Healthcare-associated MRSA Strains Research Articles

Effects of sub-inhibitory concentrations of nafcillin, vancomycin, ciprofloxacin, and rifampin on biofilm formation of clinical methicillin-resistant Staphylococcus aureus.

Bacteria can be exposed to sub-MICs of antibiotics at the beginning and end of a dosing regimen, between doses, or during low-dose therapies. Growing evidence suggests that sub-MICs of antimicrobials can stimulate MRSA biofilm formation and alter the composition of the biofilm matrix. Pevious studies have found that sub-MICs of oxacillin, methicillin, and amoxicillin promote biofilm formation in some community-acquired MRSA (CA-MRSA). We evaluated biofilm induction by sub-MICs of four different classes of antibiotics in 44 CA-MRSA and 63 healthcare-associated MRSA (HA-MRSA) strains. Our study indicated that sub-MICs of nafcillin, vancomycin, ciprofloxacin, and rifampin frequently promote biofilm induction in clinical MRSA isolates. Strong biofilm induction in sub-MICs of nafcillin, ciprofloxacin, and rifampin was more frequent in HA-MRSA than in CA-MRSA. Antibiotic-induced biofilm formation depends on the antibiotic class, MRSA strain, and antibiotic resistance. Our results emphasize the importance of maintaining effective bactericidal concentrations of antibiotics to treat biofilm-related infections.

High Incidence of Metastatic Infections in Panton-Valentine Leucocidin-Negative, Community-Acquired Methicillin-Resistant Staphylococcus aureus Bacteremia: An 11-Year Retrospective Study in Japan.

Panton-Valentine leucocidin (PVL)-negative community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was originally disseminated in Japan and has since replaced healthcare-associated MRSA (HA-MRSA). However, the clinical characteristics of CA-MRSA bacteremia (CA-MRSAB) compared with those of HA-MRSA bacteremia (HA-MRSAB) are unknown. We aim to clarify differences and investigate associations between the clinical manifestations and virulence genes associated with plasma-biofilm formation in PVL-negative CA-MRSA. From 2011 to 2021, when CA-MRSA dramatically replaced HA-MRSA, 79 MRSA strains were collected from blood cultures and analyzed via SCCmec typing and targeted virulence gene (lukSF-PV, cna, and fnbB) detection. The incidence of metastatic infection was significantly higher in CA-MRSAB than in HA-MRSAB. PVL genes were all negative, although cna and fnbB were positive in 55.6% (20/36) and 50% (18/36) of CA-MRSA strains and 3.7% (1/27) and 7.4% (2/27) of HA-MRSA strains, respectively. cna and fnbB carriage were not associated with the development of metastatic infections in MRSAB; however, the bacteremia duration was significantly longer in CA-MRSAB harboring cna. CA-MRSAB may be more likely to cause metastatic infections than HA-MRSAB. Since CA-MRSA is dominant in Japan, suspected metastatic infection foci should be identified by computed tomography, magnetic resonance imaging, and echocardiography when treating MRSAB.

Multidisciplinary treatment for infective endocarditis complicated with systemic multiple abscess due to Panton-Valentine leukocidin producing community-acquired methicillin-resistant Staphylococcus aureus and Candida albicans: a case report

BackgroundInfective endocarditis resulting from community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a rare, but often fatal heart disorder. Here, we report a case of multidisciplinary treatment for infective endocarditis with systemic multiple abscesses due to Panton-Valentine leukocidin (PVL) producing CA-MRSA and Candida albicans.Case presentationThe patient suffered from infective endocarditis, destructive thyroiditis, hemorrhagic cerebral infarction due to mycotic embolism, lung abscess, multiple skeletal muscle abscess, and disseminate intravascular coagulopathy. Aggressive medical treatment as well as mechanical circulatory support was required before the curative surgical treatment. Blood cultures were positive for MRSA and Candida albicans. Genomic analysis of MRSA revealed Staphylococcal Cassette Chromosome mec IVc and also the virulence gene encoding PVL.ConclusionsCA-MRSA strains have higher pathogenicity and are more destructive to tissue than healthcare-associated MRSA strains because of the toxins they produce, including PVL. Multidisciplinary treatment including aggressive surgery was required to rescue the patient.

Prevalence of SCCmec Types I, II, III, and pvl gene among Methicillin-Resistant Staphylococcus aureus (MRSA) isolated from clinical specimens in Sanglah General Hospital

Background: Methicillin-Resistant Staphylococcus aureus (MRSA) is a big challenge for health services worldwide which causes infections both in healthcare and community. Healthcare-associated MRSA (HA-MRSA) strains are shown to be resistant to beta-lactam antibiotics and several non-beta lactam antibiotics. At the same time, the community-associated MRSA (CA-MRSA) tends to be resistant to beta-lactam antibiotics. MRSA carried staphylococcal cassette chromosome (SCCmec) types I, II, III, IV, and V. SCCmec types I, II, and III were predominantly found in HA-MRSA strain while SCCmec types IV and V predominantly found in CA-MRSA strains. Furthermore, the panton valentine leukocidine (pvl) gene is commonly found in CA-MRSA strains. Therefore, this study aimed to determine the prevalence of SCCmec types I, II, III, and pvl gene in MRSA isolated from clinical specimens in Sanglah General Hospital. Methods: This study was a cross-sectional descriptive study. MRSA was isolated from clinical specimens (sputum, wounds, tissue, blood, etc.) from January 2020 to July 2021 and identified by the Vitek 2 Compact (Biomerieux, France) at the Clinical Microbiology Laboratory of Sanglah Hospital. Prevalence of SCCmec and pvl gene using PCR. Data were analyzed using Microsoft Excel version 2010 for Windows. Results: Most of the specimens (69.56%) were wound. Seventeen (73.91%) out of 23 MRSA isolates were positive for the SCCmec III and pvl gene, while none was positive for the SCCmec I and SCCmec II. About 19 (82.60%) isolates were resistant to two or more non-beta-lactam antibiotics. Conclusions: The isolates of MRSA in this study were predominantly isolated from wound specimens, with the most prevalent genetic element being SCCmec III. In this study, although most MRSA isolates carried SCCmec III that suggested as HA-MRSA, however, most of the strains harbored the pvl gene. This interesting phenomenon needs to be further elucidated.

Potential role of host defense antimicrobial peptide resistance in increased virulence of health care-associated MRSA strains of sequence type (ST) 5 versus livestock-associated and community-associated MRSA strains of ST72.

The most significant community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Korea is sequence type (ST) 72 with staphylococcal cassette chromosome mec (SCCmec) type IV (ST72-MRSA-IV). Although the impact of CA-MRSA on the clinical outcomes versus healthcare-associated (HA)-MRSA remains unclear, it has recently been revealed that ST5 HA-MRSA-II is associated with higher mortality compared with ST72 CA-MRSA-IV, suggesting higher virulence in ST5 HA-MRSA-II strains. In this investigation, human-/animal-originated ST72-MRSA-IV strains were examined for virulence phenotypes and compared with those of ST5-MRSA-II strains, the established HA-MRSA in Korea. Overall, ST5 HA-MRSA-II strains demonstrated higher levels of resistance to host defense-cationic antimicrobial peptides of human (LL-37), bovine (BMAP-28), and bacterial (polymyxin B) origins versus ST72-MRSA-IV strains via enhanced surface positive charge. Hemolysis profiles, gelatinase activity, and staphylococcal superantigen gene profiles were not different between ST72 CA-MRSA and ST5 HA-MRSA strains. However, ST5 HA-MRSA strains were able to downregulate initial cytokine response in murine macrophages.

Characteristics of glycopeptide-resistant Staphylococcus aureus strains isolated from inpatients of three teaching hospitals in Warsaw, Poland

BackgroundVancomycin is still one of the most commonly used drug for treatment of severe methicillin-resistant Staphylococcus aureus (MRSA) infections. Vancomycin-resistant S. aureus (VRSA) strains are a serious danger for public health. This study aimed to characterize healthcare-associated MRSA (HA-MRSA) strains, resistant to at least one of glycopeptide antibiotics: vancomycin (VRSA) and/or teicoplanin (TRSA), isolated at three Warsaw hospitals over a period of 17-years (1991–2007).MethodsAmong 600 HA-MRSA strains, isolated from patients with symptomatic infections, 47 were subjected to detailed analysis. In the study, mechanisms behind VRSA phenotypes were determined (E-tests, GRD-test, agar-dilution method and vanA/B detection). Characteristics of selected isolates on molecular level: i) by detection of resistance genes ermA/ermB/ermC, msrA/msrB, linA/linA’, aacA-aphD, aadD, aph(3”)-IIIa; ii) SCCmec-typing and iii) MLST-typing was done.ResultsIn general population of studied strains, 11/47 (23.4%) were VRSA and 36/47 (76.6%) were resistant only to teicoplanin. All isolates exhibited van-independent mechanisms of resistance. Over 80% of isolates belonged to clonal complex CC8, with the following predominant sequence types (STs)/clones: ST247-IA/Iberian, ST241-III/Finland-UK, and ST239-III/Brazilian. Most of the isolated strains harboured ermA and aacA-aphD genes, encoding additional resistance to macrolides, lincosamides, streptogramin B, and majority of aminoglycosides. They occurred also in Polish VRSA/TRSA population over the period, which was subjected for analysis: an increase in MIC values for glycopeptides, evolution in terms of the level and extent of resistance, and genetic re-assortment in epidemic clones.ConclusionsVRSA strains isolated from patients hospitalized at three Warsaw teaching hospitals in Poland, over a period of 17-years do not pose a threat as potential donors of van genes in horizontal-gene transfer processes, but are constantly evolving and represent international epidemic clones.

Resistance to Aminoglycosides of Methicillin-Resistant Strains of Staphylococcus aureus, Originating in the Surgical and Transplantation Wards of the Warsaw Clinical Center—A Retrospective Analysis

IntroductionAminoglycoside resistance (AR) is common in health care-associated methicillin-resistant Staphylococcus aureus (HA-MRSA). AR is most often associated with the production of antibiotic modifying enzymes: bidomain AAC(6′)-Ie/APH(2″)-Ia acetyltransferase and phosphotransferase, ANT(4′)-Ia nucleotidyltransferase, and APH(3″)-IIIa phosphotransferase. AimDetermination of aminoglycoside sensitivity, presence of genes encoding enzymes, and molecular typing of HA-MRSA strains derived from patients hospitalized in surgical and transplantation wards. Materials and methodsFifty-four HA-MRSA strains, isolated from various materials from patients in the surgical and transplantation wards of Warsaw's clinical hospital, hospitalized between 1991 and 2007. The MIC values of gentamicin-GEN/tobramycin-TOB/amikacin-AK/netilmicin-NET were determined by the E-test (CLSI/EUCAST). Genes mecA/aacA-aphD/aadD/aph(3″)-IIIa were detected using PCR. SCCmec types were determined according to the Oliveira method and the sequence type (ST)/clonal complex (CC) by the MLST method. ResultsOf the isolates tested, 36 (66.7%) showed resistance to at least one aminoglycoside: TOB (57.4%), GEN (53.7%), AK (55.6%), NET (24.1%). The aacA-aphD gene was present in 29 MRSA-GEN-R (most often in combination with aadD, 15/29 or aph(3″)-IIIa, 10/29); the aacA-aphD gene was the only determinant of resistance in 1 isolate. The AR variants mainly belonged to the CC8 clonal complex (ST239/247/241/254/8) and most frequently contained SCCmec type III (3A) cassettes. ConclusionsResistance to at least one aminoglycoside was present in 66.7% of HA-MRSA and in more than 22% to all of them. The presence of the aacA-aphD gene was sufficient to express the resistance phenotype to GEN/TOB/AK/NET. Resistant isolates were closely related to each other.

High frequency of SCCmec type V and agr type I among heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) in north India.

The objective of this study was to compare the genetic features of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-sensitive methicillin-resistant S. aureus (VS-MRSA) isolates. The presence of staphylococcal cassette chromosome mec (SCCmec) types, Panton-Valentine leukocidin (PVL), accessory gene regulator (agr) types, and vanA and vanB genes in hVISA and VS-MRSA isolates was evaluated by PCR. Genetic relatedness was studied by pulsed-field gel electrophoresis (PFGE). The distribution of SCCmec types in hVISA was as follows: 13/29 (44.8%) each of types II and V, 1/29 (3.4%) type III and 2/29 (6.9%) type IVa. Among VS-MRSA isolates, 20/50 (40.0%) were SCCmec type II, 17/50 (34.0%) were type III, 3/50 (6.0%) were type IVa and 10/50 (20.0%) were type V. SCCmec type V was significantly associated with hVISA, whereas SCCmec type III showed an association with VS-MRSA (P=0.020 and P=0.001, respectively). The PVL gene was detected in 9/29 hVISA (31.0%) and 13/50 VS-MRSA (26.0%). By PFGE analyses, both hVISA and VS-MRSA strains were found to be clonally unrelated. In hVISA isolates, 24/29 (82.8%) were agr type I, 3/29 (10.3%) were type III and 2/29 (6.9%) were non-typeable. However, in VS-MRSA isolates, 25/50 (50.0%) were type II, 15/50 (30.0%) were type I, 7/50 (14.0%) were type III and 3/50 (6.0%) were non-typeable. The study shows that healthcare-associated MRSA strains may harbour community-acquired MRSA genetic markers. The changing molecular epidemiology and role of agr I in reduced vancomycin susceptibility in hVISA requires further investigation.

Prevalence and Characteristics of qacA/B-positive Methicillin-resistant Staphylococcus aureus (MRSA) Bloodstream Infection Isolates in a Tertiary Hospital

BackgroundThe increasing use of chlorhexidine (CHG) for MRSA decolonization has raised concerns about the emergence of resistance or tolerance to these agents.MethodsWe evaluated the frequency and characteristics of qacA/B chlorhexidine tolerance genes among MRSA bloodstream infection (BSI) isolates at a tertiary hospital in Korea. MRSA BSI isolates collected from 2011 to 2016 was examined for carriage of qacA/B and smr genes and high-level mupirocin resistance. Staphylococcal cassette chromosome mec (SCCmec) and spa typing was also performed.ResultsOf the 203 MRSA BSI isolates, 57 (28.1%) were positive for qacA/B, 6 (3.0%) were positive for smr, and 15 (7.4%) were mupirocin resistant. Table 1 shows characteristics of qacA/B-positive vs. qacA/B-negative MRSA BSI. Patients with qacA/B-positive isolates were more often diagnosed with nosocomial BSI and catheter related BSI, but were less often diagnosed with bone and soft-tissue infections. The qacA/B-positive isolates were more often resistant to mupirocin, clindamycin, and ciprofloxacin and more often had a CHG MIC of >= 4mg/L. The qacA/B-positive isolates were more likely to belong to SCCmec II or III (84.2% vs. 38.5%, P < 0.001), which are common healthcare-associated (HA) MRSA strains in Korea. Most common spa types in qacA/B positive isolates were t2460 (64.9%) and t9353 (14.0%).ConclusionThe qacA/B carriage among MRSA BSI isolates are not uncommon in this study and showed the features of HA-MRSA BSI.Table 1.Characteristics of qacA/B-positive vs. qacA/B-negative MRSA BSI.Characteristics qacA/B (+) (n = 57) qacA/B (-) (n = 146) P Age, median years(IQR)72 (60–84)69 (56–75)0.062Nosocomial BSI44 (77.2)61 (41.8)< 0.001Catheter-related BSI35 (61.4)41 (28.1)< 0.001Primary BSI14 (24.6)38 (26.0)0.999Bone and soft-tissue infections4 (10.8)33 (22.6)0.009Pneumonia2 (3,5)12 (8.2)0.358Other infections2 (3.5)13 (8.9)0.242Clindamycin resistant56 (98.2)96 (65.8)<0.001Ciprofloxacin resistant56 (98.2)56 (38.4)<0.001Vancomycin MIC >= 2mg/L17 (29.8)26 (17.8)0.084Chlorhexidine MIC >= 4mg/L54 (94.7)50 (34.2)<0.001SCCmec II37 (64.9)39 (27.3)<0.001SCCmec III11 (19.3)16 (11.2)0.168SCCmec IV9 (15.8)88 (61.5)<0.00130 day mortality14 (24.6)35 (25.0)0.999Data are no. (%) of casesDisclosures All authors: No reported disclosures.

Social Factors Help to Spread Community-Associated MRSA

Low socioeconomic status has a long-established link with high risk for infections. Concerned about the emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in hospitals, researchers in Britain compared markers of socioeconomic deprivation with the transmission routes of CA- and healthcare-associated (HA) MRSA strains in three boroughs of South East London. From November 2011 through February 2012, …

THE FREQUENCY OF COMMUNITY-ACQUIRED METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (CA-MRSA) AMONG SAMPLES IN INSTITUTE FOR PUBLIC HEALTH IN CANTON SARAJEVO.

Background:The increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections lacking risk factors for exposure to the health care system has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). These strains have been distinguished from health care-associated MRSA (HA-MRSA) strains by epidemiological, molecular and genetic means as well as by antibiotic susceptibility profile, tissue tropism and virulence traits.Objective:To assess prevalence and antibiotic susceptibility profile of CA-MRSA in Canton Sarajevo, Bosnia and Herzegovina.Results:Out of 1.905 positive Staphylococcus aureus isolates from various samples of outpatients collected during six months, 279 (14,64%) were MRSA isolates. Out of 279 MRSA samples, 133 (47,67%) were found in nasal swabs, from which 48 (36,09%) were in the age group <1 year and 39 (29,32 %) are in the age 1-5 year. Rate of the positive skin swabs was highest among the subject of age group <1 year (46 or 54,12 %) and 1-5 year (18 or 21,18 %). Predominantly antibiotic types among MRSA strains are resistant to penicillin and cefoxitin (36,90 %) and to penicillin, cefoxitin and erythromycin (61,35 %).Conclusion:Continued monitoring of epidemiology and emerging drug resistance data is critical for the effective management of these infections.

Molecular characterization of Staphylococcus aureus from surgical site infections in orthopedic patients in an orthopedic trauma clinical medical center in Shanghai.

Staphylococcus aureus or methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of surgical site infections (SSIs). The aim of our study was to characterize molecularly S. aureus isolates from SSIs in orthopedic patients in Shanghai, China. Eighty-two S. aureus isolates (46 methicillin-susceptible Staphylococcus aureus [MSSA] and 36 MRSA) were collected from SSIs in orthopedic patients. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines and a variety of clinically important toxin genes were detected. The sequence type, spa type, and agr group were determined to analyze the genotypes of all the isolates collected. In addition, MRSA isolates were characterized by staphylococcal cassette chromosome mec (SCCmec) type as well. The strains showed susceptibility to antibiotics such as teicoplanin, minocycline, quinupristin-dalfopristin, linezolid, mupirocin, and vancomycin. Ten pvl-positive isolates (three MRSA and seven MSSA) were found among all isolates. Eight community-associated MRSA (CA-MRSA) isolates were found, six of which belonged to ST59-MRSA-IV but most MRSA isolates (20/36, 55.6%) belonged to ST239-MRSA-III-t030/t037 with a wide range of antibiotic resistance. By contrast, MSSA isolates were more diverse in both molecular characterizations and virulence factors, with eight MSSA isolates harboring more than six toxin genes detected. ST239-MRSA-III-t030/t037 was the epidemic clone, and healthcare-associated MRSA (HA-MRSA) strains might be the major pathogen causing S. aureus SSIs in orthopedic patients.

Anatomic sites of colonization with community-associated methicillin-resistant Staphylococcus aureus.

Anatomic sites of colonization with community-associated methicillin-resistant Staphylococcus aureus.

Outcomes and Treatment of Chronic Methicillin-Resistant Staphylococcus aureus Differs by Staphylococcal Cassette Chromosome mec (SCCmec) Type in Children With Cystic Fibrosis.

Methicillin-resistant Staphylococcus aureus (MRSA) infects ∼25% of patients with cystic fibrosis (CF) in the United States. We hypothesized that health-related outcomes differed between healthcare-associated (staphylococcal cassette chromosome mec [SCCmec] II) vs community-associated (SCCmec IV) MRSA strains in patients chronically infected with CF. At 7 CF centers, MRSA isolates were prospectively obtained from patients ≤18 years old with 2 or more positive MRSA cultures within 1 year. Isolates were classified by SCCmec type and Panton-Valentine-leukocidin (PVL) status at a core laboratory, and sites remained blinded to SCCmec type and PVL results. Prospective clinical data including antibiotic use, respiratory symptoms, and pulmonary exacerbations were obtained. Among the 295 cohort participants with typeable MRSA isolates, 69.5% had SCCmec II PVL(-), 13.2% had SCCmec IV PVL(-), and 17.3% had SCCmec IV PVL(+) strains. During follow-up of 287 patients with prospective data after enrollment, the risk for pulmonary exacerbations was significantly higher among participants with SCCmec II than SCCmec IV strains (risk ratio [RR] = 1.13; P = .03) and higher in those with SCCmec IV PVL(-) than SCCmec IV PVL(+) strains (RR = 1.62; P < .0001). Neither decline in lung function nor changes in nutritional outcomes differed by SCCmec type or PVL status during the study period. Participants harboring chronic SCCmec II MRSA received more antibiotics and may have more lung disease than those with SCCmec IV; PVL(+) isolates were not associated with more advanced disease.

MRSA – Hygiene-Management, Diagnostik und Therapie

Methicillin-resistant Staphyococcus aureus strains remain a challenge to both patient care and infection control efforts. In addition to the defining resistance to beta-lactams several other antibiotic classes may be ineffective. Some resistance phenotypes exhibit a characteristic distribution pattern between healthcare-associated, community-associated, and livestock-associated MRSA strains. For patients with defined risk factors a search-, destroy-, follow-up-strategy is recommended in order to identify and eliminate MRSA colonization. Mupirocin nasal ointment and extensive hygiene measures are the mainstays of decolonization efforts. Besides vancomycin several other antimicrobials such as rifampin, trimethoprim-sulfamethoxazol, clindamycin, linezolid, and daptomycin are used to treat specific MRSA infections.

Human Cathelicidin LL-37 Resistance and Increased Daptomycin MIC in Methicillin-Resistant Staphylococcus aureus Strain USA600 (ST45) Are Associated with Increased Mortality in a Hospital Setting

Bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) USA600 has been associated with increased patient mortality. We found that USA600 MRSA exhibited significantly increased resistance to human cathelicidin LL-37 killing and daptomycin MIC creep compared to non-USA600 MRSA. Virulent health care-associated MRSA strains may coevolve innate host defense peptide and antibiotic resistances.

Methicillin-resistant Staphylococcus aureus nasal cariage among hospitalized patients and healthcare workers in the Clinical center of Serbia

The aim of the present study was to provide the first comprehensive analysis of methicillin-resistant Staphylococcus aureus (MRSA) carriage among patients and healthcare workers (HCWs) in the largest healthcare facility in Serbia. Specimens from anterior nares obtained from 195 hospitalized patients and 105 HCWs were inoculated after broth enrichment onto chromogenic MRSA-ID medium. In total, 21 of 300 specimens yielded MRSA. Among hospitalized patients, 7.7% were colonized with MRSA, and 5.7% HCWs were colonized with MRSA. Five out of 21 (23.8%) tested MRSA strains were classified as community-associated MRSA (CA-MRSA), and four of them were isolated from HCWs. The remaining 16 MRSA strains had characteristics of healthcare-associated MRSA (HA-MRSA), and two of them were isolated from HCWs. The HA-MRSA strains isolated from HCWs were indistinguishable from HA-MRSA of the same cluster isolated from patients. This finding reveals the circulation of HA-MRSA strains between patients and HCWs in the Clinical Center of Serbia.

Molecular characterization of methicillin-resistant Panton-valentine leukocidin positive staphylococcus aureus clones disseminating in Tunisian hospitals and in the community.

BackgroundThe spread of MRSA strains at hospitals as well as in the community are of great concern worldwide. We characterized the MRSA clones isolated at Tunisian hospitals and in the community by comparing them to those isolated in other countries.ResultsWe characterized 69 MRSA strains isolated from two Tunisian university hospitals between the years 2004-2008. Twenty-two of 28 (79%) community-associated MRSA (CA-MRSA) strains and 21 of 41 (51%) healthcare-associated MRSA (HA-MRSA) strains were PVL-positive. The PVL-positive strains belonged to predicted founder group (FG) 80 in MLST and carried either type IVc SCCmec or nontypeable SCCmec that harbours the class B mec gene complex. In contrast, very diverse clones were identified in PVL-negative strains: three FGs (5, 15, and 22) for HA-MRSA strains and four FGs (5, 15, 45, and 80) for CA-MRSA strains; and these strains carried the SCCmec element of either type I, III, IVc or was nontypeable. The nucleotide sequencing of phi7401PVL lysogenized in a CA-MRSA strain JCSC7401, revealed that the phage was highly homologous to phiSA2mw, with nucleotide identities of more than 95%. Furthermore, all PVL positive strains were found to carry the same PVL phage, since these strains were positive in two PCR studies, identifying gene linkage between lukS and mtp (major tail protein) and the lysogeny region, both of which are in common with phi7401PVL and phiSa2mw.ConclusionsOur experiments suggest that FG80 S. aureus strains have changed to be more virulent by acquiring phi7401PVL, and to be resistant to β-lactams by acquiring SCCmec elements. These novel clones might have disseminated in the Tunisian community as well as at the Tunisian hospitals by taking over existing MRSA clones.

Epidemiological features, resistance genes, and clones among community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) isolates detected in northern Spain

Twenty-nine community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) isolates were prospectively selected according to epidemiological criteria among 374 MRSA isolates collected in our laboratory during 2009–2010 in order to determine which community-associated MRSA (CA-MRSA) and healthcare-associated MRSA (HA-MRSA) clones are circulating in the community in northern Spain. PVL genes were detected in 5 strains (17.2%) that belonged to SCCmec type IV or V and to the agr group I (ST8 and ST2050), agr group II (ST121), and agr group III (ST30 and ST852). These strains were isolated from patients with different clinical manifestations such as urinary tract infection, abscess, or pneumonia, and most of them belonged to emergency department patients with no history of visits to General Practitioners (GPs) in the year before the isolation. We considered that the prevalence of CA-MRSA in community-onset isolates was low (17.2%). A high proportion of the CO-MRSA strains (58.6%) were ST125-MRSA-IVc (CC5), responsible for most of the infections caused by HA-MRSA strains in Spain. This endemic clone is also circulating in the community of northern Spain as we could demonstrate in this study. Antimicrobial resistance was found in spa type t067 isolates linked to the presence of ant(4′)-Ia and msr(A). Most of the CO-MRSA isolates in this study corresponded to spa types more associated to the hospital environment, suggesting the interchange of genetic lineages of MRSA among community and hospital niches.

Reduced vancomycin susceptibility and staphylococcal cassette chromosome mec (SCCmec) type distribution in methicillin-resistant Staphylococcus aureus bacteraemia

Recent epidemiological evidence suggests that genotypic and phenotypic characteristics that have typically distinguished community-associated methicillin-resistant Staphylococcus aureus (MRSA) and healthcare-associated MRSA strains may be evolving. The objective of this study was to examine the association between reduced vancomycin susceptibility (RVS) and staphylococcal cassette chromosome mec (SCCmec) type in MRSA bloodstream isolates. A cohort study of patients who were hospitalized from 2007 to 2009 with S. aureus bacteraemia was conducted within a university health system. Bivariable analyses were conducted to determine the association between RVS and SCCmec type, as well as other microbiological characteristics including Panton-Valentine leucocidin, accessory gene regulator (agr) dysfunction and vancomycin heteroresistance. A total of 188 patients with MRSA bacteraemia were identified: 116 (61.7%) and 72 (38.3%) patients had infections due to healthcare-associated MRSA and community-associated MRSA, respectively. As defined by a vancomycin Etest MIC > 1.0 mg/L, the prevalence of RVS was 40.4%. Isolates with RVS were significantly more likely to be associated with SCCmec II compared with isolates without RVS (74.7% and 47.3%, respectively, P < 0.001), but not with Panton-Valentine leucocidin (P = 0.10), agr dysfunction (P = 0.19) or healthcare-associated infection (P = 0.36). The results of our study demonstrate important microbiological characteristics among MRSA isolates characterized by RVS, including a significant association between SCCmec II and elevated vancomycin MIC. It is clear that the clinical and molecular epidemiology of MRSA is evolving, and further understanding of factors determining virulence will be important for the elucidation of optimal treatment approaches for associated infections.