The epidemiology of methicillin-resistant Staphylococcus aureus at a Saudi university hospital

To determine changes in the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA), a prospective study was conducted for a 30-month period in a university hospital in the eastern province of Saudi Arabia. Of 1,096 Staphylococcus aureus isolates identified, 92 (8.4%) were MRSA. Seventy-two (78%) of the 92 isolates were from nosocomial cases and 20 (22%) isolates were from community cases. Thirteen (14%) of 20 patients with community-acquired MRSA had no discernible risk factors. The community-acquired MRSA from patients without identified risk were susceptible to a greater number of antimicrobials compared with isolates obtained from patients with community-acquired MRSA with identified risk or with nosocomially acquired MRSA. No strain resistant to vancomycin was recorded in this study. The impact of these organisms could be substantial if they become more frequent or widespread.     

Increased vancomycin MICs for Staphylococcus aureus clinical isolates from a university hospital during a 5-year period

Staphylococcus aureus is one of the most commonly isolated organisms in nosocomial infections. While the prevalence of methicillin-resistant S. aureus (MRSA) continues to increase worldwide, there is concern about an increase in vancomycin MICs among S. aureus strains. The prevalence of MRSA and vancomycin MIC trends in S. aureus from patients in a university hospital were analyzed. Clinical Laboratory Standards Institute (CLSI, formerly NCCLS) reference broth microdilution MIC testing was performed on all clinically relevant S. aureus isolates from January 2000 through December 2004. A total of 6,003 S. aureus isolates were analyzed. No vancomycin-resistant S. aureus isolates were detected. One MRSA isolate had a vancomycin MIC of 8 mug/ml and was confirmed as vancomycin-intermediate S. aureus. Among the 6,002 remaining isolates, a shift in vancomycin MICs from 相似文献   

Tracking methicillin-resistant Staphylococcus aureus clones during a 5-year period (1998 to 2002) in a Spanish hospital

Three hundred seventy-five consecutive methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates recovered between 1998 and 2002 at the Nuestra Señora de Candelaria University Hospital in Tenerife, Spain, were analyzed by molecular fingerprinting techniques to determine MRSA clonal types and their prevalence over time. After determining antibiotic susceptibility, we used SmaI-digested genomic DNA separated by pulsed-field gel electrophoresis (PFGE) to characterize MRSA isolates and to establish PFGE types. Additionally, several selected isolates representative of each major PFGE type were tested by multilocus sequence typing (MLST) and by a multiplex PCR method capable of identifying the structural type of the staphylococcal cassette chromosome mec (SCCmec), generating the corresponding sequence type (ST)-SCCmec types. Results of PFGE, supported by those of MLST and SCCmec typing, allowed us to identify six MRSA clones within the five major PFGE types and document temporal shifts in the prevalence of these MRSA clones from 1998 to 2002. Four of the clones were the pandemic “Iberian” (designated ST247-MRSA-IA), EMRSA-15 (ST22-MRSA-IV), EMRSA-16 (ST36-MRSA-II), and the so-called pediatric (ST5-MRSA-IV) clones, while the other two (ST125-MRSA-IVA and ST146-MRSA-IVA) clones could be derived from the pediatric one. The most striking temporal shift in the dominance of MRSA clones was the replacement of the multidrug-resistant and highly epidemic Iberian clone by the so-called British EMRSA-16 clone during the 5-year surveillance period. Our results are in accordance with previously stated findings showing the worldwide hospital dominance of relatively few pandemic and presumably virulent MRSA clones. We report for the first time the detection in Spain of the British EMRSA-15 and pediatric clones, as well as the abrupt replacement of the Iberian by the EMRSA-16 as the major MRSA clone.Staphylococcus aureus is the causal agent of most staphylococcal pathologies and is currently a versatile microbial pathogen that has evolved resistance to all antibiotic classes. It is associated with serious community-acquired and nosocomial diseases, although most life-threatening S. aureus infections are hospital acquired (4, 8). Its high level of adaptation to hospital environments has been deeply facilitated by the acquisition of methicillin resistance, an evolutionary step that converted S. aureus to methicillin-resistant S. aureus (MRSA), one of the most common nosocomial pathogens nowadays (19). MRSA emerged with the introduction of an exogenous DNA element into its genome, the staphylococcal cassette chromosome mec (SCCmec), which carries the methicillin resistance mecA gene (16). Recent data shows that acquisition of SCCmec has occurred on multiple occasions and that at least five different methicillin-sensitive S. aureus phylogenetic lineages acquired the element (29). Four main structural types of SCCmec, which differ in size and composition, have been described for S. aureus (14, 15, 20).Genetic studies using molecular typing methods have shown that most hospital-acquired MRSA infections worldwide are due to any of the so-called epidemic MRSA (EMRSA). These EMRSA clones present great fitness to hospital environments and, consequently, are established in many hospitals and have spread internationally (7). This situation highlights the importance of monitoring the distribution and routes of dissemination of such EMRSA clones at both levels, within hospitals and between distant locations (24). With this purpose, several molecular techniques and an international common nomenclature have been applied to track EMRSA (10, 27). Pulsed-field gel electrophoresis (PFGE) is considered the “gold standard” for establishing clonal relationships at the local level, but its detection capacity seems to make it also too discriminative for global comparisons (5, 31). By contrast, multilocus sequence typing (MLST) has been verified as an adequate method for long-term and global epidemiological studies (11, 48). Combination of MLST with SCCmec typing permits the unambiguous assignment of collections of MRSA isolates to known or new MRSA clones (10).The aim of this study was to identify MRSA clones circulating in the Nuestra Señora de Candelaria University Hospital (HUNSC), Tenerife, Spain, and to track shifts in their prevalence during a 5-year period (1998 to 2002). For this purpose, we used a combination of different molecular typing methods, including PFGE, MLST, and SCCmec typing.     

Longitudinal study of the molecular epidemiology of methicillin-resistant Staphylococcus aureus at a university hospital

Surveillance for methicillin-resistant Staphylococcus aureus (MRSA) at the University Hospital of Heidelberg revealed an increase in the numbers of newly detected MRSA isolates in recent years. We conducted a study to assess the dynamics of the changes in the MRSA population. Pulsed-field gel electrophoresis (PFGE) typing of MRSA isolates from all patients at the University Hospital of Heidelberg collected between 1993 and 2004 was performed. The microbiology database contained 1,807 entries for newly detected MRSA isolates from 1,301 patients. A total of 1,252 isolates were available for PFGE typing. The isolates could be classified into 109 different PFGE types. Most PFGE types (n=70) were detected less than five times and showed no evidence of transmission (sporadic strains). They accounted for 8.7% of all isolates, with few variations in frequency over the time. Thirty-seven PFGE types were clustered by time of detection, and transmission of the strains was likely (local epidemic strains). A total of 37.3% of the isolates belonged to this group of strains. The remaining 54.0% of the isolates belonged to only two further PFGE types (endemic strains). One endemic strain accounted for 5.0% of all isolates in 1994 and 68.2% in 2004. A second endemic strain was detected in 1.1% of all isolates in 1998 but in 12.4% in 2004. Statistical analysis of the associations between the kind of strain (sporadic, local epidemic, or endemic) and the patients' characteristics revealed a significant association for age and mode of acquisition. The remarkable increase in the rate of MRSA detection at the University Hospital of Heidelberg is mainly due to the dissemination of two different strains. Infection control measures seemed sufficient to prevent further transmission of some but not all of the strains.     

Emergence of rifampicin resistance in methicillin-resistant Staphylococcus aureus isolated at a Turkish university hospital

Twenty-three rifampicin-resistant methicillin-resistant Staphylococcus aureus (MRSA) isolated in three wards at a university hospital in Turkey between June, 2000, and February, 2001, were studied for their genetic relatedness using a combination of antibiogram, coagulase serotyping, coagulase gene polymorphism (coa-RFLP), and pulsed-field gel electrophoresis (PFGE). They all expressed high-level rifampicin resistance (MIC, >256 mg/L) and were resistant to gentamicin, kanamycin, amikacin, ciprofloxacin, tetracycline, and cadmium acetate and were susceptible to fusidic acid, vancomycin, trimethoprim, and mupirocin. They belonged to the same coagulase serotype (serotype IV) and had identical coa-RFLP patterns. In contrast, PFGE generated nine banding patterns designated type A, types A1-A5, B, C, and D. The most common PFGE pattern (type A) and its subtypes (types A1-A5) were seen in 20 (87%) of the 23 isolates in the three wards. The results demonstrated the acquisition of rifampicin resistance by different MRSA clones and the spread of one clone among patients in the three wards.     

Heterogeneity of methicillin-susceptible Staphylococcus aureus strains at a German University Hospital implicates the circulating-strain pool as a potential source of emerging methicillin-resistant S. aureus clones

Recently, we demonstrated rapid dissemination of different methicillin-resistant Staphylococcus aureus (MRSA) clones at the Institute for Microbiology at the University of Magdeburg (B. Ghebremedhin, W. K?nig, and B. K?nig, Eur. J. Clin. Microbiol. Infect. Dis. 24:388-398, 2005). The majority of them harbored the readily transmissible mec cassette type IV. Thus, theoretically, methicillin-susceptible Staphylococcus aureus (MSSA) might capture the mecA gene from circulating MRSA, or MRSA strains might catch mobile toxin genes from MSSA. Therefore, we characterized MSSA strains circulating at the University Hospital in Magdeburg. Among a total of 84 MSSA strains under study, about 40% possessed the tst (toxic shock syndrome toxin) gene and up to four additional enterotoxin genes. tst-positive MSSA strains belonged to all known agr groups (I to IV) and to 14 different spa types (t008, t012, t015, t019, t024, t056, t065, t127, t133, t162, t271, t287, t399, and t400), and they were classified by multilocus sequence typing (MLST) as ST1, ST8, ST30, ST39, ST45, ST101, ST121, ST395, and ST426. In contrast, simultaneously circulating MRSA strains (n = 24) harbored in general two or three genes of the enterotoxin gene cluster, and the tst-positive MRSA isolates belonged to the well-known epidemic types ST22, ST45, and ST228 and were classified as spa types t001, t028, and t032. From our results, one may conclude that the pool of circulating MSSA strains is an important parameter with regard to the epidemiology of hospital- and community-acquired MRSA clones and their potential virulence.     

Molecular characterization of methicillin-resistant Staphylococcus aureus isolated over a 2-year period in a Qatari hospital from multinational patients

Global spread of epidemic methicillin-resistant Staphylococcus aureus (MRSA) is an issue of increasing clinical concern especially problematic community-associated (CA) -MRSA. However, data regarding MRSA epidemiology in regions of the Middle East, including Qatar, are still insufficient. A representative subset of 61 MRSA isolates from multinational patients from hospital in Qatar during a 2-year period (2009/2010) was examined. Molecular characterization for MRSA isolates was performed by pulsed-field gel electrophoresis (PFGE), SCCmec, spa and dru typing, and PCR for the presence of the arginine catabolic mobile element and genes for the Panton–Valentine leukocidin (PVL). Prevalence of MRSA among S. aureus isolated was 176/840 (21%). Of the 61 MRSA isolates examined, three (5%) represented hospital-acquired infection. By PFGE, 32 isolates (52%) were CA-MRSA USA300 (n = 4), USA400 (n = 3), USA1100/Southwest (SW) Pacific (n = 17) and ST80-MRSA-IV (n = 8) strains. The remaining isolates were well-known healthcare-associated EMRSA-15 (n = 8) and USA800 (n = 13). Three isolates were USA900, one was USA1200 and four were unrelated to any known strains in the international database. Unexpectedly, the USA900 isolates were all positive for PVL and USA400 isolates were PVL negative. Five of the eight EMRSA-15 isolates were PVL positive. ST80-MRSA-IV and USA300 strains exhibited typical dru types (dt10a and dt9g, respectively). Eleven different spa types were observed in this study. All USA300 isolates were arginine catabolic mobile element positive. The high prevalence of CA-MRSA, especially including USA300, in this setting underscores the importance of global epidemiological monitoring to better understand and hopefully help prevent the emergence and spread of these problem pathogens in patient populations.     

Molecular genotyping of methicillin-resistant Staphylococcus aureus strains in a teaching hospital in Turkey

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of nosocomial infections in our hospital. Therefore, we aimed to characterize MRSA isolates phenotypically from patients with nosocomial infections at Cumhuriyet University Hospital between December, 1999, and June, 2001, in Sivas by analysis of antibiotic patterns and genotypically using pulsed-field gel electrophoresis (PFGE) and repetitive element sequence-based polymerase chain reaction (rep-PCR). Forty-three nosocomial isolates were collected from various wards. All isolates were resistant to penicillin, tetracycline, oxacillin, and gentamicin. By rep-PCR and by separation of SmaI fragments of genomic DNA using PFGE, one major type (eight subtypes with PFGE) was identified among the strains. This clone was found to be different than some clones such as Iberian, Brazilian, and a major clone that was found in another Turkish University Hospital in Ankara. According to our results, there is a major MRSA clone with a potential to spread in our hospital. Infection control measures should be directed toward restricting the further spread of this clone. Therefore, in accordance with these findings, a surveillance culturing program should be established.     

Heterogeneity of methicillin-resistant Staphylococcus aureus isolated in Norway

Our objective was to look for differences in susceptibility patterns between Norwegian and imported methicillin-resistant Staphylococcus aureus (MRSA) strains. All MRSA isolates from the participating hospitals (87 isolates from 81 patients) throughout the period 1994–98 were examined, to study the clonal distribution of MRSA isolated in Norway and to identify any epidemic clones among the isolates. We found that imported isolates were resistant to an average of 5.6 antibiotics, while Norwegian isolates were resistant to an average of 2.6 antibiotics. MRSA isolates imported to Norway are more often multiresistant than domestic isolates. MRSA isolates in Norway show a striking diversity. Epidemic clones are present, but no single clone is predominant.     

Lysogenicity of methicillin-resistant strains of Staphylococcus aureus

The lysogenic status of 23 strains of methicillin-resistant Staphylococcus aureus, isolated at the Royal Prince Alfred Hospital, Sydney, since 1980, was studied. Twenty strains, belonging to the four predominant phage types isolated in this hospital, carried the same lysogenic phage which we have designated C. Three other phages were isolated from five strains belonging to phage type 84/85/90. The presence of phage C had little effect on the phage-typing pattern of the strains. Similarly, lysogenization with the other three phages did not result in a significant change in phage-typing patterns. However, when strain 1489, isolated in 1969, was lysogenized with these three phages, there was a change in phage-typing pattern. Lysogenization of this strain with phage 47T resulted in a marked loss of sensitivity to both group-I and group-III phages. The lysogenic status of these methicillin-resistant strains of S. aureus was compared with that of strains isolated between 1967 and 1970. There was no evidence that the strains isolated recently were either related to, or derived from, the earlier ones.     

Heterogeneous vancomycin resistance in methicillin-resistant Staphylococcus aureus strains isolated in a large Italian hospital

Of 179 methicillin-resistant Staphylococcus aureus strains isolated from 1997 to 1998, two strains (1.1%) gave subclones for which the vancomycin MICs were 8 mg/liter. Pulsed-field gel electrophoresis showed identical restriction patterns for both isolates, suggesting transfer of a single clone between two different patients.     

Eradication of an epidemic methicillin-resistant Staphylococcus aureus (MRSA) from a geriatric university hospital: evidence from a 10-year follow-up

We report on a successful eradication of methicillin-resistant S. aureus (MRSA) after an epidemic in 1992 in the geriatric ward of a tertiary-care hospital. After identification of MRSA in seven patients, all patients and staff members in the geriatric ward underwent screening. A multifaceted intervention plan was implemented: contact isolation, optimization of infection control and decolonization of all MRSA carriers. Thirty-two patients and five staff members were found to be MRSA carriers. Twenty one of 32 (66%) patients and all five staff members were successfully decolonized. Seven of 32 (22%) patients died during the epidemic before decolonization. A couple was discharged with persisting MRSA colonization and two individuals were lost to follow-up. The eradication of the epidemic clone was proven by systematic screenings in 1995 and 1997. Since then, the strain has no longer been identified in our institution, based on epidemiological surveillance and molecular typing of all MRSA strains obtained from any specimen. This study provides strong evidence that long-term eradication of an MRSA epidemic in a hospital is feasible, and endemicity of MRSA after an outbreak can be avoided. The successful bundle approach for eradication of MRSA during an epidemic is expensive, but the long-term benefits likely outweigh the initial heavy use of resources.     

Two international methicillin-resistant Staphylococcus aureus clones endemic in a university hospital in Patras,Greece

Pulsed-field gel electrophoresis (PFGE) of SmaI macrofragments and hybridization of ClaI digests with the mecA- and Tn554-specific DNA probes were used to define the endemic clones of methicillin-resistant Staphylococcus aureus (MRSA) among strains collected in 1993 and 1998 to 2000 at the University Hospital of Patras, Patras, Greece. Representatives of each clonal type were analyzed by spaA typing, multilocus sequence typing (MLST), and staphylococcal chromosomal cassette mec (SCCmec) typing. The results indicated the existence of two successive international MRSA clones: (i) a clonal type with PFGE type A, sequence type (ST) 30 (ST30), and SCCmec type IV, which was very similar to a clone widely spread in the United Kingdom, Mexico, and Finland, and (ii) a clonal type with PFGE type B, ST239, and SCCmec III, which was related to the Brazilian clone. Both clones seem to be widespread in Greece as well. A novel MRSA clone is also described and is characterized by a new MLST type (ST80) associated with SCCmec type IV and with the presence of Panton-Valentine leukocidin genes.     

Loss of the mecA gene during storage of methicillin-resistant Staphylococcus aureus strains

The mecA gene was lost in 36 (14.4%) of 250 methicillin-resistant Staphylococcus aureus isolates after 2 years of storage at -80 degrees C with the Microbank system (Pro-lab Diagnostics, Austin, Tex.). Further analysis of 35 of these isolates confirmed loss of the mecA gene in 32 isolates. This finding has important implications for the management of strain collections.     

Heterogeneity of disease and clones of community-onset methicillin-resistant Staphylococcus aureus in children attending a paediatric hospital in Belgium

The increase in the number of methicillin-resistant Staphylococcus aureus (MRSA) infections in children has prompted paediatricians to broaden th empirical treatment of common community-onset (CO) infections in children in several countries. Most European countries have reported low rates of CO-MRSA infection, but limited data on paediatric CO-MRSA infections are available. A prospective study was conducted from January 2002 to December 2004 in Brussels. CO-MRSA was defined as MRSA first detected by culture within 48 h of admission or in outpatients. Clinical and epidemiological data were recorded. CO-MRSA strains were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Staphylococcal chromosomal cassette mec, toxin (Panton-Valentin leukocidin (PVL), toxic shock syndrome toxin 1, and Eta/b), enterotoxin and antibiotic resistance genes were detected by PCR. The antibiotic resistance phenotype was determined by disk diffusion. S. aureus was isolated in 1681 children. Among these, 107 harboured MRSA. Fifty-one children were colonized or infected by CO-MRSA, 20% of whom had no healthcare exposure. Twelve infants <3 months old and five cystic fibrosis patients were colonized. None of the 22 infected patients (59% with acute otitis media and 36% with skin and soft tissue infections (SSTIs)) required hospitalization. Two-thirds of them failed to respond to empirical antibiotic therapy. The 37 characterized CO-MRSA strains were genetically diverse. Most of them had healthcare-associated genotypes. Only six strains were PVL-positive, all of which were ciprofloxacin-susceptible and more common in children with SSTIs (p 0.001). CO-MRSA remains uncommon in our paediatric population. So far, there is no need to modify the empirical treatment of common S. aureus infections. Monitoring of MRSA rates in S. aureus CO infections remains mandatory, and further investigation is warranted to establish the source of colonization in young infants.     

Undecatungstophosphate sensitized strains of methicillin-resistant Staphylococcus aureus to beta-lactams

Previously, a factor (Factor T) was found in aged mixtures of tungstate and phosphate, which greatly sensitizes strains of methicillin-resistant Staphylococcus aureus to beta-lactams. Factor T was purified and identified as undecatungstophosphate([PW11O39]7-). Undecatungstosilicate([SiW11O39]8-), a compound closely related to undecatungstophosphate, showed a similar enhancing effect. Chemically, these compounds are classified as "polyoxotungstates", and it is expected that these tungsten compounds will be useful as a "tool" in laboratory tests: i.e., in screening media for highly resistant MRSA strains. They may be also useful to investigate the resistant mechanism of the bacterial cells.     

Nasal carriage of Staphylococcus aureus and its influence on hospital infections caused by methicillin-resistant strains

A short review of the literature on the actual epidemiological situation related to nosocomial infections caused by methicillin-resistant Staphylococcus aureus and the importance of the nasal carriage of this pathogen is given together with selected data derived from our own studies on these problems.