Pathotype and susceptibility profile of a community-acquired methicillin-resistant Staphylococcus aureus strain responsible for a case of severe pneumonia

Staphylococcus aureus ST228 and ST239 as models for expression studies of diverse markers during osteoblast infection and persistence

The ability of S. aureus to infect bone and osteoblasts is correlated with its incredible virulence armamentarium that can mediate the invasion/internalization process, cytotoxicity, membrane damage, and intracellular persistence. We comparatively analyzed the interaction, persistence, and modulation of expression of selected genes and cell viability in an ex vivo model using human MG‐63 osteoblasts of two previously studied and well‐characterized S. aureus clinical strains belonging to the ST239‐SCCmecIII‐t037 and ST228‐SCCmecI‐t041 clones at 3 h and 24 h post‐infection (p.i). S. aureus ATCC12598 ST30‐t076 was used as a control strain. Using imaging flow cytometry (IFC), we found that these strains invaded and persisted in MG‐63 osteoblasts to different extents. The invasion was evaluated at 3 h p.i and persistence at 24 h p.i., in particular: ATCC12598 internalized in 70% and persisted in 50% of MG‐63 cells; ST239‐SCCmecIII internalized in 50% and persisted in 45% of MG‐63 cells; and ST228‐SCCmecI internalized in 30% and persisted in 20% of MG‐63 cells. During the infection period, ST239‐III exerted significant cytotoxic activity resulting from overexpression of hla and psmA and increased expression of the genes involved in adhesion, probably due to the release and re‐entry of bacteria inside MG‐63 cells at 24 h p.i. The lower invasiveness of ST228‐I was also associated with non‐cytotoxic activity inside osteoblasts. This clone was unable to activate sufficient cellular reaction and succumbed inside MG‐63 cells. Our findings support the idea of considering new strategies, based on a translational approach—eukaryotic host–pathogen interaction (EHPI)—and to be applied on a large scale, to predict S. aureus /osteoblast interaction and treat bone infections. Such strategies rely on the study of the genetic and biochemical basis of both pathogen and host.

Molecular Epidemiological Characterization of Methicillin-Susceptible and -Resistant Staphylococcus aureus Isolated from Skin and Soft Tissue Infections in Bangladesh

Genetic background and molecular characteristics of Staphylococcus aureus collected from patients with skin and soft tissue infections were studied in the North-Central region of Bangladesh from 2015 to 2016. Among 430 clinical isolates, methicillin-resistant S. aureus (MRSA) accounted for 31% having SCCmec type IV (73%) and V (14%), and belonged mostly to coagulase (coa) genotypes IIa, IIIa, IVb, and XIa, while dominant coa type in methicillin-susceptible S. aureus (MSSA) was IIIa, followed by Va, IIa, and VIa. Panton-Valentine Leukocidin genes (pvl) were detected at higher rate in MSSA (54%) than in MRSA (24%). Based on multilocus sequence typing, pvl-positive MRSA isolates were classified into clonal complex 88 (CC88) (ST88, ST2884, ST4345), CC6 (ST6, ST4350), and CC1 (ST1, ST772), while pvl-negative MRSA into CC5, CC22, CC80, CC121, and CC672. The pvl-negative ST80 MRSA isolates had SCCmec-IVa (agr-III/coa-XIc, etd/edinB-positive, fusB-negative), indicating that they belong to the novel CC80 clade related to the European community-acquired MRSA clone. Among MSSA, genotypes ST121/spa-t645/coa-Va and ST2884 (CC88)/spa-t2393/coa-IIIa were identified in both pvl-positive and negative isolates, and all the ST772 isolates harbored pvl. All the ST121 isolates had a variant of elastin-binding protein gene (ebpS-v) with internal 180-nucleotide deletion. The present study suggested that CC88 (ST88, ST2884) and ST772 are the putative dominant lineages of pvl-positive MRSA/MSSA, while novel CC80 clade is one of the main pvl-negative MRSA lineages distributed endemically in Bangladesh.

Molecular characterization of nasal methicillin resistant Staphylococcus aureus isolates from workers of an automaker company in southeast Iran

Colonization of methicillin resistant Staphylococccus aureus (MRSA) can occur more commonly in healthy people who live in close together or are in close physical contact with each other. Having knowledge about the molecular characteristics of these strains provides considerable discernment into the epidemiology of this important microorganism. A total of 806 nasal swabs were collected from healthy workers of an automaker company in the southeast of Iran and were analyzed to detect MRSA isolates. Multilocus sequence typing (MLST), spa typing, and detection of staphylococcal cassette chromosome mec (SCCmec) were performed. The presence of genes encoding Panton-Valentine Leukocidin (PVL) and Arginine Catabolic Mobile Element (ACME) were also investigated. Carriage rate of S. aureus was 20%. Among 10 identified MRSA, no acme was found while high prevalence of pvl (60%) was of great concern. Seven different spa types including five new ones were identified. The most frequent sequence type was the novel one; ST 3373 (n = 3), followed by each of ST22, ST88, ST859 (n = 2) and ST1955 (n = 1). MRSA isolates were clustered into two main clonal complexes; CC22 (n = 6) and CC88 (n = 4). Low genetic diversity with the dominance of CC22, SCCmecIV was found. Distribution of previously found hospital-associated MRSA was demonstrated among our isolates.

Characterization of a PVL-negative community-acquired methicillin-resistant Staphylococcus aureus strain of sequence type 88 in China

Sequence type 88 community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strain SR434, isolated from an outpatient with skin and soft tissue infection, was subjected to whole genome sequencing, antimicrobial susceptibility testing, mouse skin infection model and hemolysis analysis to identify its virulence and resistance determinants. MRSA strain SR434 is resistant to clindamycin, erythromycin and fosfomycin. Four plasmids with resistance genes were identified in this strain, including a 20,658bp blaZ-carrying plasmid, a 2473bp ermC-carrying plasmid, a 2622bp fosB7-carrying plasmid (86% identity with plasmid in a ST2590 MRSA strain) and a 4817bp lnuA-carrying plasmid (99% identity with pLNU4 from bovine coagulase-nagetive Staphylococci). This strain contains staphylococcal cassette chromosome mec type IV and does not contain arginine catabolic mobile element or Panton-Valentine-Leukocidin. SR434 harbors genomic islands νSaα, νSaβ, νSaγ and ΦSa3 and pathogenicity islands νSa2 that carries genes encoding toxic shock syndrome toxin 1, superantigen enterotoxin C and superantigen enterotoxin L. Mouse skin infection model results show that SR434 had similar virulence potential causing invasive skin infection as a PVL-negative epidemic Korea clone HL1 (ST72). CA-MRSA strain of ST88 lineage might be a great concern for its high virulence. PVL has limited contribution to virulence phenotype among this lineage.

Rapid containment of nosocomial transmission of a rare community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) clone, responsible for the Staphylococcal Scalded Skin Syndrome (SSSS)

Background

The aims of this study were to identify the source and the transmission pathway for a Staphylococcal Scalded Skin Syndrome (SSSS) outbreak in a maternity setting in Italy over 2 months, during 2014; to implement appropriate control measures in order to prevent the epidemic spread within the maternity ward; and to identify the Methicillin-Resistant Staphylococcus aureus (MRSA) epidemic clone.

Methods

Epidemiological and microbiological investigations, based on phenotyping and genotyping methods, were performed. All neonates involved in the outbreak underwent clinical and microbiological investigations to detect the cause of illness. Parents and healthcare workers were screened for Staphylococcus aureus to identify asymptomatic carriers.

Results

The SSSS outbreak was due to the cross-transmission of a rare clone of ST5-CA-MRSA-SCCmecV-spa type t311, exfoliative toxin A-producer, isolated from three neonates, one mother (from her nose and from dermatological lesions due to pre-existing hand eczema) and from a nurse (colonized in her nose by this microorganism). The epidemiological and microbiological investigation confirmed these as two potential carriers.

Conclusions

A rapid containment of these infections was obtained only after implementation of robust swabbing of mothers and healthcare workers. The use of molecular methodologies for typing was able to identify all carriers and to trace the transmission.

In vivo development of daptomycin resistance in vancomycin-susceptible methicillin-resistant Staphylococcus aureus severe infections previously treated with glycopeptides

Our aim was to describe the clinical and microbiological features of four cases of severe vancomycin-susceptible methicillin-resistant Staphylococcus aureus (MRSA) infections in which the vancomycin non-susceptibility development and daptomycin resistance occurred under therapy with teicoplanin (three cases) and daptomycin switched to vancomycin (one case). Clinical data were retrospectively reviewed. On nine clinical epidemiologically unrelated daptomycin-susceptible (DAP-S) and daptomycin-resistant (DAP-R) MRSA, we performed: (i) DAP-VAN-TEC-CFX-RIF minimum inhibitory concentrations (MICs); (ii) glycopeptide resistance detection (GRD) by δ-hemolysis; (iii) glycopeptide population analysis; (iv) molecular characterization by PFGE-MLST-SCCmec-agr-typing; (v) rpoB and mprF single nucleotide polymorphisms (SNPs); (vi) dltA-mprF-atl-sceD expression by real-time quantitative polymerase chain reaction (qPCR). Three out of the four patients did not survive despite salvage treatment; two died with active MRSA infection and one died because of Stenotrophomonas maltophilia sepsis. The fourth patient, in which a reversion to a DAP-S phenotype occurred, survived with daptomycin plus trimethoprim/sulfamethoxazole and oxacillin treatment, and endovascular device removal. Daptomycin resistance development was preceded by a stable heterogeneous vancomycin-intermediate S. aureus (hVISA) or VISA phenotype acquisition, while in one case, daptomycin resistance was preceded by an unstable daptomycin heteroresistance (hDAP) behavior reverting to DAP-S during vancomycin plus rifampin therapy followed by high doses of daptomycin. All DAP-R strains showed hVISA or DAP-R traits, including mutations and/or up-regulation of genes involved in cell wall turnover and cell membrane perturbation. In our study, daptomycin resistance arose during glycopeptide therapy. The emergence of DAP-R isolates was preceded by a stable VISA or hVISA phenotype or by instability reverting to a DAP-S heteroresistant phenotype. Daptomycin, as first-line therapy for the treatment of severe MRSA infections, should be used at optimal dosage combined with other agents such as beta-lactams, to prevent daptomycin resistance occurrence.

Isolation of a small molecule with anti-MRSA activity from a mangrove symbiont Streptomyces sp. PVRK-1 and its biomedical studies in Zebrafish embryos

OBJECTIVE

The aim of the present study was to isolate the anti-MRSA (Methicillin Resistant Staphylococcus aureus) molecule from the Mangrove symbiont Streptomyces and its biomedical studies in Zebrafish embryos.

METHODS

MRSA was isolated from the pus samples of Colachal hospitals and confirmed by amplification of mecA gene. Anti-MRSA molecule producing strain was identified by 16s rRNA gene sequencing. Anti-MRSA compound production was optimized by Solid State Fermentation (SSF) and the purification of the active molecule was carried out by TLC and RP-HPLC. The inhibitory concentration and LC50 were calculated using Statistical software SPSS. The Biomedical studies including the cardiac assay and organ toxicity assessment were carried out in Zebrafish.

RESULTS

The bioactive anti-MRSA small molecule A2 was purified by TLC with Rf value of 0.37 with 1.389 retention time at RP-HPLC. The Inhibitory Concentration of the purified molecule A2 was 30 µg/mL but, the inhibitory concentration of the MRSA in the infected embryo was 32-34 µg/mL for TLC purified molecule A2 with LC50 mean value was 61.504 µg/mL. Zebrafish toxicity was assessed in 48-60 µg/mL by observing the physiological deformities and the heart beat rates (HBR) of embryos for anti MRSA molecule showed the mean of 41.33-41.67 HBR/15 seconds for 40 µg/mL and control was 42.33-42.67 for 15 seconds which significantly showed that the anti-MRSA molecule A2 did not affected the HBR.

CONCLUSIONS

Anti-MRSA molecule from Streptomyces sp PVRK-1 was isolated and biomedical studies in Zebrafish model assessed that the molecule was non toxic at the minimal inhibitory concentration of MRSA.

Methicillin-resistant Staphylococcus aureus nasal colonization in a department of pediatrics: a cross-sectional study

BACKGROUND

We describe methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage at admission in patients admitted to a Department of Pediatrics.

METHODS

All patients received a nasal swab at admission. A questionnaire was administered and molecular genetics analyses were performed on all identified MRSA isolates.

RESULTS

We enrolled 785 patients, affected with both acute and chronic diseases. MRSA nasal colonization prevalence was 1.15% (CI: 0.5607%-2.093%). Methicillin-sensitive Staphylococcus aureus (MSSA) nasal colonization prevalence at admission was 19.75% (CI 17.07%-22.64%). Only one MRSA isolate carried the SCCmec V variant; all other isolates carried the SCCmecIV variant. Five out of 9 MRSA-colonized patients had an underlying condition. Antibiotic therapy in the previous 6 months was a protective factor for both MRSA (OR 0,66; 95% CI: 0,46-0,96) and MSSA (OR 0,65; 95% CI: 0,45-0,97) colonization. A tendency to statistical significance was seen in the association between hospitalization in the 6 months prior to admission and MRSA colonization at admission (OR 4,92; 95% CI: 0,97-24,83). No patient was diagnosed with an S. aureus infection during hospitalization.

CONCLUSIONS

The majority of our MRSA colonizing isolates have community origins. Nevertheless, most MRSA-colonized patients had been hospitalized previously, suggesting that strains that circulate in the community also circulate in hospital settings. Further studies should elucidate the role of children with frequent contact with health care institutions in the circulation of antibiotic resistant strains between the hospital and the community.

Daptomycin efficacy in the central nervous system of a patient with disseminated methicillin-resistant Staphylococcus aureus infection: a case report

INTRODUCTION

Staphylococcus aureus has emerged as a major nosocomial pathogen in the last decades and also represents the second most common pathogen isolated from patients in outpatient settings. Although methicillin-resistant S.aureus infections were traditionally limited to hospitals, community-associated cases of methicillin-resistant S.aureus infections have been reported. In our case, we observed an unexpected event during treatment.

CASE PRESENTATION

A 60-year-old Caucasian man developed fever and multiple muscle and brain abscesses caused by Panton-Valentine leukocidin-negative community-associated methicillin-resistant S. aureus.

CONCLUSION

Although our patient was given antimicrobials active against the isolated methicillin-resistant S. aureus strain, it was only after the introduction of daptomycin that his skin, soft tissue and muscle lesions and also brain manifestations improved.

High clonal heterogeneity of Panton-Valentine leukocidin-positive meticillin-resistant Staphylococcus aureus strains from skin and soft-tissue infections in the Province of Bolzano, Northern Italy

Panton-Valentine leukocidin (PVL)-positive community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) isolates are widespread in many countries, with varying distribution and epidemiology. The aim of this study was to characterise 10 PVL-positive MRSA isolates collected during February 2010 to January 2011 from skin and soft-tissue infections in the North Italian Province of Bolzano. Accessory gene regulator (agr) typing, staphylococcal cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) gene typing, multilocus sequence typing, toxin gene profiling, polymerase chain reaction for type I arginine catabolic mobile element (ACME) and antimicrobial resistance typing were applied to the isolates. Eight different CA-MRSA clones were identified, including ST30-IVc, ST772-V, ST80-IVc, ST5-IVc, ST88-IVa, ST93-IVa, ST8-IVc and the type I ACME-positive ST8-IVa. The high heterogeneity of PVL-positive MRSA probably reflects the introduction of different clones by international travellers or immigrants.

Modulating activity of vancomycin and daptomycin on the expression of autolysis cell-wall turnover and membrane charge genes in hVISA and VISA strains

Glycopeptides are still the gold standard to treat MRSA (Methicillin Resistant Staphylococcus aureus) infections, but their widespread use has led to vancomycin-reduced susceptibility [heterogeneous Vancomycin-Intermediate-Staphylococcus aureus (hVISA) and Vancomycin-Intermediate-Staphylococcus aureus (VISA)], in which different genetic loci (regulatory, autolytic, cell-wall turnover and cell-envelope positive charge genes) are involved. In addition, reduced susceptibility to vancomycin can influence the development of resistance to daptomycin. Although the phenotypic and molecular changes of hVISA/VISA have been the focus of different papers, the molecular mechanisms responsible for these different phenotypes and for the vancomycin and daptomycin cross-resistance are not clearly understood. The aim of our study was to investigate, by real time RT-PCR, the relative quantitative expression of genes involved in autolysis (atl-lytM), cell-wall turnover (sceD), membrane charges (mprF-dltA) and regulatory mechanisms (agr-locus-graRS-walKR), in hVISA and VISA cultured with or without vancomycin and daptomycin, in order to better understand the molecular basis of vancomycin-reduced susceptibility and the modulating activity of vancomycin and daptomycin on the expression of genes implicated in their reduced susceptibility mechanisms. Our results show that hVISA and VISA present common features that distinguish them from Vancomycin-Susceptible Staphylococcus aureus (VSSA), responsible for the intermediate glycopeptide resistance i.e. an increased cell-wall turnover, an increased positive cell-wall charge responsible for a repulsion mechanism towards vancomycin and daptomycin, and reduced agr-functionality. Indeed, VISA emerges from hVISA when VISA acquires a reduced autolysis caused by a down-regulation of autolysin genes, atl/lytM, and a reduction of the net negative cell-envelope charge via dltA over-expression. Vancomycin and daptomycin, acting in a similar manner in hVISA and VISA, can influence their cross-resistance mechanisms promoting VISA behavior in hVISA and enhancing the cell-wall pathways responsible for the intermediate vancomycin resistance in VISA. Daptomycin can also induce a charge repulsion mechanism both in hVISA and VISA increasing the activity of the mprF.

Successful treatment of fulminant community-acquired Pseudomonas aeruginosa necrotizing pneumonia in a previously healthy young man

This report presents a case of fulminant community-acquired Pseudomonas aeruginosa necrotizing pneumonia in a previously healthy young man, including an analysis of the virulence of the P.aeruginosa isolated from the patient. The patient was successfully treated with intensive care and antibiotic treatment. This study analyzed the pathogenicity of the isolated strain both in vivo (using a mouse pneumonia model) and in vitro (using biofilm production), but could not explain how an otherwise healthy young man developed such severe community-acquired P.aeruginosa pneumonia. Although rare in community-acquired pneumonia, P.aeruginosa infection should be considered in patients with severe rapidly progressive pneumonia.

DNA microarray-based characterisation of Panton-Valentine leukocidin-positive community-acquired methicillin-resistant Staphylococcus aureus from Italy

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates are widespread in many countries, with varying distribution and epidemiology. The aim of this study was to collect and characterise the CA-MRSA isolates circulating in Italy, since only some case reports have been published. Eighteen Panton-Valentine-positive CA-MRSA isolates were collected from different Italian hospitals during the period 2005-2009 from severe infections (skin and soft tissue infections, n = 10; necrotising pneumonia, n = 7; and sepsis, n = 1). Accessory gene regulator (agr) typing, staphylococcal cassette chromosome (SCC) mec typing, spa typing, multi-locus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and DNA microarray were applied to categorise isolates into clones and to compare the relevant genetic features of each clone. Six different clones were identified, the most common (7 out of 18 isolates, 38.8%) being agrI/ST8/SCCmecIV, corresponding to the USA300 clone. Six out of the seven USA300 isolates did not harbour the arginine catabolic mobile element (ACME). Four strains (22.2%) were agrIII/ST80/SCCmecIV, corresponding to the European clone. Two of the other clones, namely, agrIII/ST88/SCCmecV and agrIII/ST772/SCCmecV, corresponded to CA-MRSA clones rarely found in other countries and probably originating from Africa or the Indian subcontinent. The results of microarray hybridisations showed that the distribution of resistance genes and other virulence factors was specific to each clone. Some characteristics could be exploited as specific markers for a clone or a group of isolates, e.g. the mer operon, recovered only in ACME-negative USA300 strains. DNA microarray contributed to a more complete description of the variety of different CA-MRSA clones circulating in Italy.

A field guide to pandemic, epidemic and sporadic clones of methicillin-resistant Staphylococcus aureus

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) have become a truly global challenge. In addition to the long-known healthcare-associated clones, novel strains have also emerged outside of the hospital settings, in the community as well as in livestock. The emergence and spread of virulent clones expressing Panton-Valentine leukocidin (PVL) is an additional cause for concern. In order to provide an overview of pandemic, epidemic and sporadic strains, more than 3,000 clinical and veterinary isolates of MRSA mainly from Germany, the United Kingdom, Ireland, France, Malta, Abu Dhabi, Hong Kong, Australia, Trinidad & Tobago as well as some reference strains from the United States have been genotyped by DNA microarray analysis. This technique allowed the assignment of the MRSA isolates to 34 distinct lineages which can be clearly defined based on non-mobile genes. The results were in accordance with data from multilocus sequence typing. More than 100 different strains were distinguished based on affiliation to these lineages, SCCmec type and the presence or absence of PVL. These strains are described here mainly with regard to clinically relevant antimicrobial resistance- and virulence-associated markers, but also in relation to epidemiology and geographic distribution. The findings of the study show a high level of biodiversity among MRSA, especially among strains harbouring SCCmec IV and V elements. The data also indicate a high rate of genetic recombination in MRSA involving SCC elements, bacteriophages or other mobile genetic elements and large-scale chromosomal replacements.

Factors associated with the outcome of life-threatening necrotizing pneumonia due to community-acquired Staphylococcus aureus in adult and adolescent patients

BACKGROUND

Although community-acquired Staphylococcus aureus pneumonia with highly virulent Panton-Valentine leukocidin (PVL)-positive strains, a severe disease with significant lethality, is rare, especially in adult and adolescent patients, recent reports highlight that these infections are on the rise.

OBJECTIVES

To describe the demographic and clinical features of reported cases of life-threatening community-acquired S. aureus pneumonia with usually PVL-positive strains in adult and adolescent patients, to evaluate the variables related to death, and to select a more appropriate antimicrobial treatment for this potentially deadly disease.

METHODS

We summarized all of the 92 reported cases and our case. The effect of 5 variables on mortality was measured using logistic regression.

RESULTS

S. aureus community-acquired pneumonia (CAP) with usually PVL-positive strains is a severe disease with significant lethality, i.e. 42.9%; a short duration of the time from the onset of symptoms to death, i.e. 5.5 ± 10.1 days, and prolonged hospital admissions, i.e. 33.2 ± 29.5 days. Seventy-three cases have been tested for the gene for PVL, and 71 strains have been found to carry the PVL gene. Logistic regression analysis showed that leucopenia (p = 0.002), influenza-like symptoms or laboratory-confirmed influenza (p = 0.011), and hemoptysis (p = 0.024) were the factors associated with death. Antibiotic therapies inhibiting toxin production were associated with an improved outcome in these cases (p = 0.007).

CONCLUSIONS

Physicians should pay special attention to those patients who acquired severe CAP during influenza season and have flu-like symptoms, hemoptysis, and leucopenia, and they should consider S. aureus more frequently among the possible pathogens of severe CAP. Empiric therapy for severe CAP with this distinct clinical picture should include coverage for S. aureus. Targeted treatment with antimicrobials inhibiting toxin production appears to be a more appropriate selection.

Molecular picture of community- and healthcare-associated methicillin-resistant Staphylococcus aureus circulating in a teaching hospital in Milan

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) has dramatically changed over the past 10 y with the emergence of community-associated MRSA (CA-MRSA). Recent studies have reported a frequent association of these strains with hospital outbreaks, and an incidence varying over time and by region. In order to evaluate the MRSA lineages circulating in our area of Italy, we performed a molecular characterization of CA-MRSA isolates prospectively collected from April 2006 to July 2007 at the San Paolo Hospital of Milan. We investigated the protein A-encoding gene (spa-typing), the staphylococcal chromosomal cassette SCCmec, the presence of Panton-Valentine leukocidin (PVL), and 3 adhesin genes. Twenty-five CA-MRSA isolates cultured from 25 patients were collected; an equal number of healthcare-associated (HA)-MRSA strains, from 25 patients hospitalized in various wards, were collected for comparison purposes. SCCmec type IV emerged as the most frequent genotype in both CA- and HA-MRSA. Seventeen different spa types were identified: t515 was the most common (36%), followed by t008 (20%). We detected 3 PVL-positive strains, only among the CA-MRSA. On the whole, our local MRSA epidemiology appears to be heterogeneous, with a predominant t515 spa type, only recently considered to belong to clonal EMRSA-15.

Methicillin resistance and vancomycin heteroresistance in Staphylococcus aureus in cystic fibrosis patients

Methicillin-resistant Staphylococcus aureus (MRSA) infections are increasingly being reported among cystic fibrosis (CF) populations worldwide. In this paper, we sought to examine at the epidemiology, the molecular characterisation and the antibiotic resistance of MRSA isolates in our cohort of CF patients. All MRSA strains were collected prospectively at the University Hospital of Catania, Italy, during a two-year study between mid 2005 to mid 2007 and underwent molecular, pathotype and susceptibility characterisations. Our study demonstrates persisting infections with both hospital-associated (HA-) and community-associated (CA-)MRSA, including Panton-Valentine leukocidin (PVL)-positive strains, in our CF population with an overall prevalence of 7.8%. We demonstrated that, in these patients, persistence was sustained by either identical clones that underwent subtle changes in their toxin content or by different clones over time. The isolation of MRSA in our CF population aged 7-24 years was associated with an increased severity of the disease even if, due to the small sample of patients included and the paucity of data on the clinical outcome, these results cannot be conclusive. Furthermore, three strains were heteroresistant vancomycin-intermediate S. aureus (hVISA), questioning the use of glycopeptides in the treatment of MRSA infections in these patients.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-acquired, methicillin-resistant Staphylococcus aureus isolated from children with community-onset pneumonia in China

Community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) has been associated with morbidity and mortality in various countries. In this study, we characterized the molecular and clinical features of pediatric CA-MRSA pneumonia in China. Between June 2006 and February 2008, 55 previously healthy children confined in eight hospitals countrywide were found to be afflicted with CA-MRSA pneumonia. A total of 55 strains collected from these children were analyzed by multilocus sequence typing (MLST), Staphylococcus cassette chromosome mec (SCCmec) typing, and spa typing. The Panton-Valentine leukocidin (PVL) gene was also detected. Overall, nine STs were obtained, with ST59 (40.4%) established to be the most prevalent type. We first registered the new ST1409 from a child with necrotizing pneumonia. SCCmecIVa was the most predominant type, followed by SCCmec type V. Twelve spa types were identified, of which one new spa type, t5348, was first detected and registered. One typical livestock-associated spa type, t034, was found in a 4-month-old girl living in the countryside. We also found that 40% of those isolates were PVL-positive. In addition, the median age of the children in this study was 10 months. A total of 69% (38/55) of the children with community-acquired pneumonia (CAP) had preceding influenza or influenza-like illness, and three ST910-MRSA-IV strains (PVL gene-positive) were associated with severe necrosis. The results indicated that the recent CA-MRSA found in Chinese children with CAP was largely associated with the spread of the ST59-MRSA-IV clone, and most of the PVL-positive strains in this study did not cause necrotic cases.

Hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in Italy

The aim of our study was to trace the dynamic changes of hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) lineages in Italy, comparing the genotypic backgrounds of contemporary isolates over a period of 17 years, with those of a sample of early MRSA strains from 1980.

In total, 301 non-repetitive MRSA clinical isolates, recovered from 19 Italian hospitals between 1990 and 2007 were selected and analyzed for their antibiotic resistance, typed by PFGE and SCCmec, grouped into clonal-types and further characterized using Multi Locus Sequence Typing (MLST). A sample of fifteen early MRSA strains from 1980 was also used for comparison.

The most interesting feature was the recent increase of ST228-MRSA-I (formerly the Italian clone; PFGE E) over the period 2000–2007 (57%), when compared to the period 1990–1999 (29%), and its stability to date, associated with a decrease of the highly epidemic ST247-MRSA-IA (formerly the Iberian clone; PFGE A), (23% from 1990 to 1999, 6% from 2000 to 2007). ST1-MRSA-I (1 out of 2 strains carrying ccrA₂B₂), ST8-MRSA-I (4 strains), ST15-MRSA-I (1 out of 4 carrying ccrA₂B₂) and ST30-MRSA-I (2 out of 5 carrying no ccrAB-types and ccrC) were the predominant earliest STs among the MRSA strains in 1980.

A temporal shift in the susceptibility levels to glycopeptides was observed: strains with vancomycin MIC of ≥ 2 mg/L increased from 19.4% to 35.5%.

In conclusion, we describe the alternation of MRSA clones that occurred in hospitals from 1990 to 2007 and the increase of the glycopeptide MIC levels, reflecting a worldwide trend. We document the detection of ST1, ST8, ST15 and ST30 in the 1980 isolates; we hypothesize their possible latency and their appearance as the current CA-MRSA clones.