Prospective Surveillance of Community-Onset and Healthcare-Associated Methicillin-ResistantStaphylococcus aureusIsolated from a University-Affiliated Hospital in Japan

Genomic characterization of Staphylococcus aureus isolated from patients admitted to intensive care units of a tertiary care hospital: epidemiological risk of nasal carriage of virulent clone during admission

We conducted a molecular epidemiological study of Staphylococcus aureus using whole-genome sequence data and clinical data of isolates from nasal swabs of patients admitted to the intensive care unit (ICU) of Hiroshima University hospital. The relationship between isolate genotypes and virulence factors, particularly for isolates that caused infectious diseases during ICU admission was compared with those that did not. The nasal carriage rates of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in patients admitted to the ICU were 7.0% and 20.1%, respectively. The carriage rate of community-acquired (CA)-MRSA was 2.3%, accounting for 32.8% of all MRSA isolates. Whole-genome sequencing analysis of the MRSA isolates indicated that most, including CA-MRSA and healthcare-associated (HA)-MRSA, belonged to clonal complex (CC) 8 [sequence type (ST) 8] and SCCmec type IV. Furthermore, results for three disease foci (pneumonia, skin and soft tissue infection, and deep abscess) and the assessment of virulence factor genes associated with disease conditions [bacteremia, acute respiratory distress syndrome (ARDS), disseminated intravascular coagulopathy (DIC), and septic shock] suggested that nasal colonization of S. aureus clones could represent a risk for patients within the ICU. Particularly, MRSA/J and MSSA/J may be more likely to cause deep abscess infection; ST764 may cause ventilation-associated pneumonia, hospital-acquired pneumonia and subsequent bacteremia, and ARDS, and tst-1-positive isolates may cause DIC onset.IMPORTANCENasal colonization of MRSA in patients admitted to the intensive care unit (ICU) may predict the development of MRSA infections. However, no bacteriological data are available to perform risk assessments for Staphylococcus aureus infection onset. In this single-center 2-year genomic surveillance study, we analyzed all S. aureus isolates from nasal swabs of patients admitted to the ICU and those from the blood or lesions of in-patients who developed infectious diseases in the ICU. Furthermore, we identified the virulent clones responsible for causing infectious diseases in the ICU. Herein, we report several virulent clones present in the nares that are predictive of invasive infections. This information may facilitate the design of preemptive strategies to identify and eradicate virulent MRSA strains, reducing nosocomial infections within the ICU.

Epidemiological Study on Case Definition of Methicillin-Resistant Staphylococcus aureus Enteritis

Background

Methicillin-resistant Staphylococcus aureus (MRSA) enteritis is a condition in which MRSA grows abnormally in the intestine after administration of antimicrobial agents, resulting in enteritis. Patients with MRSA detected in stool culture tests are often diagnosed with MSRA enteritis. However, uncertainty remains in the diagnostic criteria; therefore, we conducted epidemiological studies to define these cases.

Patients and Methods

Patients who tested positive for MRSA by stool culture using selective media 48 h after admission to Kochi Medical School Hospital between April 1, 2012, and December 31, 2022, and did not meet the exclusion criteria were included. We defined MRSA enteritis (Group A) as cases that were responsive to treatment with vancomycin hydrochloride powder, had a Bristol Stool Scale of ≥ 5, and a stool frequency of at least three times per day; all others were MRSA carriers (Group B). Multivariate analysis was performed to risk factors associated with MRSA enteritis.

Results

Groups A and B included 18 (25.4%) and 53 (74.6%) patients, respectively. Multivariate logistic regression analysis showed that a white blood cell count of > 10000/µL (odds ratio [OR], 5.50; 95% confidence interval [CI], 1.12-26.9), MRSA count of ≥ 2+ in stool cultures (OR, 8.91; 95% CI, 1.79-44.3), and meropenem administration within 1 month of stool specimen submission (OR, 7.47; 95% CI, 1.66-33.6) were risk factors of MRSA enteritis.

Conclusion

The case definitions reviewed for MRSA enteritis may be useful as diagnostic criteria.

Escalation of antimicrobial resistance among MRSA part 1: focus on global spread

INTRODUCTION

Staphylococcus aureus produce numerous virulence factors that influence tissue invasion, cytotoxicity, membrane damage, and intracellular persistence allowing them to be very common human pathogens. S. aureus isolates exhibit considerable diversity though specific genotypes have been associated with antimicrobial resistance (AMR) and toxin gene profiles. MRSA is an important pathogen causing both community-acquired (CA) and healthcare-acquired (HCA) infections. Importantly, over the past several decades, both HCA-MRSA and CA-MRSA have spread all over the globe. Even more concerning is that CA-MRSA clones have disseminated into hospitals and HCA-MRSA have entered the community. Factors that enhance spread of MRSA include: poor antimicrobial stewardship and inadequate infection control. The emergence and spread of multidrug resistant (MDR) MRSA has limited therapeutic options.

AREAS COVERED

The authors discuss the escalation of MRSA, both HCA-MRSA and CA-MRSA across the globe. A literature search of MRSA was performed via PubMed (up to September 2022), using the key words: antimicrobial resistance; β-lactams; community-associated MRSA; epidemiology; infection; multidrug resistance; Staphylococcus aureus.

EXPERT OPINION

Over the past several decades, MRSA has spread all over the globe. We encourage the judicious use of antimicrobials in accordance with antimicrobial stewardship programs along with infection control measures to minimize the spread of MRSA.

Pacemaker-associated infection caused by ST81/SCCmec IV methicillin-resistant, vancomycin-intermediate Staphylococcus aureus in Japan

A 76-year-old Japanese man was admitted to hospital for treatment of fever and skin lesion at the implantation site of his pacemaker. During his hospitalization, vancomycin-intermediate Staphylococcus aureus (MIC 4 μg/mL) with reduced susceptibility to daptomycin was isolated from venous blood. This isolate was identified as methicillin-resistant S. aureus with SCCmec IV and was genotyped as sequence type 81, coa VIIa and spa type t7044, harbouring blaZ, aac(6′)-aph(2″) and enterotoxin(-like) genes sea, seb, sek, sel, selx and selw. The patient was successfully treated with daptomycin, minocycline and sulfamethoxazole/trimethoprim. We describe the identification of sequence type 81/SCCmec IV vancomycin-intermediate S. aureus from pacemaker-associated septicaemia.

Interleukin-10 (IL-10) Produced by Mutant Toxic Shock Syndrome Toxin 1 Vaccine-Induced Memory T Cells Downregulates IL-17 Production and Abrogates the Protective Effect against Staphylococcus aureus Infection

Development of long-term memory is crucial for vaccine-induced adaptive immunity against infectious diseases such as Staphylococcus aureus infection. Toxic shock syndrome toxin 1 (TSST-1), one of the superantigens produced by S. aureus, is a possible vaccine candidate against infectious diseases caused by this pathogen. We previously reported that vaccination with less toxic mutant TSST-1 (mTSST-1) induced T helper 17 (Th17) cells and elicited interleukin-17A (IL-17A)-mediated protection against S. aureus infection 1 week after vaccination. In the present study, we investigated the host immune response induced by mTSST-1 vaccination in the memory phase, 12 weeks after the final vaccination. The protective effect and IL-17A production after vaccination with mTSST-1 were eliminated because of IL-10 production. In the presence of IL-10-neutralizing monoclonal antibody (mAb), IL-17A production was restored in culture supernatants of CD4⁺ T cells and macrophages sorted from the spleens of vaccinated mice. Vaccinated mice treated with anti-IL-10 mAb were protected against systemic S. aureus infection in the memory phase. From these results, it was suggested that IL-10 produced in the memory phase suppresses the IL-17A-dependent vaccine effect through downregulation of IL-17A production.

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.

Purulent lymphadenitis caused by Staphylococcus argenteus, representing the first Japanese case of Staphylococcus argenteus (multilocus sequence type 2250) infection in a 12-year-old boy

Staphylococcus argenteus is a novel species separated from a strain of coagulase-positive, non-pigmented S. aureus. Although S. argenteus has been reported to occur globally, multilocus sequence type (ST) 2250 is mainly found in Northeastern Thailand. Because conventional biochemical testing misidentifies this pathogen as S. aureus, multilocus sequence typing (MLST) or nucA sequencing is recommended to distinguish between S. argenteus and S. auereus. The patient was a previously healthy 12-year-old boy who was admitted because of right inguinal lymphadenitis and cellulitis. Although intravenous cefazolin was administered, his lymphadenitis worsened and formed an abscess on day 6 of hospitalization. Incision and drainage were performed on day 7 of hospitalization. Cefazolin was changed to oral cefaclor, and the patient was successfully treated over a period of 5 weeks. No recurrence was observed throughout 12-months of follow-up. He had a history of right axillary lymph node abscess 2 months before this admission, which was successfully treated with incision, drainage, and antibiotic therapy. He has lived in Japan since birth and never traveled abroad. He had no opportunity to interact with foreigners. His immune function, especially neutrophil function, was tested and we did not find any dysfunction. First, methicillin-sensitive S. aureus was misidentified from the abscess culture. Subsequently, the causative agent was re-identified as S. argenteus ST2250 based on MLST. To our knowledge, this is the first case of S. argenteus ST2250 infection in Japan. This pathogen should be taken into consideration in the diagnosis if the patient has atypical non-pigmented S. aureus.

Epidemiological Trends Observed from Molecular Characterization of Methicillin-Resistant Staphylococcus aureus Isolates from Blood Cultures at a Japanese University Hospital, 2012-2015

Despite increasing reports of skin and soft tissue infections caused by community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Japan, the extent to which these strains cause nosocomial infections remains unknown, and this is especially true for bloodstream infections. In this study, we molecularly characterized MRSA isolates from Japanese blood samples. Among the 151 MRSA isolates collected from 53 medical facilities in 2011, 115 (76%) and 30 (20%) were classified as staphylococcal cassette chromosome mec (SCCmec) types II and IV, respectively, while the Panton-Valentine leukocidin (PVL) gene was detected in only two isolates. Among 66 MRSA isolates collected from Tokyo Medical University Hospital between 2012 and 2015, 43 (65%) and 20 (30%) were classifiable as SCCmec types II and IV, respectively. In 2015, highly virulent strains, such as the SCCmec type IV/PVL and SCCmec type IV/ toxic shock syndrome toxin-1 clonal types, increased in number. Therefore, the SCCmec type IV clone may cause invasive infections not only in community settings but also in healthcare settings in Japan.

Potential Impact of Rapid Blood Culture Testing for Gram-Positive Bacteremia in Japan with the Verigene Gram-Positive Blood Culture Test

Background. Early detection of Gram-positive bacteremia and timely appropriate antimicrobial therapy are required for decreasing patient mortality. The purpose of our study was to evaluate the performance of the Verigene Gram-positive blood culture assay (BC-GP) in two special healthcare settings and determine the potential impact of rapid blood culture testing for Gram-positive bacteremia within the Japanese healthcare delivery system. Furthermore, the study included simulated blood cultures, which included a library of well-characterized methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) isolates reflecting different geographical regions in Japan. Methods. A total 347 BC-GP assays were performed on clinical and simulated blood cultures. BC-GP results were compared to results obtained by reference methods for genus/species identification and detection of resistance genes using molecular and MALDI-TOF MS methodologies. Results. For identification and detection of resistance genes at two clinical sites and simulated blood cultures, overall concordance of BC-GP with reference methods was 327/347 (94%). The time for identification and antimicrobial resistance detection by BC-GP was significantly shorter compared to routine testing especially at the cardiology hospital, which does not offer clinical microbiology services on weekends and holidays. Conclusion. BC-GP generated accurate identification and detection of resistance markers compared with routine laboratory methods for Gram-positive organisms in specialized clinical settings providing more rapid results than current routine testing.

Vaccination with non-toxic mutant toxic shock syndrome toxin-1 induces IL-17-dependent protection against Staphylococcus aureus infection

Toxic shock syndrome toxin-1 (TSST-1) is one of superantigens produced by Staphylococcus aureus. We have previously demonstrated that vaccination with non-toxic mutant TSST-1 (mTSST-1) develops host protection to lethal S. aureus infection in mice. However, the detailed mechanism underlying this protection is necessary to elucidate because the passive transfer of antibodies against TSST-1 fails to provide complete protection against S. aureus infection. In this study, the results showed that interleukin-17A (IL-17A)-producing cells were increased in the spleen cells of mTSST-1-vaccinated mice. The main source of IL-17A in mTSST-1-vaccinated mice was T-helper 17 (Th17) cells. The protective effect of vaccination was induced when the vaccinated wild type but not IL-17A-deficient mice were challenged with S. aureus. Gene expression of chemokines, CCL2 and CXCL1, and infiltration of neutrophils and macrophages were increased in spleens and livers of vaccinated mice after infection. The IL-17A-dependent immune response was TSST-1 specific because TSST-1-deficient S. aureus failed to induce the response. The present study suggests that mTSST-1 vaccination is able to provide the IL-17A-dependent host defense against S. aureus infection which promotes chemokine-mediated infiltration of phagocytes into the infectious foci.

Methicillin-resistant Staphylococcus aureus carriage among veterinary staff and dogs in private veterinary clinics in Hokkaido, Japan

To explore the prevalence and molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) in veterinary medical practices, MRSA carriage was tested among 96 veterinarians (Vets), 70 veterinary technicians (VTs) and 292 dogs with which they had contact at 71 private veterinary clinics (VCs) in Hokkaido, Japan. MRSA isolates were obtained from 22 Vets [22.9%] and 7 VTs [10%]. The prevalence of MRSA among Vets was as high as that found in an academic veterinary hospital in our previous study. In contrast, only two blood donor dogs and one dog with liver disease (1.0%, 3/292) yielded MRSA. All MRSA-positive dogs were reared or treated in different VCs, in each of which at least one veterinary staff member carrying MRSA worked. Sequence types (ST) identified by multilocus sequence typing, spa types, and SCCmec types for canine MRSA isolates (ST5-spa t002-SCCmec II [from two dogs] or ST30-spa t021-SCCmec IV [from a dog]) were concordant with those from veterinary staff members in the same clinics as the MRSA-positive dogs, with which they had potentially had contact. Most MRSA isolates from veterinary staff were the same genotype (SCCmec type II and spa type t002) as a major hospital-acquired MRSA clone in Japan. The remaining MRSA was the same genotypes as domestic and foreign community-associated MRSA. Measures against MRSA infection should be provided in private VCs.

Epidemiological analysis of methicillin-resistant Staphylococcus aureus carriage among veterinary staff of companion animals in Japan

Veterinary staff carrying methicillin-resistant Staphylococcus aureus(MRSA) can be a source of MRSA infection in animals. To identify risk factors of MRSA carriage among veterinary staff, MRSA carriage and epidemiological information (sex, career, contact with MRSA-identified animal patients and others) were analyzed from 96 veterinarians and 70 veterinary technicians working at 71 private veterinary clinics in Japan. Univariate analysis determined sex (percentage of MRSA carriage, male (29.2%) vs. female (10%); P=0.002) and career (veterinarians (22.9%) vs. veterinary technicians (10%); P=0.030) as risk factors. Multivariable analysis revealed that sex was independently associated with MRSA carriage (adjusted odds ratio, 3.717; 95% confidence interval, 1.555–8.889; P=0.003). Therefore, male veterinary staff had a higher risk of MRSA carriage than female staff.

[Molecular epidemiological study of community-acquired methicillin-resistant staphylococcus aureus (CA-MRSA) - an examination of commercially distributed meat as a possible vehicle for CA-MRSA]

Staphylococcus aureus has occupied an important position in public health as a cause of food poisoning and hospital-acquired MRSA (HA-MRSA) infections. The spread of community-acquired MRSA (CA-MRSA) infections has also recently become a concern. However, the sources of this infection remain unclear, and there are few reports of epidemiology information. In order to understand MRSA spread in the community, we investigated the distribution of MRSA strains in commercially distributed raw meat samples (n=305) and stool samples from outpatients with diarrhea (n=1,543) from the same meat distribution region in Oita Prefecture, Japan. 301 Staphylococcus aureus strains were isolated and 18 of them were MRSA (2 from chicken meat, 1 from duck meat, 1 from pork meat, and 14 from patients with diarrhea). All 18 MRSA strains were negative for Panton-Valentine leucocidin gene. In this study conducting a comparison of properties and a molecular epidemiological analysis of MRSA isolated from commercially distributed meat and diarrhea patient stools, the results suggest that commercially distributed meat could play a role in the prevalence of CA-MRSA in the community.

Molecular Characterization of Methicillin-ResistantStaphylococcus aureusin Hospitals in Niigata, Japan: Divergence and Transmission

The major methicillin-resistant Staphylococcus aureus(MRSA) distributed among hospitals in Japan is New York/Japan clone [multilocus sequence type 5 (ST5), agr type 2 and methicillin resistance locus type (SCC mec) II] which possesses both the toxic shock syndrome toxin 1 gene (tst) and staphylococcal enterotoxin C gene (sec). In this study, we collected 245 MRSA strains from four hospitals during 2001 to 2005 in Niigata, Japan, and analyzed tst and sec genes and SCC mec type among them. A total of 13 strains were further examined for their genotypes, virulence gene patterns and drug resistance. Among the 245 strains four tst sec genes patterns were observed; tst(+) sec(+) strains represented a majority of 86.5% and 9.4% were tst(-) sec(-). SCCmec typing revealed that 91.4% had type II, 4.1% type IV and 4.1% type I. Multilocus sequence typing (MLST) revealed that 10 of the 13 typed strains belonged to clonal complex 5 (7 had ST5 while 3 were single locus variants of ST5) with similar characteristics to the New York/Japan clone and possessed multi-drug resistance with high virulence gene content. The remaining 3 strains were ST8 (n=2) and ST91 (n=1). The ST91 strain had SCC mec IV and seemed to originate in the community, while ST8 strains exhibited SCC mec type I, which is distinct from community type IV. The data suggest that MRSA in hospitals in Niigata now mainly includes the New York/Japan clone (undergoing genomic divergence and clonal expansion) and other minor types (e.g. ST8) as well as the community type.

Two novel arginine catabolic mobile elements and staphylococcal chromosome cassette mec composite islands in community-acquired methicillin-resistant Staphylococcus aureus genotypes ST5-MRSA-V and ST5-MRSA-II

OBJECTIVES

The arginine catabolic mobile element (ACME) is a novel staphylococcal genetic island. ACME is located downstream of the staphylococcal cassette chromosome mec (SCCmec), forming the ACME-SCCmec composite island. Recently, ACME II (located upstream of SCCmec IV) was described from a methicillin-resistant Staphylococcus aureus (MRSA) strain M1 in Denmark (ST8-MRSA-IVa) and 15 MRSA isolates in Ireland (ST22-MRSA-IVh). We report the novel genetic characteristics of the ACME-SCCmec composite islands found in Japanese community-acquired MRSA (CA-MRSA) isolates.

METHODS

ACME-SCCmec composite islands from two ACME-arcA-positive CA-MRSA isolates with the genotypes ST5-MRSA-V (SR141) and ST5-MRSA-II (SR388) were characterized using long-range PCR and nucleotide sequencing.

RESULTS

Both isolates harboured a 12 kb DNA region primarily identified in ACME II in Staphylococcus epidermidis ATCC 12228 upstream of each SCCmec. The arcA and its flanking regions in SR141 and SR388 showed high sequence identity (99.8% at the highest) to those in MRSA M1 and M08/0126 (the representative of 15 Irish ST22-MRSA-IVh isolates), suggesting that the ACMEs of these four isolates originated from the same ancestral gene. The ACME II-like element in SR141 included an insertion sequence IS1182 at a position close to SCCmec, resulting in a new variant. SR388 contained ∼11.5 kb of the J1 region of type I SCCmec (J1 SCCmecI) between orfX and ACME (orfX-J1 SCCmecI-ACME II), unlike the homologous region in M08/0126 (orfX-ACME II-J1 SCCmecI).

CONCLUSIONS

This is the first report of the ACME II-like element inserted upstream of SCCmec in CA-MRSA with the genotypes ST5-MRSA-V and ST5-MRSA-II.

Prevalence and mechanism of antimicrobial resistance in Staphylococcus aureus isolates from diseased cattle, swine and chickens in Japan

Antimicrobial administration is essential for the control and treatment of diseases in animals, but the emergence and prevalence of antimicrobial-resistant Staphylococcus aureus is a significant concern during animal production. Here we investigated the antimicrobial susceptibility of S. aureus from diseased food-producing animals and molecularly characterized the methicillin-resistant and fluoroquinolone-resistant isolates. A total of 290 S. aureus isolates obtained from cattle (n=246), swine (n=16), and chickens (n=28) between 2003 and 2009 were examined for antimicrobial susceptibility against 9 antimicrobials using an agar dilution method. Resistance to penicillin (PC) was most frequently found (24.8%), followed by oxytetracycline (OTC, 10.0%), dihydrostreptomycin (4.1%), erythromycin (EM, 3.1%), enrofloxacin (ERFX, 2.1%), and kanamycin (1.7%). The PC resistance rate was significantly higher in swine than in cattle (P<0.01) and chickens (P<0.01). The resistance rates to OTC, EM and ERFX were significantly higher in swine and chickens than in cattle (P<0.05). Methicillin-resistant S. aureus (MRSA) was recovered from milk derived from a cow with mastitis in 2003; sequence type 8, SCCmec type IV and spa type t024. In the six ERFX-resistant strains isolated after 2003, amino acid substitutions in ParC with/without GyrA were detected. As the prevalence of MRSA and FQ-resistant S. aureus in the animals should be noticed, continuous monitoring is necessary to control resistance to clinically important antimicrobials in S. aureus from food-producing animals.

Methicillin-resistant Staphylococcus aureus bloodstream infections in a Japanese University Hospital between 1987 and 2004

Methicillin-resistant Staphylococcus aureus (MRSA) infections have been the most common cause of nosocomial infections in Japan, but their genetic characteristics related to bloodstream infections have not been well studied. The aim of this study was to investigate a comprehensive molecular characterization of MRSA blood isolates during the historical 18-year study period between 1987 and 2004 in a tertiary care university hospital. A total of 137 MRSA isolates recovered from the blood of inpatients at Fukuoka University Hospital were analyzed. Clinical information and antimicrobial susceptibility profiles were reviewed, and staphylococcal chromosomal cassette mec (SCCmec), accessory gene regulator (agr), and a battery of bacterial genes were tested by PCR-based assays. The relatedness of these isolates was determined by the repetitive sequence-based PCR (rep-PCR) and pulsed-field gel electrophoresis (PFGE). Although low numbers of agr type III/SCCmec type IV isolates circulated between 1987 and 1992, agr type II/SCCmec type II isolates started circulating in 1993 and were responsible for the increased MRSA isolates until 2004. The rep-PCR and PFGE identified 104 epidemic and 33 sporadic isolates. Among the 104 epidemic isolates, six major rep-PCR/PFGE types were identified, which occupied 67.3% of epidemic isolates. The SCCmec type II and agr type II isolates were observed in significantly higher proportion in epidemic isolates than in sporadic isolates (P = 0.0318, P = 0.0123, respectively). In contrast, SCCmec type IV strains were observed in significantly higher proportion in sporadic isolates than in epidemic isolates (P = 0.0494). Although isolates with sec were detected in higher rates in epidemic isolates (P = 0.0397), seh was detected in higher rates in sporadic isolates (P = 0.0350). Multivariate logistic regression analysis with forward stepping revealed that SCCmec type II was independently associated with epidemic isolates (P = 0.0067; odds ratio, 1.75; 95% confidence interval, 1.17-2.64). These data indicated that SCCmec type II MRSA isolates were responsible for the increased MRSA bloodstream infections for inpatients during the 18-year study period in the hospital.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Occurrence and molecular characteristics of methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus pseudintermedius in an academic veterinary hospital

Recently, methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP) have been increasingly isolated from veterinarians and companion animals. With a view to preventing the spread of MRSA and MRSP, we evaluated the occurrence and molecular characteristics of each in a veterinary college. MRSA and MRSP were isolated from nasal samples from veterinarians, staff members, and veterinary students affiliated with a veterinary hospital. Using stepwise logistic regression, we identified two factors associated with MRSA carriage: (i) contact with an identified animal MRSA case (odds ratio [OR], 6.9; 95% confidence interval [95% CI], 2.2 to 21.6) and (ii) being an employee (OR, 6.2; 95% CI, 2.0 to 19.4). The majority of MRSA isolates obtained from individuals affiliated with the veterinary hospital and dog patients harbored spa type t002 and a type II staphylococcal cassette chromosome mec (SCCmec), similar to the hospital-acquired MRSA isolates in Japan. MRSA isolates harboring spa type t008 and a type IV SCCmec were obtained from one veterinarian on three different sampling occasions and also from dog patients. MRSA carriers can also be a source of MRSA infection in animals. The majority of MRSP isolates (85.2%) carried hybrid SCCmec type II-III, and almost all the remaining MRSP isolates (11.1%) carried SCCmec type V. MRSA and MRSP were also isolated from environmental samples collected from the veterinary hospital (5.1% and 6.4%, respectively). The application of certain disinfection procedures is important for the prevention of nosocomial infection, and MRSA and MRSP infection control strategies should be adopted in veterinary medical practice.

Epidemiology of MRSA and current strategies in Europe and Japan

The prevalence of health-care associated infections caused by multi-drug resistant organisms has significantly increased over the past decade. Among these organisms, Methicillin-resistant Staphylococcus aureus (MRSA) plays a prominent and increasing role. Because of consequences for patients and the economic burden in course of prolonged treatment following MRSA infections and additional indirect costs for e.g. isolation or antiseptic treatment, this trend will further damage European health-care systems.

In 2006, a workshop was initiated at the 8^th International Congress of the German Society of Hospital Hygiene held in Berlin. The aim of this workshop was to give an overview of the current situation of MRSA in selected European countries and to elaborate on potential strategies to prevent MRSA-infections and dissemination. A questionnaire encompassing 20 questions addressed topics such as epidemiology, current measures and future prospects was distributed to representatives from various European countries and Japan. A variety of widely different answers was obtained. It was shown that in all countries prevalence of MRSA is on a rising tide. This trend is observable in all European countries, albeit less strong in The Netherlands, Slovenia, France, Austria and Scandinavian countries. It was conclude that prevention strategies in a united and expanding European Community will become of utmost importance and that rapid screening strategies, e.g. PCR, might be of assistance in such an approach. A potential strategy to improve infection control measures could be the requirement of health-insurance providers to sign contracts only with hospitals able to proof having an infection control management in place.

Nationwide epidemiological study revealed the dissemination of meticillin-resistant Staphylococcus aureus carrying a specific set of virulence-associated genes in Japanese hospitals

To study comprehensive toxin profiles and the chromosomal diversity of current Japanese hospital-associated meticillin-resistant Staphylococcus aureus (HA-MRSA) strains, we conducted PCR-based identification of 28 toxin genes, and staphylococcal cassette chromosome mec (SCCmec) typing and PFGE analysis of 208 MRSA strains isolated from 100 hospitals throughout Japan. Of the tested HA-MRSA strains, 80.3 % were tst-positive. The most frequent toxin gene profile was characterized by the carriage of 13 genes, tst, sec, seg, sei, sel, sem, sen, seo, lukED, hla, hlb, hld and hlg-2. Ninety of the 208 strains had this profile, which was named pattern A. Among the 118 non-pattern A strains, 100 had similar toxin gene profiles, the concordance rates to pattern A of which were more than 80 %. Consequently, 91.3 % of the examined HA-MRSA strains carried similar toxin profiles, although PFGE patterns showed a wide variation. These strains belonged to SCCmec type II, agr II and coagulase type II. We concluded that, unlike MRSA from many other countries, most of the Japanese HA-MRSA strains belonged to, or were related to, a specific group carrying the set of 13 toxin genes, irrespective of chromosomal diversity. In addition, among the 13 toxin genes, the coexistence rates of tst, sec and sel, and those of seg, sei, sem, sen and seo, were higher than for the other toxin genes. High coexistence rates of tst, sec and sel genes suggested the presence of the pathogenicity island SaPIn1 in these strains.

Prevalence of toxic shock syndrome toxin 1 (TSST-1)-producing strains of Staphylococcus aureus and antibody to TSST-1 among healthy Japanese women

Many cases of neonatal toxic shock syndrome (TSS)-like exanthematous disease but few cases of menstrual TSS (mTSS) have been reported in Japan. We determined the prevalence of mucosal colonization with Staphylococcus aureus and of positive antibodies to TSS toxin 1 (TSST-1) among 209 healthy Japanese women in Tokyo. S. aureus isolates from mucosal sites were characterized with respect to TSST-1 production and resistance genotype. Antibody titers were determined for test subjects and for 133 Japanese and 137 Caucasian control women living in the United States. S. aureus was isolated from at least one site in 108 of 209 women (52%) in Tokyo. Of the 159 S. aureus isolates recovered, 14 (9%) were TSST-1 positive (12 unique strains). Twelve of 209 women (6%) were colonized with a TSST-1-producing strain; two (<1%) had vaginal colonization. Only 2 of 12 unique toxigenic strains (14%) were methicillin resistant. Of the 12 TSST-1-positive strains isolated, 6 (50%) were pulsed-field gel electrophoresis type USA200, multilocus sequence type clonal complex 30. Fewer Japanese women in Tokyo (47%) than Caucasian and Japanese women in the United States (89% and 75%, respectively) had TSST-1 antibodies. The prevalences of colonization with TSST-1-producing S. aureus were comparable in Japan and the United States, despite low seropositivity to TSST-1 in Japan. Environmental factors appear to be important in promoting the development of anti-TSST-1 antibodies, as there was a significant difference in titers between Japanese women living in Tokyo and those living in the United States. Most colonizing TSST-1-producing S. aureus strains in Japan were genotypically similar to mTSS strains found in the United States.

Postantibiotic effects and bactericidal activities of levofloxacin and gatifloxacin at concentrations simulating those of topical ophthalmic administration against fluoroquinolone-resistant and fluoroquinolone-sensitive methicillin-resistant Staphylococcus aureus strains

The bactericidal activities and postantibiotic effects (PAEs) of levofloxacin and gatifloxacin at concentrations corresponding to those in antibiotic eye drops against methicillin-resistant Staphylococcus aureus strains were determined. Levofloxacin and gatifloxacin at concentrations simulating those in eye drops showed lower bactericidal activities and shorter PAEs against fluoroquinolone-resistant strains than against fluoroquinolone-sensitive strains.

Epidemiological characteristics of methicillin-resistant Staphylococcus aureus isolates from children with eczematous atopic dermatitis lesions

In this study, we investigated the rate of colonization of skin of children with atopic dermatitis (AD) by methicillin-resistant Staphylococcus aureus (MRSA) and characterized the isolates. Active skin lesions in pediatric AD patients were cultured with Rodac Staph (Komed, Korea). S. aureus isolates were examined for drug susceptibilities, analyzed for the eta, etb, tst, and pvl genes, and typed using agr polymorphism, pulsed-field gel electrophoresis of SmaI-restricted chromosomal DNA, and staphylococcal cassette chromosome mec (SCCmec) typing. Eighty-seven (75.4%) of 115 patients had cultivable S. aureus isolates, 16 of which (18.3%) were MRSA. All MRSA isolates were susceptible to chloramphenicol, rifampin, cotrimoxazole, and ciprofloxacin. While methicillin-susceptible S. aureus (MSSA) isolates were composed of 23 isolates of singular types and nine clusters comprising 48 isolates, MRSA isolates were typed into three clones: eight isolates of pulsotype A-agr-1-SCCmec IV, five isolates of pulsotype B-agr-3-SCCmec IIb-etb positive, and three isolates of pulsotype C-agr-3-SCCmec IV. Three SCCmec IVA MRSA isolates were tst positive, but none were positive for the pvl or eta gene. Among 71 MSSA isolates, 7 isolates were tst positive, 6 of which were pulsotype F-agr-3, and 9 of 10 agr-4 isolates were eta positive. The average ages of patients carrying MSSA, SCCmec IVA MRSA, and SCCmec IIb MRSA were 7.7 +/- 4.6, 3.1 +/- 1.5, and 8.2 +/- 3.1 years, respectively. Among the patients carrying MRSA, two patients had been treated with oral antimicrobials, and one had been admitted to the hospital 18 months previously. In conclusion, community-acquired MRSA isolates of a few clones colonized the skin of patients with AD without risk factors for the acquisition of hospital-acquired MRSA, which suggested that the skin of children with AD may represent a significant reservoir of MRSA colonization in the community.

Tetracyclines as an oral treatment option for patients with community onset skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus

Few data exist on the clinical utility of the expanded-spectrum tetracyclines doxycycline and minocycline for the treatment of community-associated methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTI). We performed a retrospective cohort study of 276 patients who presented with 282 episodes of MRSA SSTI to the emergency room or outpatient clinic at two tertiary medical centers between October 2002 and February 2007. The median percentage of patients infected with MRSA strains that were susceptible to tetracycline was 95%. Time zero was defined as the time of the first incision and drainage procedure or, if none was performed, the time of the first positive wound culture. The median patient age was 48 years. Abscesses constituted the majority of clinical presentations (75%), followed by furuncles or carbuncles (13%) and cellulitis originating from a purulent focus of infection (12%). A total of 225 patients (80%) underwent incision and drainage. Doxycycline or minocycline was administered in 90 episodes (32%); the other 192 SSTI were treated with beta-lactams. Treatment failure, defined as the need for a second incision and drainage procedure and/or admission to the hospital within at least 2 days after time zero, was diagnosed in 28 episodes (10%) at a median of 3 days after time zero. On logistic regression analysis, receipt of a beta-lactam agent was the only clinical characteristic associated with treatment failure (adjusted odds ratio, 3.94; 95% confidence interval, 1.28 to 12.15; P = 0.02). The expanded-spectrum tetracyclines appear to be a reasonable oral treatment option for patients with community onset MRSA SSTI in areas where MRSA strains are susceptible to the tetracyclines.

Characterization of oxacillin-susceptible mecA-positive Staphylococcus aureus: a new type of MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) has been defined as S. aureus having the mecA gene or showing a minimum inhibitory concentration (MIC) of oxacillin higher than 4 mg/l. However, some clinical isolates are mecA-positive and oxacillin-susceptible. Therefore, we surveyed the occurrence of S. aureus having the mecA gene and an MIC of oxacillin of less than 2 mg/l (oxacillin-susceptible MRSA; OS-MRSA) in a total of 480 strains of S. aureus collected from 11 hospitals in different location in Japan isolated from 2003 through 2005. We found 6 strains matching the criteria for OS-MRSA. All 6 strains were staphylococcal cassette chromosome (SCC) mec-positive, without exception, and 4 strains showed the SCCmec type III-variant, which is unique in Japan. These OS-MRSAs were least resistant to oxacillin among the MRSAs tested and they were within the susceptible range to seven other beta-lactam antibiotics tested. Thus, OS-MRSA may become a high-resistant MRSA upon the treatment of patients with beta-lactam antibiotics. To characterize whether these OS-MRSAs were hospital-acquired or community-acquired MRSAs, we tested for the presence of the genes encoding toxins. Genes encoding hemolysin, exfoliative toxin, enterotoxin, toxic shock syndrome toxin-1, and Panton-Valentine leukocidin were found in 6, 4, 0, 0, and 0 strains, respectively. These results revealed that OS-MRSAs could be classified as a new type of MRSA that exhibits properties distinguishable from either hospital- or community-acquired MRSA. Coagulase typing of the OS-MRSAs supported the above conclusion. In this study, the occurrence of OS-MRSA at a certain frequency was noted; precautions are called for in the classification of oxacillin-resistant S. aureus and in the treatment of OS-MRSA infection.

Methicillin-resistant Staphylococcus pseudintermedius in a veterinary teaching hospital

We surveyed methicillin-resistant coagulase-positive staphylococcus (MRCPS) strains from 57 (26 inpatient and 31 outpatient) dogs and 20 veterinary staff in a veterinary teaching hospital. From the staff, three MRCPS strains were isolated, and two were methicillin-resistant Staphylococcus aureus (MRSA). In contrast, 18 MRCPS strains were detected in both inpatient (12 of 26 [46.2%]) and outpatient (6 of 31 [19.4%]) dogs. Among them, only one strain was MRSA. Using direct sequencing of sodA and hsp60 genes, the 18 MRCPS strains other than MRSA from a staff and 17 dogs, were finally identified as Staphylococcus pseudintermedius, a novel species of Staphylococcus from a cat. All of the methicillin-resistant S. pseudintermedius (MRSP) strains were multidrug resistant to erythromycin, clindamycin, trimethoprim-sulfamethoxazole, and levofloxacin. Most of the MRSP strains showed high-level resistance to oxacillin (>/=128 mug/ml, 15 of 18 [83.3%]), and 10 of 15 (66.7%) high-level oxacillin-resistant MRSP strains carried type III SCCmec. DNA fingerprinting of MRSP strains by pulsed-field gel electrophoresis yielded eight clusters: clone A with four subtypes, clone B with four subtypes, clone C with three subtypes, and five other different single clones. MRSP strains from the staff and some inpatient and outpatient dogs shared three major clones (clones A, B, and C), but the strains of the other five different clusters were distributed independently among inpatient or outpatient dogs. This genetic diversity suggested that the MRSP strains were not only acquired in this veterinary teaching hospital but also acquired in primary veterinary clinics in the community. To our knowledge, this is the first report of MRSP in dogs and humans in a veterinary institution.

Usefulness of PCR-restriction fragment length polymorphism typing of the coagulase gene to discriminate arbekacin-resistant methicillin-resistant Staphylococcus aureus strains

We compared the results of two typing methods for 678 strains of methicillin-resistant Staphylococcus aureus and methicillin-susceptible S. aureus. PCR-restriction fragment length polymorphism typing of the coagulase gene was a more reliable method than coagulase serotyping from the viewpoint of arbekacin resistance.

Toxin gene content of the Lyon methicillin-resistant Staphylococcus aureus clone compared with that of other pandemic clones

The methicillin-resistant Staphylococcus aureus (MRSA) Lyon clone, detected throughout France, contains the enterotoxin A gene (sea), like other pandemic clones of clonal complex 8 (CC8). The egc locus was detected in MRSA pandemic clones of CC5, CC22, and CC45, occasionally with the toxic shock syndrome toxin 1 gene. The representative strain of the EMRSA-16 clone (CC30) harbored both sea and the egc locus.

Trends of Arbekacin-resistant MRSA Strains in Japanese Hospitals (1979 to 2000)

A total of 472 clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated in Japan between 1979 and 2000 were investigated for resistance to 8 aminoglycosides, 4 aminoglycoside-modifying enzyme gene profiles, and AluI-restriction fragment length polymorphism of the coagulase gene determined by polymerase chain reaction assay. The majority of MRSA strains tested belonged to 4 groups based on coa-RFLP: L21, L22, L31, and M22. About 90% of recent isolates belonged to type L21, indicating the spread of a specific type of MRSA in Japan. Of the type L21 strains, 41.9% included the aac(6')/aph(2") gene, which was one of the risk factors of arbekacin (ABK) resistance, but only 5.5% were resistant to ABK. In contrast, all of the type M22 strains carried aac(6')/aph(2") and 70.1% showed ABK resistance. Among the other types, less than 20% of strains showed ABK resistance. These results suggested that ABK has maintained potent activity. If the predominance of type L21 continues, there will be no progression to ABK resistance in MRSA. However, it may be necessary to monitor the trends in type M22 continuously.