Virulence Factor Panton-Valentine Leukocidin Research Articles

Prevalence, clinical expression, invasiveness and outcome of Staphylococcus aureus containing Panton-Valentine leukocidin in children treated in a university hospital of Lithuania

Background: There is a high prevalence of Staphylococcus aureus virulence factor Panton-Valentine leukocidin (PVL) in North-East parts of Europe. The aim was to evaluate data regarding the PVL occurrences in Lithuania, determine the relationship with Methicillin resistant Staphylococcus aureus (MRSA), association with demographic and clinical conditions, invasiveness and severity of the disease in children treated in hospital Kauno klinikos (KK).Methods: We performed a prospective case-cohort single-center study on paediatric patients hospitalized from 2012 to 2015 to KK. We compared characteristics in PVL positive [SA-PVL(+)] and PVL negative [SA-PVL(–)] groups among non-invasive and invasive infections. Logistic regression was performed to detect PVL predicting factors and Cox regression was presented to define factors associated with admission to intensive care unit (ICU).Results: PVL was detected in 51.5%, MRSA in 7.0% and MRSA-PVL(+) in 4.8% of cases. In general, PVL was associated with older age comparing with SA-PVL(–) (median 8.5 vs. 4.0 years, p < .001). Skin and soft tissue infections were presented in 87.9% of all SA-PVL(+) cases. Invasive infections (44.7% vs. 12.1%, p < .001) and co-morbidities (20.5% vs. 2.9%, p < .001) were associated with SA-PVL(–) infections compared to SA-PVL(+), but ICU admission number was higher in invasive SA-PVL(+) cases comparing to invasive SA-PVL(–) cases (41.2% vs. 10.2%, p = .007).Conclusions: There was a high prevalence of pvl gene in patients treated in KK. SA-PVL(+) infections were associated with SSTI and were not common in invasive infections, but the invasive infections caused by SA-PVL(+) were related to severe disease progression and admission to ICU.

Increase in the prevalence of Panton–Valentine leukocidin and clonal shift in community-onset methicillin-resistant Staphylococcus aureus causing skin and soft-tissue infections in the Rhine-Neckar Region, Germany, 2012–2016

Methicillin-resistant Staphylococcus aureus (MRSA) remains a major challenge for patient care. Community-associated (CA)-MRSA often have a fitness and virulence advantage compared with their nosocomial counterparts. Increased mobility, travel activities and migration accelerate the intercontinental spread of virulent CA-MRSA strains. Outpatient clinics are the most important route of entry for CA-MRSA into hospitals. However, systematic data on CA-MRSA in Germany are limited. In this study, community-onset (CO)-MRSA skin and soft-tissue infection (SSTI) isolates in the Rhine-Neckar Region from 2012-2016 were characterised to gain an insight into their molecular epidemiology and to monitor potential introduction of virulent and dominant MRSA strains into our hospital. A total of 2475 patients with S. aureus SSTI were identified in the outpatient departments of our hospital, of which 94 (3.8%) were MRSA. In addition, 40.4% of the CO-MRSA harboured the virulence factor Panton-Valentine leukocidin (PVL). ST8-t008-MRSA-IVa/c (23.7%; 9/39) and ST80-t044-MRSA-IVc (15.8%; 6/38) were the predominant PVL-positive MRSA. Molecular typing and epidemiological data revealed that 42.6% (40/94) of strains could be traced back to a local origin and 44.7% (42/94) were endemic outside of Europe. Resistance to quinolones, clindamycin and macrolides was common, whilst resistance to trimethoprim/sulfamethoxazole, tetracycline, mupirocin, chlorhexidine and fusidic acid was low. No resistance to rifampicin, fosfomycin or linezolid was observed. This study provides insight into the clonal composition of CO-MRSA in the Rhine-Neckar Region. The increase of PVL-positive MRSA and the introduction of imported strains may affect the local MRSA landscape in the near future and should be monitored closely.

Direct molecular versus culture-based assessment of Gram-positive cocci in biopsies of patients with major abscesses and diabetic foot infections.

Major abscesses and diabetic foot infections (DFIs) are predominant subtypes of complicated skin and skin structure infections (cSSSIs), and are mainly caused by Staphylococcus aureus and β-hemolytic streptococci. This study evaluates the potential benefit of direct pathogen-specific real-time polymerase chain reaction (PCR) assays in the identification of causative organisms of cSSSIs. One-hundred and fifty major abscess and 128 DFI biopsy samples were collected and microbial DNA was extracted by using the Universal Microbe Detection kit for tissue samples. Pathogen-specific PCRs were developed for S. aureus and its virulence factor Panton–Valentine leukocidin (PVL), Streptococcus pyogenes, S. agalactiae, S. dysgalactiae, and the S. anginosus group. Identification by pathogen-specific PCRs was compared to routine culture and both methods were considered as the gold standard for determination of the sensitivity and specificity of each assay. Direct real-time PCR assays of biopsy samples resulted in a 34 % higher detection of S. aureus, 37 % higher detection of S. pyogenes, 18 % higher detection of S. agalactiae, 4 % higher detection of S. dysgalactiae subspecies equisimilis, and 7 % higher detection of the S. anginosus group, compared to routine bacterial culture. The presence of PVL was mainly confined to S. aureus isolated from major abscess but not DFI biopsy samples. In conclusion, our pathogen-specific real-time PCR assays had a higher yield than culture methods and could be an additional method for the detection of relevant causative pathogens in biopsies.

A 12-year survey of methicillin-resistant Staphylococcus aureus infections in Greece: ST80-IV epidemic?

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of both healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA) infections. Severe MRSA infections have been associated with the virulence factor Panton–Valentine leukocidin (PVL). The aim of this study was to investigate susceptibility patterns, the presence of toxin genes, including that encoding PVL, and clonality among MRSA isolates collected from patients in Greece over a 12-year period. MRSA isolates were collected from January 2001 to December 2012 from six different hospitals. Antibiotic susceptibility was determined with the disk diffusion method and the Etest. The presence of the toxic shock syndrome toxin-1 gene (tst), the enterotoxin gene cluster (egc) and the PVL gene was tested with PCR. The genotypic characteristics of the strains were analysed by SCCmec and agr typing, and clonality was determined with pulsed-field gel electrophoresis and multilocus sequence typing. An increasing rate of MRSA among S. aureus infections was detected up to 2008. The majority of PVL-positive MRSA isolates belonged to a single clone, sequence type (ST)80-IV, which was disseminated both in the community and in hospitals, especially during the warmest months of the year. Carriage of tst was associated with ST30-IV, whereas egc was distributed in different clones. CA-MRSA isolates were recovered mainly from skin and soft tissue infections, whereas HA-MRSA isolates were associated with surgical and wound infections. During the period 2001–2012, ST80-IV predominated in the community and infiltrated the hospital settings in Greece, successfully replacing other PVL-positive clones. The predominance of ST239-III in HA-MRSA infections was constant, whereas new clones have also emerged. Polyclonality was statistically significantly higher among CA-MRSA isolates and isolates from adult patients.

Interactions of Methicillin Resistant Staphylococcus aureus USA300 and Pseudomonas aeruginosa in Polymicrobial Wound Infection

Understanding the pathology resulting from Staphylococcus aureus and Pseudomonas aeruginosa polymicrobial wound infections is of great importance due to their ubiquitous nature, increasing prevalence, growing resistance to antimicrobial agents, and ability to delay healing. Methicillin-resistant S. aureus USA300 is the leading cause of community-associated bacterial infections resulting in increased morbidity and mortality. We utilized a well-established porcine partial thickness wound healing model to study the synergistic effects of USA300 and P. aeruginosa on wound healing. Wound re-epithelialization was significantly delayed by mixed-species biofilms through suppression of keratinocyte growth factor 1. Pseudomonas showed an inhibitory effect on USA300 growth in vitro while both species co-existed in cutaneous wounds in vivo. Polymicrobial wound infection in the presence of P. aeruginosa resulted in induced expression of USA300 virulence factors Panton-Valentine leukocidin and α-hemolysin. These results provide evidence for the interaction of bacterial species within mixed-species biofilms in vivo and for the first time, the contribution of virulence factors to the severity of polymicrobial wound infections.

Use of antimicrobials in Equine Practice across North America: a case-based survey

designated PBP2a, which present a very low affinity for betalactam antibiotics. The mecA gene is located on a mobile genetic element, named staphylococcal cassette chromosomemec (SCCmec) inserted in the S. aureus chromosome. In addition, MRSA are frequently resistant to a wide range of additional antimicrobial classes. From January 2007 to June 2011, 912 S. aureus isolates were obtained from various clinical samples. Identification of MRSA was confirmed by amplification of the nuc (specific of S. aureus) and mecA genes. MRSA strains were typed by pulsed field gel electrophoresis (PFGE) and by Multilocus Sequence Typing (MLST). SCCmec elements (types I to VI) and genes encoding virulence factors Panton-Valentine Leukocidin (PVL), Toxic Shock Staphylococcal Toxin (TSST1) and Enterotoxin A were characterized by using a PCR approach. Susceptibility testing of MRSA isolates was performed using the agar diffusion method and following drugs were tested: erythromycin (ERY), tetracycline (TET), streptomycin (STR), gentamicin (GEN), rifampin (RIF), cotrimoxazole (TMP-SULF), chloramphenicol (CHL) and ofloxacin (OFL). Genes conferring resistance to macrolides [erm(A), erm(B), erm(C)], gentamicin [aac(6’)-aph(2’’)], and tetracyclines [tet(M)] were amplified by PCR. Among the 912 S. aureus isolates between 2007 and 2011, 19 strains were characterized as MRSA. Their prevalence increased until 6% in2010 and4% in thefirst sixmonths of 2011. 9 types could be distinguished by PFGE. MLST revealed thatMRSA isolated belonged to two sequence types, ST8 and ST398. All ST398MRSA (n1⁄47)were detected in 2010 including two isolates originating from the same farm. These results suggested possible cross-transmission of MRSA. The isolates, except two, possessed SCCmec IV and did not harbor the genes for the virulence factors PVL, TSST1, and enterotoxin A. All isolates were multiply resistant to other antimicrobials. PCR experiments showed that resistance to quinolone was active efflux, while to gentamicin and tetracycline was due to the presence of the aac(6’)-aph(2’’) and tet(M)genes, respectively. The increase in the prevalence of MRSA in horse infections is related to the emergence and spread of the ST398 type. This type is known to cause outbreaks in horses, to be responsible of cross-colonization and eventually infect humans. Farm hygiene and antimicrobial use contribute to MRSA occurrence in animals. Hygiene measures should, therefore, be maintained or reinforced to limit the transmission of S. aureus between horses and also between horses and personnel.

Methicillin-resistant Staphylococcus aureus Infection After Lung Transplantation: 5-year Review of Clinical and Molecular Epidemiology

Data on the epidemiology of MRSA infection in lung transplantation is limited. We performed a 5-year retrospective study to assess the incidence and microbiologic and clinical characteristics of methicillin-resistant Staphylococcus aureus (MRSA) infection in a cohort of 163 lung transplant recipients. Seventeen patients with MRSA colonization and/or infection were identified, for a calculated incidence rate of 76.1 cases per 1,000 transplanted-years. Pulsed-field gel electrophoresis identified 3 different distinct MRSA profiles, all of them consistent with hospital-associated MRSA infection. Despite negative polymerase chain reaction (PCR) for the virulence factor Panton-Valentine leukocidin, MRSA infections resulted in significant disease and morbidity.

Twenty-five year epidemiology of invasive methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered at a burn center

Over the past two decades, an epidemiologic emergence of methicillin-resistant Staphylococcus aureus (MRSA) infections has occurred from that of primarily hospital-associated to community-associated. This emergence change has involved MRSA of different pulsed-field types (PFT), with different virulence genes and antimicrobial resistance patterns. In this study we, evaluate the changes in PFT and antimicrobial resistance epidemiology of invasive MRSA isolates over 25 years at a single burn unit. Isolates were tested by pulsed-field gel electrophoresis (PFGE), broth microdilution antimicrobial susceptibility testing, and PCR for the virulence factors Panton–Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME), and the resistance marker staphylococcal chromosomal cassette mec (SCC mec). Forty isolates were screened, revealing stable vancomycin susceptibility MIC without changes over time but decreasing susceptibility to clindamycin and ciprofloxacin. The majority of PFGE types were MRSA USA800 carrying the SCC mec I element and USA100 carrying the SCC mec II element. No strains typically associated with community-associated MRSA, USA300 or USA400, were found. USA800 isolates were predominately found in the 1980s, USA600 isolates were primarily found in the 1990s, and USA100 isolates were found in the 2000s. The PVL gene was present in only one isolate, the sole USA500 isolate, from 1987. The virulence marker ACME was not detected in any of the isolates. Overall, a transition was found in hospital-associated MRSA isolates over the 25 years, but no introduction of community-associated MRSA isolates into this burn unit. Continued active surveillance and aggressive infection control strategies are recommended to prevent the spread of community-acquired MRSA to this burn unit.

Occult Methicillin-Resistant Staphylococcus aureus Abscesses in 2 Pediatric Patients

Methicillin-resistant Staphylococcus aureus (MRSA) infections have become more common over the last decade. Recently, severe MRSA infections including necrotizing pneumonia, purpura fulminans, and rapidly progressive skin abscesses have been reported. These severe infections frequently have been associated with the virulence factor Panton-Valentine leukocidin (PVL). Two unusual cases of occult deep tissue abscesses in children who had family members with a history of severe MRSA skin abscesses are presented in this article. Both children initially presented with fever without a focus. Deep tissue MRSA (PVL positive) abscesses evolved. Empiric antibiotic therapy for MRSA should be considered for infants and children who are hospitalized with occult fever and who have a family member with a history of MRSA infection.

Sporadic “Transitional” Community-Associated Methicillin-Resistant Staphylococcus aureus Strains from Health Care Facilities in the United States

We describe phenotypic and genotypic traits of a group of methicillin-resistant Staphylococcus aureus (MRSA) clones that are either remnants of unsuccessful community-associated MRSA (CA-MRSA) clones or represent a transitional state with some yet-to-be-acquired characteristics of CA-MRSA. These rare strains (n = 20) were identified during a 10-year period (1990-1999) from 13 unrelated health care facilities in Wisconsin. The isolates were recovered from patients in nosocomial or long-term chronic care facilities (60%) and outpatient settings (40%). Sixty percent (n = 12) of the isolates were recovered from skin and soft tissue infections, whereas the remaining isolates (n = 8) were from invasive infections. Ninety percent of isolates were susceptible to all antibiotic classes tested or resistant to erythromycin and clindamycin. Pulsed-field gel electrophoresis, multilocus sequence typing, and spa typing clustered these isolates into 8, 8, and 14 clonal groups, respectively. Eight plasmid profiles were represented in these strains. All four agr types were represented, with type IV being predominant (40%). All strains harbored subtypes of type IV staphylococcal cassette chromosome mec but lacked genes for the virulence factor Panton-Valentine leukocidin (PVL). The strains harbored one or more of the following toxin genes: sea, seb, sec, sed, see, seh, sej, sek, sel, seg, sei, sem, sen, and seo. Individual clonal groups maintained the same set of enterotoxin genes even though they were isolated over extended time periods, suggesting significant genomic stability. The potential role of PVL-carrying phages and plasmids in the success of CA-MRSA clones has been discussed.

Life-threatening community-acquired methicillin-resistant Staphylococcus aureus infection in Australia

Eight patients with invasive bacteremic community-acquired methicillin-resistant Staphylococcus aureus infection in southeast Queensland, Australia, are reported. One patient died of septic shock. Haematogenous seeding to lungs, bone, and other sites was common. All isolates carried the virulence factor Panton-Valentine leukocidin and were either the southwest Pacific clone or the newly described Queensland clone. Clinicians should consider community-acquired methicillin-resistant Staphylococcus aureus infection in any patient presenting to hospital with severe staphylococcal sepsis or pneumonia.