Molecular diversity within clonal complex 22 methicillin-resistant Staphylococcus aureus encoding Panton–Valentine leukocidin in England and Wales

Diversity of clonal complex 22 methicillin-resistant Staphylococcus aureus isolates in Kuwait hospitals

CC22-MRSA is a major MRSA lineage that is widely reported globally. To characterize CC22-MRSA for trends in antibiotic resistance and emergence of variants, a total of 636 CC22 isolates identified by DNA microarray in 2016 (n = 195), 2017 (n = 227) and 2018 (n = 214) were investigated further using staphylococcal protein A (spa) typing and multilocus sequence typing. The isolates belonged to 109 spa types dominated by t223 (n = 160), t032 (n = 60), t852 (n = 59), t005 (n = 56) and t309 (n = 30) and 10 sequence types (STs) dominated by ST22 (85.5%). Genotypes CC22-MRSA-IV [tst1⁺]; CC22-MRSA-IV UK-EMRSA-15/Barnim EMRSA variants, CC22-MRSA-IV [PVL⁺], CC22-MRSA-IV [tst1⁺/PVL⁺] and CC22-MRSA-IV + V constituted >50% of the isolates. An increase from 2016 to 2018 were shown in isolates belonging to spa types t223 (43 to 62), t032 (18 to 27) and t309 (10 to 15) and genotypes CC22-MRSA-IV [tst1⁺] (89 to 102), CC22-MRSA-IV + V (12 to 30) and CC22-MRSA-IV [tst1⁺/PVL⁺] (12 to 22). Ninety-nine CC22-MRSA isolates were multi-resistant to three or more antibiotic classes with 76.7% of them belonging to CC22-MRSA-IV [PVL⁺] and CC22-MRSA-IV [tst1⁺/PVL⁺]. The study revealed an ongoing domination of the CC22-MRSA-[tst1⁺] genotype and the emergence of new clones bearing SCCmec IV + V and multiply resistant variants.

Toxic Shock Syndrome Toxin 1 Evaluation and Antibiotic Impact in a Transgenic Model of Staphylococcal Soft Tissue Infection

Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Nonmenstrual toxic shock syndrome (nmTSS), linked to TSST-1-producing CC30 Staphylococcus aureus, is the leading manifestation of toxic shock syndrome (TSS). Due to case rarity and a lack of tractable animal models, TSS pathogenesis is poorly understood. We developed an S. aureus abscess model in HLA class II transgenic mice to investigate pathogenesis and treatment. TSST-1 sensitivity was established using murine spleen cell proliferation assays and cytokine assays following TSST-1 injection in vivo. HLA-DQ8 mice were infected subcutaneously with a tst-positive CC30 methicillin-sensitive S. aureus clinical TSS-associated isolate. Mice received intraperitoneal flucloxacillin, clindamycin, flucloxacillin and clindamycin, or a control reagent. Abscess size, bacterial counts, TSST-1 expression, and TSST-1 bioactivity were measured in tissues. Antibiotic effects were compared with the effects of control reagent. Purified TSST-1 expanded HLA-DQ8 T-cell Vβ subsets 3 and 13 in vitro and instigated cytokine release in vivo, confirming TSST-1 sensitivity. TSST-1 was detected in abscesses (0 to 8.0 μg/ml) and draining lymph nodes (0 to 0.2 μg/ml) of infected mice. Interleukin 6 (IL-6), gamma interferon (IFN-γ), KC (CXCL1), and MCP-1 were consistent markers of inflammation during infection. Clindamycin-containing antibiotic regimens reduced abscess size and TSST-1 production. Infection led to detectable TSST-1 in soft tissues, and TSST-1 was detected in draining lymph nodes, events which may be pivotal to TSS pathogenesis. The reduction in TSST-1 production and lesion size after a single dose of clindamycin underscores a potential role for adjunctive clindamycin at the start of treatment of patients suspected of having TSS to alter disease progression.

IMPORTANCE Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Clinical and Molecular Epidemiology of Staphylococcal Toxic Shock Syndrome in the United Kingdom

Staphylococcal toxic shock syndrome (TSS) was originally described in menstruating women and linked to TSS toxin 1 (TSST-1)-producing Staphylococcus aureus. Using UK national surveillance data, we ascertained clinical, molecular and superantigenic characteristics of TSS cases. Average annual TSS incidence was 0.07/100,000 population. Patients with nonmenstrual TSS were younger than those with menstrual TSS but had the same mortality rate. Children <16 years of age accounted for 39% of TSS cases, most caused by burns and skin and soft tissue infections. Nonmenstrual TSS is now more common than menstrual TSS in the UK, although both types are strongly associated with the tst+ clonal complex (CC) 30 methicillin-sensitive S. aureus lineage, which accounted for 49.4% of all TSS and produced more TSST-1 and superantigen bioactivity than did tst+ CC30 methicillin-resistant S. aureus strains. Better understanding of this MSSA lineage and infections in children could focus interventions to prevent TSS in the future.

Distribution of the Most Prevalent Spa Types among Clinical Isolates of Methicillin-Resistant and -Susceptible Staphylococcus aureus around the World: A Review

Background:Staphylococcus aureus, a leading cause of community-acquired and nosocomial infections, remains a major health problem worldwide. Molecular typing methods, such as spa typing, are vital for the control and, when typing can be made more timely, prevention of S. aureus spread around healthcare settings. The current study aims to review the literature to report the most common clinical spa types around the world, which is important for epidemiological surveys and nosocomial infection control policies.

Methods: A search via PubMed, Google Scholar, Web of Science, Embase, the Cochrane library, and Scopus was conducted for original articles reporting the most prevalent spa types among S. aureus isolates. The search terms were “Staphylococcus aureus, spa typing.”

Results: The most prevalent spa types were t032, t008 and t002 in Europe; t037 and t002 in Asia; t008, t002, and t242 in America; t037, t084, and t064 in Africa; and t020 in Australia. In Europe, all the isolates related to spa type t032 were MRSA. In addition, spa type t037 in Africa and t037and t437 in Australia also consisted exclusively of MRSA isolates. Given the fact that more than 95% of the papers we studied originated in the past decade there was no option to study the dynamics of regional clone emergence.

Conclusion: This review documents the presence of the most prevalent spa types in countries, continents and worldwide and shows big local differences in clonal distribution.

Transmission of highly virulent community-associated MRSA ST93 and livestock-associated MRSA ST398 between humans and pigs in Australia

Pigs have been recognised as a reservoir of livestock associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in Europe, Asia and North America. However, little is known about the presence and distribution of MRSA in the Australian pig population and pig industry. This study describes the presence, distribution and molecular characteristics of the human adapted Australian CA-MRSA ST93 isolated from pigs, people, and the environment within a piggery. Isolates were subjected to antibiotic susceptibility testing, DNA microarray, whole genome sequencing, multi locus sequence typing, virulence and resistance gene characterization and phylogenetic analysis. MRSA were isolated from 60% (n = 52) of farm workers where 84% of isolates returned ST93 and the rest ST398. Of the thirty-one pig isolates tested further, an equal number of ST398 and ST93 (15 each) and one as ST30-V were identified. Four of six environmental isolates were identified as ST93 and two as ST398. This study has identified for the first time in Australia the occurrence of CA-MRSA ST93 and LA-MRSA ST398 amongst farm workers, pigs, and the farm environment. Comparative genome analysis indicates that ST398 is likely to have been introduced into Australia from Europe or North America. This study also reports the first linezolid resistant MRSA isolated in Australia.

Comparative analysis of phenol-soluble modulin production and Galleria mellonella killing by community-associated and healthcare-associated meticillin-resistant Staphylococcusaureus strains

Community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) have emerged globally and have been associated with more severe disease than healthcare-associated MRSA (HA-MRSA). The purpose of this study was to determine whether laboratory measures of virulence can distinguish dominant CA-MRSA clones from HA-MRSA clones. We compared the production of phenol-soluble modulins (PSMs) and ability to kill Galleria mellonella caterpillars for a range of CA- and HA-MRSA strains. Twenty-two HA-MRSA strains [ST22-IV (EMRSA-15), ST36-II (EMRSA-16) and ST239-III] and 26 CA-MRSA strains [ST1-IV (PVL+ USA400), ST1-IV (PVL-), ST8-IV (USA300), ST22-IV (PVL+), ST30-IV, ST59-IV and ST80-IV] were analysed. PSM production was measured using and compared using t-tests and ANOVA. A G mellonella (caterpillar) pathogenicity model was performed, and differences were compared using survival analysis and the log-rank test. There was no significant difference in overall PSM production between HA and CA strains (P=0.090), but there was significant variation between clones (P=0.003). G. mellonella caterpillar killing varied significantly by clone (P<0.001), and overall killing was greater for HA compared with CA clones (P=0.007). The increased acute virulence phenotype of CA-MRSA clones in humans is not associated with increased PSM production in vitro or increased killing in an in vivo caterpillar pathogenicity model.

Genomic insights into the emergence and spread of international clones of healthcare-, community- and livestock-associated meticillin-resistant Staphylococcus aureus: Blurring of the traditional definitions

The evolution of meticillin-resistant Staphylococcus aureus (MRSA) from meticillin-susceptible S. aureus has been a result of the accumulation of genetic elements under selection pressure from antibiotics. The traditional classification of MRSA into healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA) is no longer relevant as there is significant overlap of identical clones between these groups, with an increasing recognition of human infection caused by livestock-associated MRSA (LA-MRSA). Genomic studies have enabled us to model the epidemiology of MRSA along these lines. In this review, we discuss the clinical relevance of genomic studies, particularly whole-genome sequencing, in the investigation of outbreaks. We also discuss the blurring of each of the three epidemiological groups (HA-MRSA, CA-MRSA and LA-MRSA), demonstrating the limited relevance of this classification.

Recurrent skin infection associated with nasal carriage of Panton-Valentine leukocidin-positive methicillin-susceptible Staphylococcus aureus closely related to the EMRSA-15 clone

We report the case of a soldier with recurrent skin infection associated with nasal carriage of a Panton-Valentine leukocidin (PVL)-producing methicillin-susceptible Staphylococcus aureus (MSSA), closely related to the EMRSA-15 clone. MSSA isolates causing infection not requiring hospitalization usually go unnoticed; however, their typing may be useful to understand the global distribution of successful staphylococcal lineages related to epidemic clones. PVL-positive MSSA strains might serve as reservoirs from which virulent methicillin-resistant strains may evolve and spread.

Identification of genetic variation exclusive to specific lineages associated with Staphylococcus aureus bacteraemia

BACKGROUND

Meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia cases have declined since 2003, and have mostly been due to two epidemic (E) strains, E15 (multi-locus sequence type clonal complex CC22) and E16 (CC30). By contrast, the incidence of meticillin-susceptible S. aureus (MSSA) bacteraemia has remained largely unchanged and our understanding of these isolates has remained poor.

AIM

To investigate the distribution and nucleotide sequence of heterogeneous regions between successful lineages using the 2009 British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Resistance Surveillance Programme collection of S. aureus.

METHODS

S. aureus isolates (N = 202) comprised of 103 MRSA and 99 MSSA isolates were analysed using fluorescent amplified fragment length polymorphism (FAFLP) to detect nucleotide variations due to lineage-specific sequence motifs as well as differences in the distribution of mobile genetic elements between lineages.

FINDINGS

E15 and E16 MRSA strains comprised 79% and 6% of the collection in 2009 respectively. Six lineages, including CC22 and CC30, were associated with MRSA bacteraemia in the UK and Ireland. MSSA isolates were more diverse with 19 different lineages detected. FAFLP revealed lineage-specific sequence variations in loci encoding factors such as proteases or factors involved in haem biosynthesis, both of which may affect the success of major S. aureus lineages. Proteins encoded on certain mobile genetic elements or involved in cobalamin biosynthesis were found to be exclusive to CC8, CC22, or CC30.

CONCLUSION

Overall, the genetic diversity among regions of the core genome and mobile genetic elements may alter antimicrobial resistance and the production of virulence or fitness factors that may be linked to strain success.

Whole-genome sequencing in outbreak analysis

In addition to the ever-present concern of medical professionals about epidemics of infectious diseases, the relative ease of access and low cost of obtaining, producing, and disseminating pathogenic organisms or biological toxins mean that bioterrorism activity should also be considered when facing a disease outbreak. Utilization of whole-genome sequencing (WGS) in outbreak analysis facilitates the rapid and accurate identification of virulence factors of the pathogen and can be used to identify the path of disease transmission within a population and provide information on the probable source. Molecular tools such as WGS are being refined and advanced at a rapid pace to provide robust and higher-resolution methods for identifying, comparing, and classifying pathogenic organisms. If these methods of pathogen characterization are properly applied, they will enable an improved public health response whether a disease outbreak was initiated by natural events or by accidental or deliberate human activity. The current application of next-generation sequencing (NGS) technology to microbial WGS and microbial forensics is reviewed.

Comparison of ESBL--and AmpC producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA) isolated from migratory and resident population of rooks (Corvus frugilegus) in Austria

In order to test whether rooks (Corvus frugilegus) represent good indicators for the potential circulation of antibiotics in their native habitat, two populations with different migratory behavior were tested for the presence of beta-lactamase producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA). In all, 54 and 102 samples of fresh feces of a migratory and a resident population were investigated. A total of 24 and 3 cefotaxime-resistant enterobacterial isolates were obtained from the migratory and resident population, respectively. In these isolates CTX-M-1 (n = 15), CTX-M-3 (n = 3), and CTX-M-15 (n = 3) genes were detected. TEM-1 and OXA-1 were associated with CTX-M in 3 and 2 isolates, respectively. In two E. coli isolates CMY-2 could be detected, where from one isolate displayed an overexpression of chromosomal AmpC as well. Among E. coli isolates the most common phylogenetic group was A (n = 11) and ST1683 (n = 5). In one E. coli of B2-ST131 the rfbO25b locus was detected. Three Enterobacter isolates were stably derepressed AmpC-producers. In five samples of the migratory population, PVL positive MRSA could be isolated. Two isolates were typed SCCmec IVa, spa type t127, and ST1. Three isolates carried a SCCmec type IVc, with spa type t852 and ST22. The highly significant difference of the occurrence of antibiotic resistance between the migratory population from eastern Europe compared to resident population in our study indicates that rooks may be good indicator species for the evaluation of environmental contamination with antibiotic resistant bacteria, especially due to their ecology, foraging behavior and differing migratory behavior.

Development and usage of protein microarrays for the quantitative measurement of Panton-Valentine leukocidin

Staphylococcus aureus is a human pathogen that can harbour several genes encoding exotoxins including leukocidins. A clinically most relevant factor is Panton-Valentine leukocidin (PVL) because of its association with chronic, recurrent or severe skin and soft tissue infections. In this study an antibody array was designed and used to obtain an overview about the in vitro PVL expression levels of 266 clinical isolates of MRSA as well as of MSSA belonging to a wide variety of clonal complexes. For that purpose, a novel precipitation based method was used. Unknown PVL concentrations were determined by mapping the signal intensities for spotted monoclonal antibodies to calibration curves that resulted from experiments with known concentrations of recombinant LukF-PV. In most cases, isolates belonging to one clonal complex (CC) showed similar PVL expressions. However, there were also CCs with widely varying PVL concentrations. First analyses, based on in vitro PVL measurements, showed low PVL concentrations in isolates from severe and fatal conditions that are not associated with PVL, such as sepsis, while isolates from skin and soft tissue infections yielded higher concentrations. Agr-group I and IV isolates generally produced more PVL than isolates from agr-groups II and III. The few isolates harbouring the gene encoding toxic shock syndrome toxin (tst1) were particularly low level PVL producers. However, these issues warrant further studies. The method described herein allows rapid quantification of expressed proteins such as PVL in collections of clinical isolates in order to correlate with clinical or genotypic data with a potential for further parallelisation.

Nasal Carriage of Epidemic Methicillin-Resistant Staphylococcus aureus 15 (EMRSA-15) Clone Observed in Three Chicago-Area Long-Term Care Facilities

The spread of pandemic methicillin-resistant Staphylococcus aureus (MRSA) clones such as USA300 and EMRSA-15 is a global health concern. As a part of a surveillance study of three long-term care facilities in the Greater Chicago area, phenotypic and molecular characterization of nasal MRSA isolates was performed. We report a cluster of pandemic EMRSA-15, an MRSA clone rarely reported from the United States, detected during this study.

Low prevalence of meticillin-resistant Staphylococcus aureus carriage at hospital admission: implications for risk-factor-based vs universal screening

BACKGROUND

There is debate over the optimal policy for detecting meticillin-resistant Staphylococcus aureus (MRSA) colonization at hospital admission. The emergence of community-associated (CA)-MRSA may compromise targeted screening strategies based on risk factors for healthcare-associated (HA)-MRSA.

AIM

To determine the prevalence of MRSA colonization at admission, and the genotype and molecular epidemiology of the strains involved.

METHODS

A 12-month observational study was performed at a 1200-bed London tertiary referral hospital from 1 April 2008 to 1 March 2009. All available MRSA isolates were genotyped by spa and staphylococcal cassette chromosome mec (SCCmec) typing.

FINDINGS

The overall MRSA colonization rate was 2.0% of 28,892 admissions (range 6.6% in critical care to 0.8% in obstetrics/gynaecology/neonatology). The overall frequency of previously unknown carriage of MRSA on admission was 1.4%. Most colonizing strains were epidemic HA-MRSA-15 and -16. However, heterogeneous CA strains accounted for 18% of recovered isolates, including 37.5% of MRSA from accident and emergency and 23.1% of MRSA from surgery. The CA-MRSA strain types had significantly different epidemiological associations from the HA-MRSA strains, so risk factors used for the identification of HA-MRSA may not detect CA-MRSA reliably.

CONCLUSION

The low rate of HA-MRSA in the UK increases the relative proportion due to CA-MRSA, for which conventional risk-factor-based screening strategies may be less effective. Cost-benefit analyses of universal MRSA admission screening will need to take account of this new epidemiology.

Genetic variation among Panton-Valentine leukocidin-encoding bacteriophages in Staphylococcus aureus clonal complex 30 strains

Clonal complex 30 (CC30), one of the major Staphylococcus aureus lineages, has caused extensive hospital-acquired and community-acquired infections worldwide. Recent comparative genomics studies have demonstrated that three CC30 clones-phage type 80/81, Southwest Pacific (SWP), and contemporary EMRSA-16 associated (Con) strains-shared a recent common ancestor more than 100 years ago. Panton-Valentine leukocidin (PVL), a bacteriophage encoded toxin that has been epidemiologically linked with community-associated methicillin-resistant S. aureus (CA-MRSA), has frequently been identified in CC30 clones, although the pvl gene variation and distribution of PVL-encoding phages are poorly understood. We determined here the distribution of PVL phages, PVL gene sequences, and chromosomal phage insertion sites in 52 S. aureus CC30 PVL-harboring isolates, collected from four continents over a 75-year period. Our results indicate that PVL phages with icosahedral heads, including Φ108PVL and ΦPVL, were mainly associated with phage 80/81 strains, whereas phages with elongated heads were predominantly found in SWP (ΦSa2958 and ΦTCH60) and Con (ΦSa2USA) strains. Nine single-nucleotide polymorphisms were identified in the lukSF-PV gene, with six isolates harboring the R variant that has been previously associated with CA-MRSA strains. Interestingly, all six R variant strains belonged to the same Con CC30 clone and carried a ΦSa2USA-like phage. Similar chromosomal phage insertion sites were also identified in all 52 PVL-harboring CC30 strains. These analyses provide important insights into the microepidemiology of PVL-harboring CC30 strains, while the discovery of ΦSa2USA-associated R variant strains sheds further light on the evolution of PVL-positive CA-MRSA.

Panton-Valentine leukocidin gene sequence variation and phage in methicillin-resistant and methicillin-susceptible Staphylococcus aureus from children in mainland China

To determine the variation in the Panton-Valentine leukocidin (PVL) gene sequences and different PVL-encoding phages of Staphylococcus aureus strains collected from children in mainland China, fifty-eight strains with PVL collected from 2007 to 2009 were used. Their molecular characteristics were examined. Primers were designed to sequence the PVL genes. Six PVL-encoding phages (ϕPVL, ϕ108PVL, ϕSLT, ϕSa2MW, ϕSa2958, and ϕSa2USA) were identified by PCR. Eleven sequence types (ST) were detected with ST59 (39.7%, 23/58) the most frequent ST, followed by 910 (22.4%, 13/58), and 338 (12.1%, 7/58). Single nucleotide polymorphisms (SNP) were identified at 11 locations in the PVL genes. SNP (nucleotide 1396, A→G) and SNP (nucleotide 1546, A→G) were observed in >10 sequences. Four additional SNP were non-synonymous. Both SNP (nucleotide 16, C→A) and SNP (nucleotide 62, C→T) were present in the same ST59 strain. SNP (nucleotide 527, A→G) was present in five strains belonging to ST30, 121, 1, and 93. SNP (nucleotide 1436, A→C) was present in one ST30 strain. Fifteen strains belonging to ST910, ST217, and ST30 carried a PVL phage that had an icosahedral head morphology. Nine ST59 strains carried ϕ108PVL. Three ST88 strains carried a PVL phage that had an elongated head morphology. Twenty-seven strains, including 60.9% (14/23) of ST59 and all ST338 strains, had no detectable phage. In conclusion, sequence variation in PVL genes and PVL-encoding phages was generally related to the lineage. ST59 strains may indeed carry novel PVL phages.

Characterisation of MRSA strains isolated from patients in a hospital in Riyadh, Kingdom of Saudi Arabia

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is spreading worldwide and poses a serious public health problem, being present in hospital settings and communities. However, from the Middle East and the Arabian Peninsula few molecular typing data on MRSA strains are currently available. In order to obtain data on the population structure of MRSA in Riyadh, Saudi Arabia, 107 clinical and environmental MRSA isolates were genotyped using a microarray-based assay.

Results

Five major MRSA strains from four clonal complexes were identified CC8/ST239-III (20.75%), PVL-positive as well as -negative CC22-IV (18.87% and 9.43%, respectively), PVL-positive CC30-IV (12.26%) and PVL-positive CC80-IV (17.92%). Minor strains, which accounted for less than 3% each, included CC1-IV/SCCfus, PVL-positive CC1/ST772-V, PVL-positive as well as- negative CC5-IV, CC5-IV/SCCfus, CC5-V, CC6-IV, CC45-IV, PVL-negative CC80-IV, PVL-positive CC88-IV, CC97-V and a CC9/ST834-MRSA strain.

Conclusions

Typing of MRSA strains from Riyadh revealed a high diversity of clonal complexes. The prevalence of the genes encoding the Panton-Valentine leukocidin was surprisingly high (54.21%), and a significant rate of resistance markers was detected also in strains considered as community-associated.

Molecular characterization and panton-valentine leucocidin typing of community-acquired methicillin-sensitive Staphylococcus aureus clinical isolates

Limited comprehensive molecular typing data exist currently for Panton-Valentine leucocidin (PVL)-positive, methicillin-sensitive Staphylococcus aureus (PVL-MSSA) clinical isolates. Characterization of PVL-MSSA isolates by multilocus sequence typing (MLST) and spa typing in this study showed a genetic similarity to PVL-positive, methicillin-resistant S. aureus (PVL-MRSA) strains, although three novel spa types and a novel MLST (ST1518) were detected. Furthermore, the detection of PVL phages and haplotypes in PVL-MSSA identical to those previously found in PVL-MRSA isolates highlights the role these strains may play as precursors of emerging lineages of clinical significance.

Polyclonal non multiresistant methicillin resistant Staphylococcus aureus isolates from clinical cases of infection occurring in Palermo, Italy, during a one-year surveillance period

Background

The evolving epidemiology of methicillin resistant Staphylococcus aureus (MRSA) is characterized by the emergence of infections caused by non multiresistant MRSA carrying staphylococcal chromosomal cassette (SCC)mec IV or V in the healthcare settings. A molecular epidemiological analysis of non multiresistant MRSA isolates from four acute general hospitals was performed in Palermo, Italy, during a one year period.

Methods

For the purpose of the study, MRSA isolates were defined as non multiresistant when they were susceptible to at least three classes of non β-lactam antibiotics. Seventy-five isolates were submitted to antimicrobial susceptibility testing, multilocus sequence typing (MLST) and polymerase chain reaction (PCR) for SCCmec, accessory gene regulator (agr) groups, arginine catabolic mobile element (ACME) and Panton Valentine leukocidin (PVL) toxin genes. For epidemiological typing, Multiple-Locus Variable-Number Tandem Repeat Fingerprinting (MLVF) was performed on all isolates and pulsed field gel electrophoresis (PFGE) on ST8 isolates.

Results

Non multiresistant MRSA isolates were isolated from all hospitals. Resistances to ciprofloxacin, macrolides and tetracycline were the most prevalent. MLST attributed 46 isolates with ST22, 13 with ST8, eight with ST1, three with ST50 and three with ST398. SCCmec type IV was found in all isolates. PVL was detected in one ST22 isolate. All isolates tested negative for the ACME element. MLVF identified 31 different patterns, some subtype clusters ranging in size between two and 22 isolates. The closely related PFGE patterns of the ST8 isolates differed from USA300.

Conclusions

A polyclonal circulation of non multiresistant MRSA along with blurring of boundaries between healthcare associated (HA)-MRSA and community associated (CA)-MRSA appear to be occurring in our epidemiological setting. A better understanding of spread of MRSA with the support of molecular typing can provide invaluable information in the epidemiological, microbiological and clinical fields.

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

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

Do differences in Panton-Valentine leukocidin production among international methicillin-resistant Staphylococcus aureus clones affect disease presentation and severity?

Panton-Valentine leukocidin (PVL) production by methicillin-resistant Staphylococcus aureus (MRSA) was determined in vitro using the enzyme-linked immunosorbent assay (ELISA), and associations with clinical presentation and bacterial genetic characteristics were examined. PVL production ranged from 0.02 to 4.865 μg/ml and correlated with a multilocus sequence type (MLST) clonal complex associated with specific PVL phage types. A relationship between PVL production and clinical presentation or patient demographics could not be demonstrated.

Waves of trouble: MRSA strain dynamics and assessment of the impact of infection control

There has been a sustained decline in bloodstream infections due to methicillin-resistant Staphylococcus aureus (MRSA) throughout the UK. The UK MRSA epidemic, which began in the 1990s, has been dominated by two epidemic MRSA (EMRSA) clones {EMRSA-15, of clonal complex (CC) 22 [sequence type (ST) 22], and EMRSA-16, of CC30 (ST36)}. It appears that both these clones followed a wave trajectory (initial expansion, relative stasis, then decline). Three recent studies have shown that ST36 has declined faster than ST22, a change that appears to have begun before the recent intensification of intensive control measures in the UK. The biological basis of infectious disease waves, including those of MRSA, is discussed, as are the implications of such waves for the assessment of the impact of infection control measures.

Distinct bacteriophages encoding Panton-Valentine leukocidin (PVL) among international methicillin-resistant Staphylococcus aureus clones harboring PVL

Genetically diverse community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) can harbor a bacteriophage encoding Panton-Valentine leukocidin (PVL) lysogenized into its chromosome (prophage). Six PVL phages (ΦPVL, Φ108PVL, ΦSLT, ΦSa2MW, ΦSa2USA, and ΦSa2958) are known, and single-nucleotide polymorphisms (SNPs) in the PVL genes have been reported. We sought to determine the distribution of lysogenized PVL phages among MRSA strains with PVL (PVL-MRSA strains), the PVL gene sequences, and the chromosomal phage insertion sites in 114 isolates comprising nine clones of PVL-MRSA that were selected for maximal underlying genetic diversity. The six PVL phages were identified by PCR; ΦSa2USA was present in the highest number of different lineages (multilocus sequence type clonal complex 1 [CC1], CC5, CC8, and sequence type 93 [ST93]) (n = 37 isolates). Analysis of 92 isolates confirmed that PVL phages inserted into the same chromosomal insertion locus in CC22, -30, and -80 but in a different locus in isolates of CC1, -5, -8, -59, and -88 and ST93 (and CC22 in two isolates). Within the two different loci, specific attachment motifs were found in all cases, although some limited inter- and intralineage sequence variation occurred. Overall, lineage-specific relationships between the PVL phage, the genes that encode the toxin, and the position at which the phage inserts into the host chromosome were identified. These analyses provide important insights into the microepidemiology of PVL-MRSA, will prove a valuable adjunct in outbreak investigation, and may help predict the emergence of new strains.

Enhanced discrimination of highly clonal ST22-methicillin-resistant Staphylococcus aureus IV isolates achieved by combining spa, dru, and pulsed-field gel electrophoresis typing data

ST22-methicillin-resistant Staphylococcus aureus type IV (ST22-MRSA-IV) is endemic in Irish hospitals and is designated antibiogram-resistogram type-pulsed-field group (AR-PFG) 06-01. Isolates of this highly clonal strain exhibit limited numbers of pulsed-field gel electrophoresis (PFGE) patterns and spa types. This study investigated whether combining PFGE and spa typing with DNA sequencing of the staphylococcal cassette chromosome mec element (SCCmec)-associated direct repeat unit (dru typing) would improve isolate discrimination. A total of 173 MRSA isolates recovered in one Irish hospital during periods in 2007 and 2008 were investigated using antibiogram-resistogram (AR), PFGE, spa, dru, and SCCmec typing. Isolates representative of each of the 17 pulsed-field group 01 (PFG-01) spa types identified underwent multilocus sequence typing, and all isolates were ST22. Ninety-seven percent of isolates (168 of 173) exhibited AR-PFG 06-01 or closely related AR patterns, and 163 of these isolates harbored SCCmec type IVh. The combination of PFGE, spa, and dru typing methods significantly improved discrimination of the 168 PFG-01 isolates, yielding 65 type combinations with a Simpson's index of diversity (SID) of 96.53, compared to (i) pairwise combinations of spa and dru typing, spa and PFGE typing, and dru and PFGE typing, which yielded 37, 44, and 43 type combinations with SIDs of 90.84, 91.00, and 93.57, respectively, or (ii) individual spa, dru, and PFGE typing methods, which yielded 17, 17, and 21 types with SIDs of 66.9, 77.83, and 81.34, respectively. Analysis of epidemiological information for a subset of PFG-01 isolates validated the relationships inferred using combined PFGE, spa, and dru typing data. This approach significantly enhances discrimination of ST22-MRSA-IV isolates and could be applied to epidemiological investigations of other highly clonal MRSA strains.