Frequency of α- and β-haemolysin inStaphylococcus aureusof bovine and human origin

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.

Ocular Bacterial Infections: A Ten-Year Survey and Review of Causative Organisms Based on the Oklahoma Experience

Ocular infections can be medical emergencies that result in permanent visual impairment or blindness and loss of quality of life. Bacteria are a major cause of ocular infections. Effective treatment of ocular infections requires knowledge of which bacteria are the likely cause of the infection. This survey of ocular bacterial isolates and review of ocular pathogens is based on a survey of a collection of isolates banked over a ten-year span at the Dean McGee Eye Institute in Oklahoma. These findings illustrate the diversity of bacteria isolated from the eye, ranging from common species to rare and unique species. At all sampled sites, staphylococci were the predominant bacteria isolated. Pseudomonads were the most common Gram-negative bacterial isolate, except in vitreous, where Serratia was the most common Gram-negative bacterial isolate. Here, we discuss the range of ocular infections that these species have been documented to cause and treatment options for these infections. Although a highly diverse spectrum of species has been isolated from the eye, the majority of infections are caused by Gram-positive species, and in most infections, empiric treatments are effective.

Whole Genome Sequencing of Staphylococci Isolated From Bovine Milk Samples

Staphylococci are among the commonly isolated bacteria from intramammary infections in bovines, where Staphylococcus aureus is the most studied species. This species carries a variety of virulence genes, contributing to bacterial survival and spread. Less is known about non-aureus staphylococci (NAS) and their range of virulence genes and mechanisms, but they are the most frequently isolated bacteria from bovine milk. Staphylococci can also carry a range of antimicrobial resistance genes, complicating treatment of the infections they cause. We used Illumina sequencing to whole genome sequence 93 staphylococcal isolates selected from a collection of staphylococcal isolates; 45 S. aureus isolates and 48 NAS isolates from 16 different species, determining their content of antimicrobial resistance genes and virulence genes. Antimicrobial resistance genes were frequently observed in the NAS species as a group compared to S. aureus. However, the lincosamide resistance gene lnuA and penicillin resistance gene blaZ were frequently identified in NAS, as well as a small number of S. aureus. The erm genes conferring macrolide resistance were also identified in several NAS isolates and in a small number of S. aureus isolates. In most S. aureus isolates, no antimicrobial resistance genes were detected, but in five S. aureus isolates three to six resistance genes were identified and all five of these carried the mecA gene. Virulence genes were more frequently identified in S. aureus, which contained on average five times more virulence genes compared to NAS. Among the NAS species there were also differences in content of virulence genes, such as S. chromogenes with a higher average number of virulence genes. By determining the content of a large selection of virulence genes and antimicrobial resistance genes in S. aureus and 16 different NAS species our results contribute with knowledge regarding the genetic basis for virulence and antimicrobial resistance in bovine staphylococci, especially the less studied NAS. The results can create a broader basis for further research into the virulence mechanisms of this important group of bacteria in bovine intramammary infections.

Prevalence, antibiotic resistance, virulence and genetic diversity of Staphylococcus aureus isolated from bulk tank milk samples of U.S. dairy herds

Background

Colonization of dairy cows by Staphylococcus aureus (S. aureus), especially those which are multi-drug resistant and toxin producing, is a concern for animal health and well-being as well as public health. The objective of this study was to investigate the prevalence, antibiotic resistance, gene content and virulence determinants of S. aureus in bulk tank milk samples (BTM) from U.S. dairy herds.

Results

BTM samples were collected, once in winter and once in summer, from 189 U.S. dairy herds. Of 365 BTM samples cultured, the sample and herd prevalence of S. aureus in BTM was 46.6% (170 of 365 samples) and 62.4% (118 of 189 herds), respectively. Among a subset of 138 S. aureus isolates that were stored for further analysis, 124 were genome sequenced after being confirmed as S. aureus using phenotypic tests. The most commonly identified antimicrobial resistance-associated gene was norA (99.2%) and mecA gene responsible for methicillin resistance (MRSA) was identified in one isolate (0.8%). The most frequently detected putative virulence genes were aur (100%), hlgB (100%), hlgA, hlgC, hlb (99.2%), lukE (95.9%) and lukD (94.3%). In the 53 staphylococcal enterotoxin positive isolates, sen (37.9%), sem (35.5%), sei (35.5%) and seg (33.1%) were the most frequently detected enterotoxin genes. Among the 14 sequence types (ST) and 18 spa types identified, the most common was ST2187 (20.9%) and t529 (28.2%), respectively. The most predominant clone was CC97 (47.6%) followed by CC unknown (36.3%). The single MRSA isolate belonged to ST72-CC8, spa type t126 and was negative for the tst gene but harbored all the other virulence genes investigated.

Conclusion

Our findings indicated a high prevalence of S. aureus in BTM of U.S. dairy herds, with isolates showing little evidence of resistance to antibiotics commonly used to treat mastitis. However, isolates often carried genes for the various enterotoxins. This study identified predominant genetic clones. Despite lower prevalence, the presence of MRSA and multi-drug resistant strains in BTM poses a significant risk to animal and public health if their number were to increase in dairy environment. Therefore, it is necessary to continuously monitor the use of antibiotics in dairy cows.

Antimicrobial resistance and virulence characteristics in 3 collections of staphylococci from bovine milk samples

Mastitis is a prevalent disease in dairy cattle, and staphylococci are among the most common causative pathogens. Staphylococci can express resistance to a range of antimicrobials, of which methicillin resistance is of particular public health concern. Additionally, Staphylococcus aureus carries a variety of virulence factors, although less is understood about the virulence of non-aureus staphylococci (NAS). The aim of our study was to identify and characterize 3 collections of staphylococcal isolates from bovine milk samples regarding antimicrobial resistance, with emphasis on methicillin resistance, and their carriage of virulence genes typically displayed by Staph. aureus. A total of 272 staphylococcal isolates collected in Norway and Belgium in 2016 were included, distributed as follows: group 1, Norway, 100 isolates; group 2, Flanders, Belgium, 64 isolates; group 3, Wallonia, Belgium, 108 isolates. Species identification was performed by use of MALDI-TOF mass spectrometry. Phenotypic resistance was determined via disk diffusion, and PCR was used for detection of methicillin resistance genes, mecA and mecC, and virulence genes. Antimicrobial resistance was common in Staphylococcus epidermidis and Staphylococcus haemolyticus from all different groups, with resistance to trimethoprim-sulfonamide frequently occurring in Staph. epidermidis and Staph. haemolyticus as well as in Staph. aureus. Resistance to penicillin was most frequently observed in group 1. Ten Belgian isolates (1 from group 2, 9 from group 3) carried the methicillin resistance determinant mecA: 5 Staph. aureus from 2 different farms and 5 NAS from 3 different farms. Almost all Staph. aureus isolates were positive for at least 3 of the screened virulence genes, whereas, in total, only 8 NAS isolates harbored any of the same genes. Our study contributes to the continuous need for knowledge regarding staphylococci from food-producing animals as a basis for better understanding of occurrence of resistance and virulence traits in these bacteria.

Identification and application of a neutralizing epitope within alpha-hemolysin using human serum antibodies elicited by vaccination

Staphylococcus aureus (SA), especially the methicillin-resistant variant (MRSA), is becoming a serious threat to human health in hospitals and communities, making the development of an effective vaccine urgent. Alpha-hemolysin (Hla) is a key virulence factor and also a good target for the development of SA vaccines. However, the epitopes in Hla recognized by human immunity are not characterized in detail, which hinders the design of epitope-based human vaccines against SA. In this study, we collected sera from volunteers in a phase 1b clinical trial of a novel recombinant five-antigen SA vaccine (NCT03966040). Using a Luminex-based assay, we characterized the human serologic response against Hla, and identified Hla_121-138 as a neutralizing epitope. In addition, we successfully produced ferritin nanoparticles carrying the neutralizing Hla_121-138 epitope (EpNP) in E. coli. EpNP presented as homogenous nanoparticles in aqueous solution. Immunization with EpNP elicited potent hemolysis-neutralizing antibodies and conferred significant protection in a mouse model of SA skin infection. Our data suggest that EpNP, carrying the neutralizing epitope Hla_121-138, is a good candidate for a vaccine against SA.

Correlations of Host and Bacterial Characteristics with Clinical Parameters and Survival in Staphylococcus aureus Bacteremia

Staphylococcus aureus bacteremia (SAB) is a frequent, severe condition that occurs in patients of all age groups and affects clinical departments of all medical fields. It is associated with a high mortality rate of 20-30%. In this study, we analyzed patient mortality associated with SAB at our tertiary care university hospital, assessed the clinical management in terms of administered antimicrobial therapy, and determined which factors have an impact on the clinical course and outcome of patients with this disease. We collected clinical data and blood culture isolates of 178 patients diagnosed with SAB between May 2013 and July 2015. For this study, bacteria were cultured and analyzed concerning their phenotype, hemolysis activity, biofilm formation, nuclease activity, prevalence of toxin genes, spa and agr type. Overall mortality was 24.2% and 30-day mortality was 14.6%. Inadequate initial therapy was administered to 26.2% of patients and was associated with decreased survival (p = 0.041). Other factors associated with poor survival were patient age (p = 0.003), agr type 4 (p ≤ 0.001) and pathological leukocyte counts (p = 0.029 if elevated and p = 0.003 if lowered). The type of infection focus, spa clonal complex and enterotoxin genes seg and sei had an impact on severity of inflammation. Our results indicate that mortality and burden of disease posed by SAB are high at our university hospital.

No Change, No Life? What We Know about Phase Variation in Staphylococcus aureus

Phase variation (PV) is a well-known phenomenon of high-frequency reversible gene-expression switching. PV arises from genetic and epigenetic mechanisms and confers a range of benefits to bacteria, constituting both an innate immune strategy to infection from bacteriophages as well as an adaptation strategy within an infected host. PV has been well-characterized in numerous bacterial species; however, there is limited direct evidence of PV in the human opportunistic pathogen Staphylococcus aureus. This review provides an overview of the mechanisms that generate PV and focuses on earlier and recent findings of PV in S. aureus, with a brief look at the future of the field.

Characterisation of antibiotic resistance, virulence, clonality and mortality in MRSA and MSSA bloodstream infections at a tertiary-level hospital in Hungary: a 6-year retrospective study

BACKGROUND

Staphylococcus aureus bloodstream infections (BSI) cause significant morbidity and mortality due to the frequent antibiotic resistance, toxin and adhesin production of the bacterium. These characteristics differ significantly in methicillin resistant (MRSA) and methicillin sensitive S. aureus (MSSA) and also among isolates of different MRSA clones, contributing to the outcome of S. aureus bacteraemia.

METHODS

In this study, all MRSA BSI isolates from Semmelweis University, Budapest, Hungary, isolated between 2011-2016 and the same number of matched MSSA (overall 306 isolates) were characterised in terms of antibiotic susceptibility, virulence genes, clonality and their association with all-cause 30-day mortality. Effect of patient related variables, such as age, gender and comorbidities were also investigated.

RESULTS

ST22-MRSA-IV and ST5-MRSA-II were the most prevalent clones in our study. SCCmec I isolates showed the highest resistance rates and SCCmec II carried most virulence genes. Infections caused by SCCmec IV isolates were associated with the highest mortality rate (42.2%), despite the similar comorbidity rates of the different patient groups. All-cause 30-day mortality was 39.9% in the MRSA and 30.7% in the MSSA group. Increased teicoplanin MIC was associated with high mortality rate. Resistance to ciprofloxacin, erythromycin and clindamycin was common in MRSA, whereas MSSA isolates were more sensitive to all antibiotics with the exception of doxycycline. All MRSA isolates were sensitive to glycopeptides and linezolid; resistance to rifampicin and sulfamethoxazole-trimethoprim was low. MRSA isolates carried more adhesion genes, superantigens were more frequent in MSSA. Panton-Valentine leukocidin was found in 2.3% of the isolates.

CONCLUSION

This study provides insight into the clonal composition and associated mortality of BSI S. aureus isolates in Hungary. The results suggest that the outcome of the infection is determined by the antibiotic resistance, genotype of the bacterium, and patient-related factors; rather than the virulence factors carried by the bacteria.

Different distribution of antimicrobial resistance genes and virulence profiles of Staphylococcus aureus strains isolated from clinical mastitis in six countries

Staphylococcus aureus is recognized worldwide as one of the main contagious mastitis agents in cattle and can express a set of antimicrobial resistance genes and virulence-associated genes that explain the wide range of outcomes of intramammary infections. Staphylococcus aureus strains are heterogeneous: their different resistance and virulence patterns, associated with host-level factors and treatment factors, are related to the severity of infection. The aim of this study was to determine phenotypic antibiotic susceptibility, occurrence of selected antimicrobial resistance genes and other virulence genes in 93 S. aureus strains isolated from clinical mastitis in 6 countries: Argentina, Brazil, Germany, Italy, the United States (New York State), and South Africa. These isolates were tested against a total of 16 drugs (amoxicillin-clavulanate, ampicillin, cefazolin, cefoperazone, cefquinome, enrofloxacin, erythromycin, gentamicin, kanamycin, lincomycin, oxacillin, penicillin, rifampin, spiramycin, sulfamethoxazole/trimethoprim, tylosin) by minimum inhibitory concentration (MIC) assay, and examined for the presence of 6 antibiotic-resistance genes (blaZ, mecA, mecC, ermA, ermB, ermC) and 6 virulence-associated genes (scn, chp, sak, hla, hlb, sea) via PCR analysis. The phenotypic results of this study revealed the presence of 19.4% penicillin-resistant strains, whereas 22.6% of the strains were classified as having resistance (5.4%) or intermediate resistance (17.2%) to erythromycin. Most (96.8%) of the isolates were inhibited by cephalosporins, and all were susceptible to amoxicillin-clavulanate. Two strains (1 from Germany, 1 from Italy) were resistant to oxacillin and were positive for mecA. Among the other antimicrobial resistance genes, the most frequently detected was blaZ (46.2%), and 32.3% of the isolates were positive for erm genes: ermC (21.5%) and ermB (10.8%). The most prevalent virulence gene was hla (100%), followed by hlb (84.9%) and sea (65.6%). These results show a low prevalence of antibiotic multidrug resistance in S. aureus isolates, even if the detection of selected antimicrobial resistance genes did not always correspond with the occurrence of phenotypic antibiotic resistance; the immune evasion cluster gene prevalence was quite low in the samples analyzed.

An Eye on Staphylococcus aureus Toxins: Roles in Ocular Damage and Inflammation

Staphylococcus aureus (S. aureus) is a common pathogen of the eye, capable of infecting external tissues such as the tear duct, conjunctiva, and the cornea, as well the inner and more delicate anterior and posterior chambers. S. aureus produces numerous toxins and enzymes capable of causing profound damage to tissues and organs, as well as modulating the immune response to these infections. Unfortunately, in the context of ocular infections, this can mean blindness for the patient. The role of α-toxin in corneal infection (keratitis) and infection of the interior of the eye (endophthalmitis) has been well established by comparing virulence in animal models and α-toxin-deficient isogenic mutants with their wild-type parental strains. The importance of other toxins, such as β-toxin, γ-toxin, and Panton-Valentine leukocidin (PVL), have been analyzed to a lesser degree and their roles in eye infections are less clear. Other toxins such as the phenol-soluble modulins have yet to be examined in any animal models for their contributions to virulence in eye infections. This review discusses the state of current knowledge of the roles of S. aureus toxins in eye infections and the controversies existing as a result of the use of different infection models. The strengths and limitations of these ocular infection models are discussed, as well as the need for physiological relevance in the study of staphylococcal toxins in these models.

Staphylococcus aureus Secreted Toxins and Extracellular Enzymes

Staphylococcus aureus is a formidable pathogen capable of causing infections in different sites of the body in a variety of vertebrate animals, including humans and livestock. A major contribution to the success of S. aureus as a pathogen is the plethora of virulence factors that manipulate the host's innate and adaptive immune responses. Many of these immune modulating virulence factors are secreted toxins, cofactors for activating host zymogens, and exoenzymes. Secreted toxins such as pore-forming toxins and superantigens are highly inflammatory and can cause leukocyte cell death by cytolysis and clonal deletion, respectively. Coagulases and staphylokinases are cofactors that hijack the host's coagulation system. Exoenzymes, including nucleases and proteases, cleave and inactivate various immune defense and surveillance molecules, such as complement factors, antimicrobial peptides, and surface receptors that are important for leukocyte chemotaxis. Additionally, some of these secreted toxins and exoenzymes can cause disruption of endothelial and epithelial barriers through cell lysis and cleavage of junction proteins. A unique feature when examining the repertoire of S. aureus secreted virulence factors is the apparent functional redundancy exhibited by the majority of the toxins and exoenzymes. However, closer examination of each virulence factor revealed that each has unique properties that have important functional consequences. This chapter provides a brief overview of our current understanding of the major secreted virulence factors critical for S. aureus pathogenesis.

Staphylococcus aureus Toxins and Their Molecular Activity in Infectious Diseases

Staphylococcus aureus is a microorganism resident in the skin and nasal membranes with a dreadful pathogenic potential to cause a variety of community and hospital-acquired infections. The frequency of these infections is increasing and their treatment is becoming more difficult. The ability of S. aureus to form biofilms and the emergence of multidrug-resistant strains are the main reasons determining the challenge in dealing with these infections. S. aureus' infectious capacity and its success as a pathogen is related to the expression of virulence factors, among which the production of a wide variety of toxins is highlighted. For this reason, a better understanding of S. aureus toxins is needed to enable the development of new strategies to reduce their production and consequently improve therapeutic approaches. This review focuses on understanding the toxin-based pathogenesis of S. aureus and their role on infectious diseases.

Molecular biological tools applied for identification of mastitis causing pathogens

The molecular diagnostic tools became the gold standard of mastitis diagnosis in the last few years. They enable rapid, qualitative, quantitative and large scale diagnosis. In addition to their role in diagnosis, they can identify pathogens at the subspecies level which is necessary for the epidemiological studies. They are increasingly used in mastitis control programs through identification of suitable candidates for vaccine production and through the selection of mastitis resistant cattle breeds. The present molecular techniques are continuously improved and new techniques are developed in order to provide higher sensitivity and specificity and to minimize the costs. The present work aims to provide an overview of the modern molecular tools, discuss why they replaced the traditional tools and became the new gold standard in mastitis diagnosis through comparing both traditional and molecular tools, explore the prospective of the molecular diagnostic techniques in mastitis diagnosis and control and to explore new horizons of using molecular assays in near future.

Future Directions and Molecular Basis of Ventilator Associated Pneumonia

Mechanical ventilation is a lifesaving treatment and has complications such as ventilator associated pneumonia (VAP) that lead to high morbidity and mortality. Moreover VAP is the second most common hospital-acquired infection in pediatric intensive care units. Although it is still not well understood, understanding molecular pathogenesis is essential for preventing and treating pneumonia. A lot of microbes are detected as a causative agent of VAP. The most common isolated VAP pathogens in pediatric patients are Staphylococcus aureus, Pseudomonas aeruginosa, and other gram negative bacteria. All of the bacteria have different pathogenesis due to their different virulence factors and host reactions. This review article focused on mechanisms of VAP with molecular pathogenesis of the causative bacteria one by one from the literature. We hope that we know more about molecular pathogenesis of VAP and we can investigate and focus on the management of the disease in near future.

Frequência de genes codificadores de toxinas em Staphylococcus aureus isolados de leite de tanques expansão comunitários

RESUMO: A capacidade de produção de toxinas pelo Staphylococcus aureus no leite e produtos derivados está relacionado com surtos de intoxicação alimentar. Objetivou-se nesta pesquisa, estudar a ocorrência de genes que codificam para enterotoxinas estafilocócicas (sea, seb, sed, seg, seh e sei) e toxinas α e β hemolítica (hla e hlb) em S. aureus isolados de 53 amostras de leite de tanques expansão comunitários no Estado de Alagoas, Brasil. Foram identificados 27 isolados (50,94%) como S. aureus pela amplificação do gene nuc. 13/27 isolados (48,1%) foram positivos para pelo menos um gene das enterotoxinas estudadas, sendo as frequências dos genes sea 33,3%, seh 18,5%, sei 11,1% e sed 7,4%; não entanto não foram identificados os genes seb e seg nestas bactérias. Para as toxinas hemolíticas, 51,9% dos isolados portavam ambos genes (hla e hlb), sendo a frequência para o gene hla de 81,5% e para o gene hlb de 51,9%. A frequência de genes das toxinas avaliadas é alta o que constitui um risco potencial para a saúde pública em especial, as enterotoxinas por serem termoestáveis e estarem asssociados com surtos de intoxicação alimentar.

Antibiofilm and antibacterial effects of specific chitosan molecules on Staphylococcus aureus isolates associated with bovine mastitis

Staphylococcus aureus is one of the major pathogens causing bovine intramammary infections (IMIs) and mastitis. Mastitis is the primary cause for the use of antibiotics in dairy farms but therapeutic failure is often observed. One of the reasons for the lack of effectiveness of antibiotic therapy despite the observed susceptibility of bacterial isolates in vitro are bacterial biofilms. In this study, we used chitosan of well-defined molecular weight (0.4–0.6, 1.3, 2.6 and 4.0 kDa) and investigated their antibiofilm and antibacterial activities in in vitro and in vivo models related to S. aureus IMIs. A chitosan of at least 6 units of glucosamine was necessary for maximum antibacterial activity. The 2.6 and 4.0 kDa forms were able to prevent biofilm production by the biofilm hyperproducer strain S. aureus 2117 and a bovine MRSA (methicillin-resistant S. aureus). The intramammary administration of the 2.6 kDa chitosan showed no adverse effects in mice or in cows, as opposed to the slight inflammatory effect observed in mammary glands with the 4.0 kDa derivative. The 2.6 kDa chitosan killed bacteria embedded in pre-established biofilms in a dose-dependent manner with a >3 log10 reduction in CFU at 4 mg/ml. Also, the 2.6 kDa chitosan could prevent the persistence of the internalized MRSA into the mammary epithelial cell line MAC-T. An in vitro checkerboard assay showed that the 2.6 kDa chitosan produced a synergy with the macrolide class of antibiotics (e.g., tilmicosin) and reduced the MIC of both molecules by 2–8 times. Finally, the intramammary administration of the 2.6 kDa chitosan alone (P<0.01) or in combination with tilmicosin (P<0.0001) reduced the colonization of mammary glands in a murine IMI model. Our results suggest that the use of chitosan alone or in combination with a low dose of a macrolide could help reduce antibiotic use in dairy farms.

Staphylococcal β-Toxin Modulates Human Aortic Endothelial Cell and Platelet Function through Sphingomyelinase and Biofilm Ligase Activities

Staphylococcus aureus causes many infections, such as skin and soft tissue, pneumonia, osteomyelitis, and infective endocarditis (IE). IE is an endovascular infection of native and prosthetic valves and the lining of the heart; it is characterized by the formation of cauliflower-like “vegetations” composed of fibrin, platelets, other host factors, bacteria, and bacterial products. β-Toxin is an S. aureus virulence factor that contributes to the microorganism’s ability to cause IE. This cytolysin has two enzymatic activities: sphingomyelinase (SMase) and biofilm ligase. Although both activities have functions in a rabbit model of IE, the mechanism(s) by which β-toxin directly affects human cells and is involved in the infectious process has not been elucidated. Here, we compared the in vitro effects of purified recombinant wild-type β-toxin, SMase-deficient β-toxin (H289N), and biofilm ligase-deficient β-toxin (H162A and/or D163A) on human aortic endothelial cells (HAECs) and platelets. β-Toxin was cytotoxic to HAECs and inhibited the production of interleukin 8 (IL-8) from these cells by both SMase and biofilm ligase activities. β-Toxin altered HAEC surface expression of CD40 and vascular cell adhesion molecule 1 (VCAM-1). HAECs treated with β-toxin displayed granular membrane morphology not seen in treatment with the SMase-deficient mutant. The altered morphology resulted in two possibly separable activities, cell rounding and redistribution of cell membranes into granules, which were not the result of endosome production from the Golgi apparatus or lysosomes. β-Toxin directly aggregated rabbit platelets via SMase activity.

Each year there are up to 100,000 cases of infective endocarditis (IE) in the United States. S. aureus is the most common pathogen in patients with health care-associated IE and the leading cause of community-associated IE in the developed world. Multiple clonal group strains as defined by the Centers for Disease Control and Prevention, particularly USA200 and other clones encoding β-toxin, are highly associated with IE. Considering the strong association and established contribution of β-toxin in animal models of IE, determining how β-toxin directly affects human cell types, including endothelial cells and platelets, is important. In this study, we demonstrate that β-toxin functions to modulate endothelial cells and platelets by both toxin sphingomyelinase and biofilm ligase activities. Our data suggest that these activities modulate inflammation and increase infection severity.

The pathogenicity and host adaptation of livestock-associated MRSA CC398

The presence of methicillin-resistant Staphylococcus aureus (MRSA) CC398 in livestock and their transmission to humans followed by their introduction into hospitals led to a significant burden for the human healthcare system, especially in regions with a high density of livestock breeding. The CC398 lineage made two host changes in its evolutionary history: From humans to pigs and other livestock-associated animals and back to the human host. These adaptation processes are mirrored by changes of the equipment with virulence factors necessary for successful host change. Here, we consider these factors and their special role during human colonization and infection. Host adaptation of S. aureus CC398 is accompanied by genetic changes that are mainly driven by exchanges of mobile genetic elements. So far, it is not clear, which virulence or adhesion factors are important for S. aureus CC398 in host interaction. Among human and animal-derived MRSA CC398 virulence factors, e.g. (entero-) toxins, were rarely found. Overall, this review provides a comprehensive overview on the emerging S. aureus lineage CC398 by summarizing current knowledge from microbiological, molecular and cellular interaction studies in relation to clinical and epidemiological perspectives.

Staphylococcal Immune Evasion Proteins: Structure, Function, and Host Adaptation

Staphylococcus aureus is a successful human and animal pathogen. Its pathogenicity is linked to its ability to secrete a large amount of virulence factors. These secreted proteins interfere with many critical components of the immune system, both innate and adaptive, and hamper proper immune functioning. In recent years, numerous studies have been conducted in order to understand the molecular mechanism underlying the interaction of evasion molecules with the host immune system. Structural studies have fundamentally contributed to our understanding of the mechanisms of action of the individual factors. Furthermore, such studies revealed one of the most striking characteristics of the secreted immune evasion molecules: their conserved structure. Despite high-sequence variability, most immune evasion molecules belong to a small number of structural categories. Another remarkable characteristic is that S. aureus carries most of these virulence factors on mobile genetic elements (MGE) or ex-MGE in its accessory genome. Coevolution of pathogen and host has resulted in immune evasion molecules with a highly host-specific function and prevalence. In this review, we explore how these shared structures and genomic locations relate to function and host specificity. This is discussed in the context of therapeutic options for these immune evasion molecules in infectious as well as in inflammatory diseases.

Production and applications of an N-terminally-truncated recombinant beta-haemolysin from Staphylococcus aureus

The beta-haemolysin of Staphylococcus aureus (SA-hlb) is a secreted neutral sphingomyelinase (nSMase) implicated in the pathogenesis of infection and responsible for the characteristic in vitro 'hot-cold' haemolytic ability of the bacterium. Here, we describe the production of a biologically active N-terminally-truncated recombinant SA-hlb protein for use in in vitro assays and as a research tool. Using local isolates of S. aureus, we PCR-amplified an SA-hlb DNA sequence of 891 nucleotides, 99 nucleotides shorter than the full-length molecule, before cloning and sequencing (GenBank accession no. JN580071). The pQE.TriSystem vector (Qiagen, Germany) was used to express recombinant SA-hlb (r-SA-hlb) with a C-terminal 8xHis tag in Escherichia coli JM107 cells. Both JM107 lysate and the purified r-SA-hlb possessed hot-cold lytic activity against sheep and buffalo erythrocytes, which was abolished by incubation at ≥90 °C for 30 min or exposure to dithiothreitol, and could be neutralized by bovine immune sera. Purified r-SA-hlb was also cytotoxic to buffalo mononuclear cells and was effective as a coating antigen for indirect ELISA to screen for reactive sera. Importantly, the r-SA-hlb was suitable for use as a β-toxin in the modified CAMP test. We conclude that the r-SA-hlb protein produced was functionally active and has numerous potential applications.

Staphylococcus aureus β-toxin production is common in strains with the β-toxin gene inactivated by bacteriophage

BACKGROUND

Staphylococcus aureus causes life-threatening infections, including infective endocarditis, sepsis, and pneumonia. β-toxin is a sphingomyelinase encoded for by virtually all S. aureus strains and exhibits human immune cell cytotoxicity. The toxin enhances S. aureus phenol-soluble modulin activity, and its activity is enhanced by superantigens. The bacteriophage φSa3 inserts into the β-toxin gene in human strains, inactivating it in the majority of S. aureus clonal groups. Hence, most strains are reported not to secrete β-toxin.

METHODS

This dynamic was investigated by examining β-toxin production by multiple clonal groups of S. aureus, both in vitro and in vivo during infections in rabbit models of infective endocarditis, sepsis, and pneumonia.

RESULTS

β-toxin phenotypic variants are common among strains containing φSa3. In vivo, φSa3 is differentially induced in heart vegetations, kidney abscesses, and ischemic liver compared to spleen and blood, and in vitro growth in liquid culture. Furthermore, in pneumonia, wild-type β-toxin production leads to development of large caseous lesions, and in infective endocarditis, increases the size of pathognomonic vegetations.

CONCLUSIONS

This study demonstrates the dynamic interaction between S. aureus and the infected host, where φSa3 serves as a regulator of virulence gene expression, and increased fitness and virulence in new environments.

Novel structurally designed vaccine for S. aureus α-hemolysin: protection against bacteremia and pneumonia

Staphylococcus aureus (S. aureus) is a human pathogen associated with skin and soft tissue infections (SSTI) and life threatening sepsis and pneumonia. Efforts to develop effective vaccines against S. aureus have been largely unsuccessful, in part due to the variety of virulence factors produced by this organism. S. aureus alpha-hemolysin (Hla) is a pore-forming toxin expressed by most S. aureus strains and reported to play a key role in the pathogenesis of SSTI and pneumonia. Here we report a novel recombinant subunit vaccine candidate for Hla, rationally designed based on the heptameric crystal structure. This vaccine candidate, denoted AT-62aa, was tested in pneumonia and bacteremia infection models using S. aureus strain Newman and the pandemic strain USA300 (LAC). Significant protection from lethal bacteremia/sepsis and pneumonia was observed upon vaccination with AT-62aa along with a Glucopyranosyl Lipid Adjuvant-Stable Emulsion (GLA-SE) that is currently in clinical trials. Passive transfer of rabbit immunoglobulin against AT-62aa (AT62-IgG) protected mice against intraperitoneal and intranasal challenge with USA300 and produced significant reduction in bacterial burden in blood, spleen, kidney, and lungs. Our Hla-based vaccine is the first to be reported to reduce bacterial dissemination and to provide protection in a sepsis model of S. aureus infection. AT62-IgG and sera from vaccinated mice effectively neutralized the toxin in vitro and AT62-IgG inhibited the formation of Hla heptamers, suggesting antibody-mediated neutralization as the primary mechanism of action. This remarkable efficacy makes this Hla-based vaccine a prime candidate for inclusion in future multivalent S. aureus vaccine. Furthermore, identification of protective epitopes within AT-62aa could lead to novel immunotherapy for S. aureus infection.

Study of Staphylococcus aureus collected at slaughter from dairy cows with chronic mastitis

Staphylococcus aureus is one of the most important pathogens associated with bovine mastitis. Recent studies have shown that Staph. aureus strains may differ in virulence, and in their ability to disseminate across commercial dairy herds. The goal of this study was to determine whether Staph. aureus isolates differed in their ability to colonize mammary tissue, and whether such differences could be related to molecular characteristics. Quarter milk and mammary tissues of 22 cows from two dairy herds, were collected at slaughter and bacteriological analysis was performed. All Staph. aureus isolates were characterized by Pulsed Field Gel Electrophoresis (PFGE) and microarray. Overall 45 mammary quarters were infected and 20 Staph. aureus isolates were identified. The bacteria were mostly recovered from both milk and tissue of the same quarter in significantly higher numbers from herd A cows compared with herd B. Molecular characterization of the isolates showed distinct PFGE profiles for isolates from each herd. Differences in virulence factors between herds A and B isolates were evidenced The genes for enterotoxin D, J and R were present in herd A, those for G, I, N, M, O and U were shown in herd B, whilst both components of the leukocidin lukD/E genes were only carried by herd A isolates. Furthermore, all herd A isolates showed β-haemolysin activity, which was absent in all but one isolate from herd B. Therefore our data indicate that Staph. aureus isolates showing differences in their ability to disseminate and colonize across quarters, also have significantly different virulence characteristics.

Immunopathogenesis of Staphylococcus aureus pulmonary infection

Staphylococcus aureus is a common human pathogen highly evolved as both a component of the commensal flora and as a major cause of invasive infection. Severe respiratory infection due to staphylococci has been increasing due to the prevalence of more virulent USA300 CA-MRSA strains in the general population. The ability of S. aureus to adapt to the milieu of the respiratory tract has facilitated its emergence as a respiratory pathogen. Its metabolic versatility, the ability to scavenge iron, coordinate gene expression, and the horizontal acquisition of useful genetic elements have all contributed to its success as a component of the respiratory flora, in hospitalized patients, as a complication of influenza and in normal hosts. The expression of surface adhesins facilitates its persistence in the airways. In addition, the highly sophisticated interactions of the multiple S. aureus virulence factors, particularly the α-hemolysin and protein A, with diverse immune effectors in the lung such as ADAM10, TNFR1, EGFR, immunoglobulin, and complement all contribute to the pathogenesis of staphylococcal pneumonia.

Antibiotic resistance and pathogenicity factors in Staphylococcus aureus isolated from mastitic Sahiwal cattle

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious problem in dairy animals suffering from mastitis. In the present study, the distribution of mastitic MRSA and antibiotic resistance was studied in 107 strains of S. aureus isolated from milk samples from 195 infected udders. The characterizations pathogenic factors (adhesin and toxin genes) and antibiotic susceptibility of isolates were carried out using gene amplification and disc diffusion assays, respectively. A high prevalence of MRSA was observed in the tested isolates (13.1%). The isolates were also highly resistant to antibiotics, i.e. 36.4% were resistant to streptomycin, 33.6% to oxytetracycline, 29.9% to gentamicin and 26.2% each to chloramphenicol, pristinomycin and ciprofloxacin. A significant variation in the expression of pathogenic factors (Ig, coa and clf) was observed in these isolates. The overall distribution of adhesin genes ebp, fib, bbp, fnbB, cap5, cap8, map and cna in the isolates was found to be 69.1, 67.2, 6.5, 20.5, 60.7, 26.1, 81.3 and 8.4%, respectively. The presence of fib, fnbB, bbp and map genes was considerably greater in MRSA than in methicillin-susceptible S. aureus (MSSA) isolates. The proportions of toxin genes, namely, hlb, seb, sec, sed, seg and sei, in the isolates were found to be 94.3, 0.9, 8.4, 0.9, 10.2 and 49.5%, respectively. The proportions of agr genes I, II, III and IV were found to be 39.2, 27.1, 21.5 and 12.1%, respectively. A few isolates showed similar antibiotic-resistance patterns, which could be due to identical strains or the dissemination of the same strains among animals. These findings can be utilized in mastitis treatment programmes and antimicrobials strategies in organized herd.

Immune evasion cluster-positive bacteriophages are highly prevalent among human Staphylococcus aureus strains, but they are not essential in the first stages of nasal colonization

The Staphylococcus aureus immune evasion cluster (IEC), located on β-haemolysin-converting bacteriophages (βC-Φs), encodes the immune-modulating proteins chemotaxis inhibitory protein, staphylococcal complement inhibitor (SCIN), staphylococcal enterotoxin A and staphylokinase. Its precise role in S. aureus colonization is unclear. We studied the presence of the IEC-carrying bacteriophages in human and animal S. aureus isolates, using PCR for the gene encoding SCIN (scn). Human isolates were obtained by collecting serial nasal swabs from 21 persistent carriers. S. aureus strains from 19 (90%) persistent carriers contained an IEC that was present and indistinguishable in 95% of cases at all five sampling moments over a 3-month period. Of the 77 infectious animal strains included in the study, only 26 strains (34%) were IEC-positive. Integration of these IEC-positive strains into an amplified fragment length polymorphism genotype database showed that 24 of 53 (45%) strains were human-associated and only two of 24 (8%) were 'true' animal isolates (p < 0.001). The high prevalence and stability of IEC-carrying βC-Φs in human strains suggested a role for these βC-Φs in human nasal colonization. To test this hypothesis, 23 volunteers were colonized artificially with S. aureus strain NCTC 8325-4 with or without the IEC type B-carrying βC-Φ13. Intranasal survival was monitored for 28 days after inoculation. The strain harbouring βC-Φ13 was eliminated significantly faster (median 4 days; range 1-14 days) than the strain without βC-Φ13 (median 14 days; range 2-28 days; p 0.011). In conclusion, although IEC-carrying βC-Φs are highly prevalent among human colonizing S. aureus strains, they are not essential in the first stages of S. aureus nasal colonization.

Heparan Sulfate Proteoglycans in Infection

To cause infections, microbial pathogens elaborate a multitude of factors that interact with host components. Using these host–pathogen interactions to their advantage, pathogens attach, invade, disseminate, and evade host defense mechanisms to promote their survival in the hostile host environment. Many viruses, bacteria, and parasites express adhesins that bind to cell surface heparan sulfate proteoglycans (HSPGs) to facilitate their initial attachment and subsequent cellular entry. Some pathogens also secrete virulence factors that modify HSPG expression. HSPGs are ubiquitously expressed on the cell surface of adherent cells and in the extracellular matrix. HSPGs are composed of one or several heparan sulfate (HS) glycosaminoglycan chains attached covalently to specific core proteins. For most intracellular pathogens, cell surface HSPGs serve as a scaffold that facilitates the interaction of microbes with secondary receptors that mediate host cell entry. Consistent with this mechanism, addition of HS or its pharmaceutical functional mimic, heparin, inhibits microbial attachment and entry into cultured host cells, and HS-binding pathogens can no longer attach or enter cultured host cells whose HS expression has been reduced by enzymatic treatment or chemical mutagenesis. In pathogens where the specific HS adhesin has been identified, mutant strains lacking HS adhesins are viable and show normal growth rates, suggesting that the capacity to interact with HSPGs is strictly a virulence activity. The goal of this chapter is to provide a mechanistic overview of our current understanding of how certain microbial pathogens subvert HSPGs to promote their infection, using specific HSPG–pathogen interactions as representative examples.

A coagulase-negative variant of Staphylococcus aureus from bovine mastitis milk

Bacteriological analysis of milk samples from quarters of a dairy cow suffering from subclinical mastitis yielded two isolates of Staphylococcus aureus which gave a negative reaction in the standard coagulase test. Both isolates were also clumping factor and thermonuclease negative, and gave a negative reaction in the Staphaurex® test. The isolates were identified by using commercial biochemical systems, and by PCR analysis of different staphylococcal cell surface protein and exoprotein genes. Further molecular identification of the isolates, which included sequencing of the 16S rRNA gene and RT-PCR of coagulase (coa), clumping-factor (clfA) and thermonuclease (nuc) genes, was consistent with the diagnosis phenotypically 'coagulase-negative variant of Staph. aureus'. The fact that coagulase-negative Staph. aureus variants can occur in the context of intramammary infections in cattle may result in the incorrect diagnosis 'coagulase-negative staphylococci (CNS)' in routine mastitis diagnostic, at least in rare cases. To fully ensure correct species diagnosis, sequencing of the 16S rRNA gene and amplification of specific genes such as coa is necessary in these cases.

Simultaneous lack of catalase and beta-toxin in Staphylococcus aureus leads to increased intracellular survival in macrophages and epithelial cells and to attenuated virulence in murine and ovine models

Staphylococcus aureus produces a variety of virulence factors that allow it to cause a wide range of infections in humans and animals. In the latter, S. aureus is a leading cause of intramammary infections. The contribution of catalase (KatA), an enzyme implicated in oxidative stress resistance, and beta-toxin (Hlb), a haemolysin, to the pathogenesis of S. aureus is poorly characterized. To investigate the role of these enzymes as potential virulence factors in S. aureus, we examined the intracellular survival of DeltakatA, Deltahlb and DeltakatA Deltahlb mutants in murine macrophages (J774A.1) and bovine mammary epithelial cells (MAC-T), and their virulence in different murine and ovine models. Catalase was not required for the survival of S. aureus within either J774A.1 or MAC-T cells. However, it was necessary for the intracellular proliferation of the bacterium after invasion of MAC-T cells. In addition, catalase was not needed for the full virulence of S. aureus in mice. Deletion of the hlb gene had no effect on the intracellular survival of S. aureus in J774A.1 cells but did cause a slight increase in survival in MAC-T cells. Furthermore, like catalase, beta-toxin was not required for complete virulence of S. aureus in murine models. Unexpectedly, the DeltakatA Deltahlb mutant showed a notably increased persistence in both cell lines, and was significantly less virulent for mice than were the wild-type strain and single mutants. Most interestingly, it was also markedly attenuated in intramammary and subcutaneous infections in ewes and lambs.

Comparison of Austrian, Hungarian and Macedonian methicillin-resistant and methicillin-sensitive Staphylococcus aureus strains in relation to prevalence of cytotoxin genes

Cytotoxin genes in 128 Austrian (AT) MSSA, 48 MRSA, 94 Hungarian (HU) MSSA, 110 MRSA and 67 Macedonian (MK) MSSA, 81 MRSA strains were examined. The presence of alfa-haemolysin gene (hla) was more common in HU MSSA strains compared to AT and MK (99%, 86%, 72%: p<0.001). AT and MK MRSA harboured hlb genes more frequently compared to HU (60%, 62%, 33%: p<0.001). HU and MK MRSA strains carried gamma-haemolysin gene (hlg) in higher percentage in contrast to AT (88%, 83%, 69%: p=0.01). Haemolysin gamma-variant gene (hlgv) was more prevalent in HU MSSA compared to AT and MK (84%, 56%, 69%: p<0.001). Panton-Valentine leukocidin genes were found only in AT, HU, MK MSSA and MK MRSA in 2.3%, 4%, 1.5% (p=0.53) and 1% (p=0.38), respectively. The 3-gene combination pattern comprising of hla, hlg and hld genes showed increased prevalence among AT MSSA compared to HU (27%, 11%: p<0.001). The 4-gene pattern composed of hla, hlg, hlgv and hld genes was significantly characteristic for HU MRSA in contrast to AT and MK MRSA (56%, 12.5%, 27%: p<0.001). Frequency of certain cytotoxin genes and combinations differed significantly in Staphylococcus aureus strains according to geographical origin and methicillin-resistance.

Staphylococcus aureus beta-toxin induces lung injury through syndecan-1

In pneumonia caused by the bacterium Staphylococcus aureus, the intense inflammatory response that is triggered by this infection can lead to the development of lung injury. Little is known, however, about the impact of specific virulence factors on this inflammatory disorder, which causes both significant mortality and morbidity. In this study, we examined the role of beta-toxin, a neutral sphingomyelinase, in S. aureus-induced lung injury. Our results showed that the central features of lung injury--specifically, increased neutrophilic inflammation, vascular leakage of serum proteins into the lung tissue, and exudation of proteins into the airway--are significantly attenuated in mice infected intranasally with S. aureus deficient in beta-toxin compared with mice infected with S. aureus expressing beta-toxin. In addition, intranasal administration of beta-toxin evoked the characteristic features of lung injury in wild-type mice whereas neutropenic mice were protected from such injury. However, mutant beta-toxin mice deficient in sphingomyelinase activity failed to trigger features of lung injury. Ablation of sphingomyelinase activity also interfered with the ability of beta-toxin to stimulate ectodomain shedding of syndecan-1, a major heparan sulfate proteoglycan found in epithelial cells. Moreover, syndecan-1-null mice were significantly protected from beta-toxin-induced lung injury relative to wild-type mice. These data indicate that S. aureus beta-toxin is a critical virulence factor that induces neutrophil-mediated lung injury through both its sphingomyelinase activity and syndecan-1.

Molecular types and genetic profiles of Staphylococcus aureus strains isolated from bovine intramammary infections and extramammary sites

Staphylococcus aureus isolates collected from sites of intramammary infection during a 10-month period and from extramammary sites (dairy cow teat skin, teat canals, and skin lesions; milking liners; and hands and nostrils of milking personnel) at two separately managed Finnish dairy herd establishments were analyzed to study the sources and reservoirs of bovine S. aureus intramammary infection. Selected isolates were subjected to pulsed-field gel electrophoresis (PFGE) typing and PCR analysis for genes encoding hemolysins (hla to hlg), leukocidins (lukED and lukM), superantigens (sea, sec, sed, seg to seo, seu, and tst), adhesins (fnbA and fnbB), and penicillin and methicillin resistance (blaZ and mecA). S. aureus was found throughout the herds in 94% of the cows. Nine PFGE types were found, with the herds each having their own predominant type and sharing one type. The degree of diversity of PFGE types in herd II, which integrated foreign heifers, was higher than that in herd I. For both herds, the majority of the PFGE-typed isolates both from milk and from extramammary sites represented the predominant PFGE types. In isolates from herd I, the most prevalent genes were hla-hlg, lukED, and fnbA; in those from herd II, they were hla, hld, hlg, lukED, and fnbA. The other genes were pulsotype linked within the herds. The predominant PFGE types carried both fnbA and fnbB; only fnbA was detected in the other PFGE types. No connection between specific virulence genes and the origins of isolates was found. The results suggest that for the two herds, most S. aureus isolates from extramammary sites were indistinguishable from the isolates infecting the mammary gland and that those sites can thus act as origins and reservoirs of intramammary infections. However, contamination in the opposite direction cannot be excluded.

Virulence genes of bovine Staphylococcus aureus from persistent and nonpersistent intramammary infections with different clinical characteristics

AIMS

To screen putative virulence genes in Staphylococcus aureus causing persistent and nonpersistent bovine intramammary infections (IMI) with different clinical characteristics. To examine, whether a possible relationship exists between genetic profile and infection persistence, clinical signs of infection, clonal type determined by pulsed-field gel electrophoresis (PFGE), and antimicrobial resistance.

METHODS AND RESULTS

One-hundred and sixty-one S. aureus isolates derived from bovine IMI, consisting of 17 different PFGE types, were screened by conventional and multiplex-polymerase chain reaction (PCR) for 24 virulence genes for haemolysins (hla-hlg), leukocidins (lukED, lukM), exfoliative toxins (eta, etb), enterotoxins (sea-seo, seu), toxic-shock syndrome toxin (tst), and genes encoding penicillin (blaZ) and methicillin resistance (mecA). The majority of S. aureus isolated at the onset of mastitis carried haemolysin genes (76.7-97.4%), lukED (96.6%), and at least one gene for pyrogenic toxin superantigen (PTSAg) (69.0%). Strains carrying PTSAg-encoding genes were more common among predominant PFGE types and in persistent IMI. Strains concomitantly possessing sed, sej, and blaZ, putatively plasmid-encoded, were typically found in connection with persistent IMI.

CONCLUSIONS

Our results suggest that certain genetic elements are over-representative in S. aureus isolates especially from persistent bovine mastitis. This phenomenon seems to be in connection with clonal type and is often concomitant with penicillin resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to investigate associations between a large number of bacterial factors and outcome of S. aureus mastitis. The finding that widespread clonal types of S. aureus causing bovine mastitis of low treatment response may harbour characteristic genes could be improved for strain-specific diagnostic purposes.

Structure and biological activities of beta toxin from Staphylococcus aureus

Beta toxin is a neutral sphingomyelinase secreted by certain strains of Staphylococcus aureus. This virulence factor lyses erythrocytes in order to evade the host immune system as well as scavenge nutrients. The structure of beta toxin was determined at 2.4-A resolution using crystals that were merohedrally twinned. This structure is similar to that of the sphingomyelinases of Listeria ivanovii and Bacillus cereus. Beta toxin belongs to the DNase I folding superfamily; in addition to sphingomyelinases, the proteins most structurally related to beta toxin include human endonuclease HAP1, Escherichia coli endonuclease III, bovine pancreatic DNase I, and the endonuclease domain of TRAS1 from Bombyx mori. Our biological assays demonstrated for the first time that beta toxin kills proliferating human lymphocytes. Structure-directed active site mutations show that biological activities, including hemolysis and lymphotoxicity, are due to the sphingomyelinase activity of the enzyme.

Characterization of oxacillin-susceptible mecA-positive Staphylococcus aureus: a new type of MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) has been defined as S. aureus having the mecA gene or showing a minimum inhibitory concentration (MIC) of oxacillin higher than 4 mg/l. However, some clinical isolates are mecA-positive and oxacillin-susceptible. Therefore, we surveyed the occurrence of S. aureus having the mecA gene and an MIC of oxacillin of less than 2 mg/l (oxacillin-susceptible MRSA; OS-MRSA) in a total of 480 strains of S. aureus collected from 11 hospitals in different location in Japan isolated from 2003 through 2005. We found 6 strains matching the criteria for OS-MRSA. All 6 strains were staphylococcal cassette chromosome (SCC) mec-positive, without exception, and 4 strains showed the SCCmec type III-variant, which is unique in Japan. These OS-MRSAs were least resistant to oxacillin among the MRSAs tested and they were within the susceptible range to seven other beta-lactam antibiotics tested. Thus, OS-MRSA may become a high-resistant MRSA upon the treatment of patients with beta-lactam antibiotics. To characterize whether these OS-MRSAs were hospital-acquired or community-acquired MRSAs, we tested for the presence of the genes encoding toxins. Genes encoding hemolysin, exfoliative toxin, enterotoxin, toxic shock syndrome toxin-1, and Panton-Valentine leukocidin were found in 6, 4, 0, 0, and 0 strains, respectively. These results revealed that OS-MRSAs could be classified as a new type of MRSA that exhibits properties distinguishable from either hospital- or community-acquired MRSA. Coagulase typing of the OS-MRSAs supported the above conclusion. In this study, the occurrence of OS-MRSA at a certain frequency was noted; precautions are called for in the classification of oxacillin-resistant S. aureus and in the treatment of OS-MRSA infection.

Evaluation of six commercial identification kits for the identification of Staphylococcus aureus isolated from bovine mastitis

AIMS

Comparison of six commercially available in human medicine well-established slide agglutination systems for the identification of Staphylococcus aureus.

METHODS AND RESULTS

Slide agglutination tests were compared with the conventional tube coagulase test, biochemical identification and with the molecular identification by polymerase chain reaction (PCR) amplification of species-specific parts of the gene encoding the 23S RNA. Systems evaluated included Masta-Staph (Mast Diagnostics), Staphylase-Test (Oxoid), Staphytect-Plus (Oxoid), Staphyloslide Latex (Becton Dickinson), Slidex Staph Plus (bioMerieux) and Dry Spot Staphytect Plus (Oxoid). A total of 141 staphylococcal strains isolated from cases of bovine mastitis including 90 S. aureus, 14 Staphylococcus epidermidis, 10 Staphylococcus warneri, 13 Staphylococcus xylosus, 11 Staphylococcus haemolyticus and three other coagulase-negative staphylococci were tested with each method. Staphylococcus aureus strains were selected by macrorestriction analysis with pulsed field gel electrophoresis (PFGE). Only genetically unrelated strains were included in the study. The sensitivities and specificities of the test were as follows: Masta-Staph 86.7 and 90.1%, Staphylase-Test 78.4 and 85.1%, Staphytect-Plus 81.1 and 86.5%, Staphyloslide Latex 77.8 and 84.4%, Slidex Staph Plus 77.8 and 84.4%, Dry Spot Staphytect Plus 75.6 and 83.0%.

CONCLUSIONS

The results of this evaluation suggest that the six slide agglutination methods tested can provide rapid identification of S. aureus also from bovine mastitis. The sensitivity and specificity seems to be less than those reported from human S. aureus isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is one of the first comparative reported investigations about the applicability of different commercially available slide agglutination tests for the detection of S. aureus from bovine mastitis using PFGE selected clinical isolates.

Association between phage types and antimicrobial resistance among bovine Staphylococcus aureus from 10 countries

This study was conducted to investigate the diversity of phage types and associations between penicillin resistance and phage types among 815 Staphylococcus aureus isolates from bovine mastitis in nine European countries and USA. All isolates were examined for susceptibility to antimicrobial agents and characterised by phage typing. Penicillin resistance was found among strains from all countries with an average occurrence of 32.4% (2-71.4%). A total of 76% of isolates were identifiable by phage typing and 144 different phage types were observed. The most predominant types were phage type 29 (11% of the 815 isolates), phage type 52 (5%), and phage type 80 (5%). Phage type 95 and 29/52/52A/80 were both distributed within seven countries. In the countries with the highest occurrence of penicillin resistance a reduced diversity of phage types and phage groups was observed. Phage group III was significantly associated with penicillin resistance in contrast to phage group I (P=0.0023) and phage complex-80 (P=0.0066). This study confirms that a large number of phage types of S. aureus cause bovine mastitis, but that some types predominate. In addition, these findings could indicate that the use of penicillin in the bovine environment has selected for specific types of S. aureus in countries with a high frequency of resistance.

Methods for identification of Staphylococcus aureus isolates in cases of bovine mastitis

A total of 272 staphylococcal isolates from cases of bovine mastitis (159 Staphylococcus aureus) belonging to 12 different species were identified with ID32 STAPH galleries, and 51 of them were confirmed by 16S rRNA gene (rrs) sequencing. The same isolates were examined for their hemolytic activity on sheep blood agar, DNase activity, and coagulase activity and with two rapid identification kits (Slidex Staph Plus kit and RAPIDEC Staph from Bio-Merieux). The results of this study confirm those obtained by other groups with hemolysis, DNase, and coagulase. Only 50% of S. aureus isolates from mastitis cases show coagulase activity after 4 h of incubation, and a 24-h incubation is necessary for the full sensitivity of this test. In contrast to results from other studies with human isolates, the Slidex Staph Plus kit was not sensitive enough for the identification of S. aureus from bovine mastitis samples. The aurease test of the RAPIDEC Staph kit showed 100% sensitivity and 100% specificity. Used in conjunction with hemolysis patterns, the RAPIDEC Staph kit is therefore very well adapted to rapid, efficient, and cost-effective identification of S. aureus in cultures from bovine mastitis samples. Sequencing of rrs genes also proved very efficient in identifying the Staphylococcus species encountered in these samples and confirming phenotypical identification results with unsatisfactory scores. With continuously improving technologies and decreasing costs, genetic identification methods like rrs gene sequencing will soon find a place in routine veterinary diagnostics.

Geographical variation in the presence of genes encoding superantigenic exotoxins and beta-hemolysin among Staphylococcus aureus isolated from bovine mastitis in Europe and USA

The object was to examine the geographical variation in the presence of superantigenic exotoxins and beta-hemolysin among epidemiologically independent Staphylococcus aureus isolates from bovine mastitis. A total of 462 S. aureus isolates from nine European countries and USA were examined for the presence of genes encoding staphylococcal enterotoxins A-E, and H, toxic shock toxin-1 (TSST-1), and beta-hemolysin, and 128 of these were examined for exfoliative toxins A and B. The detection was done by PCR. Phenotypic methods were used to confirm the PCR-results. None of the 128 isolates carried the genes for exfoliative toxin A or B. The total proportion of isolates in which superantigenic exotoxins were detected varied from 2% (one isolate) of the Danish isolates to 65% (32 isolates) of the Norwegian isolates. This marked and highly significant geographical variation was also present for the individual exotoxins. The genes encoding enterotoxin C, TSST-1, and enterotoxin D were the most common superantigens. The present and earlier studies demonstrate that the superantigenic exotoxins that were investigated in this study, do not play a role in the pathogenesis of bovine S. aureus mastitis. In contrast to the geographical variation among superantigenic exotoxins, 97% of the isolates were PCR-positive for and/or produced beta-hemolysin on 5% calf blood agar. Except for three isolates, the Norwegian isolates were PCR-negative, but positive on 5% calf blood agar. Sequence variation in the primer regions in the beta-hemolysin encoding gene of the Norwegian isolates is suggested, and should be investigated further. The consistent presence of beta-hemolysin suggests that this factor, or a co-existing gene correlated to beta-hemolysin, may be an active virulence factor in the pathogenesis of bovine S. aureus mastitis.

Prevention of diseases caused by Staphylococcus aureus using the peptide RIP

Staphylococcus aureus causes many diseases including cellulitis, keratitis, osteomyelitis, septic arthritis and mastitis. The heptapeptide RIP has been shown to prevent cellulitis in mice, which was induced by S. aureus strain Smith diffuse. Here we show that RIP can also significantly reduce the overall pathology and delay the onset of disease symptoms in several other models of S. aureus infections, including: keratitis (tested in rabbits against S. aureus 8325-4), osteomyelitis (tested in rabbits against S. aureus MS), mastitis (tested in cows against S. aureus Newbould 305, AE-1, and environmental infections) and septic arthritis (tested in mice against S. aureus LS-1). These findings substantiate that RIP is not strain specific in its inhibitory activity and that RIP is an effective inhibitor of bacterial pathology at multiple body sites following diverse routes and doses of administration. These findings strongly evidence the potential value of RIP as a chemotherapeutic agent.