Virulence determinants in community and hospital meticillin-resistant Staphylococcus aureus

Puerperal mastitis caused by limited community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) clones

Objective

To outline the epidemiology of puerperal mastitis caused by methicillin-resistant Staphylococcus aureus (MRSA) and evaluate the effect of an infection control bundle on its incidence.

Methods

A surge in MRSA puerperal mastitis was noted in a community hospital in September 2009. MRSA samples from mastitis cases and the environment underwent typing using multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec), gene encoding surface protein A (spa), accessory gene regulator (agr), and pulsed-field gel electrophoresis (PFGE). The phenotypic characteristics, including superantigen toxin profiles, gene encoding Panton-Valentine leucocidin (pvl), and minimal inhibitory concentration (MIC) against vancomycin, were ascertained. Subsequently, an infection control bundle emphasizing contact precautions was introduced, and mastitis incidence rates pre- and post-intervention were compared.

Results

The majority of cases occurred within 6 weeks post-delivery in first-time mothers. Of the 42 S. aureus isolates (27 from mastitis and 15 from colonized staff and environmental sources), 25 (92.6%) clinical and 3 (20%) colonized MRSA were identified as ST59-SCCmecVT-spa t437-agr group I with a vancomycin MIC of 1 mg/L, pvl-positive, and predominantly with a consistent toxin profile (seb-selk-selr). PFGE revealed 13 patterns; pulsotype B exhibited clonal relatedness between two clinical and three colonized MRSA samples. Post-intervention, the incidence of both mastitis and MRSA mastitis notably decreased from 13.01 to 1.78 and from 3.70 to 0.99 episodes per 100 deliveries, respectively.

Conclusion

Distinct community-associated MRSA (CA-MRSA) clones were detected among puerperal mastitis patients and colonized staff. The outbreak was effectively controlled following the implementation of a targeted infection control bundle.

Genomic Analysis of a Community-Acquired Methicillin-Resistant Staphylococcus aureus Sequence Type 1 Associated with Caprine Mastitis

This study aimed to investigate the genomic and epidemiological features of a methicillin-resistant Staphylococcus aureus sequence type 1 (MRSA ST1) strain associated with caprine subclinical mastitis. An S. aureus strain was isolated from goat's milk with subclinical mastitis in Paraiba, Northeastern Brazil, by means of aseptic procedures and tested for antimicrobial susceptibility using the disk-diffusion method. Whole genome sequencing was performed using the Illumina MiSeq platform. After genome assembly and annotation, in silico analyses, including multilocus sequence typing (MLST), antimicrobial resistance and stress-response genes, virulence factors, and plasmids detection were performed. A comparative SNP-based phylogenetic analysis was performed using publicly available MRSA genomes. The strain showed phenotypic resistance to cefoxitin, penicillin, and tetracycline and was identified as sequence type 1 (ST1) and spa type 128 (t128). It harbored the SCCmec type IVa (2B), as well as the lukF-PV and lukS-PV genes. The strain was phylogenetically related to six community-acquired MRSA isolates (CA-MRSA) strains associated with human clinical disease in North America, Europe, and Australia. This is the first report of a CA-MRSA strain associated with milk in the Americas. The structural and epidemiologic features reported in the MRSA ST1 carrying a mecA-SCCmec type IVa suggest highly complex mechanisms of horizontal gene transfer in MRSA. The SNP-based phylogenetic analysis suggests a zooanthroponotic transmission, i.e., a strain of human origin.

The Cell Wall, Cell Membrane and Virulence Factors of Staphylococcus aureus and Their Role in Antibiotic Resistance

Antibiotic resistant strains of bacteria are a serious threat to human health. With increasing antibiotic resistance in common human pathogens, fewer antibiotics remain effective against infectious diseases. Staphylococcus aureus is a pathogenic bacterium of particular concern to human health as it has developed resistance to many of the currently used antibiotics leaving very few remaining as effective treatment. Alternatives to conventional antibiotics are needed for treating resistant bacterial infections. A deeper understanding of the cellular characteristics of resistant bacteria beyond well characterized resistance mechanisms can allow for increased ability to properly treat them and to potentially identify targetable changes. This review looks at antibiotic resistance in S aureus in relation to its cellular components, the cell wall, cell membrane and virulence factors. Methicillin resistant S aureus bacteria are resistant to most antibiotics and some strains have even developed resistance to the last resort antibiotics vancomycin and daptomycin. Modifications in cell wall peptidoglycan and teichoic acids are noted in antibiotic resistant bacteria. Alterations in cell membrane lipids affect susceptibility to antibiotics through surface charge, permeability, fluidity, and stability of the bacterial membrane. Virulence factors such as adhesins, toxins and immunomodulators serve versatile pathogenic functions in S aureus. New antimicrobial strategies can target cell membrane lipids and virulence factors including anti-virulence treatment as an adjuvant to traditional antibiotic therapy.

Clinical characteristics and factors related to infection with SCCmec type II and IV Methicillin-resistant Staphylococcus aureus in a Japanese secondary care facility: a single-center retrospective study

OBJECTIVES

Differences in virulence genes, including psm-mec, which is a phenol-soluble modulin-mec (PSM-mec) encoding gene, of predominant staphylococcal cassette chromosome mec (SCCmec) types II and IV Methicillin-resistant Staphylococcus aureus (MRSA) may contribute to the virulence and clinical features of MRSA in Japan. We aimed to clarify the clinical characteristics and risk factors of infection among SCCmec types II and IV MRSA isolates from a Japanese secondary acute care hospital.

METHODS

We analysed 58 SCCmec type II and 83 SCCmec type IV MRSA isolates collected from blood, central venous catheter tips, deep or superficial tissues, and sputum.

RESULTS

SCCmec type II MRSA risk factors for progression to infection were seb, enterotoxin gene cluster, psm-mec mutation, and vancomycin minimum inhibitory concentrations (MIC) of 1 or 2 mg/L as virulence factors (adjusted odds ratio [aOR] = 11.8; 95% confidence interval [CI]: 2.49-77.7; P = 0.004); solid tumour was a host factor (aOR = 25.9; 95% CI: 3.66-300; P = 0.003). SCCmec type IV MRSA risk factors were sea, cna, and vancomycin MIC of 1 or 2 mg/L as virulence factors (aOR = 3.14; 95% CI: 1.06-10.6; P = 0.049) and intravascular indwelling catheter as host factors (aOR = 3.78; 95% CI: 1.03-14.5; P = 0.045). Compared with SCCmec type II, SCCmec type IV MRSA resulted in more frequent bloodstream infections and higher Sequential Organ Failure Assessment scores.

CONCLUSION

We found that factors related to virulence genes and bacteriological and host characteristics are associated with SCCmec types II and IV MRSA infection and severity. These risk factors may be useful criteria for designing infection control programs.

Whole-genome analysis uncovers loss of blaZ associated with carriage isolates belonging to methicillin-resistant Staphylococcus aureus (MRSA) clone ST5-VI in Cape Verde

•

One of the first whole genome analyses of Staphylococcus aureus carriage isolates in an African country.

•

Genome data allowed to place S. aureus isolates from Cape Verde in a phylogenetic context.

•

Loss of blaZ-carrying plasmids and transposons is not rare, which is also evident in other international MRSA isolates.

•

Steady increase in antimicrobial drug resistance in Cape Verde.

•

Data provide genomic information for the design of intervention measures to decrease antimicrobial resistance.

Objectives

Surveillance studies for Staphylococcus aureus carriage are a primary tool to survey the prevalence of methicillin-resistant S. aureus (MRSA) in the general population, patients and healthcare workers. We have previously reported S. aureus carriage in various African countries, including Cape Verde.

Methods

Whole-genome sequences of 106 S. aureus isolates from Cape Verde were determined.

Results

Staphylococcus aureus carriage isolates in Cape Verde show high genetic variability, with the detection of 27 sequence types (STs) and three primary genetic clusters associated with ST152, ST15 and ST5. One transmission event with less than eight core-genome single nucleotide polymorphisms (cgSNP) differences was detected among the ST5-VI MRSA lineage. Genetic analysis confirmed the phenotypic resistance and allowed the identification of six independent events of plasmid or transposon loss associated with the deletion of blaZ in nine isolates. In the four ST5 MRSA isolates, loss of the blaZ plasmid coincided with the acquisition of SCCmec type VI and an unusual penicillin phenotype with a minimum inhibitory concentration (MIC) at the breakpoint, indicating an adaptation trend in this endemic lineage. Similar events of blaZ plasmid loss, with concomitant acquisition SCCmec elements, were detected among ST5 isolates from different geographical origins.

Conclusion

Overall, the genome data allowed to place isolates in a phylogenetic context and to identify different blaZ gene deletions associated with plasmid or transposon loss. Genomic analysis unveiled adaptation and evolution trends, namely among emerging MRSA lineages in the country, which deserve additional consideration in the design of future infection control protocols.

Nasopharyngeal Carriage of Methicillin-Resistant Staphylococcus aureus (MRSA) among Sickle Cell Disease (SCD) Children in the Pneumococcal Conjugate Vaccine Era

The aim of this cross-sectional study was to investigate Staphylococcus aureus nasopharyngeal carriage epidemiology in relation to other nasopharyngeal bacterial colonizers among sickle cell disease (SCD) children about five years into pneumococcal conjugate vaccine 13 (PCV-13) introduction in Ghana. The study involved bacteriological culture of nasopharyngeal swabs obtained from 202 SCD children recruited from the Princess Marie Louise Children's Hospital. S. aureus isolates were identified using standard methods and subjected to antimicrobial susceptibility testing using the Kirby-Bauer disc diffusion method. Cefoxitin-resistant S. aureus isolates were screened for carriage of the mecA, pvl, and tsst-1 genes using multiplex polymerase chain reaction. The carriage prevalence of S. aureus was 57.9% (n = 117), and that of methicillin-resistant S. aureus (MRSA) was 3.5% (n = 7). Carriage of the mecA, pvl, and tsst-1 genes were respectively demonstrated in 20.0% (n = 7), 85.7% (n = 30), and 11.4% (n = 4) of the cefoxitin-resistant S. aureus isolates. PCV-13 vaccination (OR = 0.356, p = 0.004) and colonization with coagulase-negative staphylococci (CoNS) (OR = 0.044, p < 0.0001) each protected against S. aureus carriage. However, none of these and other features of the participants emerged as a determinant of MRSA carriage. The following antimicrobial resistance rates were observed in MRSA compared to methicillin-sensitive S. aureus: clindamycin (28.6% vs. 4.3%), erythromycin (42.9% vs. 19.1%), tetracycline (100% vs. 42.6%), teicoplanin (14.3% vs. 2.6%), penicillin (100% vs. 99.1%), amoxiclav (28.6% vs. 3.5%), linezolid (14.3% vs. 0.0%), ciprofloxacin (42.9% vs. 13.9%), and gentamicin (42.9% vs. 13.0%). The proportion of S. aureus isolates that were multidrug resistant was 37.7% (n = 46). We conclude that S. aureus was the predominant colonizer of the nasopharynx of the SCD children, warranting the continuous monitoring of this risk group for invasive S. aureus infections.

The incidence of toxic shock syndrome due to nosocomial methicillin-resistant Staphylococcus aureus infection in burn patients: A four-year retrospective cohort study

Among adult and pediatric patients, concern is growing in regard to toxic shock syndrome (TSS) resulting from methicillin-resistant Staphylococcus aureus (MRSA) nosocomial infection. We investigated the incidence and characteristics of this form of TSS in patients with burn injury who were admitted to our burn care units from January 2008 to December 2011. Of the 244 patients with nosocomial MRSA infection admitted during the study period, TSS occurred in 20 (8.2%) patients whose average age was 42.9 years, average total burn surface area (TBSA) was 31.7%, and average day of TSS appearance was 9.5 days after injury. There were no particular characteristics associated with age, TBSA or day of TSS appearance in these patients. All but 1 patient recovered from TSS within an average of 9.4 days. The incidence of TSS due to nosocomial MRSA infection in these burn patients was higher than expected. TSS due to nosocomial MRSA infection should be considered in burn care.

Phenotypic and genotypic characterization of clinical Staphylococcus aureus isolates from Kenya

BACKGROUND

The increase and spread of virulent-outbreak associated, methicillin and vancomycin resistant (MRSA/VRSA) Staphylococcus aureus require a better understanding of the resistance and virulence patterns of circulating and emerging strains globally. This study sought to establish the resistance phenotype, and strains of 32 non-duplicate clinical MRSA and MSSA S. aureus isolates from four Kenyan hospitals, identify their resistance and virulence genes and determine the genetic relationships of MRSA with global strains.

METHODS

Antimicrobial susceptibility profiles were determined on a Vitek 2, genomic DNA sequenced on an Illumina Miseq and isolates typed in-silico. Resistance and virulence genes were identified using ARIBA and phylogenies generated using RAxML.

RESULTS

The MRSA isolates were 100% susceptible to vancomycin, teicoplanin, linezolid, and tigecycline. Nine distinct CC, 12 ST and 15 spa types including the novel t17826 and STs (4705, 4707) were identified with CC8 and CC152 predominating. MRSA isolates distributed across 3 CCs; CC5-ST39 (1), CC8 - ST241 (4), a novel CC8-ST4705 (1), ST8 (1) and CC152 (1). There was > 90% phenotype-genotype concordance with key resistance genes identified only among MRSA isolates: gyrA, rpoB, and parC mutations, mecA, ant (4')-lb, aph (3')-IIIa, ermA, sat-4, fusA, mphC and msrA. Kenyan MRSA isolates were genetically diverse and most closely related to Tanzanian and UK isolates. There was a significant correlation between map, hlgA, selk, selq and cap8d virulence genes and severe infections.

CONCLUSION

The findings showed a heterogeneous S. aureus population with novel strain types. Though limited by the low number of isolates, this study begins to fill gaps and expand our knowledge of S. aureus epidemiology while uncovering interesting patterns of distribution of strain types which should be further explored. Although last-line treatments are still effective, the potential for outbreaks of both virulent and resistant strains remain, requiring sustained surveillance of S. aureus populations.

High Rate of Ceftobiprole Resistance among Clinical Methicillin-Resistant Staphylococcus aureus Isolates from a Hospital in Central Italy

Ceftobiprole is a fifth-generation cephalosporin with activity against methicillin-resistant Staphylococcus aureus (MRSA). One-year surveillance at the Regional Hospital of Ancona (Italy) disclosed a 12% ceftobiprole resistance rate (12/102 isolates; MIC, ≥4 mg/liter). Epidemiological characterization demonstrated that the resistant isolates all belonged to different clones. Penicillin-binding protein (PBP) analysis showed substitutions in all PBPs and a novel insertion in PBP2a. The mecB and mecC genes were not detected. Ceftobiprole susceptibility screening is essential to avoid therapeutic failure and the spread of ceftobiprole-resistant strains.

Post-resection complications: abscesses, empyemas, bronchopleural fistulas

The role of thoracic surgeons in the management of pulmonary infection has evolved over time as the medical treatments have improved. We herein review historical and current management for surgically-treated pulmonary infections-lung abscesses, empyemas, and bronchopleural fistulas. In particular, we review when the surgeons need to be involved for infectious cases, our algorithm/approach to empyemas, and summary of post-operative bronchopleural fistula in tuberculosis cases.

Frequent MRSA nasal colonization among hospitalized children and their parents in Angola and São Tomé and Príncipe

BACKGROUND

The prevalence of nosocomial meticillin-resistant Staphylococcus aureus (MRSA) was previously estimated as 23% in a paediatric hospital in Luanda, Angola and 18% in a general hospital in São Tomé and Príncipe.

AIM

To evaluate the prevalence of S. aureus/MRSA colonization among hospitalized children and their parents at two hospitals in Angola and São Tomé and Príncipe.

METHODS

In 2017, 127 hospitalized children and 129 of their parents had nasal swabs for S. aureus/MRSA carriage in the two countries. The isolates were tested for the presence of the mecA and Panton-Valentine leukocidin (PVL) genes, and characterized by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing and SCCmec typing.

FINDINGS

Twenty of 127 children (15.7%) and 13 of 129 parents (10.1%) were MRSA nasal carriers. Three lineages comprised 88% of the MRSA isolates: (i) PFGE A-ST5-SCCmec IVa (N=15; 45%), associated with spa type t105, recovered in Angola alone; (ii) PFGE N-ST8-IV/V (N=7; 21%), associated with spa types t008/t121, recovered in São Tomé and Príncipe alone; and (iii) PFGE B-ST88-IVa (N=7; 21%), associated with spa types t325/t786, present in both countries. Fifteen child/guardian pairs were colonized with identical MRSA (N=8) or meticillin-susceptible S. aureus (N=7) strains. PVL was detected in 25% of isolates, including two MRSA (ST30-V and ST8-IVa).

CONCLUSION

Hospitalized children and their parents are important reservoirs of MRSA. Infection control measures should focus on parents in order to minimize the spread of MRSA to the community.

In Vitro generation of Panton-Valentine leukocidin (PVL) in clinical Methicillin-Resistant Staphylococcus aureus (MRSA) and its correlation with PVL variant, clonal complex, infection type

The amount of Panton-Valentine leukocidin (PVL) is diverse among Staphylococcus aureus isolates from different geographical regions, and its significance in some infections is disputed. However, data concerning this information in China are limited. Fifty-one lukSF-PV⁺ methicillin-resistant Staphylococcus aureus (MRSA) isolates gathered from varying infections were used for PVL production using enzyme-linked immunosorbent assay, and the quantity was analyzed in correlation with PVL isoform, genetic background of the isolate, and disease category. All isolates generated PVL with a range of 0.43–360.87 μg/mL, of which 56.9% isolates (29/51) generated 51–200 μg/mL of PVL; 11.8% (6/51) yielded PVL more than 200 μg/mL, and the rest (31.4%, 16/51) produced PVL of ≤50 μg/mL. The amount of PVL was not related to its variant and infection type, although isolates from skin and soft tissue infection had relatively high mean and median. Clonal complex (CC) 22 isolates might be the producer of relatively high concentrations of PVL; however, the difference among CCs was not analyzed due to a small number of CC isolates. The relevance of PVL production with the infection type, toxin isoform, and genetic characteristic of isolates may vary by clone type and also needs to be further evaluated using a large sample size and best concentration on in vivo environment.

Genetic assessment of Staphylococcus aureus in an underreported locality: Ambulatory care clinic

BACKGROUND

Staphylococcus aureus has strong association with anthropogenic environments. This association has not been well supported by use of genetic tools. The aim of this study was to phylogenetically relate numerous isolates from three environments - NCBI samples from hospitals, a community, and a previously unexplored healthcare environment: an ambulatory care clinic (ACC).

METHODS

This study incorporated hospital samples from NCBI, a community database from the University of Central Florida (UCF), and newly added samples taken from employees of an ambulatory care clinic located at UCF. Samples were collected from nasal swabs of employees, and positive samples were cultured, extracted, and sequenced at seven MLST loci and one virulence locus (spa). MLST sequences were used in eBURST and TCS population structure analyses and all sequences were incorporated into a phylogenetic reconstruction of relationships.

RESULTS

A total of 185 samples were incorporated in this study (15 NCBI sequences from hospital infections, 29 from the ACC, and 141 from the community). In both phylogenetic and population genetics analyses, samples proved to be panmixic, with samples not segregating monophyletically based on sample origin.

CONCLUSION

Samples isolated from ambulatory care clinics are not significantly differentiated from either community or hospital samples at the representative loci chosen. These results strengthen previous conclusions that S. aureus may exhibit high genetic similarity across anthropogenic environments.

Increased Age-Dependent Risk of Death Associated With lukF-PV-Positive Staphylococcus aureus Bacteremia

Background.

Panton-Valentine leucocidin is a Staphylococcus aureus virulence factor encoded by lukF-PV and lukS-PV that is infrequent in S aureus bacteremia (SAB), and, therefore, little is known about risk factors and outcome of lukF-PV/lukS-PV-positive SAB.

Methods.

This report is a register-based nationwide observational cohort study. lukF-PV was detected by polymerase chain reaction. Factors associated with the presence of lukF-PV were assessed by logistic regression analysis. Adjusted 30-day hazard ratios of mortality associated with lukF-PV status were computed by Cox proportional hazards regression analysis.

Results.

Of 9490 SAB cases, 129 were lukF-PV-positive (1.4%), representing 14 different clonal complexes. lukF-PV was associated with younger age, absence of comorbidity, and methicillin-resistant S aureus. In unadjusted analysis, mortality associated with lukF-PV-positive SAB was comparable to SAB. However, lukF-PV-positive SAB nonsurvivors were significantly older and had more comorbidity. Consequently, by adjusted analysis, the risk of 30-day mortality was increased by 70% for lukF-PV-positive SAB compared with SAB (hazard ratio, 1.70; 95% confidence interval, 1.20–2.42; P = .003).

Conclusions.

lukF-PV-positive SAB is rare in Denmark but associated with a significantly increased risk of mortality. Although the risk of lukF-PV-positive SAB was highest in the younger age groups, >80% of deaths associated with lukF-PV-positive SAB occurred in individuals older than 55 years.

Molecular epidemiology and characteristic of virulence gene of community-acquired and hospital-acquired methicillin-resistant Staphylococcus aureus isolates in Sun Yat-sen Memorial hospital, Guangzhou, Southern China

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of both hospital and community infections globally. It’s important to illuminate the differences between community-acquired MRSA (CA-MRSA) and hospital-acquired MRSA (HA-MRSA), but there have been confusions on the definition, especially for the MRSA isolates identified within 48 h of admission. This study aimed to determine the molecular characteristics and virulence genes profile of CA and HA-MRSA isolates identified less than 48 h after hospital admission in our region.

Methods

A total 62 MRSA isolates identified within 48 h after admission and the clinical data were collected. Antimicrobial susceptibility test (AST) of collected isolates were performed according to the guidelines of Clinical and Laboratory Standards Institute (CLSI) 2015, and staphylococcal cassette chromosome mec (SCCmec) typing, multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and virulence gene profiling were performed to explore the molecular diversity.

Results

SCCmec III and sequence type (ST) 239 were the most prevalent SCCmec type and ST in both CA and HA-MRSA groups. HA-MRSA group had higher prevalence of SCCmec III (87.2 %) and ST239 (79.5 %) compared with CA-MRSA (60.9 and 43.4 %, both P < 0.001), while the frequency of SCCmec IV (26.0 %) and ST59 (21.7 %) were higher in CA-MRSA than its counterpart (P < 0.001 and P = 0.003). MRSA-ST239-III was the predominant type in this study (61.3 %, 38/62), especially in HA-MRSA group (76.9 %, 30/39). However, CA-MRSA strains exhibited more diversity in genotypes in this study. Meanwhile, CA-MRSA tended to have lower resistant percentage to non-β-lactams antibiotics but more virulence genes carriage, especially the staphylococcal enterotoxins (SE) genes. Notably, seb gene was only detected in CA-MRSA isolates (52.2 %), likely a significant marker for CA-MRSA isolates. Panton-Valentine leukocidin gene (PVL) was highly detected in both groups, while appeared no significantly different between CA-MRSA (47.8 %) and HA-MRSA (43.6 %).

Conclusions

Our findings support a difference in the molecular epidemiology and virulence genes profile of CA-MRSA and HA-MRSA. Furthermore, this study indicates a possible transmission from HA-MRSA to CA-MRSA, which may cause the overlap of the definition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1684-y) contains supplementary material, which is available to authorized users.

Distribution of tsst-1 and mecA Genes in Staphylococcus aureus Isolated From Clinical Specimens

Background

Staphylococcus aureus is a harmful pathogen known to express numerous virulence factors and cause severe infections. High levels of methicillin-resistant Staphylococcus aureus (MRSA) strains are one of the important healthcare problems because of the inefficient treatment of these infections.

Objectives

The purpose of the current study is to evaluate the incidence of the toxic shock syndrome toxin (tsst-1) gene and its association with the prevalence of the mecA gene and drug resistance.

Materials and Methods

The presence of the tsst-1 and mecA genes was investigated by polymerase chain reaction (PCR) among S. aureus isolated from 197 clinical samples. In addition, resistance tests to 12 antibiotics were carried out by the disc diffusion method.

Results

Among the 197 isolates, 134 (68%) contained the tsst-1 genes and 172 (87.3%) contained the mecA genes. The prevalence of both genes was higher among male cases and samples purified from wounds and blood. We found no significant correlation between the presences of the two mentioned genes within isolates. The highest resistance we observed among our samples was to penicillin. None of isolates was resistant to vancomycin or linezolid. A significant correlation was observed between the presence of the mecA gene and resistance to oxacillin, gentamicin, kanamycin, erythromycin, tetracycline, cotrimoxazole, clindamycin, cephazolin and the multi-drug resistant property, which is resistance to more than three antibiotics (P < 0.05).

Conclusions

Our outcomes showed elevated incidences of tsst-1 positive and MRSA strains with higher rates of antibiotic resistance. The conflict between our findings and other records may be due to differences in geographic regions.

Low Level of TSST-1 Antibody in Burn Patients With Toxic Shock Syndrome Caused by Methicillin-Resistant Staphylococcus aureus

Toxic shock syndrome (TSS) caused by methicillin-resistant Staphylococcus aureus (MRSA) nosocomial infection is a growing concern in both adult and pediatric patients. The reason why TSS appears in only some patients with MRSA infection remains unclear. In this study, we analyzed serial TSS toxin-1 (TSST-1) antibody in patients with burn injury to investigate the mechanisms of TSS caused by MRSA nosocomial infection. This study comprised of patients with burn injury in our burn care unit from September, 2010 to August, 2011. Serum samples were collected serially on admission, at 48 to 72 hours after injury, on the day MRSA infection appeared, and on the day MRSA infection resolved. TSST-1 antibody was measured by enzyme-linked immunosorbent assay (ELISA). TSS was diagnosed according to the criteria of the Centers for Disease Control. Serial serum samples were collected from 24 patients and nosocomial MRSA infection was detected in 12 patients. In these 12 patients, TSS occurred in five patients (TSS+ group) but did not occur in the other seven patients (TSS- group). TSST-1 antibody level was significantly lower in the TSS+ group than TSS- group on admission and on the day MRSA infection appeared. All patients in the TSS+ group received intravenous immune globulin when TSS was diagnosed, and no patients died of TSS. Patients suffering from TSS had a lower level of TSST-1 antibody than patients not suffering from TSS. Testing for TSST-1 antibody in the clinical setting might help to predict and prevent the appearance of TSS caused by nosocomial MRSA infection.

Antibodies to S. aureus LukS-PV Attenuated Subunit Vaccine Neutralize a Broad Spectrum of Canonical and Non-Canonical Bicomponent Leukotoxin Pairs

S. aureus vaccine development has proven particularly difficult. The conventional approach to achieve sterile immunity through opsonophagocytic killing has been largely unsuccessful. S. aureus is highly toxigenic and a great body of evidence suggests that a successful future vaccine for this organism should target extracellular toxins which are responsible for host tissue destruction and immunosuppression. Major staphylococcal toxins are alpha toxin (a single subunit hemolysin) along with a group of bicomponent pore-forming toxins (BCPFT), namely Panton-Valentine leukocidin (PVL), gamma hemolysins (HlgCB and AB), LukAB and LukED. In our previous report, an attenuated mutant of LukS-PV (PVL- S subunit) named as “LukS-mut9” elicited high immunogenic response as well as provided a significant protection in a mouse sepsis model. Recent discovery of PVL receptors shows that mice lack receptors for this toxin, thus the reported protection of mice with the PVL vaccine may relate to cross protective responses against other homologous toxins. This manuscript addresses this issue by demonstrating that polyclonal antibody generated by LukS-mut9 can neutralize other canonical and non-canonical leukotoxin pairs. In this report, we also demonstrated that several potent toxins can be created by non-canonical pairing of subunits. Out of 5 pairs of canonical and 8 pairs of non-canonical toxins tested, anti-LukS-mut9 polyclonal antibodies neutralized all except for LukAB. We also studied the potential hemolytic activities of canonical and noncanonical pairs among biocomponent toxins and discovered that a novel non-canonical pair consisting of HlgA and LukD is a highly toxic combination. This pair can lyse RBC from different species including human blood far better than alpha hemolysin. Moreover, to follow-up our last report, we explored the correlation between the levels of pre-existing antibodies to new sets of leukotoxins subunits and clinical outcomes in adult patients with S. aureus bacteremia. We found that there is an inversed correlation between the antibody titer to sepsis for leukotoxins LukS-mut9, LukF-PV, HlgC, LukE and LukAB, suggesting the risk of sepsis was significantly lower in the patients with higher antibody titer against those toxins.

Distribution of toxin genes among different spa types and phage types of animal Staphylococcus aureus

We analyzed distribution of toxin genes (sea-seo, eta, etb, tst, lukS/lukF-PV) among spa types and phage types of 39 Staphylococcus aureus (S. aureus) isolates from healthy and diseased animals. All isolates turned out to be mecA negative (MSSA). Nine spa types were identified: t144 and t723 (dogs), t084 (dogs and pigs), t5447 (cat), t1491 and t008 (pigs), t002, t127 and t3478 (poultry). Seven phage types were detected, enclosed within four phage groups: I (cat), II (dogs), III (pigs) and mixed group (dogs and pigs). Three poultry spa types proved to be non-typeable by phages. Toxin genes were detected in 33 out of the 39 animal isolates. Our analysis revealed that the incidence of some toxin genes in S. aureus is host specific. Canine isolates t144 of phage group II harbored exfoliative toxin gene (eta), and porcine isolates type t1491 representing phage group III showed enterotoxin A gene (sea). The enterotoxin gene cluster (egc1) and enterotoxin gene seh were found in non-typeable isolates from chicken and in one feline isolate type t5447.

The distribution of pathogenic and toxigenic genes among MRSA and MSSA clinical isolates

Staphylococcus aureus (S. aureus) is considered as a notorious nosocomial pathogen among hospitalized patients and community-dwelling subjects. Its increasing morbidity and mortality is believed to be due to antibiotic resistance. However, the data concerning molecular properties of infecting strains are few. In this study, a total of 192 S. aureus strains, including 88 (45.8%) meticillin-sensitive S. aureus (MSSA) and 104 (54.2%) meticillin-resistant S. aureus (MRSA) were recovered from clinical samples. The prevalence of subtypes containing staphylococcal cassette chromosome mec (SSCmec), staphylococcal enterotoxins (SEs), toxic shock syndrome toxin (TSST) and exfoliative toxin was assessed by PCR. Antibiotic susceptibility pattern and vancomycin resistance of each isolate were evaluated by disk diffusion method and micro-dilution method, respectively. 9 (2.3%) strains required MIC > 2 mg/l of vancomycin, which significantly increased among multi drug resistant (MDR), MRSA and SCCmec type III strains (p < 0.05). 171 (89%), 140 (72.91%), 7 (3.6), 78 (48.6%), 5 (2.6%), 151 (78.64%), 129 (67.18%), 178 (92.7%) and 15 (7.8%) of 192 isolates harbored mecA, entA, entB, entC, entD, entE, eta, etb and tsst-1 genes, respectively. 31 (16.14%), 5 (2.6%), 95 (49.48%) and 7 (3.64%) of 192 isolates carried SCCmec type I, II, III and IV, respectively. We found a significantly higher rate of MRSA and resistance to all tested antibiotics, except to penicillin G, kanamycin and linezolide among the SCCmec type III class (p < 0.05). According to our findings, MSSA isolates should be taken as seriously as MRSA strains due to the potential presence of broad spectrum virulence factor genes.

Synthesis and antibacterial evaluation of a novel series of synthetic phenylthiazole compounds against methicillin-resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus infections are a significant global health challenge in part due to the emergence of strains exhibiting resistance to nearly all classes of antibiotics. This underscores the urgent need for the rapid development of novel antimicrobials to circumvent this burgeoning problem. Previously, whole-cell screening of a library of 2,5-disubstituted thiazole compounds revealed a lead compound exhibiting potent antimicrobial activity against MRSA. The present study, conducting a more rigorous analysis of the structure-activity relationship of this compound, reveals a nonpolar, hydrophobic functional group is favored at thiazole-C2 and an ethylidenehydrazine-1-carboximidamide moiety is necessary at C5 for the compound to possess activity against MRSA. Furthermore, the MTS assay confirmed analogs 5, 22d, and 25 exhibited an improved toxicity profile (not toxic up to 40 μg/mL to mammalian cells) over the lead 1. Analysis with human liver microsomes revealed compound 5 was more metabolically stable compared to the lead compound (greater than eight-fold improvement in the half-life in human liver microsomes). Collectively the results presented demonstrate the novel thiazole derivatives synthesized warrant further exploration for potential use as future antimicrobial agents for the treatment of multidrug-resistant S. aureus infections.

Genetic and molecular predictors of high vancomycin MIC in Staphylococcus aureus bacteremia isolates

An elevated vancomycin MIC is associated with poor outcomes in Staphylococcus aureus bacteremia (SAB) and is reported in patients with methicillin-susceptible S. aureus (MSSA) bacteremia in the absence of vancomycin treatment. Here, using DNA microarray and phenotype analysis, we investigated the genetic predictors and accessory gene regulator (agr) function and their relationship with elevated vancomycin MIC using blood culture isolates from a multicenter binational cohort of patients with SAB. Specific clonal complexes were associated with elevated (clonal complex 8 [CC8] [P < 0.001]) or low (CC22 [P < 0.001], CC88 [P < 0.001], and CC188 [P = 0.002]) vancomycin MIC. agr dysfunction (P = 0.014) or agr genotype II (P = 0.043) were also associated with an elevated vancomycin MIC. Specific resistance and virulence genes were also linked to an elevated vancomycin MIC, including blaZ (P = 0.002), sea (P < 0.001), clfA (P < 0.001), splA (P = 0.001), and the arginine catabolic mobile element (ACME) locus (P = 0.02). These data suggest that inherent organism characteristics may explain the link between elevated vancomycin MICs and poor outcomes in patients with SAB, regardless of the antibiotic treatment received. A consideration of clonal specificity should be included in future research when attempting to ascertain treatment effects or clinical outcomes.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Costa Rican children

We collected all Staphylococcus aureus isolates from the National Children's Hospital in Costa Rica to evaluate the prevalence and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA). Of 299 S. aureus isolates, 61% were MRSA. Most MRSA isolates (94.5%) carried SCCmec IV, and 45.6% carried Panton-Valentine leukocidin-encoding genes. The high prevalence of MRSA in this population highlights the need for improvement of antibiotic prescription and infection control measures.

The multifaceted resources and microevolution of the successful human and animal pathogen methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important bacterial pathogens based on its incidence and the severity of its associated infections. In addition, severe MRSA infections can occur in hospitalised patients or healthy individuals from the community. Studies have shown the infiltration of MRSA isolates of community origin into hospitals and variants of hospital-associated MRSA have caused infections in the community. These rapid epidemiological changes represent a challenge for the molecular characterisation of such bacteria as a hospital or community-acquired pathogen. To efficiently control the spread of MRSA, it is important to promptly detect the mecA gene, which is the determinant of methicillin resistance, using a polymerase chain reaction-based test or other rapidly and accurate methods that detect the mecA product penicillin-binding protein (PBP)2a or PBP2'. The recent emergence of MRSA isolates that harbour a mecA allotype, i.e., the mecC gene, infecting animals and humans has raised an additional and significant issue regarding MRSA laboratory detection. Antimicrobial drugs for MRSA therapy are becoming depleted and vancomycin is still the main choice in many cases. In this review, we present an overview of MRSA infections in community and healthcare settings with focus on recent changes in the global epidemiology, with special reference to the MRSA picture in Brazil.

Staphylococcal bicomponent pore-forming toxins: targets for prophylaxis and immunotherapy

Staphylococccus aureus represents one of the most challenging human pathogens as well as a common colonizer of human skin and mucosal surfaces. S. aureus causes a wide range of diseases from skin and soft tissue infection (SSTI) to debilitating and life-threatening conditions such as osteomyelitis, endocarditis, and necrotizing pneumonia. The range of diseases reflects the remarkable diversity of the virulence factors produced by this pathogen, including surface antigens involved in the establishment of infection and a large number of toxins that mediate a vast array of cellular responses. The staphylococcal toxins are generally believed to have evolved to disarm the innate immune system, the first line of defense against this pathogen. This review focuses on recent advances on elucidating the biological functions of S. aureus bicomponent pore-forming toxins (BCPFTs) and their utility as targets for preventive and therapeutic intervention. These toxins are cytolytic to a variety of immune cells, primarily neutrophils, as well as cells with a critical barrier function. The lytic activity of BCPFTs towards immune cells implies a critical role in immune evasion, and a number of epidemiological studies and animal experiments relate these toxins to clinical disease, particularly SSTI and necrotizing pneumonia. Antibody-mediated neutralization of this lytic activity may provide a strategy for development of toxoid-based vaccines or immunotherapeutics for prevention or mitigation of clinical diseases. However, certain BCPFTs have been proposed to act as danger signals that may alert the immune system through an inflammatory response. The utility of a neutralizing vaccination strategy must be weighed against such immune-activating potential.

[Cases of MRSA in nursing homes in Oslo 2005-11]

BACKGROUND

The number of infections caused by MRSA has increased substantially in Norway in the past decade. It is an objective to prevent MRSA from becoming established in nursing homes and hospitals. The purpose of the article is to describe the features of the development of MRSA cases found in nursing homes in Oslo.

MATERIALS AND METHOD

We carried out a retrospective study of registered cases of MRSA (both sufferers and carriers) in Oslo in 2005-11. Data were obtained from the City of Oslo municipal health services' MRSA database and from genotyping carried out at Akershus University Hospital.

RESULTS

The annual number of cases of MRSA found in Oslo increased during the period 2005-11 from 92 in 2005 to 268 in 2011, a total of 1198 cases. Of these, 224 cases (19%) were registered in nursing homes, distributed among 22 institutions, 158 residents and 66 staff, with an average of 32 cases annually (14-58 spread). Twenty-eight of 50 nursing homes had no cases of MRSA, while 159 of the cases were related to outbreaks of MRSA. Three of 20 outbreaks affected residents only. The nursing home isolates consisted of 40 different spa types, of which 160 (71%) of the isolates were clustered in three clonal complexes. The most common spa type t304 was found in 116 (52%) of the cases.

INTERPRETATION

Cases of MRSA in Oslo in total increased sharply from 2005 to 2011, while the number of cases in nursing homes was stable. It is, however, uncertain whether this reflects the actual incidence.

Molecular typing and virulence characteristic of methicillin-resistant Staphylococcus aureus isolates from pediatric patients in Bucaramanga, Colombia

Background

Staphylococcus aureus is among the most common global nosocomial pathogens. The emergence and spread of methicillin-resistant Staphylococcus aureus (MRSA) is a public health problem worldwide that causes nosocomial and community infections. The goals of this study were to establish the clonal complexes (CC) of the isolates of MRSA obtained from pediatric patients in a university hospital in Colombia and to investigate its molecular characteristics based on the virulence genes and the genes of staphylococcal toxins and adhesins.

Methods

A total of 53 MRSA isolates from pediatric patients with local or systemic infections were collected. The MRSA isolates were typed based on the SCCmec, MLST, spa and agr genes. The molecular characterization included the detection of Panton-Valentine Leukocidin, superantigenic and exfoliative toxins, and adhesin genes. The correlation between the molecular types identified and the profile of virulence factors was determined for all isolates.

Results

Four CC were identified, including CC8, CC5, CC80 and CC78. The ST8-MRSA-IVc-agrI was the predominant clone among the isolates, followed by the ST5-MRSA-I-agrII and ST5-MRSA-IVc-agrII clones. Twelve spa types were identified, of which t10796 and t10799 were new repeat sequences. The isolates were carriers of toxin genes, and hlg (100%), sek (92%) and pvl (88%) were the most frequent. Ten toxin gene profiles were observed, and the most frequent were seq-sek-hlg (22.6%), sek-hlg (22.6%), seb-seq-sek-hlg (18.9%) and seb-sek-hlg (15.1%). The adhesion genes were present in most of the MRSA isolates, including the following: clf-A (89%), clf-B (87%), fnb-A (83%) and ica (83%). The majority of the strains carried SCCmec-IVc and were identified as causing nosocomial infection. No significant association between a molecular type and the virulence factors was found.

Conclusion

Four major MRSA clone complexes were identified among the isolates. ST8-MRSA-IVc-agrI pvl+ (USA300-LV) was the most frequent, confirming the presence of community-associated MRSA in Colombian hospitals.

Molecular and phenotypic evidence for the spread of three major methicillin-resistant Staphylococcus aureus clones associated with two characteristic antimicrobial resistance profiles in China

OBJECTIVES

The distribution of methicillin-resistant Staphylococcus aureus (MRSA) clones is dynamic and geographically unique. To understand the changing epidemiology of MRSA infections in China, we performed a prospective, multicity surveillance study with molecular typing and phenotypic analysis to determine the association of major prevalent clones with their antimicrobial resistance profiles.

METHODS

A total of 517 S. aureus isolates collected between January 2009 and March 2012 from six cities in China were subjected to antibiogram analysis and molecular typing, including staphylococcal cassette chromosome mec typing, multilocus sequence typing, staphylococcal protein A gene typing and PFGE typing.

RESULTS

Among the isolates collected, 309 were characterized as MRSA, with a prevalence of 59.8%. Three major clones were found to be prevalent in China: ST239-MRSA-III-t030, ST239-MRSA-III-t037 and ST5-MRSA-II-t002. These three clones were associated with two characteristic resistance profiles, namely, gentamicin/ciprofloxacin/rifampicin/levofloxacin for the first clone and gentamicin/ciprofloxacin/clindamycin/erythromycin/tetracycline/levofloxacin/trimethoprim/sulfamethoxazole for the latter two. Several geographically unique minor clones were also identified.

CONCLUSIONS

The predominant MRSA clones in China were associated with characteristic antimicrobial resistance profiles. Antibiotics for treating patients with MRSA infections can be selected based on the strain typing data.

Structurally designed attenuated subunit vaccines for S. aureus LukS-PV and LukF-PV confer protection in a mouse bacteremia model

Previous efforts towards S. aureus vaccine development have largely focused on cell surface antigens to induce opsonophagocytic killing aimed at providing sterile immunity, a concept successfully applied to other Gram-positive pathogens such as Streptococcus pneumoniae. However, these approaches have largely failed, possibly in part due to the remarkable diversity of the staphylococcal virulence factors such as secreted immunosuppressive and tissue destructive toxins. S. aureus produces several pore-forming toxins including the single subunit alpha hemolysin as well as bicomponent leukotoxins such as Panton-Valentine leukocidin (PVL), gamma hemolysins (Hlg), and LukED. Here we report the generation of highly attenuated mutants of PVL subunits LukS-PV and LukF-PV that were rationally designed, based on an octameric structural model of the toxin, to be deficient in oligomerization. The attenuated subunit vaccines were highly immunogenic and showed significant protection in a mouse model of S. aureus USA300 sepsis. Protection against sepsis was also demonstrated by passive transfer of rabbit immunoglobulin raised against LukS-PV. Antibodies to LukS-PV inhibited the homologous oligomerization of LukS-PV with LukF-PV as well heterologous oligomerization with HlgB. Importantly, immune sera from mice vaccinated with the LukS mutant not only inhibited the PMN lytic activity produced by the PVL-positive USA300 but also blocked PMN lysis induced by supernatants of PVL-negative strains suggesting a broad protective activity towards other bicomponent toxins. These findings strongly support the novel concept of an anti-virulence, toxin-based vaccine intended for prevention of clinical S. aureus invasive disease, rather than achieving sterile immunity. Such a multivalent vaccine may include attenuated leukotoxins, alpha hemolysin, and superantigens.

Methicillin resistance is not a predictor of severity in community-acquired Staphylococcus aureus necrotizing pneumonia--results of a prospective observational study

Staphylococcal necrotizing pneumonia (NP) is a severe disease associated with Panton-Valentine leucocidin (PVL). NP was initially described for methicillin-susceptible Staphylococcus aureus (MSSA) infection, but cases associated with methicillin-resistant S. aureus (MRSA) infection have increased concomitantly with the incidence of community-acquired MRSA worldwide. The role of methicillin resistance in the severity of NP remains controversial. The characteristics and outcomes of 133 patients with PVL-positive S. aureus community-acquired pneumonia (CAP) were compared according to methicillin resistance. Data from patients hospitalized for PVL-positive S. aureus CAP in France from 1986 to 2010 were reported to the National Reference Centre for Staphylococci and were included in the study. The primary end point was mortality. Multivariate logistic modelling and the Cox regression were used for subsequent analyses. We analysed 29 cases of PVL-MRSA and 104 cases of PVL-MSSA pneumonia. Airway haemorrhages were more frequently associated with PVL-MSSA pneumonia. However, no differences in the initial severity or the management were found between these two types of pneumonia. The rate of lethality was 39% regardless of methicillin resistance. By Cox regression analysis, methicillin resistance was not found to be a significant independent predictor of mortality at 7 or 30 days (p 0.65 and p 0.71, respectively). Our study demonstrates that methicillin resistance is not associated with the severity of staphylococcal necrotizing pneumonia.

Genetic characterization of Panton-Valentine leukocidin-producing methicillin-resistant Staphylococcus aureus in Western Austria

BACKGROUND

Community-acquired methicillin-resistant Staphylococcus aureus (caMRSA) is an emerging pathogen which causes potentially severe infections in young and healthy individuals due to the ability of most strains to produce Panton-Valentine leukocidin (PVL). The aim of this study was to evaluate the prevalence of PVL-positive (PVL(+))-MRSA strains in Western Austria in the period from December 2005 to May 2010 and to characterize the identified PVL(+)-MRSA strains.

METHODS

Six hundred and fifty MRSA strains from Innsbruck Medical University hospital, district hospitals, and general practitioners were investigated for the presence of lukS-lukF gene (encoding for PVL). Antimicrobial resistance testing, SCCmec-, agr-, MLST- and spa-typing, as well as arcA determination were performed on PVL(+)-MRSA.

RESULTS

Among 650 MRSA strains collected from various body sites from hospitalized patients and outpatients, 31 strains (4.8 %) were positive for lukS-lukF and thus identified as PVL(+)-MRSA. Agr-1 was the most common agr-type (n = 18, 58.1 %) and SCCmec-IV or variants IVa and IVc were the most common SCCmec types (n = 27, 87.1 %). All tested strains showed in-vitro susceptibility to vancomycin and rifampicin, but resistance against cotrimoxazol (6.4 %), clindamycin (9.7 %), gentamicin (9.7 %), fusidic acid (12.9 %), levofloxacin (12.9 %), and erythromycin (61.3 %) was found. Most lukS-lukF-positive MRSA detected in our survey shared ST8 and t008 and were positive for arcA.

CONCLUSIONS

The major lukS-lukF-positive MRSA lineage found in our population was ST8, t008 and positive for arcA which is mainly found in the USA. In contrast, ST80 strains were not found as frequently in our region as in many other European countries.

Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

Virulence and antibiotic resistance are significant determinants of the types of infections caused by Staphylococcus aureus and paediatric groups remain among the most commonly affected populations. The goal of this study was to characterise virulence genes of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains isolated from a paediatric population of a Colombian University Hospital during 2009. Sixty MSSA and MRSA isolates were obtained from paediatric patients between zero-14 years. We identified the genes encoding virulence factors, which included Panton-Valentine leucocidine (PVL), staphylococcal enterotoxins A-E, exfoliative toxins A and B and toxic shock syndrome toxin 1. Typing of the staphylococcal chromosome cassette mec (SCCmec) was performed in MRSA strains. The virulence genes were more diverse and frequent in MSSA than in MRSA isolates (83% vs. 73%). MRSA strains harboured SCCmec types IVc (60%), I (30%), IVa (7%) and V (3%). SCCmec type IVc isolates frequently carried the PVL encoding genes and harboured virulence determinants resembling susceptible strains while SCCmec type I isolates were often negative. PVL was not exclusive to skin and soft tissue infections. As previously suggested, these differences in the distribution of virulence factor genes may be due to the fitness cost associated with methicillin resistance.

Receptor-dependent and -independent immunomodulatory effects of phenol-soluble modulin peptides from Staphylococcus aureus on human neutrophils are abrogated through peptide inactivation by reactive oxygen species

The virulence and pathogenesis mechanisms of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains depend on a newly described group of phenol-soluble modulin (PSM) peptides (the PSMα peptides) with cytolytic activity. These toxins are α-helical peptides with a formyl group at the N terminus, and they activate neutrophils through formyl peptide receptor 2 (FPR2), a function closely correlated to the capacity of staphylococcal species to cause invasive infections. The effects of two synthetic PSMα peptides were investigated, and we show that they utilize FPR2 and promote neutrophils to produce reactive oxygen species (ROS) which in turn trigger inactivation of the peptides. Independently of FPR2, the PSMα peptides also downregulate the neutrophil response to other stimuli and exert a cytolytic effect to which apoptotic neutrophils are more sensitive than viable cells. The novel immunomodulatory functions of the PSMα peptides were sensitive to ROS generated by the neutrophil myeloperoxidase (MPO)-H(2)O(2) system, suggesting a role for this enzyme system in counteracting bacterial virulence.

Evolutionary dynamics of Staphylococcus aureus during progression from carriage to disease

Whole-genome sequencing offers new insights into the evolution of bacterial pathogens and the etiology of bacterial disease. Staphylococcus aureus is a major cause of bacteria-associated mortality and invasive disease and is carried asymptomatically by 27% of adults. Eighty percent of bacteremias match the carried strain. However, the role of evolutionary change in the pathogen during the progression from carriage to disease is incompletely understood. Here we use high-throughput genome sequencing to discover the genetic changes that accompany the transition from nasal carriage to fatal bloodstream infection in an individual colonized with methicillin-sensitive S. aureus. We found a single, cohesive population exhibiting a repertoire of 30 single-nucleotide polymorphisms and four insertion/deletion variants. Mutations accumulated at a steady rate over a 13-mo period, except for a cluster of mutations preceding the transition to disease. Although bloodstream bacteria differed by just eight mutations from the original nasally carried bacteria, half of those mutations caused truncation of proteins, including a premature stop codon in an AraC-family transcriptional regulator that has been implicated in pathogenicity. Comparison with evolution in two asymptomatic carriers supported the conclusion that clusters of protein-truncating mutations are highly unusual. Our results demonstrate that bacterial diversity in vivo is limited but nonetheless detectable by whole-genome sequencing, enabling the study of evolutionary dynamics within the host. Regulatory or structural changes that occur during carriage may be functionally important for pathogenesis; therefore identifying those changes is a crucial step in understanding the biological causes of invasive bacterial disease.

Molecular typing and phenotype characterization of methicillin-resistant Staphylococcus aureus isolates from blood in Taiwan

Background

Staphylococcus aureus causes a variety of severe infections such as bacteremia and sepsis. At present, 60–80% of S. aureus isolates from Taiwan are methicillin resistant (MRSA). It has been shown that certain MRSA clones circulate worldwide. The goals of this study were to identify MRSA clones in Taiwan and to correlate the molecular types of isolates with their phenotypes.

Methods

A total of 157 MRSA isolates from bacteremic patients were collected from nine medical centers. They were typed based on polymorphisms in agr, SCCmec, MLST, spa, and dru. Phenotypes characterized included Panton-Valentine leucocidin (pvl), inducible macrolide-lincosamide-streptogramin B resistance (MLSBi), vancomycin (VA) and daptomycin (DAP) minimal inhibitory concentrations (MIC), and superantigenic toxin gene profiles. Difference between two consecutive samples was determined by Mann-Whitney-U test, and difference between two categorical variables was determined by Fisher's exact test.

Results

Four major MRSA clone complexes CC1, CC5, CC8, and CC59 were found, including 4 CC1, 9 CC5, 111 CC8, and 28 CC59 isolates. These clones had the following molecular types: CC1: SCCmecIV and ST573; CC5: SCCmecII and ST5; CC8: SCCmecIII, ST239, and ST241, and CC59: SCCmecIV, SCCmecV_T, ST59, and ST338. The toxin gene profiles of these clones were CC1: sec-seg-(sei)-sell-selm-(seln)-selo; CC5: sec-seg-sei-sell-selm-(seln)-selp-tst1; CC8: sea-selk-selq, and CC59: seb-selk-selq. Most isolates with SCCmecV_T, ST59, spat437, and dru11 types were pvl⁺ (13 isolates), while multidrug resistance (≥4 antimicrobials) were associated with SCCmecIII, ST239, spa t037, agrI, and dru14 (119 isolates) (p<0.001). One hundred and twenty four isolates with the following molecular types had higher VA MIC: SCCmecII and SCCmecIII; ST5, ST239, and ST241; spa t002, t037, and t421; dru4, dru10, dru12, dru13, and dru14 (p<0.05). No particular molecular types were found to be associated with MLSBi phenotype.

Conclusions

Four major MRSA clone complexes were found in Taiwan. Further studies are needed to delineate the evolution of MRSA isolates.

The rise of methicillin-resistant staphylococcus aureus in U.S. correctional populations

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging threat to public health, especially in correctional settings. Outbreaks have been seen in jails and prisons in Mississippi, California, Texas, and Georgia in recent years. Also, many correctional settings have seen an increase in MRSA infection greater than in the general population. This article examines the lessons that have been learned about MRSA in correctional settings and ponders what is yet to be learned about this disease in these populations.

[Necrotizing community-acquired Staphylococcus aureus pneumonia]

Acute necrotizing pneumonia due to Panton-Valentine secreting Staphylococcus aureus was identified as a clinical entity by Gilet et al., in 2002. This severe acute necrotizing pneumonia occurring in previously healthy children and adolescents can lead to a rapid fatal outcome even if quickly diagnosed and treated. We report the case of a healthy 10-year-old girl presenting with hemorrhagic necrotizing pneumonia and septic shock. Bacteriological cultures yielded methicillin-susceptible Staphylococcus aureus. The course of the disease was characterized by recurrent uncontrolled hemoptysia leading to refractory hypoxemia. The details of the hospital stay are presented. We discuss the clinical features of the disease and describe recent epidemiologic data and Panton-Valentine toxin research results as well as primary hospital care and treatment.

An evaluation of the emerging vaccines and immunotherapy against staphylococcal pneumonia in children

Background

Staphylococcus aureus is a commensal of human skin and nares. It is also one of the leading nosocomial pathogens in both developed and developing countries and is responsible for a wide range of life threatening infections, especially in patients who are immunocompromised, post-surgery, undergoing haemodialysis and those who are treated with catheters and ventilators. Over the past two decades, the incidence of nosocomial staphylococcal infections has increased dramatically. Currently there are at least seven vaccine and immunotherapy candidates against S. aureus in the developmental phase targeting both active and passive immunization.

Methods

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In Stage I, we systematically reviewed the literature related to emerging vaccines against Staphylococcus aureus relevant to several criteria of interest: answerability; cost of development, production and implementation; efficacy and effectiveness; deliverability, affordability and sustainability; maximum potential impact on disease burden reduction; acceptability to the end users and health workers; and effect on equity. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies) to participate. The policy makers and industry representatives accepted our invitation on the condition of anonymity, due to sensitive nature of their involvement in such exercises. They answered questions from CHNRI framework and their “collective optimism” towards each criterion was documented on a scale from 0 to 100%.

Results

The panel of experts expressed low levels of optimism (score around or below 50%) on the criteria of answerability, efficacy, maximum disease burden reduction potential, low cost of production, low cost of implementation and affordability; moderate levels of optimism (scores around 60 to 80%) that these vaccines could be developed at a low cost, and thus on the deliverability, sustainability and impact on equity; and high levels of optimism (scores above 80%) regarding acceptable of such a product to both the end-users and health workers. While assessing the candidates for passive immunization against S.aureus, the experts were poorly optimistic regarding low production cost, low implementation cost, efficacy, deliverability, sustainability, affordability and equity; moderately optimistic regarding answerability and acceptability to health workers and end-users. They were of the opinion that these interventions would have only a modest impact (3 to 5%) on the burden of childhood pneumonia. .

Conclusion

In order to provide an effective vaccine against S. aureus, a number of unresolved issues in vaccine development relating to optimal antigenic target identification, criteria for acceptable efficacy, identification of target population, commercial development limitations, optimal timing of immunization strategy, storage, cold chain requirements and cost need to be addressed properly. There is still a great deal unknown about the complex interaction between S. aureus and the human host. However, given the nature of S. aureus and the lessons learned from the recent failure of two emerging vaccines, it is clear that a multi-component vaccine is essential. Combating only one virulence factor is not sufficient in the human host but finding the right combination of factors will be very challenging.