A survey of methicillin-resistant Staphylococcus aureus affecting patients 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.

Evolutionary Processes Driving the Rise and Fall of Staphylococcus aureus ST239, a Dominant Hybrid Pathogen

Selection plays a key role in the spread of antibiotic resistance, but the evolutionary drivers of clinically important resistant strains remain poorly understood. Here, we use genomic analyses and competition experiments to study Staphylococcus aureus ST239, a prominent MRSA strain that is thought to have been formed by large-scale recombination between ST8 and ST30. Genomic analyses allowed us to refine the hybrid model for the origin of ST239 and to date the origin of ST239 to 1920 to 1945, which predates the clinical introduction of methicillin in 1959. Although purifying selection has dominated the evolution of ST239, parallel evolution has occurred in genes involved in antibiotic resistance and virulence, suggesting that ST239 has evolved toward an increasingly pathogenic lifestyle. Crucially, ST239 isolates have low competitive fitness relative to both ST8 and ST30 isolates, supporting the idea that fitness costs have driven the demise of this once-dominant pathogen strain.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Poultry-Like pA+ Biotype of Staphylococcus aureus CC346/084 Clone in Human Population

The aim of the study was (1) to analyse the prevalence of P-like pA+ biotype of S. aureus in material from healthy and diseased individuals, not employed at slaughterhouses or meat processing plants, and (2) to analyse the relatedness of these strains and their genetic variability. The study included 344 strains of Staphylococcus aureus isolated from hospitalized patients with staphylococcal infections and from healthy carriers. The biotypes of S. aureus were determined on the basis of fibrinolysin and β-haemolysin production, coagulation of bovine plasma, and type of growth on crystal violet agar. Additionally, the strains were tested for the synthesis of protein A in order to distinguish between P-like pA+ and poultry biotypes. Fibrinolysin gene (sak) and methicillin resistance (mecA) were detected by means of PCR. The clonal structure of studied strains was analysed using pulsed field gel electrophoresis and sequencing of spa gene. Finally, the strains were typed with a basic set of 23 bacteriophages. The strains belonging to P-like pA+ biotype corresponded to nearly 20 % of all the studied strains. In contrast to the human biotype, they formed one clonal complex, spa-CC346/084. The P-like pA+ biotype strains did not synthesize fibrinolysin, lacked the sak gene, and showed susceptibility to methicillin. In contrast to the human biotype strains, they belonged mostly to phage group II. The P-like pA+ biotype strains, previously described solely in meat products and meat industry workers, can be also present in hospitalized patients and extra-hospital carriers. These strains form a single, fibrinolysin-negative, clonal complex t084/CC346.

High prevalence of toxic shock syndrome toxin-producing epidemic methicillin-resistant Staphylococcus aureus 15 (EMRSA-15) strains in Kuwait hospitals

This study characterized EMRSA-15 isolates obtained from patients in Kuwait hospitals for their genotypic relatedness, antibiotic resistance and carriage of virulence genes using pulsed-field gel electrophoresis (PFGE), coagulase serotyping, SCCmec subtyping, spa typing, multilocus sequence typing and DNA microarray. The isolates were resistant to trimethoprim (75.6%), ciprofloxacin (29.7%), erythromycin and clindamycin (24.3%), tetracycline (19.0%), and gentamicin and kanamycin (21.6%). All 37 isolates belonged to sequence type (ST) 22, coagulase type XI, three PFGE types and eight subtypes, ten spa types including t223 (51.3%), t852 (13.5%), t032 (8.1%), t790 (8.1%), t3107 (5.4%) and one each of t309, t2251, t3935, t5708 and t5983. Twenty-six isolates (70.2%) carried SCCmec IVa, eight isolates carried SCCmec IV and three isolates carried SCCmec IVh. All isolates carried agr1, cap5 and egc gene cluster (seg, sei, selm, seln, selo, and selu). tst (toxic shock syndrome toxin) was detected in 23 isolates. Eight isolates (21.6%) were positive for Panton-Valentine leukocidin (PVL). Genotypic analysis revealed that 62.1% of the isolates comprising ST22-IVa-t223 (51.3%) and ST22-IVa-t309/t2251/t3935/t5708 (10.8%) were CC22-[tst1⁺] UK EMRSA-15/Middle Eastern variant, 21.6% were CC22-PVL⁺ EMRSA-15 variant and 16.2% were CC22-UK EMRSA-15/Barnim clone. These results show that the tst1 positive-ST22-IVa-t223 (Middle Eastern variant) and the CC22-PVL⁺ EMRSA-15 variant were the dominant EMRSA-15 variants in Kuwait hospitals.

Worldwide Epidemiology and Antibiotic Resistance of Staphylococcus aureus

Staphylococcus aureus is an important human pathogen, responsible for infections in the community and the healthcare setting. Although much of the attention is focused on the methicillin-resistant "variant" MRSA, the methicillin-susceptible counterpart (MSSA) remains a prime species in infections. The epidemiology of S. aureus, especially of MRSA, showed a rapid evolution in the last years. After representing a typical nosocomial multidrug-resistant pathogen, MRSA has recently emerged in the community and among farmed animals thanks to its ability to evolve and adapt to different settings. Global surveillance has shown that MRSA represents a problem in all continents and countries where studies have been carried out, determining an increase in mortality and the need to use last-resource expensive antibiotics. S. aureus can easily acquire resistance to antibiotics and MRSA is characteristically multidrug resistant. Resistance to vancomycin, the principal anti-MRSA antibiotic is rare, although isolates with decreased susceptibility are recovered in many areas. Resistance to the more recently introduced antibiotics, linezolid and daptomycin, has emerged; however, they remain substantially active against the large majority of MSSA and MRSA. Newer antistaphylococcal drugs have been developed, but since their clinical use has been very limited so far, little is known about the emergence of resistance. Molecular typing techniques have allowed to identify the major successful clones and lineages of MSSA and MRSA, including high-risk clones, and to trace their diffusion. In the face of a continuously evolving scenario, this review depicts the most common clones circulating in different geographical areas and in different settings at present. Since the evolution of S. aureus will continue, it is important to maintain the attention on the epidemiology of S. aureus in the future with a global view.

Building a genomic framework for prospective MRSA surveillance in the United Kingdom and the Republic of Ireland

The correct interpretation of microbial sequencing data applied to surveillance and outbreak investigation depends on accessible genomic databases to provide vital genetic context. Our aim was to construct and describe a United Kingdom MRSA database containing over 1000 methicillin-resistant Staphylococcus aureus (MRSA) genomes drawn from England, Northern Ireland, Wales, Scotland, and the Republic of Ireland over a decade. We sequenced 1013 MRSA submitted to the British Society for Antimicrobial Chemotherapy by 46 laboratories between 2001 and 2010. Each isolate was assigned to a regional healthcare referral network in England and was otherwise grouped based on country of origin. Phylogenetic reconstructions were used to contextualize MRSA outbreak investigations and to detect the spread of resistance. The majority of isolates (n = 783, 77%) belonged to CC22, which contains the dominant United Kingdom epidemic clone (EMRSA-15). There was marked geographic structuring of EMRSA-15, consistent with widespread dissemination prior to the sampling decade followed by local diversification. The addition of MRSA genomes from two outbreaks and one pseudo-outbreak demonstrated the certainty with which outbreaks could be confirmed or refuted. We identified local and regional differences in antibiotic resistance profiles, with examples of local expansion, as well as widespread circulation of mobile genetic elements across the bacterial population. We have generated a resource for the future surveillance and outbreak investigation of MRSA in the United Kingdom and Ireland and have shown the value of this during outbreak investigation and tracking of antimicrobial resistance.

The Control of Methicillin-Resistant Staphylococcus aureus Blood Stream Infections in England

Methicillin-resistant Staphylococcus aureus (MRSA) blood stream infection (BSI) is a major healthcare burden in some but not all healthcare settings, and it is associated with 10%-20% mortality. The introduction of mandatory reporting in England of MRSA BSI in 2001 was followed in 2004 by the setting of target reductions for all National Health Service hospitals. The original national target of a 50% reduction in MRSA BSI was considered by many experts to be unattainable, and yet this goal has been far exceeded (∼80% reduction with rates still declining). The transformation from endemic to sporadic MRSA BSI involved the implementation of serial national infection prevention directives, and the deployment of expert improvement teams in organizations failed to meet their improvement trajectory targets. We describe and appraise the components of the major public health infection prevention campaign that yielded major reductions in MRSA infection. There are important lessons and opportunities for other healthcare systems where MRSA infection remains endemic.

Community-associated and healthcare-associated methicillin-resistant Staphylococcus aureus virulence toward Caenorhabditis elegans compared

Community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) strains have emerged as major human pathogens. CA-MRSA virulence appears to be distinct from healthcare-associated (HA) MRSA with several factors [α-hemolysin (Hla), Panton-Valentine leukocidin (PVL), α-type phenol soluble modulins (PSMα) and SCCmec IV] postulated to enhance virulence or fitness. Using the Caenorhabditis elegans infection model, we compared the virulence of clinical and laboratory isolates of CA-MRSA and HA-MRSA and explored the contribution of CA-MRSA associated virulence factors to nematode killing. All CA-MRSA strains were highly pathogenic to nematodes, while HA-MRSA strains demonstrated variable nematode killing. Nematode killing by isogenic mutants of hla or the loci for PVL, PSMα, PSMβ, PSMδ or SCCmec IV was not different than the parental strains. These results demonstrate that CA-MRSA is highly virulent, shows some strains of HA-MRSA are equally virulent toward nematodes and suggests CA-MRSA virulence in C. elegans is not linked to a single virulence factor.

Comparative genomics and drug resistance of a geographic variant of ST239 methicillin-resistant Staphylococcus aureus emerged in Russia

Two distinct classes of methicillin-resistant Staphylococcus aureus (MRSA) are spreading in hospitals (as hospital-acquired MRSA, HA-MRSA) and in the community (as community-acquired MRSA, CA-MRSA). Multilocus sequence type (ST) 239 MRSA, one of the most worldwide-disseminated lineages, has been noted as a representative HA-MRSA. Here, we isolated ST239 MRSA (spa type 3 [t037] and staphylococcal cassette chromosome mec [SCCmec] type III.1.1.1) and its novel variant with ST239/spa351 (t030)/SCCmecIII.1.1.4 (SCCmecIII_R) not only from hospitals but also from patients with urethritis in the community in Russia. The Russian variant (strain 16K) possessed a hybrid genome consisting of CC8 and CC30, similar to the ST239/spa3/SCCmecIII.1.1.1 HA-MRSA (TW20) genome, but with marked diversity. The 16K′ CC30 section had SCCmecIII_R carrying the dcs-carrying unit (which corresponded to the SCCmecIVc J3 joining region of ST30 CA-MRSA), lacked SCCmercury, and possessed a novel mobile element structure (MES16K) carrying the ccrC-carrying unit (with the recombinase gene ccrC1 allele 3) and drug resistance tranposons. The Russian variant included strains with a high ability to transfer its multiple drug resistance by conjugation; e.g., for strain 16K, the transfer frequency of a chloramphenicol resistance plasmid (p16K-1 with 2.9 kb in size) reached 1.4×10⁻², followed by Tn554 conjugative transfer at 3.6×l0⁻⁴. The Russian variant, which has been increasing recently, included divergent strains with different plasmid patterns and pulsed field gel electrophoresis profiles. The data demonstrate the alternative nature of ST239 MRSA as CA-MRSA and also as a drug resistance disseminator, and its micro but dynamic evolution in Russia.

Methicillin-resistant Staphylococcus aureus in Northeastern Scotland in 2003 to 2007: evolving strain distribution and resistance patterns

This study explored strain distribution and resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) over a 5-year period in northeastern Scotland. We noted a shift in the relative rates of epidemic strains and an increase in community-associated strains. Use of oral antibiotics to eradicate throat carriage may have contributed to trimethoprim resistance, which was observed to increase 10-fold.

Screening for methicillin-resistant Staphylococcus aureus in clinical swabs using a high-throughput real-time PCR-based method

The presence of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals and the community is a serious problem. Accordingly, a comprehensive plan has been implemented in the County of Vejle, Denmark, to identify colonised and/or infected individuals and to control the spread of MRSA. Since 2005, all patients and healthcare personnel have been screened for MRSA colonisation, involving analysis of 300-400 samples daily. To deal with this number of samples, a PCR-based method customised for high-throughput analysis and a system for fast reporting of MRSA carrier status were developed. Swab samples were incubated overnight in a selective tryptone soya broth and were analysed by PCR the following day. Using this strategy, non-colonised individuals were identified within 24 h, while MRSA-positive samples were analysed further by traditional microbiological methods to determine the resistance pattern. This is a cost-effective approach, as the greatest expense in hospitals involves the isolation of patients of unknown MRSA status. The method was evaluated by testing 2194 clinical samples, with a sensitivity and specificity of 100% and 94%, respectively. The analytical sensitivity was 97%, with 161 of 166 different MRSA strains and isolates generating positive results according to PCR analysis. Using four control strains, the inter-assay variation was revealed to be a maximum of 2.6%, indicating good reproducibility.

Staphylococcus aureus of phage type 187 isolated from people occurred to be a genes carrier of eneterotoxin C and toxic shock syndrome toxin-1 (TSST-1)

The aim of this study was to examine the genotype properties of Staphylococcus aureus of phage type 187 strains that constitute a separate group among the strains of S. aureus. Sixteen strains were collected from the hospital patients (n=12) and the healthy carriers (n=4) in 13 medical centres in Poland during 1991 and 2005. Biotyping, antibiotic susceptibility, phage typing, detection the genes of enterotoxins and toxic shock syndrome toxin, genotyping of chromosomal DNA by pulsed-field gel electrophoresis (PFGE), also amplification and restriction analysis of the coagulase (coa) and the protein A genes (spa) (PCR/restriction fragment length polymorphism (RFLP)) was tested. The results of this study showed that all staphylococcus of phage type 187 belonged to the human biotype (A) and appeared to be sensitive to all of the tested antibiotics, including methicillin (MSSA). Finding out the toxin genes showed that almost all of them (93.8%) had the enterotoxin C gene (sec) and TSST-1 gene (tst). The PFGE typing proved that the phage type 187 strains (except for one) constitute one PFGE type. These results and the identical restriction patterns in the PCR/RFLP method, also the same biotype, sensitivity to antibiotics and the presence genes of the same type of toxins confirmed that the phage type 187 strains constitute one clone within our country. Additionally, the fact that almost all of them have the enterotoxin genes and tst gene allows to consider them the strains of potentially high virulence.

Antibacterial resistance and their genetic location in MRSA isolated in Kuwait hospitals, 1994-2004

Background

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major cause of serious infections in hospitals and in the community worldwide. In this study, MRSA isolated from patients in Kuwait hospitals were analyzed for resistance trends and the genetic location of their resistance determinants.

Methods

Between April 1994 and December 2004, 5644 MRSA isolates obtained from different clinical samples were studied for resistance to antibacterial agents according to guidelines from the National Committee for Clinical Laboratory Standards and the British Society for Antimicrobial Chemotherapy. The genetic location of their resistance determinants was determined by curing and transfer experiments.

Results

They were resistant to aminoglycosides, erythromycin, tetracycline, trimethoprim, fusidic acid, ciprofloxacin, chloramphenicol, rifampicin, mupirocin, cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide but susceptible to vancomycin, teicoplanin and linezolid. The proportion of the isolates resistant to erythromycin, ciprofloxacin and fusidic acid increased during the study period. In contrast, the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined. High-level mupirocin resistance increased rapidly from 1996 to 1999 and then declined. They contained plasmids of 1.9, 2.8, 3.0, 4.4, 27 and 38 kilobases. Genetic studies revealed that they carried plasmid-borne resistance to high-level mupirocin resistance (38 kb), chloramphenicol (2.8 – 4.4 kb), erythromycin (2.8–3.0 kb) and cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide (27 kb) and chromosomal location for methicillin, the aminoglycosides, tetracycline, fusidic acid, ciprofloxacin and trimethoprim resistance. Thus, the 27 kb plasmids had resistance phenotypes similar to plasmids reported in MRSA isolates in South East Asia.

Conclusion

The prevalence of resistance to erythromycin, ciprofloxacin, high-level mupirocin and fusidic acid increased whereas the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined during the study period. They contained 27-kb plasmids encoding resistance to cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide similar to plasmids isolated in MRSA from South East Asia. Molecular typing of these isolates will clarify their relationship to MRSA from South East Asia.

Emergence and resurgence of meticillin-resistant Staphylococcus aureus as a public-health threat

Staphylococcus aureus is a gram-positive bacterium that colonises the skin and is present in the anterior nares in about 25-30% of healthy people. Dependent on its intrinsic virulence or the ability of the host to contain its opportunistic behaviour, S aureus can cause a range of diseases in man. The bacterium readily acquires resistance against all classes of antibiotics by one of two distinct mechanisms: mutation of an existing bacterial gene or horizontal transfer of a resistance gene from another bacterium. Several mobile genetic elements carrying exogenous antibiotic resistance genes might mediate resistance acquisition. Of all the resistance traits S aureus has acquired since the introduction of antimicrobial chemotherapy in the 1930s, meticillin resistance is clinically the most important, since a single genetic element confers resistance to the most commonly prescribed class of antimicrobials--the beta-lactam antibiotics, which include penicillins, cephalosporins, and carbapenems.

Outbreak of epidemic methicillin-resistant Staphylococcus aureus in a regional burns unit: Management and implications

Colonization of burn patients with methicillin-resistant Staphylococcus aureus (MRSA) is not uncommon, however an outbreak that necessitates closure of a burns unit is relatively rare. The objective of this study was to present the experience of a regional adult burns unit where an outbreak of epidemic MRSA-15 (EMRSA-15) took place. During the studied period, 176 patients were admitted to the unit, 52 with burns, 48 for elective plastic surgery procedures while the remainder belonged to other specialties. Patients admitted under burns and plastic surgery were investigated together with 46 staff members to control the outbreak. MRSA was isolated in 18 patients out of which 12 had EMRSA-15. Among the staff members, MRSA was isolated in nine of which five had EMRSA-15. The burns unit was closed to all admissions to terminate this outbreak. The MRSA positive staff members were sent on "special leave" and underwent treatment with nasal mupirocin and triclosan body wash. All staff members were able to return to work after one week's treatment. The burns unit underwent re-furbishment and decontamination while it was closed. In conclusion, the study shows that an outbreak of EMRSA was controlled successfully, however, it highlights the implications of such an event for a regional burn service with regard to staff, patients and guidelines for management.

Evolution and molecular characterization of methicillin-resistant Staphylococcus aureus epidemic and sporadic clones in Cordoba, Argentina

Since 1999, a new, epidemic, methicillin-resistant Staphylococcus aureus (MRSA) strain, named the "Cordobes clone," has emerged in Argentina and coexists with the pandemic Brazilian clone. The purpose of this study was to determine the stability over time of the new clone and to investigate its evolutionary relationship with epidemic international MRSA lineages and with other MRSA and methicillin-susceptible S. aureus (MSSA) major clones distributed in this region. One hundred three MRSA isolates recovered in 2001 from Cordoba, Argentina, hospitals and 31 MSSA strains collected from 1999 to 2002 were analyzed by their antibiotic resistance patterns, phage typing, and pulsed-field gel electrophoresis. Additionally, representative members of most MRSA defined genotypes (A, B, C, E, K, and I) were characterized by multilocus sequence typing (MLST) and spaA and SCCmec typing. The most prevalent MSSA pulsotypes were also analyzed by MLST. Our results support the displacement of the Brazilian clone (sequence type [ST] 239, spaA type WGKAOMQ, SCCmec type IIIA) by the Cordobes clone (ST5, spaA type TIMEMDMGMGMK, SCCmec type I) in the hospital environment. MRSA and MSSA isolates shared only ST5. The data support the origin of the Cordobes clone as a member of a lineage that includes the pediatric and New York/Japan international clones and that is genetically related to the British EMRSA-3 strain. Interestingly, the pediatric clone, isolated from most community-acquired infections in Cordoba, was characterized by ST100, a single-locus variant of ST5 and a new variant of SCCmec type related to SCCmec type IVc.

Surveillance and epidemiology of MRSA bacteraemia in the UK

Surveillance of bacteraemia caused by methicillin-resistant Staphylococcus aureus (MRSA) in the UK has involved collection of data from hospital microbiology laboratories via several mechanisms, including a voluntary reporting scheme that has been operational in England and Wales since 1989 and mandatory reporting schemes that have been running independently in England, Wales, Scotland and Northern Ireland since 2001. In addition, surveillance schemes involving panels of participating sentinel laboratories that submit isolates for centralized susceptibility testing, such as the Bacteraemia Resistance Surveillance Programme run by the BSAC, have also been established. Each of these data sources have particular advantages, but they also have their individual limitations, with the result that they each give an incomplete picture if considered in isolation. However, by pooling the findings from these different but complementary surveillance programmes, a much more comprehensive and credible picture of the problem posed by MRSA is produced. These schemes have shown both a dramatic rise in the total numbers of cases of S. aureus bacteraemia reported annually and an increase in the proportion of such cases that involve MRSA (from 2% in 1990 to >40% in the early 2000s), although the most recent data indicate a slight reversal of these trends. Characterization of isolates of MRSA shows a marked temporal relationship between the rise in MRSA bacteraemias and the emergence and spread of two strains of epidemic MRSA, EMRSA-15 and EMRSA-16. Surveillance and control of MRSA infection continue to be high profile and further developments to the mandatory surveillance system in England are likely in the near future.

Use of Liposomes to Deliver Bactericides to Bacterial Biofilms

Methods are described for the preparation of anionic and cationic liposomes and proteoliposomes with covalently linked lectins or antibodies by the extrusion technique (vesicles by extrusion, VETs). The liposomes are prepared from the phospholipid dipalmitoylphosphatidylcholine (DPPC), together with the anionic lipid phosphatidylinositol (PI) or the cationic amphiphile dioctadecyldimethylammonium bromide (DDAB) together with the reactive lipid DPPE-MBS, the m-maleimidobenzoyl-N-hydroxysuccinimide (MBS) derivative of dipalmitoylphosphatidylethanolamine (DPPE). Proteins (lectin or antibody), after derivatization with N-succinimidyl-S-acetylthioacetate (SATA), can be covalently linked to the surface of the liposomes by reaction with the reactive lipid, DPPE-MBS. The physical and chemical characterization of the liposomes and proteoliposomes by photon correlation spectroscopy (PCS) and protein analysis, to determine the number of chemically linked protein molecules (lectin or antibody) per liposome, are described. The liposomes can be used for carrying oil-soluble bactericides (e.g., Triclosan) or water-soluble antibiotics (e.g., vancomycin or benzylpenicillin) and targeted to immobilized bacterial biofilms of oral or skin-associated bacteria adsorbed on microtiter plates. Techniques for the preparation of immobilized bacterial biofilms, applicable to a wide range of bacterial suspensions, and for the analysis of the adsorption (targeting) of the liposomes to the bacterial biofilms are given. The mode of delivery and assessment of antibacterial activity of liposomes encapsulating bactericides and antibiotics, when targeted to the bacterial biofilms, by use of an automated microtiter plate reader, are illustrated, with specific reference to the delivery of the antibiotic benzylpenicillin encapsulated in anionic liposomes to biofilms of Staphylococcus aureus. The methods have potential application for the delivery of oil-soluble or water-soluble bactericidal compounds to a wide range of adsorbed bacteria responsible for infections in implanted devices such as catheters, heart valves, and artificial joints.

Emergence, spread, and characterization of phage variants of epidemic methicillin-resistant Staphylococcus aureus 16 in England and Wales

Epidemic methicillin-resistant Staphylococcus aureus 16 (EMRSA-16) and EMRSA-15 are the two most important and prevalent EMRSA strains found in the United Kingdom and have also been found in a number of European countries and the United States. We describe for the first time the spread of an EMRSA strain (EMRSA-16) from its point of origin in one hospital to the surrounding hospitals and regions over the following 2 years. In the first 18 months after its original appearance, 136 hospitals referred EMRSA-16 isolates for typing, and interhospital and intraregional spread were reported: it was more prevalent in males between 60 and 80 years old and was isolated from sputum and throat more often than EMRSA-15. Important characteristics, e.g., carriage of the enterotoxin A (sea) and toxic shock syndrome toxin (tst) genes and production of urease, are described. Phage-variant strains of EMRSA-16 which share some of the characteristics of the classical strain, including toxin carriage and urease production, emerged, but without genotypic investigations, their relationship could only be inferred. A total of 129 clinical isolates from 52 hospitals, collected between March 1998 and April 1999 and representing classical EMRSA-16 (49 isolates) or phage variants (80 isolates), were compared by phage typing, pulsed-field gel electrophoresis (PFGE) following SmaI macrorestriction, antimicrobial susceptibility testing, urease production, and PCR detection of toxin gene carriage. PFGE analysis revealed 29 profiles, A1 to A29, with A1 representing the prototypic strain, NCTC 13143. All other profiles differed from A1 by 1 to 6 bands, but some differed from each other by up to 10 bands.

Regional audit: perioperative management of MRSA orthopaedic patients in the Oxford region

AIM

Methicillin resistant staphylococcus aureus (MRSA) colonisation or infection is of particular importance in patients undergoing operations involving implantable materials, such as in orthopaedic surgery. An audit of the perioperative management of orthopaedic patients in the Oxford region was carried out to assess the level of clinician awareness and the uniformity of current guidelines between hospitals.

METHODS

A postal questionnaire was designed for asking information on various aspects of perioperative management of MRSA patients and was sent to each hospital.

RESULTS

Responses were obtained from nine of 10 hospitals in the region. The average response rate for each hospital was 75%, and the overall individual response rate was 67.5% (27/40). Seventy-eight per cent of respondents knew that there was a pre-admission screening policy. Fifteen per cent were unaware of any MRSA policy. Forty-four per cent indicated that teicoplanin was used for prophylaxis in implant surgery whilst 44% used vancomycin. Eighteen per cent believed that cefuroxime was used for prophylaxis. Forty-eight per cent of hospitals had an MRSA-free zone for orthopaedic patients.

CONCLUSION

This study indicates a lack of uniformity in the perioperative management of MRSA-positive patients in the region and a lack of awareness of both MRSA guidelines and their implementation. Uniformity of MRSA guidelines is necessary to allow better clinician awareness and compliance, especially in surgical trainees who are travelling between different training hospitals in the region. Implementation of such a policy with re-audit of subsequent awareness and compliance is proposed.

Quantification of virulence-associated gene transcripts in epidemic methicillin resistant Staphylococcus aureus by real-time PCR

The control of Staphylococcus aureus virulence gene expression is complex and few data are available for the epidemic methicillin resistant S. aureus clones circulating in the UK. Quantitative real-time PCRs were developed for key gene transcripts involved in S. aureus infection (RNAIII, hla and spa) and for the 16S rRNA. These assays were applied to log and stationary phase cultures of the important EMRSA strains. To correct for inconsistencies in extract yield, results were calculated as ratios using the 16S rRNA values as denominator. The quantitative assays were sensitive and reproducible. The number of copies of each transcript present differed greatly between the EMRSA strains tested. Strains within an EMRSA clone or type gave similar results. High levels of RNAIII transcripts were not consistently linked to elevated levels of hla transcripts or to low levels of the spa transcript. In addition, strains showed significant variations in their patterns of induction (or repression) of all three transcripts. A complex interplay exists between the regulatory factors that control the expression of proteins required for colonisation and survival in the host. The transcript level data suggest that this pattern shows great diversity among the currently important EMRSA strains.

Multilocus sequence typing and the evolution of methicillin-resistant Staphylococcus aureus

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in many countries is increasing and, in hospitals in some areas, more than half of all S. aureus disease isolates are MRSA. MRSA strains are becoming increasingly multiresistant, and have recently developed resistance to vancomycin, used successfully to treat MRSA for more than 30 years. This review summarises recent studies that have elucidated the evolutionary history of MRSA. The first MRSA isolate evolved from a sensitive, epidemic strain prevalent in Europe, and its progeny-the first MRSA clone-quickly spread to other continents. Analyses of epidemic MRSA isolates from hospitals in different countries by molecular methods, including multilocus sequence typing (MLST) and DNA microarray analysis, reveal that MRSA strains have evolved separately within five distinct epidemic, sensitive lineages. However, resistance has been transferred to S. aureus on many more than five occasions, as some lineages have acquired different structural types of the element carrying the methicillin resistance gene. The emergence of MRSA as a community pathogen has been noted in several countries, and MLST and SCCmec typing have been used to demonstrate that community-acquired MRSA strains are typically related only distantly to hospital MRSA strains, and thus represent novel acquisitions of SCCmec.

Evolutionary models of the emergence of methicillin-resistant Staphylococcus aureus

Five major lineages of methicillin-resistant Staphylococcus aureus (MRSA) have evolved since the introduction of methicillin for the treatment of infections caused by penicillin-resistant S. aureus in 1959. The clones of these lineages are responsible for the vast majority of hospital-acquired MRSA disease globally. We have constructed high-resolution evolutionary models for each lineage using a parsimony approach with 15 partial gene sequences from 147 geographically diverse isolates. On the basis of these models, we infer that MRSA has emerged at least 20 times upon acquisition of the methicillin resistance determinant, which is carried on a mobile genetic element called the staphylococcal cassette chromosome mec (SCCmec). The acquisition of SCCmec by sensitive clones was four times more common than the replacement of one SCCmec with another. Notably, SCCmec type IV was found in twice as many clones as any other SCCmec type, and it is this SCCmec type which is commonly found in clones from patients with community-acquired MRSA disease. Our findings suggest that most clones of MRSA arise by the acquisition of SCCmec type IV by methicillin-sensitive isolates.

National surveillance of methicillin-sensitive and methicillin-resistant Staphylococcus aureus in Austrian hospitals: 1994-1998

In 1994, the Austrian Federal Ministry for Labour, Health and Social Affairs initiated a nationwide survey of the prevalence of methicillin-sensitive (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) in Austrian hospitals. A questionnaire had to be filled out by the medical directors of participating hospitals. During the five years of surveillance (1994-1998), a total of 9385 MRSA and 71510 MSSA episodes of infection/colonization were reported. The rate of MRSA decreased from 15.8% in 1994 to 8.2% in 1998. However, the frequency per 1000 hospital admissions increased from 0.85 to 1.29 with a maximum of 2.42 MRSA episodes per 1000 admissions in 1997. Overall, in 53.6% of 5020 S. aureus episodes, signs and symptoms of an infection were reported, of these 9.3% (251/2692) were due to MRSA. For large hospitals with more than 1000 beds, 20.9% of reported MRSA episodes were associated with infection, 54.9% of MRSA episodes from hospitals with 301-1000 beds, 60.1% from hospitals with 101-300 beds, and 80.0% from small hospitals with less than 100 beds. Our data do not support the hypothesis of higher virulence of MRSA compared with MSSA. Indeed, in this survey, MSSA episodes were more frequently associated with signs and symptoms of infection (OR=1.35, 95% CI: 1.12-1.62, P<0.001).

Phenotypic and genotypic properties of methicillin resistant Staphylococcus aureus strains isolated in Hungary, 1997-2000

An account is given on the activity of the National Center for Phage Typing of Staphylococci in Hungary in the period between 1997 and 2000 related to methicillin resistant Staphylococcus aureus (MRSA) strains originating mainly from hospital infections and sporadic cases. The rate of multiresistant MRSA strains has decreased gradually from 98.1% in 1997 to 74.6% in 2000, accordingly the typability by phages showed a considerable improvement by the international basic phages. Resistance pattern of MRSA strains became narrower in the period of the examinations. With the exception of erythromycin the rate of resistance decreased probably as a consequence of the increased use of erythromycin. The typing method was completed with the phenotypic and genotypic characterization of macrolide resistance. Among 73 MRSA strains type A was the most frequent macrolide resistance group, while type B, C1 and C2 occurred rarely. Type A was frequent also among the few MSSA and CNS strains. Out of the 168 examined S. aureus strains ermA genes occurred in 81.5%; in MSSA and CNS strains ermC1 genes were frequent, both genes are responsible for the target modification. The msrA gene, encoding the increased efflux, occurred only in CNS strains. Comparing the results obtained by phenotyping (phage typing) and genotyping (AP-PCR) methods it is of note that MRSA strains which proved non-typable by phage typing gave suitable results by the AP-PCR.

Molecular epidemiology of predominant clones and sporadic strains of methicillin resistant Staphylococcus aureus in Switzerland and comparison with European epidemic clones

OBJECTIVE

To assess the molecular epidemiology and risk factors of predominant clones and sporadic strains of methicillin-resistant Staphylococcus aureus (MRSA) in Swiss hospitals and to compare them with European strains of epidemic clones.

MATERIAL AND METHODS

One-year national survey of MRSA cases. Analysis of epidemiological and molecular typing data (PFGE) of MRSA strains.

RESULTS

In 1997, 385 cases of MRSA were recorded in the five Swiss university hospitals and in 47 community hospitals. Half of the cases were found in Geneva hospitals where MRSA was already known to be endemic. Molecular typing of 288 isolates (one per case) showed that 186 (65%) belong to four predominant clones, three of which were mostly present in Geneva hospitals. In contrast, the fourth clone (85 cases) was found in 23 hospitals (in one to 16 cases per hospital). The remaining 35% of the strains were clustered into 62 pulsed field gel electrophoresis types. They accounted for one to five patients per hospital and were defined as sporadic. Multivariate analysis revealed no independent risk factors for harboring a predominant versus a sporadic strain, except that transfer from a foreign hospital increases the risk of harboring a sporadic strain (OR, 42; 95% CI, 5-360).

CONCLUSION

While cases with predominant clones were due to the local spread of these clones, most sporadic cases appear to be due to the continuous introduction of new strains into the country. With the exception of a transfer from a hospital outside Switzerland, no difference in the clinical or epidemiological characteristics was observed between patients harboring a predominant clone and those with a sporadic strain.

Clinical aromatherapy and AIDS

Clinical aromatherapy is the use of essential oils for expected outcomes that are measurable and is a therapy that is used as part of nursing care in Switzerland, Germany, Australia, Canada, the United Kingdom, and, more recently, the United States. Essential oils are steam distillates obtained from aromatic plants. These volatile extracts have been used for many years by French hospitals against airborne bacteria and fungi. As antimicrobial agents, essential oils may be appropriate in HIV/AIDS for specific opportunistic infections. Aromatherapy can also alter perceptions of chronic pain, help maintain skin integrity, and is useful in stress management. Methods of application vary depending on the site of infection and the psychological profile of the patient and can include inhalation, compresses, baths, massage, and the "m" technique. This article will explore the potential use of essential oils in HIV/AIDS focusing on four opportunistic infections: Cryptococcus neoformans, Candida albicans, methicillin-resistant Staphylococcus aureus, and herpes simplex types I and II.

Nine-year surveillance of methicillin-resistant Staphylococcus aureus in a hospital suggests instability of mecA DNA region in an epidemic strain

The distributions of the antibiotic resistance patterns in a population of Staphylococcus aureus isolates from a teaching hospital were studied over a 9-year period. The results indicate the existence of successive major epidemic methicillin-resistant strains and the emergence of a methicillin-susceptible strain with an unusual resistance pattern. Our findings suggest that this methicillin-susceptible S. aureus strain could be derived from the dominant gentamicin-susceptible methicillin-resistant S. aureus strain with the loss of a 40-kb DNA fragment.

Methicillin-resistant Staphylococcus aureus in geriatric patients: usefulness of screening in a chronic-care setting

OBJECTIVE

To evaluate the contribution of screening to the detection of cases of methicillin-resistant Staphylococcus aureus (MRSA) in a chronic-care facility.

DESIGN

Surveillance and laboratory observational study.

METHODS

During a 7-month period, we compared imported and acquired MRSA in a chronic-care center by screening patients for carriage of MRSA on admission and discharge, and by recording all cases of clinical specimens positive for MRSA.

SETTING

The study was conducted in a 120-bed chronic-care center. This center admits approximately 850 patients per year. Approximately 90% of the patients were elderly and were admitted from other hospitals.

RESULTS

Of 519 patients admitted during the study period, 129 were positive for MRSA at some point during their residence, including 60 (11.6%) with MRSA found within 48 hours of admission and 69 (13.3%; 53% of all positives) with nosocomial MRSA Of the 519 admissions, 332 (64%) were discharged, of whom 62 (19%) were positive for MRSA Of these 62, 43 (69%) acquired their MRSA during their stay in the center.

CONCLUSIONS

Our study confirms the amplification effect of chronic-care facilities on MRSA propagation. It also shows that screening for MRSA carriage in a chronic-care center facilitates the early identification of a large proportion of patients with MRSA.

Antibiotic resistance is a major risk factor for epidemic behavior of Acinetobacter baumannii

OBJECTIVE

To study the presence of bacterial factors in clinical isolates of Acinetobacter species in order to identify markers of epidemic potential.

DESIGN

Case-control study.

METHODS

Forty-six isolates of Acinetobacter species, including 23 epidemic and 23 sporadic strains from different outbreaks in nine European countries, were compared for the presence of the following factors: hemagglutination, presence of capsules and fimbriae, binding to salivary mucins, resistance to drying, and antibiogram typing. Genotyping of all strains was performed by amplified fragment-length polymorphism (AFLP).

RESULTS

All outbreak strains except two (91%) were identified as Acinetobacter baumannii. Binding to salivary mucins and resistance to antibiotics were significantly associated with epidemic behavior. Antibiogram typing showed clustering of predominantly A baumannii strains within one group, and these strains were significantly more resistant to antibiotics than sporadic strains. AFLP genotyping revealed a great heterogeneity among the different European Acinetobacter strains. Cluster analysis of AFLP fingerprints showed several small clusters of different A baumannii outbreak strains. AFLP genotyping could not identify a common epidemic marker within the strains studied.

CONCLUSIONS

Antibiogram typing can be used in routine clinical laboratories as a screening method to recognize potentially epidemic A baumannii strains. Several other factors were found, both in different outbreaks as well as in sporadic Acinetobacter isolates. These characteristics were unable to predict epidemic behavior and therefore cannot be used as discriminative epidemic markers. AFLP genotyping demonstrated no common clonal origin of European epidemic A baumannii strains. This indicates that any clinical A baumannii isolate with resistance to multiple antibiotics can be a potential nosocomial outbreak strain.

Methicillin-resistant Staphylococcus aureus: phylogenetic relatedness between European epidemic clones and Swiss sporadic strains

We have compared the phylogenetic diversity of methicillin-resistant Staphylococcus aureus (MRSA) strains from Switzerland and their phylogenetic relationships with European epidemic clones, using multiprimer random amplification polymorphic DNA (RAPD). Strains included 24 European epidemic clones (59 strains), 66 sporadic strains isolated in Switzerland in 1996-1997, and 15 reference strains of five other Staphylococcus species. Similarity and clustering analysis with the Jaccard's coefficient showed that the maximum genetic distance between MRSA strains was 0.43, whereas the minimum genetic distance between the six Staphylococcus species was 0.97, indicating that the method permits phylogenetic hierarchization. The 24 MRSA clones reported to be epidemic in European countries during the 1990s were distributed into seven different genetic clusters with a maximum distance of 0.29 among them. This clustering pattern was confirmed by the analysis of a subset of MRSA strains by multilocus enzyme electrophoresis at 12 loci. Most of the sporadic Swiss strains were distributed into these seven different genetic clusters, together with the epidemic MRSA clones. This suggests that there is no phylogenetic cluster specific to epidemic clones of MRSA.

Identification and characterization of phage variants of a strain of epidemic methicillin-resistant Staphylococcus aureus (EMRSA-15)

EMRSA-15 is one of the most important strains of epidemic methicillin-resistant Staphylococcus aureus (EMRSA) found in the United Kingdom. It was originally characterized by weak lysis with phage 75 and production of enterotoxin C but not urease. Two variant strains of EMRSA-15 which show a broader phage pattern than the progenitor strain have emerged. A total of 153 recent clinical isolates representing classical EMRSA-15 (55 isolates) or these phage variants (98 isolates) were compared by SmaI macrorestriction profiles in pulsed-field gel electrophoresis (PFGE) as well as by urease and enterotoxin C production. Eight of the 98 isolates were shown to be other unrelated strains by both PFGE and their production of urease, a misidentification rate of 8% by phage typing. Seventy-one EMRSA-15 isolates were enterotoxin C negative, and the majority of these were sensitive to phage 81. Examination of PFGE profiles and Southern blotting studies suggest that the enterotoxin C gene locus is encoded on a potentially mobile DNA segment of ca. 15 kb. After elimination of the eight non-EMRSA-15 isolates, the remaining 145 were characterized by PFGE, yielding 22 profiles. All profiles were within five band differences of at least one other profile. Classical EMRSA-15 isolates showed nine PFGE profiles, with the majority of isolates (68%) in profile B1. Six of these nine PFGE profiles were unique to the classical EMRSA-15 isolates. Among the phage variants of EMRSA-15, 16 profiles were seen, but the majority of isolates (83%) fell into 1 of 4 profiles (B2, B3, B4, and B7) which correlated well with phage patterns. The most divergent PFGE profiles among the EMRSA-15 isolates had as many as 12 band differences from one another, suggesting that in examining isolates belonging to such a temporally and geographically disseminated epidemic strain, the range of PFGE profiles must be regarded as a continuum and analyzed by relating the profiles back to the most common or progenitor profile.

Methicillin-resistant Staphylococcus aureus in the community: new battlefronts, or are the battles lost?

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections worldwide. Interpretation of community MRSA trends is problematical, in that the term is ill-defined, and related data are difficult to put into context. There are four relevant battlefronts, all of interest to risk assessment and prevention. These comprise the following: the issues relating to an increasing pool of patients with MRSA discharged from hospitals into the community; MRSA spreading to patients in nursing and residential homes; and MRSA spreading from patients and healthcare workers to others in the community. There are often difficulties in determining whether the fourth issue, MRSA arising apparently de novo in the community, is in fact due to one of these other fronts. All these battlefronts are important and not yet lost. However, we must agree on definitions and design-appropriate surveillance strategies, so that we can best inform prevention and control activities to contain these emerged or emerging problems.

Methicillin-resistant Staphylococcus aureus typing methods: which should be the international standard?

Methicillin-resistant Staphylococcus aureus (MRSA) has spread to all parts of the world. Effective control measures are dependent on a thorough knowledge of the organism's epidemiology which requires a typing technique that can be universally applied. Many typing methods have been developed for MRSA but none has been adopted as the internationally recognized standard. This review summarizes the information available on each in order to assess their suitability as a reference procedure. The majority of phenotypic and genotypic techniques are not sufficiently discriminatory, reproducible, stable or useful in an outbreak to be acceptable. The methods which do fulfil these requirements and have a potential for standardization, such as pulsed-field gel electrophoresis, binary typing or a combination of more rapid techniques, require further systematic evaluation.

The population impact of MRSA in a country: the national survey of MRSA in Wales, 1997

Continuous data collection on all new isolates of MRSA via CoSurv has taken place in Wales since January 1996. In order to audit this data collection, and to address some of the issues that it does not include, a survey of MRSA was carried out. Questionnaires were completed by infection control teams. Rates were calculated using hospital throughput denominators. Results from the one-day prevalence survey, the two-week incidence survey, and the follow-up survey carried out on new MRSA patients identified in the incidence survey, are presented. Results were found to be broadly similar to those collected via routine surveillance. MRSA was found frequently and disproportionately in the elderly, with higher rates in male than female patients. The highest incidence of total and invasive MRSA was in males aged 75 and over (total: 12.5/1000 finished consultant episodes; invasive: 2.8/1000). Although there was a large community reservoir of MRSA, most appeared to have been acquired in hospital, since most patients had a history of hospitalization, often with multiple hospital admissions. Community-based isolates from cases with no hospital history tended to have been from ulcers. Prevalence and incidence of MRSA was relatively low compared with hospital throughput (mean prevalence: 2.4/100 occupied beds; mean incidence: 3.6/1000 finished consultant episodes), there was also quite large variation between sites, even when screening samples were removed. Patients with MRSA had strikingly long stays before isolation of the organism (prevalence survey: 39 days; incidence survey: 31 days) and highest incidence occurred in elderly care wards. The outcome survey showed that approximately half of the patients were treated with some type of antimicrobial therapy for MRSA. Decontamination therapy was associated with clearance of MRSA only when controlling for sex of the patient. The majority of patients were discharged still with MRSA, mostly to their own homes. The survey emphasizes the need to continue surveillance to detect any changes, to allow guidelines based on evidence to be developed and to monitor the effectiveness of such guidelines.

Unusual spread of a penicillin-susceptible methicillin-resistant Staphylococcus aureus clone in a geographic area of low incidence

We describe the unusual spread of a penicillin-susceptible methicillin-resistant Staphylococcus aureus (MRSA) clone in hospitals in western Switzerland, where the incidence of MRSA is usually low. During a 2-year period, this clone had been responsible for several outbreaks and had been isolated from >156 persons in 21 institutions. Molecular typing by pulsed-field gel electrophoresis (PFGE) demonstrated that all of these isolates belonged to the same clone. In 1 of the outbreaks, involving 30 cases, the clone was responsible for at least 17 secondary cases. In contrast, during the period of the latter outbreak, 9 other patients harboring different MRSA strains, as assessed by PFGE, were hospitalized in the same wards, but no secondary cases occurred. These observations suggest that this clone, compared with other MRSA strains, had some intrinsic factor(s) that contributed to its ability to disseminate and could thus be considered epidemic.

PCR-RFLP analysis of the coagulase gene of Staphylococcus aureus: application to the differentiation of epidemic and sporadic methicillin-resistant strains

Preventing cross-infection with epidemic strains of methicillin-resistant Staphylococcus aureus (MRSA) requires effective control measures. These call for simple, rapid, discriminatory and reproducible methods for typing this pathogen. In this study 140 isolates/strains from 105 hospitals in England and Wales, representing 72 diverse phage types, were analysed by bacteriophage typing and PCR coagulase (coa) gene restriction fragment length polymorphism (RFLP). Isolates gave a coa gene PCR product that was either 660 base pairs (bp), 603 bp or 547 pb in size. The PCR products were digested with Alu I and Cfo I, and the fragments separated by gel electrophoresis. Eight coa gene RFLP patterns, numbered 1 to 8, were observed. Pattern 3 was most common (N = 25 isolates), followed by patterns 2 and 5 (18 isolates each), pattern 1 (14 isolates), pattern 4 (11 isolates), pattern 7 (10 isolates), pattern 8 (eight isolates) and pattern 6 (six isolates). Isolates of the same phage type often gave different coa gene RFLP patterns, and the patterns within the epidemic types EMRSA-03, EMRSA-15 and EMRSA-16 were heterogeneous. Thus, representatives of EMRSA-03 were subtyped to coa RFLP patterns 1 and 2, those of EMRSA-05 to coa RFLP patterns 1, 2, 7 and 8, and those for EMRSA-16 to coa RFLP patterns 2, 3, 4, 5 and 6. The range of patterns within single phage types of S. aureus could help to discriminate between isolates/strains, and in a hierarchical approach coa gene RFLP could occupy an intermediate position between phage typing and pulsed-field gel electrophoresis (PFGE).

Use of fluorescent amplified fragment length polymorphism (fAELP) to characterise methicillin-resistant Staphylococcus aureus

The new PCR-based genotyping technique, fluorescent amplified fragment length polymorphism (fAFLP), was compared for discriminatory power and reproducibility with standard phenotypic methods, a coagulase gene (coa) restriction fragment length polymorphism (RFLP) method and pulsed-field gel electrophoresis (PFGE), in typing 34 isolates and four reference strains of methicillin-resistant Staphylococcus aureus (MRSA). The fAFLP showed from 40 to 75 fragments, 50 to 450 base pairs (bp) in size. Based on replicate studies, the isolates were judged indistinguishable when their fAFLP pattern was >93.7% similar. Only two of the isolates were indistinguishable by this criterion. Thirty-one MRSA fell into four major fAFLP groups (1, 2, 3 and 4) at the level of >79.9% similarity. Three other isolates and an EMRSA-16 strain fell outside these major groups. Within both fAFLP groups 1 and 2, two subgroups, A and B, could be identified at approximately 82.0% similarity. While most isolates within group 1 could also be separated by their phenotypic and coagulase gene (coa) RFLP pattern, all the isolates within fAFLP groups 2A and 2B were identical on the basis of these characters. The MRSA within fAFLP groups 3 and 4 were heterogeneous by their phenotypic characteristics and coa gene RFLP patterns. fAFLP was reproducible and distinguished between MRSA isolates that appeared identical by other methods. It is likely to contribute to the epidemiological analysis of outbreaks of MRSA infection.

Antibacterial action of extracellular mammalian group IIA phospholipase A2 against grossly clumped Staphylococcus aureus

Fibrinogen-dependent interactions of Staphylococcus aureus are believed to contribute to bacterial virulence by promoting bacterial attachment to fibrinogen-coated surfaces and inducing the formation of bacterial clumps that are likely resistant to phagocytosis. Although S. aureus produces several fibrinogen-binding proteins, the cell wall-associated protein clumping factor (encoded by clfA) appears to be most important in bacterial interactions with immobilized or soluble purified fibrinogen. We have compared bacterial clumping in several strains of S. aureus, including isogenic ClfA+ and ClfA- Newman strains, in the presence of purified rabbit fibrinogen, human plasma, and inflammatory fluid and examined the effect of clumping on bacterial sensitivity to mammalian group IIA phospholipase A2 (PLA2). This enzyme is the major extracellular bactericidal agent in inflammatory fluid active against S. aureus. Both ClfA-dependent and ClfA-independent bacterial clumping was observed, depending on the source and fibrinogen content of the biological fluid. In each case, clumping only partially reduced the antibacterial activity of PLA2, suggesting that this extracellular enzyme can substantially penetrate dense bacterial clumps. Bacterial clumps could be dispersed by added proteases, restoring full antibacterial activity to PLA2. Thus, the extracellular mobilization of group IIA PLA2 during inflammation may provide a mechanism by which the host can control the proliferation and survival of S. aureus even after bacterial clumping.

All Wales surveillance of methicillin-resistant Staphylococcus aureus (MRSA): the first year's results

Over the last five years, hospitals in Wales have experienced difficulties with increasing numbers of isolates of methicillin-resistant Staphylococcus aureus (MRSA). Continuous total population surveillance of MRSA was introduced with the objectives of gaining an understanding of the extent and variation in time and place of its occurrence, the burden of disease and possible risk factors associated with its isolation and resistance to other antibiotics. All first isolates of MRSA from both hospital and community settings and all isolates of methicillin-sensitive Staphylococcus aureus (MSSA) associated with bacteraemia and cerebrospinal fluid (CSF) isolates detected in medical microbiology laboratories in Wales were collected via CoSurv, a set of interconnected data-base modules for communicable disease control. A data set was collected on each isolate and the patient associated with that isolate and compiled centrally at CDSC (Wales) for all-Wales analysis of the MRSA situation. Surveillance started in January 1996 and at the end of the first year, 2700 new isolates of MRSA had been reported from hospital and community settings, giving a rate of 92.43/100,000 population. The incidence of MRSA from bacteraemias and CSF was 5.20/100,000 compared with 12.70/100,000 for MSSA. MRSA from bacteraemia and CSF was significantly more commonly associated with male patients than MSSA. MRSA patients were significantly older. For all MRSA isolates, the highest reporting rate was in men aged 75+ (647.21/100,000). The highest incidence of invasive disease was also in men aged 75+ (45.69/100,000). Isolates from post-surgical patients were more likely to be involved in invasive disease (OR = 2.59), P < 0.001) than strains from other sources. The majority of isolates were resistant to at least two antibiotics in addition to methicillin, most frequently erythromycin and the fluoroquinolones. Very little resistance to fusidic acid, mupirocin or rifampicin was reported. Continuous total population surveillance has provided a minimum incidence of MRSA in Wales and has allowed a simple and intelligible picture of the problem to be determined, which has been fed back to hospitals to assist decisions on control.

Antibiotic resistance among clinically important gram-positive bacteria in the UK

The resistance of bacteria to antibiotics, particularly those used for first-line therapy, is an increasing cause for concern. In the UK, the prevalence of resistance to methicillin and mupirocin in Staphylococcus aureus, and to penicillin and macrolides in Streptococcus pneumoniae, appear to be increasing. There has also been an increase in the number of hospitals where glycopeptide-resistant enterococci are known to have been isolated. The increases in methicillin-resistant S. aureus and glycopeptide-resistant enterococci are due, in part, to the inter-hospital spread of epidemic strains. Although new quinolones and streptogramins with activity against Gram-positive bacteria (including strains resistant to currently available agents) are under development, there is no reason to believe that resistance to these agents will not emerge. The control of resistance in Gram-positive bacteria will require a multi-faceted approach, including continued and improved surveillance, a reduction in the unnecessary use of antibiotics, and the application of other strategies such as vaccination.

Control of an outbreak of an epidemic methicillin-resistant Staphylococcus aureus also resistant to mupirocin

An epidemic methicillin-resistant Staphlococcus aureus (EMRSA-3) appeared in a District hospital in June 1989 as part of a regional outbreak. The dynamics of the outbreak were complex and involved patient transfer between hospitals and wards. Control measures followed UK guidelines and included the use of nasal mupirocin. During these efforts a mupirocin-resistant MRSA [MuMRSA: mupirocin minimum inhibitor concentration (MIC) > 256 mg/L] emerged, probably in a patient who had been given eight mupirocin courses over nine months. The MuMRSA had a narrower phage-typing pattern than EMRSA-3, but was indistinguishable by pulsed-field gel electrophoresis of SmaI chromosomal restriction enzyme digests and its susceptibility pattern to other antibiotics. The results of in vitro curing and gene probing indicated that mupirocin resistance was encoded on a 48 Md plasmid. MuMRSA spread occurred in 12 patients and 11 staff. The affected patients were nursed on the same ward. The strain was eradicated from patients with oral ciprofloxacin and rifampicin, triclosan skin treatment and nasal fusidic acid and bacitracin cream. The control of the outbreak had significant medical, social and financial implications. Fortunately, there were alternative topical agents to mupirocin, an agent which has played such a key role in MRSA eradication in recent years.

Clonal analysis and identification of epidemic strains of methicillin-resistant Staphylococcus aureus by antibiotyping and determination of protein A gene and coagulase gene polymorphisms

Forty-three methicillin-resistant Staphylococcus aureus (MRSA) isolates with known genetic and epidemiological relatedness and different degrees of transmission were analyzed by antibiotyping, protein A gene polymorphism analysis, and coagulase gene polymorphism analysis. The three typing systems were evaluated for their performance and convenience to define clones and to discriminate between epidemic MRSA (EMRSA) and sporadic MRSA (SMRSA). Antibiotyping and AluI restriction fragment length polymorphism analysis of the coagulase gene were able to define clones in the same way as DNA macrorestriction analysis (SmaI). However, both techniques presented disadvantages, making neither of them useful as a single typing method. Protein A gene polymorphism analysis appeared to be of no value for clonal analysis. None of the three typing methods was able to differentiate between EMRSA and SMRSA.