The international spread of methicillin-resistant Staphylococcus aureus

Remodeling of pSK1 Family Plasmids and Enhanced Chlorhexidine Tolerance in a Dominant Hospital Lineage of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is a significant human pathogen whose evolution and adaptation have been shaped in part by mobile genetic elements (MGEs), facilitating the global spread of extensive antimicrobial resistance. However, our understanding of the evolutionary dynamics surrounding MGEs, in particular, how changes in the structure of multidrug resistance (MDR) plasmids may influence important staphylococcal phenotypes, is incomplete. Here, we undertook a population and functional genomics study of 212 methicillin-resistant S. aureus (MRSA) sequence type 239 (ST239) isolates collected over 32 years to explore the evolution of the pSK1 family of MDR plasmids, illustrating how these plasmids have coevolved with and contributed to the successful adaptation of this persistent MRSA lineage. Using complete genomes and temporal phylogenomics, we reconstructed the evolution of the pSK1 family lineage from its emergence in the late 1970s and found that multiple structural variants have arisen. Plasmid maintenance and stability were linked to IS256- and IS257-mediated chromosomal integration and disruption of the plasmid replication machinery. Overlaying genomic comparisons with phenotypic susceptibility data for gentamicin, trimethoprim, and chlorhexidine, it appeared that pSK1 has contributed to enhanced resistance in ST239 MRSA isolates through two mechanisms: (i) acquisition of plasmid-borne resistance mechanisms increasing the rates of gentamicin resistance and reduced chlorhexidine susceptibility and (ii) changes in the plasmid configuration linked with further enhancement of chlorhexidine tolerance. While the exact mechanism of enhanced tolerance remains elusive, this research has uncovered a potential evolutionary response of ST239 MRSA to biocides, one of which may contribute to the ongoing persistence and adaptation of this lineage within health care institutions.

The Relationship Between Prevalence of Antibiotics Resistance and Virulence Factors Genes of MRSA and MSSA Strains Isolated from Clinical Samples, West Iran

Objectives

We sought to evaluate the relationship between the prevalence of antibiotics resistance and virulence factors genes in methicillin-resistant Staphylococcal aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains from clinical samples taken in west Iran.

Methods

We performed a cross-sectional study using 100 MRSA and 100 MSSA samples isolated from clinical specimens. We used biochemical methods to identify the isolates, which were confirmed by the polymerase chain reaction (PCR) assay. Antibiotic susceptibility testing was performed using disk diffusion. PCR detected the presence of virulence factors, including enterotoxin genes, toxic shock syndrome toxin-1 (TSST-1), and exfoliative toxin.

Results

The majority of MRSA isolates exhibited a high level of resistance to common antibiotics and susceptible to vancomycin, while most MSSA isolates were also resistant to erythromycin and ciprofloxacin. The prevalence of Staphylococcal enterotoxins (SEs) were reported 147 (73.5%). Among 100 MRSA samples, 92 (92.0%) harbored SAg genes. The most frequent toxin gene was sea (45.0%) followed by sec (39.0%). Among 100 MSSA isolates, 89 (89.0%) harbored SAg genes and the most prevalent genes were sea (42.0%), sek (38.0%), sec (35.0%,), and TSST-1 (10.0%). The prevalence of TSST-1 and exfoliative toxin genes in MRSA samples were 12 (12.0%). The association of SAg genes with MRSA and MSSA isolates showed a high prevalence of enterotoxin seq, seg, and sei in MRSA than MSSA with a statistically significant difference (p < 0.050).

Conclusions

The prevalence of MRSA and the association of pathogenic agents with antibiotics resistance genes can lead to the emergence of strains with higher pathogenicity and less susceptibility.

Nosocomial MRSA Infection in Vascular Surgery Patients: Impact on Patient Outcome

Although methicillin-resistant Staphylococcus aureus(MRSA) infection is a worldwide problem, data on its significance among vascular surgery patients remain scant and conflicting. This study was designed to evaluate the association between nosocomial MRSA infection and patient outcome following vascular surgery procedures. Outcomes among patients with MRSA infection were also compared to those infected with methicillin-sensitive Staphylococcus aureus(MSSA). All patients admitted to a tertiary care Vascular Surgery ward during the year 2002 were included in this retrospective review. In addition to information on demographic and comorbid conditions, data on surgical interventions, nosocomial infection incidence rates as defined by the Center for Disease Control guidelines, and MRSA screening results were collected. Primary outcome was in-hospital death. Secondary outcomes measures included length of hospital stay, readmissions, or repeat surgeries, and ICU admissions. Of a total of 408 subjects, 110 were documented with a nosocomial infection (27.0%). Of these, 16 patients (3.9%) were colonized with MRSA on screening at time of admission, 22 (5.4%) had acquired MRSA infection during hospitalization, and 15 (3.7%) had MSSA infection. Patients with MRSA, MSSA, and non-MRSA infection had similar baseline characteristics except for hypertension and tobacco use. Age and MRSA infection were significant risk factors for in-hospital deaths (OR 1.07, 95% CI 1.01–1.13, p = 0.01 and OR 7.44, 95% CI 1.63–33.9, p = 0.01, respectively). Adjusted for the effects of age, MRSA infection remained a significant independent risk factor associated with in-hospital deaths (OR 4.38, 95% CI 1.09–17.7, p = 0.04). After adjustment for baseline risk factors, MRSA infection was also independently associated with secondary outcome measures. Although risks of non-MRSA infections were also associated with adverse outcomes in the multivariate analyses, MRSA posed higher risks, as reflected by higher odds ratio in all instances. The 22 patients with documented MRSA infection had significantly longer hospital stays than those with MSSA infection (median 24 days vs 8 days, p = 0.02). However, no significant differences were noted between the 2 groups in terms of secondary outcome. These results show that MRSA infection is a significant risk factor for adverse clinical outcomes among patients undergoing vascular surgery procedures. Infection with MRSA results in a greater risk of these outcomes when compared with non-MRSA infection. However, despite concerns regarding the virulence of this strain of staphylococcus, patients infected with MRSA had no higher rates of morbidity or mortality except for increased length of hospital stay when compared to patients with MSSA.

The growing challenges of antibacterial drug resistance in Ethiopia

Infectious diseases of bacterial origin are a major cause of morbidity and mortality in developing countries such as Ethiopia. To minimise such burdens, proper use of antibiotics has played a vital role and saved countless lives. However, use of antimicrobials as therapeutic agents is compromised by the potential development of drug-resistant micro-organisms. Currently, antimicrobial drug resistance has become a public health concern both in developing and developed countries. Antimicrobial drug resistance is dramatically accelerated when antimicrobials are misused. This is critical, especially in developing countries where they are not only misused but are often underused due to financial constraints. Although large-scale studies on antimicrobial resistance in Ethiopia have not yet been conducted, the available reports indicate a trend towards increasing resistance rates among pathogens such as Escherichia coli, Shigella spp., Salmonella spp. and Staphylococcus aureus to commonly prescribed antibiotics, including ampicillin, amoxicillin, penicillin, tetracycline and trimethoprim/sulfamethoxazole. This review summarises the existing data on antibacterial drug resistance in this country.

Superantigen gene profiles and presence of exfoliative toxin genes in community-acquired meticillin-resistant Staphylococcus aureus isolated from Chinese children

This study aimed to evaluate the distribution of superantigen gene profiles and the presence of exfoliative toxin genes in community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA) isolated from Chinese children, and simultaneously to assess virulence gene profiles and genetic background. Of the CA-MRSA isolates, 88.9 % (88/99) harboured toxin genes, with sek as the most frequent toxin gene (62.6 %), followed by seq (61.6 %), seb (60.6 %) and sea (35.4 %). The eta gene was detected only in one ST398-IVa-spa t034 strain. The sed and etd genes were not found in any of the isolates tested. A total of 38 virulence genotypes were observed, of which the genotype seb-sek-seq (27.3 %, 24/88) comprised the majority, followed by sea-seb-sek-seq (18.2 %, 16/88). The enterotoxin gene cluster including seg-sei-sem-sen-seo-seu predominated at a rate of 15.1 %. The relationship among toxin genotypes, toxin genes encoding profiles of mobile genetic elements and genetic background was analysed. Among 66 clonal complex (CC) 59 isolates, 87.9 % (58/66) were positive for toxin genes, and 75.8 % (50/66) harboured the toxin gene combination seb-sek-seq. Among seb-sek-seq-positive CC59 strains, 42.0 % (21/50) also carried the sea gene. CC59 corresponded exclusively to accessory gene regulator 1 (agr-1). The data presented here enhance our current knowledge on the virulence determinants of CA-MRSA.

Antibacterial activity of hydroxychalcone against methicillin-resistant Staphylococcus aureus

Anti-candidal hydroxychalcone, 2,4,2'-trihydroxy-5'-methylchalcone (THMC), was investigated for its antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). THMC showed the minimum inhibitory concentrations of 25.0-50.0 mug/ml against tested 20 strains, at which the effect was based on a bacteriostatic action. THMC of 25.0 mug/ml completely inhibited the incorporation of radio-labelled thymidine and uridine into MRSA cells. In combination with antibiotics, the fractional inhibitory concentration indices were 0.47 for gentamicin and 0.79 for vancomycin, indicating that THMC acts synergistically with these agents. THMC would be a potent therapeutic agent for MRSA infections.

Imported methicillin-resistant Staphylococcus aureus, Sweden

Knowledge of different risks for infection will improve control measures.

Countries such as Sweden that have a low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) offer the opportunity to discern and study transmission of imported cases of MRSA. We analyzed 444 imported cases of MRSA acquisition reported in Sweden during 2000–2003. Risk for MRSA in returning travelers ranged from 0.1 (95% confidence interval [CI] 0.01–0.4) per 1 million travelers to Nordic countries to 59.4 (95% CI 44.5–79.3) per 1 million travelers to North Africa and the Middle East. Most imported cases (246, 55%) were healthcare acquired, but regions with the highest risk for MRSA in travelers showed a correlation with community acquisition (r = 0.81, p = 0.001). Characteristic differences in MRSA strains acquired were dependent on the region from which they originated and whether they were community or healthcare acquired. Knowledge of differences in transmission of MRSA may improve control measures against imported cases.

Analysis of the prototypical Staphylococcus aureus multiresistance plasmid pSK1

The Staphylococcus aureus multiresistance plasmid pSK1 is the prototype of a family of structurally related plasmids that were first identified in epidemic S. aureus strains isolated in Australia during the 1980s and subsequently in Europe. Here we present the complete 28.15kb nucleotide sequence of pSK1 and discuss the genetic content and evolution of the 14kb region that is conserved throughout the pSK1 plasmid family. In addition to the previously characterized plasmid maintenance functions, this backbone region encodes 12 putative gene products, including a lipoprotein, teichoic acid translocation permease, cell wall anchored surface protein and an Fst-like toxin as part of a Type I toxin-antitoxin system. Furthermore, transcriptional profiling has revealed that plasmid carriage most likely has a minimal impact on the host, a factor that may contribute to the ability of pSK1 family plasmids to carry multiple resistance determinants.

Methicillin resistant Staphylococcus aureus in a Japanese community hospital: 5-year experience

Methicillin resistant Staphylococcus aureus (MRSA) is exceptionally critical to infection treatment and control in the health-care setting. MRSA has been detected at high levels in Japan, and the frequency of MRSA infection must be ascertained to provide a baseline with which to assess various infection control efforts. We studied MRSA infection rate at a general hospital in Japan in all 65,135 inpatients of Sendai Kousei Hospital from January 2004 to December 2008. MRSA's prevalence among strains of S. aureus and the rate of MRSA detection were studied. Identification of MRSA infection is according to the laboratory-based ward liaison surveillance. The minimal inhibitory concentrations (MICs) of vancomycin, teicoplanin, and arbekacin for the various isolates were determined. During the period studied, there were 621 MRSA-positive patients. MRSA prevalence among strains of S. aureus was 45.5% (621/1,365). The rate of MRSA detection in inpatients was 0.953/100 inpatients. Of the 621 patients from whom MRSA was isolated, 51 (8.2%) had an MRSA infection (MRSA infection rate 0.078/100 inpatients). MRSA was often detected from the respiratory tract, but this seldom led to infection, since many of those affected were merely carriers. MICs against MRSA was 0.5-4 μg/ml for vancomycin, 0.5-16 μg/ml for teicoplanin, and 0.5 to >16 μg/ml for arbekacin, with no tendency for tolerance observed for these drugs. Findings suggest that whereas MRSA remains prevalent, there is a low incidence of infection in a general hospital in Japan.

Antimicrobial natural products: an update on future antibiotic drug candidates

Over the last decade, it has become clear that antimicrobial drugs are losing their effectiveness due to the evolution of pathogen resistance. There is therefore a continuing need to search for new antibiotics, especially as new drugs only rarely reach the market. Natural products are both fundamental sources of new chemical diversity and integral components of today's pharmaceutical compendium, and the aim of this review is to explore and highlight the diverse natural products that have potential to lead to more effective and less toxic antimicrobial drugs. Although more than 300 natural metabolites with antimicrobial activity have been reported in the period 2000-2008, this review will describe only those with potentially useful antimicrobial activity, viz. with MICs in the range 0.02-10 microg mL(-1). A total of 145 compounds from 13 structural classes are discussed, and over 100 references are cited.

Changing molecular epidemiology of methicillin-resistant Staphylococcus aureus in a small geographic area over an eight-year period

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at an international level shows that most MRSA strains belong to a few pandemic clones. At the local level, a predominance of one or two clones was generally reported. However, the situation is evolving and new clones are emerging worldwide, some of them with specific biological characteristics, such as the presence of Panton-Valentine leucocidin (PVL). Understanding these changes at the local and international levels is of great importance. Our objective was to analyze the evolution of MRSA epidemiology at multiple sites on a local level (Western Switzerland) over a period of 8 years. Data were based on MRSA reports from seven sentinel laboratories and infection control programs covering different areas. Pulsed-field gel electrophoresis was used to type MRSA isolates. From 1997 to 2004, a total of 2,256 patients with MRSA were reported. Results showed the presence of four predominant clones (accounting for 86% of patients), which could be related to known international clones (Berlin, New York/Japan, Southern Germany, and Iberian clones). Within the small geographic region, the 8-year follow-up period in the different areas showed spacio-temporal differences in the relative proportions of the four clones. Other international MRSA clones, as well as clones showing genetic characteristics identical to those of community-acquired MRSA (SCCmec type IV and the presence of PVL genes), were also identified but presumably did not disseminate. Despite the worldwide predominance of a few MRSA clones, our data showed that at a local level, the epidemiology of MRSA might be different from one hospital to another. Moreover, MRSA clones were replaced by other emerging clones, suggesting a rapid change.

Inducible clindamycin resistance in Staphylococcus aureus isolates causing bacteremia at a university hospital in southern Taiwan

A major concern while prescribing clindamycin to treat infections caused by inducible macrolide, lincosamide, and group B streptogramin (iMLS(B))-resistant strains is clinical therapy failure. In this study, we determined the prevalence, mechanism, and clonality of the iMLS(B) phenotype in oxacillin-resistant Staphylococcus aureus (ORSA) and oxacillin-susceptible S. aureus (OSSA). Among the 729 OSSA isolates collected from July 1995 to March 2006, 72 (10%) were clindamycin sensitive (Cli(s)) and erythromycin resistant (Erm(r)), and 55 (8%) had the iMLS(B) phenotype. In the 709 ORSA isolates collected from January 1997 to March 2006, 31 (4%) were Cli(s) and Erm(r), and 29 (4%) isolates demonstrated the iMLS(B) phenotype. In OSSA, ermC was the predominant (51 of 55 isolates) genetic determinant responsible for the iMLS(B) phenotype, whereas in ORSA, ermA was predominant (27 of 29). Pulsed-field gel electrophoresis showed that 8 pulsed types (RA to RH) were present in ORSA isolates (n = 27), and pulsed type RC was predominant in 17 isolates with 5 identifiable subtypes (RC1 to RC5); this type was prevalent from November 1997 to June 2004. In the OSSA (n = 24) isolates, 14 different pulsed types (SA to SN) were identified, but none was predominant. These results indicate that the incidence of iMLS(B) resistance phenotype is higher in OSSA than ORSA in Taiwan, and the genetic determinants responsible for the iMLS(B) phenotype vary in OSSA and ORSA.

Community-Acquired Methicillin Resistant Staphylococcus aureus Skin Infection

Staphylococcus aureus is one of the most common pathogens in skin and soft tissue infections, as well as in potentially serious nosocomial infections in patients who acquire it when hospitalized. Penicillin was introduced in the 1940's as an effective treatment against S. aureus. However, shortly after penicillin's introduction, penicillin resistance to S. aureus emerged due to a plasmid-mediated beta-lactamase enzyme. In 1959, a semisynthetic penicillin, methicillin was introduced to overcome the resistance problem. However, within a year, bacteria resistant to methicillin and other penicillinase stable beta-lactams, were present. Worldwide emergence of methicillin-resistant S aureus (MRSA) was established by the 1980's. Since that time, MRSA has become widespread in hospitals and long-term care facilities around the world, accounting for numerous nosocomial infections. Recently, there has been an alarming increase in the incidence of community-acquired MRSA (CA-MRSA). Patients with CA-MRSA began to be reported in the early 1990's and its prevalence has continued to increase. This paper summarizes the current information known about CA-MRSA as it relates to skin infections including populations at risk, clinical presentation, and treatment options.

Antibacterial resistance and molecular typing of methicillin-resistant Staphylococcus aureus in a Kuwaiti general hospital

OBJECTIVE

To investigate antibiotic resistance and genetic relatedness of methicillin-resistant Staphylococcus aureus (MRSA) isolated in a general hospital in Kuwait over a period from 1996 to 1998 and 2001.

MATERIAL AND METHODS

The isolates were characterized by antibacterial susceptibility testing, coagulase serotyping, coagulase gene polymorphism (coag-RFLP) and pulsed-field gel electrophoresis (PFGE).

RESULTS

The MRSA isolates were highly resistant to gentamicin, kanamycin, ciprofloxacin, tetracycline, fusidic acid and mupirocin. The prevalence of gentamicin, kanamycin, streptomycin, tetracycline and erythromycin resistance remained high (80-96%) throughout the study period, but the prevalence of resistance to ciprofloxacin, fusidic acid and mupirocin steadily increased. The already high mupirocin resistance level increased from 12.5 in 1996, to 85.7% in 2001, and the fusidic acid resistance varied between 70.8 and 85.7%. In contrast, chloramphenicol and trimethoprim resistance declined from 25 and 29% in 1996 to 4.7 and 14.2% in 2001, respectively. The majority (91.5%) of the isolates were coagulase serotype 4. AluI restriction endonuclease analysis of amplified coagulase gene generated four coag-RFLP patterns: 92% of them were coag-RFLP type 1, while types 2, 3 and 4 were 3.5, 4.6 and 1.1% respectively. PFGE differentiated them into seven pulsotypes (PFGE types 1-7). The PFGE type 1 pulsotype constituted 90.2% of the isolates. Isolates with the type A coag-RFLP also had the type1 PFGE pulsotypes.

CONCLUSION

The concordant results of PFGE and coag-RFLP demonstrated the presence of a persistent MRSA clone in the hospital during the study period.

Genetic diversity among community methicillin-resistant Staphylococcus aureus strains causing outpatient infections in Australia

Increasing reports of the appearance of novel nonmultiresistant methicillin-resistant Staphylococcus aureus MRSA (MRSA) strains in the community and of the spread of hospital MRSA strains into the community are cause for public health concern. We conducted two national surveys of unique isolates of S. aureus from clinical specimens collected from nonhospitalized patients commencing in 2000 and 2002, respectively. A total of 11.7% of 2,498 isolates from 2000 and 15.4% of 2,486 isolates from 2002 were MRSA. Approximately 54% of the MRSA isolates were nonmultiresistant (resistant to less than three of nine antibiotics) in both surveys. The majority of multiresistant MRSA isolates in both surveys belonged to two strains (strains AUS-2 and AUS-3), as determined by pulsed-field gel electrophoresis (PFGE) and resistogram typing. The 3 AUS-2 isolates and 10 of the 11 AUS-3 isolates selected for multilocus sequence typing (MLST) and staphylococcal chromosomal cassette mec (SCCmec) analysis were ST239-MRSA-III (where ST is the sequence type) and thus belonged to the same clone as the eastern Australian MRSA strain of the 1980s, which spread internationally. Four predominant clones of novel nonmultiresistant MRSA were identified by PFGE, MLST, and SCCmec analysis: ST22-MRSA-IV (strain EMRSA-15), ST1-MRSA-IV (strain WA-1), ST30-MRSA-IV (strain SWP), and ST93-MRSA-IV (strain Queensland). The last three clones are associated with community acquisition. A total of 14 STs were identified in the surveys, including six unique clones of novel nonmultiresistant MRSA, namely, STs 73, 93, 129, 75, and 80slv and a new ST. SCCmec types IV and V were present in diverse genetic backgrounds. These findings provide support for the acquisition of SCCmec by multiple lineages of S. aureus. They also confirm that both hospital and community strains of MRSA are now common in nonhospitalized patients throughout Australia.

Microbiologic evaluation of skin wounds: alarming trend toward antibiotic resistance in an inpatient dermatology service during a 10-year period

BACKGROUND

Increasing resistance to commonly used antibiotics has been seen for patients with superficial skin wounds and leg ulcers.

OBJECTIVES

We sought to evaluate bacterial isolates from leg ulcers and superficial wounds for resistance to commonly used antibiotics and to compare current data with previous data.

METHODS

We performed a chart review for patients admitted to a tertiary care dermatology inpatient unit from January to December 2001. Comparison was made with 2 previous surveys of the same inpatient service from 1992 and 1996.

RESULTS

Bacterial isolates were cultured from 148 patients, 84% (72 of 86) with leg ulcers and 38% (76 of 202) with superficial wounds. Staphylococcus aureus and Pseudomonas aeruginosa were the most common bacterial isolates in both groups. For patients with leg ulcers, S aureus grew in 67% of isolates (48/72) of which 75% (36/48) were methicillin-resistant (MRSA). Of leg ulcers, 35% (25/72) grew P aeruginosa, which was resistant to quinolones in 56% of cultures (14/25). For patients with superficial wounds, S aureus was isolated in 75% (57/76) and 44% were MRSA (25/57). P aeruginosa grew in 17% of isolates (13/76) and was resistant to quinolones in 18%. We found a marked increase in antibiotic resistance for both leg ulcers and superficial wounds. Over time, MRSA increased in leg ulcers from 26% in 1992 to 75% in 2001. For superficial wounds, MRSA increased from 7% in 1992 to 44% in 2001. P aeruginosa resistance to quinolones in leg ulcers increased from 19% in 1992 to 56% in 2001, whereas for superficial wounds there was no resistance in 1992 and 18% resistance in 2001.

CONCLUSION

Rapid emergence of antibiotic-resistant bacteria continues and is a problem of increasing significance in dermatology. Common pathogenic bacteria, S aureus and P aeruginosa, showed increased resistance to commonly used antibiotics. Selection of antibiotics should be on the basis of local surveillance programs.

Molecular epidemiology of clinical isolates of methicillin-resistant Staphylococcus aureus in Taiwan

During July 2000 and October 2001, a total of 595 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were collected from six medical centers distributed in northern, central, and southern Taiwan. Specimen sources included blood (n = 279), pus (n = 173), sputum (n = 94), body fluids (n = 21), catheter tips (n = 20), and urine (n = 8). Pulsed-field gel electrophoresis (PFGE) with SmaI digestion was used to fingerprint these isolates. A total of 31 genotypes with 97 type-subtypes were identified. Subtypes could be identified in 7 genotypes. While there were 6 to 15 genotypes in each hospital, 433 isolates (73%) were shown to belong to a major type (genotype A, with 29 subtypes). This genotype was not only the type prevailing in all six hospitals but also the predominant clone in each hospital, accounting for 46 to 89% of all isolates in each hospital. Genotype C (16 subtypes) was the second dominant genotype, accounting for 9% of all isolates, and was distributed in five hospitals. Genotypes D (11 subtypes), E (5 subtypes), and B (6 subtypes) were distributed in five, four, and three hospitals, respectively. The other 26 types (30 type-subtypes) were minor. We conclude that the majority of MRSA clinical isolates shared a common PFGE pattern, indicating the presence of a single, epidemic MRSA clone prevailing in major hospitals in Taiwan.

STAR gene restriction profile analysis in epidemiological typing of methicillin-resistant Staphylococcus aureus: description of the new method and comparison with other polymerase chain reaction (PCR)-based methods

A method based on restriction profile analysis of the STAR repetitive element PCR (STAR-RP PCR) product obtained by digestion with AluI and Tru9I was developed for typing methicillin resistant Staphylococcus aureus (MRSA). We evaluated a well defined collection of MRSA from Argentina, previously characterized by PFGE (pulsed field gel electrophoresis) of chromosomal SmaI digests and hybridization with DNA probes for probes ClaI-mecA and ClaI-Tn554. We comparatively evaluated STAR-RP analysis with other PCR based methods such as Inter IS256-PCR, Rep-MP3 PCR and Coa-RP. The discriminatory power (D) of STAR-RP (0.86) was similar to that of PFGE (0.84) at the type level. Comparable results were obtained with Inter IS256 PCR (0.85) and Rep-MP3 PCR (0.80). A lower value (0.74) was obtained for Coa-RP. An excellent reproducibility (100%) of STAR-RP was observed. Good concordance between STAR-RP and other molecular typing methods was found for MRSA isolates (n = 39). STAR-RP typing showed 87% concordance with mecA::Tn554::PFGE, 87% with Inter IS256 PCR and 71% with Rep-MP3 typing. STAR-RP is suggested as an adequate molecular typing assay for MRSA epidemiologic assessment.

Antibacterial activity of isoflavonoids isolated from Erythrina variegata against methicillin-resistant Staphylococcus aureus

AIMS

To screen 16 isoflavonoids isolated from Erythrina variegata (Leguminosae) for their antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).

METHODS AND RESULTS

The roots of E. variegata were macerated with acetone. The chloroform-soluble fraction of the residue was subjected to repeated silica gel column chromatography followed by elution with various solvents. Structures of the isolated compounds were determined by extensive spectroscopic studies. Each compound was dissolved in dimethyl sulphoxide and added to agar plates (final concentration 1.56-100 microg ml(-1) and suspensions of MRSA spotted onto the agar plates to determine the minimum inhibitory concentration (MIC). Repeated silica gel chromatography yielded 16 compounds and spectroscopic studies revealed that all were isoflavonoids. Whilst 14 compounds showed antibacterial activity in this concentration range, the MIC values varied significantly among them. Of the active compounds, 3,9-dihydroxy-2,10-di(gamma,gamma-dimethylallyl)-6a,11a-dehydropterocarpan (erycristagallin) and 9-hydroxy-3-methoxy-2-gamma,gamma-dimethylallylpterocarpan (orientanol B) exhibited the highest activity with MIC values of 3.13-6.25 microg ml(-1).

CONCLUSIONS

Erycristagallin and orientanol B showed the highest anti-MRSA activity (3.13-6.25 microg ml(-1).

SIGNIFICANCE AND IMPACT OF THE STUDY

Erycristagallin and orientanol B could be leading compounds for phytotherapeutic agents against MRSA infections.

Molecular epidemiology and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus in Taiwan

Methicillin-resistant Staphylococcus aureus (MRSA) has become an important nosocomial pathogen and has increased frequency in the past 20 years. It is highly transmissible between wards, hospitals, and cities. In most major hospitals in Taiwan, MRSA accounts for more than 60% of the S. aureus isolates. Whether there is a predominant strain, which is spread over the whole of Taiwan has not yet been studied. We collected 208 sequential clinical isolates of MRSA from 22 hospitals: seven in northern Taiwan, seven in western Taiwan, five in southern Taiwan, and three in eastern Taiwan during a three-month period in 1998. Using pulsed-field gel electrophoresis, 112 MRSA isolates were shown to belong to one major type,--type C, and this type was shown to have spread widely across all of Taiwan. Ninety-six isolates belonged to 20 other minor types. Most MRSA isolates of this major type were multi-drug resistant and only susceptible to vancomycin and rifampin. We concluded that the high prevalence of MRSA in Taiwan was partly due to the spreading of a predominant strain and most of them were multi-drug resistant. This might imply that more effort should be made to control the spread of MRSA in Taiwan.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a pediatric ward

BACKGROUND

Nosocomial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are one of the most serious problems in pediatric wards. Epidemiological analysis of strains isolated in the ward is essential for infection control. There have been few reports in which a molecular epidemiological study of MRSA was performed in pediatric wards.

METHODS

Fifty-six MRSA strains isolated in the pediatric ward of Asahikawa Medical College Hospital between 1995 and 1997 were studied. Fifty-two and four isolates were obtained from 27 patients and from two medical staff members, respectively. Forty-one isolates were regarded as colonizing strains and 15 were causes of infections. Genotypes of the isolates were investigated by pulsed-field gel electrophoresis (PFGE).

RESULTS

The PFGE patterns of 56 isolates were classified into nine types: type A, its subtypes, A1 and A2, and types B through to G. Seventeen isolates were type A, 32 were type A1, and one of each type of A2 and B through to G were identified. Fifty of 56 isolates, which were isolated from 24 of 29 cases, belonged to type A or its subtypes.

CONCLUSIONS

The predominant strain of MRSA isolates in the pediatric ward was a certain strain that may be originated from the one clone. Cross-infection control therefore is the major procedure in the prevention of MRSA dissemination in the ward.

Development of a Canadian standardized protocol for subtyping methicillin-resistant Staphylococcus aureus using pulsed-field gel electrophoresis

A panel of 24 methicillin-resistant Staphylococcus aureus strains was distributed to 15 laboratories in Canada to evaluate their in-house pulsed-field gel electrophoresis (PFGE) protocols and interpretation criteria. Attempts to compare fingerprint images using computer-aided analysis were not successful due to variability in individual laboratory PFGE protocols. In addition, individual site interpretation of the fingerprint patterns was inadequate, as 7 of 13 sites (54%) made at least one error in interpreting the fingerprints from the panel. A 2-day standardized PFGE protocol (culture to gel image) was developed and distributed to all of the sites. Each site was requested to use the standardized protocol on five strains from the original panel. Thirteen sites submitted gel images for comparisons. The protocol demonstrated excellent reproducibility and allowed interlaboratory comparisons with Molecular Analyst DST software (Bio-Rad) and 1.5% band tolerance.

Surveillance of antibiotic resistance in European ICUs

Antibiotic resistance among bacteria causing hospital-acquired infections poses a threat, particularly to patients in intensive care units (ICUs). In order to control the spread of resistant bacteria, local, regional and national resistance surveillance data must be used to develop efficient intervention strategies. In an attempt to identify national differences and the dynamics of antibiotic resistance in European ICUs, data have been merged from several networks of resistance surveillance performed during the 1990s. It should be stressed, however, that comparisons of results from different studies using different methods and different population samples must be made with caution. Antibiotic resistance across all species and drugs was, with some exceptions, highest in southern European countries and Russia, and lowest in Scandinavia. More effective strategies are needed to control the selection and spread of resistant organisms. Antibiotic intervention policies, efficient infection control measures and an overall awareness of the serious implications at public health level will contribute to the management of antibiotic resistance.

Genetic relatedness of multidrug-resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates from SENTRY Antimicrobial Resistance Surveillance Centers worldwide, 1998

We reviewed Staphylococcus aureus bloodstream infection isolates from SENTRY centers worldwide during 1998 to evaluate the molecular epidemiology of multiply drug-resistant methicillin (oxacillin)-resistant S. aureus (MDR-MRSA). MDR-MRSA was defined as a S. aureus isolate with a MIC for oxacillin at >2 microg/ml and with four or more additional resistances. A total of 325 unique patient isolates of MDR-MRSA from five continents were analyzed using ribotyping and pulsed-field gel electrophoresis (PFGE). The frequency of MDR-MRSA among all S. aureus BSI isolates ranged from only 2.2% in Canada to 35.6% in the Asia-Pacific region. Forty-eight ribotypes (RT) were distinguished, but over 80% of the isolates were contained within the 10 most prevalent RTs. The most common RT, RT 184.5, which included 30% of all MDR-MRSA, was found on four of five continents. PFGE provided superior discrimination and identified numerous clusters of possible clonal dissemination of MDR-MRSA within individual medical centers and between institutions that are in geographic proximity. In four instances, strains with indistinguishable PFGE patterns were found on more than one continent. The predominant PFGE subtype in South America (RT 893.5/Ia) was isolated from patients at centers in Brazil, Argentina, and Portugal, and closely related subtypes were isolated in Chile and Italy. There is great geographic variation in rates of methicillin- and multidrug-resistance among S. aureus bloodstream isolates worldwide. Although many MDR-MRSA strains group geographically, a few closely related epidemic strains have wide regional and even global range.

Methicillin-resistant Staphylococcal aureus evolution in Australia over 35 years

Australia has a long association methicillin-resistant Staphylococcus aureus (MRSA). Its unique geographic and demographic features have led to the emergence and spread of three types of MRSA over 35 years. Classical multiresistant hospital-acquired MRSA were first noted in Australia in 1965. By the end of the 1970s, strains of this type of MRSA were well established in the complex tertiary care hospitals in the capital cities on the eastern seaboard of mainland Australia. Characterized by resistance to beta-lactams, erythromycin, tetracycline, gentamicin, and trimethoprim-sulfamethoxazole, these strains have persisted and diversified genetically and have acquired a variety of new resistances. They have proven pathogenicity and are a prominent cause of hospital infection in the endemic institutions. More recently they have become endemic in some central state tertiary care hospitals. Community-acquired strains of MRSA first appeared in the north of Western Australia in the mid-1980s. Strains have subsequently appeared in the south of the state and in the two adjacent central states, and are more frequently isolated from Aboriginal patients. Although harboring few or no additional resistances apart from resistance to beta-lactams initially, these strains are also accumulating additional resistances. A different variety of community-acquired MRSA has recently been noted in eastern Australia. It has a similar antibiogram to the western strains, but an entirely different epidemiology, resembling that currently being experienced in parts of New Zealand, and associated with patients of south Pacific island origin.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains: state of affairs and tomorrow' s possibilities

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have posed a clinical threat for nearly 40 years. During these years, an array of additional technologies suited for identification of MRSA below the species level has become available. The technologies, whether they assess phenotype or genotype, provide data that can be used for elucidation of the routes of dissemination of individual MRSA types. This review summarizes the current state of affairs with respect to the quality of the various laboratory techniques and includes descriptions of novel strategies such as binary typing and multilocus sequence typing (MLST). Drawbacks of procedures will be compared, and the value of molecular typing in the elucidation of complex biological phenomena, such as epidemicity, carriage, and reduced vancomycin susceptibility, will be indicated. Means for integrated assessment of bacterial biology, epidemiology, and population structure will be discussed.

Epidemiology of MRSA

Staphylococcus aureus is recognized as one of the major causes of infections in humans occurring in both the community and the hospital. Up to now one of the most serious aspects as far as treatment of S. aureus infections is concerned is resistance to methicillin, which in clinical terms indicates resistance to all beta-lactam antibiotics. The growing incidence of methicillin-resistant S. aureus (MRSA) infections worldwide, their multidrug resistance, several reservoirs of resistant strains, the facility to spread also outside hospitals and to cause outbreaks requires efficacious infection control measures. For this reason microbiological and epidemiological studies are of crucial importance.

Replication of staphylococcal multiresistance plasmids

Based on structural and functional properties, three groups of large staphylococcal multiresistance plasmids have been recognized, viz., the pSK1 family, pSK41-like conjugative plasmids, and beta-lactamase-heavy-metal resistance plasmids. Here we describe an analysis of the replication functions of a representative of each of these plasmid groups. The replication initiation genes from the Staphylococcus aureus plasmids pSK1, pSK41, and pI9789::Tn552 were found to be related to each other and to the Staphylococcus xylosus plasmid pSX267 and are also related to rep genes of several plasmids from other gram-positive genera. Nucleotide sequence similarity between pSK1 and pI9789::Tn552 extended beyond their rep genes, encompassing upstream divergently transcribed genes, orf245 and orf256, respectively. Our analyses revealed that genes encoding proteins related to the deduced orf245 product are variously represented, in several types of organization, on plasmids possessing six seemingly evolutionarily distinct types of replication initiation genes and including both theta-mode and rolling-circle replicons. Construction of minireplicons and subsequent functional analysis demonstrated that orf245 is required for the segregational stability of the pSK1 replicon. In contrast, no gene equivalent to orf245 is evident on the conjugative plasmid pSK41, and a minireplicon encoding only the pSK41 rep gene was found to exhibit a segregational stability approaching that of the parent plasmid. Significantly, the results described establish that many of the large multiresistance plasmids that have been identified in clinical staphylococci, which were formerly presumed to be unrelated, actually utilize an evolutionarily related theta-mode replication system.

Methicillin-resistant Staphylococcus aureus in French hospitals: A 2-month survey in 43 hospitals, 1995

OBJECTIVE

To estimate the incidence of methicillin-resistant Staphylococcus aureus (MRSA) in patients hospitalized in French public hospitals.

DESIGN

A 2-month survey that included 163,573 patients and 140,114 admissions.

SETTING AND PATIENTS

Forty-three public or public-affiliated hospitals throughout France, including 12 university-affiliated hospitals. Information was recorded on all patients having MRSA recovered from culture of any clinical sample.

RESULTS

The overall median incidence rate (per 1,000 admissions) of clinically detected MRSA was 5.9 (range, 1.8-15.8); median rates were similar in hospitals affiliated or not affiliated to universities (6.4 and 5.9, respectively). Smaller unaffiliated hospitals (<500 beds) had higher MRSA incidence rates (mean, 7.2) than larger (>500 beds) unaffiliated hospitals or university hospitals (mean, 6.7 and 6.1, respectively). The incidence density (per 1,000 patient-days) of MRSA was higher in intensive-care units [ICUs] 2.39/1,000) than in surgical (0.80/1,000) and medical (0.70/1,000) wards, respectively; comparable rates were recorded in rehabilitation units (0.67/1,000), whereas in long-term-stay units, the incidence density of MRSA was 0.27/1,000 patient-days. Of 958 MRSA isolates, 660 (69%) also were resistant to all aminoglycosides. In 411 (43%) of 958 patients, the MRSA isolate was considered imported (ie, first recovered within 72 hours of the patient's admission to the unit). More than one half (53%) of imported cases were transfer patients from other hospitals, and 17% originated from ICUs.

CONCLUSION

MRSA is extensive in French hospitals. All categories of hospitals are involved to a similar extent, and there is intense circulation of patients colonized or infected with MRSA between units and hospitals. Containment of MRSA would mandate increasing resources devoted to infection control, especially in smaller hospitals, and control programs should involve notification of carriers and screening of patients at risk of MRSA carriage on admission to detect carriers and to implement isolation precautions rapidly.

Epidemiological and biological characteristics of methicillin-resistant staphylococcal infections in a Mexican hospital

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide since 1960. However, there is little information concerning methicillin-resistant coagulase-negative staphylococci (MRCNS) infections.

METHODS

In order to study the clinical and epidemiological characteristics of methicillin-resistant staphylococci (MRS) infections and to determine the relationship between MRS and both synergistic hemolysis (SH) and slime production (SP), a laboratory-based survey and non-matched case-control study were carried out at a tertiary-care center in Mexico City. In regard to patients, from May 1991 to October 1992, 46 cases of MRS infection and 86 patients (controls) infected by methicillin-susceptible staphylococci (MSS) were included. Clinical and epidemiologic variables were analyzed. The isolates were identified and tested for antimicrobial susceptibility by standard methods. An MIC of oxacillin > or = 8 micrograms/mL was defined as an MRS.

RESULTS

During the study, 94 nosocomial staphylococcal infections were diagnosed: S. aureus, 35 and CNS, 59; 43 (45.7%) by MRS (rate of MRS infections was 1.12 per 100 in-patients); 2 MRSA; 41 MRCNS, and only 19 were symptomatic. Three infections were community-acquired, including one MRSA and two MRCNS. After multivariate analysis, the significant risk factors were previous antimicrobial therapy (p = 0.013) and catheter-related (p = 0.009) and urinary-tract source (p = 0.0001). Forty-nine percent of MRS showed SH while only 15% of MSS (p < 0.001) showed SH, especially in 10/10 MR-S. hemolyticus. Additionally, 48% of MRCNS showed SP, as did 18% of MSCNS (p = 0.019), particularly in 15/20 MR-S. epidermidis. Of all MRS isolates, 38% showed a homogeneous phenotype, a trait associated with multi-drug resistance (p < 0.01) and SH (p < 0.001).

CONCLUSIONS

CNS predominated as the cause of MRS infections in our setting. The homogenous phenotype was associated with SH and multi-drug resistance.

Methicillin-resistant Staphylococcus aureus versus the burn patient

Methicillin-resistant Staphylococcus aureus (MRSA) has become a frequent cause of nosocomial infection, its increasing prevalence posing serious therapeutic and infection control problems within the hospital environment. MRSA is a major challenge to the burn patient, with potential to cause significant morbidity and mortality. Burn patients have been shown to become colonised and infected more readily than other patient groups. Extensive burn injuries are particularly susceptible to infection as a result of the disruption of the normal skin barrier and accompanying depression of immune responses. Extended hospitalisation and antibiotic therapy have been identified as additional risk factors for MRSA carriage and infection. Microbial surveillance, epidemiological studies and the introduction of strict infection control regimes can reduce the prevalence of MRSA but may be insufficient for eradication or prevention of outbreak situations. Recognition of the clinical importance of MRSA to the burn patient highlights the need to take appropriate measures to minimise transmission and infection in this vulnerable group of patients.

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.

Structural characterization of peptidoglycan muropeptides by matrix-assisted laser desorption ionization mass spectrometry and postsource decay analysis

In this study we report the development of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS)-based methods for the structural characterization of muropeptides derived from peptidoglycan. Prior to analysis, peptidoglycan samples were subjected to enzymatic digestion with muramidase and the resulting muropeptides were purified by HPLC. A new matrix, 5-chloro-2-mercaptobenzothiazole, was employed for the MALDI-MS analysis. The results have demonstrated that sub-picomole to femtomole detection can be achieved in both positive mode and negative mode, allowing unambiguous determination of the molecular masses of monomeric and oligomeric muropeptides. Structural information from monomeric muropeptides was obtained by further postsource decay (PSD) analysis. Fragmentation patterns in positive mode and negative mode PSD were complementary for the elucidation of the peptide chain sequence. Lysostaphin digestion was also incorporated with MALDI mass mapping analysis for determination of peptide chain cross-linking patterns of muropeptide oligomers from Staphylococcus aureus strains.

Antibacterial activity of xanthones from guttiferaeous plants against methicillin-resistant Staphylococcus aureus

Extracts of Garcinia mangostana (Guttiferae) showing inhibitory effects against the growth of S. aureus NIHJ 209p were fractionated according to guidance obtained from bioassay and some of the components with activity against methicillin-resistant Staphylococcus aureus (MRSA) were characterized. One active isolate, alpha-mangostin, a xanthone derivative, had a minimum inhibitory concentration (MIC) of 1.57-12.5 micrograms mL-1. Other related xanthones were also examined to determine their anti-MRSA activity. Rubraxanthone, which was isolated from Garcinia dioica and has a structure similar to that of alpha-mangostin, had the highest activity against staphylococcal strains (MIC = 0.31-1.25 micrograms mL-1), an activity which was greater than that of the antibiotic vancomycin (3.13-6.25 micrograms mL-1). The inhibitory effect against strains of MRSA of two of the compounds when used in conjunction with other antibiotics was also studied. The anti-MRSA activity of alpha-mangostin was clearly increased by the presence of vancomycin; this behaviour was not observed for rubraxanthone. The strong in-vitro antibacterial activity of xanthone derivatives against both methicillin-resistant and methicillin-sensitive Staphylococcus aureus suggests the compounds might find wide pharmaceutical use.

Comparative study on the antibacterial activity of phytochemical flavanones against methicillin-resistant Staphylococcus aureus

Differently substituted flavanones were isolated from Leguminosae and their antibacterial activity was comparatively studied against methicillin-resistant Staphylococcus aureus (MRSA). The minimum inhibitory concentrations (MICs) of phytochemical flavanones to clinical isolates of MRSA were determined by a serial agar dilution method. The structure-activity relationship has indicated that 2',4'- or 2',6'-dihydroxylation of the B ring and 5,7-dihydroxylation of the A ring in the flavanone structure are important for significant anti-MRSA activity and that substitution with a certain aliphatic group at the 6- or 8-position also enhances the activity. Among the thirteen flavanones tested, tetrahydroxyflavanones with these structural characteristics isolated from Sophora exigua and Echinosophora koreensis showed intensive activity to inhibit the growth of all MRSA strains at 3.13-6.25 micrograms/ml. The present hydroxyflavanones would be useful in the phytotherapeutic strategy against MRSA infections.

Antibacterial activity of flavanostilbenes against methicillin-resistant Staphylococcus aureus

Three phytochemical compounds (alopecurone A-C), flavanostilbenes which are produced by condensation between a hydroxyflavanone and a hydroxystilbene, were isolated as major components from the root of Sophora alopecuroides. They uniformly inhibited the growth of 21 strains of methicillin-resistant Staphylococcus aureus with minimum inhibitory concentrations of 3.13-6.25 micrograms ml-1.

Immunological detection of penicillin-binding protein 2' of methicillin-resistant staphylococci by using monoclonal antibodies prepared from synthetic peptides

Two synthetic peptides 31 and 32 amino acids in length were prepared as deduced from a known amino acid sequence of penicillin-binding protein 2' (PBP2') of methicillin-resistant Staphylococcus aureus. Two monoclonal antibodies were generated from fused cells of myeloma cells and splenic cells of mice immunized with the synthetic peptides. Western blot (immunoblot) analysis demonstrated specific binding of the antibodies to PBP2' of a methicillin-resistant S. aureus strain. An immunoradiometric assay was developed by using these antibodies for simple detection of PBP2'.

Detection of methicillin-resistant Staphylococcus aureus (MRSA) with antibodies against synthetic peptides derived from penicillin-binding protein 2'

Ten kinds of peptides (21 to 32 amino acids in length) were synthesized based on the reported amino acid sequences of the penicillin-binding protein 2' (PBP2') of methicillin-resistant Staphylococcus aureus (MRSA). Antibodies against these synthetic peptides (SPs) were generated by immunizing rabbits. The antibodies raised against all the peptides except for one reacted to PBP2' of MRSA and to SPs used for immunization but not to any other protein of MRSA or methicillin-susceptible S. aureus (MSSA) tested by ELISA and Western blotting. A sandwich immunoradiometric assay (IRMA) for the detection of PBP2' was developed using these antibodies. The method could detect PBP2' extracted from as few as 3 x 10(4) cells of a clinical MRSA isolate, and a good correlation between cell number and signal radio-count was observed. IRMA was positive for all 51 methicillin-resistant staphylococci isolated from patients, and was negative for all the 28 methicillin-susceptible ones and 19 strains of other bacterial species. IRMA could be a simple and reliable method for MRSA detection in the clinical bacterial laboratory.

Typing of Staphylococcus aureus strains by PCR-amplification of variable-length 16S-23S rDNA spacer regions: characterization of spacer sequences

To develop a rapid and accurate method of typing large numbers of clinical isolates of Staphylococcus aureus, the spacer region C of the rRNA operon [1391-507 (16S-23S)] was enzymically amplified from 322 strains. When the products were separated by denaturing PAGE, 15 variable-length rrn alleles were demonstrated, ranging in size from 906 to 1223 bp. The variable-length HpaII-digested region C [(region E; 1446-196 (16S-23S)] amplification products were cloned into M13mp18RF to sequence separate variable-length alleles. A total of 17 region E inserts were sequenced, aligned and divided into nine alleles by length (938-1174) and sequence properties. The 16S-23S spacer rDNA varied in length (303-551 bp) and in properties; three alleles contained a tRNAIle gene alone, two alleles contained a tRNAIle and a tRNAAla gene, and four alleles lacked tRNA genes. The sequences of two alleles showed less than 1% variation when isolated from two or three S. aureus strains. The 48 penicillin- and methicillin-sensitive strains were divided into 26 ribotypes; in contrast, the 274 methicillin-resistant S. aureus (MRSA) strains were divided into nine ribotypes (A-I) with 97% typing as either ribotype A or B (rrnL was missing in B). The sequence conservation of the rrn operons argues for the use of the 16S-23S spacer region as a stable and direct indicator of the evolutionary divergence of S. aureus strains.

Flavanones with potent antibacterial activity against methicillin-resistant Staphylococcus aureus

With the therapeutic concept of using the defensive ability of plants against microbial infections, phytoalexin, an antimicrobial phytochemical was studied for its ability to inhibit the growth of methicillin-resistant Staphylococcus aureus (MRSA). Extracts from Sophora exigua (Leguminosae) were fractionated by serial chromatography and the anti-MRSA activity of each fraction was determined by the agar-plate method. Among the active isolates, 5,7,2',6'-tetrahydroxy-6-isoprenyl-8-lavandulyl-4'-methox yflavanone (exiguaflavanone D) completely inhibited the growth of all the MRSA strains examined at the concentration of 1.56-6.25 micrograms mL-1, and 5, 2',6'-trihydroxy-8-lavandulyl-7-methoxy-flavanone (exiguaflavanone B) inhibited at a concentration of 50 micrograms mL-1. This former compound is expected to be a phytotherapeutic agent for MRSA infections as an alternative to conventional antibiotics with unwanted side-effects or the appearance of antibiotic-resistant bacteria.

Teicoplanin versus cefamandole in the prevention of infection in total hip replacement

In a prospective, controlled, single-blind study the efficacy of teicoplanin versus cefamandole in preventing infections in total hip replacement was investigated in 496 consecutive patients. A single intravenous dose of teicoplanin (400 mg) was as effective as two intravenous doses of cefamandole (2 g before and 1 g after surgery). No major complications were observed in either group. Infective wound complications were observed only in the cefamandole group. These infections, although not dangerous for the patients, required supplementary antibiotic treatment in all cases. Teicoplanin is a reasonable choice as a prophylactic agent in orthopaedic surgery when a high risk of infection due to staphylococci is present.

Ribotyping of Staphylococcus aureus: an assessment using well-defined strains

Ribotyping, with homologous or heterologous (Escherichia coli) r-RNA, of the propagating strains for phages of the international set for strains of Staphylococcus aureus of human origin was undertaken to determine the discrimination of this typing method. Ribotyping could distinguish between strains of different phage groups, but could not distinguish between seven phage group III strains of different phage type. Ribotying may be a useful adjunct to phage typing in S. aureus but is unlikely to replace it as the primary method of epidemiological typing.

Prospective study of infection, colonization and carriage of methicillin-resistant Staphylococcus aureus in an outbreak affecting 990 patients

In the three years between November 1989 and October 1992, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) affected 990 patients at a university hospital. The distribution of patients with carriage, colonization or infection was investigated prospectively. Nosocomial acquisition was confirmed in at least 928 patients, 525 of whom were identified from clinical specimens as being infected (n = 418) or colonized (n = 107) by MRSA. An additional 403 patients were identified from screening specimens, of whom 58 subsequently became infected and 18 colonized. Screening of the nose, throat and perineum detected 98% of all carriers. Of the 580 infections in 476 patients, surgical wound, urinary tract and skin infections accounted for 58% of the infections. Of the 476 infected patients, death was attributable to MRSA infection in 13%. Colonization with MRSA was found in 127 patients and 42% of 165 colonized sites were the skin. Auto-infection from nasal carriage or cross-infection, probably via staff hands, seemed to be the most common mode of acquisition of MRSA infections.

The significance of methicillin-resistant Staphylococcus aureus infection in general surgery: a multivariate analysis of risk factors and preventive approaches

To investigate the characteristics, risk factors, and prevention of methicillin-resistant Staphylococcus aureus (MRSA), a total of 3,627 patients were studied. Among these, 1,336 patients with various infections were used in a risk factor analysis of MRSA to determine the relationship between the use of antibiotics and the incidence of MRSA. Only 3.0% of infections were attributed to MRSA, the esophagus and colorectal region being highly involved, as anastomotic or pelvic abscesses, while the lung had a lower incidence. Almost half the patients with MRSA infections (47.6%) had concomitant infection. A univariate analysis revealed the following significant factors: The coexistence of gastrointestinal or metastatic malignancy, sepsis, tracheostomy, and the prior use of antibiotics such as the beta-lactam compounds or aminoglycosides. A multivariate analysis showed that gastrointestinal malignancy, sepsis, and the prior use of aminoglycosides, tetracycline, macrolides, and carbapenems were independently significant factors. To promote the education of doctors and nurses, regular in-service meetings on MRSA were held in the ward. Moreover, preventive approaches such as patient isolation, strategically placed hand washing equipment, and the use of disposable gloves and contaminated waste bags, have been initiated, and the incidence of MRSA has decreased significantly since then. Thus, to control MRSA, the following steps should be taken: (1) constant and careful surveillance, (2) regular risk factor analyses, (3) the optimal administration of antibiotics, and (4) the education of all hospital staff.

Hospital infections in Spain. I. Staphylococcus aureus (1978-91)

This study was undertaken to determine the distribution of phage types of Staphylococcus aureus isolates from hospital outbreaks or sporadic cases received in our laboratory during the past 14 years. The records for 15,803 isolates from 55 Spanish hospitals have been analysed. In relation to sporadic isolates we have been able to detect the predominance of phage group I and non-typable staphylococcal strains. Since 1989, we have observed a considerable increase in hospital infection caused by methicillin-resistant S. aureus strains which we could differentiate in to two groups; one belonging to phage group III (6/47/54/75/77/84/85) and other groups of nontypable strains which could be classified as phage group I-III after heat treatment (29/77/84) and with similar patterns by reverse typing (6/47/53/54/75/83A/84/85/W57/1030/18042). During 1990 and 1991, these strains have extended widely to at least six different autonomous regions creating an epidemic situation in Spain.