cross-sectional study

Staphylococcus aureus is a major mastitis pathogen in dairy cattle worldwide, responsible for substantial economic losses. Environmental factors, milking routine, and good maintenance of milking equipment have been described as important factors to prevent intramammary infections (IMI). Staphylococcus aureus IMI can be widespread within the farm or the infection can be limited to few animals. Several studies have reported that Staph. aureus genotypes differ in their ability to spread within a herd. In particular, Staph. aureus belonging to ribosomal spacer PCR genotype B (GTB)/clonal complex 8 (CC8) is associated with high within-herd prevalence of IMI, whereas other genotypes are generally associated with individual cow disease. The adlb gene seems to be strictly related to Staph. aureus GTB/CC8, and is a potential marker of contagiousness. We investigated Staph. aureus IMI prevalence in 60 herds in northern Italy. In the same farms, we assessed specific indicators linked to milking management (e.g., teat condition score and udder hygiene score) and additional milking risk factors for IMI spread. Ribosomal spacer-PCR and adlb-targeted PCR were performed on 262 Staph. aureus isolates, of which 77 underwent multilocus sequence typing. In most of the herds (90%), a predominant genotype was identified, especially Staph. aureus CC8 (30%). In 19 of 60 herds, the predominant circulating Staph. aureus was adlb-positive and the observed IMI prevalence was relevant. Moreover, the adlb gene was detected only in genotypes of CC8 and CC97. Statistical analysis showed a strong association between the prevalence of Staph. aureus IMI, the specific CCs, and carriage of adlb, with the predominant circulating CC and presence of the gene alone explaining the total variation. Interestingly, the difference in the odds ratio obtained in the models for CC8 and CC97 suggests that it is carriage of the adlb gene, rather than the circulation of these CCs per se, that leads to higher within-herd prevalence of Staph. aureus. In addition, the model showed that environmental and milking management factors had no or minimal effect on Staph. aureus IMI prevalence. In conclusion, the circulation of adlb-positive Staph. aureus strains within a herd has a strong effect on the prevalence of IMI. Thus, adlb can be proposed as a genetic marker of contagiousness for Staph. aureus IMI in cattle. However, further analyses using whole-genome sequencing are required to understand the role of genes other than adlb that may be involved in the mechanisms of contagiousness of Staph. aureus strains associated with high prevalence of IMI.

Bovine-associated staphylococci and mammaliicocci trigger T-lymphocyte proliferative response and cytokine production differently

We examined whether distinct staphylococcal and mammaliicoccal species and strains trigger B- and T-lymphocyte proliferation and interleukin (IL)-17A and interferon (IFN)-γ production by peripheral blood mononuclear cells in nulliparous, primiparous, and multiparous dairy cows. Flow cytometry was used to measure lymphocyte proliferation with the Ki67 antibody, and specific monoclonal antibodies were used to identify CD3, CD4, and CD8 T lymphocyte and CD21 B lymphocyte populations. The supernatant of the peripheral blood mononuclear cell culture was used to measure IL-17A and IFN-γ production. Two distinct, inactivated strains of bovine-associated Staphylococcus aureus [one causing a persistent intramammary infection (IMI) and the other from the nose], 2 inactivated Staphylococcus chromogenes strains [one causing an IMI and the other from a teat apex), as well as an inactivated Mammaliicoccus fleurettii strain originating from sawdust from a dairy farm, and the mitogens concanavalin A and phytohemagglutinin M-form (both specifically to measure lymphocyte proliferation) were studied. In contrast to the "commensal" Staph. aureus strain originating from the nose, the Staph. aureus strain causing a persistent IMI triggered proliferation of CD4⁺ and CD8⁺ subpopulations of T lymphocytes. The M. fleurettii strain and the 2 Staph. chromogenes strains had no effect on T- or B-cell proliferation. Furthermore, both Staph. aureus and Staph. chromogenes strains causing persistent IMI significantly increased IL-17A and IFN-γ production by peripheral blood mononuclear cells. Overall, multiparous cows tended to have a higher B-lymphocyte and a lower T-lymphocyte proliferative response than primiparous and nulliparous cows. Peripheral blood mononuclear cells of multiparous cows also produced significantly more IL-17A and IFN-γ. In contrast to concanavalin A, phytohemagglutinin M-form selectively stimulated T-cell proliferation.

Genome sequencing and comparative genomic analysis of bovine mastitis-associated Staphylococcus aureus strains from India

BACKGROUND

Bovine mastitis accounts for significant economic losses to the dairy industry worldwide. Staphylococcus aureus is the most common causative agent of bovine mastitis. Investigating the prevalence of virulence factors and antimicrobial resistance would provide insight into the molecular epidemiology of mastitis-associated S. aureus strains. The present study is focused on the whole genome sequencing and comparative genomic analysis of 41 mastitis-associated S. aureus strains isolated from India.

RESULTS

The results elucidate explicit knowledge of 15 diverse sequence types (STs) and five clonal complexes (CCs). The clonal complexes CC8 and CC97 were found to be the predominant genotypes comprising 21 and 10 isolates, respectively. The mean genome size was 2.7 Mbp with a 32.7% average GC content. The pan-genome of the Indian strains of mastitis-associated S. aureus is almost closed. The genome-wide SNP-based phylogenetic analysis differentiated 41 strains into six major clades. Sixteen different spa types were identified, and eight isolates were untypeable. The cgMLST analysis of all S. aureus genome sequences reported from India revealed that S. aureus strain MUF256, isolated from wound fluids of a diabetic patient, was the common ancestor. Further, we observed that all the Indian mastitis-associated S. aureus isolates belonging to the CC97 are mastitis-associated. We identified 17 different antimicrobial resistance (AMR) genes among these isolates, and all the isolates used in this study were susceptible to methicillin. We also identified 108 virulence-associated genes and discuss their associations with different genotypes.

CONCLUSION

This is the first study presenting a comprehensive whole genome analysis of bovine mastitis-associated S. aureus isolates from India. Comparative genomic analysis revealed the genome diversity, major genotypes, antimicrobial resistome, and virulome of clinical and subclinical mastitis-associated S. aureus strains.

Association of Staphylococcus aureus genotypes with milk or colonization of extramammary sites in Dutch dairy cattle indicates strain variation in reservoirs for intramammary infections

Staphylococcus aureus (S. aureus) is a major mastitis pathogen with a detrimental impact on udder health in dairy cattle. Although S. aureus is generally classified as a contagious mastitis pathogen, control measures aimed at preventing contagious transmission are not always effective. Previous studies showed that various extramammary sites can be colonized with S. aureus and could be a reservoir for S. aureus intramammary infections (IMI). The aim of this study was to determine the prevalence of S. aureus extramammary site colonization in Dutch dairy cattle and to compare the spa genotypes of S. aureus isolates from IMI to spa genotypes of isolates from extramammary sites. Six herds were visited and from cows with a composite milk somatic cell count ≥200,000 cells/mL quarter milk samples and swabs from various extramammary sites (hock, groin, udder cleft, nares, and feces) were taken. Extramammary site samples were processed by a two-step high salt selective culture and presence of S. aureus was confirmed by femA PCR. S. aureus isolates from milk and extramammary sites were compared by spa typing. The cow level colonization varied from 0% to 73%, and the prevalence of IMI in the sampled cows varied from 0% to 61% between herds. The extramammary site with the highest prevalence of colonization was the hock (23%) and the lowest prevalence of colonization was found for the nares (5%) and feces (5%). Spa typing of S. aureus isolates from either extramammary sites or milk showed that in most herds there were one or two predominant S. aureus spa genotypes present. Different S. aureus spa genotypes could be categorized into three groups based on the distribution between milk or extramammary sites: i) predominantly milk associated, ii) associated with both milk and extramammary sites, and iii) associated with extramammary sites. In conclusion, we showed that the prevalence of extramammary site colonization differed significantly between herds and extramammary sites and that specific S. aureus spa genotypes were associated with milk (IMI) or extramammary site colonization. Extramammary S. aureus reservoirs could be a source for IMI that cannot be eradicated by intervention measures aimed at contagious mastitis pathogens.

Bovine Staphylococcus aureus: a European study of contagiousness and antimicrobial resistance

In dairy herds managements, mastitis is the leading cause of economic losses. One of the most important pathogens responsible for intra-mammary infections is Staphylococcus aureus. The genetic properties of S. aureus have a strong influence on its pathogenicity and contagiousness. In this study, we aimed to obtain a comprehensive overview of the key bovine S. aureus clinical properties, such as contagiousness and antimicrobial resistance, present in European strains. For this, 211 bovine S. aureus strains from ten European countries that were used in a previous study were used in this study. Contagiousness was assessed using qPCR for the detection of the marker gene adlb. Antimicrobial resistance was evaluated using a broth microdilution assay and mPCR for the detection of genes involved in penicillin resistance (blaI, blaR1, and blaZ). It was found that adlb was present in CC8/CLB strains; however, in Germany, it was found in CC97/CLI and in an unknown CC/CLR strains. CC705/CLC strains from all countries were found to be susceptible to all tested antibiotics. Major resistance to penicillin/ampicillin, chloramphenicol, clindamycin and tetracycline was detected. Resistance to oxacillin, trimethoprim/sulfamethoxazole and cephalosporins was rarely observed. In addition, contagiousness and antibiotic resistance seem to correlate with different CCs and genotypic clusters. Hence, it is recommended that multilocus sequence typing or genotyping be utilized as a clinical instrument to identify the most appropriate antibiotic to use in mastitis treatment. Actualization of the breakpoints of veterinary strains is necessary to address the existing antibiotic resistance of the bacteria involved in veterinary mastitis.

Assessment of Foodborne Bacterial Pathogens in Buffalo Raw Milk Using Polymerase Chain Reaction Based Assay

Milk is a putrescible commodity that is extremely prone to microbial contamination. Primarily, milk and dairy products are believed to be easily contaminated by pathogenic microorganisms, including Listeria monocytogenes, Salmonella spp., and Staphylococcus aureus. The microbiological quality of raw milk and dairy products regarding foodborne pathogens is of paramount importance due to concern of human health. In this study 400 buffalo raw milk samples were screened for assessing the prevalence of L. monocytogenes, Salmonella spp., and S. aureus. This study implemented uniplex-polymerase chain reaction (u-PCR) and multiplex-polymerase chain reaction (m-PCR) assays for the fast simultaneous detection of these pathogens comparing to the conventional culturing methods. Raw milk samples were found contaminated with the prevalence of 2.2%, 4.0%, and 14.2% for L. monocytogenes, Salmonella spp., and S. aureus, respectively. These pathogens were detected with the optimized polymerase chain reaction assays after 6 h of enrichment. u-PCR and m-PCR demonstrated the limit of detection as 10⁴, 10², and 10 cells/mL after 6, 12, 18, and 24 h for each culture of the pathogens. A high sensitivity (10 colony-forming unit [CFU]/mL) of the m-PCR protocol was noted. The developed protocol is a cost-effective and rapid method for the simultaneous detection of pathogens associated with raw milk and dairy industries.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Staphylococcus aureus in cattle and horses

Staphylococcus aureus (S. aureus) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for cattle and horses in previous scientific opinions. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9, and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR S. aureus can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (60-90% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1, 2 and 4 (Categories A, B and D; 1-5%, 5-10% and 10-33% probability of meeting the criteria, respectively) and the AHAW Panel was uncertain whether it meets the criteria in Sections 3 and 5 (Categories C and E, 33-90% and 60-90% probability of meeting the criteria, respectively). The animal species to be listed for AMR S. aureus according to Article 8 criteria include mainly mammals, birds, reptiles and fish.

Diversity and pathogenesis of Staphylococcus aureus from bovine mastitis: current understanding and future perspectives

Staphylococcus aureus is a leading cause of bovine mastitis worldwide. Despite some improved understanding of disease pathogenesis, progress towards new methods for the control of intramammary infections (IMI) has been limited, particularly in the field of vaccination. Although herd management programs have helped to reduce the number of clinical cases, S. aureus mastitis remains a major disease burden. This review summarizes the past 16 years of research on bovine S. aureus population genetics, and molecular pathogenesis that have been conducted worldwide. We describe the diversity of S. aureus associated with bovine mastitis and the geographical distribution of S. aureus clones in different continents. We also describe studies investigating the evolution of bovine S. aureus and the importance of host-adaptation in its emergence as a mastitis pathogen. The available information on the prevalence of virulence determinants and their functional relevance during the pathogenesis of bovine mastitis are also discussed. Although traits such as biofilm formation and innate immune evasion are critical for the persistence of bacteria, the current understanding of the key host-pathogen interactions that determine the outcome of S. aureus IMI is very limited. We suggest that greater investment in research into the genetic and molecular basis of bovine S. aureus pathogenesis is essential for the identification of novel therapeutic and vaccine targets.

Bacteriophages Combined With Subtherapeutic Doses of Flucloxacillin Act Synergistically Against Staphylococcus aureus Experimental Infective Endocarditis

Background

The potential of phage therapy for the treatment of endovascular Staphylococcus aureus infections remains to be evaluated.

Methods and Results

The efficacy of a phage cocktail combining Herelleviridae phage vB_SauH_2002 and Podoviriae phage 66 was evaluated against a methicillin‐sensitive S. aureus strain in vitro and in vivo in a rodent model of experimental endocarditis. Six hours after bacterial challenge, animals were treated with (1) the phage cocktail. (2) subtherapeutic flucloxacillin dosage, (3) combination of the phage cocktail and flucloxacillin, or (4) saline. Bacterial loads in cardiac vegetations at 30 hours were the primary outcome. Secondary outcomes were phage loads at 30 hours in cardiac vegetations, blood, spleen, liver, and kidneys. We evaluated phage resistance 30 hours post infection in vegetations of rats under combination treatment. In vitro, phages synergized against S. aureus planktonic cells and the cocktail synergized with flucloxacillin to eradicated biofilms. In infected animals, the phage cocktail achieved bacteriostatic effect. The addition of low‐dose flucloxacillin elevated bacterial suppression (∆ of −5.25 log₁₀ colony forming unit/g [CFU/g] versus treatment onset, P<0.0001) and synergism was confirmed (∆ of −2.15 log₁₀ CFU/g versus low‐dose flucloxacillin alone, P<0.01). Importantly, 9/12 rats given the combination treatment had sterile vegetations at 30 hours. In vivo phage replication was partially suppressed by the antibiotic and selection of resistance to the Podoviridae component of the phage cocktail occurred. Plasma‐mediated inhibition of phage killing activity was observed in vitro.

Conclusions

Combining phages with a low‐dose standard of care antibiotic represents a promising strategy for the treatment of S. aureus infective endocarditis.

A stochastic modelling approach to determine the effect of diverse Staphylococcus aureus strains on the economic and epidemiological outcomes of mastitis intervention strategies in dairy cattle

Staphylococcus aureus (S. aureus) strains with considerable genetic and phenotypic differences have previously been identified. The economic and epidemiologic impact of S. aureus mastitis has been investigated, but none of these studies took differences between strains into account. Here we aimed to investigate how differences between S. aureus strains affect the economic and epidemiologic outcome of various intervention strategies against clinical and subclinical intramammary infections. Five S. aureus strains were modelled using a stochastic bio-economic model simulating a dairy herd of 200 cows using single-day time steps. The strain characteristics of the five simulated S. aureus strains (general, contagious, spill-over, clinical and persistent) were based on divergent phenotypes as described in literature. Outcomes of the model included incidence (both clinical and subclinical), number of antibiotic treatment days, number of culled cows, and net income. Intervention strategies against clinical and subclinical intramammary infections were based on (variations of) intramammary antibiotic treatment, testing, and culling. Both single and multiple pathogen (intramammary infection caused by S. aureus, Escherichia coli, and non-aureus staphylococci) scenarios were simulated to determine the effect of the five S. aureus strains on the impact of 19 different intervention strategies. The results showed that the incidence (both clinical and subclinical), number of treatment days, number of culled cows, and net income varied considerably for the different S. aureus strains. Comparison of the model outcomes within and between strains showed that for most intervention strategies the relative impact differed per strain. However, the intervention strategy with the best outcome for most variables and strains was the culling of cows with a recovery probability lower than 50%. This shows that the relative economic and epidemiologic impact of most of the modelled intervention strategies were strain-dependent, while some intervention strategies were not strain-dependent. From this, we conclude that, depending on the intervention strategy applied on a farm, it could be advantageous to type S. aureus to determine whether it would be economically and epidemiologically beneficial for the existing intervention strategy to be changed.

Distinct behavior of bovine-associated staphylococci species in their ability to resist phagocytosis and trigger respiratory burst activity by blood and milk polymorphonuclear leukocytes in dairy cows

Mastitis affects a high proportion of dairy cows and is still one of the greatest challenges faced by the dairy industry. Staphylococcal bacteria remain the most important cause of mastitis worldwide. We investigated how distinct staphylococcal species evade some critical host defense mechanisms, which may dictate the establishment, severity, and persistence of infection and the outcome of possible therapeutic and prevention interventions. Thus, the present study investigated variations among distinct bovine-associated staphylococci in their capability to resist phagocytosis and to trigger respiratory burst activity of blood and milk polymorphonuclear neutrophil leukocytes (PMNL) in dairy cows. To do so, PMNL of 6 primiparous and 6 multiparous dairy cows were used. A collection of 38 non-aureus staphylococci (NAS) and 12 Staphylococcus aureus were included. The phagocytosis and intracellular reactive oxygen species (ROS) production by blood and milk PMNL were analyzed by flow cytometry. Phagocytosis, by both blood and milk PMNL, did not differ between S. aureus and NAS as a group, although within-NAS species differences were observed. Staphylococcus chromogenes (a so-called milk-adapted NAS species) better resisted phagocytosis by blood PMNL than the so-called environmental (i.e., Staphylococcus fleurettii) and opportunistic (i.e., Staphylococcus haemolyticus) NAS species. Otherwise, S. haemolyticus was better phagocytosed by blood PMNL than S. aureus, S. fleurettii, and S. chromogenes. No influence of the origin of the isolates within the staphylococci species in the resistance to phagocytosis by blood and milk PMNL was found. Overall, both S. aureus and NAS did not inhibit intracellular ROS production in blood and milk PMNL. Non-aureus staphylococci induced fewer ROS by milk PMNL than S. aureus, which was not true for blood PMNL, although species-specific differences in the intensity of ROS production were observed. Staphylococcus chromogenes induced more blood PMNL ROS than S. fleurettii and S. haemolyticus, and as much as S. aureus. Conversely, S. chromogenes induced fewer milk PMNL ROS than S. aureus. The origin of the isolates within the staphylococci species did not affect the ROS production by blood and milk PMNL. In conclusion, our study showed differences in staphylococci species in evading phagocytosis and triggering ROS production, which may explain the ability of some staphylococci species (i.e., S. aureus and S. chromogenes) to cause persistent infection and induce inflammation.

The spread and antimicrobial resistance of Staphylococcus aureus in South African dairy herds - A review

Staphylococcus aureus is internationally recognised as a principal agent of mastitis and the foremost reason for economic loss in the dairy industry. The limited data available on organism-specific antibiotic resistance surveillance in dairy cattle have stimulated the need for such a review article. The objective of this study was to review relevant literature on antimicrobial resistance of mastitis-causing staphylococci isolated from dairy cows in South Africa compared to other countries. Factors relating to the incidence of mastitis and treatment strategies in terms of the One Health concept and food security were included. The Web of Science (all databases) and relevant websites were used, and articles not written in English were excluded. The incidence of mastitis varied between South Africa and other countries. Antimicrobial resistance patterns caused by S. aureus also varied in regions within Southern Africa and those of other countries although some similarities were shown. Antimicrobial resistance differed between S. aureus bacteria that were maltose positive and negative (an emerging pathogen). The results highlighted the importance of the availability of organism-specific surveillance data of the incidence of mastitis and antibiotic resistance for specific countries and within similar climatic conditions. Accurate knowledge about whether a specific pathogen is resistant to an antibiotic within a certain climate, country, area or farm should reduce the incidence of unnecessary or incorrect treatment with antibiotics. This should enable dairy farmers to deal with these organisms in a more effective manner. Therefore such research should be ongoing.

Transmission dynamics of Staphylococcus aureus and Streptococcus agalactiae in a Dutch dairy herd using an automatic milking system

Staphylococcus aureus and Streptococcus agalactiae are important contagious mastitis pathogens and are considered to mainly transmit between cows through the milking machine. Controlling contagious mastitis on dairy farms requires a reduction of the transmission rate or the duration of intramammary infections (IMI), or both. These parameters may differ in dairy herds milked with an automatic milking system (AMS) as compared to those milked with a conventional milking system (CMS). The aims of this prospective longitudinal study were to estimate the transmission rate, the median duration of IMI and the basic reproduction number (R₀) of Staph. aureus and Strep. agalactiae in a Dutch AMS herd. Bacteriological cultures of quarter milk samples were collected every 2 wks. Using 3 different definitions of IMI, we estimated the transmission rate for Staph. aureus to be within the range of 0.002 (95 % CI: 0-0.005) quarter-day^-1 to 0.019 (95 % CI: 0.010-0.032) quarter-day^-1, and for Strep. agalactiae of 0.007 (95 % CI: 0.005-0.010) quarter-day^-1 to 0.019 (95 % CI: 0.011-0.032) quarter-day^-1, the median duration of chronic IMI at 95 (95 % CI: 72-125) days for Staph. aureus and at 86 (95 % CI: 67-111) days for Strep. agalactiae, and the R₀ between 0.16 (95 % CI: 0.05-0.27) and 0.34 (95 % CI: 0.20-0.48) for Staph. aureus, and between 0.64 (95 % CI: 0.41-0.87) and 0.68 (95 % CI: 0.48-0.88) for Strep. agalactiae. Transmission of these two contagious pathogens in this herd was limited and theoretically the IMI would not sustain, given that R₀ of both pathogens was lower than 1. The estimated transmission rate of Staph. aureus in this AMS herd was found to be comparable to those described for CMS herds, while for Strep. agalactiae, it was slightly higher than in CMS herds. The duration of Staph. aureus IMI was in line with results from CMS farms, while the duration of Strep. agalactiae was lower than what has been described in CMS herds. The R₀ of these contagious pathogens was found to be lower than the estimates in CMS herds. Our study suggests that the transmission rate of these two contagious pathogens in this AMS herd were comparable to what has been reported about well-performing CMS herds that have a low rate of transmission.

Update on molecular diversity and multipathogenicity of staphylococcal superantigen toxins

Staphylococcal superantigen (SAg) toxins are the most notable virulence factors associated with Staphylococcus aureus, which is a pathogen associated with serious community and hospital acquired infections in humans and various diseases in animals. Recently, SAg toxins have become a superfamily with 29 types, including staphylococcal enterotoxins (SEs) with emetic activity, SE-like toxins (SEls) that do not induce emesis in primate models or have yet not  been tested, and toxic shock syndrome toxin-1 (TSST-1). SEs and SEls can be subdivided into classical types (SEA to SEE) and novel types (SEG to SElY, SE01, SE02, SEl26 and SEl27). The genes of SAg toxins are located in diverse accessory genetic elements and share certain structural and biological properties. SAg toxins are heat-stable proteins that exhibit pyrogenicity, superantigenicity and capacity to induce lethal hypersensitivity to endotoxin in humans and animals. They have multiple pathogenicities that can interfere with normal immune function of host, increase the chances of survival and transmission of pathogenic bacteria in host, consequently contribute to the occurrence and development of various infections, persistent infections or food poisoning. This review focuses on the following aspects of SAg toxins: (1) superfamily members of classic and novelty discovered staphylococcal SAgs; (2) diversity of gene locations and molecular structural characteristics; (3) biological characteristics and activities; (4) multi-pathogenicity of SAgs in animal and human diseases, including bovine mastitis, swine sepsis, abscesses and skin edema in pig, arthritis and septicemia in poultry, and nosocomial infections and food-borne diseases in humans.

Staphylococcus aureus in Agriculture: Lessons in Evolution from a Multispecies Pathogen

Staphylococcus aureus is a formidable bacterial pathogen that is responsible for infections in humans and various species of wild, companion, and agricultural animals. The ability of S. aureus to move between humans and livestock is due to specific characteristics of this bacterium as well as modern agricultural practices. Pathoadaptive clonal lineages of S. aureus have emerged and caused significant economic losses in the agricultural sector. While humans appear to be a primary reservoir for S. aureus, the continued expansion of the livestock industry, globalization, and ubiquitous use of antibiotics has increased the dissemination of pathoadaptive S. aureus in this environment. This review comprehensively summarizes the available literature on the epidemiology, pathophysiology, genomics, antibiotic resistance (ABR), and clinical manifestations of S. aureus infections in domesticated livestock. The availability of S. aureus whole-genome sequence data has provided insight into the mechanisms of host adaptation and host specificity. Several lineages of S. aureus are specifically adapted to a narrow host range on a short evolutionary time scale. However, on a longer evolutionary time scale, host-specific S. aureus has jumped the species barrier between livestock and humans in both directions several times. S. aureus illustrates how close contact between humans and animals in high-density environments can drive evolution. The use of antibiotics in agriculture also drives the emergence of antibiotic-resistant strains, making the possible emergence of human-adapted ABR strains from agricultural practices concerning. Addressing the concerns of ABR S. aureus, without negatively affecting agricultural productivity, is a challenging priority.

Staphylococcal Enterotoxin Gene Cluster: Prediction of Enterotoxin (SEG and SEI) Production and of the Source of Food Poisoning on the Basis of vSaβ Typing

Besides the infection properties in human and animals, S. aureus can produce different enterotoxins in food. The enterotoxins can cause vomiting and diarrhea, often involving many people.

Currently, only 5 (SEA to SEE) out of 27 known staphylococcal enterotoxins can be analyzed using commercially available kits. Six genes (seg, sei, sem, sen, seo, and seu), encoding putative and undetectable enterotoxins, are located on the enterotoxin gene cluster (egc), which is part of the Staphylococcus aureus genomic island vSaβ. These enterotoxins have been described as likely being involved in staphylococcal food-poisoning outbreaks. The aim of the present study was to determine if whole-genome data can be used for the prediction of staphylococcal egc enterotoxin production, particularly enterotoxin G (SEG) and enterotoxin I (SEI). For this purpose, whole-genome sequences of 75 Staphylococcus aureus strains from different origins (food-poisoning outbreaks, human, and animal) were investigated by applying bioinformatics methods (phylogenetic analysis using the core genome and different alignments). SEG and SEI expression was tested in vitro using a sandwich enzyme-linked immunosorbent assay method. Strains could be allocated to 14 different vSaβ types, each type being associated with a single clonal complex (CC). In addition, the vSaβ type and CC were associated with the origin of the strain (human or cattle derived). The amount of SEG and SEI produced also correlated with the vSaβ type and the CC of a strain. The present results show promising indications that the in vitro production of SEG and SEI can be predicted based on the vSaβ type or CC of a strain.

IMPORTANCE Besides having infectious properties in human and animals, S. aureus can produce different enterotoxins in food. The enterotoxins can cause vomiting and diarrhea, often involving many people. Most of these outbreaks remain undiscovered, as detection methods for enterotoxins are only available for a few enterotoxins but not for the more recently discovered enterotoxins G (SEG) and I (SEI). In this study, we show promising results that in vitro production of SEG and SEI can be predicted based on the whole-genome sequencing data of a strain. In addition, these data could be used to find the source (human or cattle derived) of an outbreak strain, which is the key for a better understanding of the role SEG and SEI play in foodborne outbreaks caused by S. aureus.

Molecular diversity of Staphylococcus aureus and the role of milking equipment adherences or biofilm as a source for bulk tank milk contamination

Staphylococcus aureus is one of the most frequent pathogens causing intramammary infections in dairy herds. Consequently, virulence factors, pathobiology, and epidemiology of Staphylococcus aureus strains have been widely assessed through the years. Nevertheless, not much has been described about the epidemiology of Staph. aureus strains from bulk tank milk (BTM) and adherences on milking equipment (AMES), even when these strains may play a role in the quality of milk that is intended for human consumption. The objective of this study was to assess the strain diversity of 166 Staph. aureus isolates collected from 3 consecutive BTM samples, and from AMES in contact with milk from 23 Chilean dairy farms. Isolates were analyzed and typed using pulsed-field gel electrophoresis. Diversity of strains, both within and among farms, was assessed using Simpson's index of diversity (SID). On farms where Staph. aureus was isolated from both AMES and BTM (n = 8), pulsotypes were further analyzed to evaluate the role of AMES as a potential source of Staph. aureus strains in BTM. Among all Staph. aureus analyzed by pulsed-field gel electrophoresis, a total of 42 pulsotypes (19 main pulsotypes and 23 subtypes) were identified. Among dairy farms, strain diversity was highly heterogeneous (SID = 0.99). Within dairy farms, Staph. aureus strain diversity was variable (SID = 0 to 1), and 18 dairy operations (81.8%) had one pulsotype that was shared between at least 2 successive BTM samples. In those farms where Staph. aureus was isolated in both AMES and BTM (n = 8), 7 (87.5%) showed a clonal distribution of Staph. aureus strains between these 2 types of samples. The overlapping of certain Staph. aureus strains among dairy farms may point out common sources of Staph. aureus among otherwise epidemiologically unrelated farms. Indistinguishable Staph. aureus strains between AMES and BTM across dairy farms suggest that Staph. aureus-containing AMES may represent a source for BTM contamination, thus affecting milk quality. Our study highlights the role of viable Staph. aureus in AMES as a source for BTM contamination on dairy farms, and also describes the overlapping and presence of specific BTM and AMES pulsotypes among farms.

Antimicrobial Blue Light versus Pathogenic Bacteria: Mechanism, Application in the Food Industry, Hurdle Technologies and Potential Resistance

Blue light primarily exhibits antimicrobial activity through the activation of endogenous photosensitizers, which leads to the formation of reactive oxygen species that attack components of bacterial cells. Current data show that blue light is innocuous on the skin, but may inflict photo-damage to the eyes. Laboratory measurements indicate that antimicrobial blue light has minimal effects on the sensorial and nutritional properties of foods, although future research using human panels is required to ascertain these findings. Food properties also affect the efficacy of antimicrobial blue light, with attenuation or enhancement of the bactericidal activity observed in the presence of absorptive materials (for example, proteins on meats) or photosensitizers (for example, riboflavin in milk), respectively. Blue light can also be coupled with other treatments, such as polyphenols, essential oils and organic acids. While complete resistance to blue light has not been reported, isolated evidence suggests that bacterial tolerance to blue light may occur over time, especially through gene mutations, although at a slower rate than antibiotic resistance. Future studies can aim at characterizing the amount and type of intracellular photosensitizers across bacterial species and at assessing the oxygen-independent mechanism of blue light-for example, the inactivation of spoilage bacteria in vacuum-packed meats.

Molecular Typing and Antimicrobial Susceptibility Profile of Staphylococcus aureus Isolates Recovered from Bovine Mastitis and Nasal Samples

Simple Summary

Staphylococcus aureus is a major, prevalent mastitis pathogen, representing a real issue for bovine udder health, with unquestionable importance in human and veterinary medicine. The present study thus aimed to determine the antimicrobial resistance and the diversity of S. aureus recovered from transient and persistent intramammary infections and from extramammary niches (e.g., nares/muzzles) in dairy cows. We found that a large proportion of S. aureus strains exhibited multidrug resistance to antimicrobials, including resistance to antimicrobials that are critically important to human health. S. aureus isolates from transient and persistent IMIs did not differ, suggesting that the persistence of bovine intramammary infections (IMIs) was mainly determined by host factors, although S. aureus isolated from extramammary niches are not an important source of S. aureus intramammary infections. Furthermore, a discrepancy in antimicrobial resistance between S. aureus strains isolated from nares/muzzles and intramammary infections was observed.

Abstract

In the present study, we aimed to determine the antimicrobial resistance and molecular typing of Staphylococcus aureus recovered from transient and persistent intramammary infections and nares/muzzles in dairy cows. We investigated the antimicrobial resistance of 189 S. aureus strains using a broad antimicrobial susceptibility profile. Furthermore, 107 S. aureus isolates were strain-typed using staphylococcal protein-A (spa) typing. A large proportion of strains exhibited multidrug resistance to antimicrobials, including resistance to critically important antimicrobials, although no methicillin-resistant S. aureus strains were found. Our study did not strengthen the idea that extramammary niches (i.e., nares/muzzles) are an important source of S. aureus for bovine mastitis. A discrepancy in the antimicrobial resistance between S. aureus strains isolated from nares/muzzles and milk samples was observed. Furthermore, S. aureus isolates from transient and persistent intramammary infections (IMIs) did not differ by spa typing, suggesting that the persistence of bovine IMIs was determined by cow factors. Thus, the high level of multidrug-resistant S. aureus found in the two herds, considered together with the predominance of a well udder-adapted S. aureus strain, may contribute to our knowledge of the history of the high prevalence of mastitis caused by S. aureus, which is of great concern for animal and public health.

Genomic analysis of European bovine Staphylococcus aureus from clinical versus subclinical mastitis

Intramammary infections (IMI) with Staphylococcus aureus are a common cause of bovine mastitis and can result in both clinical (CM) or subclinical mastitis (SCM). Although bacterial isolates of S. aureus differ in their virulence potential it is largely unclear which bacterial virulence factors are responsible for increased clinical severity. We performed a genome wide association study and used a generalized linear mixed model to investigate the correlation between gene carriage, lineage and clinical outcome of IMI in a collection of S. aureus isolates from cattle with CM (n = 125) and SCM (n = 151) from 11 European countries. An additional aim was to describe the genetic variation of bovine S. aureus in Europa. The dominant lineages in our collection were clonal complex (CC) 151 (81/276, 29.3%), CC97 (54/276, 19.6%), CC479 (32/276, 11.6%) and CC398 (19/276, 6.9%). Virulence and antimicrobial resistance (AMR) gene carriage was highly associated with CC. Among a selection of nine virulence and AMR genes, CC151, CC479 and CC133 carried more virulence genes than other CCs, and CC398 was associated with AMR gene carriage. Whereas CC151, CC97 were widespread in Europe, CC479, CC398 and CC8 were only found in specific countries. Compared to CC151, CC479 was associated with CM rather than SCM (OR 3.62; 95% CI 1.38-9.50) and the other CCs were not. Multiple genes were associated with CM, but due to the clustering within CC of carriage of these genes, it was not possible to differentiate between the effect of gene carriage and CC on clinical outcome of IMI. Nevertheless, this study demonstrates that characterization of S. aureus CC and virulence genes helps to predict the likelihood of the occurrence of CM following S. aureus IMI and highlights the potential benefit of diagnostics tools to identify S. aureus CC during bovine mastitis.

The occurrence and distribution of livestock-associated methicillin-resistant Staphylococcus aureus ST398 on German dairy farms

The objective of this study was to investigate the occurrence and distribution of methicillin-resistant Staphylococcus aureus (MRSA) on 20 German dairy farms. Farms were selected based on previous MRSA reports from phenotypic susceptibility testing of mastitis pathogens. Samples were collected from predefined groups of cows, young stock, farm personnel, and the environment. A high MRSA-positive test rate was detected in swab samples from milk-fed calves (22.7%; 46/203). In postweaning calves, the MRSA-positive test rate was 9.1% (17/187). From prefresh heifers, both nasal swabs and udder cleft swabs were collected if possible. Including both sample types, the MRSA-positive test rate in prefresh heifers was 13.0% (26/200). The positive test rate was 8.9% (17/191) in nasal swabs and 6.5% (11/170) in udder cleft swabs. In quarter milk samples (QMS), the MRSA-positive test rate was 2.9% (67/2347), and on cow level, 7.9% (47/597) of the dairy cows were affected. Among all cows included in this study, the geometric mean of somatic cell counts was higher in QMS that carried MRSA (345,000 cells/mL) in comparison to all QMS (114,000 cells/mL). No differences in parity or the affected mammary quarter position on the udder were observed among the 47 infected cows. Methicillin-resistant S. aureus was also detected in boot swab samples (dust), teat liners, and in suckers from automatic calf feeders. All isolates belonged to livestock-associated sequence type 398 and most common staphylococcal protein A (spa)-types were t011 and t034. Most isolates harbored the staphylococcal cassette chromosome mec (SCCmec)-type V, with the exception of some isolates with SCCmec-type IVa on 1 farm. Similar MRSA genotypes in samples from humans and dairy cows underline the possible zoonotic and reverse-zoonotic transmission of livestock-associated MRSA strains from dairy farms. Similar MRSA genotypes in pig and cattle barns were detected on only 1 of 5 farms that kept both cattle and pigs. Similar MRSA spa-types were detected in samples from different sources (dairy cows, young stock, environment, and humans), suggesting a possible contagious transmission on some of the farms. Sporadically, up to 3 different MRSA spa-types were detected in QMS from the respective farms. On MRSA-affected farms, improper milking hygiene procedures and elevated bulk-tank milk somatic cell counts (>250,000 cells/mL) were observed. The occurrence of livestock-associated MRSA ST398 in different samples from dairy farms, and especially in young calves, should be considered for future MRSA-monitoring programs and biosecurity guidelines.

Short communication: Characterization of an atypical maltose-negative Staphylococcus aureus through the use of phenotypic and molecular techniques

The most clinically relevant staphylococci in veterinary medicine are those that are coagulase-positive, namely Staphylococcus aureus. During microbiological udder health monitoring (2009-2018), a new S. aureus strain (coagulase-positive and maltose-negative) was discovered as an emerging udder pathogen during routine examinations of South African dairy herds. This study challenged the conventional microbiological diagnosis of staphylococci by comparing its results to those of the MALDI-TOF mass spectrometry and 16S rRNA sequencing. Both of these tests confirmed that the maltose-negative staphylococcus (MNS), identified as Staphylococcus pseudintermedius by conventional microbiology, was S. aureus ST2992. Multi locus sequence typing was performed on 3 of the MNS isolates and indicated that these isolates were of single origin. These strains tested positive for both MALA and MALR genes (control: S. aureus ATCC 25923). Although the α-glucosidase gene was present, it was not expressed phenotypically. The latter may be attributed to the abnormal stop codon identified in the MALA gene sequence of S. aureus ST2992 (GenBank accession number, MN531305). The newly identified MNS has a field behavior different to that of maltose-positive S. aureus, and more similar to the low virulence of non-aureus staphylococci.

Staphylococcus aureus Population Structure and Genomic Profiles in Asymptomatic Carriers in Switzerland

Staphylococcus aureus is a leading cause for clinical infections and food intoxications, causing over 100,000 yearly cases of bacteremia in the United States and 434 food-borne outbreaks in the European Union. Approximately 30% of the population permanently carry S. aureus asymptomatically in their nasal cavity. The risk of infection and transmission to food items or the environment is higher in individuals that are nasally colonized. In addition, S. aureus can acquire various antimicrobial resistances leading to therapeutic failure, additional medical costs, and fatalities. Methicillin-resistant S. aureus (MRSA) cause a considerable burden of disease in humans and animals. MRSA carriage has been associated with animal and in particular livestock contact. Extensive current data on the virulence gene profiles, as well as data on antimicrobial resistance determinants is crucial in developing effective strategies to mitigate the burden of disease. To this end, we screened the anterior nares of 160 test subjects (87 pupils and 73 members of farmer families) in Switzerland for S. aureus carriage. A total of 73 S. aureus isolates were obtained. Factors such as exposure to farm or companion animals and personal medical history were recorded using a questionnaire. Using a DNA microarray, isolates were assigned to clonal complexes (CCs), and virulence and resistance gene profiles were determined. The collected strains were assigned to 20 CCs, among others CC1, CC7, CC8, CC15, CC30, CC45, CC97, and CC398. Two MRSA strains and one multiresistant isolate carrying genes blaZ/I/R, InuA, aadD, tetK, and fosB were isolated from farmers with intensive exposure to animals. Strains carrying pvl, causing severe skin lesions and necrotizing pneumonia, as well as tetracycline, erythromycin, and kanamycin resistance genes were found in individuals that had taken antibiotics during the last year. A variety of superantigenic toxin genes was detected, including among others, the toxic shock syndrome toxin (tst1), and various enterotoxins (sea, sec, sel, and the egc cluster). Contact to chickens was identified as a significant factor contributing to S. aureus colonization.

In vitro Antibiotic Susceptibility, Virulence Genes Distribution and Biofilm Production of Staphylococcus aureus Isolates from Bovine Mastitis in the Liaoning Province of China

Purpose

The aim of this study was to identify the subtype, characterize the antimicrobial resistance, determine the virulence gene distribution, and analyze the biofilm production of Staphylococcus aureus isolates from bovine mastitis milk samples in the Liaoning Province of China.

Materials and Methods

In total, 56 Staph. aureus isolates were collected and identified in this study; the isolates were divided into different spa types based on the sequence of the polymorphic X region of the spa gene. Additionally, antimicrobial susceptibility was investigated using the broth microdilution method, and 18 virulence genes were detected using PCR. Biofilm formation was measured by spectrophotometry with crystal violet staining and observed using confocal laser scanning microscopy.

Results

There were 12.12% (56/462) milk samples that were positive for Staph. aureus. These isolates were nonsusceptible to sulfamethoxazole (100%), penicillin (76.9%), daptomycin (76.79%), clindamycin (69.64%), and oxacillin (60.71%); however, the majority of the isolates (80.4%) were susceptible to amoxicillin/clavulanate. The predominant virulence genes encoded the cytotoxins, hla (94.64%) and hlb (89.29%), and the adhesion factors clfA (89.29%), clfB (89.29%), and fnbB (80.36%). Comparatively, virulence genes related to other adhesion factors such as cna (8.93%) and enterotoxins, such as seg (26.79%), sea (16.07%), seb (7.14%), and sec (7.14%) were detected at relatively lower rates. The following eight spa types were identified: t267 (35.84%), t730 (22.64%), t518 (15.09%), t1190 (11.32%), t1456 (9.43%), t224 (1.88%), t9129 (1.88%), and t177 (1.88%). The highest biofilm production was observed for t267. Staph. aureus exhibited various patterns of biofilm formation, with the biofilm often being associated with a tower-shaped structure or a thicker biofilm.

Conclusion

Our results indicated that Staph. aureus isolates from dairy cows with mastitis in the Liaoning Province of China were non-susceptible to sulfamethoxazole, penicillin, daptomycin, oxacillin, and clindamycin. Additionally, the most prevalent subtype was t267, which displayed resistance to multiple antimicrobial agents and harbored several virulence genes, including clfA, clfB, fnbB, hla, and hlb.

Characterization and Comparative Analysis of the Staphylococcus aureus Genomic Island vSaβ: an In Silico Approach

Staphylococcus aureus is a widespread opportunistic pathogen to humans and animals. Of its genome, 20 to 25% varies between strains and consists of phages, pathogenicity islands, transposons, and genomic islands. S. aureus harbors up to three genomic islands, vSaα, vSaβ, and vSaγ. The vSaβ region of S. aureus can encode a number of virulence-associated factors, such as serine proteases, leukocidins, enterotoxins, bacteriocins, or a hyaluronate lyase. In this study, the vSaβ regions of 103 clinically relevant S. aureus strains were characterized in silico and compared to the three predefined vSaβ types. We here suggest a superordinate system of 15 different vSaβ types, of which 12 were newly defined. Each vSaβ type has a distinct structure with a distinct set of genes, which are both highly conserved. Between the different types, gene content and composition vary substantially. Based on our data, a strain's vSaβ type is strongly coupled with its clonal complex, suggesting that vSaβ was acquired in an ancestral S. aureus strain, arguably by phage mediation, before differentiation into clonal complexes. In addition, we addressed the issue of ambiguous nomenclature in the serine protease gene cluster and propose a novel, phylogeny-based nomenclature of the cluster contained in the vSaβ region.IMPORTANCE With the rapid increase of available sequencing data on clinically relevant bacterial species such as S. aureus, the genomic basis of clinical phenotypes can be investigated in much more detail, allowing a much deeper understanding of the mechanisms involved in disease. We characterized in detail the S. aureus genomic island vSaβ and defined a superordinate system to categorize S. aureus strains based on their vSaβ type, providing information about the strains' virulence-associated genes and clinical potential.

On-Farm Surfaces in Contact with Milk: The Role of Staphylococcus aureus-Containing Biofilms for Udder Health and Milk Quality

Staphylococcus aureus is a Gram-positive bacterium that causes intramammary infections and bulk tank milk (BTM) contamination in dairy operations around the world in spite of on-farm application of preventive measures. The study was conducted on a 30-cow dairy farm in the Ñuble Region of Chile. For BTM culture and somatic cell count (SCC) analysis, three consecutive BTM samples were collected. Samples for bacterial culture (n = 16) were collected from macroscopic adherence on previously washed, sanitized, and dry milking equipment surfaces in direct contact with milk during milking or cooling. A total of 48 S. aureus isolates from BTM, milking equipment, and cows' quarters with intramammary infections were analyzed by pulsed-field gel electrophoresis (PFGE). Selected milking equipment pieces were removed for biofilm visualization using scanning electron microscopy (SEM). S. aureus was isolated from all three BTM samples; the average SCC for the three BTM samples was 1,429,333 cells/mL. Fourteen of the 16 samples of milking equipment (87.5%) were culture positive for S. aureus. Biofilms were visualized by SEM in all four removed milking equipment pieces. Microorganisms observed by SEM in those biofilms were mainly coccus-shaped bacteria, and microbiological culture of these biofilms yielded viable S. aureus isolates in all samples. All pulsotypes observed among S. aureus isolates from BTM were indistinguishable from those in milking equipment surfaces. All PFGE pulsotypes observed among S. aureus isolates from biofilms on rubber liners were indistinguishable from isolates from intramammary infections in cows. Our findings suggest that milking equipment films may act as source of S. aureus contamination for BTM and cows during milking, thus compromising the microbiological quality of milk used for manufacturing dairy products.