Emergence and spread of gentamicin-susceptible strains of methicillin-resistant Staphylococcus aureus in Belgian hospitals

Global prevalence and distribution of vancomycin resistant, vancomycin intermediate and heterogeneously vancomycin intermediate Staphylococcus aureus clinical isolates: a systematic review and meta-analysis

Vancomycin-resistant Staphylococcus aureus (VRSA), Vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) are subject to vancomycin treatment failure. The aim of the present study was to determine their precise prevalence and investigate prevalence variability depending on different years and locations. Several international databases including Medline (PubMed), Embase and Web of Sciences were searched (data from 1997 to 2019) to identify studies that addressed the prevalence of VRSA, VISA and hVISA among human clinical isolates around the world. Subgroup analyses and meta-regression were conducted to indicate potential source of variation. Publication bias was assessed using Egger's test. Statistical analyses were conducted using STATA software (version 14.0). Data analysis showed that VRSA, VISA and hVISA isolates were reported in 23, 50 and 82 studies, with an overall prevalence of 1.5% among 5855 S. aureus isolates, 1.7% among 22,277 strains and 4.6% among 47,721 strains, respectively. The overall prevalence of VRSA, VISA, and hVISA before 2010 was 1.2%, 1.2%, and 4%, respectively, while their prevalence after this year has reached 2.4%, 4.3%, and 5.3%. The results of this study showed that the frequency of VRSA, VISA and hVISA after 2010 represent a 2.0, 3.6 and 1.3-fold increase over prior years. In a subgroup analysis of different strain origins, the highest frequency of VRSA (3.6%) and hVISA (5.2%) was encountered in the USA while VISA (2.1%) was more prevalent in Asia. Meta-regression analysis showed significant increasing of VISA prevalence in recent years (p value ≤ 0.05). Based on the results of case reports (which were not included in the calculations mentioned above), the numbers of VRSA, VISA and hVISA isolates were 12, 24 and 14, respectively, among different continents. Since the prevalence of VRSA, VISA and hVISA has been increasing in recent years (especially in the Asian and American continents), rigorous monitoring of vancomycin treatment, it's the therapeutic response and the definition of appropriate control guidelines depending on geographical regions is highly recommended and essential to prevent the further spread of vancomycin-resistant S. aureus.

Dynamic of livestock-associated methicillin-resistant Staphylococcus aureus CC398 in pig farm households: a pilot study

The aim of this study was to determine the long-term carriage rates and transmission dynamics of methicillin-resistant Staphylococcus aureus (MRSA) in pig farmers and their household members. During a 6-month period in 2009-2010, 4 pig farms in Denmark, Belgium, and the Netherlands, respectively, were studied for the presence of MRSA. The proportion of persistent carriers was significantly higher among farmers than among household members (87% vs. 11%) and significantly higher in household members from Belgium compared to those from Denmark and the Netherlands (29% vs. 0% vs. 6%). Determinant analysis of MRSA carriage revealed that pig contact was the most important determinant for MRSA carriage among household members and that the increased MRSA carriage rate observed among household members from Belgium is linked to country-specific differences in pig exposure. These findings demonstrated that even in pig farms with very high carriage rates of MRSA both in livestock and farmers, the risk for household members to acquire MRSA is limited and still depends strongly on pig exposure. By restricting access to the stables and exposure to pigs, MRSA acquisition by household members could be greatly reduced.

Epidemiological investigation of a nosocomial outbreak of multidrug-resistant Corynebacterium striatum at one Belgian university hospital

During an 8-month period, 24 Corynebacterium striatum isolates recovered from lower respiratory tract specimens of 10 hospitalized patients were characterized. The organisms were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and by 16S rRNA gene sequencing. The cluster of C. striatum exclusively affected patients who had been admitted to an intensive care unit and/or subsequently transferred to one medium-size respiratory care unit. Prolonged duration of hospitalization, advanced stage of chronic obstructive pulmonary disease, recent administration of antibiotics and exposure to an invasive diagnostic procedure were the most commonly found risk factors in these patients. Seven patients were colonized and three infected. All strains displayed a similar broad spectrum resistance to antimicrobial agents, remaining susceptible to vancomycin only. Typing analysis by MALDI-TOF MS and by semi-automated repetitive sequence-based PCR (DiversiLab typing) showed that all outbreak-associated C. striatum isolates clustered together in one single type while they differed markedly from epidemiologically unrelated C. striatum isolates. Pulsed-field gel electrophoresis (PFGE) profiles revealed three distinct PFGE types among the C. striatum isolates associated with the outbreak while all external strains except one belonged to a distinct type. We conclude that C. striatum is an opportunistic nosocomial pathogen in long-term hospitalized patients and can be at the origin of major outbreaks. The routine use of MALDI-TOF MS greatly facilitated the recognition/identification of this organism in clinical samples and this technique could also offer the potential to be used as an easy and rapid epidemiological typing tool for outbreak investigation.

CC8 MRSA strains harboring SCCmec type IVc are predominant in Colombian hospitals

Background

Recent reports highlight the incursion of community-associated MRSA within healthcare settings. However, knowledge of this phenomenon remains limited in Latin America. The aim of this study was to evaluate the molecular epidemiology of MRSA in three tertiary-care hospitals in Medellín, Colombia.

Methods

An observational cross-sectional study was conducted from 2008–2010. MRSA infections were classified as either community-associated (CA-MRSA) or healthcare-associated (HA-MRSA), with HA-MRSA further classified as hospital-onset (HAHO-MRSA) or community-onset (HACO-MRSA) according to standard epidemiological definitions established by the U.S. Centers for Disease Control and Prevention (CDC). Genotypic analysis included SCCmec typing, spa typing, PFGE and MLST.

Results

Out of 538 total MRSA isolates, 68 (12.6%) were defined as CA-MRSA, 243 (45.2%) as HACO-MRSA and 227 (42.2%) as HAHO-MRSA. The majority harbored SCCmec type IVc (306, 58.7%), followed by SCCmec type I (174, 33.4%). The prevalence of type IVc among CA-, HACO- and HAHO-MRSA isolates was 92.4%, 65.1% and 43.6%, respectively. From 2008 to 2010, the prevalence of type IVc-bearing strains increased significantly, from 50.0% to 68.2% (p = 0.004). Strains harboring SCCmec IVc were mainly associated with spa types t1610, t008 and t024 (MLST clonal complex 8), while PFGE confirmed that the t008 and t1610 strains were closely related to the USA300-0114 CA-MRSA clone. Notably, strains belonging to these three spa types exhibited high levels of tetracycline resistance (45.9%).

Conclusion

CC8 MRSA strains harboring SCCmec type IVc are becoming predominant in Medellín hospitals, displacing previously reported CC5 HA-MRSA clones. Based on shared characteristics including SCCmec IVc, absence of the ACME element and tetracycline resistance, the USA300-related isolates in this study are most likely related to USA300-LV, the recently-described ‘Latin American variant’ of USA300.

Diversity of accessory genome of human and livestock-associated ST398 methicillin resistant Staphylococcus aureus strains

BACKGROUND

Molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) has documented the diversity of the genetic background of strains associated with healthcare (HA-MRSA), community (CA-MRSA) and livestock (LA-MRSA). The accessory and core-variable genomes of those strains however remain largely unknown.

OBJECTIVE

To compare the genetic background and accessory and core variable gene content of ST398 LA-MRSA strains with those of HA-and CA-MRSA strains from the same region.

METHODS

Representative strains of HA- (n=21), CA- (n=13) and ST398 LA-MRSA (n=18) were selected from Belgian National Reference Laboratory collections. The accessory and core-variable genomes of these strains were characterized by a DNA-microarray composed of oligonucleotide probes targeting ~400 resistance, adhesion and virulence associated genes.

RESULTS

ST398 strains displayed very homogenous hybridization profiles irrespective of their host origin. This ST398 genomic profile was moderately related to that of certain human HA- or CA-lineages but distinctively lacked several virulence- and colonization-associated genes implicated in carriage in humans, such as proteases and adhesins. No enterotoxin gene was found among ST398 strains. Differences were observed in the mobile resistance gene content of ST398 strains, including antibiotic resistance determinants.

CONCLUSION

LA-MRSA strains represent a homogenous lineage distinct from co-local HA- and CA-MRSA strains, especially in its accessory genome content characterized by a lack of human-associated virulence and adhesion determinants. The absence of detectable enterotoxin gene among ST398 LA-MRSA strains from a wide host range is reassuring regarding their foodborne pathogenic potential.

Molecular characterization of resistance to Rifampicin in an emerging hospital-associated Methicillin-resistant Staphylococcus aureus clone ST228, Spain

Background

Methicillin-resistant S. aureus (MRSA) has been endemic in Hospital Universitari de Bellvitge, Barcelona, since 1990. During the 1990-95 period the Iberian clone (ST-247; SCCmec-I) was dominant. Isolates of clonal complex 5 (ST-125; SCCmec-IV) gradually replaced the Iberian clone from 1996 to 2003. A new multiresistant MRSA phenotype showing rifampicin resistance emerged in 2004 and rapidly increased from 25% in 2004 to 45% in 2006. The aims of this study were i) the molecular characterisation of rifampicin resistant MRSA isolates, ii) the study of the rifampicin resistance expression by disk diffusion, microdilution and E-test, and iii) the analysis of the rpoB gene mutations involved in rifampicin resistance.

Results

A sample of representative 108 rifampicin-resistant MRSA isolates belonged to a single PFGE genotype, ST-228, SCCmec type I and spa type t041. Of 108 isolates, 104 (96%) had a low-level rifampicin resistance (MICs, 2 to 4 mg/L) and 4 a high-level rifampicin resistance (MICs, 128 - ≥ 256 mg/L). Disk diffusion and E-test methods failed to identify a low-level rifampicin resistance in 20 and 12 isolates, respectively. A low-level rifampicin resistance was associated with amino acid substitution 481His/Asn in the beta-subunit of RNA polymerase. Isolates with a high-level rifampicin resistance carried additional mutations in the rpoB gene.

Conclusions

The emergence of MRSA clone ST228-SCCmecI, related to the Southern Germany clone, involved a therapeutical challenge for treating serious MRSA infections. Decreased susceptibility to rifampicin in MRSA strains of ST228-SCCmecI was associated with one or two specific mutations in the rpoB gene. One fifth of isolates with low-level rifampicin-resistance were missed by the diffusion methods.

Emergence of SCCmec type IV and SCCmec type V methicillin-resistant Staphylococcus aureus containing the Panton-Valentine leukocidin genes in a large academic teaching hospital in central Switzerland: external invaders or persisting circulators?

The hospital epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) has changed in the past few years due to the encroachment of community-associated MRSA (CA-MRSA) strains into health care settings. MRSA strains that were isolated during a 2-year period from patients of the Luzerner Kantonsspital were analyzed to elucidate their epidemiology. Moreover, extended surveillance of individuals who were contacts of those patients was carried out for 6 months to identify the routes of spread and to assess the quality of the infection control measures used in our setting. Patient data were collected to distinguish CA-MRSA strains from health care-associated MRSA (HA-MRSA) strains by epidemiological criteria, as defined by the Centers for Disease Control and Prevention (CDC). On the basis of the CDC definition, the majority of the strains were considered to be HA-MRSA. However, 87% of them belonged to staphylococcal cassette chromosome mec (SCCmec) types IV and V, which are traditionally associated with CA-MRSA. Surprisingly, classical nosocomial SCCmec types I and II represented a minority, whereas SCCmec type III was completely absent. By PFGE analysis, four predominant clonal lineages and 21 highly variable sporadic genotypes were detected. Twenty-eight percent of the MRSA strains studied carried the genes encoding the Panton-Valentine leukocidin (PVL), of which 21% and 83% were associated with SCCmec types IV and V, respectively. Among 289 contact individuals screened for MRSA carriage throughout the extended surveillance, a single secondary patient was discovered. The possibility of nosocomial transmission could be excluded. The high proportions of SCCmec type IV and V strains as well as PVL-positive strains suggest strong infiltration of CA-MRSA into our institution. Moreover, the low endemic prevalence of MRSA demonstrates that current infection control measures are sufficient to limit its spreading and the emergence of large epidemic outbreaks.

Epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) among residents of nursing homes in Belgium

OBJECTIVES

A national survey was conducted to determine the prevalence, risk factors and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) carriage among nursing home (NH) residents in Belgium.

METHODS

A random stratified, cross-sectional prevalence survey was conducted in NH residents who were screened for MRSA carriage by multisite enriched culture. Characteristics of NHs and residents were collected by a questionnaire survey and analysed by two-stage logistic regression modelling. MRSA isolates were genotyped by PFGE, staphylococcal cassette chromosome mec (SCCmec) typing, multilocus sequence typing (MLST) and resistance genes.

RESULTS

Of 2953 residents screened in 60 NHs, 587 (19.9%) were MRSA carriers. Risk factors included hospital contact, antibiotic exposure, impaired mobility and skin lesions at the resident level, and lack of MRSA surveillance, lack of antibiotic therapeutic formulary and the combination of less-developed infection control activities and a high ratio of physicians to residents at the institution level. MRSA isolates showed eight major types, three of which were predominant: B2-ST45-SCCmec IV (49%; where ST stands for sequence type); A21-ST8-SCCmec IV (13%); and A20-ST8-SCCmec IV (10%). Each was recovered in 55, 21 and 25 NHs, respectively. The geographical distribution of NH genotypes paralleled that of acute-care hospitals.

CONCLUSIONS

A high prevalence of MRSA carriage in NH residents was associated with hospital care, co-morbidities and less-developed coordination of institutional care. The predominant MRSA strains from NH residents and hospitalized patients of the same area were identical. Strengthening and coordination of MRSA surveillance and control activities are warranted within and between NHs and hospitals.

StaphVar-DNA microarray analysis of accessory genome elements of community-acquired methicillin-resistant Staphylococcus aureus

OBJECTIVES

Approximately 75% of the genome of Staphylococcus aureus (the 'core' genome) is highly conserved between strains, whereas the remaining 25% (the 'accessory' genome) is composed of mobile genetic elements (MGEs), containing virulence and resistance genes. We developed a composite microarray focused on resistance and virulence genes located on the accessory or core-variable genome to characterize a collection of Belgian community-acquired methicillin-resistant S. aureus (CA-MRSA) strains.

METHODS

Oligonucleotide probes targeting 403 genes encoding antimicrobial resistance (35%), virulence (28%) and adhesion (31%) factors were designed among eight S. aureus sequenced genomes. The StaphVar Array was validated by testing five of the strains used for the design and utilized to characterize 13 CA-MRSA strains representative of the multilocus sequence typing (MLST) sequence types circulating in Belgium.

RESULTS

Analysis of the gene content of the five reference strains by the StaphVar Array matched 90% to 97% of the theoretical results. Analysis of CA-MRSA strains showed that 54.4% of the genes tested were strain-dependent. Strains presented specific exotoxin, enterotoxin, cytolysin and adhesin gene profiles by MLST lineage. One exception to these 'lineage-specific' profiles was the variable presence of the arginine catabolic mobile element (characteristic of the USA300 clone) within ST8 strains.

CONCLUSIONS

The StaphVar Array enables the characterization of approximately 400 variable resistance and virulence determinants in S. aureus. CA-MRSA strains displayed extensive diversity in virulence and resistance profiles. The presence of the USA300 clone in Belgium was confirmed. Although mainly located on MGEs, associations of virulence genes were highly conserved within strains of the same MLST lineage.

Intracellular activity of antibiotics in a model of human THP-1 macrophages infected by a Staphylococcus aureus small-colony variant strain isolated from a cystic fibrosis patient: pharmacodynamic evaluation and comparison with isogenic normal-phenotype and revertant strains

Small-colony variant (SCV) strains of Staphylococcus aureus show reduced antibiotic susceptibility and intracellular persistence, potentially explaining therapeutic failures. The activities of oxacillin, fusidic acid, clindamycin, gentamicin, rifampin, vancomycin, linezolid, quinupristin-dalfopristin, daptomycin, tigecycline, moxifloxacin, telavancin, and oritavancin have been examined in THP-1 macrophages infected by a stable thymidine-dependent SCV strain in comparison with normal-phenotype and revertant isogenic strains isolated from the same cystic fibrosis patient. The SCV strain grew slowly extracellularly and intracellularly (1- and 0.2-log CFU increase in 24 h, respectively). In confocal and electron microscopy, SCV and the normal-phenotype bacteria remain confined in acid vacuoles. All antibiotics tested, except tigecycline, caused a net reduction in bacterial counts that was both time and concentration dependent. At an extracellular concentration corresponding to the maximum concentration in human serum (total drug), oritavancin caused a 2-log CFU reduction at 24 h; rifampin, moxifloxacin, and quinupristin-dalfopristin caused a similar reduction at 72 h; and all other antibiotics had only a static effect at 24 h and a 1-log CFU reduction at 72 h. In concentration dependence experiments, response to oritavancin was bimodal (two successive plateaus of -0.4 and -3.1 log CFU); tigecycline, moxifloxacin, and rifampin showed maximal effects of -1.1 to -1.7 log CFU; and the other antibiotics produced results of -0.6 log CFU or less. Addition of thymidine restored intracellular growth of the SCV strain but did not modify the activity of antibiotics (except quinupristin-dalfopristin). All drugs (except tigecycline and oritavancin) showed higher intracellular activity against normal or revertant phenotypes than against SCV strains. The data may help rationalizing the design of further studies with intracellular SCV strains.

Community strains of methicillin-resistant Staphylococcus aureus as potential cause of healthcare-associated infections, Uruguay, 2002-2004

Community-associated MRSA appears to be replacing healthcare-associated MRSA strain types in at least 1 facility and is a cause of healthcare-onset infections.

Community-associated MRSA (CA-MRSA) strains have emerged in Uruguay. We reviewed Staphylococcus aureus isolates from a large healthcare facility in Montevideo (center A) and obtained information from 3 additional hospitals on patients infected with CA-MRSA. An infection was defined as healthcare-onset if the culture was obtained >48 hours after hospital admission. At center A, the proportion of S. aureus infections caused by CA-MRSA increased from 4% to 23% over 2 years; the proportion caused by healthcare-associated MRSA (HA-MRSA) decreased from 25% to 5%. Of 182 patients infected with CA-MRSA, 38 (21%) had healthcare-onset infections. Pulsed-field gel electrophoresis determined that 22 (92%) of 24 isolates were USA1100, a community strain. CA-MRSA has emerged in Uruguay and appears to have replaced HA-MRSA strains at 1 healthcare facility. In addition, CA-MRSA appears to cause healthcare-onset infections, a finding that emphasizes the need for infection control measures to prevent transmission within healthcare settings.

Evolutionary relationships between sporadic and epidemic strains of healthcare-associated methicillin-resistant Staphylococcus aureus

National surveillance of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates by pulsed-field gel electrophoresis (PFGE) typing allowed identification of rarely occurring 'sporadic' isolates with patterns significantly distinct from those of major epidemic clones of methicillin-resistant S. aureus (MRSA) circulating in Belgian hospitals. The aim of the present study was to compare the genetic background, antibiotic susceptibility profile and in vitro growth rates of 36 MRSA isolates with either 'epidemic' or 'sporadic' PFGE profiles to identify factors that could be involved in the epidemic behaviour of S. aureus. Sequence analysis of seven housekeeping genes (multilocus sequence typing) and seven surface-associated genes, combined with staphylococcal cassette chromosome mec (SCCmec) typing and spa typing results, segregated sporadic isolates into four groups: (1) isolates phylogenetically distant from epidemic HA-MRSA clones that possessed several properties of community-acquired MRSA strains; (2) isolates derived from the same methicillin-susceptible S. aureus ancestor as epidemic isolates but possessing a distinct type of SCCmec; and (3) and (4) isolates that were closely related to epidemic strains, either as recent descendants of these or as intermediate evolutionary steps between epidemic HA-MRSA strains and their putative ancestors. Sporadic isolates did not show slower growth in vitro than epidemic isolates. These findings suggest that the SCCmec type and insertion/deletion of other mobile genetic elements may be involved in modulating the epidemic behaviour of MRSA strains of similar genetic background, independently of fitness cost.

Evaluation of new Vitek 2 card and disk diffusion method for determining susceptibility of Staphylococcus aureus to oxacillin

Detection of methicillin resistance in Staphylococcus aureus is a challenge, especially low-level resistance, which is often misdiagnosed. The aim of this study was to compare the diagnostic accuracies of the automated Vitek 2 system and disk diffusion tests, using cefoxitin and moxalactam, for the detection of methicillin resistance in S. aureus strains. Four sets of genotypically diverse isolates were selected from a national reference collection, including mecA-negative S. aureus isolates (n = 56), hospital-acquired (n = 88) and community-acquired (n = 40) S. aureus isolates, and heterogeneous methicillin-resistant S. aureus isolates (n = 29). Oxacillin susceptibility was tested by the Vitek 2 system with the AST P549 card and by disk diffusion methods using 10, 30, and 60 microg cefoxitin and 30 microg moxalactam. Oxacillin resistance was confirmed by PCR for the mecA gene. The overall sensitivities for oxacillin resistance detection were 97.5% for the Vitek 2 automated system, 98.7% for 60-microg cefoxitin and moxalactam disk diffusion, and 99.6% for 10- and 30-microg cefoxitin disks, respectively. Methicillin-susceptible S. aureus isolates were correctly reported as susceptible by all methods. The median times for methicillin testing were 7 h for the Vitek 2 system versus 24 h for disk diffusion methods. In conclusion, the cefoxitin and moxalactam disk diffusion methods and the Vitek 2 automated system are highly accurate methods for methicillin resistance detection, including a range of representative Belgian methicillin-resistant S. aureus strains and unusual strains exhibiting cryptic or low-level oxacillin resistance.

Emergence in Brazil of methicillin-resistant Staphylococcus aureus isolates carrying SCCmecIV that are related genetically to the USA800 clone

An increasing incidence of nosocomial infections caused by non-multiresistant methicillin-resistant Staphylococcus aureus (nMMRSA) has been reported worldwide. The present study genotyped nMMRSA isolates obtained from hospitals in two cities in Brazil. The hospital isolates displayed pulsed-field gel electrophoresis (PFGE) patterns that were similar to those of the USA100 (ST5-SCCmecII) and USA 800 (ST5-SCCmecIV) strains, which are related to the New York/Japan and paediatric clones, respectively. Carriage of SCCmecIV and the classification by multilocus sequence typing (MLST) of a representative of this PFGE pattern in clonal complex 5 (CC5) confirmed the genetic relationship of the Brazilian isolates with USA800. The USA800-related Brazilian isolates were responsible for severe nosocomial infections in compromised adults and elderly patients in Brazil. A higher growth rate, an ability to form biofilm on inert polystyrene surfaces and the presence of the egc locus may have contributed, at least in part, to the fitness of these organisms as global nosocomial pathogens.

Changes in the clonal nature and antibiotic resistance profiles of methicillin-resistant Staphylococcus aureus isolates associated with spread of the EMRSA-15 clone in a tertiary care Portuguese hospital

Two hundred eighty methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates recovered from a tertiary care hospital in Oporto, Portugal, between 2003 and 2005 were studied by a combination of molecular typing techniques in order to investigate the genetic backgrounds associated with the changes in the resistance phenotypes observed since 2001 and compare them to those previously found in the hospital. All MRSA isolates were grouped into resistance profiles for a panel of seven antibiotics and characterized by pulsed-field gel electrophoresis (PFGE) and SCCmec (staphylococcal cassette chromosome mec) typing. Representative isolates of PFGE types were further studied by spa typing and multilocus sequence typing. Our findings clearly document that the increasing isolation of nonmultiresistant MRSA strains was associated with the decline (from 69% in 1996 to 2000 to 12% in 2003 to 2005) and massive replacement of the multiresistant Brazilian clone (ST239-IIIA) by the epidemic EMRSA-15 clone (ST22-IV), in which resistance to antibiotics other than beta-lactams is very rare, as the major clone (80% of isolates). The Iberian clone (ST247-IA), a major clone in 1992 to 1993, was represented in the present study by just one isolate. Two other pandemic MRSA clones were detected, as sporadic isolates, for the first time in our hospital: the New York/Japan (ST5-II) and the EMRSA-16 (ST36-II) clones. Furthermore, the pattern of susceptibility of MRSA isolates both to gentamicin and to trimethoprim-sulfamethoxazole was shown to be an excellent phenotypic marker for the discrimination of the EMRSA-15 clone from other nonmultiresistant MRSA clones present in our hospital.

National survey of molecular epidemiology of Staphylococcus aureus colonization in Belgian cystic fibrosis patients

OBJECTIVES

Epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is poorly defined in cystic fibrosis (CF) patients, and S. aureus detection may be hampered by the presence of small colony variants (SCVs). We conducted a multicentre survey to determine the prevalence of S. aureus and MRSA colonization in Belgian CF patients and characterize the phenotype and clonal distribution of their staphylococcal strains.

METHODS

S. aureus isolated from CF patients attending nine CF centres were collected. Oxacillin resistance was detected by oxacillin agar screen and mecA PCR. Antibiotic susceptibility was tested by microdilution. MRSA strains were genotyped by PFGE and SCCmec typing and compared with hospital-associated MRSA strains.

RESULTS

Laboratories used a diversity of sputum culture procedures, many of which appeared substandard. S. aureus was isolated from 275/627 (44%) CF patients (20% to 72% by centre). The prevalence of SCV colonization was 4%, but SCVs were almost exclusively recovered from patients in two centres performing an SCV search. Phenotypically, 14% of S. aureus isolates were oxacillin-resistant: 79% carried mecA and 19% were SCVs lacking mecA. The mean prevalence of 'true' MRSA colonization was 5% (0% to 17% by centre). By PFGE typing, 67% of CF-associated MRSA were related to five epidemic clones widespread in Belgian hospitals.

CONCLUSIONS

This first survey of S. aureus colonization in the Belgian CF population indicated a diversity in local prevalence rates and in proportion of oxacillin-resistant and SCV phenotypes, probably related to variation in bacteriological methods. These findings underscore the need for standard S. aureus detection methods and MRSA control policies in Belgian CF centres.

Genetic relatedness between methicillin-susceptible and methicillin-resistant Staphylococcus aureus: results of a national survey

OBJECTIVES

Surveillance of hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) infections has shown the emergence and spread of several epidemic MRSA clones over the past 10 years in Belgium. Whether these clones have been imported from abroad or else have arisen locally via staphylococcal cassette chromosome mec (SCCmec) acquisition by successful methicillin-susceptible S. aureus (MSSA) clones is unknown.

METHODS

We determined by PFGE, spa typing, multi-locus sequence typing (MLST) and agr group analysis the genetic relatedness of 103 MSSA and 511 MRSA strains from a national survey of patients admitted to 112 Belgian hospitals in 2003.

RESULTS

The 103 MSSA strains presented very diverse genetic backgrounds, they were distributed into 40 distinct PFGE types and clustered in 15 distinct MLST CCs. Up to 45% harboured the same genotype as five major epidemic HA-MRSA clones. These MRSA clones all harbour a type IV SCCmec element.

CONCLUSIONS

These findings are consistent with multiple recent acquisitions of the more mobile type IV SCCmec by MSSA and suggest that certain genetic backgrounds are conferring a selective advantage, regardless of the resistance profile. However, since the predominant MSSA and MRSA lineages identified in Belgium are disseminated worldwide, importation of epidemic MRSA strains remains an alternative hypothesis.

Validation of pulsed-field gel electrophoresis and spa typing for long-term, nationwide epidemiological surveillance studies of Staphylococcus aureus infections

Pulsed-field gel electrophoresis (PFGE) of genomic macrorestriction fragments has been used by the Belgian Reference Laboratory for Staphylococci for national hospital surveys of methicillin-resistant Staphylococcus aureus since 1992. The sequencing of the polymorphic X region of the protein A gene (spa typing) offers significant advantages over PFGE in terms of speed, ease of interpretation, and exportability. To validate its potential use for national surveillance, we evaluated the robustness of spa typing compared with that of PFGE based on a collection of 217 S. aureus strains representative of the Belgian S. aureus epidemiology during the last 13 years. spa typing and PFGE both showed high discriminatory power (discriminatory indexes of 0.98 and 0.96, respectively) and achieved high concordance (95.9%) in type classification. Both methods also showed good concordance with multilocus sequence typing (MLST) (95.5%). However, we observed occasional "violations" of MLST clonal complex assignment by spa typing. Our results suggest that both PFGE and spa typing are reliable methods for long-term, nationwide epidemiological surveillance studies. We suggest that spa typing, which is a single-locus-based method, should preferably be used in combination with additional markers, such as staphylococcal cassette chromosome mec typing or resistance or virulence gene detection.

In vitro activities of ceftobiprole, tigecycline, daptomycin, and 19 other antimicrobials against methicillin-resistant Staphylococcus aureus strains from a national survey of Belgian hospitals

The in vitro activities of 22 antimicrobial agents, including ceftobiprole, daptomycin, and tigecycline, against 511 methicillin-resistant Staphylococcus aureus (MRSA) isolates from 112 Belgian hospitals were studied by using the CLSI agar dilution method. Isolates were characterized by pulsed-field gel electrophoresis (PFGE) analysis and by PCR detection of determinants of resistance to aminoglycosides, macrolides-lincosamides-streptogramins, and tetracyclines. A representative set of isolates with different PFGE genotypes was further characterized by multilocus sequence typing, determination of staphylococcal cassette chromosome mec (SCCmec) type, and multiplex PCR for toxic shock syndrome type 1 (TSST-1) and Panton-Valentine leukocidin genes. MRSA isolates belonged to nine epidemic MRSA clones, of which sequence type 45 (ST45)-SCCmec IV and ST8-SCCmec IV were predominant, accounting for 49 and 20% of isolates, respectively. The distribution of antimicrobial resistance and TSST-1 genes was strongly linked to clonal types. Ceftobiprole, daptomycin, and tigecycline showed high activity against all isolates of these sporadic and epidemic MRSA clones, as indicated by MIC(90)s of 2 mg/liter, 0.5 mg/liter, and 0.25 mg/liter, respectively. The MIC distribution of daptomycin and tigecycline was not different in isolates with decreased susceptibility to glycopeptides or tetracyclines, respectively. Ceftobiprole MICs were not correlated with oxacillin and cefoxitin MICs. These data indicate excellent activity of the newly developed agents ceftobiprole, daptomycin, and tigecycline against MRSA isolates recently recovered from hospitalized patients in Belgium, supporting their therapeutic potential for nosocomial MRSA infections.

Guidelines for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK

These evidence-based guidelines have been produced after a literature review of the treatment and prophylaxis of methicillin-resistant Staphylococcus aureus (MRSA) infection. The guidelines were further informed by antibiotic susceptibility data on MRSA from the UK. Recommendations are given for the treatment of common infections caused by MRSA, elimination of MRSA from carriage sites and prophylaxis of surgical site infection. There are several antibiotics currently available that are suitable for use in the management of this problem and potentially useful new agents are continuing to emerge.

Changes in the Epidemiology of Methicillin-Resistant Staphylococcus aureus in Intensive Care Units in US Hospitals, 1992-2003

The proportion of Staphylococcus aureus isolates that were methicillin resistant (MRSA) increased from 35.9% in 1992 to 64.4% in 2003 for hospitals in the National Nosocomial Infections Surveillance system. During the same period, there was a decrease in resistance rates for several non- beta -lactam drugs among the MRSA isolates.

Genetic differentiation of methicillin-resistant Staphylococcus aureus strains from Korea and Japan

In this study, we evaluated genetic differentiation between methicillin-resistant Staphylococcus aureus (MRSA) strains from Korea and Japan. Seventy-five MRSA strains, including 25 h VISA strains, were analyzed by molecular typing methods, including multilocus sequence typing (MLST), SCC mec typing, and spa typing. The most prevalent genotype of MRSA strains, in both Korea and Japan, was ST 5-MRSA-II with the DMGMK spa motif, characteristic of the New York/Japan MRSA clone. In spite of these common features in MRSA strains from Korea and Japan, we also observed some genotypic divergence in MRSA from the two countries. Several spa types might be differentiated from a prevalent prototype (TJMBMDMGMK) that is shared by the two countries, revealing a unique geographic distribution. SCC mec type II lacking pUB110, designated type IIA, was found more frequently in Korea than in Japan. The rate of gentamicin resistance was also dramatically different between the two countries: 87.2% (Korea) vs. 28.6% (Japan). These preliminary findings suggested that MRSA strains from Korea and Japan might have originated from a common ancestor, but then clearly differentiated according to locality. A further comprehensive study should be performed to document the hypotheses from this study.

Staphylococcus aureus carriage among participants at the 13th European Congress of Clinical Microbiology and Infectious Diseases

The aim of this study was to measure the rate of Staphylococcus aureus nasal colonization among attendees of the 13th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), particularly with regard to methicillin-resistant (MRSA) strains. The 31.4% rate of Staphylococcus aureus colonization detected among the participants was in line with colonization rates reported previously for healthcare workers. A statistical difference was found between the rates of Staphylococcus aureus carriage in physicians (37.4%) and non-physicians (21.7%) but not between males (35.0%) and females (28.9%). Only one participant (a Belgian physician) was found to carry MRSA. Surprisingly, the rate of methicillin-susceptible Staphylococcus aureus carriage was significantly higher among participants from countries with a low prevalence of MRSA.

Evaluation of the Vitek 2 system for identification and antimicrobial susceptibility testing of Staphylococcus spp

The Vitek 2 system was assessed against reference methods with 197 methicillin-resistant Staphylococcus aureus from Belgian hospitals and 121 clinically significant blood culture isolates of Staphylococcus spp. Vitek 2 identified 95% of staphylococcal isolates correctly, detected oxacillin resistance with a sensitivity/specificity of 99/96%, and showed acceptable accuracy for susceptibility testing of five of eight other evaluable antibiotics. The median time for reporting results was 2 h 45 min for identification and 7 h for susceptibility tests.

Microbiology of nosocomial infections: progress and challenges

Technological advances have expanded the role of the clinical microbiology laboratory in supporting management and control of health-care-associated infections (HAI). Diagnostic capabilities have been complemented by new methods for characterisation of microbial antigens and nucleic acids. Genomic "fingerprinting" enables the study of transmission of nosocomial pathogens. Monitoring of their antimicrobial resistance patterns has gained critical importance. However, cost-effective application of microbiological testing for improved treatment and prevention of HAI requires further study.

National surveillance of methicillin-resistant Staphylococcus aureus in Belgian hospitals indicates rapid diversification of epidemic clones

Methicillin-resistant Staphylococcus aureus (MRSA) strains (n = 455) collected in 2001 from 100 Belgian hospitals were characterized by molecular typing and by resistance gene distribution to macrolides-lincosamides-streptogramins and to aminoglycoside antibiotics. Rapid diversification of MRSA clones, compared with results of previous surveys, was evidenced by the broad geographic distribution of seven major clones belonging to the pandemic MRSA clonal complexes 5, 8, 22, 30, and 45 by multilocus sequence typing.