Healthcare-associated MRSA Isolates Research Articles

Quorum Sensing, Virulence, and Antibiotic Resistance of USA100 Methicillin-Resistant Staphylococcus aureus Isolates.

Methicillin-resistant Staphylococcus aureus (MRSA) infections impact all patient populations both in the community and in health care settings. Despite advances in our knowledge of MRSA virulence, little is known about the regulatory mechanisms of USA100 health care-associated MRSA isolates, which are the second most frequently identified MRSA isolates found in all infections. This work focused on the contribution of the USA100 agr type II quorum-sensing system to virulence and antibiotic resistance. From a MRSA strain collection, we selected 16 representative USA100 isolates, constructed mutants with Δagr mutations, and characterized selected strain pairs for virulence factor expression, murine skin infection, and antibiotic resistance. For each strain pair, hemolysis and extracellular protease expression were significantly greater in the wild-type (WT) strains than in the Δagr mutants. Similarly, mice challenged with the WT strains had larger areas of dermonecrosis and greater weight loss than those challenged with the Δagr mutants, demonstrating that the USA100 agr system regulates virulence. Although USA100 isolates exhibit a high level of antibiotic resistance, the WT and Δagr strain pairs showed no difference in MICs by MIC testing. However, in the presence of a sub-MIC of vancomycin, most of the USA100 Δagr mutants exhibited slower growth than the WT isolates, and a couple of the Δagr mutants also grew more slowly in the presence of a sub-MIC of cefoxitin. Altogether, our findings demonstrate that the USA100 agr system is a critical regulator of virulence, and it may have a contribution to the optimal survival of these MRSA strains in the presence of antibiotics.IMPORTANCE USA100 health care-associated MRSA isolates are highly antibiotic resistant and can cause invasive disease across all patient populations. Even though USA100 strains are some of the most frequently identified causes of infections, little is known about virulence regulation in these isolates. Our study demonstrates that the USA100 agr quorum-sensing system is important for the control of toxin and exoenzyme production and that the agr system has a key role in skin infection. In some USA100 isolates, the agr system is important for growth in the presence of low levels of antibiotics. Altogether, our findings demonstrate that the USA100 agr system is a critical regulator of virulence and that it may make a contribution to the optimal survival of these MRSA strains in the presence of antibiotics.

Abstract P-174: CLONAL AND DRUG-RESISTANCE DYNAMICS OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS IN PEDIATRIC POPULATIONS IN CHINA

Aims & Objectives: We aimed to evaluate the clonal and drug-resistance dynamics of (Methicillin-resistant Staphylococcus aureus) MRSA in Chinese children from 2010 to 2016. Methods Totally 170 MRSA isolates were recovered from Beijing Children’s hospital from 2010 to 2016. The genotypic characteristics of all strains were determined. Antimicrobial susceptibility testing was performed by agar dilution method except sulphamethoxazole/trimethoprim (E-test method). Panton-Valentine leukocidin (pvl) gene was detected by PCR assay. Results Eighty-four isolates were classified as Community-associated Methicillin-resistant Staphylococcus aureus (CA-MRSA). ST59-SCCmecIV-t437-agrI was the most prevalent both in CA-MRSA (47.6%) and healthcare-associated MRSA (HA-MRSA) (46.5%). ST239-SCCmecIII-t030-agrI accounted for 14.0% of total HA-MRSA isolates, which had not been determined in 2016. The prevalence of pvl was similar among CA- and HA- MRSA (p=0.0805). There were no changes in antibiotic resistance in CA-MRSA from 2010 to 2016. HA-MRSA demonstrated an overall trend of decreased resistant to tetracycline, gentamicin, ciprofloxacin, rifampin, and an increased resistant to chloramphenicol during the studied period, which were basically consistent with the difference of antibiotic resistance patterns between ST59-SCCmecIV and ST239-SCCmecIII isolates. The percentage of isolates with minimal inhibitory concentration (MIC) ≥1 mg/L increased from 45.0% in 2010–2013 to 87.1% in 2016, and meanwhile, the percentage of isolates with MIC=0.5 mg/L decreased from 55.0% (55/100) to 12.9 (p<0.0001). Conclusions ST59-SCCmecIV had spread to hospital and replaced the traditional hospital associated ST239-SCCmecIII clone, which were accompanied by changes in drug resistance. Furthermore, vancomycin MIC creep indicated that the rational use of antibiotics should be taken seriously.

Predominance of ST5-II-t311 clone among healthcare-associated methicillin-resistant Staphylococcus aureus isolates recovered from Zhejiang, China

ObjectivesTo determine the molecular characteristics and antimicrobial susceptibility of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in Zhejiang Province. MethodsA total of 391 HA-MRSA isolates were collected from 12 hospitals in five cities of Zhejiang Province, between January 2012 and May 2013. Susceptibility to vancomycin, teicoplanin, linezolid, tigecycline, and daptomycin was determined. Resistant isolates were screened for resistance mutations. Ten isolates from each hospital were then chosen at random for molecular typing. ResultsThe isolates showed good susceptibility to all five anti-MRSA agents; only five sporadic non-susceptible isolates were detected. CC5/ST5-MRSA-II-t311 (39/120, 32.5%) was found to be the predominant HA-MRSA clone and was spread between the different hospitals in Hangzhou. CC5/ST5-MRSA-II-t002 was the most prevalent clone in Ningbo, while CC239/ST239-MRSA was epidemic only in certain hospitals in Wenzhou and Shaoxing. Fifteen ST59 isolates (15/120, 12.5%) were identified among the HA-MRSA isolates. ConclusionsCC5/ST5-MRSA-II-t311 has become the predominant HA-MRSA clone in Hangzhou, Zhejiang Province. ST59 MRSA has spread into hospitals. The isolates showed good susceptibility to all five anti-MRSA agents.

Emergence of methicillin-resistant Staphylococcus aureus SCCmec type IV/V epidemic clones in a large teaching hospital in China

To investigate the staphylococcal cassette chromosome mec (SCCmec) genotype and molecular epidemiological characteristics of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in a large teaching hospital in China. From January 2012 to December 2012, a total of 71 nonduplicate HA-MRSA were collected in a teaching hospital in Changsha, China. SCCmec types were determined by multiplex PCR, and Panton-Valentine leukocidin (PVL) gene was detected by PCR. The homology among the tested isolates was determined using pulsed-field gel electrophoresis (PFGE). Of the 71 HA-MRSA isolates, 49 (69.0%) carried SCCmec III, 10 (14.1%) carried SCCmec IV, 3 (4.2%) carried SCCmec V and 3 (4.2%) carried SCCmec II; the remaining 6 isolates were not typeable by PCR. Compared with patients having SCCmec I/II/III MRSA infections, those with SCCmec IV/V MRSA infections had a significantly younger age and a similar duration of hospital stay before the first MRSA-positive culture and total hospital stay. PVL genes were strongly associated with SCCmec type IV/V MRSA infections. HA-SCCmec IV/V MRSA strains showed a greater susceptibility to rifampicin, gentamicin, levofloxacin, ciprofloxacin, and tetracycline than HA-SCCmec I/II/III MRSA strains. The 13 HA-SCCmec IV/V MRSA isolates formed one large group at the 55% similarity level. Three PFGE clusters with a similarity index of 85% or more were identified, and unique PFGE profiles were observed in 4 isolates. This is the first report of HA-MRSA isolates carrying SCCmec V in Chinese hospitals. SCCmec types IV and V MRSA clones have emerged in Chinese hospitals, which urges more rigorous surveillance of their spread in healthcare facilities in China.

Chlorhexidine whole-body washing of patients reduces methicillin-resistant Staphylococcus aureus and has a direct effect on the distribution of the ST5-MRSA-II (New York/Japan) clone.

Methicillin-resistant Staphylococcus aureus (MRSA) colonizes the skin of hospitalized patients and is associated with high morbidity and mortality. To prevent colonization and infection by S. aureus, better disinfection practices are required. Therefore, we evaluated the effect of chlorhexidine whole-body washing on hospital-acquired S. aureus infections among intensive care unit (ICU) patients in a tertiary hospital in Mexico. The study was conducted over 18 months to evaluate the effect of 2 % chlorhexidine gluconate (CXG) whole-body washing of ICU adult patients on chlorhexidine and antibiotic resistance, biofilm production and clonal distribution of S. aureus in a tertiary care hospital. Minimum inhibitory concentrations for CXG, antibiotic susceptibility and biofilm production by S. aureus isolates were determined. Pulsed-field gel electrophoresis, multilocus sequence typing (MLST) and PCR for Panton-Valentine leucocidin (PVL) were used for molecular typing of MRSA isolates.Results/Key findings. We included 158 isolates. A reduction in antibiotic resistance in the study period was observed for clindamycin, levofloxacin, norfloxacin, oxacillin and trimethoprim/sulfamethoxazole. None of the isolates showed reduced susceptibility to CXG. Most of the isolates were non-biofilm producers (147/158). The most commonly identified clone was a descendant of the ST5-MRSA-II (New York/Japan) clone. This clone decreased during the intervention period and reappeared markedly in the post-intervention period. During the post-intervention period, two isolates were related with the clone ST8-MRSA-IV (also known as USA300). Our findings suggest that the CXG bathing favored the reduction of healthcare-associated MRSA isolates and a temporary reduction of the predominant ST5-MRSA-II (New York/Japan) clone.

Effects of toluidine blue O (TBO)-photodynamic inactivation on community-associated methicillin-resistant Staphylococcus aureus isolates

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was recognized as a leading pathogen and has been shown to be genetically different from the health care-associated MRSA (HA-MRSA). Photodynamic therapy (PDT) is considered a potential alternative method for the treatment of resistant bacterial infections, but the effect of PDT on CA-MRSA is unknown. The purpose of this study was to compare the bactericidal effects of toluidine blue O (TBO) on CA-MRSA and HA-MRSA and investigate the photodynamic inactivation effects of TBO (TBO-PDI) against bacterial virulence factors. TBO-PDI effects were determined by measuring the survival fractions for four strains and bactericidal activities for 26 CA-MRSA isolates and 26 HA-MRSA isolates. The influences of TBO-PDI on DNA fragmentation and the activities of protease, lipase, staphylococcal α-hemolysin, and enterotoxin were studied. TBO-PDI has effective bactericidal activity against both CA- and HA-MRSA. However, the bactericidal activity of TBO-PDI was significantly higher against HA-MRSA than CA-MRSA isolates. In addition, TBO-PDI treatment using a sublethal TBO concentration led to reduced production of several virulence factors, including protease, lipase, staphylococcal α-hemolysin, and enterotoxin. Although TBO-PDI is slightly less effective against CA-MRSA than HA-MRSA isolates, TBO-PDI could reduce the production of virulence factors at a sublethal TBO concentration, which would be beneficial for treating CA-MRSA infections.

Emergence of community-acquired methicillin-resistant Staphylococcus aureus in an Iranian referral paediatric hospital

ABSTRACTThe epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals has been changed in recent years due to the arrival of community-associated MRSA (CA-MRSA) strains into healthcare settings. The aim of this study is to investigate the distribution of staphylococcal cassette chromosome mec (SCCmec) type V as well as SCCmec IV subtypes, which have been associated with community-acquired infection among healthcare-associated MRSA (HA-MRSA) isolates. Antimicrobial susceptibility, SCCmec type, spa type and the presence of Panton-Valentine leukocidin (PVL) genes were determined for all HA-MRSA isolates in an Iranian referral hospital. In this study of 48 HA-MRSA isolates, 13 (27%), three (6.2%), five (10.4%) and one (2%) belonged to SCCmec subtypes IVa, IVb, IVc and IVd, respectively. Only two isolates (4.2%) belonged to SCCmec types V. Notably, one isolate was found to harbour concurrent SCCmec subtypes IVb and IVd. MRSA containing SCCmec subtype IVb, IVc and IVd as well as type V isolates were all susceptible to chloramphenicol, clindamycin and rifampicin, while the sensitivity to these antibiotics was lower among MRSA containing SCCmec subtype IVa. The most frequently observed spa ttype was t037, accounting for 88% (22/25). Three other spa type was t002, t1816 and t4478. Large reservoirs of MRSA containing type IV subtypes and type V now exist in patients in this Iranian hospital. Therefore, effective infection control management in order to control the spread of CA-MRSA is highly recommended.

A 12-year survey of methicillin-resistant Staphylococcus aureus infections in Greece: ST80-IV epidemic?

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of both healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA) infections. Severe MRSA infections have been associated with the virulence factor Panton–Valentine leukocidin (PVL). The aim of this study was to investigate susceptibility patterns, the presence of toxin genes, including that encoding PVL, and clonality among MRSA isolates collected from patients in Greece over a 12-year period. MRSA isolates were collected from January 2001 to December 2012 from six different hospitals. Antibiotic susceptibility was determined with the disk diffusion method and the Etest. The presence of the toxic shock syndrome toxin-1 gene (tst), the enterotoxin gene cluster (egc) and the PVL gene was tested with PCR. The genotypic characteristics of the strains were analysed by SCCmec and agr typing, and clonality was determined with pulsed-field gel electrophoresis and multilocus sequence typing. An increasing rate of MRSA among S. aureus infections was detected up to 2008. The majority of PVL-positive MRSA isolates belonged to a single clone, sequence type (ST)80-IV, which was disseminated both in the community and in hospitals, especially during the warmest months of the year. Carriage of tst was associated with ST30-IV, whereas egc was distributed in different clones. CA-MRSA isolates were recovered mainly from skin and soft tissue infections, whereas HA-MRSA isolates were associated with surgical and wound infections. During the period 2001–2012, ST80-IV predominated in the community and infiltrated the hospital settings in Greece, successfully replacing other PVL-positive clones. The predominance of ST239-III in HA-MRSA infections was constant, whereas new clones have also emerged. Polyclonality was statistically significantly higher among CA-MRSA isolates and isolates from adult patients.

Community-genotype strains of methicillin-resistant Staphylococcus aureus with high-level mupirocin resistance in a neonatal intensive care unit

AimThe aim of this study was to investigate the genotypes of mupirocin-resistant methicillin-resistant Staphylococcus aureus (MR-MRSA) isolates in our neonatal intensive care unit (NICU) and their potential source. Study designOne hundred one MRSA isolates obtained from 59 inborn and 42 outborn infants were identified and their antimicrobial susceptibility determined. Using pulse-field gel electrophoresis (PFGE) analysis, MR-MRSA isolates obtained from the neonatal patients in the NICU were compared with those from adult hospitalized in the same hospital and with community-associated MRSA (CA-MRSA) isolates recovered from different hospitals in Korea. ResultsOverall, 47% of CA-MRSA and 79% of healthcare-associated MRSA isolates exhibited high-level mupirocin resistance (HLMR). Forty-five percent of the outborn infants were considered to have CA-MRSA at the time of admission to our NICU. Most HLMR-MRSA isolates from neonates were grouped into a single cluster by PFGE analysis, and which included CA-MRSA isolates with HLMR recovered from outborn infants who were already colonized when they were transferred to our NICU. They belonged to the same PFGE group as the community-genotype strains isolated from different hospitals in Korea. HLMR-MRSA isolates from adults patients were classified as different clones. None of the attending staff in the NICU were nasal carriers. ConclusionCommunity-genotype strains of MRSA with HLMR may be imported to our NICU through obstetrics clinics and contribute to MRSA colonization or infection in facilities with a high rate of admission of outborn infants.

Hospital-associated MRSA and antibiotic resistance—What have we learned from genomics?

In many parts of the world, MRSA are responsible for a high proportion of S. aureus infections in patients in contact with healthcare. Molecular studies have shown this is due to one or more MRSA clones that have become endemic in each hospital or healthcare facility, resulting in hospital- or healthcare-associated MRSA (HA-MRSA). The infection rate and clones responsible for HA-MRSA can vary substantially in different geographical locations. Molecular methods have allowed clones to be categorized, as well as the opportunity to track the evolution and spread of clones in healthcare settings and around the world. The genomes of HA-MRSA isolates belonging to the same clonal group can show dramatic variability particularly in the carriage of mobile genetic elements (MGEs) encoding virulence and resistance genes. HA-MRSA are potentially resistant to all classes of antibiotics, although individual isolates that are fully drug resistant are not reported. The incidence of fluoroquinolone resistance in HA-MRSA is remarkably high, suggesting use of this class of antibiotics as well as the β-lactams contributes to the selection and success of HA-MRSA clones in the hospital setting.

Prevalence of antiseptic resistance genes qacA/B and specific sequence types of methicillin-resistant Staphylococcus aureus in the era of hand hygiene

Sir, In an attempt to control the spread of methicillin-resistant Staphylococcus aureus (MRSA) and other multiresistant organisms in hospitalized patients, hand hygiene campaigns have promoted the widespread use of alcohol-based hand solutions containing antiseptic agents such as chlorhexidine and quaternary ammonium compounds. The use of these products, however, has led to increased resistance to these antiseptic agents in MRSA strains. – 5 qacA/B are plasmid-borne resistance genes coding for multidrug efflux pumps that confer high-level resistance to chlorhexidine, quaternary ammonium compounds and other antiseptic compounds commonly used in hand hygiene solutions. They are associated with higher MICs and tolerance of these antiseptic agents. qacA/B genes have been found in healthcare-associated MRSA (HA-MRSA) isolates from around the world. – 8 In addition, the prevalence of qacA/B genes has been associated with particular sequence types (STs) of HA-MRSA. To our knowledge, the prevalence of MRSA strains harbouring these genes has not been researched in Australia. In this study, we characterize the prevalence of qacA/B genes in HA-MRSA isolates in our institution spanning 10 years, from 2000 to 2009. We determined whether the national hand hygiene campaign implemented in 2006 had any impact on the prevalence of these genes and, in addition, if any relationship exists between the different STs of HA-MRSA and qacA/B gene prevalence. All (total 151) clinically significant unique HA-MRSA isolates from the period 2000–09 from Nepean Hospital, a 490 bed tertiary referral hospital in Sydney, were used in this study. The presence of qacA/B genes in these isolates was evaluated by real-time PCR using the following primers: qacA/B forward primer 5′-CTATGGCAATAGGAGATATGGTGT and reverse primer 5′-CCACTACAGATTCTTCAGCTACATG. The HA-MRSA isolates were categorized into STs using their antibiograms and correlations with pre-existing typing performed on HA-MRSA isolates in our institution by the Australian Group on Antimicrobial Resistance. Quantities of hand hygiene solutions used by the hospital were obtained via the pharmacy database. A sustained .6-fold increase in antiseptic-containing alcoholbased hand solution use occurred as a result of the hand hygiene campaign (‘Clean hands saves lives’) implemented in 2006 [amounts of 0.5% chlorhexidine gluconate and quaternary ammonium compounds used (average litres per year) were 968 and 150 L before the hand hygiene campaign (2004–06) and 3967 and 2958 L after the hand hygiene campaign (2007–09), respectively]. The yearly prevalence of qacA/B genes in HA-MRSA isolates from 2000 to 2009 ranged from 65.0% to 94.7% (mean 78.6%). This is higher than that previously found in the UK (8%–26%), Europe (63%) and Asia (33%–61%), but comparable to that found in a recent study in Geneva (79%). The HA-MRSA isolates in this study comprise two STs: ST239 MRSA-III Aus-2 EMRSA and ST22 MRSA-IV EMRSA-15. The ST239 type was the predominant strain throughout the study period (mean yearly prevalence of ST239 from 2000 to 2009 was 84.3%, range 75%–100%). Comparing the prevalence of the qacA/B genes before (2000– 06) and after (2007–09) the hand hygiene campaign, we did not find an increase in the prevalence of these genes despite the marked increase in antiseptic hand solutions after 2006 [mean yearly prevalence of qacA/B-positive MRSA isolates between 2000 and 2006 and between 2007 and 2009 was 78.6% and 73.5%, respectively (P1⁄40.53; x1⁄40.39, df1⁄41)]. Similarly, there was no change in the incidence of MRSA ST239 [mean yearly prevalence of MRSA ST239 between 2000 and 2006 and between 2007 and 2009 was 85.6% and 78.6%, respectively (P1⁄40.37; x1⁄40.81, df1⁄41)]. Interestingly, we found a significant association between qacA/B gene positivity and MRSA type ST239 [94.5% of qacA/Bpositive isolates were ST239 and 88.9% of ST239 isolates were qacA/B positive (OR1⁄429.09, CI1⁄48.93–94.82)]. This relationship between qacA/B and MRSA ST239 has been suggested in previous studies in the UK and Taiwan; however, the prevalence of this MRSA strain, as well as qacA/B genes, was much lower in these studies. MRSA ST239 is found in significantly high numbers in Eastern Australia, and is associated with a broad spectrum of antimicrobial resistance and epidemic potential. The qacA/B genes are thought to be located on multiresistance plasmids, such as pSK1, and co-transmitted with plasmid-mediated antimicrobial resistance genes; hence their association with this multiresistant strain of MRSA is logical. The high prevalence of this ST239 strain could be due to selective pressure from the use of antiseptic products and/or the widespread use of antimicrobial agents. Our findings suggest the latter, given the absence of a corresponding rise in qacA/B genes with increased antiseptic hand solution use; however, the baseline use of antiseptic agents within the hospital could also explain the high prevalence of qacA/B genes even prior to the hand hygiene campaign.

Methicillin-ResistantStaphylococcus aureusUSA400 Clone, Italy

To the Editor: In the past 30 years, methicillin-resistant Staphylococcus aureus (MRSA) has been the leading cause of nosocomial infections throughout the world. Healthcare-associated MRSA (HA-MRSA) isolates are resistant to multiple antimicrobial drugs. This resistance severely hampers treatment options. During the past decade, MRSA isolates have also emerged as major pathogens in the community, first in the United States and later worldwide. Community-associated MRSA (CA-MRSA) isolates are usually more susceptible to antimicrobial drugs but are more virulent than HA-MRSA isolates. Among various determinants involved in the pathogenesis of CA-MRSA infections, special attention has been focused on the Panton-Valentine leukocidin (PVL), which has a strong epidemiologic link with CA-MRSA clones (1). It has been suggested that CA-MRSA might move to healthcare settings, blurring the line between HA- and CA-MRSA (2). Nevertheless, CA-MRSA isolates are increasingly being reported as pathogens in the general population in persons with no risk factors for HA-MRSA acquisition. These pathogens are generally associated with skin and soft tissue infections, but also with more severe infections such as necrotizing pneumonia or septicemia. CA-MRSA strains usually harbor a staphylococcal cassette chromosome (SCC) mec (type IV or V) that is smaller than the type I–III SCCmec elements commonly found in HA-MRSA strains. To date, 5 major CA-MRSA clonal lineages from diverse genetic backgrounds have been recognized by pulsed-field gel electrophoresis and multilocus sequence typing; certain clones predominate in specific areas of the world (1). The most common lineages in the United States are sequence type (ST) 1 (USA400) and ST8 (USA300), which usually carry type IV SCCmec and PVL-encoding genes. Over the past few years, ST8 (USA300) has become predominant in the United States (3), also emerging as a major cause of nosocomial infections (4). In Europe, data are more limited, but the situation appears to be more varied: the predominant CA-MRSA clonal lineage is ST80 (5), although single cases or small clusters caused by ST8 (USA300) have increasingly been reported (6–8). In contrast, the ST1 (USA400) clone is still rare in Europe (9,10). We describe the importation of ST1 (USA400) into Italy and its isolation in the country. The organism was isolated from an Italian woman with a skin infection that she contracted in the United States. In late November 2007, a 36-year-old Italian woman was seen at Pordenone Hospital (northeastern Italy) for spider-bite–like skin lesions on the face, characterized by rapid evolution to furuncles and small abscesses. The infection had started ≈1 month earlier in California, where she had spent several months on business (wine import-export), and where she had been treated empirically with amoxicillin/clavulanate for 10 days (1 g, 3×/day), with no clinical improvement. Culture of the pus from the abscesses yielded an MRSA isolate that was resistant to oxacillin and susceptible to all non-β-lactam antimicrobial drugs tested by Vitek 2 AST-P536 card (bioMerieux, Marcy l’Etoile, France). Such a particular susceptibility pattern and the community origin of the infection prompted molecular investigation and typing by established methods, which confirmed the isolate to be CA-MRSA and identified it as belonging to the USA400 clone (ST1, type IVa SCCmec, presence of PVL genes, agr type III, spa type t128). Notably, t128 is the spa type found in MW2, the highly virulent prototype strain of USA400. Treatment with oral levofloxacin for 7 days (500 mg, 1×/day) led to complete resolution of the infection. After more than a year, the patient has experienced no recurrences. All 3 previously reported cases of CA-MRSA infection in Italy were caused by type IV SCCmec, PVL-positive strains, none of which, however, belonged to the ST80 clonal lineage that predominates in Europe (7). The first case (in 2005) was a necrotizing pneumonia caused by an ST30 isolate; the 2 other cases (2006) were severe invasive sepsis and a neck abscess, both caused by ST8 (USA300) isolates. The case we note here documents the importation of a US pathogen into a country in Europe, from an area where the pathogen is widespread and has been highly virulent since the late 1990s, to an area where its penetration in the past has been poor.

Complex Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus Isolates From Children With Cystic Fibrosis in the Era of Epidemic Community-Associated Methicillin-Resistant S aureus

Limited data exist about the molecular types of methicillin-resistant Staphylococcus aureus (MRSA) strains found in children with cystic fibrosis (CF). We sought to characterize MRSA strains from these patients and compare them with MRSA strains from non-CF pediatric patients. All MRSA isolates were collected prospectively at Children's Medical Center in Dallas, TX, and the University of Chicago Comer Children's Hospital in 2004 to 2005. All CF MRSA isolates underwent susceptibility testing, multilocus sequence typing, Panton-Valentine leukocidin gene detection (pvl+), and staphylococcal chromosome cassette mec (SCCmec) typing. A total of 22 of 34 MRSA isolates (64.7%) from patients with CF belonged to clonal complex (CC) 5 and contained SCCmec II, so-called health-care associated MRSA (HA-MRSA) strains. Nine of 34 MRSA strains (26.5%) were CC 8, and contained SCCmec IV, so-called community-associated MRSA (CA-MRSA) strains. The CA-MRSA strains tended to be isolated from newly colonized CF patients. In contrast, CC8 isolates predominated among the non-CF patients (294 of 331 patients; 88.8%). MRSA isolates from children with CF were more likely to be resistant to clindamycin (65% vs 19%, respectively) and ciprofloxacin (62% vs 17%, respectively) compared with strains from non-CF patients (p < 0.001). There was no difference in the rate of pvl+ isolate recovery from children with CF undergoing a surveillance culture (7 of 23 children) compared with those with pulmonary exacerbation (3 of 11 children; p = 1.0). Both CA-MRSA (CC8) isolates and HA-MRSA (CC5) isolates populate the respiratory tracts of children with CF. HA-MRSA isolates predominated, but CA-MRSA strains predominated among CF patients with newly acquired MRSA strains and among the non-CF patients. The presence of CA-MRSA strains in children with CF was not associated with exacerbation or necrotizing pneumonia.

Community- and health care-associated methicillin-resistant Staphylococcus aureus: a comparison of molecular epidemiology and antimicrobial activities of various agents

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is changing. We determined the inhibitory and bactericidal activity of select antimicrobial agents utilizing a well-characterized group of 200 staphylococcal cassette chromosome mec (SCC mec) type IV community-associated MRSA (CAMRSA) and 50 SCC mec type II health care-associated MRSA (HAMRSA). Differences in carriage of the Panton-Valentine leukocidin (PVL) genes, agr group, and agr function in CAMRSA and HAMRSA were also examined. Pulsed-field gel electrophoresis (PFGE) patterns were determined for a subset of study strains. CAMRSA typically belonged to the USA 300 PFGE profile, were associated with high rates of PVL carriage (78%), and primarily were agr group I. Susceptibility to daptomycin, linezolid, teicoplanin, and vancomycin was 100%. In contrast, HAMRSA isolates typically belonged to the USA 100 PFGE profile, were associated with low rates of PVL carriage (8%), and primarily were agr group II. Comparing susceptibilities between the 2 types of MRSA strains, there was a 2-fold increase in MIC for daptomycin, doxycycline, teicoplanin, trimethoprim–sulfamethoxazole (TMP/SMX), and vancomycin in HAMRSA versus CAMRSA. Levofloxacin and clindamycin susceptibly decreased dramatically by 66% and 54%, respectively, against HAMRSA versus CAMRSA. With respect to agr function, 3.5% of CAMRSA and 48% of HAMRSA displayed a down-regulated agr gene cluster. The comparative bactericidal activities of daptomycin were similar to those of vancomycin and clindamycin, but were significantly greater than those of linezolid, teicoplanin, and TMP/SMX against CAMRSA at 24-h terminal end points. Further studies are warranted against a larger number of molecularly defined, geographically diverse CAMRSA to confirm these findings.

Staphylococcal Cassette Chromosome mec and Panton-Valentine Leukocidin Characterization of Methicillin-Resistant Staphylococcus aureus Clones

Staphylococcal cassette chromosome mec (SCCmec) types and Panton-Valentine leukocidin (PVL) gene carriage were compared among suspected community-associated methicillin-resistant Staphylococcus aureus MRSA (CA-MRSA) and health care-associated MRSA (HA-MRSA) isolates. CA-MRSA isolates carried the SCCmec type IV complex, and most were PVL positive. The HA-MRSA isolates carried the SCCmec type II complex and did not harbor the PVL genes.

Methicillin-resistant Staphylococcus aureus: a new community-acquired pathogen?

The main goal of this review is to describe the emergence of methicillin-resistant Staphylococcus aureus (MRSA) as a community pathogen. Community-acquired MRSA has emerged as an important infection in the community setting. It has primarily been associated with skin and soft-tissue infections, but can also cause severe pulmonary infections, including pneumonia and empyema. Community-acquired MRSA is typically more susceptible to a wider class of antibiotics than healthcare-associated MRSA. Community-acquired MRSA is also more virulent compared with healthcare-associated MRSA isolates. Community-acquired MRSA usually contains the gene encoding Panton-Valentive leukocidin, which is a toxin that creates lytic pores in the cell membranes of neutrophils and induces the release of neutrophil chemotactic factors that promote inflammation and tissue destruction. The optimal antibiotic treatment for Panton-Valentive leukocidin-positive community-acquired MRSA is unknown; however, antibiotics with activity against MRSA and the ability to inhibit toxin production may be optimal (linezolid or clindamycin for susceptible isolates). Clinicians should be aware of the emergence of community-acquired MRSA as an important cause of serious infections arising in the community setting. Appropriate antibiotic therapy should be initiated as soon as infection with this pathogen is suspected.