Biotyping of enterotoxigenic Staphylococcus aureus by enterotoxin gene cluster (egc) polymorphism and spa typing analyses

Molecular Epidemiology and Characterization of Multidrug-Resistant MRSA ST398 and ST239 in Himachal Pradesh, India

Aim

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of severe and difficult-to-treat infections in humans and animals. We aimed to identify the predominant lineages of methicillin-resistant S. aureus in Himachal Pradesh, India, to understand the genomic epidemiology along with the genotypic and phenotypic characteristics.

Methods

We isolated 250 S. aureus from two district hospitals in Himachal Pradesh, India. Methicillin-Resistant S. aureus (MRSA) isolates were subjected to MLST, SCCmec typing, and resistance as well as virulence determinants were determined by PCR and sequencing. Bio-typing was also performed for source tracking.

Results

A 17.6% (44/250) of isolates were classified as MRSA by both the MRSA detection kit and disc diffusion methods. Antimicrobial Susceptibility Testing of MRSA isolates (n = 44) showed high resistance to oxacillin (77.27%), erythromycin (77.27%), tetracycline (75%), cefoxitin (65.9%), and gentamicin (61.36%), while low resistance was observed for teicoplanin (36.36%), vancomycin and levofloxacin (31.81%) and fusidic acid (18.18%). All isolates were sensitive to linezolid, quinupristin-dulfopristin, dalbavancin, and cefazoline. The SCCmec-II was observed in 20.45% of isolates, SCCmec-I in 11.36%, SCCmec-III in 9%, SCCmec-IV in 40.9% and SCCmec-V in 18.18%. The mecA gene was present in all isolates (n = 44) and 50% also had the vanA gene. 35% of isolates had the lukS-PV/lukf-PV toxin gene and 11.36% had the co-existence of mecA, vanA, and lukS-PV/lukf-PV. The major strain was ST398 (39%) followed by ST239 (27%), ST217 (16%), ST121 (11%), and ST338 (7%). The MRSA isolates produced staphylokinase and β-hemolysis but were negative for bovine plasma coagulation tests.

In Conclusion

The predominant MRSA clones in Himachal Pradesh, India, were hospital-associated multi-drug resistant-MRSA ST239 with PVL and community-associated MRSA ST398.

Prevalence and Diversity of Staphylococcus aureus and Staphylococcal Enterotoxins in Raw Milk From Northern Portugal

Staphylococcus aureus and staphylococcal enterotoxins are a serious public health concern associated with hospital and community-acquired illnesses. Dairy animals frequently shed S. aureus into the milk supply which can lead to food poisoning in humans. This study aims to investigate the prevalence and genetic diversity of S. aureus and staphylococcal enterotoxins in raw milk from the main dairy region of mainland Portugal. S. aureus was found in 53.0% (95% CI: 40.6-65.4%) of 100 raw cow's milk samples collected from bulk cooling tanks. The highest contamination level was 3.4 log10 CFU.mL-1, and in some samples more than one S. aureus strain was identified. Staphylococcal enterotoxins (SEA-SEE) were detected in one sample. Spa typing revealed 62 distinct S. aureus isolates, being t529 (17.7%, 95% CI: 8.2-27.3%) and t1403 (16.1%, 95% CI: 7.0-25.3%) the predominant types, commonly associated with livestock infection or carriage. The antimicrobial susceptibility test showed that 35.5% of the S. aureus isolates were resistant to at least one antimicrobial agent, with resistance to penicillin being the highest (32.3%, 95% CI: 20.6-43.9%) followed by tetracycline (24.2%, 95% CI: 13.5-34.9%), ciprofloxacin (16.1%, 95% CI: 7.0-25.3%) and chloramphenicol (16.1%, 95% CI: 7.0-25.3%). Moreover, five isolates (8.1%, 95% CI: 1.3-14.8%) were identified as methicillin-resistant S. aureus (MRSA, cefoxitin resistant). Regarding virulence/resistance genes, 46,8% (95% CI: 34.4-59.2%) isolates harbored at least one enterotoxin-encoding gene, and the seg gene was the most frequently detected (41.9%, 95% CI: 29.7-54.2%) followed by the sei (40.3%, 95% CI: 28.1-52.5%), sec (6.5%, 95% CI: 0.3-12.6%), seh (4.8%, 95% CI: 0.0-10.2%), and sea (1.6%, 95% CI: 0.0-4.7%) genes. Five (8.1%, 95% CI: 1.3-14.8%) non-enterotoxigenic isolates carried the mecA gene (corresponding to isolates phenotypically classified as MRSA), and 4.8% (95% CI: 0.0-10.2%) enterotoxigenic strains also had the tsst-1 gene. Our study confirm that raw milk can be a zoonotic source of S. aureus, including enterotoxigenic and MRSA strains. Furthermore, the majority of enterotoxigenic isolates were found to contain genes encoding SEs (SEG, SEH and SEI) not routinely screened. This shows the need for a broader SE screening in food safety control, as well as the relevance of risk mitigation measures to control S. aureus transmission along the food chain in Portugal.

Optimized surface plasmon resonance immunoassay for staphylococcal enterotoxin G detection using silica nanoparticles

Staphylococcal enterotoxins are one of the most important causative agents of food poisoning. These molecules function as both gastrointestinal toxins and superantigens (SAgs) which can simultaneously bind MHC-II and T cell receptor leading to a non-specific polyclonal T cell activation and massive proinflammatory cytokine release. Common symptoms include vomiting and diarrhea; however, in more severe cases, systemic dissemination may result in toxic shock syndrome and can be lethal in a few hours. Only small amounts of these heat-stable toxins are needed to cause the disease. Therefore, it is highly important to detect quickly low concentrations of SAgs in biological samples. In this work, we report a surface plasmon resonance (SPR)-based capture immunoassay for the detection of the SAg SEG. We analyzed the use of different amplification strategies. The SPR-based double-antibody sandwich approach could detect picomolar levels of SEG. The use of antibody-coated silica nanoparticles (AbSiNPs) as an alternative enhancing reagent also detected SEG in the picomolar range. Although AbSiNPs did not improve the limit of detection, for the same amount of SAg tested, AbSiNPs gave a higher response level than free antibodies. This work highlights the suitability of silica nanoparticles for signal amplification in SPR-based biosensors. Overall, SPR biosensors offer the capability for continuous real-time monitoring and high sensitivity that can be befitting for the detection of enterotoxins in food industries, laboratories and regulatory agencies.

Staphylococcus argenteus isolated from retail foods in China: Incidence, antibiotic resistance, biofilm formation and toxin gene profile

Staphylococcus argenteus is a novel species of coagulase-positive staphylococci which was separated from Staphylococcus aureus in 2014. It can threaten human health like S. aureus but can not identify with conventional biochemical or other phenotypic testing. From 2011 to 2016, 1581 S. aureus strains were isolated from 4300 samples from retail foods covering most provincial capitals in China. According to multilocus sequence typing (MLST) and PCR confirmation, 7.2% of isolates (114/1581) were confirmed as S. argenteus. The pathogen was distributed in 22 of 39 sampled cities and all food types. Interestingly, most S. argenteus positive samples were collected from coastal cities in South China. MLST detected 8 different sequence types (STs), including five new STs. CC2250 was the predominant lineage of S. argenteus, followed by CC1223. To further characterize the isolates, their antibiotic resistance, virulence genes, biofilm formation and biofilm-related genes were examined. The pvl gene was not detected in S. argenteus, and only 1 isolate (0.9%) was positive for the tsst-1 gene. For 18 enterotoxin genes, 16.7% (19/114) of isolates harboured more than three genes, whereas 70.2% (80/114) of isolates had none of the investigated genes. Penicillin and ampicillin were the major antibiotics to which the S. argenteus isolates were resistant, followed by tetracycline, kanamycin and fusidic acid. A total of 94.7% of isolates had the ability to produce biofilms and all isolates harboured icaA, fnbA, and fib genes. Other biofilm-related genes, such as eno, clfB, fnbB, and icaC, were also found in 99.1%, 92.1%, 88.6%, and 74.6% of isolates, respectively. This study is the first systematic investigation of the prevalence of S. argenteus in retail foods in China and shows their ubiquity in food. We also provide comprehensive surveillance of the incidence of S. argenteus in retail foods and information to enable more accurate and effective treatment of infections of this new species.

Novel insights into the enterotoxigenic potential and genomic background of Staphylococcus aureus isolated from raw milk

In this study, 53 Staphylococcus (S.) aureus strains were typed by 16S-23S rDNA intergenic spacer region (ISR) typing and staphylococcal enterotoxin gene (SEg) typing for all the staphylococcal enterotoxin (se) and staphylococcal enterotoxin-like toxin (sel) genes known to date, revealing a higher discriminatory power than that of multi locus sequence typing. Six strains, one of each ISR- and SEg-type, were genome sequenced and the ability to produce some classical and new SEs when growing in milk was investigated. The manual analysis of the six genomes allowed us to confirm, correct and expand the results of common available genomic data pipelines such as VirulenceFinder. Moreover, it enabled us to (i) investigate the actual location of se and sel genes, even for genes such as selY, whose location (in the core genome) was so far unknown, (ii) find novel allelic variants of se and sel genes and pseudogenes, (iii) correctly annotate se and sel genes and pseudogenes, and (iv) discover a novel type of enterotoxin gene cluster (egc), i.e. the egc type 5 in strains 356P and 364P, while S. argenteus MSHR1132 harbored the egc type 6. Four of the six S. aureus strains produced sufficient amounts of SEA, SEC, SED and SEH in milk to cause staphylococcal food poisoning (SFP), with S. aureus 372 P being the highest producer of SED in milk found to date, producing as much as ca. 47,300 ng/mL and 49,200 ng/mL of SED, after 24 and 48 h of incubation in milk at 37 °C, respectively. S. aureus 372 P released a low amount of SER in milk, most likely because the seR gene was present as a pseudogene, putatively encoding only 51 amino acids. These findings confirm that not only the classical SEs, but also the new ones can represent a potential hazard for the consumers' health if produced in foods in sufficient amounts. Therefore, the detection of SEs in foods, especially if involved in SFP cases, should focus not only on classical, but also on all the new SEs and SEls known to date. Where reference methods are unavailable, the presence of the relevant genes, by using the conventional and real time PCR protocols we exhaustively provided herein, and their nucleotide sequences, should be investigated.

Differences in virulence between the two more prevalent Staphylococcus aureus clonal complexes in rabbitries (CC121 and CC96) using an experimental model of mammary gland infection

Staphylococcal mastitis is a major health problem in humans and livestock that leads to economic loss running in millions. This process is currently one of the main reasons for culling adult rabbit does. Surprisingly, the two most prevalent S. aureus lineages isolated from non-differentiable natural clinical mastitis in rabbits (ST121 and ST96) generate different immune responses. This study aimed to genetically compare both types of strains to search for possible dissimilarities to explain differences in immune response, and to check whether they showed similar virulence in in vitro tests as in experimental intramammary in vivo infection. The main differences were observed in the enterotoxin gene cluster (egc) and the immune-evasion-cluster (IEC) genes. While isolate ST121 harboured all six egc cluster members (seg, sei, selm, seln, selo, selu), isolate ST96 lacked the egc cluster. Strain ST96 carried a phage integrase Sa3 (Sa3int), compatible with a phage integrated into the hlb gene (β-haemolysin-converting bacteriophages) with IEC type F, while isolate ST121 lacked IEC genes and the hlb gene was intact. Moreover, the in vitro tests confirmed a different virulence capacity between strains as ST121 showed greater cytotoxicity for erythrocytes, polymorphonuclear leukocytes and macrophages than strain ST96. Differences were also found 7 days after experimental intramammary infection with 100 colony-forming units. The animals inoculated with strain ST121 developed more severe gross and histological mastitis, higher counts of macrophages in tissue and of all the cell populations in peripheral blood, and a significantly larger total number of bacteria than those infected by strain ST96.

egc Superantigens Impair Monocytes/Macrophages Inducing Cell Death and Inefficient Activation

Bacterial superantigens (SAgs) are enterotoxins that bind to MHC-II and TCR molecules, activating as much as 20% of the T cell population and promoting a cytokine storm which enhances susceptibility to endotoxic shock, causing immunosuppression, and hindering the immune response against bacterial infection. Since monocytes/macrophages are one of the first cells SAgs find in infected host and considering the effect these cells have on directing the immune response, here, we investigated the effect of four non-classical SAgs of the staphylococcal egc operon, namely, SEG, SEI, SEO, and SEM on monocytic-macrophagic cells, in the absence of T cells. We also analyzed the molecular targets on APCs which could mediate SAg effects. We found that egc SAgs depleted the pool of innate immune effector cells and induced an inefficient activation of monocytic-macrophagic cells, driving the immune response to an impaired proinflammatory profile, which could be mediated directly or indirectly by interactions with MHC class II. In addition, performing surface plasmon resonance assays, we demonstrated that non-classical SAgs bind the gp130 molecule, which is also present in the monocytic cell surface, among other cells.

Short communication: Characterization of Staphylococcus aureus isolated along the raw milk cheese production process in artisan dairies in Italy

Staphylococcus aureus is a common cause of food-borne intoxications. Several staphylococcal food poisoning outbreaks have been linked to consumption of raw milk cheeses and artisanal cheese production. However, information on Staph. aureus isolated from artisanal raw milk cheeses and small-scale dairy production environments is very limited. Therefore, we aimed to characterize Staph. aureus isolated along the artisanal raw milk production chain by determining (1) the population structure, and (2) the presence/absence of enterotoxin genes, mecA/C, and pvl. We collected 276 samples from different production stages (raw milk, whey, curd, brine, drying worktops, and cheese) at 36 artisan dairies in Italy. A total of 102 samples from 25 dairies tested positive for Staph. aureus, with 80% positive samples among the tested artisan cheeses. All isolates were further characterized by spa typing and PCR screening for staphylococcal enterotoxin genes, the mecA/mecC genes characteristic for methicillin-resistant Staph. aureus, and the pvl gene encoding Panton-Valentine leukocidin. The 102 isolates represented 15 different spa types and were assigned to 32 different Staph. aureus strains. The spa type most frequently detected was t2953 (30%), which is associated with genotype B strains causing high within-herd levels of bovine mastitis. In addition, 3 novel spa types (t13269, t13277, and t13278) were identified. Although none of the strains harbored mecA/mecC or pvl, 55% of the isolates exhibited at least one enterotoxin gene. Many strains were present in samples from multiple dairies from different regions and years, highlighting the spread of Staph. aureus in small-scale cheese production plants. Our findings demonstrate that enterotoxigenic Staph. aureus and in particular t2953 (genotype B) isolates commonly occur in artisanal dairies and raw milk cheeses in Italy. It is particularly alarming that 80% of the artisan cheeses sampled in our study were positive for Staph. aureus. These findings stress the need for effective measures preventing staphylococcal food poisoning by limiting Staph. aureus growth and enterotoxin formation along the production chain and in the final product.

Phenotypic and genotypic characterization of antibiotic resistance of methicillin-resistant Staphylococcus aureus isolated from hospital food

BACKGROUND

Pathogenic biotypes of the Methicillin-resistant Staphylococcus aureus (MRSA) strains are considered to be one of the major cause of food-borne diseases in hospitals. The present investigation was done to study the pattern of antibiotic resistance and prevalence of antibiotic resistance genes of different biotypes of the MRSA strains isolated from various types of hospital food samples.

METHODS

Four-hundred and eighty-five raw and cooked hospital food samples were cultured and MRSA strains were identified using the oxacillin and cefoxitin disk diffusion tests and mecA-based PCR amplification. Isolated strains were subjected to biotyping and their antibiotic resistance patterns were analyzed using the disk diffusion and PCR methods.

RESULTS

Prevalence of S. aureus and MRSA were 9.69 and 7.62%, respectively. Meat and chicken barbecues had the highest prevalence of MRSA. Prevalence of bovine, ovine, poultry and human-based biotypes in the MRSA strains were 8.10, 8.10, 32.43 and 48.64%, respectively. All of the MRSA strains recovered from soup, salad and rice samples were related to human-based biotypes. MRSA strains harbored the highest prevalence of resistance against penicillin (100%), ceftaroline (100%), tetracycline (100%), erythromycin (89.18%) and trimethoprim-sulfamethoxazole (83.78%). TetK (72.97%), ermA (72.97%), msrA (64.86%) and aacA-D (62.16%) were the most commonly detected antibiotic resistance genes.

CONCLUSIONS

Pattern of antibiotic resistance and also distribution of antibiotic resistance genes were related to the biotype of MRSA strains. Presence of multi-drug resistance and also simultaneous presence of several antibiotic resistance genes in some MRSA isolates showed an important public health issue Further researches are required to found additional epidemiological aspects of the MRSA strains in hospital food samples.

Molecular Epidemiology of Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus in the Ovine Dairy Chain and in Farm-Related Humans

Staphylococcus aureus is a major cause of clinical infections in humans and its enterotoxins cause foodborne disease. In the present study, we tested a total of 51 isolates of S. aureus from small-ruminant dairy farms with artisan dairy facilities, all located in Latium, Italy. The farms have a known history of a high prevalence of methicillin-resistant S. aureus (MRSA). Most of the MRSA isolates (27 of 51) belonged to spa-type t127 (43.1%), followed by t2678 (3.9%), t044 (2%), t1166 (2%), and t1773 (2%). PFGE performed on mecA positive strains identified one cluster (≥ 80% of similarity), comprising 22 MRSA. Nine of twenty-two MRSA isolates were assigned human host origin, and 13 isolates did not belong to a specific host. During the characterization study, one strain isolated from bulk tank milk samples harbored the pvl gene; the strain was not enterotoxigenic with a non-specific host according to the biotyping scheme, highlighting the possible emerging risk of transmission of bacterial virulence factors by foods, the environment, and foodhandlers. These findings stress the importance of hygienic measures at all processing steps of the food production chain and underline that monitoring for the presence of MRSA throughout the food chain is essential for public health.

Molecular Typing and Virulence Gene Profiles of Enterotoxin Gene Cluster (egc)-Positive Staphylococcus aureus Isolates Obtained from Various Food and Clinical Specimens

The enterotoxin gene cluster (egc) has been proposed to contribute to the Staphylococcus aureus colonization, which highlights the need to evaluate genetic diversity and virulence gene profiles of the egc-positive population. Here, a total of 43 egc-positive isolates (16.2%) were identified from 266 S. aureus isolates that were obtained from various food and clinical specimens in Shanghai. Seven different egc profiles were found based on the polymerase chain reaction (PCR) result for egc genes. Then, these 43 egc-positive isolates were further typed by multilocus sequence typing, pulsed-field gel electrophoresis (PFGE), multiple-locus variable-number tandem-repeat analysis (MLVA), and accessory gene regulatory (agr) typing. It showed that the 43 egc-positive isolates displayed 17 sequence types, 28 PFGE patterns, 29 MLVA types, and 4 agr types, respectively. Among them, the dominant clonal lineage was CC5-agr II (48.84%). Thirty toxin and 20 adhesion-associated genes were detected by PCR in egc-positive isolates. Notably, invasive toxin genes showed a high prevalence, such as 76.7% for Panton-Valentine leukocidin encoding genes, 27.9% for sec, and 23.3% for tsst-1. Most of the examined adhesion-associated genes were found to be conserved (76.7-100%), whereas the fnbB gene was only found in 8 (18.6%) isolates. In addition, 33 toxin gene profiles and 13 adhesion gene profiles were identified, respectively. Our results imply that isolates belonging to the same clonal lineage harbored similar adhesion gene profiles but diverse toxin gene profiles. Overall, the high prevalence of invasive virulence genes increases the potential risk of egc-positive isolates in S. aureus infection.

In Vitro Antimicrobial Efficacy of Tobramycin Against Staphylococcus aureus Biofilms in Combination With or Without DNase I and/or Dispersin B: A Preliminary Investigation

Staphylococcus aureus in biofilms is highly resistant to the treatment with antibiotics, to which the planktonic cells are susceptible. This is likely to be due to the biofilm creating a protective barrier that prevents antibiotics from accessing the live pathogens buried in the biofilm. S. aureus biofilms consist of an extracellular matrix comprising, but not limited to, extracellular bacterial DNA (eDNA) and poly-β-1, 6-N-acetyl-d-glucosamine (PNAG). Our study revealed that despite inferiority of dispersin B (an enzyme that degrades PNAG) to DNase I that cleaves eDNA, in dispersing the biofilm of S. aureus, both enzymes were equally efficient in enhancing the antibacterial efficiency of tobramycin, a relatively narrow-spectrum antibiotic against infections caused by gram-positive and gram-negative pathogens, including S. aureus, used in this investigation. However, a combination of these two biofilm-degrading enzymes was found to be significantly less effective in enhancing the antimicrobial efficacy of tobramycin than the individual application of the enzymes. These findings indicate that combinations of different biofilm-degrading enzymes may compromise the antimicrobial efficacy of antibiotics and need to be carefully assessed in vitro before being used for treating medical devices or in pharmaceutical formulations for use in the treatment of chronic ear or respiratory infections.

Relationship between super antigenicity, antimicrobial resistance and origin of Staphylococcus aureus isolated

INTRODUCTION

Staphylococcus aureus is a pathogen that causes food poisoning as well as hospital and community acquired infections.

OBJECTIVE

Establish the profile of superantigen genes among hospital isolates in relation to clinical specimen type, susceptibility to antibiotics and hospital or community acquisition.

METHODS

Eighty one isolates obtained from patients at Colombian hospital, were classified by antimicrobial susceptibility, specimen type and hospital or community acquired . The PCR uniplex and multiplex was used for detection of 22 superantigen genes (18 enterotoxins, tsst-1 and three exfoliative toxins).

RESULTS

Ninety five point one percent of isolates harbored one or more of the genes with an average of 5.6 genes. Prevalence of individual genes was variable and the most prevalent was seg (51.9%). Thirty nine genotypes were obtained, and the genotype gimnou (complete egc cluster) was the most prevalent alone (16.0%) and in association with other genes (13.6%). The correlation between presence of superantigens and clinical specimen or antimicrobial susceptibility showed no significant difference. But there was significant difference between presence of superantigens and the origin of the isolates, hospital or community acquired (p= 0.049).

CONCLUSIONS

The results show the variability of the superantigen genes profile in hospital isolates and shows no conclusive relationship with the clinical sample type and antimicrobial susceptibility, but there was correlation with community and hospital isolates. The analysis of the interplay between virulence, epidemic and antibiotic resistance of bacterial populations is needed to predict the future of infectious diseases.

Screening of virulence genes in Staphylococcus aureus isolates from rabbits

<p><em>Staphylococcus aureus</em> is a versatile pathogen able to cause disease in both humans and animals. In rabbits, this bacterium infects animals of different ages, producing several purulent lesions. The ability of <em>S. aureus</em> to cause disease depends on a combination of virulence factors. The aim of this study was therefore to investigate the distribution of bacterial virulence determinants in 69 <em>S. aureus</em> isolates from rabbits. Some virulence factors (7 adhesins, 1 toxin and 1 protease) were positive in all rabbit <em>S. aureus</em> isolates analysed, while others (1 adhesin and 10 toxins) were always negative. The remaining virulence factors were more variable among isolates. An association between genotype and the different profiles of virulence factors was observed, but not with the type of lesion (P&lt;0.05). One strain of each genotype was further analysed by multilocus sequence typing, generating ST121, ST96 and ST2951, determining a greater number of enterotoxins in ST121 isolates compared to ST96 and ST2951 isolates, which could justify the different pathogenicity between strains. </p>

Impacts of enterotoxin gene cluster-encoded superantigens on local and systemic experimental Staphylococcus aureus infections

Staphylococcus aureus is both a component of the normal skin flora and an important pathogen. It expresses a range of recognized and putative virulence factors, such as enterotoxins with superantigenic properties. Several superantigen genes, i.e., seg, sei, selm, seln, and selo, are encoded by the enterotoxin gene cluster (egc), which is found in the majority of S. aureus isolates. Carriage of egc is associated with fitness of S. aureus in the gut microbiota, but it is not known if it contributes to pathogenicity. We constructed egc+ (functional for the seg, selm, and selo genes) and isogenic egc- S. aureus mutants, and investigated their virulence profiles in murine infection models. No effect of egc was seen in a local skin and soft tissue infection model, but in an invasive infection model, increased weight loss was observed after infection with the egc+ as compared to the egc- mutant. Mortality and arthritis were not affected by egc status. Our data suggest that egc has limited effects on the virulence of S. aureus. It may primarily function as a colonization factor increasing commensal fitness, although it might have some aggravating effects on the infection when the bacteria reach the blood.

Superantigens in Staphylococcus aureus isolated from prosthetic joint infection

Staphylococcus aureus is a common cause of prosthetic joint infection (PJI). The prevalence of superantigens (SAgs) among PJI-associated S. aureus is unknown. Eighty-four S. aureus isolates associated with PJI isolated between 1999 and 2006 were studied. SAg genes, sea, seb, sec, sed, see, seg, seh, sei, and tst, were assayed by PCR. Seventy-eight (92.9%) isolates carried at least 1 SAg gene studied, with 61 (72.6%) harboring more than 1. seg was most commonly (70.2%), and seh was least frequently (4.8%) detected. tst-positive isolates were associated with early infection and increased erythrocyte sedimentation rate at diagnosis (P=0.006 and P=0.021, respectively). seg and sei were associated with methicillin resistance (P=0.008 and P=0.002, respectively). A majority of PJI-associated isolates studied produced biologically active SAgs in both planktonic and biofilm growth modes. SAg genes are prevalent in S. aureus causing PJI.

Characterization of colonizing Staphylococcus aureus isolated from surgical wards' patients in a Nigerian university hospital

In contrast to developed countries, only limited data on the prevalence, resistance and clonal structure of Staphylococcus aureus are available for African countries. Since S. aureus carriage is a risk factor for postoperative wound infection, patients who had been hospitalized in surgical wards in a Nigerian University Teaching Hospital were screened for S. aureus carriage. All S. aureus isolates were genotyped (spa, agr) and assigned to multilocus sequence types (MLST). Species affiliation, methicillin-resistance, and the possession of pyrogenic toxin superantigens (PTSAg), exfoliative toxins (ETs) and Panton-Valentine Leukocidin (PVL) were analyzed. Of 192 patients screened, the S. aureus carrier rate was 31.8 % (n = 61). Of these isolates, 7 (11.5%) were methicillin-resistant (MRSA). The isolates comprised 24 spa types. The most frequent spa types were t064, t084, t311, and t1931, while the most prevalent MLST clonal complexes were CC5 and CC15. The most frequent PTSAg genes detected were seg/sei (41.0%) followed by seb (29.5%), sea (19.7%), seh (14.7%) and sec (11.5). The difference between the possession of classical and newly described PTSAg genes was not significant (63.9% versus 59.0% respectively; P = 0.602). PVL encoding genes were found in 39.3% isolates. All MRSA isolates were PVL negative, SCCmec types I and VI in MLST CC 5 and CC 30, respectively. Typing of the accessory gene regulator (agr) showed the following distribution: agr group 1 (n = 20), group II (n = 17), group III (n = 14) and group IV (n = 10). Compared to European data, enterotoxin gene seb and PVL-encoding genes were more prevalent in Nigerian methicillin-susceptible S. aureus isolates, which may therefore act as potential reservoir for PVL and PTSAg genes.

Detection of methicillin-susceptible Staphylococcus aureus ST398 and ST133 strains in gut microbiota of healthy humans in Spain

Fecal samples of 100 healthy humans were tested for Staphylococcus aureus recovery. Fifteen samples (15 %) contained S. aureus, all methicillin-susceptible (MSSA), being one isolate/sample further studied. These 15 isolates were characterized by spa and agr typing as well as multi-locus sequence typing. High diversity of spa types (n = 11) and sequences types (n = 8) was detected. Two S. aureus of lineages ST398 or ST133 were detected, and six isolates were ascribed to clonal complex 30 (CC30). Strains were susceptible to most of the 17 antimicrobial agents tested with exceptions: erythromycin/clindamycin (three strains, containing erm(C) and/or erm(A) + mph(C) genes) and tobramycin and mupirocin (one strain containing ant(4')-Ia + mup(A) genes). The presence of 18 staphylococcal enterotoxin genes was studied by PCR, and isolates were negative for lukF/lukS-PV genes, although strain ST133 harbored the lukD-lukE + lukM genes. Other virulence genes detected were (number of strains): tsst-1 (6), hla (15), hlb (9), hld (15), hlg (6), hlgv (9), cna (2), aur (14), and egc-like cluster (3). Analysis of immune evasion cluster genes showed six types, highlighting their absence in two strains of lineages ST133 and ST5. A high clonal diversity of MSSA strains was identified in the intestinal microbiota of healthy humans, being CC30 the most frequent one. This is the first report of MSSA ST133 and ST398 isolates in gut microbiota of healthy humans.

The Staphylococcus aureus peptidoglycan protects mice against the pathogen and eradicates experimentally induced infection

Staphylococcus aureus, in spite of antibiotics, is still a major human pathogen causing a wide range of infections. The present study describes the new vaccine A170PG, a peptidoglycan-based vaccine. In a mouse model of infection, A170PG protects mice against a lethal dose of S. aureus. Protection lasts at least 40 weeks and correlates with increased survival and reduced colonization. Protection extends into drug-resistant (MRSA or VISA) and genetically diverse clinical strains. The vaccine is effective when administered - in a single dose and without adjuvant - by the intramuscular, intravenous or the aerosol routes and induces active as well as passive immunization. Of note, A170PG also displays therapeutic activity, eradicating staphylococci, even when infection is systemic. Sustained antibacterial activity and induction of a strong and rapid anti-inflammatory response are the mechanisms conferring therapeutic efficacy to A170PG.

Bacteriophage-resistant Staphylococcus aureus mutant confers broad immunity against staphylococcal infection in mice

In the presence of a bacteriophage (a bacteria-attacking virus) resistance is clearly beneficial to the bacteria. As expected in such conditions, resistant bacteria emerge rapidly. However, in the absence of the phage, resistant bacteria often display reduced fitness, compared to their sensitive counterparts. The present study explored the fitness cost associated with phage-resistance as an opportunity to isolate an attenuated strain of S. aureus. The phage-resistant strain A172 was isolated from the phage-sensitive strain A170 in the presence of the M^Sa phage. Acquisition of phage-resistance altered several properties of A172, causing reduced growth rate, under-expression of numerous genes and production of capsular polysaccharide. In vivo, A172 modulated the transcription of the TNF-α, IFN-γ and Il-1β genes and, given intramuscularly, protected mice from a lethal dose of A170 (18/20). The heat-killed vaccine also afforded protection from heterologous methicillin-resistant S. aureus (MRSA) (8/10 mice) or vancomycin-intermediate S. aureus (VISA) (9/10 mice). The same vaccine was also effective when administered as an aerosol. Anti-A172 mouse antibodies, in the dose of 10 µl/mouse, protected the animals (10/10, in two independent experiments) from a lethal dose of A170. Consisting predominantly of the sugars glucose and galactose, the capsular polysaccharide of A172, given in the dose of 25 µg/mouse, also protected the mice (20/20) from a lethal dose of A170. The above results demonstrate that selection for phage-resistance can facilitate bacterial vaccine preparation.

Diversity of Staphylococcus species strains based on partial kat (catalase) gene sequences and design of a PCR-restriction fragment length polymorphism assay for identification and differentiation of coagulase-positive species (S. aureus, S. delphini, S. hyicus, S. intermedius, S. pseudintermedius, and S. schleiferi subsp. coagulans)

A set of degenerate PCR primers was designed and used to amplify and sequence about 75% of the catalase (kat) gene from each of 49 staphylococcal strains. In some strains of Staphylococcus xylosus, S. saprophyticus, and S. equorum, two catalase genes, katA and katB, were found. A phylogenetic tree was generated and showed diversities among 66 partial (about 900-bp) staphylococcal kat nucleotide sequences (including 17 sequences found in GenBank) representing 26 different species. The topology of this tree showed a distribution of staphylococcal species similar, but not identical, to those reported previously based on 16S rRNA, hsp60, sodA, rpoB, tuf, and gap genes. The kat gene sequences were less conserved than those of 16S rRNA, rpoB, hsp60, and tuf genes and slightly more conserved than those of the gap gene. Therefore, kat gene sequence analysis may provide an additional marker for inferring phylogenetic relationships of staphylococci. Moreover, the discrete nucleotide polymorphism revealed in this gene could be exploited for rapid, low-cost identification of staphylococcal species through PCR-restriction fragment length polymorphism (RFLP) analysis. In this study, a PCR-RFLP assay performed by using only the TaqI restriction enzyme was successfully developed for rapid unequivocal identification/differentiation, at species and subspecies levels, of coagulase-positive staphylococci (CPS). The assay was validated by testing the DNA from 100 staphylococcal strains, including reference and wild CPS strains isolated from different environments. This reliable, rapid, and low-cost approach (requiring about 6 h from DNA isolation to the achievement of results and <5 Euros for each strain tested) allowed unambiguous identification of all the strains assayed, including the newly described S. delphini and S. pseudintermedius CPS species.

Associations between enterotoxin gene cluster types egc1, egc2 and egc3, agr types, enterotoxin and enterotoxin-like gene profiles, and molecular typing characteristics of human nasal carriage and animal isolates of Staphylococcus aureus

Twenty genes encoding enterotoxin and enterotoxin-like proteins have been described in Staphylococcus aureus strains. Five of these occur commonly in the enterotoxin gene cluster (egc: selo, selm, sei, seln and seg). In the sei-seln intergenic region, two pseudogenes, psient1 and psient2, can be present or an additional gene designated selu or a variant selu(v). Whilst frequencies of loci bearing pseudogenes (egc1) or the selu gene (egc2) have been reported, the distinction between selu-bearing and selu(v)-bearing (egc3) loci has rarely been made. A PCR-RFLP procedure involving cleavage of the sei-seln intergenic region by restriction endonuclease BbvI or TseI was developed that allowed differentiation of selu(+) and selu(v)(+) loci. In addition, PCR primers were designed to yield a 203 bp amplimer for sequencing of a selu or selu(v) intragenic region, which encompassed ten signature nucleotide differences. A total of 43 egc(+) human nasal isolates and 53 egc(+) bovine, ovine, caprine, leporine and gallinaceous isolates were egc typed and agr typed. None of the animal isolates was of agr type III. A total of 12 out of 17 egc3(+) human nasal isolates were of agr type III, the other 5 being agr type I. On the basis of representative multilocus sequence typing, agr type III/egc3(+) strains belonged to CC30. Human nasal isolates bearing an egc1 locus were distributed evenly across agr types I, II and III. Only two nasal isolates had an egc2 locus. All 14 agr type IV isolates, only 1 of which was of human origin, possessed an egc2 locus. The agr IV nasal isolate was fusidic acid sensitive and was found to be ST123 (CC121). There were strong associations between bovine, leporine and gallinaceous S. aureus clonal types and egc locus types. The PCR-RFLP procedure was used to screen an additional 45 S. aureus isolates from dogs, cats, rats, pigs and horses for egc locus types. Of these, 33 were egc(-). Six equine isolates were selu(+). One canine and three porcine isolates possessed pseudogenes psient1 and psient2. One porcine and one canine isolate each had the selu(v) gene. Putative relationships between disease-causing propensity and egc type need (re-)evaluation.

Diversity and enterotoxigenicity of Staphylococcus spp. associated with domiati cheese

A total of 87 samples of fresh and stored Domiati cheese (an Egyptian soft cheese) were examined for the presence of Staphylococcus spp. Fifteen Staphylococcus isolates identified as S. aureus (2 isolates), S. xylosus (4), S. caprae (4), and S. chromogenes (5) were recovered from 15 cheese samples. The S. aureus isolates were resistant to penicillin G and ampicillin, and one isolate was also resistant to tetracycline. S. aureus isolates harbored classical staphylococcal enterotoxin (SE) genes (sea and seb) and recently characterized SE-like genes (selg, seli, selm, and selo). One S. aureus isolate contained a single SE gene (sea), whereas another isolate contained five SE genes (seb, selg, seli, selm, and selo). These results suggest that Domiati cheese is a source for various Staphylococcus species, including S. aureus strains that could be enterotoxigenic.

Development and validation of microarray-based assay for epidemiological study of MRSA

We have developed a microarray-based assay for the genotyping of Staphylococcus aureus strains. A DNA microarray consisting of 221 genes with 390 oligonucleotide probes was designed to identify characteristic genes or gene alleles of S. aureus. The 221 genes were chosen on the basis of the following criteria: (i) genes used as control for the microarray system, (ii) virulence genes, (iii) resistance genes and their regulators, and (iv) genes constituting genomic islands, e.g., SCCmec. The microarray system was established by determining the method to prepare targets by random-primer labeling with chromosomal DNA and the conditions for hybridization. We verified the system by using DNAs of seven strains, the genome of which has been fully sequenced. Furthermore, the presence of 32 genes and the types of SCCmec elements and coagulase genes carried by another 27 strains were examined and compared with the results of PCR. As a result, the presence or absence of 182 genes out of the 221 genes was verified. Our data showed the usefulness of the oligonucleotide microarray based assay in identifying important marker sets, such as toxin genes, resistance genes, SCCmec elements, and coagulase genes, for the molecular epidemiology of S. aureus.

Pulsed-field gel electrophoresis of Staphylococcus aureus isolates from atopic patients revealing presence of similar strains in isolates from children and their parents

Skin colonization with Staphylococcus aureus is often associated with atopic dermatitis, and staphylococcal enterotoxins have been implicated in the etiology of atopic disease. In this study, the colonization of patients with atopic dermatitis and their parents was investigated in order to evaluate the possibility of intrafamiliar transmission. S. aureus strains were isolated from 30 of 45 patients (66%). In 19 of 29 families (65%), at least one parent carried S. aureus, and the overall colonization rate of the parents was 48%. All strains were typed by pulsed-field gel electrophoresis (PFGE), and the presence of enterotoxin genes in the strains was assayed by multiplex PCR. A high percentage (84%) of the isolates present on the children and on at least one of their parents displayed identical PFGE and enterotoxin patterns as well as identical antibiotic resistance profiles, indicating intrafamiliar transmission. Forty-five percent of the strains did not carry any enterotoxin gene. The most frequently found enterotoxin genes were seg and sei, which were present in 36% of the strains, and seb, which was found in 24% of the strains. The other toxin genes occurred only in low frequencies. Most strains were resistant to penicillin (82%), and 15% showed resistance to more than one antibiotic. Intermediately-vancomycin-resistant S. aureus or methicillin-resistant S. aureus strains were not detected. In conclusion, this study indicates that the colonization rate of parents of atopic children is rather high and may increase the risk of recolonization of the child.

Understanding the physiology and adaptation of staphylococci: A post-genomic approach

Staphylococcus aureus as well as coagulase-negative staphylococci are medically highly important pathogens characterized by an increasing resistance rate toward many antibiotics. Although normally being skin and mucosa commensals, some staphylococcal species and strains have the capacity to cause a wide range of infectious diseases. Many of these infections affect immunocompromised patients in hospitals. However, community-acquired staphylococcal infections due to resistant strains are also currently on the rise. In the light of this development, there is an urgent need for novel anti-staphylococcal therapeutic and prevention strategies for which a better understanding of the physiology of these bacteria is an essential prerequisite. Within the past years, staphylococci have been in the focus of genomic research, resulting in the determination and publication of a range of full-genome sequences of different staphylococcal species and strains which provided the basis for the design and application of DNA microarrays and other genomic tools. Here we summarize the results of the project group 'Staphylococci' within the research network 'Pathogenomics' giving new insights into the genome structure, molecular epidemiology, physiology, and genetic adaptation of both S. aureus and coagulase-negative staphylococci.

Coupling immunomagnetic separation on magnetic beads with matrix-assisted laser desorption ionization-time of flight mass spectrometry for detection of staphylococcal enterotoxin B

The growing importance of mass spectrometry for the identification and characterization of bacterial protein toxins is a consequence of the improved sensitivity and specificity of mass spectrometry-based techniques, especially when these techniques are combined with affinity methods. Here we describe a novel method based on the use of immunoaffinity capture and matrix-assisted laser desorption ionization-time of flight mass spectrometry for selective purification and detection of staphylococcal enterotoxin B (SEB). SEB is a potent bacterial protein toxin responsible for food poisoning, as well as a potential biological warfare agent. Unambiguous detection of SEB at low-nanogram levels in complex matrices is thus an important objective. In this work, an affinity molecular probe was prepared by immobilizing anti-SEB antibody on the surface of para-toluene-sulfonyl-functionalized monodisperse magnetic particles and used to selectively isolate SEB. Immobilization and affinity capture procedures were optimized to maximize the density of anti-SEB immunoglobulin G and the amount of captured SEB, respectively, on the surface of magnetic beads. SEB could be detected directly "on beads" by placing the molecular probe on the matrix-assisted laser desorption ionization target plate or, alternatively, "off beads" after its acidic elution. Application of this method to complex biological matrices was demonstrated by selective detection of SEB present in different matrices, such as cultivation media of Staphylococcus aureus strains and raw milk samples.

Rapid differentiation of Staphylococcus aureus isolates harbouring egc loci with pseudogenes psient1 and psient2 and the selu or seluv gene using PCR-RFLP

The egc locus of Staphylococus aureus harbours two enterotoxin genes (seg and sei) and three enterotoxin-like genes (selm, seln and selo). Between the sei and seln genes are located two pseudogenes, psient1 and psient2, or the selu or seluv gene. While these two alternative sei-seln intergenic regions can be distinguished by PCR, to date, DNA sequencing has been the only confirmatory option because of the very high degree of sequence similarity between egc loci bearing the pseudogenes and the selu or seluv gene. In silico restriction enzyme digestion of genomic regions encompassing the egc locus from the 3' end of the sei gene through the 5' first quarter of the seln gene allowed pseudogene- and selu- or seluv-bearing egc loci to be distinguished by PCR-RFLP. Experimental application of these findings demonstrated that endonuclease HindIII cleaved PCR amplimers bearing pseudogenes but not those with a selu or seluv gene, while selu- or seluv-bearing amplimers were susceptible to cleavage by endonuclease HphI, but not by endonuclease HindIII. The restriction enzyme BccI cleaved selu- or seluv-harbouring amplimers at a unique restriction site created by their signature 15 bp insertion compared with pseudogene-bearing amplimers, thereby allowing distinction of these egc loci. PCR-RFLP analysis using these restriction enzymes provides a rapid, easy to interpret alternative to DNA sequencing for verification of PCR findings on the nature of an egc locus type, and can also be used for the primary identification of the intergenic sei-seln egc locus type.

Necrotizing fasciitis due to a methicillin-sensitive Staphylococcus aureus isolate harboring an enterotoxin gene cluster

Benign papular eruption on the left leg of a 72-year-old diabetic man developed into rapidly spreading necrotizing fasciitis despite antimicrobial therapy and surgical debridements. This led to eventual amputation to control the infection. The etiological agent was a Staphylococcus aureus isolate harboring the enterotoxin gene cluster seg, sei, sem, sen, and seo but lacked all common toxin genes, including Panton-Valentine leukocidin.