Molecular characterization of Staphylococcus aureus isolates from a 2005 clinical trial of uncomplicated skin and skin structure infections

A clinical trial of uncomplicated skin and skin structure infections (39 locations in 19 states) observed that community-associated or community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) represented 23% of all pathogens at baseline culture and 53% of 190 S. aureus isolates. CO-MRSA strains typically were Panton-Valentine leukocidin (PVL) positive (95%), contained staphylococcal cassette chromosome mec type IVa (99%), were USA300 or USA400 clones (92%), and exhibited minimal coresistances (macrolides and/or fluoroquinolones). Clinical results remained identical (89% cures) regardless of the antimicrobial used or CO-MRSA molecular patterns, PVL production, or antimicrobial susceptibility profiles.

Performance of the BD GeneOhm methicillin-resistant Staphylococcus aureus test before and during high-volume clinical use

We evaluated the use of the BD GeneOhm MRSA real-time PCR assay (BD Diagnostics, San Diego, CA) for the detection of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA). The initial evaluation consisted of 403 paired nasal swabs and was done using the specimen preparation provided with the kit and an in-house lysis method that was specifically developed to accommodate large-volume testing using a minimal amount of personnel time. One swab was placed in an achromopeptidase (ACP) lysis solution, and the other was first used for culture and then prepared according to the kit protocol. PCR was performed on both lysates, and results were compared to those for culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay were 98%, 96%, 77%, and 99.7% with the kit lysate and 98%, 95%, 75%, and 99.7% with the ACP lysate (P, not significant), respectively. The second evaluation was done after implementation of all-admission surveillance using PCR with ACP lysis and a sampling of 1,107 PCR-negative samples and 215 PCR-positive samples that were confirmed by culture. The results of this sampling showed an NPV of 99.9% and a PPV of 73.5% (prevalence, 6%), consistent with our initial findings. The BD GeneOhm MRSA assay is an accurate and rapid way to detect MRSA nasal colonization. When one is dealing with large specimen numbers, the ACP lysis method offers easier processing without negatively affecting the sensitivity or specificity of the PCR assay.

Nationwide trends in molecular epidemiology of methicillin-resistant Staphylococcus aureus, Finland, 1997-2004

Background

In Finland, the annual number of MRSA notifications to the National Infectious Disease Register (NIDR) has constantly increased since 1995, and molecular typing has revealed numerous outbreak isolates of MRSA. We analyzed the data on MRSA notifications of the NIDR, and MRSA isolates were identified mainly by pulsed-field gel electrophoresis (PFGE) at the National Reference Laboratory (NRL) in Finland during 1997–2004. One isolate representative of each major PFGE type was further characterized by multilocus sequence (MLST)-, staphylococcal cassette chromosome mec (SCCmec)-, and Panton-Valentine leukocidin (PVL)-typing.

Results

The annual number of MRSA notifications to the NIDR rose over ten-fold, from 120 in 1997 to 1458 in 2004, and the proportion of MRSA among S. aureus blood isolates tripled, from <1% during 1997–2003 to 2.8% in 2004. During the same period of time, 253 different strains among 4091 MRSA isolates were identified by PFGE: 215 were sporadic and 38 outbreak/epidemic strains, including 24 new strains. Two epidemic strains resembling internationally recognized MRSA clones accounted for most of the increase: FIN-16 (ST125:IA) from <1% in 1997 to 25% in 2004, and FIN-21 (ST228:I) from 6% in 2002 to 28% in 2004. Half of the ten most common strains carried SCCmec IV or V.

Conclusion

The predominant MRSA strains seem to change over time, which encourages us to continue implementing active control measures with each new MRSA case.

Staphylococcus aureus colonization and infection in New York State prisons

Methicillin-resistant Staphylococcus aureus is increasingly responsible for staphylococcal outbreaks in prison. There is limited information on the source of the outbreak strains, risk factors for infection, and transmission of these strains within a prison. We conducted a survey to determine the prevalence of nasal colonization with S. aureus in 2 New York State prisons. S. aureus isolates from clinical cultures collected from all New York State prisons during a 6-month period were compared with the colonizing strains. Analyses were conducted to determine whether prison-level characteristics were associated with colonization or infection with S. aureus. The colonization rate was 25.5% (124/487); 10.5% of the isolates were methicillin resistant, all were staphylococcal chromosomal cassette (SCC)mec type IV, and 61.5% were Panton Valentine leukocidin (PVL) positive. Surprisingly, 21.6% of the methicillin-susceptible isolates were also PVL positive. Of the clinical isolates, 48.3% were methicillin resistant, with 93.1% of the latter being SCCmec type IV and 48.3% being PVL positive. The predominant clone was USA 300. Prison-level risk factors for infection included the proportion of inmates with drug offenses, the length of inmate stay, and the jail from which inmates originated. This study suggests that both new and long-term inmates act as sources of S. aureus strains, with the more virulent of the latter preferentially being selected as pathogens.

Impact of community-acquired methicillin-resistant Staphylococcus aureus in the hospital setting

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is undergoing a transformation as isolates of this historically health care-associated pathogen are reported with increasing frequency in otherwise healthy community-dwelling individuals. This article provides a brief review of the differences between health care-associated and community-acquired MRSA and discusses the potential impact of the changing epidemiology of MRSA on the hospital setting.

Effect of Saliva miltiorrhiza bunge on antimicrobial activity and resistant gene regulation against methicillin-resistant Staphylococcus aureus (MRSA)

This study was conducted in an effort to evaluate the antimicrobial activity and antibiotic-resistant gene regulation from Saliva miltiorrhiza Bunge on methicillin-resistant Staphylococcus aureus (MRSA). A variety of solvent fractions and methanol extracts of S. miltiorrhiza Bunge were tested in order to determine its antimicrobial activities against S. aureus and MRSA. As a result, the hexane fraction of S. miltiorrhiza Bunge evidenced the highest levels of antimicrobial activity against S. aureus and MRSA. The MICs of the hexane fraction against various MRSA specimens were 64<MICs<or=128 microg/ml. The hexane fraction evidenced inhibitory effects superior to those of the chloroform fraction. The results showed inhibition zones of hexane (16 mm) and chloroform (14 mm) fractions against MRSA KCCM 40511 at 1,000 microg/disc. The hexane and chloroform fractions inhibited the expression of the resistant genes, mecA, mecR1, and femA in mRNA. Moreover, the results of Western blotting assays indicated that the hexane and chloroform fractions inhibited the expression of the resistant protein, PBP2a. These results reveal that the hexane and chloroform fractions of S. miltiorrhiza Bunge may prove to be a valuable choice for studies targeted toward the development of new antimicrobial agents.

Molecular epidemiology of community-acquired methicillin-resistant Staphylococcus aureus bacteremia in a teaching hospital

BACKGROUND AND PURPOSE

Methicillin-resistant Staphylococcus aureus (MRSA) is a key nosocomial pathogen globally. Community-acquired MRSA (CA-MRSA) infections have become a growing problem in recent years. The purpose of this 4-year retrospective study was to analyze the molecular epidemiology and susceptibility pattern of isolates from adults (> or =18 years of age) with CA-MRSA bacteremia in northern Taiwan.

METHODS

Molecular epidemiology of CA-MRSA isolates was analyzed by pulsed-field gel electrophoresis. Antimicrobial susceptibility was tested by the disk diffusion method and the minimal inhibitory concentration was determined by Etest.

RESULTS

Thirty eight patients with CA-MRSA bacteremia were enrolled. Thirty one CA-MRSA isolates were available for further molecular typing and susceptibility testing. A total of 13 distinct genotypes were identified and 48.4% (15/31) of the isolates were found to belong to genotype A. Genotype A CA-MRSA isolates were closely associated with the nosocomial strains. All CA-MRSA isolates were multidrug resistant (19.4% susceptible to clindamycin and 25.8% to trimethoprim-sulfamethoxazole) and consistent susceptibility was only observed to glycopeptides, rifampin, and linezolid.

CONCLUSIONS

This study demonstrated that although CA-MRSA genotypes were heterogeneous, the predominant genotype that was circulating in our community was genotype A. Also, the multidrug resistance of CA-MRSA might be connected to the spreading of nosocomial strains in the community.

Allelic variation in genes encoding Panton–Valentine leukocidin from community-associated Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus isolates characteristically contain the genes for Panton-Valentine leukocidin (PVL), which is a proposed virulence factor. To determine whether different alleles of the PVL genes lukS-PV and lukF-PV occur, and whether they are associated with specific genetic lineages of S. aureus, sequences from 28 S. aureus isolates, representing four different multilocus sequence types, and bacteriophages SLT and PVL were compared. Seven nucleotide polymorphisms were identified, which defined three groups of the lukS-PV and lukF-PV sequence. Only one polymorphism resulted in an amino-acid change. Bacteriophage SLT and isolates of bacteriophage type 80/81 contained the prototypic (founder) lukS-PV and lukF-PV sequence. The alleles were not lineage-specific.

Genetic characterization of erythromycin- and methicillin-resistant community-acquired Staphylococcus aureus isolated from children in Texas

Prevalence of Panton-Valentine leukocidin (PVL) toxin, SCCmec, and accessory gene regulator (agr) types were studied in 197 community-acquired methicillin-resistant Staphylococcus aureus (MRSA) from children in Texas. The majority of pediatric macrolide-resistant clindamycin-susceptible community-associated MRSA belonged to PVL(+)/SCC type IV/agr type I group with msrA gene encoding for macrolide resistance. PVL(-)/SCC type II/agr type II strains, although rare, were consistently present in the community throughout the study period.

Panton-Valentine leukocidin genes and staphylococcal chromosomal cassette mec types amongst Finnish community-acquired methicillin-resistant Staphylococcus aureus strains, 1997–1999

Methicillin-resistant Staphylococcus aureus (MRSA) strains from Finland covering years 1997-1999 were studied for the presence of Panton-Valentine leukocidin (PVL) gene loci, and the clinically well-defined community-acquired MRSA (CA-MRSA) strains (n = 108) also for staphylococcal chromosomal cassette mec (SCCmec) and multilocus sequence types (MLST). Only a minority (12%) of the CA-MRSA strains contained the PVL gene loci and possessed genotypes formerly described as typical to CA-MRSA strains. The majority of these strains were heterogenous by MLST and pulsed-field gel electrophoresis (PFGE) analysis but, however, harboured the SCCmec cassette type IV. In conclusion, it seems doubtful to consider only molecular characteristics such as the presence of PVL genes as definite markers for CA-MRSA strains.

Linezolid versus Vancomycin for Prosthetic Joint Infections: a Cost Analysis

BACKGROUND

Prosthetic joint infections (PJIs) caused by methicillin-resistant gram-positive bacteria are primarily treated by intravenous vancomycin. Linezolid, active against methicillin-resistant strains and available in oral and intravenous dosage forms, is a potential alternative to vancomycin for the treatment of PJIs.

OBJECTIVE

To analyze the cost of linezolid therapy (outpatient setting) and vancomycin therapy (inpatient and outpatient settings) for PJIs caused by methicillin-resistant gram-positive bacteria.

METHODS

A decision tree was designed to simulate the clinical outcome and healthcare resource utilization of linezolid, vancomycin by outpatient and home parenteral antimicrobial therapies (OHPAT) and vancomycin administered in inpatient setting (rehabilitation facility) for patients with PJIs caused by methicillin-resistant strains. Clinical inputs were estimated from literature and the cost analysis was conducted from the perspective of the public healthcare provider in Hong Kong.

RESULTS

The base-case analysis showed that the vancomycin (OHPAT) group (USD14,470 per patient) was the least costly alternative, followed by the linezolid group (USD17,877 per patient) and the vancomycin (rehabilitation) group (USD19,980 per patient) (1USD = 7.8HKD). The clinical treatment success rates of vancomycin and linezolid were influential factors. Monte Carlo 10,000 simulations showed that the vancomycin (OHPAT) group was less costly than the arms of linezolid and vancomycin (rehabilitation) 64% and 100% of the time, respectively. The linezolid group was less costly than the vancomycin (rehabilitation) group in 65%of the times.

CONCLUSION

Home-infusion of vancomycin therapy appears to be the least costly treatment approach for PJIs caused by methicillin-resistant gram-positive bacteria from the perspective of a Hong Kong public health organization.

Staphylococcal cassette chromosome mec in MRSA, Taiwan

To determine the predominant staphylococcal cassette chromosome (SCC) mec element in methicillin-resistant Staphylococcus aureus, we typed 190 isolates from a hospital in Taiwan. We found a shift from type IV to type III SCCmec element during 1992–2003, perhaps caused by selective pressure from indiscriminate use of antimicrobial drugs.

[Genotypes of Staphylococcus aureus strains with methicillin resistant phenotype]

BACKGROUND

Methicillin resistant strains of Staphylococcus aureus (MRSA) are an important cause of nosocomial infections.

AIM

To determine the genotypes of MRSA strains.

MATERIAL AND METHODS

Fifty five strains of MRSA, isolated from patients hospitalized in Hospital Base Valdivia, were studied. The phenotype was determined through MicroScan in all strains and by minimum inhibitory concentration (MIC) in 41. The genotype of the strains was analyzed by a duplex polymerase chain reaction (PCR) of the mecA gene, amplifying eight hypervariable DNA regions associated to such gene.

RESULTS

According to MIC, 88% of strains had a pattern of resistance against multiple antimicrobial (penicillin, ampicillin, cephradine, gentamycin, ciprofloxacin, lincomycin and erythromycin). Vancomicin resistan strains were not detected. Only 53 strains (96%) had at least one of the eight hypervariable regions and were classified as MRSA. Genotypic patterns types 15 were the most commonly detected in 38% and 34% of strains, respectively. MicroScan erroneously classified five strains in an incorrect phenotype, according to results obtained with duplex PCR. MIC results did not differ from those of duplex PCR.

CONCLUSIONS

Duplex- PCR is a useful tool to detect hyper variable regions associated to mecA gene.

Evolution, antimicrobial susceptibility and assignment to international clones of methicillin-resistant Staphylococcus aureus isolated over a 9-year period in two Spanish hospitals

Antimicrobial resistance profiles, restriction fragment length polymorphism of the coagulase gene and repetitive element sequence-based PCR were used to classify 210 methicillin-resistant Staphylococcus aureus isolates recovered between 1997 and 2005 in two hospitals in Vigo, north-west Spain. Representative isolates belonging to the epidemic clones were analysed by spa typing and multilocus sequence typing, and the staphylococcal chromosomal cassette (SCC)mec type was determined for all isolates. The New York/Japan clone (t002-ST5-II) was detected in Spain for the first time. However, the New York/Japan and the Brazilian (t037-ST239-IIIA) clones were replaced by EMRSA-16 (t018-ST36-II), which at present is the predominant clone.

[Investigation of the presence of panton-valentin leucocidin (PVL) in Staphylococcus aureus strains isolated from clinical samples]

Panton-Valentin leucocidin (PVL) is a cytotoxin which causes tissue necrosis by degradating leucocytes and other cell types. PVL has recently become very up to date as it has been shown to be the major virulance factor of community acquired methicillin resistant Staphylococcus aureus strains. In this study, the presence of PVL was investigated in methicillin sensitive and resistant S. aureus (MSSA and MRSA, respectively) strains which were isolated from clinical samples between January 2005-May 2006 at Dokuz Eylul University Hospital, Izmir. Fifty five MRSA and 79 MSSA strains which were isolated from blood, wound and respiratory tract samples were randomly included to the study. The presence of PVL was evaluated by multiplex polymerase chain reaction (PCR) which detects pvl and S. aureus-specific nuc genes. As a result, PVL positivities were detected in two (5%) of 40 MSSA and four (10.3%) of 39 MSSA strains isolated in the years 2005 and 2006, respectively. None of the MRSA isolates had pvl gene. Although this cytotoxin was rarely detected among MSSA isolates, it was interesting to note that the prevalence of PVL was twice more in the year 2006 compared to 2005. It was also worth to notify that four of six (66.7%) PVL positive strains had been isolated from the patients of general surgery inpatient or outpatient clinics.

[Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases]

Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent pathogens associated with nosocomial infections. However, most recently, MRSA has arisen as an emerging community pathogen, causing serious infections, mainly among young patients. We herein describe 33 cases of infections caused by community-acquired MRSA (C-MRSA), diagnosed between May 2005 and June 2006, at "Eva Perón" Hospital. The isolations were retrospectively studied. Methicillin resistance was confirmed by means of the detection of the mecA gene, and the genes for two virulence factors (Panton-Valentine Leucocidin -PVL- and gamma-haemolysin) as well as the cassette mec type were screened by PCR. All the patients were previously healthy. Four patients under 12, presented bacteremia, one had serious pneumonia, and the three remaining patients had osteoarticular infections; all the patients over 12, had skin and soft tissue infections without systemic damage. The C-MRSA strains harboured cassette mec type IV, and the PVL and gamma-haemolysin genes. They were methicillin-resistant, with no other associated resistances. It is important to consider the presence of these community- acquired strains in order to develop strategies for their correct treatment.

Clonal spread of SCCmec type IV methicillin-resistant Staphylococcus aureus between community and hospital

The staphylococcal chromosome cassette (SCC)mec types of 382 hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates in Taiwan were analysed over a 7-year period (1999-2005). There was an abrupt increase in SCCmec type IV in HA-MRSA during 2005. The molecular epidemiology of a subset (n = 69) of HA-MRSA isolates with SCCmec types III, IV or V was characterised and compared with that of community-acquired MRSA (CA-MRSA) (n = 26, collected during 2005). Pulsed-field gel electrophoresis revealed three major pulsotypes (A, B and C) and 15 minor clones. Pulsotypes B and C, which contained isolates carrying SCCmec types IV and V, respectively, included both CA-MRSA and HA-MRSA isolates. Among 24 toxin genes analysed, five genes had significant differential distribution between CA-MRSA and SCCmec type III HA-MRSA. Furthermore, among SCCmec type IV isolates, the seb gene was detected more commonly in HA-MRSA. Analysis of representative members of the three major pulsotypes by multilocus sequence typing revealed two sequence types (STs), namely ST239 (SCCmecIII) and ST59 (SCCmecIV or SCCmecV). This suggests that ST59:SCCmecIV, which is usually community-acquired, has become an important nosocomial pathogen in the hospital studied.

Application of loop-mediated isothermal amplification technique to rapid and direct detection of methicillin-resistant Staphylococcus aureus (MRSA) in blood cultures

Staphylococcus aureus is the most important pathogen in nosocomial infections, including bloodstream infections. Prompt identification of S. aureus from blood cultures and detection of methicillin resistance are essential in cases of suspected sepsis. A novel nucleic acid amplification technique, loop-mediated isothermal amplification (LAMP), which amplifies DNA under isothermal conditions (63 degrees C) with high specificity, efficiency, and rapidity, was applied to detect methicillin-resistant S. aureus (MRSA) directly from positive blood culture bottles. MRSA-LAMP, which targets the spa gene, encoding S. aureus-specific protein A, and the mecA gene, encoding penicillin-binding protein-2' for methicillin resistance, could detect MRSA within 2 h after the blood culture signal became positive. The diagnostic values of LAMP, compared to a duplex real-time polymerase chain reaction (Drt-PCR) assay, were 92.3% and 96.2% sensitivity, 100% and 100% specificity, 100% and 100% positive predictive value (PPV), and 96.9% and 98.4% negative predictive value (NPV), respectively. These two methods had almost the same results, but the LAMP method is more cost-effective and provides excellent availability for rapid examination in a hospital clinical laboratory. Therefore, the LAMP assay appears to be a sensitive and reliable new method to diagnose MRSA bloodstream infection for appropriate antibiotic therapy.

The emergence and importation of diverse genotypes of methicillin-resistant Staphylococcus aureus (MRSA) harboring the Panton-Valentine leukocidin gene (pvl) reveal that pvl is a poor marker for community-acquired MRSA strains in Ireland

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) carrying pvl is an emerging problem worldwide. CA-MRSA tends to harbor staphylococcal cassette chromosome mec type IV (SCCmec IV), to be non-multiantibiotic resistant, and to have different genotypes from the local hospital-acquired MRSA (HA-MRSA). However, in Ireland, 80% of HA-MRSA isolates have the non-multiantibiotic-resistant genotype ST22-MRSA-IV. This study investigated MRSA isolates from Ireland (CA-MRSA, health care-associated MRSA, and HA-MRSA) for the carriage of pvl and determined the genotypic characteristics of all pvl-positive isolates identified. All 1,389 MRSA isolates were investigated by antibiogram-resistogram typing and SmaI DNA macrorestriction analysis. pvl-positive isolates were further characterized by multilocus sequence typing and SCCmec, agr, and toxin gene typing. Twenty-five (1.8%) MRSA isolates belonging to six genotypes (ST30, ST8, ST22, ST80, ST5, and ST154) harbored pvl. Nineteen of these (76%) were CA-MRSA isolates, but a prospective study of MRSA isolates from 401 patients showed that only 6.7% (2/30) of patients with CA-MRSA yielded pvl-positive isolates. Thus, pvl cannot be used as a sole marker for CA-MRSA. Fifty-two percent of pvl-positive MRSA isolates were recovered from patients with skin and soft tissue infections; thirty-six percent were from patients of non-Irish ethnic origin, reflecting the increasing heterogeneity of the Irish population due to immigration. All 25 pvl-positive isolates carried SCCmec IV; 14 (56%) harbored SCCmec IV.1 or IV.3, and the remaining 11 isolates could not be subtyped. This study demonstrates that pvl is not a reliable marker for CA-MRSA in Ireland and reveals the emergence and importation of diverse genotypes of pvl-positive MRSA in Ireland.

Update to the multiplex PCR strategy for assignment of mec element types in Staphylococcus aureus

Staphylococcal cassette chromosome mec (SCCmec) typing is important for the identification and definition of methicillin-resistant Staphylococcus aureus clones, and for routine purposes, multiplex PCR assays are the most adequate for SCCmec typing. Here, we describe an update to the multiplex PCR strategy for SCCmec typing that we described in 2002 so that SCCmec types IV and V may be properly identified.

Sporadic "transitional" community-associated methicillin-resistant Staphylococcus aureus strains from health care facilities in the United States

We describe phenotypic and genotypic traits of a group of methicillin-resistant Staphylococcus aureus (MRSA) clones that are either remnants of unsuccessful community-associated MRSA (CA-MRSA) clones or represent a transitional state with some yet-to-be-acquired characteristics of CA-MRSA. These rare strains (n = 20) were identified during a 10-year period (1990-1999) from 13 unrelated health care facilities in Wisconsin. The isolates were recovered from patients in nosocomial or long-term chronic care facilities (60%) and outpatient settings (40%). Sixty percent (n = 12) of the isolates were recovered from skin and soft tissue infections, whereas the remaining isolates (n = 8) were from invasive infections. Ninety percent of isolates were susceptible to all antibiotic classes tested or resistant to erythromycin and clindamycin. Pulsed-field gel electrophoresis, multilocus sequence typing, and spa typing clustered these isolates into 8, 8, and 14 clonal groups, respectively. Eight plasmid profiles were represented in these strains. All four agr types were represented, with type IV being predominant (40%). All strains harbored subtypes of type IV staphylococcal cassette chromosome mec but lacked genes for the virulence factor Panton-Valentine leukocidin (PVL). The strains harbored one or more of the following toxin genes: sea, seb, sec, sed, see, seh, sej, sek, sel, seg, sei, sem, sen, and seo. Individual clonal groups maintained the same set of enterotoxin genes even though they were isolated over extended time periods, suggesting significant genomic stability. The potential role of PVL-carrying phages and plasmids in the success of CA-MRSA clones has been discussed.

Retapamulin inhibition of translation and 50S ribosomal subunit formation in Staphylococcus aureus cells

Retapamulin inhibited protein biosynthesis and cell viability in methicillin-sensitive and methicillin-resistant Staphylococcus aureus organisms. A specific inhibitory effect on 50S ribosomal subunit formation was also found. Pulse-chase labeling experiments confirmed the specific inhibition of 50S subunit biogenesis. Turnover of 23S rRNA was found, with no effect on 16S rRNA amounts.