Spontaneous community-acquired PVL-producing Staphylococcus aureus mediastinitis in an immunocompetent adult - a case report.

BACKGROUND: Mediastinitis caused by hematogenous spread of an infection is rare. We report the first known case of community-acquired mediastinitis from hematogenous origin in an immunocompetent adult. This rare invasive infection was due to Panton-Valentine Leucocidin-producing (PVL+) methicillin-susceptible Staphylococcus aureus (MSSA). CASE PRESENTATION: A 22-year-old obese man without other medical history was hospitalized for febrile precordial chest pain. He reported a cutaneous back abscess 3 weeks before. CT-scan was consistent with mediastinitis and blood cultures grew for a PVL+ MSSA. Intravenous clindamycin (600 mg t.i.d) and cloxacillin (2 g q.i.d.), secondary changed for fosfomycin (4 g q.i.d.) because of a related toxidermia, was administered. Surgical drainage was performed and confirmed the presence of a mediastinal abscess associated with a fistula between the mediastinum and right pleural space. All local bacteriological samples also grew for PVL+ MSSA. In addition to clindamycin, intravenous fosfomycin was switched to trimethoprim-sulfamethoxazole after 4 weeks for a total of 10 weeks of antibiotics. CONCLUSIONS: We present the first community-acquired mediastinitis of hematogenous origin with PVL+ MSSA. Clinical evolution was favorable after surgical drainage and 10 weeks of antibiotics. The specific virulence of MSSA PVL+ strains played presumably a key role in this rare invasive clinical presentation.

Osteomyelitis, Venous Thrombosis, and Septic Emboli in a Pediatric Patient: A Case Report.

New virulence factors, such as the Panton-Valentine leukocidin (PVL), are appearing during Staphylococcus aureus infections occurring in the pediatric population. Such factors increase the aggressiveness and risk of dissemination of the bacteria, causing infections to be life-threatening. An early diagnosis is thus especially important. We present a case of osteomyelitis, venous thrombosis, and septic emboli occurring in a pediatric patient that should trigger suspicion of a PVL-positive strain. A multidisciplinary approach is necessary to enable rapid diagnosis and early treatment, which is essential for successful management of these infections. Management is based on broad-spectrum antibiotics, in combination with aggressive surgical treatment and antithrombotic therapy. In patients infected with S. aureus whose condition worsens quickly, PVL gene sequencing should be considered.

[Investigation of the presence of pantone-valentine leukocidin in Staphylococcus aureus strains isolated from orthopedic surgical site infections]. / Ortopedik cerrahi alan enfeksiyonlarindan izole edilen Staphylococcus aureus'larda panton-valentine lökosidin varliginin arastirilmasi.

Staphylococcus aureus is one of the most clinically important bacteria causing infection in humans. It is an important pathogen in surgical site infections (SSIs), especially after orthopedic surgery. Pantone-valentine leukocidin (PVL) has a great importance in the virulence of S.aureus because it can destroy polymorphonuclear cells by necrosis or apoptosis. The spread of PVL positive S.aureus is a great concern, since it may become an important factor for increased morbidity and mortality in SSIs, especially after surgery. In this study, we aimed to investigate the presence of PVL in S.aureus strains isolated from patients who had surgical site infections after orthopedic surgery, and also the clinical status of these patients. Between 2013 and 2017, 101 patients who had SSIs due to S.aureus after orthopedic surgery were included in the study. Identification of the strains was determined by conventional methods and "Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry" (MALDI-TOF MS). Methicillin resistance was determined by Kirby-Bauer disc diffusion method and automated system (Vitek 2, bioMérieux, France). The PVL gene region was investigated by polymerase chain reaction (PCR) method by using the primers Luk-PV-1 and Luk-PV-2. The duration of the patients' hospitalization, C-reactive protein (CRP) and sedimentation levels and clinical status were obtained from the hospital information system, retrospectively. Fifteen (14.9%) of the isolates were methicillin resistance S.aureus (MRSA) and 86 (85.1%) were methicillin susceptibility S.aureus (MSSA). PVL positivity was detected in 14 (13.9%) isolates (3 MRSA, 11 MSSA). The mean hospital stays in PVL-negative patients were 17 (5-73) days and 46 (21-103) days in PVL-positive patients. It was observed that the serologic markers CRP and sedimentation were between 5-7 and 40-60 in PVL negative patients, and between 11-20 and 90-110 in PVL positive patients, respectively. In PVL-negative patients, serologic markers improved in 7-10 days, while in PVL-positive patients they were improved in 17-32 days. Osteomyelitis occurred in six patients (2 PVL positive MRSA, 1 PVL positive MSSA and 3 PVL negative MRSA). In two of the patients who have developed osteomyelitis with PVL-positive MRSA, PVL gene positive S.aureus isolates were observed in their orthopedic SSIs. We also determined that these isolates increased the hospitalization days, improvement time of serological markers and mortality. It is worrisome to isolate PVL-positive S.aureus strains in SSIs. Therefore, we believe that it would be useful to take infection control measures to prevent the spread of these strains in the hospital setting.

Prevalence of Panton-Valentine leucocidin and phenotypic and genotypic characterization of biofilm formation among Staphylococcus aureus strains isolated from children with adenoid hypertrophy.

Adenoids as a first line of host defense against respiratory microbes play an important role in majority of upper airway infectious and noninfectious illnesses. Bacterial pathogen can colonize on the adenoid tissue and probably act as a reservoir for them. To determine phenotypic and genotypic characterization of biofilm forming capacity of Staphylococcus aureus isolates from children with adenoid hypertrophy and prevalence of Panton-Valentine leukocidin (PVL) gene we collected 17 consecutive, clinically significant S. aureus isolates from children with adenoid hypertrophy undergoing adenoidectomy with one or more of the upper airway obstruction symptoms, nasal obstruction, mouth breathing, snoring, or sleep apnea. Biofilm formation was evaluated by colorimetric microtiter plate's assay. Gene encoding PVL and adhesion- or biofilm formation-encoding genes were targeted by polymerase chain reaction (PCR) assay. According to the results, all strains produced biofilm. Seven (41.2%) isolates produced strong biofilm whereas 7 (41.2%) isolates produced week and 3 (17.6%) isolates produced medium biofilm. Regarding the adhesion- or biofilm formation-encoding genes, 16 (94.1%) isolates were positive for the gene eno, 13(76.4%) for icaA, 13 (76.4%) for icaD, 10 (58.8%) for fib, 10 (58.8%) for fnbB, 4(23.5%) for can, and 1(5.8%) for fnbA. The high prevalence of genes encoding biofilms and adhesins and phenotypic ability to form a biofilm by S. aureus strains emphasizes the pathogenic character of strains isolated from children with adenoid hypertrophy.

Evaluation of the R-Biopharm RIDA®GENE Panton-Valentine leukocidin (PVL) kit for the detection of Staphylococcus aureus PVL from pus samples.

Staphylococcus aureus Panton-Valentine leukocidin (PVL) is associated with primary skin and soft-tissue infections (SSTI). We aimed to divert the RIDA®GENE PVL kit (RBiopharm) from its intended use on cultures to the detection of PVL-encoding genes directly from pus samples. Performance was compared with that of the in-house PCR method developed by the French National Reference Centre for Staphylococci. From June 2013 to May 2014, pus samples from S. aureus SSTI were tested. Our in-house PCR was performed on parallel cultures as the gold standard, while the RIDA®GENE PVL assay was used directly on pus samples from the sterile container, or a swab or an Eswab previously dipped in the pus. The kit specificity was also evaluated with pus samples that grew Streptococcus pyogenes. S. aureus reference strains harboring PVL-encoding genes, including known polymorphisms, were also tested. A total of 56 S. aureus-containing pus samples (28 PVL + and 28 PVL-) were collected and analyzed. Sensitivity and specificity of the commercial kit were 96.4 % and 100 % respectively, with equal performance whether tested directly from the sterile container or the Eswab. Sensitivity was lower (67.9 %) when the test was performed from a regular SSTI swab. None of the Streptococcus pyogenes pus samples scored positive (n = 5). Specificity was assessed using reference strains (n = 14); in all strains the PVL gene was correctly detected. This study identified the RIDA®GENE PVL kit as an efficient, sensitive, and specific tool for the rapid detection of PVL-encoding genes in pus samples.

Panton-Valentine leukocidin positive Staphylococcal aureus infections of the head and neck: case series and brief review of literature.

Panton-valentine leukocidin (PVL) is a pore-forming cytotoxin produced by some clones of Staphylococcus aureus that is associated with infections ranging from uncomplicated skin and soft tissue infections to life-threatening necrotizing pneumonia. PVL S aureus-associated maxillofacial infections are rarely reported; therefore, a high degree of clinical suspicion is warranted and close liaison with microbiologists and appropriate samples are required for optimal management. This report discusses the management and learning points from 3 such cases managed by the Greater Glasgow and Clyde National Health Service maxillofacial surgical teams.

[Ecthyma gangrenosum associated with infection involving a methicillin-sensitive, Panton-Valentine-negative strain of Staphylococcus aureus]. / Ecthyma gangréneux dû à une souche de Staphylococcus aureus sensible à la méthicilline et non sécrétrice de toxine de Panton-Valentine.

BACKGROUND: Ecthyma gangrenosum (EG) is an anatomoclinical syndrome commonly associated with Pseudomonas aeruginosa cutaneous infection. Other microorganisms have also been incriminated on occasion, with other viral, fungal and bacterial agents potentially causing EG. In this report, we present an extremely rare case of an EG caused by methicillin-sensitive Staphylococcus aureus (MSSA) infection. This case, highly characteristic of EG both clinically and histologically, calls into question the physiopathological mechanisms of the disease and provides a reminder that it may be caused by a variety of organisms. PATIENTS AND METHODS: A 62-year-old woman, followed for HIV seropositivity at the AIDS stage, developed a painful purpuric skin rash evolving towards necrotic nodules characteristic of ecthyma gangrenosum. Skin biopsy confirmed the diagnosis of EG due to methicillin-sensitive S. aureus (MSSA) infection without toxins or bacteraemia. DISCUSSION: To the best of our knowledge, this is the first case in the literature in which MSSA is reported as the underlying cause of such lesions.

[Panton-Valentine leukocidin in patients with chronic wounds. Results from a clinical investigation in 100 patients]. / Panton-Valentine Leukozidin in chronischen Wunden. Ergebnisse einer klinischen Untersuchung bei 100 Patienten.

BACKGROUND: The toxin Panton-Valentine leukocidin (PVL) produced by S. aureus is known as a virulence factor that leads to severe infections of skin and soft tissue. However the effect of PVL on wound healing is not known yet. Therefore we examined the detection rate of PVL in patients with chronic wounds. PATIENTS AND METHODS: The study included 100 patients with chronic wounds of the lower limb. We determined in all S. aureus isolates the presence of the PVL gene using a PCR technique. RESULTS: Altogether 94% of the patients had a leg ulcer, while 6% had a foot ulcer; 65% were women. PVL was found in two patients. One of the strains was methicillin-resistant (MRSA) and the other was methicillin-sensitive (MSSA). CONCLUSION: In our investigation there was detection rate for PVL of 2% of all S. aureus isolates in patients with chronic wounds of the lower extremities. Although the role of PVL as a virulence factor of S. aureus in wound healing remains unclear, the detection of PVL should be taken as a cause for a consequent topical antimicrobial wound therapy because of the increased risk of serious infections.

Community-acquired skin infections caused by Staphylococcus aureus: What is the role of the Panton-Valentine leukocidin toxin?

BACKGROUND: The data concerning frequency and relevance of the toxin Panton-Valentine leukocidin (PVL) in skin infections caused by Staphylococcus aureus is controversial. The objective of the study was the identification of the role of the toxin in community-acquired skin infections caused by S. aureus. PATIENTS AND METHODS: We performed a retrospective analysis of 112 patients with the diagnosis of skin infections caused by S. aureus. Frequency of PVL was investigated by PCR for the lukSF gene. Risk factors and severity of the disease were analyzed. Furthermore, spa typing was done in 55 of the isolated S. aureus. RESULTS: PVL occurred in 45 % of patients with skin infections caused by methicillin-susceptible S. aureus; methicillin-resistant strains were positive in 63 %. Mean age was 30.9 years in PVL-positive infections and thus statistically highly significantly lower than in PVL-negative infections. There was no correlation between presence of PVL and severity and course of skin infections or presence of special risk factors. The spa types showed a high variability in PVL-positive as well as in PVL-negative strains. CONCLUSIONS: In our study the PVL status of S. aureus isolated from skin infections was neither correlated with methicillin-resistance nor with the severity of disease. Remarkably, PVL-positive S. aureus strains appeared to be more frequent in younger than in older patients. Our results demonstrate that routine determination of PVL status is not required since the outcome has no diagnostic or therapeutic consequences in daily dermatological practice.

Effects of linezolid on suppressing in vivo production of staphylococcal toxins and improving survival outcomes in a rabbit model of methicillin-resistant Staphylococcus aureus necrotizing pneumonia.

BACKGROUND: Linezolid is recommended for treatment of pneumonia and other invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA). The premise underlying this recommendation is that linezolid inhibits in vivo production of potent staphylococcal exotoxins, including Panton-Valentine leukocidin (PVL) and α-hemolysin (Hla), although supporting evidence is lacking. METHODS: A rabbit model of necrotizing pneumonia using MRSA clone USA300 was used to compare therapeutic effects of linezolid (50 mg/kg 3 times/day) and vancomycin (30 mg/kg 2 times/day) administered 1.5, 4, and 9 hours after infection on host survival outcomes and in vivo bacterial toxin production. RESULTS: Mortality rates were 100% for untreated rabbits and 83%-100% for vancomycin-treated rabbits. In contrast, mortality rates were 25%, 50%, and 100% for rabbits treated with linezolid 1.5, 4, and 9 hours after infection, respectively. Compared with untreated and vancomycin-treated rabbits, improved survival of rabbits treated 1.5 hours after infection with linezolid was associated with a significant decrease in bacterial counts, suppressed bacterial production of PVL and Hla, and reduced production of the neutrophil-chemoattractant interleukin 8 in the lungs. CONCLUSIONS: Across the study interval, only early treatment with linezolid resulted in significant suppression of exotoxin synthesis and improved survival outcomes in a rabbit model of MRSA necrotizing pneumonia.

Rapid detection of Panton-Valentine leukocidin in Staphylococcus aureus cultures by use of a lateral flow assay based on monoclonal antibodies.

Panton-Valentine leukocidin (PVL) is a virulence factor of Staphylococcus aureus, which is associated with skin and soft-tissue infections and necrotizing pneumonia. To develop a rapid phenotypic assay, recombinant PVL F component was used to generate monoclonal antibodies by phage display. These antibodies were spotted on protein microarrays and screened using different lukF-PV preparations and detection antibodies. This led to the identification of the optimal antibody combination that was then used to establish a lateral flow assay. This test was used to detect PVL in S. aureus cultures. The detection limit of the assay with purified native and recombinant antigens was determined to be around 1 ng/ml. Overnight cultures from various solid and liquid media proved suitable for PVL detection. Six hundred strains and clinical isolates from patients from America, Europe, Australia, Africa, and the Middle East were tested. Isolates were genotyped in parallel by DNA microarray hybridization for confirmation of PVL status and assignment to clonal complexes. The sensitivity, specificity, and positive and negative predictive values of the assay in this trial were 99.7, 98.3, 98.4, and 99.7%, respectively. A total of 302 clinical isolates and reference strains were PVL positive and were assigned to 21 different clonal complexes. In summary, the lateral flow test allows rapid and economical detection of PVL in a routine bacteriology laboratory. As the test utilizes cultures from standard media and does not require sophisticated equipment, it can be easily integrated into a laboratory's workflow and might contribute to timely therapy of PVL-associated infections.

[t030 is the most common spa type among methicillin-resistant Staphylococcus aureus strains isolated from Turkish hospitals]. / t030, Türkiye'deki Hastanelerden Izole Edilen Metisiline Dirençli Staphylococcus aureus Izolatlari Arasinda En Yaygin spa Tipidir.

Staphylococcus aureus is one of the most frequent agents causing hospital infections. S.aureus has a great ability to adapt itself to variety of conditions and successful clones can be epidemic and even pandemic by its ability spread from one continent to another. The aims of this study were to detect spa types of 397 methicillin-resistant S.aureus (MRSA) strains isolated from 12 centers in different geographical regions of Turkey from 2006 to 2008, and to investigate their clonality by PFGE and MLST typing. Additionally, 91 MRSA from four of those 12 centers isolated during 2011 were also studied for their spa types. PFGE profiles indicated the presence of a major pulsotype, namely pulsotype A with a rate of 91.4% (363/397), followed by pulsotype B (n= 18, 4.5%) and pulsotype C (n= 11, 2.8%). Among isolates tested 363 (91.4%) were SCCmec type III, 30 (7.6%) were SCCmec type IV. Sequence analysis of representative isolates revealed that ST239 (85.1%) was the most common MLST type followed by two MLST types ST737 (4%), and ST97 (2.8%), both SCCmec type IV. Two isolates were ST80 with SCCmec type IV. Of 397 isolates, 338 (85.1%) were t030, followed by t005 (2.5%) and t632 (2%). Among MRSA isolated during 2011, 64 (70.3%) of 91 were t030, 4 (4.4%) were t005, 2 (2.2%) were t015, and 2 (2.2%) were t1094. Among centers the t030 prevalence of 2006-2008 isolates ranged from 59-100%. The highest t030 prevalence was found in Ankara (100%) and lowest in Trabzon (59%) provinces which are located at central and northestern Anatolia, respectively. In Istanbul province, the prevalence of t030 was 94.5% among 2006-2008 isolates which decreased to 55.5% among 2011 isolates. Also a decrease in t030 rates was observed among samples from Konya and Trabzon but not from Aydin. Our results showed that the most common MRSA clone in Turkey is ST 239-SCCmec type III, t030 which persisted during the six years of the study period. Presence of PVL toxin gene was tested by PCR and 5 (3%) isolates found to be positive, of them two were SCCmec Type IV-ST80 and three were SCCmec Type III-ST239. This study is the largest epidemiological survey ever done in Turkey which showed presence of a hospital Turkish clone TR09 (ST239-SCCmecIII-t030) and a community clone TR10 (ST737-SCCmecIV-t005) largely disseminated in Turkey.

[Molecular epidemiology of Panton-Valentine leukocidin (PVL) -positive Staphylococcus aureus associated with skin and soft tissue infection].

Panton-Valentine leukocidin (PVL) secreted by Staphylococcus aureus is known to cause severe skin, soft tissue and lung infections. To assess the prevalence and genetic characteristics of PVL-positive S. aureus in our hospital, we investigated 86 S. aureus isolates isolated from skin and soft tissue pus between September 2011 and May 2012 at Daisan Hospital, the Jikei University School of Medicine (Tokyo, Japan). All isolates were investigated for the mecA gene and PVL gene by PCR amplification. The MRSA isolates confirmed were genotyped using SCCmec typing. PVL-gene positive isolates confirmed by the PVL-RPLA (reverse passive latex agglutination) assay were characterized by agr typing and multilocus sequence typing (MLST). Overall 6 (3 MSSA isolates and 3 MRSA isolates) PVL-positive strains (7.0%) were detected. The PVL prevalence was 11.1% in MRSA and 5.1% in MSSA. PVL-positive strains were isolated from young adults (range: 8-47 years) outpatient. Patients infected with PVL-positive MRSA were significantly younger than those infected with PVL-negative MRSA(32 and 68 years, respectively; P = 0.009, t-test). The 6 PVL positive strains were assigned by the MLST to 6 STs that were prevalent among PVL-positive strains. The SCCmec type of the PVL-positive MRSA were classified into 2 types (type IV or V) that were generally characteristic of CA-MRSA. Our data are consistent with some previous reports showing that PVL gene is found in certain ST strains. The PVL-positive strain must be taken into account when S. aureus is isolated from young adult SSTI.

Ovarian hyperstimulation syndrome complicated by severe community-acquired pneumonia due to methicillin-resistant Staphylococcus aureus positive for Panton-Valentine leukocidin.

We report a case of severe ovarian hyperstimulation syndrome (OHSS) complicated by community-acquired methicillin-resistant Staphylococcus aureus-Panton-Valentine leukocidin positive (CAMRSA-PVL[+]) necrotizing pneumonia, sepsis and multiple organ failure (MOF) in a previously immunocompetent female. The patient required prolonged ventilatory support and intensive care unit (ICU) hospitalization. Multiple cavities and severely affected lung function persist 1 year after discharge.

[Community-acquired methicillin resistant Staphylococcus aureus skin and soft tissue infections in Madrid: prevalence study]. / Prevalencia de infecciones de piel y tejidos blandos producidas por Staphylococcus aureus resistente a Meticilina Comunitario en Madrid.

INTRODUCTION: Since it was first described in the 1990s, Methicillin-Resistant Staphylococcus aureus infection among people with no contact with a hospital setting or with no traditional risk factors, has spread worldwide and is now an important epidemiological and public health problem. METHODS: The present prospective and observational study was carried out from April to November 2010. All adult patients with community-acquired suppurative skin and soft tissue infection (SSTI) attending the Emergency Department were enrolled. Clinical, microbiological and epidemiological features of the infection were assessed. RESULTS: A total of 59 samples were collected from 59 patients and CA-MRSA was isolated in 13 of them. Prevalence of CA-MRSA in patients with suppurative SSTI seen in the emergency department was 22.03%, and was 33.3% in patients with staphylococcal infection. Is worth noting the greater presence of necrosis detected in CA-MRSA lesions. Only 3 patients required hospital admission. Eleven of the 13 strains were Panton-Valentine leucocidin producers, and 5 were resistant to non-betalactam antibiotics. CA MRSA infection is still more frequent in the immigrant population. CONCLUSION: Data on CA-MRSA prevalence in Spain are sparse. This study aims to emphasise the current importance of this emergent pathogen in our area. About one third of suppurative staphylococcal SSTI presenting in our emergency department are caused by this agent, confirming a rapid spread in our country. Some clinical features, such as the high presence of necrosis, are closely related to CA-MRSA.

Multiplex real-time PCR assay for detection of methicillin-resistant Staphylococcus aureus and associated toxin genes.

We describe a real-time PCR assay for the detection of methicillin-resistant Staphylococcus aureus and genes encoding toxic shock syndrome toxin 1 and Panton-Valentine leukocidin. Rapid screening and detection of toxins is a useful tool for surveillance studies and outbreak investigations involving large numbers of isolates.

The matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS)-based protein peaks of 4448 and 5302 Da are not associated with the presence of Panton-Valentine leukocidin.

The Panton-Valentine leukocidin (PVL) of Staphylococcus aureus plays an important role in the pathogenesis of necrotizing pneumonia and recurrent skin and soft tissue infections. The gene encoding for PVL, lukS/F-PV, is distributed by prophages and can thus spread between isolates. Molecular methods have normally been used to identify lukS/F-PV-positive strains. Recently, however, a matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS)-based method has been described to identify PVL-positive S. aureus strains. The aim of this study was thus to investigate the association of distinct MALDI-TOF MS peaks to the toxin profile in molecularly characterized methicillin-susceptible (MSSA) and methicillin-resistant S. aureus (MRSA) strains harbouring lukS/F-PV. In contrast to the previous results, the MALDI-TOF MS peaks were detected in all 104 recently described molecularly divergent MRSA irrespective of the presence of PVL. Our result indicates that these described peaks seem to be independent of the presence of PVL.

Panton-Valentine leukocidin-positive Staphylococcus aureus strains are associated with follicular skin infections.

BACKGROUND/AIMS: Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus have been associated with suppurative infections; however, their precise role in skin infections has not been elucidated. We studied the rate of PVL-positive S. aureus in the different types of skin infections and compared follicular to nonfollicular skin infections. METHODS: In our institution, patients with a skin infection caused by S. aureus were enrolled in a prospective, observational cohort study (from July 1, 2003 to June 30, 2010). We studied the rate of PVL-positive S. aureus in the different clinical types of skin infections and compared the rate of PVL-positive S. aureus in follicular infections to that in nonfollicular infections. RESULTS: A total 229 skin infections were included: 97 (42.5%) were caused by PVL-positive strains. Thirty-nine of the 53 (74%) follicular infections [8 of the 17 (47%) with folliculitis, 30 of the 35 (85.5%) with furuncles and 1 with a carbuncle (100%)] were caused by PVL-positive S. aureus, compared to 16 of the 131 (12%) nonfollicular infections (p < 0.001). CONCLUSION: PVL-positive S. aureus strains are mainly associated with follicular skin infections.