Panton-Valentine Leukocidin Production Research Articles

Reduction of Panton-Valentine Leukocidin Production in the Staphylococcal Strain USA300 After In Vitro Ascorbic Acid and Nicotinamide Treatment.

Background Panton-Valentine leukocidin (PVL) is one of the most important determinants of virulence in Staphylococcus aureus. It is associated with a propensity for complicating skin and soft tissue infections and necrotizing pneumonia. This study aims to quantitively examine the effect of ascorbic acid and nicotinamide on PVL production in the reference strain USA300. Methodology Sandwich enzyme-linked immunosorbent assay (ELISA) was used to quantitively measure the production of PVL via the commercial LukS sandwich ELISA kit (IBT Bio-services, MD, USA). Results Incubating USA300 with subinhibitory concentrations of antioxidants resulted in a statistically significant eight-fold reduction in PVL production at 1.25 mg/mL and 30 mg/mL for ascorbic acid and nicotinamide, respectively. Although the mechanism by which antioxidants inhibit PVL production is yet to be elucidated, we suggest that it can be due to interrupting PVL gene expression. Conclusions Ascorbic acid and nicotinamide have the potential to be toxin-suppressing agents that may be effective in supporting the bactericidal effect of antibiotics to improve the outcome of PVL-associated infections; however, further extensive research is required.

Occurrence of community-acquired Panton-Valentine leukocidin-producing and enterotoxin-producing methicillin-resistant staphylococci in companion dogs

In Nigeria, available data on drug-resistant bacterial infections that are caused by companion dogs are scarce. Hence the present study evaluated the occurrence of some community-acquired toxigenic methicillin-resistant staphylococci (MRS) on companion dogs harboured in Nigerian homes, as a pointer to the extent of exposure of humans to these pathogens. Samples were collected from 70 healthy companion dogs during dry and rainy season periods by swabbing a 125 cm2 fur area on the lumbar and thoracic sites. Phenotypic tests, Kirby Bauer disc diffusion test and 16S rRNA gene analysis were used to identify presumptive colonies of staphylococci and MRS. Molecular methods were employed to detect Panton-Valentine leukocidin (PVL) and prototypic enterotoxin B in MRS isolates. The counts of staphylococci on fur of companion dogs during the rainy season exceeded usual limits of bacteria (≤ 2.54 log10 CFU cm-2) on a healthy dog, thus, suggesting that companion dogs harboured in homes situated in Nigeria may be reservoirs of bacteria, especially during rainy season. The mean counts of staphylococci during the rainy season were estimated at 3.09 ± 2.78 log10 CFU cm-2 and 2.77 ± 2.43 log10 CFU cm-2 in Edo and Delta States, respectively. The main Staphylococcus species that were carried on fur of companion dogs included S. pseudintermedius, S. aureus, S. epidermidis, S. simulans and S. saprophyticus. Amongst the staphylococci, expression of methicillin and multidrug resistance was mainly exhibited by S. pseudintermedius and S. aureus, while enterotoxigenicity was mainly expressed by methicillin-resistant S. aureus. Enterotoxigenic S. aureus was carried on the fur of companion dogs during the rainy season at estimated prevalence of 8.57% in both Edo and Delta States, respectively; while PVL-producing S. aureus was estimated at 5.71% and 2.86%, with PVL-producing S. pseudintermedius estimated at 25.71% and 34.29%, respectively. The high prevalence of toxigenic-producing isolates seen on the fur of companion dogs, especially during rainy season, could pose a risk for humans, particularly those that harbour pet dogs at their homes.

Osteoarticular Infections in Pediatric Hospitals in Europe: A Prospective Cohort Study From the EUCLIDS Consortium.

BackgroundPediatric osteoarticular infections (POAIs) are serious diseases requiring early diagnosis and treatment.MethodsIn this prospective multicenter cohort study, children with POAIs were selected from the European Union Childhood Life-threatening Infectious Diseases Study (EUCLIDS) database to analyze their demographic, clinical, and microbiological data.ResultsA cohort of 380 patients with POAIs, 203 with osteomyelitis (OM), 158 with septic arthritis (SA), and 19 with both OM and SA, was analyzed. Thirty-five patients were admitted to the Pediatric Intensive Care Unit; out of these, six suffered from shock, one needed an amputation of the right foot and of four left toes, and two had skin transplantation. According to the Pediatric Overall Performance Score, 36 (10.5%) showed a mild overall disability, 3 (0.8%) a moderate, and 1 (0.2%) a severe overall disability at discharge. A causative organism was detected in 65% (247/380) of patients. Staphylococcus aureus (S. aureus) was identified in 57.1% (141/247) of microbiological confirmed cases, including 1 (0.7%) methicillin-resistant S. aureus (MRSA) and 6 (4.2%) Panton-Valentine leukocidin (PVL)-producing S. aureus, followed by Group A Streptococcus (18.2%) and Kingella kingae (8.9%). K. kingae and PVL production in S. aureus were less frequently reported than expected from the literature.ConclusionPOAIs are associated with a substantial morbidity in European children, with S. aureus being the major detected pathogen. In one-third of patients, no causative organism is identified. Our observations show an urgent need for the development of a vaccine against S. aureus and for the development of new microbiologic diagnostic guidelines for POAIs in European pediatric hospitals.

Clonal diversity and genomic characterization of Panton-valentine Leukocidin (PVL)-positive Staphylococcus aureus in Tehran, Iran

BackgroundSome Staphylococcus aureus strains produce Panton-Valentine leukocidin (PVL), a bi-component pore-forming toxin, which causes leukocyte lysis and tissue necrosis. Currently, there is very limited information on the molecular epidemiology of PVL-encoding S. aureus strains in Iran. This study aimed to determine the molecular epidemiology and genetic background of PVL-positive S. aureus clinical strains isolated from Iranian patients.MethodsA total of 28 PVL-positive S. aureus strains were detected from 600 S. aureus isolates between February 2015 and March 2018 from different hospitals in Tehran, Iran. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Molecular genotyping was performed using SCCmec and accessory gene regulator (agr) typing, PVL haplotyping, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE).ResultsThe highest antibiotic resistance rate was found to be against erythromycin (57.1%), followed by ciprofloxacin (42.8%) and clindamycin (35.7%). Moreover, 19 (67.9%) out of 28 S. aureus isolates were identified as MRSA, including CA-MRSA (14/19, 73.7%) and HA-MRSA (5/19, 26.3%). SCCmec type IVa was detected as the predominant type (10/19, 52.6%), followed by type III (5/19, 26.3%) and type V (4/19, 21.1%). The agr type I was identified as the most common type (14/28, 50%), and H and R haplotype groups were observed at frequencies of 67.9 and 32.1%, respectively. Among H variants, the predominant variant was H2 (78/9%). The isolates encompassed 21 different sequence types (STs), including 16 new STs (ST5147 to ST5162). Based on eBURST analysis, the isolates were clustered into five CCs, including CC30, CC22, CC1, CC8, and CC5 (ST5160), and nine singletons. PFGE typing showed that 24 isolates were clustered into A (4 pulsotypes), B (9 pulsotypes), and C (11 pulsotypes) clusters.ConclusionsA high prevalence of PVL-positive CA-MRSA strains was detected in Iran. The majority of PVL-positive isolates were of H (mostly H2) variant, while R variant was harbored by 100% of PVL-positive MRSA strains. Also, CC8, CC22, and CC30 were identified as the dominant clones among PVL-encoding S. aureus strains. This study promotes a better understanding of the molecular epidemiology and evolution of PVL-positive S. aureus strains in Iran.

The First Report of a Methicillin-Resistant Staphylococcus aureus Isolate Harboring Type IV SCCmec in Thailand.

Methicillin-resistant Staphylococcus aureus (MRSA) is mostly found in Thailand in the hospital as a nosocomial pathogen. This study aimed to report the genetic characterization of a clinical community-acquired MRSA (CA-MRSA) isolate collected from hospitalized patients in Thailand. Among 26 MRSA isolates, S. aureus no. S17 preliminarily displayed the presence of a staphylococcal cassette chromosome mec (SCCmec) type IV pattern. The bacterial genomic DNA was subjected to whole-genome sequencing. Panton–Valentine leukocidin (PVL) production, virulence toxins, and antibiotic resistance genes were identified, and multi-locus sequence typing (MLST) and spa typing were performed. The strain was matched by sequence to MLST type 2885 and spa type t13880. This strain carried type IV SCCmec with no PVL production. Five acquired antimicrobial resistance genes, namely blaZ, mecA, Inu(A), tet(K), and dfrG conferring resistance to β-lactams, lincosamides, tetracycline, and trimethoprim, were identified. The detected toxins were exfoliative toxin A, gamma-hemolysin, leukocidin D, and leukocidin E. Moreover, there were differences in seven regions in CR-MRSA no. S17 compared to CA-MRSA type 300. In summary, we have reported the ST2885-SCCmec IV CA-MRSA clinical strain in Thailand for the first time, highlighting the problem of methicillin resistance in community settings and the consideration in choosing appropriate antibiotic therapy.

#82: Osteomyelitis with Panton-Valentine Leukocidin Producing Staphylococcus aureus Strains, Experience in a Tertiary Pediatric Hospital in Mexico City

Abstract Background S. aureus is the most common cause of osteomyelitis in children. Panton-Valentine leucocidin (PVL) is an exotoxin produced by certain S. aureus strains, which can be detected in both methicillin-sensitive and -resistant strains of staphylococci. Pediatric osteomyelitis by PVL producing S. aureus constitute a rare, but highly critical event. They are characterized by a rapid course of marked inflammation, worsening under conservative therapy, and a high rate of recurrence. No information is available on osteomyelitis and Panton-Valentine leukocidin producing S. aureus in Mexico. Objective The aim of this study was to determine the molecular characterization of S. aureus strains isolated in pediatric patients with osteomyelitis and their clinical features in a tertiary hospital in Mexico City. Methods We conducted a prospective study of children admitted for osteomyelitis, between December 2018 and November 2019, at Instituto Nacional de Pediatría. We obtained an informed consent in children under 12 years of age and an informed assent in children over 12. The confirmation of the S. aureus isolates was performed by amplification and analysis of 16S rRNA and nuc genes. The mecA and pvl genes were detected by PCR, the clinical features were obtained at the admission. Results Fifty patients were included and 26 cases of osteomyelitis were diagnosed, 13 were due to staphylococcus aureus genus and 6 due to S. aureus; all of them were methicillin susceptible and two were PVL producers. Both patients had a severe initial presentation, with extensive local abscesses, and one required three surgical procedures and developed septic pulmonary embolism. The two patients received double antimicrobial treatment and required a long therapy interval. Conclusions Osteomyelitis with Panton-Valentine Leukocidin producing S. aureus seems to be more severe. In patients with severe osteomyelitis, it is essential to detect the PVL toxin because they require early surgical intervention and prolonged intravenous therapy. Our findings suggest that the severity of the osteomyelitis is linked with PVL production more than with methicillin resistance due to that all our isolates were methicillin susceptible.

Rapidly fatal tropical pyomyositis in an elderly diabetic woman

Necrotizing soft tissue infection, with or without myositis, is classified among the most dangerous infectious emergencies in clinical practice. The authors report a case of an older diabetic woman who presented to the orthopedic service with right elbow pain after a small trauma with skin abrasion and released with an analgesic prescription. After 48h, she presented to the emergency room with a history of developing bullous and necrotic lesions in the upper right limb, hypotension, and numbness, with rapid and fatal evolution despite adequate clinical and surgical therapeutic support. Muscle biopsy showed necrotizing myositis. Blood culture was positive for Panton-Valentine leukocidin producing (PVL-positive) methicillin-resistant S. aureus. Although PVL has a strong epidemiologic association with Community-Acquired Methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, it can also be found in CA-MSSA in the context of necrotizing pneumonia and skin and soft tissue infections. Although infrequent, CA-MRSA or CA-MSSA PVL+ infections should always be suspected in high-risk patients because they can rapidly evolve with severe, sometimes fatal complications.

Recurrent mucocutaneous infections caused by PVL-positive Staphylococcus aureus strains: a challenge in clinical practice.

Recurrent mucocutaneous infections caused by PVL-positive Staphylococcus (S.) aureus strains represent an increasing problem in Germany. Although there have been several outbreaks at day care centers and in urban communities in recent years, there are currently no diagnostic algorithms or treatment recommendations for these particular infections in Germany. We performed a literature search in the PubMed/MEDLINE database with the goal of developing an algorithm for diagnosis and treatment of these infections. National and international recommendations were also considered. Panton-Valentine leukocidin (PVL) is a pore-forming protein produced by certain S.aureus strains. Both methicillin-susceptible (MSSA) and methicillin-resistant S.aureus (MRSA) strains may carry the lukS-lukF gene responsible for PVL production. The clinical presentation of infections caused by PVL-positive S.aureus ranges from isolated recurrent abscesses to extensive furunculosis. Despite adequate treatment of primary infections, approximately 40% of patients develop recurrent disease. The choice of treatment regimen is guided by the clinical presentation of the infection. In addition, some scientific literature recommends bacteriological screening of patients and their contacts, followed by decolonization of affected individuals. The present article focuses on the pathogenesis and risk factors of recurrent mucocutaneous infections caused by PVL-positive S.aureus strains and proposes a diagnostic and therapeutic algorithm for optimal patient care.

Timing Is Everything: Impact of Naturally Occurring Staphylococcus aureus AgrC Cytoplasmic Domain Adaptive Mutations on Autoinduction.

Mutations in the polymorphic Staphylococcus aureusagr locus responsible for quorum sensing (QS)-dependent virulence gene regulation occur frequently during host adaptation. In two genomically closely related S. aureus clinical isolates exhibiting marked differences in Panton-Valentine leukocidin production, a mutation conferring an N267I substitution was identified in the cytoplasmic domain of the QS sensor kinase, AgrC. This natural mutation delayed the onset and accumulation of autoinducing peptide (AIP) and showed reduced responsiveness to exogenous AIPs. Other S. aureus strains harboring naturally occurring AgrC cytoplasmic domain mutations were identified, including T247I, I311T, A343T, L245S, and F264C. These mutations were associated with reduced cytotoxicity, delayed/reduced AIP production, and impaired sensitivity to exogenous AIP. Molecular dynamics simulations were used to model the AgrC cytoplasmic domain conformational changes arising. Although mutations were localized in different parts of the C-terminal domain, their impact on molecular structure was manifested by twisting of the leading helical hairpin α1-α2, accompanied by repositioning of the H-box and G-box, along with closure of the flexible loop connecting the two and occlusion of the ATP-binding site. Such conformational rearrangements of key functional subdomains in these mutants highlight the cooperative response of molecular structure involving dimerization and ATP binding and phosphorylation, as well as the binding site for the downstream response element AgrA. These appear to increase the threshold for agr activation via AIP-dependent autoinduction, thus reducing virulence and maintaining S. aureus in an agr-downregulated "colonization" mode.IMPORTANCE Virulence factor expression in Staphylococcus aureus is regulated via autoinducing peptide (AIP)-dependent activation of the sensor kinase AgrC, which forms an integral part of the agr quorum sensing system. In response to bound AIP, the cytoplasmic domain of AgrC (AgrC-cyt) undergoes conformational changes resulting in dimerization, autophosphorylation, and phosphotransfer to the response regulator AgrA. Naturally occurring mutations in AgrC-cyt are consistent with repositioning of key functional domains, impairing dimerization and restricting access to the ATP-binding pocket. Strains harboring specific AgrC-cyt mutations exhibit reduced AIP autoinduction efficiency and a timing-dependent attenuation of cytotoxicity which may confer a survival advantage during established infection by promoting colonization while restricting unnecessary overproduction of exotoxins.

Bone and joint infections with Staphylococcus aureus strains producing Panton-Valentine Leukocidin in French Guiana.

The aim of this study was to describe the clinical features of bone and joint infections (BJI) due to Panton-Valentine Leukocidin producing (PVL+) Staphylococcus aureus (SA) in French Guiana.A multicenter study that consists of a retrospective charts review of children admitted for PVL+ S. aureus BJI between January 2010 and December 2015.Six patients with SA-PVL BJI were identified during the study period: 2 osteomyelitis, 1 septic arthritis, and 3 disseminated BJI. The median age was 11 years old (4–14 years), and fever lasted for 3.2 days (2–5 days) before diagnosis. An open skin wound preceded the BJI in 5/6 patients. One patient presented with a septic thrombophlebitis of the femoral-popliteal vein on admission. Methicillin-susceptible Staphylococcus aureus (MSSA) were identified for all patients. Three patients had complications: 2 cases of necrotizing pneumonia and 2 pericarditis, with 1 death caused by cardiac tamponade.SA-PVL BJI was not frequent. Strains were susceptible to methicillin, but responsible of severe BJI. Early diagnosis and a multidisciplinary management of these infections are essential to prevent further complications.

Tokiinshi, a traditional Japanese medicine (Kampo), suppresses Panton-Valentine leukocidin production in the methicillin-resistant Staphylococcus aureus USA300 clone.

It is necessary to develop agents other than antimicrobials for the treatment of Staphylococcus aureus infections to prevent the emergence of antimicrobial-resistant strains. Particularly, anti-virulence agents against the Panton-Valentine leukocidin (PVL)-positive methicillin-resistant S. aureus (MRSA), USA300 clone, is desired due to its high pathogenicity. Here, we investigated the potential anti-virulence effect of Tokiinshi, which is a traditional Japanese medicine (Kampo) used for skin diseases, against the USA300 clone. A growth inhibition assay showed that a conventional dose (20 mg/ml) of Tokiinshi has bactericidal effects against the clinical USA300 clones. Notably, the growth inhibition effects of Tokiinshi against S. epidermidis strains, which are the major constituents of the skin microbiome, was a bacteriostatic effect. The data suggested that Tokiinshi is unlikely to affect skin flora of S. epidermidis. Furthermore, PVL production and the expression of its gene were significantly suppressed in the USA300 clone by a lower concentration (5 mg/ml) of Tokiinshi. This did not affect the number of viable bacteria. Moreover, Tokiinshi significantly suppressed the expression of the agrA gene, which regulates PVL gene expression. For the first time, our findings strongly suggest that Tokiinshi has the potential to attenuate the virulence of the USA300 clone by suppressing PVL production via agrA gene suppression.

The effects of iclaprim on exotoxin production in methicillin-resistant and vancomycin-intermediate Staphylococcus aureus.

Extracellular protein toxins contribute to the pathogenesis of Staphylococcus aureus infections. The present study compared the effects of iclaprim and trimethoprim - two folic acid synthesis inhibitors - with nafcillin and vancomycin on production of Panton-Valentine leukocidin (PVL), alpha haemolysin (AH) and toxic-shock syndrome toxin I (TSST-1) in methicillin-resistant and vancomycin-intermediate S. aureus (MRSA and VISA, respectively). Northern blotting and RT-PCR were used to assess gene transcription; toxin-specific bioassays were used to measure protein toxin production. As shown previously, sub-inhibitory concentrations (sub-MIC) of nafcillin increased and prolonged MRSA toxin gene transcription and enhanced PVL, TSST-1 and AH production. Sub-inhibitory doses of iclaprim and trimethoprim delayed maximal AH gene (hla) transcription and suppressed AH production; both drugs delayed, but neither reduced, maximal TSST-1 production. Trimethoprim significantly increased lukF-PV expression and PVL production compared to both untreated and iclaprim-treated cultures. Higher concentrations of iclaprim and trimethoprim markedly suppressed MRSA growth, mRNA synthesis and toxin production. In VISA, iclaprim, vancomycin and nafcillin variably increased tst and hla expression, but only nafcillin increased toxin production. Despite its ability to increase hla expression, iclaprim was the most potent inhibitor of AH production. We conclude that, due to its ability to suppress toxin production, iclaprim should be effective against severe staphylococcal infections caused by toxin-producing MRSA and VISA strains, especially given its ability to concentrate at sites of infection such as skin and skin structures and the lung.

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.

Effects of Iclaprim and Trimethoprim on Exotoxin Production by Methicillin-resistant Staphylococcus aureus

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) causes serious, often life-threatening, infections. Exotoxins such as alpha-hemolysin (AH), Panton Valentine leukocidin (PVL), and Toxic shock syndrome toxin 1 (TSST-1) mediate pathogenesis and inhibition of toxin production is an important consideration in choosing appropriate treatments. Vancomycin is recommended for severe MRSA infections; however, increasing vancomycin resistance, poor clinical outcomes and nephrotoxicity are serious concerns. Thus newer agents are needed, including those that block bacterial toxin production. In the current study, we compared the effects of sub-inhibitory doses (sub-MIC) of two folic acid inhibitor antibiotics (iclaprim, trimethoprim) with cell wall-active agents (nafcillin, vancomycin) on transcription and translation of AH, PVL and TSST-1 in two clinical MRSA isolates.MethodsCommunity-acquired MRSA strains 1560 (a USA400 strain; AH+, TSST-1+, PVL-) and 04014 (CDC strain 368–04; AH+, TSST-1-, PVL+) were studied. MICs were determined by standard microbroth dilution. Gene expression was studied by northern blotting and/or qRT-PCR; toxins were quantitated by ELISA (PVL and TSST-1) and rabbit erythrocyte lysate assay (AH).ResultsIn agreement with our previous findings, nafcillin increased production of AH, TSST-1, and PVL compared with untreated control cultures. In both MRSA strains, iclaprim and trimethoprim delayed the onset of mRNA production and shifted its peak production to later time points. Both iclaprim and trimethoprim suppressed AH production in both strains of MRSA and delayed, but did not reduce, maximal TSST-1 production in MRSA1560. Trimethoprim significantly increased maximal PVL production over both untreated and iclaprim-treated cultures.ConclusionThe folic acid antagonist antibiotics, iclaprim and trimethoprim, altered both mRNA synthesis dynamics and protein toxin production in MRSA at concentrations below those that inhibit bacterial growth. These results, plus the fact that iclaprim is 15-fold more active than trimethoprim (MICs = 0.13 and 2.0 ug/ml, respectively), provide additional rationale for the use of iclaprim to treat complicated MRSA infections.Disclosures A. Bryant, Motif Biosciences: Grant Investigator, Research grant; D. Huang, Motif Bio: Employee, Salary; D. Stevens, Motif Biosciences: Grant Investigator, Research grant

Un cas atypique de pneumopathie nécrosante staphylococcique !

Some strains of Staphylococcus aureus produce a toxin known as Panton-Valentine leukocidin. These strains notably cause a necrotizing pneumonia which is associated with a high mortality. A 70-year-old woman presented with sub-acute onset dyspnea, low-grade fever, and hemoptysis after a trip to Dubai and New Zealand. Computed tomography showed bilateral necrotizing pneumonia, suggesting the diagnosis of pneumonia caused by S.aureus producing Panton-Valentine toxin. It was confirmed by microbiological investigation. The rapid initiation of adequate antimicrobial therapy including an effective antitoxin was essential for successful treatment, without the need for ventilatory support. Necrotizing pneumonia caused by S.aureus producing Panton-Valentine leukocidin usually occurs in young subjects without comorbidities. Typical symptoms are a combination of hypoxemia, high fever, hemoptysis, leukopenia, and a rapidly worsening condition. Panton-Valentine leukocidin should not be discarded if not all the symptoms are typical. Antibiotic therapy including an antitoxin drug such as linezolid or clindamycin should be initiated promptly.

GENETIC MECHANISMS OF METHICILLIN RESISTANCE IN STAPHYLOCOCCUS AUREUS (MRSA) AND ITS CAPACITY OF TRANSMISSION: A BRIEF REVIEW

Methicillin-resistant Staphylococcus aureus is one of the most important human pathogens. Th ese bacteria have the ability to colonize animals andcross species barriers. Th ree major groups of MRSA strains have emerged. Healthcare associated MRSA and community acquired MRSA strains have potential to spread worldwide and oft en persist in hospitals and communities as clonal strains. Th e livestock-associated MRSA has been isolated from healthy human carriers but also from infected patients all around the world. Molecular typing of staphylococcal cassette chromosome mec (SCCmec), multilocus sequence typing in combination with pulse fi eld gel electrophoresis and spa typing are most frequently used for genetic characterization of MRSA strains. Th e community-acquired MRSA strains are capable of producing Panton Valentine leukocidin (PVL) cytotoxin which is their major virulence determinant. MRSA strains possess a number of virulence factors that are common in other bacteria and it is still not entirely explained which virulence factors or mechanisms of their regulation are important for the pathogenic potential, persistence in the environment or the ability to cause detrimental infection in patients. Recently, as a contribution to the progress of molecular biology, peculiar mechanisms of genetic regulation of virulence genes have been discovered and their role in pathogenesis of infection and epidemiology of MRSA has been studied.

Frequency of Fibronectin Binding Protein A and Panton-Valentine Leukocidin in Methicillin-Resistant Staphylococcus aureus Collected From Educational Hospitals in Qazvin, Iran

Background: Staphylococcus aureus is one of the most important organisms involved in nosocomial infection acquired by patients. In recent years, the appearance of methicillin-resistant S. aureus (MRSA) has turned the treatment of these infections into a serious challenge. Surface proteins, such as fibronectin binding proteins (FnBP), and the ability to produce Panton-Valentine leukocidin (PVL) are important factors in pathogenesis of this organism. Objectives: The purpose of this study was to determine the prevalence of disease-associated genes in the clinical isolates of S. aureus encoding FNB and PVL, collected from the educational hospitals of Qazvin, Iran. Patients and Methods: This was a descriptive, cross-sectional study in which a total of 103 isolates of methicillin-resistant S. aureus were collected from hospitalized patients in teaching hospitals of Qazvin, during 2013 - 2014. Initially, the identification of isolates was performed according to the standard laboratory methods, followed by confirming the presence of the femA gene, a gene specific to S. aureus. Later, the prevalence of virulence genes (fnb and pvl) was investigated by the PCR method, using specific primers. PCR products were sequenced to confirm the presence of the target genes. Results: The results of this study showed that among 103 isolates of S. aureus resistant to methicillin, 88 isolates were positive for the presence of the pvl and fnb genes, with the fnb gene present in 86 (83.5%) isolates and the pvl gene only in 2 (1.9%) isolates. Conclusions: The results of the present study indicate the presence of the pvl and fnb genes in the strains of S. aureus isolated from clinical specimens collected from the patients admitted to teaching hospitals in Qazvin. Considering the clinical significance of these organisms, and their potential in threatening public health systems, the identification, treatment, and infection control management of patients infected with these organisms is of prime necessity.

Outbreak of Panton-Valentine Leukocidin-Associated Methicillin-Susceptible Staphylococcus aureus Infection in a Rugby Team, France, 2010-2011.

Staphylococcus aureus strains that produce Panton-Valentine leukocidin are known to cause community infections. We describe an outbreak of skin abscesses caused by Panton-Valentine leukocidin–producing methicillin-susceptible S. aureus (clonal complex 121) in a professional rugby team in France during July 2010–February 2011. Eight team members were carriers; 7 had skin abscesses.

Necrotizing pneumonia due to clonally diverse Staphylococcus aureus strains producing Panton-Valentine leukocidin: the Czech experience.

A prospective study (2007-2013) was undertaken to investigate clinical features and prognostic factors of necrotizing pneumonia caused by Staphylococcus aureus producing Panton-Valentine leukocidin (PVL) in the Czech Republic. Twelve cases of necrotizing pneumonia were detected in 12 patients (median age 25 years) without severe underlying disease. Eight cases occurred in December and January and the accumulation of cases in the winter months preceding the influenza season was statistically significant (P < 0·001). The course of pneumonia was very rapid, leading to early sepsis and/or septic shock in all but one patient. Seven patients died and mortality was fourfold higher in those patients presenting with primary pneumonia than with pneumonia complicating other staphylococcal/pyogenic infection elsewhere in the body. The S. aureus isolates displayed considerable genetic variability and were assigned to five lineages CC8 (n = 3), CC15 (n = 2), CC30 (n = 2), CC80 (n = 1), and CC121 (n = 3) and one was a singleton of ST154 (n = 1), all were reported to be associated with community-acquired infection. Four strains were methicillin resistant. The high case-fatality rate can only be reduced by improving the speed of diagnosis and a rapid test to detect S. aureus in the airways is needed.

Infections sévères à Staphylococcus aureus sécréteurs de la leucocidine de Panton–Valentine chez l’enfant : un large spectre de presentations cliniques

Panton-Valentine leukocidin (PVL) is a major toxic virulence factor secreted by community-acquired methicillin-sensitive or methicillin-resistant Staphylococcus aureus (SA). SA-PVL can be responsible for life-threatening infections in healthy children with a wide spectrum of clinical presentations involving lung, skin, and soft tissues or bones and joints. PVL production should always be considered in severe SA infections. The pediatric medicine community remains poorly informed regarding the therapeutic management of this infection, which should be early and aggressive. Intravenous empiric antibiotics against SA and its toxins must be given with early and sometimes iterative surgical procedures to drain abscesses and to stop bacterial proliferation and necrosis in the tissues. Here, we report the cases of three patients admitted for SA-PVL infections to the pediatric intensive care unit. Initial clinical presentation in the three patients was multifocal osteomyelitis associated with necrotizing pneumonia; severe skin infection with septic shock; and non-necrotic pneumonia with pleural and pericardial effusion. Appropriate treatments resulted in a good outcome in all cases. Following these illustrations, we describe a number of practical key points in the optimal medical and surgical management of severe SA-PVL infections, with a review of the literature.