Methicillin resistant S. aureus in human and bovine mastitis

Detection and characterization of methicillin-resistant and susceptible coagulase-negative staphylococci in milk from cows with clinical mastitis in Tunisia

OBJECTIVES

This study investigated prevalence of methicillin-resistant (MR) and methicillin-susceptible (MS) coagulase-negative staphylococci (CNS) and the implicated mechanisms of resistance and virulence in milk of mastitis cows. In addition, the presence of SCCmec type was analyzed in MR Staphylococcus epidermidis (MRSE).

RESULTS

Three hundred milk samples from cows with clinical mastitis were obtained from 30 dairy farms in different regions of Tunisia. Sixty-eight of the 300 tested samples contained CNS strains. Various CNS species were identified, with Staphylococcus xylosus being the most frequently found (40%) followed by Staphylococcus warneri (12%). The mecA gene was present in 14 of 20 MR-CNS isolates. All of them were lacking the mecC gene. The SCCmecIVa was identified in four MRSE isolates. Most of CNS isolates showed penicillin resistance (70.6%) and 58.3% of them carried the blaZ gene. MR-CNS isolates (n = 20) showed resistance to erythromycin, tetracycline and trimethoprim-sulfametoxazole harboring different resistance genes such us erm(B), erm(T), erm(C), mph(C) or msr(A), tet(K) and dfr(A). However, a lower percentage of resistance was observed among 48 MS-CNS isolates: erythromycin (8.3%), tetracycline (6.2%), streptomycin (6.2%), clindamycin (6.2%), and trimethoprim-sulfametoxazole (2%). The Inu(B) gene was detected in one Staphylococcus xylosus strain that showed clindamycin resistance. The virulence gene tsst-1 was observed in one MR-CNS strain.

DISCUSSION

Coagulase-negative staphylococci containing a diversity of antimicrobial resistance genes are frequently detected in milk of mastitis cows. This fact emphasizes the importance of identifying CNS when an intramammary infection is present because of the potential risk of lateral transfer of resistant genes among staphylococcal species and other pathogenic bacteria.

Antimicrobial Resistance among Staphylococci of Animal Origin

Antimicrobial resistance among staphylococci of animal origin is based on a wide variety of resistance genes. These genes mediate resistance to many classes of antimicrobial agents approved for use in animals, such as penicillins, cephalosporins, tetracyclines, macrolides, lincosamides, phenicols, aminoglycosides, aminocyclitols, pleuromutilins, and diaminopyrimidines. In addition, numerous mutations have been identified that confer resistance to specific antimicrobial agents, such as ansamycins and fluoroquinolones. The gene products of some of these resistance genes confer resistance to only specific members of a class of antimicrobial agents, whereas others confer resistance to the entire class or even to members of different classes of antimicrobial agents, including agents approved solely for human use. The resistance genes code for all three major resistance mechanisms: enzymatic inactivation, active efflux, and protection/modification/replacement of the cellular target sites of the antimicrobial agents. Mobile genetic elements, in particular plasmids and transposons, play a major role as carriers of antimicrobial resistance genes in animal staphylococci. They facilitate not only the exchange of resistance genes among members of the same and/or different staphylococcal species, but also between staphylococci and other Gram-positive bacteria. The observation that plasmids of staphylococci often harbor more than one resistance gene points toward coselection and persistence of resistance genes even without direct selective pressure by a specific antimicrobial agent. This chapter provides an overview of the resistance genes and resistance-mediating mutations known to occur in staphylococci of animal origin.

Repurposing Ionophores as novel antimicrobial agents for the treatment of bovine mastitis caused by Gram-positive pathogens

Increasing reports of multidrug-resistant bacterial infections in animals has created a need for novel antimicrobial agents that do not promote cross-resistance to critically important antimicrobial classes used in human medicine. In response to the recent emergence of antimicrobial resistance in several bovine mastitis pathogens, in vitro antimicrobial susceptibility was determined for four polyether ionophores (lasalocid, monensin, narasin and salinomycin) against Staphylococcus spp. and Streptococcus spp. isolated from clinical cases. In addition, erythrocyte haemolysis and WST-1 cell proliferation assays were used to assess in vitro mammalian cell cytotoxicity and biofilm susceptibility testing was performed using the minimum biofilm eradication concentration (MBEC™) biofilm assay. Lasalocid, monensin, narasin and salinomycin exhibited bacteriostatic antimicrobial activity against all pathogens tested, including methicillin-resistant staphylococci, with MIC₉₀ values <16 μg/ml. Narasin and monensin displayed the least toxicity against mammalian cell lines and all compounds significantly reduced viable cell numbers in a Staphylococcus aureus biofilm. Based on in vitro characterization, all four ionophores offer potentially novel treatments against bovine mastitis but in vivo studies will be essential to determine whether acceptable safety and efficacy is present following intramammary administration.

Genomic investigation of Staphylococcus aureus isolates from bulk tank milk and dairy cows with clinical mastitis

Staphylococcus aureus is one of the most common pathogens that cause mastitis in dairy cows. Various subtypes, virulence genes and mobile genetic elements have been associated with isolates from bulk tank milk and clinical mastitis. So far, no Danish cattle associated S. aureus isolates have been whole-genome sequenced and further analyzed. Thus, the main objective was to investigate the population structure and genomic content of isolates from bulk tank milk and clinical mastitis, using whole-genome sequencing. This may reveal the origin of strains that cause clinical mastitis. S. aureus isolates from bulk tank milk (n = 94) and clinical mastitis (n = 63) were collected from 91 and 24 different farms, respectively and whole-genome sequenced. The genomic content was analyzed and a phylogenetic tree based on single nucleotide polymorphisms was constructed. In general, the isolates from both bulk tank milk and clinical mastitis were of similar genetic background. This suggests that dairy cows are natural carriers of the S. aureus subtypes that cause clinical mastitis if the right conditions are present and that a broad range of subtypes cause mastitis. A phylogenetic cluster that mostly consisted of ST151 isolates carried three mobile genetic elements that were primarily found in this group. The prevalence of resistance genes was generally low. However, the first ST398 methicillin resistant S. aureus isolate from a Danish dairy cow with clinical mastitis was detected.

An update on environmental mastitis: Challenging perceptions

Environmental mastitis is the most common and costly form of mastitis in modern dairy herds where contagious transmission of intramammary pathogens is controlled through implementation of standard mastitis prevention programmes. Environmental mastitis can be caused by a wide range of bacterial species, and binary classification of species as contagious or environmental is misleading, particularly for Staphylococcus aureus, Streptococcus uberis and other streptococcal species, including Streptococcus agalactiae. Bovine faeces, the indoor environment and used pasture are major sources of mastitis pathogens, including Escherichia coli and S. uberis. A faeco-oral transmission cycle may perpetuate and amplify the presence of such pathogens, including Klebsiella pneumoniae and S. agalactiae. Because of societal pressure to reduce reliance on antimicrobials as tools for mastitis control, management of environmental mastitis will increasingly need to be based on prevention. This requires a reduction in environmental exposure through bedding, pasture and pre-milking management and enhancement of the host response to bacterial challenge. Efficacious vaccines are available to reduce the impact of coliform mastitis, but vaccine development for gram-positive mastitis has not progressed beyond the "promising" stage for decades. Improved diagnostic tools to identify causative agents and transmission patterns may contribute to targeted use of antimicrobials and intervention measures. The most important tool for improved uptake of known mastitis prevention measures is communication. Development of better technical or biological tools for management of environmental mastitis must be accompanied by development of appropriate incentives and communication strategies for farmers and veterinarians, who may be confronted with government-mandated antimicrobial use targets if voluntary reduction is not implemented.

Knowledge gaps and research priorities in Staphylococcus aureus mastitis control

This study assessed knowledge gaps and suggested research priorities in the field of Staphylococcus aureus mastitis. Staphylococcus aureus infecting the mammary gland remains a major problem to the dairy industry worldwide because of its pathogenicity, contagiousness, persistence in the cow environment, colonization of skin or mucosal epithelia, and the poor curing efficacy of treatments. Staphylococcus aureus also constitutes a threat to public health due to food safety and antibiotic usage issues and the potential for bidirectional transmission of strains between humans and dairy animals (cows and small ruminants). Gaps have been identified in (i) understanding the molecular basis for pathogenesis of S. aureus mastitis, (ii) identifying staphylococcal antigens inducing protection and (iii) determining the cell-mediated immune responses to infection and vaccination. The recommended priorities for research are (i) improved diagnostic methods for early detection of infection and intervention through treatment or management, (ii) development of experimental models to investigate the strategies used by S. aureus to survive within the mammary gland and resist treatment with anti-microbials, (iii) investigation of the basis for cow-to-cow variation in response to S. aureus mastitis, (iv) identification of the immune responses (adaptive and innate) induced by infection or vaccination and (v) antibacterial discovery programmes to develop new, more effective, narrow spectrum antibacterial agents for the treatment of S. aureus mastitis. With the availability and ongoing improvement of molecular research tools, these objectives may not be out of reach in the future.

Genetic diversity and antibiotic susceptibility of Staphylococcus aureus isolates from wild boars

We here report the occurrence of S. aureus in wild boars and characterize isolates genotypically and phenotypically in order to get knowledge about the occurrence of clonal lineages and genotypes in free-living wild animals. Forty-one S. aureus isolates obtained from 111 wild boars hunted in Lower Saxony, Germany, were investigated and compared to human and livestock isolates. The S. aureus belonged to multilocus sequence types ST1, ST7, ST30, ST133, ST425, ST804, ST890 and to the new ST3237, ST3238, ST3255 and ST3369. The livestock associated CC398-MRSA lineage, however, was not found. In addition to well-known spa types, the new types t14999, t15000, t15001 and t15002 were detected. Macrorestriction analysis revealed a variety of different SmaI fragment patterns. Most isolates were susceptible to all antimicrobials tested, including methicillin, and resistance was detected only to ampicillin, penicillin and erythromycin. PCR analysis confirmed the presence of staphylococcal enterotoxin genes (seh) in all t127-ST1 isolates. A high degree of genetic diversity was detected with many spa types and clonal lineages previously reported in humans and livestock animals.

Molecular Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Australian Animals and Veterinarians

This study aimed to determine the frequency and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) from Australian animals and whether animal-derived MRSA was similar to that from Australian veterinarians. A total of 1,080 clinical coagulase positive Staphylococcus isolates from Australian animals were collected during 2013. Sixteen (4%) of 360 S. aureus isolates were MRSA. Most MRSA came from companion animals, while none came from livestock. MRSA isolates were characterized using whole genome sequencing. ST22-IV (EMRSA-15) was the most common clone in dogs and cats. Clonal complex (CC) 8 was most common in horses. Most ST22-IV isolates were resistant to ciprofloxacin. Animal-derived MRSA genomes were interrogated for the presence of host-specific genetic markers (staphylokinase gene [scn], chemotaxis-inhibiting proteins gene [chp], staphylococcal complement inhibitor gene [sak], enterotoxin A gene [sea], and Von Willebrand Factor binding protein gene [vwb]). A subset of MRSA genomes previously collected from Australian veterinarians was also interrogated. There was no clear pattern in the distribution of host-specific markers among animal and veterinarian isolates. Animal- and veterinarian-derived MRSA were intermingled in the phylogenetic tree. The absence of MRSA in Australian livestock is in stark contrast with its presence in livestock from other countries. Possible explanations include Australia's geographic isolation, the absence of live animal importation into Australia, and most notably, the restrictions placed on the use of antimicrobials of critical importance in Australian livestock.

Draft Genome Sequence of a Sequence Type 398 Methicillin-Resistant Staphylococcus aureus Isolate from a Danish Dairy Cow with Mastitis

Livestock-associated (LA) methicillin-resistant Staphylococcus aureus (MRSA) strains of sequence type 398 (ST398) colonize both humans and various livestock species. In 2016, an ST398 LA-MRSA isolate (Sa52) was collected from a Danish dairy cow with mastitis, and here, we report the draft genome sequence of strain Sa52.

Antimicrobial resistance and virulence characterization of Staphylococcus aureus and coagulase-negative staphylococci from imported beef meat

BACKGROUND

The objectives of this study were to characterize the diversity and magnitude of antimicrobial resistance among Staphylococcus species recovered from imported beef meat sold in the Egyptian market and the potential mechanisms underlying the antimicrobial resistance phenotypes including harboring of resistance genes (mecA, cfr, gyrA, gyrB, and grlA) and biofilm formation.

RESULTS

The resistance gene mecA was detected in 50% of methicillin-resistant non-Staphylococcus aureus isolates (4/8). Interestingly, our results showed that: (i) resistance genes mecA, gyrA, gyrB, grlA, and cfr were absent in Staphylococcus hominis and Staphylococcus hemolyticus isolates, although S. hominis was phenotypically resistant to methicillin (MR-non-S. aureus) while S. hemolyticus was resistant to vancomycin only; (ii) S. aureus isolates did not carry the mecA gene (100%) and were phenotypically characterized as methicillin- susceptible S. aureus (MSS); and (iii) the resistance gene mecA was present in one isolate (1/3) of Staphylococcus lugdunensis that was phenotypically characterized as methicillin-susceptible non-S. aureus (MSNSA).

CONCLUSIONS

Our findings highlight the potential risk for consumers, in the absence of actionable risk management information systems, of imported foods and advice a strict implementation of international standards by different venues such as CODEX to avoid the increase in prevalence of coagulase positive and coagulase negative Staphylococcus isolates and their antibiotic resistance genes in imported beef meat at the Egyptian market.

Can methicillin-resistant Staphylococcus aureus prevalence from dairy cows in India act as potential risk for community-associated infections?: A review

Methicillin-resistant Staphylococcus aureus (MRSA) is classified as hospital associated (HA), community associated (CA), livestock associated (LA) and is a global concern. Developing countries, like India, are densely populated country challenging for public hygiene practices. HA-MRSA is comfortably recorded in India, and CA-MRSA is also reported as increasing one. CA-MRSA is serious disease which affects the community as endemic. MRSA is one among major mastitis-causing organisms in India as LA-MRSA. There were reports for transmission of MRSA as community between milk handlers and cow in global perspective. In India reports of MRSA in short among milk handlers and also transmission between animal and human. Hence, proper monitoring of MRSA transmission in India should be elucidated in account among milk handlers and dairy cows to avoid emerging CA-MRSA as outbreak.

A fibronectin-binding protein (FbpA) of Weissella cibaria inhibits colonization and infection of Staphylococcus aureus in mammary glands

Staphylococcus aureus (S. aureus) is a frequent cause of infections in both humans and animals. Probiotics are known to inhibit colonization of pathogens on host tissues. However, mechanisms for the inhibition are still elusive due to complex host-microbe and microbe-microbe interactions. Here, we show that reduced abilities of S. aureus to infect mammary glands in the presence of Weissella cibaria (W. cibaria) were correlated with its poor adherence to mammary epithelial cells. Such inhibition by W. cibaria isolates was at least partially attributed to a fibronectin-binding protein (FbpA) on this lactic acid bacterium. Three W. cibaria isolates containing fbpA had higher inhibitory abilities than other three LAB isolates without the gene. The fbpA-deficient mutant of W. cibaria isolate LW1, LW1ΔfbpA, lost the inhibitory activity to reduce the adhesion of S. aureus to mammary epithelial cells and was less able to reduce the colonization of S. aureus in mammary glands. Expression of FbpA to the surface of LW1ΔfbpA reversed its inhibitory activities. Furthermore, addition of purified FbpA inhibited S. aureus biofilm formation. Our results suggest that W. cibaria FbpA hinders S. aureus colonization and infection through interfering with the S. aureus invasion pathway mediated by fibronectin-binding proteins and inhibiting biofilm formation of S. aureus.

Treatment of Staphylococcus aureus Infections

Staphylococcus aureus, although generally identified as a commensal, is also a common cause of human bacterial infections, including of the skin and other soft tissues, bones, bloodstream, and respiratory tract. The history of S. aureus treatment is marked by the development of resistance to each new class of antistaphylococcal antimicrobial drugs, including the penicillins, sulfonamides, tetracyclines, glycopeptides, and others, complicating therapy. S. aureus isolates identified in the 1960s were sometimes resistant to methicillin, a ß-lactam antimicrobial active initially against a majority S. aureus strains. These MRSA isolates, resistant to nearly all ß-lactam antimicrobials, were first largely confined to the health care environment and the patients who attended it. However, in the mid-1990s, new strains, known as community-associated (CA-) MRSA strains, emerged. CA-MRSA organisms, compared with health care-associated (HA-) MRSA strain types, are more often susceptible to multiple classes of non ß-lactam antimicrobials. While infections caused by methicillin-susceptible S. aureus (MSSA) strains are usually treated with drugs in the ß-lactam class, such as cephalosporins, oxacillin or nafcillin, MRSA infections are treated with drugs in other antimicrobial classes. The glycopeptide drug vancomycin, and in some countries teicoplanin, is the most common drug used to treat severe MRSA infections. There are now other classes of antimicrobials available to treat staphylococcal infections, including several that have been approved after 2009. The antimicrobial management of invasive and noninvasive S. aureus infections in the ambulatory and in-patient settings is the topic of this review. Also discussed are common adverse effects of antistaphylococcal antimicrobial agents, advantages of one agent over another for specific clinical syndromes, and the use of adjunctive therapies such as surgery and intravenous immunoglobulin. We have detailed considerations in the therapy of noninvasive and invasive S. aureus infections. This is followed by sections on specific clinical infectious syndromes including skin and soft tissue infections, bacteremia, endocarditis and intravascular infections, pneumonia, osteomyelitis and vertebral discitis, epidural abscess, septic arthritis, pyomyositis, mastitis, necrotizing fasciitis, orbital infections, endophthalmitis, parotitis, staphylococcal toxinoses, urogenital infections, and central nervous system infections.

Genome-Wide Transcriptional and Post-transcriptional Regulation of Innate Immune and Defense Responses of Bovine Mammary Gland to Staphylococcus aureus

Staphylococcus aureus (S. aureus) is problematic for lactating mammals and public health. Understanding of mechanisms by which the hosts respond to severe invasion of S. aureus remains elusive. In this study, the genome-wide expression of mRNAs and miRNAs in bovine mammary gland cells were interrogated at 24 h after intra-mammary infection (IMI) with high or low concentrations of S. aureus. Compared to the negative control quarters, 194 highly-confident responsive genes were identified in the quarters with high concentration (10⁹ cfu/mL) of S. aureus, which were predominantly implicated in pathways and biological processes pertaining to innate immune system, such as cytokine-cytokine receptor interaction and inflammatory response. In contrast, only 21 highly-confident genes were significantly differentially expressed in face of low concentration (10⁶ cfu/mL) of S. aureus, which slightly perturbed the cell signaling and invoked corresponding responses like vasoconstriction, indicating limited perturbations and immunological evading. Additionally, the significant up-regulations of bta-mir-223 and bta-mir-21-3p were observed in the quarters infected by high concentration of S. aureus. Network analysis suggested that the two miRNAs' pivotal roles in defending hosts against bacterial infection probably through inhibiting CXCL14 and KIT. The significant down-regulation of CXCL14 was also observed in bovine mammary epithelial cells at 24 h post-infection of S. aureus (10⁸ cfu/mL) in vitro. Integrated analysis with QTL database further suggested 28 genes (e.g., CXCL14, KIT, and SLC4A11) as candidates of bovine mastitis. This study first systematically revealed transcriptional and post-transcriptional responses of bovine mammary gland cells to invading S. aureus in a dosage-dependent pattern, and highlighted a complicated responsive mechanism in a network of miRNA-gene-pathway interplay.

Diversity of species and antimicrobial resistance determinants of staphylococci in superficial waters in Spain

The objectives were to determine the presence and diversity of staphylococcal species in surface waters in La Rioja region (Spain), and to characterize recovered isolates. Staphylococci were detected in 42 of 47 evaluable samples, and 72 isolates were obtained, of which 13 were coagulase-positive (CoPS) and 59 were coagulase-negative (CoNS). Twelve CoPS were identified as S. aureus and typed as follows (number of strains): t002/t502/ST5 (four), t10668/ST425 (one), t10712//ST1643 (one), t843/ST130 (one), t10855/ST2461 (one), t3369/ST2657 (one), t1166/ST133 (one), t8083/ST2049 (one) and t045/ST2460 (one); and one as S. pseudintermedius ST147. Virulence genes tst, cna and lukS/F-I were detected, and one strain showed the immune evasion cluster type F. Regarding CoNS, 12 different species were recovered (number of strains): S. epidermidis (11), S. vitulinus (10), S. sciuri (nine), S. fleurettii (seven), S. lentus (six), S. simulans (five), S. xylosus (four), S. chromogenes (two), S. hominis (two), and S. equorum, S. succinus and S. warneri (one each). Fourteen CoNS isolates presented a multidrug resistance phenotype, with the following resistance genes: blaZ, mecA, fusB, fusC, erm(C), mph(C), erm(A), msr(A)/(B), mph(C), ant(4')-Ia, tet(K), tet(L), cat_pc194 and str The high diversity of staphylococcal species, as well as multiple resistance and virulence genes, highlights the importance of surface waters as a temporary reservoir and source of transmission.

Prevalence of Staphylococcus aureus and of methicillin-resistant S. aureus clonal complexes in bulk tank milk from dairy cattle herds in Lombardy Region (Northern Italy)

Staphylococcus aureus is the most important causative agent of subclinical mastitis in cattle resulting in reduced milk production and quality. Methicillin-resistant S. aureus (MRSA) strains has a clear zoonotic relevance, especially in the case of occupational exposure. The aim of the study was to evaluate the prevalence of S. aureus and MRSA in bulk tank milk (BTM) from dairy cattle herds in the Lombardy Region (Northern Italy) and to identify the main MRSA circulating genotypes. MRSA strains were characterized by susceptibility testing, multi-locus sequence typing (MLST), spa typing and SCCmec typing. A total 844 BTM samples were analysed and S. aureus and MRSA were detected in 47·2% and 3·8% of dairy herds, respectively. MLST showed that the majority (28/32) of isolates belonged to the typical livestock-associated lineages: ST398, ST97 and ST1. Interestingly, in this study we report for the first time the new ST3211, a single locus variant of ST(CC)22, with the newly described 462 aroE allele. Our study indicates high diffusion of S. aureus mastitis and low, but not negligible, prevalence of MRSA in the considered area, suggesting the need for planning specific control programmes for bovine mastitis caused by S. aureus, especially when MRSA is implicated.

Genotypic and Phenotypic Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Bovine Mastitic Milk in Korea

Staphylococcus aureus is a major etiological pathogen for bovine mastitis, foodborne illness, and various clinical infections. Methicillin-resistant S. aureus (MRSA) has been isolated from bovine mastitic milk, and the presence of MRSA in milk is a major public health concern. We investigated the frequency of MRSA isolation from mastitic raw milk in Korea and characterized the patterns of antimicrobial resistance, virulence, and genotypes of the MRSA isolates. A total of 1,222 raw milk samples were collected from 47 dairy farms in Gyeonggi province from 2011 to 2012. Of these samples, 649 were considered mastitic milk based on somatic cell counts of more than 200,000 cells per ml, and 165 S. aureus isolates (from 25.4% of samples) were obtained from these samples. Of these isolates, 23 (13.9%) collected from five farms were confirmed as MRSA by detection of the mecA gene. Disk diffusion and MIC tests for antibiotic resistance revealed that all MRSA isolates were resistant to four or more antimicrobial agents. All MRSA isolates had staphylococcal enterotoxin genes, and two clusters of these genes were identified: seg-sei-sek-sem-sen-seo (20 isolates, 87%) and sed-seg-sei-sej-sem-sen-seo (3 isolates, 13%). Each MRSA-positive farm had only one spa-SCCmec type. Nine MRSA isolates (39.1%) with the t324-IVa genotype, which is related to community-acquired MRSA infection, were isolated from three dairy farms. Additional genotypes of t148-IVa and t002-II were detected and related to human MRSA strains. Most MRSA isolates had distinct pulsed-field gel electrophoresis subtypes, indicating they were not the same clones. Only two isolates collected from the same farm during different years had an identical electrophoresis type, indicating persistence of the clone at this farm. Taken together, these findings may indicate an increased virulence and risk of MRSA strains on dairy farms. Therefore, an efficient surveillance and control program is needed to prevent the transmission of MRSA from animals to humans.

Bovine mastitis outbreak in Japan caused by methicillin-resistant Staphylococcus aureus New York/Japan clone

Many methicillin-resistant Staphylococcus aureus (MRSA) strains are multidrug-resistant; consequently, infectious diseases involving MRSA are recognized as troublesome diseases not only in human health care but also in animal health care. A bovine mastitis case caused by MRSA isolates of the New York/Japan clone (NJC), which occurred in Japan in 2005, was monitored in the current study. Isolates of the NJC are typical of hospital-acquired MRSA in Japan. The genetic backgrounds of these strains differ from those of bovine-associated S. aureus, which are typically of clonal complex (CC)97, CC705, and CC133. Moreover, the NJC isolates in this bovine outbreak possessed a β-hemolysin-converting bacteriophage and an immune evasion cluster, as found in the NJC isolates from humans, so it is possible that this clone was introduced into the dairy herd by a human carrier. Most bovine intramammary infections (IMIs) caused by the NJC isolates in our study were asymptomatic, and obvious clinical signs were recognized in only the first 3 infected cows. Of a total of 78 cows, 31 cows were MRSA carriers, and these carrier cows were detected by testing the milk of all lactating cows at 1-month intervals. These S. aureus carrier cows were culled or the infected quarter was dried off and no longer milked. Both IMI and mastitis caused by MRSA were completely eradicated after 5 months. Genotyping data suggested that exchanging of the staphylococcal cassette chromosome mec (the determining factor in methicillin resistance) occurred easily between MRSA and methicillin-sensitive S. aureus in the udders of carrier cows. This case study demonstrates an effective procedure against the spread of MRSA in a dairy herd, and highlights the risk of emergence of new MRSA strains in a dairy herd.

Influence of biomaterial nanotopography on the adhesive and elastic properties of Staphylococcus aureus cells

Despite the well-known beneficial effects of biomaterial nanopatterning on host tissue integration, the influence of controlled nanoscale topography on bacterial colonisation and infection remains unknown.

Amphixenosic Aspects of Staphylococcus aureus Infection in Man and Animals

According to the mode of transmission, Staphylococcus aureus infection between hosts is classified as "direct zoonoses," or infection that is transmitted from an infected vertebrate host to a susceptible host (man) by direct contact, by contact with a fomite or by a mechanical vector. The agent itself undergoes little or no propagative or developmental changes during transmission. According to the reservoir host, staphylococcosis is most precisely defined as "zooanthroponoses" or infections transmitted from man to lower vertebrate animals (e.g., streptococci, diphtheria, Enterobacteriaceae, human tuberculosis in cattle and parrots), but also "anthropozoonoses" or infections transmitted to man from lower vertebrate animals. In particular, actually, the correct definition of S. aureus infections between humans and animals is "amphixenoses" or infections maintained in both man and lower vertebrate animals and transmitted in either direction. S. aureus exhibits tropisms to many distinct animal hosts. While spillover events can occur wherever there is an interface between host species, changes in host tropism only occur with the establishment of sustained transmission in the new host species, leading to clonal expansion. Although the genomic variation underpinning adaptation in S. aureus genotypes infecting bovids and poultry has been well characterized, the frequency of switches from one host to another remains obscure. In this review, we sought to identify the sustained switches in host tropism in the S. aureus population, both anthroponotic and zoonotic, and their distribution over the species phylogeny. S. aureus is an organism with the capacity to switch into and adapt to novel hosts, even after long periods of isolation in a single host species. Based on this evidence, animal-adapted S. aureus lineages exhibiting resistance to antibiotics must be considered a major threat to public health, as they can adapt to the human population.

Presence of mecA-positive multidrug-resistant Staphylococcus epidermidis in bovine milk samples in Brazil

Bacteria of the genus Staphylococcus are one of the major pathogens causing bovine mastitis. In recent decades, resistance of this genus to oxacillin (methicillin) has been a matter of concern due to the possibility of reducing the effectiveness of mastitis treatments and the transfer of resistance determinants to other bacteria. Oxacillin resistance was studied in 170 staphylococci from bovine milk samples, including 79 Staphylococcus aureus and 91 coagulase-negative staphylococci (CNS). The susceptibility profile of 10 antimicrobial agents used in veterinary practice was determined by the Etest method. In addition to the Etest, the phenotypic characterization of oxacillin resistance was tested using the cefoxitin disk diffusion test. All isolates were screened by PCR to detect the mecA gene in 2 different regions of the gene. The isolates with an oxacillin minimum inhibitory concentration ≥0.5 µg/mL or resistant to cefoxitin were identified by sequencing a 536-bp fragment of the 16S rRNA gene. This group of isolates was also evaluated for the presence of blaZ and mecC genes. Molecular analysis of the mecA gene was carried out by typing of the staphylococcal cassette chromosome mec (SCCmec). The relatedness of the mecA-positive isolates was evaluated by macrorestriction of chromosomal DNA followed by pulsed-field gel electrophoresis. With the exception of penicillin and oxacillin, 86% of the isolates showed susceptibility to cephalothin, gentamicin, erythromycin, sulfonamide, trimethoprim-sulfamethoxazole, and tetracycline. All S. aureus isolates were susceptible to oxacillin, whereas 47% (n=43) of the CNS isolates were resistant. The CNS isolates showed a higher resistance to cephalothin, erythromycin, tetracycline, and gentamicin in comparison with S. aureus. The mecA gene was only detected in 10 CNS isolates, identified as Staphylococcus epidermidis, and classified into 3 pulsotypes (A, B, and C) and 4 subtypes (A1, B1, B2, and B3). Among the isolates with an oxacillin resistance phenotype, 12 were positive for the blaZ gene, and 9 of them were mecA-positive. Two of the oxacillin-resistant isolates amplified the mecA homolog gene of Staphylococcus sciuri and none amplified mecC. Three SCCmec types, I, IV, and V, were found. Our results suggest that Staphylococcus epidermidis can be a reservoir for mecA for other Staphylococcus species. Studies investigating the molecular and phenotypic profile of antimicrobial resistance in staphylococcal species should be performed for controlling the spread of resistance and the selection of appropriate therapeutic measures.

Immunization routes in cattle impact the levels and neutralizing capacity of antibodies induced against S. aureus immune evasion proteins

Vaccines against S. aureus bovine mastitis are scarce and show limited protection only. All currently available vaccines are applied via the parenteral (usually intramuscular) route. It is unknown, however, whether this route is the most suitable to specifically increase intramammary immunity to combat S. aureus at the site of infection. Hence, in the present study, immunization via mucosal (intranasal; IN), intramuscular (triangle of the neck; IM), intramammary (IMM) and subcutaneous (suspensory ligament; SC) routes were analyzed for their effects on the quantity of the antibody responses in serum and milk as well as the neutralizing capacity of the antibodies within serum. The experimental vaccine comprised the recombinant S. aureus immune evasion proteins extracellular fibrinogen-binding protein (Efb) and the leukotoxin subunit LukM in an oil-in-water adjuvant combined with a hydrogel and alginate. The highest titer increases for both Efb and LukM specific IgG1 and IgG2 antibody levels in serum and milk were observed following SC/SC immunizations. Furthermore, the harmful effects of Efb and leukotoxin LukMF’ on host-defense were neutralized by serum antibodies in a route-dependent manner. SC/SC immunization resulted in a significant increase in the neutralizing capacity of serum antibodies towards Efb and LukMF’, shown by increased phagocytosis of S. aureus and increased viability of bovine leukocytes. Therefore, a SC immunization route should be considered when aiming to optimize humoral immunity against S. aureus mastitis in cattle.

Fecal Indicator and Pathogenic Bacteria and Their Antibiotic Resistance in Alluvial Groundwater of an Irrigated Agricultural Region with Dairies

Surveys of microbiological groundwater quality were conducted in a region with intensive animal agriculture in California, USA. The survey included monitoring and domestic wells in eight concentrated animal feeding operations (CAFOs) and 200 small (domestic and community supply district) supply wells across the region. was not detected in groundwater, whereas O157:H7 and were each detected in 2 of 190 CAFO monitoring well samples. Nonpathogenic generic and spp. were detected in 24.2% (46/190) and 97.4% (185/190) groundwater samples from CAFO monitoring wells and in 4.2% (1/24) and 87.5% (21/24) of CAFO domestic wells, respectively. Concentrations of both generic and spp. were significantly associated with well depth, season, and the type of adjacent land use in the CAFO. No pathogenic bacteria were detected in groundwater from 200 small supply wells in the extended survey. However, 4.5 to 10.3% groundwater samples were positive for generic and . Concentrations of generic were not significantly associated with any factors, but concentrations of were significantly associated with proximity to CAFOs, seasons, and concentrations of potassium in water. Among a subset of and isolates from both surveys, the majority of (63.6%) and (86.1%) isolates exhibited resistance to multiple (≥3) antibiotics. Findings confirm significant microbial and antibiotic resistance loading to CAFO groundwater. Results also demonstrate significant attenuative capacity of the unconfined alluvial aquifer system with respect to microbial transport.

Coexistence of heavy metal and antibiotic resistance within a novel composite staphylococcal cassette chromosome in a Staphylococcus haemolyticus isolate from bovine mastitis milk

The structure of a composite staphylococcal cassette chromosome (SCC) carried by a methicillin-resistant Staphylococcus haemolyticus (NW19A) isolated from a bovine milk sample was analyzed. The formation of the circular forms of both single SCC elements and composite SCC elements was detected in NW19A. Twenty heavy metal and antibiotic resistance-related genes coexisted in this composite SCC, suggesting that these genes might be coselected under environmental pressure. The mec gene complex in NW19A, designated type C3, is different from classic C1 or C2 gene complexes structurally and likely evolves differently. Furthermore, results from alignment of the SCC composite island of NW19A with 50 related sequences from different staphylococcal strains provided additional evidence to support the notion that coagulase-negative staphylococci (CoNS) are the original host of heavy metal resistance genes among staphylococci. Given that a SCC composite island could transfer freely among different staphylococcal species from different hosts, more attention should be paid to contamination with heavy metals and antibiotics in dairy farming environments, including wastewater, soil, feces, and feed.

Diversity and antimicrobial susceptibility profiling of staphylococci isolated from bovine mastitis cases and close human contacts

The objectives of this study were to examine the diversity of Staphylococcus spp. recovered from bovine intramammary infections and humans working in close contact with the animals and to evaluate the susceptibility of the staphylococcal isolates to different antimicrobials. A total of 3,387 milk samples and 79 human nasal swabs were collected from 13 sampling sites in the KwaZulu-Natal province of South Africa. In total, 146 Staph. aureus isolates and 102 coagulase-negative staphylococci (CNS) were recovered from clinical and subclinical milk samples. Staphylococcusaureus was isolated from 12 (15.2%) of the human nasal swabs and 95 representative CNS were recovered for further characterization. The CNS were identified using multiplex-PCR assays, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and tuf gene sequencing. Seven Staphylococcus spp. were identified among the CNS of bovine origin, with Staph.chromogenes (78.4%) predominating. The predominant CNS species recovered from the human nasal swabs was Staph.epidermidis (80%) followed by Staph.chromogenes (6.3%). The antimicrobial susceptibility of all staphylococcal isolates was evaluated using disk diffusion and was supplemented by screening for specific antimicrobial resistance genes. Ninety-eight (67.1%) Staph.aureus isolates of bovine origin were pansusceptible; 39 (26.7%) isolates were resistant to a single class, and 7 (4.8%) isolates were resistant to 2 classes of antimicrobials. Two Staph. aureus (1.4%) isolates were multidrug-resistant. Resistance to penicillin was common, with 28.8% of the bovine and 75% of the human Staph. aureus isolates exhibiting resistance. A similar observation was made with the CNS, where 37.3% of the bovine and 89.5% of the human isolates were resistant to penicillin. Multidrug-resistance was common among the human CNS, with 39% of the isolates exhibiting resistance to 3 or more classes of antimicrobials. The antimicrobial susceptibility results suggest that resistance among staphylococci causing bovine intramammary infections in South Africa is uncommon and not a significant cause for concern. In contrast, antimicrobial resistance was frequently observed in staphylococcal isolates of human origin, highlighting a possible reservoir of resistance genes. Continued monitoring of staphylococcal isolates is warranted to monitor changes in the susceptibility of isolates to different classes of antimicrobials.

Short communication: Prevalence of Staphylococcus aureus and methicillin-resistant S. aureus in bulk tank milk from dairy goat farms in Northern Italy

Staphylococcus aureus is regarded as a leading cause of mastitis in goats. However, few data are available on the presence of methicillin-resistant S. aureus (MRSA) in this species. The aim of this study was to assess the prevalence of S. aureus and MRSA in bulk tank milk samples from dairy goat farms in Northern Italy. Eighty-five out of 197 samples (43.1%) tested positive for S. aureus with counts ranging from 10 to more than 1.5 × 10(4) cfu/mL. The MRSA was screened by both direct plating followed by a disk diffusion test to evaluate methicillin resistance and a selective enrichment method. Methicillin-resistance was confirmed by mecA-specific PCR. Methicillin-resistant S. aureus was identified in 4 samples (2.0%) and multilocus sequence typing (MLST) showed the presence of livestock-associated MRSA belonging to lineages ST398 (n = 3) and ST1 (n = 1). In one case we demonstrated that the same MRSA strain was able to persist over time on the farm, being isolated from both bulk tank milk and the udder of 3 goats 1 yr after the first isolation. The high prevalence of S. aureus-positive herds detected in this study and the presence of MRSA strains belonging to livestock-associated genotypes is of concern, and represents a novel finding in the Italian dairy goat production system. The application of stringent measures for the control of S. aureus mastitis at the farm level seems appropriate to reduce the economic losses, and to minimize the risk of foodborne illness and the transmission of MRSA to humans by occupational exposure.

Two TIR-like domain containing proteins in a newly emerging zoonotic Staphylococcus aureus strain sequence type 398 are potential virulence factors by impacting on the host innate immune response

Staphylococcus aureus, sequence type (ST) 398, is an emerging pathogen and the leading cause of livestock-associated methicillin-resistant S. aureus infections in Europe and North America. This strain is characterized by high promiscuity in terms of host-species and also lacks several traditional S. aureus virulence factors. This does not, however, explain the apparent ease with which it crosses species-barriers. Recently, TIR-domain containing proteins (Tcps) which inhibit the innate immune response were identified in some Gram-negative bacteria. Here we report the presence of two proteins, S. aureus TIR-like Protein 1 (SaTlp1) and S. aureus TIR-like Protein 2 (SaTlp2), expressed by ST398 which contain domain of unknown function 1863 (DUF1863), similar to the Toll/IL-1 receptor (TIR) domain. In contrast to the Tcps in Gram-negative bacteria, our data suggest that SaTlp1 and SaTlp2 increase activation of the transcription factor NF-κB as well as downstream pro-inflammatory cytokines and immune effectors. To assess the role of both proteins as potential virulence factors knock-out mutants were created. These showed a slightly enhanced survival rate in a murine infectious model compared to the wild-type strain at one dose. Our data suggest that both proteins may act as factors contributing to the enhanced ability of ST398 to cross species-barriers.

Evaluation of biofilm formation using milk in a flow cell model and microarray characterization of Staphylococcus aureus strains from bovine mastitis

It was hypothesized that biofilm could play an important role in the establishment of chronic Staphylococcus aureus bovine mastitis. The in vitro evaluation of biofilm formation can be performed either in closed/static or in flow-based systems. Efforts have been made to characterize the biofilm-forming ability of S. aureus mastitis isolates, however most authors used static systems and matrices other than UHT milk. It is not clear whether such results could be extrapolated to the mammary gland environment. Therefore, the present study aimed to investigate the biofilm-forming ability of S. aureus strains from subclinical bovine mastitis using the static method and a flow-based one. One hundred and twelve strains were tested by the classic tissue culture plate assay (TCP) and 30 out of them were also tested by a dynamic semi-quantitative assay using commercial UHT milk as culture medium (Milk Flow Culture, MFC) or Tryptic Soy Broth as control medium (TS Flow Culture, TSFC). Only 6 (20%) strains formed biofilm in milk under flow conditions, while 36.6% were considered biofilm-producers in TCP, and 93.3% produced biofilm in TSFC. No agreement was found between TCP, MFC and TSFC results. The association between strain genetic profile, determined by microarray, and biofilm-forming ability in milk was evaluated. Biofilm formation in MFC was significantly associated with the presence of those genes commonly found in bovine-associated strains, assigned to clonal complexes typically detected in mastitis. Based on our results, biofilm-forming potential of bovine strains should be critically analysed and tested applying conditions similar to mammary environment.

Staphylococcus aureus from 152 cases of bovine, ovine and caprine mastitis investigated by Multiple-locus variable number of tandem repeat analysis (MLVA)

Staphylococcus aureus is one of the main etiological agents of mastitis in ruminants. In the present retrospective study, we evaluated the potential interest of a previously described automated multiple loci Variable Number of Tandem Repeats (VNTR) Assay (MLVA) comprising 16 loci as a first line tool to investigate the population structure of S. aureus from mastitis. We determined the genetic diversity of S. aureus strains from cases of clinical and subclinical mastitis in dairy cattle (n = 118, of which 16 were methicillin-resistant), sheep (n = 18) and goats (n = 16). The 152 strains could be subdivided into 115 MLVA genotypes (including 14 genotypes for the ovine strains and 15 genotypes for the caprine strains). This corresponds to a discriminatory index (D) value of 0.9936. Comparison with published MLVA data obtained using the same protocol applied to strains from diverse human and animal origins revealed a low number (8.5%) of human-related MLVA genotypes among the present collection. Eighteen percent of the S. aureus mastitis collection belonged to clonal complexes apparently not associated with other pathological conditions. Some of them displayed a relatively low level of diversity in agreement with a restricted ecological niche. These findings provide arguments suggesting that specific S. aureus lineages particularly adapted to ruminant mammary glands have emerged and that MLVA is a convenient tool to provide a broad overview of the population, owing to the availability via internet of databases compiling published MLVA genotypes.

Frequency of resistance to methicillin and other antimicrobial agents among Staphylococcus aureus strains isolated from pigs and their human handlers in Trinidad

Background

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged recently worldwide in production animals, particularly pigs and veal calves, which act as reservoirs for MRSA strains for human infection. The study determined the prevalence of MRSA and other resistant strains of S. aureus isolated from the anterior nares of pigs and human handlers on pig farms in Trinidad.

Methods

Isolation of S. aureus was done by concurrently inoculating Baird-Parker agar (BPA) and Chromagar MRSA (CHROM) with swab samples and isolates were identified using standard methods. Suspect MRSA isolates from Chromagar and BPA were subjected to confirmatory test using Oxoid PBP2 latex agglutination test. The disc diffusion method was used to determine resistance to antimicrobial agents.

Results

The frequency of isolation of MRSA was 2.1% (15 of 723) for pigs but 0.0% (0 of 72) for humans. Generally, for isolates of S. aureus from humans there was a high frequency of resistance compared with those from pigs, which had moderate resistance to the following antimicrobials: penicillin G (54.5%, 51.5%), ampicillin (59.1%, 49.5%), and streptomycin (59.1%, 37.1%), respectively. There was moderate resistance to tetracycline (36.4%, 41.2%) and gentamycin (27.2%, 23.7%) for human and pig S. aureus isolates, respectively, and low resistance to sulfamethoxazole-trimethoprim (4.5%, 6.2%) and norfloxacin (9.1%, 12.4%), respectively. The frequency of resistance to oxacillin by the disc method was 36.4 and 34.0% from S. aureus isolates from humans and pigs, respectively. Out of a total of 78 isolates of S. aureus from both human and pig sources that were resistant to oxacillin by the disc diffusion method, only 15 (19.2%) were confirmed as MRSA by the PBP'2 latex test kit.

Conclusions

The detection of MRSA strains in pigs, albeit at a low frequency, coupled with a high frequency of resistance to commonly used antimicrobial agents in pig and humans could have zoonotic and therapeutic implications. Finally, the diagnostic limitation of using CHROMagar and testing for oxacillin resistance by the disc diffusion method alone to determine MRSA strains without performing confirmatory tests cannot be overemphasized because the possibility of overdiagnosis of MRSA infections cannot be ignored.

Antimicrobial resistance and toxin gene profiles of Staphylococcus aureus strains from Holstein milk

Isolation of Staphylococcus aureus (Staph. aureus) from Holstein milk samples with mastitis and nonmastitis was conducted to estimate its prevalence, antimicrobial resistance and toxin genes. A total of 353 milk samples were collected from three Chinese Holstein herds. Fifty-three Staph. aureus isolates collected from 29 Staph. aureus-positive samples were characterized via antimicrobial susceptibility, toxin genes and Pulsed-field Gel Electrophoresis (PFGE) profiles. The prevalence of Staph. aureus was 4·0-9·5% in mastitic and 7·3-11·5% in nonmastitic samples in the analysed herds. Approximately 61·0% of Staph. aureus strains isolated from mastitis cows were resistant to ≥10 antimicrobials compared with 0% of isolates with nonmastitis. The most frequently observed super antigenic toxin gene was pvl (41·5%) followed by seh + pvl (13·2%). We did not find mecA-positive methicillin-resistant Staph. aureus (MRSA) strains, while mecA-negative MRSA strains were identified in the three herds. PFGE results suggested potential transmission of Staph. aureus strains in different farms. These results open new insights into Staph. aureus transmission and antimicrobial resistance of Holstein dairy cows and into developing strategies for udder health improvement of dairy cattle.

SIGNIFICANCE AND IMPACT OF THE STUDY

Significantly higher levels of antibiotic resistance of Staphylococcus aureus strains were detected in the lactating Holstein milk with clinical mastitis compared with that without clinical mastitis. PFGE results suggest potential transmission of Staph. aureus strains in different dairy farms. The results imply that the dairy farms need to select effective antibiotics in the treatment of Staph. aureus-infected cows and prevent the transmission of Staph. aureus strains from one herd to another.

High incidence of oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) associated with bovine mastitis in China

Staphylococcus aureus is a main cause of bovine mastitis and a major pathogen affecting human health. The emergence and spread of methicillin-resistant Staphylococcus aureus (MRSA) has become a significant concern for both animal health and public health. This study investigated the incidence of MRSA in milk samples collected from dairy cows with clinical mastitis and characterized the MRSA isolates using antimicrobial susceptibility tests and genetic typing methods. In total, 103 S. aureus isolates were obtained from dairy farms in 4 different provinces in China, including Gansu, Shanghai, Sichuan, and Guizhou. Antimicrobial susceptibility testing of these isolates revealed that the resistance rates to penicillin and sulfamethoxazole were high, while the resistance rates to ciprofloxacin and vancomycin were low. Among the 103 isolates, 49 (47.6%) were found to be mecA-positive, indicating the high incidence of MRSA. However, 37 of the 49 mecA-positive isolates were susceptible to oxacillin as determined by antimicrobial susceptibility assays and were thus classified as oxacillin-susceptible mecA-positive S. aureus (OS-MRSA). These isolates could be misclassified as methicillin susceptible Staphylococcus aureus (MSSA) if genetic detection of mecA was not performed. Molecular characterization of selected mecA-positive isolates showed that they were all negative with Panton-Valentine leukocidin (PVL), but belonged to different spa types and SCCmec types. These results indicate that OS-MRSA is common in bovine mastitis in China and underscore the need for genetic methods (in addition to phenotypic tests) to accurately identify MRSA.

Humans and cattle: a review of bovine zoonoses

Infectious disease prevention and control has been among the top public health objectives during the last century. However, controlling disease due to pathogens that move between animals and humans has been challenging. Such zoonotic pathogens have been responsible for the majority of new human disease threats and a number of recent international epidemics. Currently, our surveillance systems often lack the ability to monitor the human-animal interface for emergent pathogens. Identifying and ultimately addressing emergent cross-species infections will require a "One Health" approach in which resources from public veterinary, environmental, and human health function as part of an integrative system. Here we review the epidemiology of bovine zoonoses from a public health perspective.

High genetic diversity of methicillin-susceptible Staphylococcus aureus (MSSA) from humans and animals on livestock farms and presence of SCCmec remnant DNA in MSSA CC398

OBJECTIVES

To investigate the genetic diversity of methicillin-susceptible Staphylococcus aureus (MSSA) carriage isolates from animals and humans on pig, veal, dairy, beef and broiler farms.

METHODS

S. aureus isolates were genotyped using spa typing and multilocus sequence typing (MLST). Antimicrobial susceptibility phenotypes and genotypes were determined. The presence of staphylococcal cassette chromosome mec (SCCmec)-associated DNA was characterized by PCR and sequencing among isolates of clonal complex (CC) 398.

RESULTS

Overall, 41 MSSA isolates in humans and 141 in animals were found, originating from all farm types. These MSSA were mainly assigned to CC398, CC1, CC5, CC9, CC30, CC97, CC133 and CC705/151. MSSA CC398 showed resistance to tetracycline, trimethoprim, macrolides and/or lincosamides, aminoglycosides, ciprofloxacin, spectinomycin and quinupristin/dalfopristin, whereas non-CC398 MSSA showed considerably less resistance. Three porcine MSSA CC398-t011 isolates harboured remnant DNA of a composite SCCmec V(5C2&5)c element that lacked the mec gene complex. This resulted from an MRSA-to-MSSA conversion due to recombination between the ccrC genes flanking the mec gene complex. The SCC remnant still contained an intact J1 region harbouring czrC and tet(K), encoding zinc and tetracycline resistance, respectively, thereby illustrating the capacity of S. aureus CC398 to adapt to different antibiotic selection pressures in the farming environment. Processes such as mec gene complex deletion probably contribute to the enormous diversity of SCC(mec) elements observed in staphylococci.

CONCLUSIONS

MSSA CC398 precursors from which MRSA CC398 might (re)emerge were present on pig, veal and broiler farms, all of which are livestock sectors commonly known to be affected by MRSA CC398. The multiresistance phenotype of S. aureus CC398 appears to be independent of methicillin resistance.

Staphylococcus aureus in veterinary medicine

Staphylococcus aureus is a major opportunistic pathogen in humans and one of the most important pathogenic Staphylococcus species in veterinary medicine. S. aureus is dangerous because of its deleterious effects on animal health and its potential for transmission from animals to humans and vice-versa. It thus has a huge impact on animal health and welfare and causes major economic losses in livestock production. Increasing attention is therefore being paid to both livestock and companion animals in terms of this pathogen. In this review, we summarise the current knowledge on the animal host adaptation of S. aureus. Different types of S. aureus infections in animals are also presented, with particular emphasis on mastitis in dairy herds, which is probably the costliest and therefore the best documented S. aureus infection seen in animals.