Emergence of Community-Associated Methicillin-Resistant Staphylococcus aureus USA300 Genotype as a Major Cause of Health Care--Associated Blood Stream Infections

Complete Circular Genome Sequence of Successful ST8/SCCmecIV Community-Associated Methicillin-Resistant Staphylococcus aureus (OC8) in Russia: One-Megabase Genomic Inversion, IS256's Spread, and Evolution of Russia ST8-IV

ST8/SCCmecIV community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has been a common threat, with large USA300 epidemics in the United States. The global geographical structure of ST8/SCCmecIV has not yet been fully elucidated. We herein determined the complete circular genome sequence of ST8/SCCmecIVc strain OC8 from Siberian Russia. We found that 36.0% of the genome was inverted relative to USA300. Two IS256, oppositely oriented, at IS256-enriched hot spots were implicated with the one-megabase genomic inversion (MbIN) and vSaβ split. The behavior of IS256 was flexible: its insertion site (att) sequences on the genome and junction sequences of extrachromosomal circular DNA were all divergent, albeit with fixed sizes. A similar multi-IS256 system was detected, even in prevalent ST239 healthcare-associated MRSA in Russia, suggesting IS256’s strong transmission potential and advantage in evolution. Regarding epidemiology, all ST8/SCCmecIVc strains from European, Siberian, and Far Eastern Russia, examined had MbIN, and geographical expansion accompanied divergent spa types and resistance to fluoroquinolones, chloramphenicol, and often rifampicin. Russia ST8/SCCmecIVc has been associated with life-threatening infections such as pneumonia and sepsis in both community and hospital settings. Regarding virulence, the OC8 genome carried a series of toxin and immune evasion genes, a truncated giant surface protein gene, and IS256 insertion adjacent to a pan-regulatory gene. These results suggest that unique single ST8/spa1(t008)/SCCmecIVc CA-MRSA (clade, Russia ST8-IVc) emerged in Russia, and this was followed by large geographical expansion, with MbIN as an epidemiological marker, and fluoroquinolone resistance, multiple virulence factors, and possibly a multi-IS256 system as selective advantages.

Living Conditions as a Driving Factor in Persistent Methicillin-resistant Staphylococcus aureus Colonization Among HIV-infected Youth

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) colonization has been linked to HIV-related sexual and social behaviors. MRSA risk factors may be different for HIV-infected children, adolescents and young adults. We investigated the association of MRSA colonization, persistent colonization and genotypes with potential risk factors among HIV-infected youth.

METHODS

For this case-control study, patients 24 years of age or younger attending 2 HIV reference centers were recruited from February to August 2012 and followed for 1 year. Nasal swabs were collected at enrollment and every 3 months. MRSA clones were characterized by staphylococcal chromosomal cassette mec typing, spa typing and multilocus sequence typing. We compared MRSA colonization and persistent colonization with patient demographic and clinical characteristics.

RESULTS

Among 117 participants, MRSA colonization frequency (calculated for each collection based on the number of positive cultures per patient) was 12.8% at the first collection. The average MRSA colonization frequency was 10.4%. Our results showed 11.1% were persistent carriers (subjects with more than 1 positive culture in at least 3). Crowding was the only factor associated with MRSA colonization (P = 0.018). Persistent carriers had significantly higher (4.2 times) odds of living in a crowded household (95% confidence interval-1.1-16.2). We observed high genetic diversity among MRSA isolates, with t002/ST5 and t318/ST30 being the most frequent.

CONCLUSIONS

MRSA colonization among HIV-infected youth is more closely related to living in a low-income or slum community than to HIV-related clinical factors. High genetic MRSA isolate diversity in our population suggests frequent transmission.

Molecular characterization of Staphylococcus aureus isolates from various healthcare institutions in Nairobi, Kenya: a cross sectional study

Background

Staphylococcus aureus (S. aureus) has established itself over the years as a major cause of morbidity and mortality both within the community and in healthcare settings. Methicillin resistant S. aureus (MRSA) in particular has been a major cause of nosocomial infections resulting in significant increase in healthcare costs. In Africa, the MRSA prevalence has been shown to vary across different countries. In order to better understand the epidemiology of MRSA in a setting, it is important to define its population structure using molecular tools as different clones have been found to predominate in certain geographical locations.

Methods

We carried out PFGE, MLST, SCCmec and spa typing of selected S. aureus isolates from a private and public referral hospital in Nairobi, Kenya.

Results

A total of 93 S. aureus isolates were grouped into 19 PFGE clonal complexes (A–S) and 12 singletons. From these, 55 (32 MRSA and 23 MSSA) representative isolates from each PFGE clonal complex and all singletons were spa typed. There were 18 different MRSA spa types and 22 MSSA spa types. The predominant MRSA spa type was t037 comprising 40.6 % (13/32) of all MRSA. In contrast, the MSSA were quite heterogeneous, only 2 out of 23 MSSA shared the same spa type. Two new MRSA spa types (t13149 and t13150) and 3 new MSSA spa types (t13182, t13193 and t13194) were identified. The predominant clonal complex was CC 5 which included multi-locus sequence types 1, 8 and 241.

Conclusion

In contrast to previous studies published from Kenya, there’s marked genetic diversity amongst clinical MRSA isolates in Nairobi including the presence of well-known epidemic MRSA clones. Given that these clones are resident within our referral hospitals, adherence to strict infection control measures needs to be ensured to reduce morbidity and mortality associated with hospital acquired MRSA infections.

Shifts in the Clonal Distribution of Methicillin-Resistant Staphylococcus aureus in Kuwait Hospitals: 1992-2010

Background

As the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is constantly changing globally, determining the prevailing MRSA clones in a local healthcare facility is important for better management of infections. This study investigated clonal composition and distribution of MRSA isolates in Kuwait’s hospitals using a combination of molecular typing methods.

Materials and Methods

In total, 400 non-repeat MRSA isolates were obtained between 1992 and 2010 in 13 public hospitals and were characterized using antibiogram, SCCmec typing, spa typing, and multilocus-sequence typing. Clonal assignment and detection of virulence factors and antibiotic resistance genes were performed by DNA microarray.

Results

The isolates were resistant to kanamycin (74.2%), erythromycin (69.5%), tetracycline (66.7%), gentamicin (61%), ciprofloxacin, (61%), fusidic acid (53.5%), clindamycin (41.5%), high-level mupirocin resistance (5.2%) and carried aphA3, aacA-aphD, ermA, ermC, mupA, tetK, tetM, fusC and far1. Molecular typing revealed 31 different MRSA clones consisting of ST239-MRSA-III (52.2%), ST22-MRSA-IV (9.2%), ST80-MRSA-IV (7.5%), ST5-MRSA-II/IV/V/VI (6.5%), ST30-MRSA-IV (3.5%), ST241-MRSA-III (2.7%), ST6-MRSA-IV (2.2%), ST36-MRSA-II (2%) and ST772-MRSA-V (1.75%). The isolates differed in the carriage of genes for enterotoxins, Panton–Valentine leukocidin (PVL), toxic shock syndrome toxin (tst-1), arginine catabolic mobile element (ACME) and exfoliative toxins. The number of clones increased from one (ST239-III-t037) in 1992 to 30 in 2010 including ST8-IV-t008 [PVL+] [ACME+] (USA300), ST772-V (Bengal Bay clone) and ST2816 identified for the first time in Kuwait.

Conclusion

The study revealed that the MRSA isolates belonged to diverse clones that changed in numbers and diversity overtime. Although ST239-MRSA-III, a healthcare-associated clone remained the dominant MRSA clone overtime, the newly emerged clones consisted mostly of community-associated.

The Epidemiology of Staphylococcus aureus and Panton-Valentine Leucocidin (pvl) in Central Australia, 2006-2010

Background

The Central Australian Indigenous population has a high incidence of Staphylococcus aureus bacteremia (SAB) but little is known about the local molecular epidemiology.

Methods

Prospective observational study of bacteremic and nasal colonizing S.aureus isolates between June 2006 to June 2010. All isolates underwent single nucleotide polymorphism (SNP) genotyping and testing for the presence of the Panton-Valentine Leucocidin (pvl) gene.

Results

Invasive isolates (n = 97) were predominantly ST93 (26.6 %) and pvl positive (54.3 %), which was associated with skin and soft tissue infections (OR 4.35, 95 % CI 1.16, 16.31). Non-multiresistant MRSA accounted for 31.9 % of bacteremic samples and showed a trend to being healthcare associated (OR 2.16, 95 % CI 0.86, 5.40). Non-invasive isolates (n = 54) were rarely ST93 (1.9 %) or pvl positive (7.4 %).

Conclusions

In Central Australia, ST93 was the dominant S.aureus clone, and was frequently pvl positive and associated with an aggressive clinical phenotype. Whether non-nasal carriage is more important with invasive clones or whether colonization occurs only transiently remains to be elucidated.

Genomics of Natural Populations of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen and an important cause of livestock infections. The first S. aureus genomes to be published, 15 years ago, provided the first view of genome structure and gene content. Since then, thousands of genomes from a wide array of strains from different sources have been sequenced. Comparison of these sequences has resulted in broad insights into population structure, bacterial evolution, clone emergence and expansion, and the molecular basis of niche adaptation. Furthermore, this information is now being applied clinically in outbreak investigations to inform infection control measures and to determine appropriate treatment regimens. In this review, we summarize some of the broad insights into S. aureus biology gained from the analysis of genomes and discuss future directions and opportunities in this dynamic field of research.

Telavancin in the treatment of Staphylococcus aureus hospital-acquired and ventilator-associated pneumonia: clinical evidence and experience

Telavancin (TLV) is a lipoglycopeptide derivative of vancomycin (VAN), which has activity against Gram-positive aerobic bacteria, and is especially effective against methicillin-resistant Staphylococcus aureus (MRSA) and Gram-positive bacteria resistant to VAN. Comparative clinical studies of TLV have demonstrated noninferiority compared with VAN in the treatment of hospital-acquired Gram-positive pneumonia, with high cure rates for TLV-treated patients with monomicrobial S. aureus infection, including isolates with reduced VAN susceptibility. The results based on the patients' clinical response were supported by supplemental post-hoc analyses of 28-day mortality. In Europe and the USA, TLV is approved as a useful alternative for patients with difficult-to-treat, hospital-acquired MRSA pneumonia when there are very few alternatives. The present article reviews TLV's pharmacological characteristics and clinical efficacy resulting from clinical trials giving a detailed picture of its properties and position in the management of hospital-acquired pneumonia.

Emergence of Community-Associated Methicillin-ResistantStaphylococcus aureusInfection Among Patients With End-Stage Renal Disease

Objective.

To evaluate the frequency of infections due to community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) strains among our patients with end-stage renal disease.

Design.

Prospective observational clinical and laboratory study of patients in 2005. Molecular features of isolates recovered from these patients were compared with those of isolates recovered in 2000 from patients with end-stage renal disease.

Setting.

A 600-bed urban academic medical center.

Patients.

Thirty-two patients with end-stage renal disease and MRSA infection at the time of hospitalization from 2005 were evaluated. For comparison, laboratory analysis was performed for 17 MRSA isolates recovered from patients with end-stage renal disease in 2000.

Results.

The patients from 2005 were more likely than the patients from 2000 to have infection with strains that carried the staphylococcal cassette chromosome (SCC)mectype IV complex (50% vs 11.8%; relative risk, 4.25 [95% confidence interval, 1.17-25.98];P= .012) and the Panton-Valentine leukocidin toxin genes (25% vs 0%;P= .038). Eight patients from 2005 were infected with a strain that is identical to MRSA clone USA300 in terms of molecular type and presence of SCCmectype IV and Panton-Valentine leukocidin genes. Among the patients from 2005, those infected with SCCmectype IV strains (ie, CA-MRSA strains) and those infected with SCCmectype II strains (ie, healthcare-associated MRSA [HA-MRSA] strains) were similar with respect to demographic characteristics, risk factors, and outcomes.

Conclusions.

We documented an increased proportion of infections with CA-MRSA strains, including clone USA300, among our population of patients undergoing dialysis. Patients infected with CA-MRSA strains and HA-MRSA strains were similar with respect to presenting illness and outcomes.

Characterization of Staphylococcus aureus faecal isolates associated with food-borne disease in Korea

AIMS

To characterize Staphylococcus aureus faecal isolates from people suspected to be infected with food poisoning by using antimicrobial susceptibility testing and molecular techniques.

METHODS AND RESULTS

A total of 340 Staph. aureus isolates from 6226 people suspected to be infected with food poisoning were identified and characterized by biochemical methods, antimicrobial susceptibility testing and PCR. Samples were obtained from January 2006 to December 2008 from the National Notifiable Diseases Surveillance System at the Research Institute of Public Health and Environment in Seoul Metropolitan, Korea. All strains carried at least one of the eight staphylococcal enterotoxin (se) genes tested and a total of 27 se profiles were produced; the most frequent se profile was seg-sei and the next was sea. Among the total isolates, 36 methicillin-resistant Staphylococcus aureus (MRSAs) isolates were further analysed by multilocus sequence typing (MLST), Staphylococcal cassette chromosome mec (SCCmec) typing, pulsed-field gel electrophoresis (PFGE) and PCR detection for pvl. ST72-SCCmec type IV was the most predominant clone (27 isolates, 75%) followed by ST1-SCCmec type IV (five isolates, 13·8%), ST20-SCCmec type IV (one isolate, 2·8%), ST493-SCCmec type IV (one isolate, 2·8%), ST903-SCCmec type IV (one isolate, 2·8%) and ST5-SCCmec type II (one isolate, 2·8%). By PFGE typing, MRSAs isolated during the same period were grouped together although they were isolated from different regions. None of MRSAs had PVL gene and nine MRSAs were multidrug resistant.

CONCLUSIONS

Analysis of MRSAs by MLST, SCCmec typing, PFGE and pvl detection showed that the majority of strain associated with food-borne diseases belonged to a Korean community-acquired (CA) MRSA clone with ST72-SCCmec type IV-PVL negative-SEG/SEI and its variations while one strain was hospital-acquired (HA) MRSA.

SIGNIFICANCE AND IMPACT OF THE STUDY

CA-MRSA clone which possessed ST72-SCCmec type IV-PVL negative-SEG/SEI was spread most commonly among MRSAs that were associated with food-borne diseases. This is the first report of ST903 strain in Korea.

Characteristics of the community-genotype sequence type 72 methicillin-resistant Staphylococcus aureus isolates that underlie their persistence in hospitals

Panton-Valentine leukocidin-negative methicillin-resistant Staphylococcus aureus (MRSA) clone ST72, known as a major community-associated MRSA in Korea, has emerged as an important pathogen in hospitals. To understand bacterial properties that underlie transformation of this clone into a nosocomial pathogen, we compared characteristics of the community-genotype ST72 MRSA isolates with those of ST5 and ST239 MRSA, which have been predominant nosocomial MRSA clones in Korea. Several genes associated with adhesion and virulence were absent or rarely found in ST72 isolates. Many ST72 isolates (70.1%) belonged to agr group I, but the agr group of other ST72 isolates could not be determined. As indicated by d-hemolysin production, ST72 isolates expressed fully functional agr, whereas agr dysfunction was observed in ST5 and ST239 isolates. In the biofilm formation assay, no upregulation of biofilm-forming activity of ST72 MRSA was detected. However, ST72 isolates demonstrated persistence under hypotonic and desiccating conditions (survival rates 72.3% and 33.9%, respectively), which was similar to characteristics of ST5 or ST239 isolates. ST72- MRSA isolates showed low virulence, but properties of their functional agr system could facilitate their spread in hospitals. In conclusion, tolerance to stressful environments, e.g., hypotonic and dry conditions, may also contribute to survival of the community-associated MRSA clones in healthcare facilities.

Emergence of Panton-Valentine leucocidin-positive ST8-methicillin-resistant Staphylococcus aureus (USA300 clone) in Korea causing healthcare-associated and hospital-acquired bacteraemia

Panton-Valentine leucocidin (PVL)-positive sequence type (ST)8-MRSA-SCCmec IVa (USA300) is the epidemic strain of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in North America. USA300 is extremely rare in South Korea, and PVL-negative ST72 SCCmec type IVc is the predominant CA-MRSA clone. In a multicentre, prospective cohort study of S. aureus bacteraemia, we identified PVL-positive ST8-MRSA isolates by performing multilocus sequence typing and PCR for PVL. We analyzed the clinical characteristics of patients with PVL-positive ST8-MRSA bacteraemia, and performed SCCmec, spa, and agr typing, PCR for arginine catabolic mobile element (ACME), virulence gene profiling, and pulsed-field gel electrophoresis (PFGE). Among a total of 818 MRSA isolates, we identified ten isolates of PVL-positive ST8-MRSA (USA300) (3 from Hospital D, 4 from Hospital G, and 3 from Hospital A), all of which involved exclusively healthcare-associated (5 isolates) and hospital-acquired bacteraemia (5 isolates). This strain accounted for 8~10 % of the hospital-acquired MRSA bacteraemia in Hospitals D and G. Bacteraemia of unknown origin was the most common type of infection followed by pneumonia. All the isolates were SCCmec type IVa, spa type t008, and agr group I. Eight of the isolates harboured ACME. In a PFGE analysis, four isolates were identical to the USA300 control strain, five differed by a single band, and the remaining one differed by two bands. All the isolates were pulsed-field type USA300. This is the first report of healthcare-associated and hospital-acquired bacteraemia caused by USA300 in South Korea. USA300 seems to be an emerging hospital clone in this country.

Managing drug-resistant organisms in acute care

The purpose of this article is to provide practitioners with therapeutic considerations for infections caused by drug-resistant organisms in the acute care setting. Proper identification of organisms and appropriate use of antibiotics are imperative strategies to help reduce the development and spread of antimicrobial resistance.

Pan-genomic perspective on the evolution of the Staphylococcus aureus USA300 epidemic

Staphylococcus aureus USA300 represents the dominant community-associated methicillin-resistant S. aureus lineage in the USA, where it is a major cause of skin and soft tissue infections. Previous comparative genomic studies have described the population structure and evolution of USA300 based on geographically restricted isolate collections. Here, we investigated the USA300 population by sequencing genomes of a geographically distributed panel of 191 clinical S. aureus isolates belonging to clonal complex 8 (CC8), derived from the Tigecycline Evaluation and Surveillance Trial program. Isolates were collected at 12 healthcare centres across nine USA states in 2004, 2009 or 2010. Reconstruction of evolutionary relationships revealed that CC8 was dominated by USA300 isolates (154/191, 81 %), which were heterogeneous and demonstrated limited phylogeographic clustering. Analysis of the USA300 core genomes revealed an increase in median pairwise SNP distance from 62 to 98 between 2004 and 2010, with a stable pattern of above average dN/dS ratios. The phylogeny of the USA300 population indicated that early diversification events led to the formation of nested clades, which arose through cumulative acquisition of predominantly non-synonymous SNPs in various coding sequences. The accessory genome of USA300 was largely homogenous and consisted of elements previously associated with this lineage. We observed an emergence of SCCmec negative and ACME negative USA300 isolates amongst more recent samples, and an increase in the prevalence of ϕSa5 prophage. Together, the analysed S. aureus USA300 collection revealed an evolving pan-genome through increased core genome heterogeneity and temporal variation in the frequency of certain accessory elements.

Systematic Surveillance Detects Multiple Silent Introductions and Household Transmission of Methicillin-Resistant Staphylococcus aureus USA300 in the East of England

Background. The spread of USA300 methicillin-resistant Staphylococcus aureus (MRSA) across the United States resulted in an epidemic of infections. In Europe, only sporadic cases or small clusters of USA300 infections are described, and its prevalence in England is unknown. We conducted prospective surveillance for USA300 in the east of England.

Methods. We undertook a 12-month prospective observational cohort study of all individuals with MRSA isolated from community and hospital samples submitted to a microbiology laboratory. At least 1 MRSA isolate from each individual underwent whole-genome sequencing. USA300 was identified on the basis of sequence analysis, and phylogenetic comparisons were made between these and USA300 genomes from the United States.

Results. Between April 2012 and April 2013, we sequenced 2283 MRSA isolates (detected during carriage screening and in clinical samples) from 1465 individuals. USA300 was isolated from 24 cases (1.6%). Ten cases (42%) had skin and soft tissue infection, and 2 cases had invasive disease. Phylogenetic analyses identified multiple introductions and household transmission of USA300.

Conclusions. Use of a diagnostic laboratory as a sentinel for surveillance has identified repeated introductions of USA300 in eastern England in 2012–2013, with evidence for limited transmission. Our results show how systematic surveillance could provide an early warning of strain emergence and dissemination.

A persistent antimicrobial resistance pattern and limited methicillin-resistance-associated genotype in a short-term Staphylococcus aureus carriage isolated from a student population

The aim of the present study was to assess and compare the antimicrobial susceptibility pattern against a panel of antibiotics and molecular and methicillin resistance-associated genotypes of 120 carriage S. aureus isolates previously isolated from a student population at two isolation events within a one-month interval. The antibiotic susceptibility of isolates was determined using the Kirby-Bauer disc-diffusion method (cefoxitin by Etest). The MRSA was screened using polymerase chain reaction for the presence of the mecA gene. The mecA-positive isolates were subjected to staphylococcal cassette chromosome (SCC) mec typing, multilocus sequence typing (MLST) and eBURST analysis. All isolates were characterized for the presence of the Panton-Valentine leukocidin (PVL) gene, an enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) pattern and the spa type. For the two occasions where S. aureus was isolated, the highest frequency of resistance was observed for penicillin (70% and 65%, respectively), with a lower rate against erythromycin and tetracycline (<12%). All isolates were susceptible to ciprofloxacin and gentamycin. As for methicillin resistance, eight isolates had minimum inhibitory concentrations (MIC) of resistant categories, but 10 isolates (8.33%) were positive for the mecA gene. The mecA-positive isolates belonged to SCCmec types I (n=9) and V (n=1). MLST was resolved for only three MRSAs, ST508 (n=1), ST88 (n=1) and ST96 (n=1). The results of the eBURST analysis showed that the MRSA isolates analyzed in the present study were potentially related to MRSA identified in other countries. Approximately half of the persistent S. aureus carriers harbored S. aureus of a similar spa type in the respective individuals during both isolation events. A persistent antimicrobial pattern and limited distinct MRSAs were observed over the short study period. The latter frequently exhibited SCCmec type I, commonly associated with hospital-acquired (HA) characteristics, but further delineation is needed to justify the origins of these bacteria.

Molecular and phenotypic characterization of methicillin-resistant Staphylococcus aureus isolates from a tertiary hospital in the Philippines

Background

Methicillin-resistant Staphylococcus aureus (MRSA) poses a major threat to public health worldwide. There are relatively few studies addressing the molecular epidemiology of MRSA in the Philippines.

Methods

This study characterized MRSA isolates in terms of their antimicrobial susceptibility profile, the SCCmec type, and the presence of lukF-lukS genes for Panton-Valentine leukocidin (PVL) and determined the relatedness of the isolates by random amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR).

Results

A total of 236 S. aureus were isolated from clinical specimens of the Makati Medical Center in Makati City, Philippines, between January 2013 and June 2013, and 108 or 45.76 % were found to be MRSA. Results showed that the MRSA strains were resistant to trimethoprim-sulfamethoxazole (20.37 %), azithromycin (10.19 %), gentamicin (5.56 %), and linezolid (4.63 %), while all were susceptible to vancomycin, nitrofurantoin, levofloxacin, minocycline, rifampin, and tetracycline. One isolate was found positive for inducible clindamycin resistance. All of the 108 MRSA strains were confirmed to carry the mecA and SCCmec genes, while the PVL genes were detected in 41 (38 %) of the isolates. Ninety-six isolates (89 %) carried SCCmec type IV, while the remaining isolates carried SCCmec type I (11 isolates) or type III (one isolate).

Conclusion

This study is the first to present a comprehensive MRSA surveillance data with molecular characterization in a tertiary hospital in the Philippines.

Detection of ST772 Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus (Bengal Bay clone) and ST22 S. aureus isolates with a genetic variant of elastin binding protein in Nepal

Genetic characteristics were analysed for recent clinical isolates of methicillin-resistant and -susceptible Staphylococcus aureus (MRSA and MSSA respectively) in Kathmandu, Nepal. MRSA isolates harbouring Panton-Valentine leukocidin (PVL) genes were classified into ST1, ST22 and ST88 with SCCmec-IV and ST772 with SCCmec-V (Bengal Bay clone), while PVL-positive MSSA into ST22, ST30 and ST772. ST22 isolates (PVL-positive MRSA and MSSA, PVL-negative MRSA) possessed a variant of elastin binding protein gene (ebpS) with an internal deletion of 180 bp, which was similar to that reported for ST121 S. aureus previously outside Nepal. Phylogenetic analysis indicated that the ebpS variant in ST22 might have occurred independently of ST121 strains. This is the first report of ST772 PVL-positive MRSA in Nepal and detection of the deletion variant of ebpS in ST22 S. aureus.

Risk factors for long-term mortality of Staphylococcus aureus bacteremia

Staphylococcus aureus bacteremia (SAB) is a fatal disease. We aimed to describe risk factors for long-term mortality with SAB. We analyzed data from a retrospectively collected database including 1,692 patients with SAB. We considered variables of infection and background conditions for the analysis of long-term survival. The Kaplan-Meier procedure was used for analysis of long-term survival. Variables significantly associated with mortality were analyzed using a Cox regression model. We included 1,692 patients in the analysis. Patients were followed for up to 22 years. Within one year, 62% of patients died and within 5 years 72% died. A total of 82% of patients aged 65 years and older died within 5 years. Independent predictors of long-term mortality were older age (Hazard ratio 1.029, 95% confidence interval 1.022-1.036), female gender (HR 1.302, 95% CI 1.118-1.517), pneumonia or primary/ unknown source of infection (HR 1.441, 95% CI 1.230-1.689), dementia (HR 1.234, 95% CI 1.004-1.516), higher Charlson score (HR 1.155, 95% CI 1.115-1.196), shock at onset (HR 1.776, 95% CI 1.430-2.207) and arrival to hospitalization from an institution (HR 1.319, 95% CI 1.095-1.563). Long-term survival of patients older than 65 years and of women with SAB is severely curtailed.

The population genetics of drug resistance evolution in natural populations of viral, bacterial and eukaryotic pathogens

Drug resistance is a costly consequence of pathogen evolution and a major concern in public health. In this review, we show how population genetics can be used to study the evolution of drug resistance and also how drug resistance evolution is informative as an evolutionary model system. We highlight five examples from diverse organisms with particular focus on: (i) identifying drug resistance loci in the malaria parasite Plasmodium falciparum using the genomic signatures of selective sweeps, (ii) determining the role of epistasis in drug resistance evolution in influenza, (iii) quantifying the role of standing genetic variation in the evolution of drug resistance in HIV, (iv) using drug resistance mutations to study clonal interference dynamics in tuberculosis and (v) analysing the population structure of the core and accessory genome of Staphylococcus aureus to understand the spread of methicillin resistance. Throughout this review, we discuss the uses of sequence data and population genetic theory in studying the evolution of drug resistance.

Understanding Staphylococcal Nomenclature

Bacteria are often grouped by a variety of properties, including biochemical activity, appearance, and more recently, nucleic acid sequence differences. In the case of human pathogens, significant work goes into "typing" strains to understand relatedness. This is especially true when trying to understand the epidemiology of these organisms. In attempts to group Staphylococci, a variety of methods and nomenclatures have been employed, which can often serve as a point of confusion to those entering the field. Therefore, the intent of this chapter is to give a brief overview of some common methods and associated nomenclature used to type Staphylococci, with S. aureus as an example.

Carriage, Clinical Microbiology and Transmission of Staphylococcus aureus

Staphylococcus aureus is one of the most important bacterial pathogens in clinical practice and a major diagnostic focus for the routine microbiology laboratory. It is carried as a harmless commensal in up to two-thirds of the population at any one time predominantly not only in the anterior nares, but also in multiple other sites such as the groin, axilla, throat, perineum, vagina and rectum. It colonizes skin breach sites, such as ulcers and wounds, and causes superficial and deep skin and soft tissue infections and life-threatening deep seated infections particularly endocarditis and osteomyelitis. S. aureus is constantly evolving through mutation and uptake of mobile genetic elements that confer increasing resistance and virulence. Since the 1960s, hospitals have had to contend with emergence of methicillin-resistant S. aureus (MRSA) strains that spread better in hospitals than methicillin-susceptible S. aureus (MSSA) and are harder to treat. Since the 1980s, distinct community MRSA strains have also emerged that cause severe skin and respiratory infections. Conventional identification of MSSA and MRSA in the microbiology laboratory involves microscopy, culture and biochemical analysis that for most samples is straightforward but slow, taking at least 48 h. This delay has significant consequences for individual patient care and public health, through inadequate or excessive empiric antibiotic use, and failure to implement appropriate infection control measures for MRSA-colonized patients during those first 48 h. This unmet need has driven development of rapid molecular diagnostics that either complement or replace conventional culture techniques in the laboratory, or can be placed in the clinical environment as point-of-care (POC) devices. These new technologies provide results to clinicians anything from within an hour to 24 h, depending on sample and clinical setting, and should transform management of patients with S. aureus and other bacterial diseases; however, uptake is often slow due to the disruptive effect of new technologies, costs of transition and uncertainty of the optimal solution given successive advances. More evidence of the health economic, clinical and antimicrobial resistance benefit will help support introduction of these new technologies. Finally, preventing MRSA transmission has been a priority for healthcare organizations for many years. There have been significant recent reductions in transmission following local and national campaigns to re-enforce basic and heightened infection control interventions such as universal hand hygiene, barrier nursing, decolonization and isolation of MRSA-colonized patients detected through routine culture or screening policies. Developments in whole genome sequencing are providing greater insight into reservoirs and routes of transmission that should help better target interventions to ensure sustainable control of endemic strains and to identify and prevent emergence of new strains.

Drug resistance and genetic characteristics of clinical isolates of staphylococci in Myanmar: high prevalence of PVL among methicillin-susceptible Staphylococcus aureus belonging to various sequence types

Prevalence, drug resistance and genetic characteristics were analysed for a total of 128 clinical isolates of staphylococci obtained from a tertiary hospital in Myanmar. The dominant species were S. aureus (39%) and S. haemolyticus (35%), followed by S. epidermidis (6%) and S. saprophyticus (5%). The majority of S. haemolyticus isolates (71.1%) harboured mecA, showing high resistance rates to ampicillin, cephalosporins, erythromycin and levofloxacin, while methicillin-resistant S. aureus (MRSA) was only 8% (four isolates) among S. aureus with type IV SCCmec. Panton-Valentine leukocidin (PVL) genes were detected in 20 isolates of S. aureus (40%), among which only one isolate was MRSA belonging to sequence type (ST) 88/agr-III/coa-IIIa, and the other 19 methicillin-susceptible S. aureus (MSSA) isolates were classified into six STs (ST88, ST121, ST1153, ST1155, ST1930, ST3206). An ST1153 MSSA isolate with PVL was revealed to belong to a novel coa type, XIIIa. ST121 S. aureus was the most common in the PVL-positive MSSA (47%, 9/19), harbouring genes of bone sialoprotein and variant of elastin binding protein as a distinctive feature. Although PVL-positive MSSA was susceptible to most of the antimicrobial agents examined, ST1930 isolates were resistant to erythromycin and levofloxacin. ST59 PVL-negative MRSA and MSSA had more resistance genes than other MRSA and PVL-positive MSSA, showing resistance to more antimicrobial agents. This study indicated higher prevalence of mecA associated with multiple drug resistance in S. haemolyticus than in S. aureus, and dissemination of PVL genes to multiple clones of MSSA, with ST121 being dominant, among hospital isolates in Myanmar.

Evaluation of double locus (clfB and spa) sequence typing for studying molecular epidemiology of methicillin-resistant Staphylococcus aureus in Taiwan

BACKGROUND

Pulsed-field gel electrophoresis (PFGE) is the "gold standard" for epidemiological investigation of methicillin-resistant Staphylococcus aureus (MRSA), but several DNA sequence-based methods have been developed in MRSA typing because of the unambiguous results.

METHODS

Ninety-one MRSA isolates were collected from the blood cultures of different patients from July 2008 to December 2008 in central Taiwan. The molecular characteristics of each isolate, including double locus sequence typing (DLST; spa and clfB typing), Staphylococcus cassette chromosome mec (SCCmec), and PFGE were determined for comparison.

RESULTS

Five major clfB types (types A-E), 18 spa types, 33 DLST genotypes, five SCCmec types, 17 pulsotypes have been observed. Three major DLST genotypes (A1-t002, C0-t037, and B1-t437) and two major pulsotypes (6 and 8) were identified. Most clfB type A isolates (97.1%) were SCCmec type II and all clfB type C isolates (100%) were SCCmec type III. Most clfB type B isolates (88.9%) were SCCmec type IV (59.3%) and V_T (29.6%). All (100%) clfB subtypes A1, A2, and C isolates and 70.4% of clfB type B isolates belonged to healthcare-associated-MRSA. The average congruence was 57.7% between DLST and PFGE, and 96.6% between clfB and SCCmec type. The index of discrimination of SCCmec, clfB, spa, PFGE, and DLST was 0.72, 0.79, 0.80, 0.81, and 0.87, respectively.

CONCLUSION

ClfB type has high congruence with SCCmec type. The DLST method in this study yielded a higher discriminatory power than PFGE in local investigation of molecular epidemiology of MRSA and a promising alternative to PFGE.

Kinase Inhibitors that Increase the Sensitivity of Methicillin Resistant Staphylococcus aureus to β-Lactam Antibiotics

Staphylococcus aureus are Gram-positive bacteria that are the leading cause of recurrent infections in humans that include pneumonia, bacteremia, osteomyelitis, arthritis, endocarditis, and toxic shock syndrome. The emergence of methicillin resistant S. aureus strains (MRSA) has imposed a significant concern in sustained measures of treatment against these infections. Recently, MRSA strains deficient in expression of a serine/threonine kinase (Stk1 or PknB) were described to exhibit increased sensitivity to β-lactam antibiotics. In this study, we screened a library consisting of 280 drug-like, low-molecular-weight compounds with the ability to inhibit protein kinases for those that increased the sensitivity of wild-type MRSA to β-lactams and then evaluated their toxicity in mice. We report the identification of four kinase inhibitors, the sulfonamides ST085384, ST085404, ST085405, and ST085399 that increased sensitivity of WT MRSA to sub-lethal concentrations of β-lactams. Furthermore, these inhibitors lacked alerting structures commonly associated with toxic effects, and toxicity was not observed with ST085384 or ST085405 in vivo in a murine model. These results suggest that kinase inhibitors may be useful in therapeutic strategies against MRSA infections.

Molecular epidemiology of methicillin resistant staphylococcus aureus colonizing the anterior Nares of school children of Udupi Taluk

CONTEXT

Community associated methicillin resistant Staphylococcus aureus (CA-MRSA) cause serious skin and soft tissue infections including necrotizing fasciitis and necrotizing pneumonia. Production of Panton Valentine Leucocidine (PVL) toxin is implicated in its enhanced virulence. A variant of epidemic MRSA-15 (EMRSA-15) which produces PVL toxin has been isolated and characterized by pulsed-field gel electrophoresis (PFGE) method from the Indian population both in hospital and community settings.

AIMS

Identify the epidemiological type of MRSA colonizing the anterior nares of school children in Udupi taluk.

SETTINGS AND DESIGN

The study population included children of the age group of 5-16 years belonging to the Udupi taluk of Karnataka, India. A total of 1503 children were screened for MRSA colonization during July 2009 to December 2010.

MATERIALS AND METHODS

PVL assay, Staphylococcal Cassette Chromosome (SCC) mec typing and PFGE typing were carried out with all the MRSA isolates.

STATISTICAL ANALYSIS USED

Frequency distribution of different variables was assessed by SPSS.

RESULTS

Among the 1.1% of MRSA, 58.8% (10/17) of isolates were positive for pvl and 41.7% (7/17) were identified as SCC mec type IV. PFGE patterns of all the strains were identical with Indian variant EMRSA-15; however they were different from classical EMRSA-15 in 3-4 bands.

CONCLUSIONS

The Indian variant EMRSA-15 gains much epidemiological relevance owing to the acquisition of pvl gene. In spite of low prevalence of nasal colonization of MRSA, emergence of the virulent Indian variant EMRSA-15 in our community is a worrisome fact to be reckoned with.

Evolving Epidemiology of Staphylococcus aureus Bacteremia

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infections due to USA300 have become widespread in community and healthcare settings. It is unclear whether risk factors for bloodstream infections (BSIs) differ by strain type.

OBJECTIVE

To examine the epidemiology of S. aureus BSIs, including USA300 and non-USA300 MRSA strains.

DESIGN

Retrospective observational study with molecular analysis.

SETTING

Large urban public hospital.

PATIENTS

Individuals with S. aureus BSIs from January 1, 2007 through December 31, 2013.

METHODS

We used electronic surveillance data to identify cases of S. aureus BSI. Available MRSA isolates were analyzed by pulsed-field gel electrophoresis. Poisson regression was used to evaluate changes in BSI incidence over time. Risk factor data were collected by medical chart review and logistic regression was used for multivariate analysis of risk factors.

RESULTS

A total of 1,015 cases of S. aureus BSIs were identified during the study period; 36% were due to MRSA. The incidence of hospital-onset (HO) MRSA BSIs decreased while that of community-onset (CO) MRSA BSIs remained stable. The rate of CO- and HO- methicillin-susceptible S. aureus infections both decreased over time. More than half of HO-MRSA BSIs were due to the USA300 strain type and for 4 years, the proportion of HO-MRSA BSIs due to USA300 exceeded 60%. On multivariate analysis, current or former drug use was the only epidemiologic risk factor for CO- or HO-MRSA BSIs due to USA300 strains.

CONCLUSIONS

USA300 MRSA is endemic in communities and hospitals and certain populations (eg, those who use illicit drugs) may benefit from enhanced prevention efforts in the community.

Whole genome sequence typing and microarray profiling of nasal and blood stream methicillin-resistant Staphylococcus aureus isolates: Clues to phylogeny and invasiveness

Hospital-associated methicillin-resistant Staphylococcus aureus (MRSA) infections are frequently caused by predominant clusters of closely related isolates that cannot be discriminated by conventional diagnostic typing methods. Whole genome sequencing (WGS) and DNA microarray (MA) now allow for better discrimination within a prevalent clonal complex (CC). This single center exploratory study aims to distinguish invasive (blood stream infection) and non-invasive (nasal colonization) MRSA isolates of the same CC5 into phylogenetic- and virulence-associated genotypic subgroups by WGS and MA. A cohort of twelve blood stream and fifteen nasal MRSA isolates of CC5 (spa-types t003 and t504) was selected. Isolates were propagated at the same period of time from unrelated patients treated at the University of Saarland Medical Center, Germany. Rooted phylotyping based on WGS with core-genome single nucleotide polymorphism (SNP) analysis revealed two local clusters of closely related CC5 subgroups (t504 and Clade1 t003) which were separated from other local t003 isolates and from unrelated CC5 MRSA reference isolates of German origin. Phylogenetic subtyping was not associated with invasiveness when comparing blood stream and nasal isolates. Clustering based on MA profiles was not concordant with WGS phylotyping, but MA profiles may identify subgroups of isolates with nasal and blood stream origin. Among the new putative virulence associated genes identified by WGS, the strongest association with blood stream infections was shown for ebhB mutants. Analysis of the core-genome together with the accessory genome enables subtyping of closely related MRSA isolates according to phylogeny and presumably also to the potential virulence capacity of isolates.

Molecular Characteristics of Disease-Causing and Commensal Staphylococcus lugdunensis Isolates from 2003 to 2013 at a Tertiary Hospital in Taiwan

Objectives

Staphylococcus lugdunensis can cause community- and healthcare-associated infections. This study investigated the molecular characteristics of S. lugdunensis isolates collected at our hospital and compared the characteristics of the infectious and commensal isolates.

Methods

We collected the S. lugdunensis isolates between 2003 and 2013. The antimicrobial resistance test, SCCmec typing, accessory gene regulator (agr) typing, pulsed-field gel electrophoresis (PFGE), and δ-like hemolysin activity were performed.

Results

In total, 118 S. lugdunensis isolates were collected, of which 67 (56.8%) were classified into the infection group and 51 (43.2%) into the commensal group. The oxacillin resistance rate was 36.4%. The most common SCCmec types were SCCmec types V (51.4%) and II (32.6%). In total, 34 pulsotypes were identified. The PFGE typing revealed five clones (pulsotypes A, J, M, N, and P) at our hospital. Pulsotypes A and N caused the spread of high oxacillin resistance. In total, 10.2% (12 of 118) of the isolates lacked δ-like hemolysin activity. Compared with the infection group, the commensal group showed a higher percentage of multiple drug resistance and carried a higher percentage of SCCmec type II (11 of 22, 50% and 3 of 21, 14.3%) and a lower percentage of SCCmec type V (8 of 22, 36.4% and 14 of 21, 66.7%). The commensal group (27 PFGE types) showed higher genetic diversity than did the infection group (20 PFGE types). No difference was observed in the distribution of the five main pulsotypes, agr typing, and the presence of δ-like hemolysin activity between the two groups.

Conclusions

Five main clones were identified at our hospital. The commensal group showed higher genetic diversity, had a higher percentage of multidrug resistance, and carried a higher percentage of SCCmec type II and a lower percentage of SCCmec type V than did the infection group.

Repurposing celecoxib as a topical antimicrobial agent

There is an urgent need for new antibiotics and alternative strategies to combat multidrug-resistant bacterial pathogens, which are a growing clinical issue. Repurposing existing approved drugs with known pharmacology and toxicology is an alternative strategy to accelerate antimicrobial research and development. In this study, we show that celecoxib, a marketed inhibitor of cyclooxygenase-2, exhibits broad-spectrum antimicrobial activity against Gram-positive pathogens from a variety of genera, including Staphylococcus, Streptococcus, Listeria, Bacillus, and Mycobacterium, but not against Gram-negative pathogens. However, celecoxib is active against all of the Gram-negative bacteria tested, including strains of, Acinetobacter, and Pseudomonas, when their intrinsic resistance is artificially compromised by outer membrane permeabilizing agents such as colistin. The effect of celecoxib on incorporation of radioactive precursors into macromolecules in Staphylococcus aureus was examined. The primary antimicrobial mechanism of action of celecoxib was the dose-dependent inhibition of RNA, DNA, and protein synthesis. Further, we demonstrate the in vivo efficacy of celecoxib in a methicillin-resistant S. aureus (MRSA) infected Caenorhabditis elegans whole animal model. Topical application of celecoxib (1 and 2%) significantly reduced the mean bacterial count in a mouse model of MRSA skin infection. Further, celecoxib decreased the levels of all inflammatory cytokines tested, including tumor necrosis factor-α, interleukin-6, interleukin-1 beta, and monocyte chemo attractant protein-1 in wounds caused by MRSA infection. Celecoxib also exhibited synergy with many conventional antimicrobials when tested against four clinical isolates of S. aureus. Collectively, these results demonstrate that celecoxib alone, or in combination with traditional antimicrobials, has a potential to use as a topical drug for the treatment of bacterial skin infections.

Genotyping of community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) in a tertiary care centre in Mysore, South India: ST2371-SCCmec IV emerges as the major clone

The burden of community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) is on the rise in population and clinical settings on account of the adaptability and virulence traits of this pathogen. We characterized 45 non-duplicate CA-MRSA strains implicated mainly in skin and soft tissue infections (SSTIs) in a tertiary care hospital in Mysore, South India. All the isolates were genotyped by staphylococcal cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing, accessory gene regulator (agr) typing, and multi-locus sequence typing (MLST). Four sequence types (STs) belonging to three major clonal complexes (CCs) were identified among the isolates: CC22 (ST2371 and ST22), CC1 (ST772) and CC8 (ST8). The majority (53.3%) of the isolates was of the genotype ST2371-t852-SCCmec IV [sequence type-spa type-SCCmec type], followed by ST22-t852-SCCmec IV (22.2%), ST772-t657-SCCmec V (13.3%) and ST8-t008-SCCmec IV (11.1%). ST237I, a single locus variant of ST22 (EMRSA-15 clone), has not been reported previously from any of the Asian countries. Our study also documents for the first time, the appearance of ST8-SCCmec IV (USA300) strains in India. Representative strains of the STs were further analyzed by pulsed field gel electrophoresis (PFGE). agr typing detected type I or II alleles in the majority of the isolates. All the isolates were positive for the leukotoxin gene, pvl (Panton-Valentine leukocidin) and the staphylococcal enterotoxin gene cluster, egc. Interestingly, multidrug resistance (resistance to ⩾3 classes of non-beta-lactam antibiotics) was observed in 77.8% (n=35) of the isolates. The highest (75.5%) resistance was recorded for ciprofloxacin, followed by erythromycin (53.3%), and quinupristin-dalfopristin (51.1%). Inducible clindamycin-resistance was identified in 37.7% of the isolates and it was attributed to the presence of erm(A), erm(C) and a combination of erm(A) and erm(C) genes. Isolates which showed a phenotypic pattern of M(R)/L(S) (macrolide-resistance/lincosamide-sensitivity) harbored the msr(A) gene. In conclusion, we report a high rate of multidrug resistance among Indian strains of CA-MRSA and the emergence of the lineages ST2371 and ST8 in India.

Community-associated methicillin-resistant Staphylococcus aureus: prevalence in skin and soft tissue infections at emergency departments in the Greater Toronto Area and associated risk factors

Objective:

Community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA), which is caused primarily by the Canadian methicillin-resistantStaphylococcus aureus-10 (CMRSA-10) strain (also known as the USA300 strain) has emerged rapidly in the United States and is now emerging in Canada. We assessed the prevalence, risk factors, microbiological characteristics and outcomes of CA-MRSA in patients with purulent skin and soft tissue infections (SSTIs) presenting to emergency departments (EDs) in the Greater Toronto Area.

Methods:

Patients withStaphylococcus aureusSSTIs who presented to 7 EDs between Mar. 1 and Jun. 30, 2007, were eligible for inclusion in this study. Antimicrobial susceptibilities and molecular characteristics of MRSA strains were identified. Demographic, risk factor and clinical data were collected through telephone interviews.

Results:

MRSA was isolated from 58 (19%) of 299 eligible patients. CMRSA-10 was identified at 6 of the 7 study sites and accounted for 29 (50%) of all cases of MRSA. Telephone interviews were completed for 161 of the eligible patients. Individuals with CMRSA-10 were younger (median 34 v. 63 yr,p= 0.002), less likely to report recent antibiotic use (22% v. 67%,p= 0.046) or health care–related risk factors (33% v. 72%,p= 0.097) and more likely to report community-related risk factors (56% v. 6%,p= 0.008) than patients with other MRSA strains. CMRSA-10 SSTIs were treated with incision and drainage (1 patient), antibiotic therapy (3 patients) or both (5 patients), and all resolved. CMRSA-10 isolates were susceptible to clindamycin, tetracycline and trimethoprimsulfamethoxazole.

Conclusion:

CA-MRSA is a significant cause of SSTIs in the Greater Toronto Area, and can affect patients without known community-related risk factors. The changing epidemiology of CA-MRSA necessitates further surveillance to inform prevention strategies and empiric treatment guidelines.

Single-molecule sequencing reveals the molecular basis of multidrug-resistance in ST772 methicillin-resistant Staphylococcus aureus

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-associated infection, but there is growing awareness of the emergence of multidrug-resistant lineages in community settings around the world. One such lineage is ST772-MRSA-V, which has disseminated globally and is increasingly prevalent in India. Here, we present the complete genome sequence of DAR4145, a strain of the ST772-MRSA-V lineage from India, and investigate its genomic characteristics in regards to antibiotic resistance and virulence factors.

RESULTS

Sequencing using single-molecule real-time technology resulted in the assembly of a single continuous chromosomal sequence, which was error-corrected, annotated and compared to nine draft genome assemblies of ST772-MRSA-V from Australia, Malaysia and India. We discovered numerous and redundant resistance genes associated with mobile genetic elements (MGEs) and known core genome mutations that explain the highly antibiotic resistant phenotype of DAR4145. Staphylococcal toxins and superantigens, including the leukotoxin Panton-Valentinin Leukocidin, were predominantly associated with genomic islands and the phage φ-IND772PVL. Some of these mobile resistance and virulence factors were variably present in other strains of the ST772-MRSA-V lineage.

CONCLUSIONS

The genomic characteristics presented here emphasize the contribution of MGEs to the emergence of multidrug-resistant and highly virulent strains of community-associated MRSA. Antibiotic resistance was further augmented by chromosomal mutations and redundancy of resistance genes. The complete genome of DAR4145 provides a valuable resource for future investigations into the global dissemination and phylogeography of ST772-MRSA-V.

Vancomycin in the treatment of methicillin-resistant Staphylococcus aureus - a clinician's guide to the science informing current practice

Clinicians treating an infection assess a patient in terms of disease manifestation, causative organism and available antibiotic options with the aim of devising a therapeutic strategy under the creed of 'first, do no harm'. It is often only when treatment is failing or options are limited, as in the scenario of multidrug-resistant organisms, that consideration is given to the interplay that occurs between the microbe and the host. The emergence of Staphylococcus aureus with reduced susceptibility to vancomycin provides a prime example of these dynamic interactions. This review shall explore these concepts in relation to vancomycin for the treatment of methicillin-resistant S. aureus, with the aim of providing an informed approach to the utilization of this drug.

The prevalence and influencing factors of methicillin-resistant Staphylococcus aureus carriage in people in contact with livestock: A systematic review

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is becoming a serious epidemic worldwide. Recently, studies have shown that people in contact with livestock may have a greater chance of MRSA carriage. We aimed to establish the prevalence of MRSA among people in contact with livestock and review the factors influencing MRSA carriage.

METHODS

We systematically examined published epidemiologic studies on MRSA prevalence in people in contact with livestock using Pubmed, Medline, Embase, Ovid, and the Cochrane Library. Prevalence estimates were pooled using a random-effects model. Study heterogeneity was assessed using Q statistics and quantified with I(2) statistics.

RESULTS

Thirty-three eligible studies were included in this systematic review. Prevalence of MRSA ranged from 0.0%-85.8%. The pooled prevalence estimate of MRSA was 14.2% (95% confidence interval, 9.1%-20.1%) for people in contact with livestock. Substantial heterogeneity in eligible studies was noted (χ(2) = 1,025; P < .001; I(2) = 96.9%). Subgroup analysis showed the prevalence of MRSA was high in people from Europe (15.9%), farmers (18.2%), and by longitudinal study design (38.9%). Animal contact and intensity of animal contact were associated with increased risk of MRSA carriage.

CONCLUSION

Our findings suggest that there may be transmission of MRSA between animals and humans.

Ability of the GENSPEED(®) MRSA test kit to detect the novel mecA homologue mecC in Staphylococcus aureus

The aim of this study was to evaluate the GENSPEED(®) MRSA Test Kit that in addition to the traditional MRSA gene mecA, also incorporates a probe for detection of the newly described mecA homologue mecC. So far only one commercial system is able to detect this new gene. The specific objective was to evaluate the ability of the kit to detect and separate Stapyhylococcus aureus containing either mecA, mecC or no methicillin-resistance determinant. Ninety-five MRSA isolates from humans were included in the test and additional mecC-positive isolates from animals and methicillin-sensitive S. aureus were tested. The kit demonstrated 100% sensitivity and 100% specificity compared to a standard PCR method. The kit provides the ability to perform rapid and reliable detection of both mecA-MRSA and mecC-MRSA.

Staphylococcus aureus infections: transmission within households and the community

Staphylococcus aureus, both methicillin susceptible and resistant, are now major community-based pathogens worldwide. The basis for this is multifactorial and includes the emergence of epidemic clones with enhanced virulence, antibiotic resistance, colonization potential, or transmissibility. Household reservoirs of these unique strains are crucial to their success as community-based pathogens. Staphylococci become resident in households, either as colonizers or environmental contaminants, increasing the risk for recurrent infections. Interactions of household members with others in different households or at community sites, including schools and daycare facilities, have a critical role in the ability of these strains to become endemic. Colonization density at these sites appears to have an important role in facilitating transmission. The integration of research tools, including whole-genome sequencing (WGS), mathematical modeling, and social network analysis, has provided additional insight into the transmission dynamics of these strains. Thus far, interventions designed to reduce recurrent infections among household members have had limited success, likely due to the multiplicity of potential sources for recolonization. The development of better strategies to reduce the number of household-based infections will depend on greater insight into the different factors that contribute to the success of these uniquely successful epidemic clones of S. aureus.

Role of healthcare apparel and other healthcare textiles in the transmission of pathogens: a review of the literature

Healthcare workers (HCWs) wear uniforms, such as scrubs and lab coats, for several reasons: (1) to identify themselves as hospital personnel to their patients and employers; (2) to display professionalism; and (3) to provide barrier protection for street clothes from unexpected exposures during the work shift. A growing body of evidence suggests that HCWs' apparel is often contaminated with micro-organisms or pathogens that can cause infections or illnesses. While the majority of scrubs and lab coats are still made of the same traditional textiles used to make street clothes, new evidence suggests that current innovative textiles function as an engineering control, minimizing the acquisition, retention and transmission of infectious pathogens by reducing the levels of bioburden and microbial sustainability. This paper summarizes recent literature on the role of apparel worn in healthcare settings in the acquisition and transmission of healthcare-associated pathogens. It proposes solutions or technological interventions that can reduce the risk of transmission of micro-organisms that are associated with the healthcare environment. Healthcare apparel is the emerging frontier in epidemiologically important environmental surfaces.

Synergistic Effects Between Thioxanthones and Oxacillin Against Methicillin-Resistant Staphylococcus aureus

The extensive use of antimicrobials is leaving medicine with few effective therapeutic options to treat many infections due to the fact that many organisms developed resistance to commonly used drugs. It is therefore pertinent to search not only for new antimicrobials but also for compounds able to restore or potentiate the activity of existing antibiotics. We have screened a library consisting of 40 (thio)xanthone derivatives for antibacterial activity and possible synergistic effects when used in combination with antibiotics. Nine out of the 40 compounds exhibited antibacterial activity against Gram-positive bacteria. Two xanthone derivatives, 1-formyl-4-hydroxy-3-methoxy (7), 2-formyl-3-hydroxy-4-methoxyxanthone (8) and the thioxanthone derivative 1-((2-(diethylamino)ethyl)amino)-4-propoxythioxanthone (10) and its hydrochloride form 13, showed activity against a methicillin-resistant Staphylococcus aureus (MRSA) isolate with minimum inhibitory concentration (MIC) values lower than 256 μg/ml. Thioxanthone 10 demonstrated antibacterial activity and also synergy when combined with ampicillin and oxacillin against MRSA. Additionally, thioxanthone 1-(piperidin-1-yl)-4-propoxythioxanthone (9), despite not having antibacterial activity presented remarkable synergy with oxacillin against MRSA; the MIC of tioxanthone 9 and oxacillin when both were in combination were 128 and 8 μg/ml, respectively. Thioxanthones 9 and 10 were also found to be synergistic when both were combined. Subsequently, docking simulations between thioxanthones 9 and 10 and the allosteric domain of penicillin-binding protein 2A (PBP2A) were undertaken in AutoDock Vina. Both compounds had the ability to bind with an allosteric domain of PBP2A, which may explain their synergy with oxacillin. These two thioxanthone derivatives with different profiles may be promising tools for restoring the activity of oxacillin against MRSA.

Impact of prior healthcare-associated exposure on clinical and molecular characterization of methicillin-susceptible Staphylococcus aureus bacteremia: results from a retrospective cohort study

By virtue of medical advances and an aging society, people have increased opportunities for healthcare exposure. Little is known about the impact of healthcare exposure on the clinical features and molecular typing of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. We classified the onset of MSSA bacteremia into 3 mutually exclusive categories according to the Centers for Disease Control definition, and conducted a retrospective cohort study to investigate the differences among patients with community-associated (CA), healthcare-associated community onset (HACO), and hospital onset (HO) MSSA bacteremia at a medical center from January 1, 2002 through December 31, 2011. Antibiotic susceptibilities and multilocus sequence typing of MSSA isolates were also determined. A total of 290 patients with MSSA bacteremia, including of 165 (56.9%), 91 (31.4%), and 34 (11.7%) of HACO, HO, and CA, respectively, were studied. ST188 (29.3%) was the most common sequence type regardless of classification. Patients with HACO bacteremia were significantly older, had more solid tumors, higher Charlson scores, and more catheter-related bloodstream infections than those with CA bacteremia. The proportions of osteoarticular infections among patients with both HACO and CA bacteremia were higher than that of patients with HO bacteremia. By univariate analysis, patients with HO bacteremia had significantly higher in-hospital mortality compared to those with CA or HACO bacteremia (31.9% vs 18.8% and 20.4%). Multivariate analysis showed that Charlson score (odds ratio [OR], 1.29; 95% confidence interval [CI], 1.10-1.52), septic shock (OR, 5.28; 95% CI, 2.37-11.78), liver cirrhosis (OR, 3.57; 95% CI, 1.14-11.24), receipt of β-lactams other than oxacillin and cefazolin as definitive therapy (OR, 9.27; 95% CI, 4.25-20.23), and higher oxacillin minimum inhibitory concentration (MIC) (≥0.5 mg/L) (OR, 2.35; 95% CI, 1.05-5.25) of the causative pathogen were independently associated with in-hospital mortality. In conclusion, patients with HACO bacteremia had different host factors compared with those with CA bacteremia. Infection foci varied with different onset settings. Overall, ST188 was the most predominant sequence type. Onset settings were not independently associated with outcomes.

Persistent Environmental Contamination with USA300 Methicillin-Resistant Staphylococcus aureus and Other Pathogenic Strain Types in Households with S. aureus Skin Infections

Objective.

To understand the genotypic spectrum of environmental contamination ofStaphylococcus aureusin households and its persistence

Design.

Prospective longitudinal cohort investigation.

Setting.

Index participants identified at 2 academic medical centers.

Participants.

Adults and children withS. aureusskin infections and their household contacts in Los Angeles and Chicago.

Methods.

Household fomites were surveyed for contamination at baseline and 3 months. All isolates underwent genetic typing.

Results.

We enrolled 346 households, 88% of which completed the 3-month follow-up visit.S. aureusenvironmental contamination was 49% at baseline and 51% at 3 months. Among households with a USA300 methicillin-resistantS. aureus(MRSA) body infection isolate, environmental contamination with an indistinguishable MRSA strain was 58% at baseline and 63% at 3 months. Baseline factors associated with environmental contamination by the index subject’s infection isolate were body colonization by any household member with the index subject’s infection isolate at baseline (odds ratio [OR], 10.93 [95% confidence interval (CI), 5.75–20.79]), higher housing density (OR, 1.47 [95% CI, 1.10–1.96]), and more frequent household fomite cleaning (OR, 1.62 [95% CI, 1.16–2.27]). Household environmental contamination with the index subject’s infection strain at 3 months was associated with USA300 MRSA and a synergistic interaction between baseline environmental contamination and body colonization by any household member with the index subject’s infection strain.

Conclusions.

We found that infectingS. aureusisolates frequently persisted environmentally in households 3 months after skin infection. Presence of pathogenicS. aureusstrain type in the environment in a household may represent a persistent reservoir that places household members at risk of future infection.

Infect Control Hosp Epidemiol2014;35(11):1373–1382

Telavancin in vitro activity against a collection of methicillin-resistant Staphylococcus aureus isolates, including resistant subsets, from the United States

Telavancin had MIC50, MIC90, and MIC100 values of 0.03, 0.06, and 0.12 μg/ml, respectively, against methicillin-susceptible Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and non-multidrug-resistant (non-MDR) and MDR subsets. MRSA with elevated MIC values for vancomycin (2 to 4 μg/ml) or daptomycin (1 to 2 μg/ml) had telavancin MIC50 (0.06 μg/ml) values 2-fold higher than those of isolates with lower MIC results (MIC50, 0.03 μg/ml). However, telavancin had MIC90 and MIC100 results of 0.06 and 0.12 μg/ml (100% susceptible), respectively, regardless of the MRSA subset.

Adaptive change inferred from genomic population analysis of the ST93 epidemic clone of community-associated methicillin-resistant Staphylococcus aureus

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as a major public health problem around the world. In Australia, ST93-IV[2B] is the dominant CA-MRSA clone and displays significantly greater virulence than other S. aureus. Here, we have examined the evolution of ST93 via genomic analysis of 12 MSSA and 44 MRSA ST93 isolates, collected from around Australia over a 17-year period. Comparative analysis revealed a core genome of 2.6 Mb, sharing greater than 99.7% nucleotide identity. The accessory genome was 0.45 Mb and comprised additional mobile DNA elements, harboring resistance to erythromycin, trimethoprim, and tetracycline. Phylogenetic inference revealed a molecular clock and suggested that a single clone of methicillin susceptible, Panton-Valentine leukocidin (PVL) positive, ST93 S. aureus likely spread from North Western Australia in the early 1970s, acquiring methicillin resistance at least twice in the mid 1990s. We also explored associations between genotype and important MRSA phenotypes including oxacillin MIC and production of exotoxins (α-hemolysin [Hla], δ-hemolysin [Hld], PSMα3, and PVL). High-level expression of Hla is a signature feature of ST93 and reduced expression in eight isolates was readily explained by mutations in the agr locus. However, subtle but significant decreases in Hld were also noted over time that coincided with decreasing oxacillin resistance and were independent of agr mutations. The evolution of ST93 S. aureus is thus associated with a reduction in both exotoxin expression and oxacillin MIC, suggesting MRSA ST93 isolates are under pressure for adaptive change.

Increasing Incidence of Sterile-Site Infections Due to Non-Multidrug-Resistant, Oxacillin-Resistant Staphylococcus aureus Among Hospitalized Patients

The incidence of community-associated, healthcare-associated, and hospital-acquired sterile-site infections due to methicillin-re-sistant Staphylococcus aureus (MRSA) isolates and the susceptibility of the isolates to non-β-lactam antibiotics were evaluated for 549 hospitalized patients during a 3-year period. The incidence of community-associated MRSA infection increased significantly. The annual percentage of MRSA isolates from cases of healthcare-associated and hospital-acquired infection that were susceptible to 3 or more non-β-lactam antibiotics increased significantly.

Colonization With Multidrug-Resistant Organisms in Evacuees After Hurricane Katrina

After Hurricane Katrina, 50 patients were evacuated to Grady Memorial Hospital in Atlanta, Georgia, with limited medical records. The infection control department ordered contact precautions for 16 Patients. Surveillance cultures performed on admission identified colonization with multidrug-resistant (MDR) bacteria in 9 patients (18%). Presence of a wound was the strongest predictor for MDR colonization. More data are needed to reliably predict MDR bacterial colonization.

Legislative Mandates for Use of Active Surveillance Cultures to Screen for Methicillin-ResistantStaphylococcus aureusand Vancomycin-Resistant Enterococci: Position Statement From the Joint SHEA and APIC Task Force

Legislation aimed at controlling antimicrobial-resistant pathogens through the use of active surveillance cultures to screen hospitalized patients has been introduced in at least 2 US states. In response to the proposed legislation, the Society for Healthcare Epidemiology of America (SHEA) and the Association of Professionals in Infection Control and Epidemiology (APIC) have developed this joint position statement. Both organizations are dedicated to combating healthcare-associated infections with a wide array of methods, including the use of active surveillance cultures in appropriate circumstances. This position statement reviews the proposed legislation and the rationale for use of active surveillance cultures, examines the scientific evidence supporting the use of this strategy, and discusses a number of unresolved issues surrounding legislation mandating use of active surveillance cultures. The following 5 consensus points are offered. (1) Although reducing the burden of antimicrobial-resistant pathogens, including methicillin-resistantStaphylococcus aureus(MRSA) and vancomycin-resistant enterococci (VRE), is of preeminent importance, APIC and SHEA do not support legislation to mandate use of active surveillance cultures to screen for MRSA, VRE, or other antimicrobial-resistant pathogens. (2) SHEA and APIC support the continued development, validation, and application of efficacious and cost-effective strategies for the prevention of infections caused by MRSA, VRE, and other antimicrobial-resistant and antimicrobial-susceptible pathogens. (3) APIC and SHEA welcome efforts by healthcare consumers, together with private, local, state, and federal policy makers, to focus attention on and formulate solutions for the growing problem of antimicrobial resistance and healthcare-associated infections. (4) SHEA and APIC support ongoing additional research to determine and optimize the appropriateness, utility, feasibility, and cost-effectiveness of using active surveillance cultures to screen both lower-risk and high-risk populations. (5) APIC and SHEA support stronger collaboration between state and local public health authorities and institutional infection prevention and control experts.

Prevalence of Colonization With Community-Associated Methicillin-ResistantStaphylococcus aureusAmong End-Stage Renal Disease Patients and Healthcare Workers

Objective.

To evaluate the prevalence, epidemiologic features, and molecular characteristics of colonization with community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) among hospitalized dialysis patients and their healthcare workers (HCWs).

Design.

Prospective observational clinical and laboratory study of nasal colonization.

Setting.

A 600-bed urban academic medical center.

Subjects.

One hundred twenty hospitalized dialysis inpatients and 100 HCWs.

Results.

Of 120 patients, 40 (33%) were colonized withS. aureus; 26 (65%) of these 40 were colonized with MRSA. Among the 26 MRSA isolates, 10 (38.5%) carried staphylococcal cassette chromosome (SCC)mectype IV (ie, CA-MRSA), and 7 of these 10 carried the genes for the Panton-Valentine leukocidin (PVL) toxin. Patients colonized with healthcare-associated MRSA strains and those colonized with CA-MRSA strains were similar, except for a higher frequency of a history of congestive heart failure among those with healthcare-associated MRSA strains (P= .014). Among 10 patients who presented with or developed anS. aureusinfection while hospitalized, 8 were colonized withS. aureus, 7 with MRSA, and 3 with SCCmectype IV strains. Among 100 HCWs, 31 were colonized withS. aureus, including 6 with MRSA; 2 of the MRSA isolates belonged to CA-MRSA strains, and soft-tissue infections were reported in one of the HCWs and in the family member of the other HCW colonized with these strains.

Conclusions.

There is a high rate of colonization with MRSA and CA-MRSA among hospitalized dialysis patients and their HCWs. As other studies have found, it appears that individuals are being colonized with both CA-MRSA strains and healthcare-associated MRSA strains.

Epidemiology of Healthcare-Associated Bloodstream Infection Caused by USA300 Strains of Methicillin-ResistantStaphylococcus aureusin 3 Affiliated Hospitals

Objective.

To describe the epidemiology of bloodstream infection caused by USA300 strains of methicillin-resistantStaphylococcus aureus(MRSA), which are traditionally associated with cases of community-acquired infection, in the healthcare setting.

Design.

Retrospective cohort study.

Setting.

Three academically affiliated hospitals in Denver, Colorado.

Methods.

Review of cases of S.aureusbloodstream infection during the period from 2003 through 2007. Polymerase chain reaction was used to identify MRSA USA300 isolates.

Results.

A total of 330 cases of MRSA bloodstream infection occurred during the study period, of which 286 (87%) were healthcare-associated. The rates of methicillin resistance among theS. aureusisolates recovered did not vary during the study period and were similar among the 3 hospitals. However, the percentages of cases of healthcare-associated MRSA bloodstream infection due to USA300 strains varied substantially among the 3 hospitals: 62%, 19%, and 36% (P< .001) for community-onset cases and 33%, 3%, and 33% (P= .005) for hospital-onset cases, in hospitals A, B, and C, respectively. In addition, the number of cases of healthcare-associated MRSA bloodstream infection caused by USA300 strains increased during the study period at 2 of the 3 hospitals. At each hospital, USA300 strains were most common among cases of community-associated infection and were least common among cases of hospital-onset infection. Admission to hospital A (a safety-net hospital), injection drug use, and human immunodeficiency virus infection were independent risk factors for healthcare-associated MRSA bloodstream infection due to USA300 strains.

Conclusions.

The prevalence of USA300 strains among cases of healthcare-associated MRSA bloodstream infection varied dramatically among geographically clustered hospitals. USA300 strains are replacing traditional healthcare-related strains of MRSA in some healthcare settings. Our data suggest that the prevalence of USA300 strains in the community is the dominant factor affecting the prevalence of this strain type in the healthcare setting.

USA300 Methicillin-Resistant Staphylococcus aureus Emerging as a Cause of Bloodstream Infections at Military Medical Centers

Background.

USA300 methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of skin and soft-tissue infection (SSTI) in military personnel. USA300 MRSA has emerged as an important cause of healthcare-associated bloodstream infection (BSI) in metropolitan centers.

Objective.

To determine the prevalence, risk factors, and patient outcomes associated with USA300 MRSA BSI in military tertiary medical centers.

Design.

Retrospective case-control study.

Patients.

Patients admitted during the period 2001–2009 with MRSA BSI.

Setting.

Walter Reed Army Medical Center (Washington, DC) and National Naval Medical Center (Bethesda, MD) tertiary medical centers with 500 inpatient beds combined, which provide care to active duty service members and military beneficiaries.

Methods.

After identifying patients with MRSA BSI, we collected epidemiological data from electronic medical records and characterized bacterial isolates using pulsed-field gel electrophoresis (PFGE).

Results.

A total of 245 MRSA BSI cases were identified, and 151 isolates were available for analysis. Epidemiological characteristics for the 151 patients with available isolates included the following: mean age, 61 years; male sex, 70%; white race, 62%; and combat-wounded service members, 11%. The crude in-hospital mortality rate was 17%. PFGE demonstrated that 30 (20%) of 151 MRSA BSI cases with isolates available for analysis were due to USA300, and 27 (87%) of these 30 cases were healthcare-associated infection. USA300 was associated with a significantly increasing proportion of MRSA BSI when examined over sequential time periods: 2 (4%) of 51 isolates during 2001–2003, 9 (19%) of 47 isolates during 2004–2006, and 19 (36%) of 53 isolates during 2007–2009 (P<.001).

Conclusion.

USA300 MRSA is emerging as a cause of healthcare-associated BSI in tertiary military medical centers.

Emergence of Community-Associated Methicillin-ResistantStaphylococcus aureusStrains as a Cause of Healthcare-Associated Bloodstream Infections in Korea

Background.

The prevalence of community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) strains causing bloodstream infection (BSI) has not been studied in Korea.

Objective.

We sought to determine the prevalence of CA-MRSA strains among isolates recovered from patients with MRSA BSIs and to explore epidemiological changes in Korea. We also sought to evaluate clinical characteristics relevant to the development of healthcare-associated BSIs.

Methods.

We prospectively collected consecutive MRSA isolates from patients with BSI at 4 hospitals from July 1 through November 30, 2007, and we also included MRSA isolates recovered from culture of blood samples collected during a previous year (October 1, 2004 through September 30, 2005) at a different hospital. Molecular typing studies were performed, including pulsed-field gel electrophoresis (PFGE), multilocus sequence typing,Staphylococcusprotein A (spa) typing, and staphylococcal cassette chromosomemec(SCCmec) typing. We compared the clinical characteristics and outcomes of patients with healthcare-associated BSI due to CA-MRSA strains with those of patients with healthcare-associated BSI due to healthcare-associated MRSA (HA-MRSA) strains.

Results.

There were 76 cases of MRSA BSI, of which 4 (5.3%) were community-associated and 72 (94.7%) were healthcare-associated. Among the 72 HA-MRSA BSIs, 18 (25%) were community onset, and 54 (75%) were hospital onset. PFGE type D-ST72–spaB-SCCmectype IVA MRSA, the predominant genotype of CA-MRSA in Korea, accounted for 19 (25%) of all 76 MRSA BSIs, including 17 (23.6%) of 72 HA-MRSA BSIs and 11 (20.8%) of 53 hospital-onset HA-MRSA BSIs. Patients with healthcare-associated BSIs due to CA-MRSA strains carrying SCCmectype IVA tended to have fewer healthcare-associated risk factors, compared with patients with healthcare-associated BSIs due to HA-MRSA strains carrying other SCCmectypes. The presence of a central venous catheter or other invasive device was the only independent factor differentiating patients infected with hospital-associated genotype strains from patients infected with other strains. Clinical outcomes were similar between both groups.

Conclusions.

CA-MRSA strains are emerging as a major cause of BSI in healthcare settings in Korea. This changing epidemiology of MRSA poses a challenge to public health and infection control in hospital settings.