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Concept: Panton-Valentine leukocidin

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BACKGROUND: Hitherto, methicillin-resistant Staphylococcus aureus (MRSA) has not been detected in Swedish cattle. However, due to the report of mecC, a novel homologue to the mecA gene, there was reason to re-evaluate susceptibility results from strain collections of Staphylococcus aureus and test suspected isolates for the presence of mecC. FINDINGS: Bovine isolates of S. aureus with elevated minimum inhibitory concentrations of beta-lactams were retrospectively tested for presence of mecC. In four of the isolates mecC was detected. CONCLUSION: In Sweden, this is the first finding of MRSA in cattle and the first detection of MRSA harbouring mecC of domestic animal origin. MRSA in animal populations has implications as a potential reservoir with risk for spread to humans. Occurrence of MRSA among Swedish cattle appears still very limited.

Concepts: Staphylococcus aureus, Antibiotic resistance, Milk, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Cattle, Oxacillin

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USA300 is a pandemic clonal lineage of hypervirulent, community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) with specific molecular characteristics. Despite its high clinical relevance, the evolutionary origin of USA300 remained unclear. We used comparative genomics of 224 temporal and spatial diverse S. aureus isolates of multilocus sequence type (ST) 8 to reconstruct the molecular evolution and global dissemination of ST8, including USA300. Analyses of core SNP diversity and accessory genome variations showed that the ancestor of all ST8 S. aureus most likely emerged in Central Europe in the mid-19th century. From here, ST8 was exported to North America in the early 20th century and progressively acquired the USA300 characteristics Panton-Valentine leukocidin (PVL), SCCmec IVa, the arginine catabolic mobile element (ACME), and a specific mutation in capsular polysaccharide gene cap5E Although the PVL-encoding phage ϕSa2USA was introduced into the ST8 background only once, various SCCmec types were introduced to ST8 at different times and places. Starting from North America, USA300 spread globally, including Africa. African USA300 isolates have aberrant spa-types (t112, t121) and form a monophyletic group within the clade of North American USA300. Large parts of ST8 methicillin-susceptible S. aureus (MSSA) isolated in Africa represent a symplesiomorphic group of ST8 (i.e., a group representing the characteristics of the ancestor), which are rarely found in other world regions. Isolates previously discussed as USA300 ancestors, including USA500 and a “historic” CA-MRSA from Western Australia, were shown to be only distantly related to recent USA300 clones.

Concepts: Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Staphylococcaceae, Oxacillin, ST8:USA300

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Patients with methicillin-resistant Staphylococcus aureus (MRSA) infections caused by isolates with a high but ‘susceptible’ minimum inhibitory concentration (MIC) to vancomycin may suffer poor outcomes. The aim of this study was to determine the association of high compared to low vancomycin MICs and clinical outcomes (treatment failure and mortality) in patients with MRSA infections.

Concepts: Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Linezolid, Vancomycin, Panton-Valentine leukocidin, Staphylococcaceae, Vancomycin-resistant Staphylococcus aureus

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A better understanding of virulence gene profiling and molecular characterization of Staphylococcus aureus isolates associated with bloodstream infection (BSI) may provide further insights related to clinical outcomes with these infections. We analyzed 89 S. aureus isolates including 37 MRSA isolates (41.6%) recovered from 89 adult patients with BSI from 4 hospitals in Zhejiang province, eastern China. Thirty-five (94.6%) of MRSA isolates and 4 (7.7%) of methicillin-sensitive S. aureus (MSSA) isolates were resistant to multiple antimicrobials. All isolates harbored at least 2 of 22 possible virulence genes, including sdrC (92.1%), icaA (89.9%), hla (80.9%), clf (69.7%), sea (68.5%), sdrD (67.4%), hlb (67.4%), sdrE (65.2%), sei (51.7%), seg (50.6%), and cna (50.6%). Forty-four (49.4%) of all S. aureus BSI isolates, including 23 (62.2%) of MRSA isolates, harbored ≥10 of the virulence genes evaluated in this study. Sixteen (43.2%) MRSA isolates and 5 (9.6%) MSSA isolates harbored the gene encoding Panton-Valentine leukocidin (PVL). Collective genes for pvl, sdrE, sed, seg, and sei among MRSA isolates were significantly more frequent relative to MSSA isolates (P < 0.05). A total of 22 sequence types (STs), including novel ST2184, ST2199, and ST2200, and 33 spa types, including novel spa types t9530 and t9532, were identified among S. aureus BSI isolates, among which ST188 (15.7%) and ST7 (15.7%), and t091 (12.4%) and t189 (12.4%), seldom noted for Chinese isolates previously, were major STs and spa types, respectively. In contrast to previous reports, no predominant clones were found in the present study. Among the MRSA isolates, although ST239-MRSA-SCCmecIII, predominant clone in China, still represented the most common clone, it only accounted for 18.9%. However, ST188-MRSA- SCCmecIV seldom reported before accounted for 10.8%. Among the MSSA isolates, ST7-MSSA represented the most common clone (23.1%), followed by ST188-MSSA and ST630-MSSA (9.6% each). In conclusion, simultaneous carriage of multiple virulence genes and genetically considerable diversity were common among S. aureus BSI isolates. Furthermore, MRSA isolates exhibited more frequent carriage of superantigen genes and pvl relative to MSSA isolates. Taken together, there are distinctive virulence gene profiling and molecular characteristic among S. aureus isolates associated with bloodstream infection in China.

Concepts: Pneumonia, Staphylococcus aureus, Infection, Antibiotic resistance, Staphylococcus, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin

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Even though community-acquired methicillin resistant Staphylococcus aureus (CA-MRSA) was described a decade ago, reports from Brazil are scarce and cases occurred in large urban centers. We report MRSA sepsis in a 16-year-old male from a small town and who had no history of exposure to healthcare or recent travel. After trauma during a soccer match, he presented swelling in the right thigh, which evolved in a month to cellulitis complicated by local abscess, orchitis and pneumonia. The patient presented severe sepsis, with fever and respiratory failure. Laboratory findings included blood leukocyte counts above 40,000/mm(3) and thrombocytopenia. He was submitted to mechanical ventilation and therapy with vancomycin and imipenem. He had a slow but favorable response to therapy and was discharged after six weeks of hospitalization. MRSA grew from blood cultures and respiratory aspirates obtained before antimicrobial therapy. The isolate belonged to sequence type 5, spa type t311, harbored SCCmec type IV and genes for Panton-Valentine leukocidin and Enterotoxin A. The pulsed-field gel electrophoresis pattern was distinct from North American classic CA-MRSA clones. However, the sequence type and the spa type revealed that the clone belong to the same clonal complex isolated in Argentina. This is the first CA-MRSA infection reported in that region, with significant epidemiologic and clinical implications.

Concepts: Inflammation, Pneumonia, Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Sepsis

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BACKGROUND: Meticillin-resistant Staphylococcus aureus (MRSA) is a significant cause of mortality and morbidity in healthcare and community settings; however, there is a paucity of large-scale, longitudinal studies monitoring the occurrence of MRSA in the care home setting. AIM: To determine the molecular epidemiology of MRSA colonizing elderly residents of care homes. METHODS: Residents in 65 care homes in Leeds, UK, were screened for MRSA nasal colonization in four consecutive years (2006-2009). Isolates were characterized using antibiotic susceptibility testing, detection of the Panton-Valentine leucocidin (PVL) locus, accessory gene regulator allotyping, characterization of the staphylococcal cassette chromosome mec element, spa-typing and pulsed-field gel electrophoresis. FINDINGS: MRSA was recovered from 888 nasal swabs of 2492 residents and prevalence was similar (19-22%) throughout the study. Resistance to ≥3 antibiotic classes was common (34%), but resistance to only β-lactam agents was rare (3%); no PVL-positive isolates were identified. Most isolates were related to healthcare-associated epidemic-MRSA type 15 (EMRSA-15, ST22-IV); such isolates decreased in prevalence during the study (86-72%; P < 0.0001, χ(2)-test). The remainder belonged to five different multi-locus sequence type clonal complexes (CC). Most notably, CC59 strains increased in prevalence (10-25%; P < 0.0001, χ(2)-test) and were associated with high-level mupirocin resistance. CONCLUSIONS: The molecular epidemiology of MRSA in care homes is complex and dynamic. There was a high, consistent prevalence of MRSA nasal colonization, dominated by healthcare-associated strains. Vigilance is recommended; however, as high-level mupirocin resistance was associated with a single clonal group (CC59) that significantly increased in prevalence during the study.

Concepts: Epidemiology, Staphylococcus aureus, Antibiotic resistance, Staphylococcus, Methicillin-resistant Staphylococcus aureus, Panton-Valentine leukocidin, Staphylococcaceae, Mupirocin

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Although the nosocomial prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in Angola is over 60% and one of the highest in Africa, the extent of MRSA in the community is unknown. To fill this gap, we conducted a hospital-based study in which 158 children attending the emergency ward and ambulatory services of a pediatric hospital in Luanda, the capital of Angola, were screened for S. aureus nasal colonization. Overall, 70 (44.3%) individuals were colonized with S. aureus, of which 20 (28.6%) carried MRSA, resulting in a prevalence of 12.7% (20/158) of MRSA in the population screened. Molecular characterization by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing, and SCCmec typing distributed the isolates into two major MRSA clones and one dominant methicillin-susceptible S. aureus (MSSA) lineage, corresponding to the main clones circulating in hospitals in Luanda. The MRSA isolates mainly belonged to clones A (PFGE type A, spa type t105, ST5-IVa-65%) and B (PFGE B, t3869, ST88-IVa-30%), while MSSA isolates mainly belonged to clone L (PFGE type L, t861, ST508-42%). S. aureus isolates showed resistance to penicillin (96%), rifampin (87%), and trimethoprim-sulfamethoxazole (21%). In conclusion, the prevalence of MRSA among children in the community in Luanda is high and seems to originate from hospitals, warranting continuous monitoring and implementation of additional infection control measures.

Concepts: Africa, Pneumonia, Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Dicloxacillin

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Superficial skin and soft tissue infections (SSTIs) are common among the Indigenous population of the desert regions of Central Australia. However, the overall burden of disease and molecular epidemiology of Staphylococcus aureus complicated SSTIs has yet to be described in this unique population.

Concepts: Epidemiology, Staphylococcus aureus, Panton-Valentine leukocidin, Skin, Papua New Guinea, Indigenous Australians, Northern Territory, Desert

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Methicillin-resistant Staphylococcus aureus (MRSA) infection is still a major global healthcare problem. Of concern is S. aureus bacteremia, which exhibits high rates of morbidity and mortality and can cause metastatic or complicated infections such as infective endocarditis or sepsis. MRSA is responsible for most global S. aureus bacteremia cases, and compared with methicillin-sensitive S. aureus, MRSA infection is associated with poorer clinical outcomes. S. aureus virulence is affected by the unique combination of toxin and immune-modulatory gene products, which may differ by geographic location and healthcare- or community-associated acquisition. Management of S. aureus bacteremia involves timely identification of the infecting strain and source of infection, proper choice of antibiotic treatment, and robust prevention strategies. Resistance and nonsusceptibility to first-line antimicrobials combined with a lack of equally effective alternatives complicates MRSA bacteremia treatment. This review describes trends in epidemiology and factors that influence the incidence of MRSA bacteremia. Current and developing diagnostic tools, treatments, and prevention strategies are also discussed.

Concepts: Pneumonia, Staphylococcus aureus, Infection, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Infective endocarditis

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Pigs, cattle and poultry are colonized with MRSA and the zoonotic transmission of such MRSA to humans via direct animal contact, environmental contaminations or meat are a matter of concern. Livestock-associated (LA) MRSA are mostly belonging to clonal complex (CC) 398 as defined by multilocus sequence typing. However, MRSA of other clonal lineages including CC5, CC9 and CC97 have also been detected in livestock animals in Germany. Within the framework of a Dutch-German network project (EUREGIO), 14,036 MRSA isolated from clinical and screening specimens (January 2008 - June 2012) derived from human patients in hospitals as well as general or specialized practices in a German region characterized by a high density of livestock production, were subjected to S. aureus protein A (spa) sequence typing. The prevalence of putative LA-MRSA among the human MRSA isolates was determined by analyzing the detection of livestock-indicator (LI) spa types which had already been reported in German livestock. Overall, 578 spa types were detected among the MRSA isolates. LI spa types t011, t034, t108, t1451, t2011, t571, t1456, t1250, t1255, t1580, t2970, t2346, t1344, t2576, t2330 and t2510 (all of which are indicative for LA-MRSA CC398) accounted for 18.6% of all human isolates. The LI spa types t1430 (CC9), t3992 (CC97), t002 (CC5) and t007 (CC30) were found in 0.14%, 0.01%, 1.01% and 0.04% of all human MRSA isolates, respectively. LI spa types associated with CC398 represented 23% of all MRSA from screening samples and a varying proportion among isolates from clinical specimens ranging between 0% in cerebrospinal fluid, 8% in blood cultures and 14% in deep respiratory fluids. Our findings indicate that LA-MRSA are a major cause for human infection and stress the need for close surveillance. Although LA-MRSA CC398 predominates, the occurrence of putative LA-MRSA from other clonal lineages should be monitored.

Concepts: Pneumonia, Staphylococcus aureus, Antibiotic resistance, Methicillin-resistant Staphylococcus aureus, Vancomycin, Panton-Valentine leukocidin, Livestock, Oxacillin