Molecular characterization of methicillin-resistant Staphylococcus aureus isolates in Korea

Molecular characterization and antibiotic resistance of Staphylococcus aureus strains isolated from patients with diarrhea in Korea between the years 2007 and 2022

To investigate the molecular characteristics and antibiotic resistance of Staphylococcus aureus isolates from patients with diarrhea in Korea, 327 S. aureus strains were collected between 2007 and 2022. The presence of staphylococcal enterotoxin (SE) and toxic shock syndrome toxin-1 (TSST-1) genes in S. aureus isolates was determined by PCR. The highest expression of the TSST-1 gene was found in the GIMNO type (43.1% of GIMNO type). GIMNO type (Type I) refers to each staphylococcal enterotoxin (SE) gene gene (initials of genes): G = seg; I = sei; M = selm; N = seln; O = selo. Moreover, Type I isolates showed a significantly higher resistance to most antibiotics. A total of 195 GIMNO-type S. aureus strains were analyzed using multilocus sequence typing (MLST), and 18 unique sequence types (STs) were identified. The most frequent sequence type was ST72 (36.9%), followed by ST5 (22.1%) and ST30 (16.9%). Interestingly, ST72 strains showed a higher prevalence of MRSA than the other STs. In conclusion, our results were the first reported for S. aureus strains in Korea, which significantly expanded S. aureus genotype information for the surveillance of pathogenic S. aureus and may provide important epidemiological information to resolve several infectious diseases caused by S. aureus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01478-9.

Clinical and microbiological characteristics of rifampicin-resistant MRSA bacteraemia

OBJECTIVES

The clinical significance of rifampicin resistance in Staphylococcus aureus infections has not been demonstrated. Here, we evaluated the clinical characteristics of rifampicin-resistant S. aureus infection.

METHODS

Data were collected from adult patients who were hospitalized with MRSA bacteraemia between March 2007 and May 2020 at a tertiary hospital in South Korea. The clinical characteristics and treatment outcomes of patients infected with rifampicin-resistant MRSA were compared with those of rifampicin-susceptible isolates. All-cause death and recurrence of MRSA infection were assessed for 90 days.

RESULTS

Of the 961 patients with MRSA bacteraemia, 61 (6.3%) were infected by rifampicin-resistant isolates. The type of infection focus and duration of bacteraemia did not significantly differ between the two groups. Rifampicin-resistant MRSA isolates were more likely to have multidrug resistance and a higher vancomycin MIC relative to the rifampicin-susceptible isolates. The 90-day recurrence rate was higher in the patients infected with rifampicin-resistant MRSA compared with those with rifampicin-susceptible MRSA (18.0% versus 6.2%, P < 0.001), whereas the 90-day mortality was comparable between the two groups (27.9% versus 29.2%, P = 0.94). After adjusting for potential confounding factors, rifampicin resistance was significantly associated with 90-day recurrence (subdistributional HR: 2.31; 95% CI: 1.05-5.10; P = 0.04).

CONCLUSIONS

Rifampicin-resistant MRSA isolates showed distinct microbiological features in terms of multidrug resistance and a high vancomycin MIC. Although the management of MRSA bacteraemia was not significantly different between the two groups, recurrence was significantly more common in the rifampicin-resistant group. Rifampicin resistance may play a significant role in infection recurrence.

Clinical and Microbiological Characteristics of Hospital-Acquired Methicillin-Resistant Staphylococcus aureus Bacteremia Caused by a Community-Associated PVL-Negative Strain

Background

ST72-SCCmecIV, a community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain in Korea, originated in the community and has been spreading in health care settings. Herein, we describe the clinical and microbiological characteristics of patients with hospital-acquired MRSA bacteremia (MRSAB) caused by community-associated strains.

Methods

We analyzed hospital-acquired MRSAB cases caused by ST72-SCCmecIV using a prospective cohort of patients with SAB in a tertiary hospital in Korea from July 2008 to December 2018. We compared the clinical and microbiological characteristics of ST72-SCCmecIV with ST5-SCCmecII, a representative hospital-associated genotype strain.

Results

Of the 1782 S. aureus bacteremia (SAB) cases, 628 (35.2%) were hospital-acquired MRSAB. Of the 628 isolates, 431 (68.6%) were ST5-SCCmecII and 152 (24.2%) were ST72-SCCmecIV. Patients with ST72-SCCmecIV were younger than those with ST5-SCCmecII and less likely to have a history of recent surgery, antibiotic treatment, nasal MRSA colonization, and central venous catheter placement. Compared with ST5-SCCmecII, ST72-SCCmecIV isolates were more likely to have vancomycin MICs ≤1.0 mg/L (P < .001). Osteoarticular infection as the site of infection (7.2% [11/152] vs 1.4% [6/431]) was more common in patients with ST72-SCCmecIV. There were no significant differences in the rate of recurrence (≤90 days), persistent bacteremia (≥7 days), or 30- and 90-day mortality rates between the 2 groups.

Conclusions

Osteoarticular infections were more prevalent in ST72-SCCmecIV MRSAB. Mortality rates between the ST72-SCCmecIV and ST5-SCCmecII groups were not significantly different.

MoWa: A Disinfectant for Hospital Surfaces Contaminated With Methicillin-Resistant Staphylococcus aureus (MRSA) and Other Nosocomial Pathogens

Introduction

Staphylococcus aureus strains, including methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA), are a main cause of nosocomial infection in the world. The majority of nosocomial S. aureus-infection are traced back to a source of contaminated surfaces including surgery tables. We assessed the efficacy of a mixture of levulinic acid (LA) and sodium dodecyl sulfate (SDS), hereafter called MoWa, to eradicate nosocomial pathogens from contaminated surfaces.

Methods and Results

A dose response study demonstrated that MoWa killed 24 h planktonic cultures of S. aureus strains starting at a concentration of (LA) 8.2/(SDS) 0.3 mM while 24 h preformed biofilms were eradicated with 32/1.3 mM. A time course study further showed that attached MRSA bacteria were eradicated within 4 h of incubation with 65/2 mM MoWa. Staphylococci were killed as confirmed by bacterial counts, and fluorescence micrographs that were stained with the live/dead bacterial assay. We then simulated contamination of hospital surfaces by inoculating bacteria on a surface prone to contamination. Once dried, contaminated surfaces were sprayed with MoWa or mock-treated, and treated contaminated surfaces were swabbed and bacteria counted. While bacteria in the mock-treated samples grew at a density of ~10⁴ cfu/cm², those treated for ~1 min with MoWa (1.0/0.04 M) had been eradicated below limit of detection. A similar eradication efficacy was obtained when surfaces were contaminated with other nosocomial pathogens, such as Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, or Staphylococcus epidermidis.

Conclusions

MoWa kills planktonic and biofilms made by MRSA and MSSA strains and showed great efficacy to disinfect MRSA-, and MSSA-contaminated, surfaces and surfaces contaminated with other important nosocomial pathogens.

Livestock-associated methicillin-resistant Staphylococcus aureus in Korea: antimicrobial resistance and molecular characteristics of LA-MRSA strains isolated from pigs, pig farmers, and farm environment

The emergence of livestock-associated (LA)-methicillin-resistant Staphylococcus aureus (MRSA) in livestock animal has become a significant zoonotic concern. In the present study, we investigated nationwide prevalence of LA-MRSA across pork production chain including pig farms, slaughterhouses, and retail markets. A total of 40 MRSA strains were isolated during the investigation and the overall prevalence of MRSA was 3.4% (n = 37), 0.6% (n = 2), and 0.4% (n = 1) in pig farms, slaughterhouses, and retail markets, respectively. Multilocus sequence typing analyses revealed that the 2 most significant clonal lineages in pork production chain in Korea were ST398 (n = 25) and ST541 (n = 6). All of the 40 MRSA isolates were further characterized to investigate key genotypic and phenotypic correlates associated with the emergence and spread of clonal complex 398 (CC398; ST398, and ST541) LA-MRSA. Although the prevalence of swine-associated MRSA was still relatively low and mostly restricted to pig farms, multidrug-resistant CC398 LA-MRSA isolates with new spa types (t18102 and t18103) were identified as a major clonal lineage. The CC398 LA-MRSA strains tended to exhibit increased levels of multiple drug resistance (MDR) phenotype compared with non-CC398 MRSA strains. Of note, in comparison with non-CC398 MRSA isolates, CC398 LA-MRSA isolates exhibited significantly enhanced tetracycline (TET) and zinc resistance. These findings suggested that co-selection pressure associated with MDR phenotype, especially TET resistance, and zinc resistance may have played a significant role in the emergence and persistence of CC398 LA-MRSA in pig farms in Korea.

Molecular epidemiology and virulence factors of methicillin-resistant Staphylococcus aureus isolated from patients with bacteremia

BACKGROUND

The various virulence factors of methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) are associated with a high mortality rate worldwide. Further studies are warranted to confirm the significant relationship between the strains and virulence genes. Here, we prospectively investigated the molecular characteristics underlying the genotypes and virulence factors of MRSA isolated from patients with bacteremia.

METHODS

We collected 59 MRSA isolates from adult patients with bacteremia. Antimicrobial susceptibility results were obtained with the Vitek2 automated system. Genotypes were identified with multi-locus sequence typing (MLST) and pulse-field gel electrophoresis (PFGE), and 21 virulence genes were detected with polymerase chain reaction (PCR).

RESULTS

The 59 MRSA isolates mainly comprised ST5 (n = 31, 52.5%) and ST72 (n = 22, 37.2%). Most ST5 isolates and all ST72 isolates were clustered into one and two PFGE groups, respectively. The mean number of virulence genes was higher in ST5 than in ST72. Sel was more frequently detected in ST5 than in ST72, whereas sec and sed were found only in ST5. ST5 had significantly higher resistance against many antibiotics than ST72.

CONCLUSION

Most MRSA isolates causing bacteremia were ST5 (CC5) and ST72 (CC8), and those belonging to the same STs were divided into only a few PFGE groups. ST5 was associated with higher antibiotic resistance and staphylococcal superantigen toxin genes, than ST72, which may be related to its higher virulence.

A comparative genomic analysis between methicillin-resistant Staphylococcus aureus strains of hospital acquired and community infections in Yunnan province of China

BACKGROUND

Currently, Staphylococcus aureus is one of the most important pathogens worldwide, especially for methicillin-resistant S. aureus (MRSA) infection. However, few reports referred to patients' MRSA infections in Yunnan province, southwest China.

METHODS

In this study, we selected representative MRSA strains from patients' systemic surveillance in Yunnan province of China, performed the genomic sequencing and compared their features, together with some food derived strains.

RESULTS

Among sixty selective isolates, forty strains were isolated from patients, and twenty isolated from food. Among the patients' strains, sixteen were recognized as community-acquired (CA), compared with 24 for hospital-acquired (HA). ST6-t701, ST59-t437 and ST239-t030 were the three major genotype profiles. ST6-t701 was predominated in food strains, while ST59-t437 and ST239-t030 were the primary clones in patients. The clinical features between CA and HA-MRSA of patients were statistical different. Compared the antibiotic resistant results between patients and food indicated that higher antibiotic resistant rates were found in patients' strains. Totally, the average genome sizes of 60 isolates were 2.79 ± 0.05 Mbp, with GC content 33% and 84.50 ± 0.20% of coding rate. The core genomes of these isolates were 1593 genes. Phylogenetic analysis based on pan-genome and SNP of strains showed that five clustering groups were generated. Clustering ST239-t030 contained all the HA-MRSA cases in this study; clustering ST6-t701 referred to food and CA-MRSA infections in community; clustering ST59-t437 showed the heterogeneity for provoking different clinical diseases in both community and hospital. Phylogenetic tree, incorporating 24 isolates from different regions, indicated ST239-t030 strains in this study were more closely related to T0131 isolate from Tianjin, China, belonged to 'Turkish clade' from Eastern Europe; two groups of ST59-t437 clones of MRSA in Yunnan province were generated, belonged to the 'Asian-Pacific' clone (AP) and 'Taiwan' clone (TW) respectively.

CONCLUSIONS

ST239-t030, ST59-t437 and ST6-t701 were the three major MRSA clones in Yunnan province of China. ST239-t030 clonal Yunnan isolates demonstrated the local endemic of clone establishment for a number of years, whereas ST59-t437 strains revealed the multi-origins of this clone. In general, genomic study on epidemic clones of MRSA in southwest China provided the features and evolution of this pathogen.

Molecular Epidemiology of Staphylococcus aureus in Skin and Soft Tissue Infections and Bone and Joint Infections in Korean Children

BACKGROUND

Community acquired-methicillin resistant Staphylococcus aureus (MRSA) clones, including ST1, ST8, and ST30 are reported worldwide. However, data among Korean children are limited. Thus, we investigated the molecular characteristics of S. aureus among children in Korea.

METHODS

S. aureus isolated from Korean children diagnosed with skin and soft tissue infection (SSTI) or bone and joint infection due to S. aureus infection at Seoul National University Bundang Hospital, from August 2010 to November 2016, were analyzed for multilocus sequence type (ST) and SCCmec typing. Polymerase chain reaction of Panton-Valentine leukocidin (PVL), qac A/B, smr and mupA genes were also performed. Electronic medical records were reviewed for clinical data and antibiotic susceptibility results. Cases were classified into three groups: health care-associated community-onset (HACO) infections, hospital-onset (HO) infections, and community-acquired (CA) infections.

RESULTS

A total of 67 strains from children with SSTI (41/67, 61.2%) and bone and joint infection (26/67, 38.8%) were included. Among all isolates, 29.9% (20/67) were MRSA, and 70% (14/20) were classified as CA, 20% (4/20) as HACO and 10% (2/20) as HO infections. MRSA rate according to disease was 34.1% (14/41) for SSTI and 23.1% (6/26) for bone and joint infection. MRSA strains included ST72-SCCmec IV (14/20, 70.0%), ST5-SCCmec II (3/20, 15.0%) and ST1-SCCmec IV (2/20, 10.0%). ST30 was the most common cause of SSTI and bone and joint infections and 96.6% (28/29) were methicillin-susceptible Staphylococcus aureus (MSSA). PVL genes were detected in 3 strains (3.8%, ST30-SCCmec IV n = 1, MSSA ST30 n = 2), qac A/B in 3 (MRSA = 3), smr in 3 (MSSA = 1, MRSA = 2) and mupA in 7 (MRSA = 5, MSSA = 2).

CONCLUSION

Molecular epidemiology of S. aureus in Korean children with SSTI and bone and joint infection showed that ST30 was predominant and mostly MSSA. Among MRSA, ST72-SCCmec type IV was the most common strain.

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

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

A Risk-Scoring System for Predicting Methicillin Resistance in Community-Onset Staphylococcus aureus Bacteremia in Korea

AIMS

We aimed to develop a simple scoring system to predict risk for methicillin resistance in community-onset Staphylococcus aureus bacteremia (CO-SAB) by identifying the clinical and epidemiological risk factors for community-onset methicillin-resistant S. aureus (MRSA).

METHODS

We retrospectively analyzed data from three multicenter cohort studies in Korea in which patient information was prospectively collected and risk factors for methicillin resistance in CO-SAB were identified. We then developed and validated a risk-scoring system.

RESULTS

To analyze the 1,802 cases of CO-SAB, we included the four most powerful predictors of methicillin resistance that we identified in the scoring system: underlying hematologic disease (-1 point), endovascular infection as the primary site of infection (-1 point), history of hospitalization or surgery in ≤1 year (+0.5 points), and previous isolation of MRSA in ≤6 months (+1.5 points). With this scoring system, cases were classified into low (less than -0.5), intermediate (-0.5-1.5), and high (≥1.5) risk groups. The proportions of MRSA cases in each group were 24.7% (22/89), 39.0% (607/1,557), and 78.8% (123/156), respectively, and 16.7% (1/6), 33.8% (112/331), and 76.9% (10/13) in a validation set.

CONCLUSIONS

This risk-scoring system for methicillin resistance in CO-SAB may help physicians select appropriate empirical antibiotics more quickly.

Emergence of Daptomycin-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Clinical Isolates Among Daptomycin-Naive Patients in Korea

This study was conducted to assess emergence of daptomycin-nonsusceptible (DAP-NS) phenotype in DAP-naive patients with invasive Staphylococcus aureus (ISA) infections in Korea. A total of 208 S. aureus clinical isolates were selected from a previous prospective study on ISA infections and evaluated for DAP-NS. Although DAP has never been introduced in Korea, five DAP-NS S. aureus strains (2.4%) were identified among 208 S. aureus strains collected from ISA infections. The DAP-NS phenotype was observed only in methicillin-resistant S. aureus (MRSA) strains, but not in methicillin-susceptible S. aureus strains. One DAP-NS MRSA strain belonged to sequence type 72 (ST72) and four were ST5 MRSA strains, three of which were heteroresistant vancomycin (VAN)-intermediate S. aureus. All these five DAP-NS MRSA strains were from healthcare-associated infections without prior exposure to VAN within 30 days. While the ST72 MRSA strain exhibited DAP-NS phenotype via charge repulsion mechanism, four ST5 DAP-NS S. aureus strains had charge-independent DAP-NS mechanism. None of the five DAP-NS strains displayed significant increase in cell wall thickness, indicating that altered cell wall thickness was not associated with the observed DAP-NS phenotype.

Emergence of Community-Genotype Methicillin-Resistant Staphylococcus aureus in Korean Hospitals: Clinical Characteristics of Nosocomial Infections by Community-Genotype Strain

Background

As community-genotype methicillin-resistant Staphylococcus aureus (MRSA) strains spread into hospitals, the genotypes of the MRSA strains causing hospital-acquired (HA) infections have become more diverse. We describe clinical characteristics of nosocomial MRSA infections by a community-genotype of sequence type (ST) 72.

Materials and Methods

A case-control study was designed among patients with HA-MRSA infections. Forty patients with infections caused by ST72-MRSA SCCmec type IV were selected as cases. Cases were matched to the controls with 106 patients infected with ST5/ST239 MRSA, which are representative hospital genotypes in Korea.

Results

Patients infected with ST72 isolates were younger than those with ST5/ST239 isolates. Female gender predominated among ST72 MRSA group compared to ST5/ST239 MRSA group. Solid tumor was a more frequent underlying disease in MRSA infections by ST72 isolates, whereas underlying renal, lung, heart, and neurologic diseases were more frequently found in those by ST5/ST239 isolates. The most common type of infection was pneumonia in both ST72 and ST5/ST239 groups (45.0% vs. 51.9%), followed by skin and soft tissue infection (SSTI). Female gender and underlying solid tumor were identified to be independent predictors for MRSA infections by ST72 isolates. All-cause mortality rates (20.0% vs. 30.2%) were not different between the groups.

Conclusion

A community-genotype MRSA, ST72 isolate has emerged as a nosocomial pathogen presenting as hospital-acquired pneumonia and SSTI. Although differences in underlying disorders were found, the distribution of infection type and mortality rate did not differ between the groups.

Clinical and Molecular Characterization of Invasive Heteroresistant Vancomycin-Intermediate Staphylococcus aureus Infections in Korean Hospitals

Invasive heteroresistant vancomycin-intermediate Staphylococcus aureus (h-VISA) isolates were identified and characterized in 10 Korean hospitals from July 2009 to June 2011. The prevalence of h-VISA infections was 3.3% (42/1,289). Most (41/42) were health care-associated infections caused by strains belonging to sequence type 5. Cases of persistent bacteremia were frequent (17/42), and 30-day mortality was high (16/40).

New epidemiology of Staphylococcus aureus infection in Asia

Not only is Asia the most populous region in the world, but inappropriate therapy, including self-medication with over-the-counter antimicrobial agents, is a common response to infectious diseases. The high antibiotic selective pressure among the overcrowded inhabitants creates an environment that is suitable for the rapid development and efficient spread of numerous multidrug-resistant pathogens. Indeed, Asia is among the regions with the highest prevalence rates of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated methicillin-resistant S. aureus (CA-MRSA) in the world. Most hospitals in Asia are endemic for multidrug-resistant methicillin-resistant S. aureus (MRSA), with an estimated proportion from 28% (in Hong Kong and Indonesia) to >70% (in Korea) among all clinical S. aureus isolates in the early 2010s. Isolates with reduced susceptibility or a high level of resistance to glycopeptides have also been increasingly identified in the past few years. In contrast, the proportion of MRSA among community-associated S. aureus infections in Asian countries varies markedly, from <5% to >35%. Two pandemic HA-MRSA clones, namely multilocus sequence type (ST) 239 and ST5, are disseminated internationally in Asia, whereas the molecular epidemiology of CA-MRSA in Asia is characterized by clonal heterogeneity, similar to that in Europe. In this review, the epidemiology of S. aureus in both healthcare facilities and communities in Asia is addressed, with an emphasis on the prevalence, clonal structure and antibiotic resistant profiles of the MRSA strains. The novel MRSA strains from livestock animals have been considered to constitute a public health threat in western countries. The emerging livestock-associated MRSA strains in Asia are also included in this review.

agr dysfunction affects staphylococcal cassette chromosome mec type-dependent clinical outcomes in methicillin-resistant Staphylococcus aureus bacteremia

Staphylococcal cassette chromosome mec element (SCCmec) type-dependent clinical outcomes may vary due to geographical variation in the presence of virulence determinants. We compared the microbiological factors and mortality attributed to methicillin-resistant Staphylococcus aureus (MRSA) bacteremia between SCCmec types II/III and type IV. All episodes of MRSA bacteremia in a tertiary-care hospital (South Korea) over a 4.5-year period were reviewed. We studied the microbiological factors associated with all blood MRSA isolates, including spa type, agr type, agr dysfunction, and the genes for Panton-Valentine leukocidin (PVL) and phenol-soluble modulin (PSM)-mec, in addition to SCCmec type. Of 195 cases, 137 involved SCCmec types II/III, and 58 involved type IV. The mortality attributed to MRSA bacteremia was less frequent among the SCCmec type IV (5/58) than that among types II/III (39/137, P = 0.002). This difference remained significant when adjusted for clinical factors (adjusted odds ratio [aOR], 0.14; 95% confidence interval [CI], 0.04 to 0.49; P = 0.002). Of the microbiological factors tested, agr dysfunction was the only significant factor that showed different positivity between the SCCmec types, and it was independently associated with MRSA bacteremia-attributed mortality (aOR, 4.71; 95% CI, 1.72 to 12.92; P = 0.003). SCCmec type IV is associated with lower MRSA bacteremia-attributed mortality than are types II/III, which might be explained by the high rate of agr dysfunction in SCCmec types II/III in South Korea.

Clinical importance and epidemiology of quinolone resistance

The quinolone class of antimicrobial agents is one of most widely used classes of antimicrobial agents in outpatient and inpatient treatment. However, quinolone resistance in gram-positive and gram-negative bacteria has emerged and increased globally. This resistance limits the usefulness of quinolones in clinical practice. The review summarizes mechanisms of quinolone resistance and its epidemiology and implications in the most common clinical settings, urinary tract infections, respiratory tract infections, intraabdominal infections, skin and skin structure infections, and sexually transmitted diseases.

Clinical and epidemiological factors associated with methicillin resistance in community-onset invasive Staphylococcus aureus infections: prospective multicenter cross-sectional study in Korea

Successful empirical therapy of Staphylococcus aureus infections requires the ability to predict methicillin resistance. Our aim was to identify predictors of methicillin resistance in community-onset (CO) invasive S. aureus infections. Sixteen hospitals across Korea participated in this study from May to December 2012. We prospectively included cases of S. aureus infection in which S. aureus was isolated from sterile clinical specimens ≤72 hours after hospitalization. Clinical and epidemiological data were gathered and compared in methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) cases. Community-associated (CA) infections were defined as in previous studies. In total, there were 786 cases of community-onset S. aureus infection, 102 (13.0%) of which were CA-MRSA. In addition to known risk factors, exposure to 3rd generation cephalosporins in the past 6 months [odds ratio (OR), 1.922; 95% confidence interval (CI), 1.176–3.142] and close contact with chronically ill patients in the past month (OR, 2.647; 95% CI, 1.189–5.891) were independent risk factors for MRSA infection. However, no clinical predictors of CA-MRSA were identified. Methicillin resistance, CO infection, and appropriateness of empirical antibiotics were not significantly related to 30-day mortality. MRSA infection should be suspected in patients recently exposed to 3rd generation cephalosporins or chronically-ill patients. There were no reliable predictors of CA-MRSA infection, and mortality was not affected by methicillin resistance.

Community-associated MRSA strain ST72-SCCmecIV causing bloodstream infections: clinical outcomes and bacterial virulence factors

OBJECTIVES

Community-associated MRSA (CA-MRSA) has emerged in the community and has recently been spreading in healthcare settings. The objectives of this study were to evaluate the clinical outcomes and bacterial virulence factors of the Korean CA-MRSA (ST72-SCCmecIV) strain, which causes bloodstream infections.

METHODS

All adult patients with MRSA bacteraemia were prospectively enrolled. Clinical outcomes, microbiological characteristics and 40 bacterial virulence factors were evaluated.

RESULTS

Of the 352 typed MRSA isolates, 342 isolates (97.2%) belonged to three Panton-Valentine leucocidin-negative strains: ST5-SCCmecII (70.2%), ST72-SCCmecIV (22.4%) and ST239-SCCmecIII (4.6%). The remaining 10 (2.8%) isolates from minor strains were excluded from the final analysis. After controlling for several confounding factors, ST72-SCCmecIV was associated with the lowest mortality (compared with ST5-SCCmecII, adjusted OR=0.26; 95% CI=0.13-0.54). However, MRSA isolates with vancomycin MICs of ≥ 1.5 mg/L were more common in ST72-SCCmecIV compared with ST5-SCCmecII (84.8% versus 66.7%; P=0.002). Reduced vancomycin susceptibility and vancomycin heteroresistance were not associated with mortality. Compared with ST5-SCCmecII isolates, ST72-SCCmecIV isolates were less likely to harbour multiple virulence genes. Of these genes, three staphylococcal superantigen genes were associated with mortality: sec (OR=2.31; P=0.002), sel (OR=2.55; P=0.003) and tst (OR=2.76; P<0.001).

CONCLUSIONS

After controlling for confounding factors, ST72-SCCmecIV was independently associated with lower mortality compared with ST5-SCCmecII, suggesting this CA-MRSA strain to be of lower virulence. The lack of virulence genes, including staphylococcal superantigen genes, may play a role in the lower virulence of this strain.

Outbreak among healthy newborns due to a new variant of USA300-related meticillin-resistant Staphylococcus aureus

BACKGROUND

The prevalence of community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) is increasing throughout the world and is an important cause of skin and soft tissue infection (SSTI) in children and neonates.

AIM

To describe the successful control of an outbreak caused by a new strain of CA-MRSA in a newborn nursery.

METHODS

The investigation of the outbreak in July 2012 is reported with the control measures taken. Molecular typing of the MRSA isolates was performed.

FINDINGS

An outbreak of SSTI caused by CA-MRSA occurred in a newborn nursery. Six neonates were infected in a one-month period [infection rate: 8.5% (6/71)]. A new variant of CA-MRSA was responsible, which was characterized as USA300-related, Panton-Valentine Leucocidin (PVL) positive, arginine catabolic mobile element (ACME) negative, sequence type 8 (ST8), staphylococcal cassette chromosome mec (SCCmec) type IVa, agr type I and spa type t008. The outbreak among term neonates followed a rapid transmission pattern and was successfully controlled by implementing various outbreak control measures, including universal chlorhexidine bathing.

CONCLUSION

This is the first report of a hospital outbreak caused by a USA300-related CA-MRSA clone in Korea. Early recognition and reinforcement of infection control measures are important in decreasing transmission of CA-MRSA in a hospital setting.

Community-associated methicillin-resistant Staphylococcus aureus case studies

Over the past decade, the emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has changed the landscape of S. aureus infections around the globe. Initially recognized for its ability to cause disease in young and healthy individuals without healthcare exposures as well as for its distinct genotype and phenotype, this original description no longer fully encompasses the diversity of CA-MRSA as it continues to expand its niche. Using four case studies, we highlight a wide range of the clinical presentations and challenges of CA-MRSA. Based on these cases we further explore the globally polygenetic background of CA-MRSA with a special emphasis on generally less characterized populations.

Association of norB overexpression and fluoroquinolone resistance in clinical isolates of Staphylococcus aureus from Korea

OBJECTIVES

Although the prevalence of fluoroquinolone resistance among methicillin-resistant Staphylococcus aureus (MRSA) is known to be higher than in methicillin-susceptible S. aureus (MSSA), the reasons have never been identified.

METHODS

We randomly selected 115 isolates of S. aureus collected from 10 different hospitals in Korea between June 2009 and May 2011. To investigate the difference in fluoroquinolone resistance mechanisms between MRSA and MSSA, we evaluated gyrA and parC mutations and the relative expression of the multidrug efflux pump genes norA, norB and norC.

RESULTS

All 62 ciprofloxacin-resistant S. aureus had either gyrA or parC mutations. The S84L mutation of gyrA (59/62, 95.2%) and the S80F mutation of parC (61/62, 98.4%) were the most common. Fifty-eight (93.6%) strains had both the S84L mutation of gyrA and the S80F mutation of parC. Among the 115 isolates, norB overexpression was the most common, occurring in 49 (42.6%) strains. There were only two (1.7%) strains with norA overexpression and none with norC overexpression. Strains overexpressing norB were more common among ciprofloxacin-resistant S. aureus (33/62, 53.2%) than ciprofloxacin-susceptible S. aureus (16/53, 30.2%) (P = 0.013). When we analysed 62 ciprofloxacin-resistant S. aureus strains, those overexpressing norB were more common in ciprofloxacin-resistant MRSA (28/46, 60.9%) than in ciprofloxacin-resistant MSSA (5/16, 31.3%) (P = 0.041).

CONCLUSIONS

Increased expression of norB can be a factor that contributes to ciprofloxacin resistance in MRSA strains.

Evolution of community- and healthcare-associated methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a prominent cause of human infections globally. The high prevalence of infections is compounded by antibiotic resistance--a significant problem for treatment. Methicillin-resistant S. aureus (MRSA) is endemic in hospitals and healthcare facilities worldwide, and is an increasingly common cause of community-associated bacterial infections in industrialized countries. Although much focus is placed on the role of S. aureus as a human pathogen, it is in fact a human commensal organism that has had a relatively long coexistence with the human host. Many S. aureus infections can be explained by host susceptibility or other predisposing risk factors. On the other hand, the emergence/re-emergence of successful S. aureus clones (referred to as epidemic waves) suggests a rapid bacterial adaption and evolution, which includes the emergence of antibiotic resistance and increased virulence and/or transmissibility. It is within this context that we review our understanding of selected S. aureus epidemic waves, and highlight the use of genome sequencing as a means to better understand the evolution of each lineage.

Difference in agr dysfunction and reduced vancomycin susceptibility between MRSA bacteremia involving SCCmec types IV/IVa and I-III

BACKGROUND

Dysfunction of agr, with reduced susceptibility or hetero-resistance to vancomycin, is thought to be associated with a worse outcome of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia (MRSAB). However, the difference in agr dysfunction according to the SCCmec type in MRSA infection is undetermined. We compared the prevalence of agr dysfunction, reduced vancomycin susceptibility and the outcomes of SCCmec IV/IVa and I-III MRSAB.

METHODS

The study included 307 cases of MRSAB. SCCmec types were determined by multiplex PCR. The clinical and microbiological features and outcomes of 58 SCCmec IV/IVa MRSAB were compared with those of 249 SCCmec I-III MRSAB.

RESULTS

Compared with SCCmec I-III MRSAB, SCCmec IV/IVa MRSAB was associated with lower rates of agr dysfunction (3% vs. 43%), vancomycin minimum inhibitory concentration (MIC) = 2 µg/mL (3% vs. 15%), and hetero-resistance to vancomycin (0% vs. 8%) (all P<0.05). However, the 30-day and S. aureus-related mortality in patients with SCCmec IV/IVa MRSAB were not different from those in patients with SCCmec I-III MRSAB in multivariate analyses (HR 1.168, 95% CI 0.705-1.938; HR 1.025, 95% CI 0.556-1.889).

CONCLUSIONS

SCCmec IV/IVa MRSAB was associated with lower rates of agr dysfunction and hetero-resistance to vancomycin and a lower vancomycin MIC, compared with SCCmec I-III MRSAB. However, the outcomes of SCCmec IV/IVa MRSAB did not differ from those of SCCmec I-III MRSAB.