Comparison of adhesion and virulence of two predominant hospital-acquired methicillin-resistant Staphylococcus aureus clones and clonal methicillin-susceptible S. aureus isolates

The virulence of SCCmec type IV hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates belonging to the major sequence type 8 (ST8 [Lyon clone]) and to a minor upcoming clone, ST5, was compared with that of methicillin-susceptible S. aureus (MSSA) isolates of matching sequence types. In vitro adhesion to human airway epithelial cells (HAECs) as an indicator of dissemination and mortality in a murine sepsis model as an indicator of virulence were evaluated. Ten MRSA isolates and 8 MSSA isolates of ST8 and 8 MRSA isolates and 8 MSSA isolates of ST5 were characterized with respect to multilocus sequence type; agr, spa, and capsule typing; in vitro doubling time; toxin and adhesin gene profiles; and adherence to HAECs. Adherence was significantly lower in the MRSA ST5 group than in the ST8 groups. Infections with MRSA and MSSA isolates ST8 and ST5 were compared. No change in virulence related to the presence of SCCmec was observed, since ST8 but not ST5 caused a significantly lower mortality in its presence. Despite their similar genetic backgrounds, individual clonal MRSA and MSSA isolates were heterogeneous in adherence and virulence. No one of these specific virulence factors determined in vitro was related to mouse mortality. In conclusion, in a bacteremic model, mortality was dependent on the ST and was differentially modulated by SCCmec; within an ST, clonality was not associated with a homogenous outcome.     

Countrywide molecular survey of methicillin-resistant Staphylococcus aureus strains in Poland

The present investigation was undertaken to assess the proportion of methicillin-resistant Staphylococcus aureus (MRSA) strains among hospital-acquired isolates and to determine the clones of MRSA currently circulating in Poland by using a number of molecular techniques. Between January and May 2005, methicillin resistance was investigated among a total of 915 S. aureus isolates collected from 39 hospitals. A total of 208 (22.7%) isolates were positive for the mecA gene by PCR. The molecular characterization of MRSA isolates was carried out by the multiple-locus variable-number tandem repeat fingerprinting, pulsed-field gel electrophoresis, multilocus sequence typing, and staphylococcal chromosomal cassette mec (SCCmec) typing methods. The Hungarian (PFGE B; ST239, SCCmec type III [ST239-III]), Iberian (ST247-I), and Berlin (ST45-IV) clones were predominant, representing approximately 52.9, 11.5, and 10.0% of the MRSA isolates, respectively. A decline in the proportion of earlier MRSA clones, such as ST5-IV (a Pediatric clone), ST80-IV) (a Mediterranean clone), ST239-III (a Polish and Brazilian clone), and ST30-IV (a southwest Pacific clone) was observed. Additionally, the emergence of an MRSA clone with SCCmec type V, possibly representing a community-acquired strain, was observed in two hospitals during this study.     

Comparison of genetic backgrounds of methicillin-resistant and -susceptible Staphylococcus aureus isolates from Portuguese hospitals and the community

In order to understand the origins of the dominant methicillin-resistant Staphylococcus aureus (MRSA) clones in Portuguese hospitals, we compared the genetic backgrounds of nosocomial MRSA with methicillin-susceptible S. aureus (MSSA) isolates from the same hospitals (n = 155) and from the community (n = 157) where they were located. Pulsed-field gel electrophoresis, spa typing, multilocus sequence typing, and agr type analysis revealed that the genetic backgrounds correspondent to the dominant MRSA clones in Portuguese hospitals during the last 15 years (Iberian ST247, Brazilian ST239, and EMRSA-15 ST22) were scarcely or not found among the present MSSA collection. The four major MSSA clones encountered (A-ST30, B-ST34, C-ST5, and H-ST45) correspond, or are very similar, to the background of other international MRSA pandemic clones, i.e., EMRSA-16, New York/Japan, Pediatric, and Berlin clones. However, with the exception of the Pediatric clone, none of these MRSA clones has been detected in Portugal. Our findings suggest the three major MRSA clones identified in Portuguese hospitals have not originated from the introduction of SCCmec into dominant MSSA backgrounds present in the Portuguese nosocomial or community environment but were probably imported from abroad. In contrast, the MRSA Pediatric clone might have originated in our country by the acquisition of SCCmec type IV into MSSA clone C. Furthermore, we provide evidence that the introduction of SCCmec into sensitive clones is most likely a relatively infrequent event that seems to depend not exclusively on the presence of a successful MSSA lineage.     

Clinical isolates of Staphylococcus aureus from the Arkhangelsk region,Russia: antimicrobial susceptibility,molecular epidemiology,and distribution of Panton‐Valentine leucocidin genes

A total of 91 consecutive clinical isolates of Staphylococcus aureus were collected at the Regional Hospital of Arkhangelsk, Russia, from May to December 2004, and examined for antimicrobial susceptibility, methicillin resistance and presence of Panton‐Valentine leucocidin (PVL) genes. Epidemiological typing was performed by pulsed‐field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Methicillin‐resistant S. aureus (MRSA) isolates were examined by staphylococcal cassette chromosome mec (SCCmec) typing. High‐to‐moderate rates of resistance to penicillin (β‐lactamase production; 93%), tetracycline (40%), erythromycin and clindamycin (32%) were observed. Forty out of ninety‐one (44%) isolates were positive for PVL genes. Thirty‐six (40%) PVL‐positive methicillin‐susceptible S. aureus (MSSA) strains were shown by PFGE and MLST typing (ST121, ST681, ST837) to be part of a nosocomial outbreak caused by clonal complex (CC) 121. PFGE, MLST and SCCmec typing revealed three MRSA clones. Sequence type (ST) 239‐III (n=11), ST1097‐III (n=1) and ST8‐IV (n=3) belong to CC8 of epidemic multiresistant MRSA, whereas ST426‐MRSA‐IV/CC395 (n=1) has not been reported previously. All MRSA strains were PVL negative. The overall results underline the necessity of microbiological sampling, antimicrobial susceptibility testing, and epidemiological typing as a rational basis for antimicrobial treatment of S. aureus infections, and infection control measures to limit the spread of multiresistant MRSA and epidemic MSSA clones.     

A comparison of methicillin-resistant and methicillin-susceptible Staphylococcus aureus reveals no clinical and epidemiological but molecular differences

Most studies on Staphylococcus aureus have focused on the molecular epidemiology of methicillin-resistant S. aureus (MRSA) infections. In contrast, little information is available regarding the molecular epidemiology of currently circulating methicillin-susceptible S. aureus (MSSA) isolates in hospital settings, an epoch when the epidemiology of S. aureus has undergone significant changes. We conducted a cross-sectional study to compare the clinical, epidemiological, and genetic characteristics of MSSA and MRSA isolates at 3 tertiary-care hospitals in Medellín, Colombia, from February 2008 to June 2010. The infections were classified according to the Centers for Disease Control and Prevention (CDC) definitions. Genotypic analysis included spa typing, multilocus sequence typing (MLST) and staphylococcal cassette chromosome (mec) (SCCmec) typing. A total of 810 patients was enrolled. One hundred infections (12.3%) were classified as community-associated (31 CA-MSSA, 69 CA-MRSA), 379 (46.8%) as healthcare-associated community-onset (136 HACO-MSSA, 243 HACO-MRSA), and 331 (40.9%) as healthcare-associated hospital-onset (104 HAHO-MSSA, 227 HAHO-MRSA). Genotype analyses showed a higher diversity and a more varied spa type repertoire in MSSA than in MRSA strains. Most of the clinical-epidemiological characteristics and risk factors evaluated did not allow for discriminating MRSA- from MSSA-infected patients. The lack of equivalence among the genetic backgrounds of the major MSSA and MRSA clones would suggest that the MRSA clones are imported instead of arising from successful MSSA clones. This study emphasizes the importance of local surveillance to create public awareness on the changing S. aureus epidemiology.     

Pediatric Staphylococcus aureus Isolate Genotypes and Infections from the Dawn of the Community-Associated Methicillin-Resistant S. aureus Epidemic Era in Chicago, 1994 to 1997

Widespread infections with community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) have occurred in the United States with the dissemination of the USA300 strain beginning in 2000. We examined 105 isolates obtained from children treated at the University of Chicago from 1994 to 1997 (75 methicillin-susceptible S. aureus [MSSA] and 30 MRSA isolates) in order to investigate for possible evidence of USA300 during this period. Infections were defined epidemiologically based on medical record review. The isolates underwent multilocus sequence typing (MLST), as well as assays for the Panton-Valentine leukocidin (PVL) genes, the protein A gene (spa), and arcA and opp3, proxy markers for the arginine catabolic mobile element (ACME), characteristic of USA300 MRSA. MRSA isolates also underwent staphylococcal cassette chromosome mec (SCCmec) typing and pulsed-field gel electrophoresis (PFGE) subtyping. MSSA isolates belonged to 17 sequence type (ST) groups. The 12 epidemiologically defined CA-MRSA infection isolates were either ST1 (n = 4) or ST8 (n = 8). They belonged to 3 different PFGE types: USA100 (n = 1), USA400 (n = 5), and USA500 (n = 6). Among the CA-MRSA infection isolates, 8 (67%) were PVL⁺. None of the MRSA or MSSA isolates contained arcA or opp3. Only one MRSA isolate was USA300 by PFGE. This was a health care-associated (HA) MRSA isolate, negative for PVL, that carried SCCmec type II. USA300 with its characteristic features was not identified in the collection from the years 1994 to 1997.     

The dominant methicillin‐resistant Staphylococcus aureus clone from hospitals in Cape Town has an unusual genotype: ST612

There is currently limited information available on the molecular epidemiology of methicillin‐resistant Staphylococcus aureus (MRSA) in South Africa. A molecular characterization of 100 MRSA from five hospitals in Cape Town was carried out in this study. The strains were separated into six clusters by pulsed‐field gel electrophoresis, indicating transmission of MRSA between local hospitals. None of the strains carried the Panton‐Valentine Leukocidin gene. SCCmec typing, multilocus sequence typing and spa typing were used to further characterize the MRSA. Three clones corresponded to frequently described pandemic clones: ST239‐MRSA‐III, ST36‐MRSA‐II and ST5‐MRSA‐I. ST239‐MRSA‐III and ST36‐MRSA‐II were minor clones and collectively accounted for 16% of the isolates. ST5‐MRSA‐I was the second‐most prevalent clone and accounted for 37% of the isolates. The dominant local clone was the infrequently described ST612‐MRSA‐IV (44% of isolates), which has only been described in South Africa and Australia.     

Genetic Correlation of Community-Associated Methicillin-Resistant Staphylococcus aureus Strains from Carriers and from Patients with Clinical Infection in One Region of Korea

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an increasingly common worldwide and colonizing S. aureus strains may serve as the causative pathogen for overt clinical infections. This study was performed to determine whether the pathogenic CA-MRSA isolate in clinical infections was genetically related to the MRSA isolates in community carriers. We prospectively collected a total of 42 CA-MRSA isolates (23 clinical infection isolates and 19 colonization isolates) in a local region of Korea. Antimicrobial susceptibility tests, staphylococcal toxin assays, SCCmec typing, multilocus sequence typing (MLST), and spa (staphylococcal protein A) typing were performed with all isolates. Thirty-four (81%) of 42 CA-MRSA isolates belonged to sequence type (ST) 72 in the MLST analysis. The distribution of STs did not differ significantly between colonization and clinical infection isolates (89.5% [17/19] vs. 73.9% [17/23], P=0.26). Among the ST72-MRSA isolates, spa type t664 (18, 52.9%) and t324 (8, 23.5%) were common in both groups. This study demonstrates that the community-associated MRSA strains from patients with clinical infections are closely related to the strains found in carriers from one local community.     

A longitudinal molecular surveillance of clinical methicillin-resistant Staphylococcus aureus isolates in neonatal units in a teaching hospital, 2003–2018

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) has been an important nosocomial pathogen in our neonatal units since 1990s. To understand the longitudinal changing molecular epidemiology of these MRSA isolates, we conducted this study.MaterialsFrom 2003 to 2018, we collected clinical MRSA isolates from 536 infants hospitalized at neonatal units of a medical center in northern Taiwan. First isolate from each infant was characterized.ResultsThe case/isolate number ranged from 7 cases/isolates (the lowest) in 2010 to 71 cases/isolates (the highest) in 2004. Of the 536 isolates, a total of 15 pulsotypes were identified. Three major clones were identified and characterized as sequence type (ST) 239/pulsotype A/staphylococcal chromosomal cassette (SCC) mec III/Panton-Valentine leukocidin (PVL)-negative, accounting for 22.2% of the isolates, ST59/pulsotype C/SCCmec IV/PVL-negative, accounting for 34.3% and ST59/pulsotype D/SCCmec V_T/PVL-positive, accounting for 30.0%. The first clone (hospital strains) dominated in the first two years, and became weakened from 2005 through 2016. Clonal complex (CC) 59 (combined the second and third clones) dominated (>50% of the isolates) from 2005 through 2018. One community clone (ST573) demonstrated a marked increase since 2007 and vanished abruptly since 2010. Several minor MRSA clones emerged after 2010.ConclusionThe molecular epidemiology of MRSA isolates in our neonatal units from 2003 to 2018 revealed that an epidemic as well as endemic hospital clone of ST239 dominated before 2005 and was replaced by the local community clone of CC59 thereafter.     

Characterization of methicillin-resistant Staphylococcus aureus from healthy carrier chickens

Methicillin-resistant Staphylococcus aureus (MRSA) has long been recognized as an important pathogen in human medicine leading to hospital and community-acquired infections. However, it is now also considered a growing problem in veterinary medicine, although causing little or no disease. Although MRSA has already been detected in livestock including poultry, little is known about the epidemiology of MRSA in broiler and layer chickens. We therefore investigated 372 poultry farms in Belgium. We also compared the isolation method recommended by the European Food Safety Authority using two enrichment steps with an isolation method using only one enrichment step. Isolated MRSA was characterized by means of antimicrobial resistance profiling, spa typing, multi-locus sequence typing, and SCCmec typing. MRSA prevalence was 0.8% using the double broth enrichment method, while using the single broth enrichment method it was 1.8%. Five MRSA strains belonged to the livestock-associated (LA) MRSA ST398 (four with spa type t011 and one with t899), and three to the hospital-acquired MRSA ST239 spa type t037. The ST239 strains carried SCCmec type III while those belonging to ST398 carried SCCmec type IV or V. All isolates showed additional resistance to erythromycin and tetracycline apart from the expected resistance to cefoxitin and penicillin. All strains were susceptible to linezolid, mupirocin and vancomycin. In conclusion, a higher sensitivity for the isolation of LA-MRSA was obtained using only one enrichment step. While the typical LA-MRSA ST398 was present at low prevalence in poultry, human-associated strains have also been found.     

Comparison of Genotypes and Enterotoxin Genes Between Staphylococcus aureus Isolates from Blood and Nasal Colonizers in a Korean Hospital

In this study, we investigated the genetic background of 70 Staphylococcus aureus isolates (36 methicillin-resistant S. aureus [MRSA] and 34 methicillin-susceptible S. aureus [MSSA]) obtained from blood at a Korean tertiary-care hospital, using spa typing, multilocus sequence typing, and SCCmec typing. In addition, the prevalence of enterotoxin (sea, seb, sec, sed, see, seg, seh, sei, and sek), tst, and pvl genes among the samples was assessed via polymerase chain reaction, and the results were compared with those of 95 isolates of S. aureus obtained from nasal swabs. All MRSA isolates from blood, except one, belonged to three major clones: sequence type (ST)5-MRSA-II, ST72-MRSA-II (or IVA), and ST239-MRSA-III, among which ST5-MRSA-II was the predominant clone. The prevalence of enterotoxin genes in the S. aureus isolates obtained from blood differed significantly from those from the nasal swabs for the sea, seb, sec, and seh gene. In particular, the seb and sec genes were detected exclusively in the MRSA isolates of ST5 or spa-CC002, thereby suggesting the co-adaptation of virulence genes with the genetic background and their contribution to biological fitness.     

Population structure analyses of Staphylococcus aureus at Tygerberg Hospital,South Africa,reveals a diverse population,a high prevalence of Panton–Valentine leukocidin genes,and unique local methicillin-resistant S. aureus clones

Studies reporting on the population structure of Staphylococcus aureus in South Africa have focused only on methicillin-resistant S. aureus (MRSA). This study describes the population structure of S. aureus, including methicillin-susceptible S. aureus (MSSA) isolated from patients at Tygerberg Academic Hospital, Western Cape province. Pulsed-field gel electrophoresis (PFGE), detection of Panton–Valentine leukocidin (PVL), spa typing, multilocus sequence typing (MLST), agr typing and SCCmec typing were used to characterize strains. Of 367 non-repetitive S. aureus isolates collected over a period of 1 year, 56 (15.3%) were MRSA. Skin and soft tissue infections were the most frequent source (54.8%), followed by bone and joint (15.3%) and respiratory tract infections (7.7%). For strain typing, PFGE was the most discriminative method, and resulted in 31 pulsotypes (n = 345, 94.0%), as compared with 16 spa clonal complexes (CCs) (n = 344, 93.4%). Four MLST CCs were identified after eBURST of sequence types (STs) of selected isolates. One hundred and sixty isolates (MSSA, n = 155, 42.2%) were PVL-positive, and agr types I–IV and SCCmec types I–V were identified. Our S. aureus population consisted of genotypically diverse strains, with PVL being a common characteristic of MSSA. MSSA and MRSA isolates clustered in different clones. However, the dominant MRSA clone (ST612) also contained an MSSA isolate, and had a unique genotype. Common global epidemic MRSA clones, such as ST239-MRSA-III and ST36-MRSA-II, were identified. A local clone, ST612-MRSA-IV, was found to be the dominant MRSA clone.     

High frequency of multidrug‐resistant Staphylococcus aureus with SCCmec type III and Spa types t037 and t631 isolated from burn patients in southwest of Iran

Methicilin resistance Staphylococcus aureus (MRSA) infections are the major challenges in hospitals, especially in the burn units. The use of molecular typing methods is essential for tracking the spread of S. aureus infection and epidemiological investigations. The aim of this study was to find the profile of the spa types and also the prevalence of each SCCmec type of S. aureus strains in a central burn hospital in southwest of Iran. A total of 81 non‐duplicate S. aureus were isolated from burn patients between April 2011 and February 2012. The susceptibility of the isolates against 13 different antibiotics was tested by disk agar diffusion (DAD) method. MRSA strains were identified by amplification of mecA gene. Multiplex‐polymerase chain reaction (PCR) technique was used to determine the SCCmec types of MRSA strains and all the S. aureus isolates were typed by spa typing method. Detection of mecA gene showed that 70 (86.4%) of the isolates were MRSA. The highest rate of resistance was observed for penicillin (97.5%) and erythromycin (77.8%). None of the isolates were resistant to vancomycin. Sixty‐seven of the 70 MRSA isolates harbored only SCCmec type III and three untypeable isolates. Five different spa types were detected. The most common spa types were t037 (42.5%) and t631 (34.5%) and were only found in MRSA isolates. Only SCCmec type III was found in burn patients which emphasizes the HA‐MRSA origin of these strains. Only five different spa types identified in this study are in accordance with one SCCmec type which indicates that a limited number of bacterial colons are circulated in the burn unit in this hospital.     

Molecular characterization of nasal methicillin resistant Staphylococcus aureus isolates from workers of an automaker company in southeast Iran

Colonization of methicillin resistant Staphylococccus aureus (MRSA) can occur more commonly in healthy people who live in close together or are in close physical contact with each other. Having knowledge about the molecular characteristics of these strains provides considerable discernment into the epidemiology of this important microorganism. A total of 806 nasal swabs were collected from healthy workers of an automaker company in the southeast of Iran and were analyzed to detect MRSA isolates. Multilocus sequence typing (MLST), spa typing, and detection of staphylococcal cassette chromosome mec (SCCmec) were performed. The presence of genes encoding Panton‐Valentine Leukocidin (PVL) and Arginine Catabolic Mobile Element (ACME) were also investigated. Carriage rate of S. aureus was 20%. Among 10 identified MRSA, no acme was found while high prevalence of pvl (60%) was of great concern. Seven different spa types including five new ones were identified. The most frequent sequence type was the novel one; ST 3373 (n = 3), followed by each of ST22, ST88, ST859 (n = 2) and ST1955 (n = 1). MRSA isolates were clustered into two main clonal complexes; CC22 (n = 6) and CC88 (n = 4). Low genetic diversity with the dominance of CC22, SCCmecIV was found. Distribution of previously found hospital‐associated MRSA was demonstrated among our isolates.     

The distribution of pathogenic and toxigenic genes among MRSA and MSSA clinical isolates

Staphylococcus aureus (S. aureus) is considered as a notorious nosocomial pathogen among hospitalized patients and community-dwelling subjects. Its increasing morbidity and mortality is believed to be due to antibiotic resistance. However, the data concerning molecular properties of infecting strains are few.In this study, a total of 192 S. aureus strains, including 88 (45.8%) meticillin-sensitive S. aureus (MSSA) and 104 (54.2%) meticillin-resistant S. aureus (MRSA) were recovered from clinical samples. The prevalence of subtypes containing staphylococcal cassette chromosome mec (SSCmec), staphylococcal enterotoxins (SEs), toxic shock syndrome toxin (TSST) and exfoliative toxin was assessed by PCR. Antibiotic susceptibility pattern and vancomycin resistance of each isolate were evaluated by disk diffusion method and micro-dilution method, respectively.9 (2.3%) strains required MIC > 2 mg/l of vancomycin, which significantly increased among multi drug resistant (MDR), MRSA and SCCmec type III strains (p < 0.05). 171 (89%), 140 (72.91%), 7 (3.6), 78 (48.6%), 5 (2.6%), 151 (78.64%), 129 (67.18%), 178 (92.7%) and 15 (7.8%) of 192 isolates harbored mecA, entA, entB, entC, entD, entE, eta, etb and tsst-1 genes, respectively. 31 (16.14%), 5 (2.6%), 95 (49.48%) and 7 (3.64%) of 192 isolates carried SCCmec type I, II, III and IV, respectively. We found a significantly higher rate of MRSA and resistance to all tested antibiotics, except to penicillin G, kanamycin and linezolide among the SCCmec type III class (p < 0.05).According to our findings, MSSA isolates should be taken as seriously as MRSA strains due to the potential presence of broad spectrum virulence factor genes.     

Prevalence and Characterization of Methicillin-Resistant Staphylococcus aureus Isolates from Retail Meat and Humans in Georgia

There is increasing interest in the presence of Staphylococcus aureus, specifically methicillin-resistant S. aureus (MRSA), on retail meat products. In this study, staphylococci were isolated from retail pork and retail beef in Georgia, and MRSA from the products was compared to human MRSA from the same geographic area using broth microdilution antimicrobial susceptibility testing, multilocus sequence typing (MLST), spa typing, SCCmec typing, and pulsed-field gel electrophoresis (PFGE). S. aureus was isolated from 45% (45/100) of pork products and 63% (63/100) of beef products; mecA was detected in S. aureus from both pork (3/100; 3%) and beef (4/100; 4%). Fifty percent (50/100) of human S. aureus also contained mecA. Multidrug resistance was detected among MRSA from all sources. All MRSA (n = 57) was SCCmec type IV, and nine different spa types were present among the isolates (t002, t008, t012, t024, t179, t337, t548, t681, and t1062). Four sequence types (ST5, ST8, ST9, and ST30) were detected using MLST; the majority of MRSA isolates belonged to ST8, followed by ST5. One retail beef MRSA isolate belonged to ST8, while the remaining three were ST5. In retail pork MRSA, ST5, ST9, and ST30 were observed. The majority of human MRSA isolates belonged to ST8. Thirty-seven MRSA isolates, one of which was a retail beef MRSA isolate, were pvl⁺. Using PFGE, MLST, and spa typing, three retail beef MRSA isolates were found to be identical in PFGE pattern, ST, and spa type to two human clonal MRSA isolates (USA100 and USA300). One additional retail beef MRSA isolate had a PFGE pattern similar to that of a human MRSA isolate, whereas none of the retail pork MRSA isolates had PFGE patterns similar to those of human MRSA isolates. These data suggest that the retail beef samples were contaminated by a human source, possibly during processing of the meat, and may present a source of MRSA for consumers and others who handle raw meat.     

Population Structure of Staphylococcus aureus Strains Isolated from Intensive Care Unit Patients in The Netherlands over an 11-Year Period (1996 to 2006)

The genetic background and the presence of several virulence factors of Staphylococcus aureus isolates from intensive care unit (ICU) patients from 14 hospitals in The Netherlands isolated from 1996 until 2006 were investigated. In total, 936 methicillin-susceptible S. aureus (MSSA) and 7 methicillin-resistant S. aureus (MRSA) isolates were collected. The genetic background was determined by spa typing and multilocus sequence typing (MLST). The virulence determinants Panton-Valentine leukocidin (PVL), toxic shock syndrome toxin 1 (TSST-1), and collagen adhesion (CNA) were detected with real-time PCR assays. On the MRSA isolates, mobile resistance staphylococcal cassette chromosome mec (SCCmec) typing was performed. Among the MSSA isolates, 313 different spa types were observed. A genetic background common to MRSA clones, e.g., MLST clonal complex 1 (CC1), CC5, CC8, CC22, CC30, and CC45, was observed among 62% of the isolates. The remaining isolates were associated with MSSA-related MLST CCs. MLST CC1, CC25, and CC30 were continuously present, and other MLST CCs fluctuated over time. Two percent of the MSSA isolates harbored PVL, 21% had TSST-1, and 46% were positive for CNA. There were no changes in the prevalence of the virulence factors over time. Four MRSA isolates were typed as ST8-MRSA-IV (where ST is the MLST sequence type and IV is the SCCmec type), two were ST5-MRSA-II, and one was ST228-MRSA-I. All MRSA isolates were PVL, CNA, and TSST-1 negative except for the two ST5-MRSA-II isolates, which were TSST-1 positive. No changes in the S. aureus genetic background and the prevalence of the virulence factors PVL, CNA, and TSST-1 were observed in ICU patients in The Netherlands over time.Around 20% of all patients in intensive case units (ICUs) acquire an ICU-related infection as a consequence of frequent use of antibiotics and intensive treatment procedures (1, 31). Of all ICU-related infections, 25% are caused by Staphylococcus aureus (31). Knowledge of the S. aureus population structure and of the prevalence of virulence factors has been proven crucial for the investigation of the epidemiology of S. aureus throughout the world (34).Methicillin-resistant S. aureus (MRSA) clones can emerge by horizontal transfer of the staphylococcal cassette chromosome mec (SCCmec) between methicillin-resistant coagulase-negative Staphylococcus or MRSA and methicillin-susceptible S. aureus (MSSA) (51). In the event of antibiotic pressure, the MSSA isolates have a high risk of SCCmec transfer and survive. As shown in the literature, MSSA lineages with a MRSA-unrelated background may not provide a stable genomic environment for the integration of SCCmec (4, 23, 30, 32, 36, 43). SCCmec transfer has been found to be stable in MSSA with a MRSA-related genetic background, i.e., multilocus sequence typing (MLST) clonal complex 1 (CC1), CC5, CC8, CC22, CC30, and CC45 (39). The MSSA lineages with a MRSA background possess certain characteristics that favor their persistence in the host as well as the transfer between hosts.As the highest antibiotic pressure in hospitals is found in ICUs, changes in the genetic background will be the most obvious among isolates from ICU patients. However, little is known about the genetic backgrounds of ICU isolates over time, and, therefore, this study investigates the genetic background and the virulence of S. aureus isolates obtained from 1996 to 2006 from ICU patients from 14 hospitals in The Netherlands.     

National Surveillance of Methicillin-Resistant Staphylococcus aureus in China Highlights a Still-Evolving Epidemiology with 15 Novel Emerging Multilocus Sequence Types

The global spread of methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem, particularly in mainland China. In order to better understand the national molecular epidemiology and resistance profiles of hospital-associated MRSA (HA-MRSA) in China, a laboratory-based multicenter surveillance study was conducted. Sixty-nine hospitals in 45 large cities in 27 provinces were involved, and a total of 1,141 HA-MRSA isolates were collected during the 6-month study period in 2011. All MRSA isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, detection of the Panton-Valentine leukocidin (PVL) locus (lukS-PV and lukF-PV), and antibiogram analysis. ST239-III-t030, ST239-III-t037, and ST5-II-t002 were the predominant HA-MRSA clones (overall prevalence rates, 57.1%, 12.9%, and 8.1%, respectively), although the prevalence rates of these major clones varied markedly in different administrative regions. Of note, 6.6% of the HA-MRSA isolates were found to belong to ST59, which had typical community-associated MRSA (CA-MRSA) features, including carriage of SCCmec type IV or V and PVL and less antimicrobial resistance than other major HA-MRSA clones. Moreover, among 36 MLST sequence types (STs) identified, 15 STs, accounting for 3.5% of total isolates, were novel. A novel ST designated ST2590, which is a single-locus variant of ST5-II-t002, was identified in three hospitals in two large cities, with a total of 17 isolates. To further monitor trends in HA-MRSA prevalence, epidemic clonal shifts, clone emergence, and transmission between community and health care settings, longitudinal national MRSA surveillance is required.