Emergence of Panton-Valentine leucocidin-positive ST8-methicillin-resistant Staphylococcus aureus (USA300 clone) in Korea causing healthcare-associated and hospital-acquired bacteraemia

Dissemination of meticillin-resistant Staphylococcus aureus sequence type 8 (USA300) in Taiwan

BACKGROUND

In Taiwan, sequence type (ST) 239 and ST59 were two major clones among meticillin-resistant Staphylococcus aureus (MRSA) clinical isolates in the past two decades. USA300 (ST8) prevailed in the Americas but not in outside areas. Recently USA300 (ST8) emerged and was increasingly identified in Taiwan; we thus conducted an island-wide study to explore the role of USA300 among MRSA isolates.

METHODS

One hundred MRSA bloodstream isolates identified in 2020 from each of the six participating hospitals in Taiwan were collected and characterized. The first 10 ST8 isolates from each hospital were further analysed by whole-genome sequencing.

RESULTS

Of the 590 confirmed MRSA isolates, a total of 22 pulsotypes and 21 STs were identified. The strain of pulsotype AI/ST8 was the most common lineage identified, accounting for 187 isolates (31.7%) and dominating in five of six hospitals, followed by pulsotype A/ST239 (14.7%), pulsotype C/ST59 (13.9%) and pulsotype D/ST59 (9.2%). Of the 187 pulsotype AI/ST8 isolates, 184 isolates were characterized as USA300 and clustered in three major sub-pulsotypes, accounting for 78%. Ninety per cent of the 60 ST8 isolates for whole-genome sequencing were clustered in three major clades.

CONCLUSIONS

In 2020, USA300 became the most common clone of MRSA in Taiwan, accounting for >30% of MRSA bloodstream isolates island wide. Most of USA300 isolates circulating in Taiwan might have been imported on multiple occasions and evolved into at least three successful local clades. MRSA USA300 has successfully established its role in Taiwan, an area outside of the Americas.

The origin of sequence type 72 community-associated methicillin-resistant Staphylococcus aureus (MRSA) and fusidic acid (FA) resistant sequence type 5 MRSA: Analysis of FA resistance and spa type in a single center in South Korea

INTRODUCTION

We investigated the prevalence of fusidic acid (FA) resistance in MSSA and MRSA stratified by sequence (ST) and spa types, and determined the prevalence of FA resistance mechanisms.

METHODS

From August 2014 to April 2020, S. aureus blood isolates were collected in Asan Medical Center, Seoul, South Korea. Antimicrobial susceptibility tests were performed using broth microdilution and interpreted according to EUCAST's FA criteria. We performed spa typing for fusA mutation presence and acquired FA resistance determinants (fusB, fusC, and fusD) by PCR.

RESULTS

Of the 590 MRSA isolates, 372 were FA resistant, and among 425 MSSA isolates, 136 were resistant. Of the 380 ST5-MRSA isolates, 350 were FA resistant, whereas only 1 of 14 ST5-MSSA isolates was FA resistant. Conversely, of the 163 ST72-MRSA isolates, only 8 were resistant, whereas 37 of 42 ST72-MSSA were resistant. The fusA mutation (80%) was the most common determinant. The one FA resistant ST5-MSSA isolate belonged to the t2460 spa type, the most common spa type (24 of 35 isolates) of FA resistant ST5-MRSA. In addition, t324 and t148, which are minor spa types of ST72-MSSA, were susceptible to FA, in contrast to other ST72-MSSA spa types, and the major spa type of ST72-MRSA (110 of 163 isolates).

CONCLUSIONS

FA resistance was common in ST5-MRSA and ST72-MSSA, and rare in ST5-MSSA and ST72-MRSA. Our findings suggest that minor clones of ST5-MSSA isolates, with the fusA mutation and minor clones of ST72-MSSA susceptible to FA, may have evolved to harbor the mecA gene.

Significant increase in the prevalence of Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus, particularly the USA300 variant ΨUSA300, in the Japanese community

IMPORTANCE

USA300 is an MRSA clone producing PVL, a toxin associated with SSTIs. ΨUSA300 is a USA300 variant recently identified in Japan by Takadama et al. (15). Here, we found that the prevalence rate of PVL-positive MRSA in S. aureus was elevated in the Japanese community, and ΨUSA300 accounted for most of them. ΨUSA300 strains have been isolated from several areas in Japan and were associated with deep-seated SSTIs. This study highlighted the emerging threat posed by ΨUSA300 in Japan.

Insight into the Clonal Lineage and Antimicrobial Resistance of Staphylococcus aureus from Vascular Access Infections before and during the COVID-19 Pandemic

Patients receiving hemodialysis are at risk of vascular access infections (VAIs) and are particularly vulnerable to the opportunistic pathogen Staphylococcus aureus. Hemodialysis patients were also at increased risk of infection during the COVID-19 pandemic. Therefore, this study determined the change in the molecular and antibiotic resistance profiles of S. aureus isolates from VAIs during the pandemic compared with before. A total of 102 S. aureus isolates were collected from VAIs between November 2013 and December 2021. Before the pandemic, 69 isolates were collected, 58%, 39.1%, and 2.9% from arteriovenous grafts (AVGs), tunneled cuffed catheters (TCCs), and arteriovenous fistulas (AVFs), respectively. The prevalence of AVG and TCC isolates changed to 39.4% and 60.6%, respectively, of the 33 isolates during the pandemic. Sequence type (ST)59 was the predominant clone in TCC methicillin-resistant S. aureus (MRSA) and AVG-MRSA before the pandemic, whereas the predominant clone was ST8 in AVG-MRSA during the pandemic. ST59 carrying the ermB gene was resistant to clindamycin and erythromycin. By contrast, ST8 carrying the msrA gene was exclusively resistant to erythromycin. The ST distribution for different VAIs changed from before to during the pandemic. The change in antibiotic resistance rate for different VAIs was closely related to the distribution of specific STs.

Emergence of community-associated methicillin-resistant Staphylococcus aureus ΨUSA300 among Japanese people with HIV, resulted from stepwise mutations in 2010s

Although infection with the methicillin-resistant Staphylococcus aureus (MRSA) clone USA300 is extremely rare in Japan, the uniquely evolved clone ΨUSA300 has been reported in Japan. An outbreak of a distinct USA300 clone was recently reported in an HIV/AIDS referral hospital in Tokyo. The present study investigated the evolutionary origin and genetic diversity of USA300-related clones causing regional outbreaks among people living with HIV (PLWHIV) in Tokyo. MRSA isolates collected from PLWHIV in an HIV/AIDS referral center in Tokyo were subjected to whole-genome sequencing and their genetic features were compared with those of previously described USA300 MRSA genomes. Of the 28 MRSAs isolated in 2016-2019, 23 (82.1%) were identified as USA300, with 22 (95.6%) of the latter identified as ΨUSA300. Although the genomic structure of ΨUSA300 was identical to the structures of reference USA300 strains, one clade (cluster A) was found to have acquired 29 previously identified lineage-specific mutations in a stepwise manner. The estimated divergence dates of ΨUSA300 and Cluster A were 2009 and 2012, respectively. These findings suggested that the ΨUSA300 clone had spread among PLWHIVs in Tokyo in the early 2010s, with stepwise acquisition of lineage-specific nonsynonymous mutations.

Sequence type 8 as an emerging clone of methicillin-resistant Staphylococcus aureus causing bloodstream infections in Taiwan

Sequence type (ST) 8 has not been a common methicillin-resistant Staphylococcus aureus (MRSA) clone in Asia until recently. We aimed to determine the clinical significance and microbiological characteristics of MRSA bacteraemia (MRSAB) caused by ST8 and other endemic clones. A total of 281 non-duplicated MRSAB were identified in a medical centre between 2016 and 2018. Sequencing of target genes was performed to determine ST and to confirm ST8 belonging to USA300. Antimicrobial susceptibility testing was performing by using Sensititre standard panel. In total, ST8 accounted for 18.5% of MRSAB ranking after ST239 (31.0%) and ST59 (23.5%). However, it increased to become the most prevalent clone finally. All ST8 isolates belonged to spa clonal complex008, and carried SCCmec IV/IVa, PVL and ACME genes, indicating USA300. ST8/USA300 isolates were highly susceptible to non-β-lactams antibiotics, except fluoroquinolone and erythromycin. ST8/USA300 MRSAB is commonly developed in community settings with either healthcare risks or not (71.2%). Compared to other STs MRSAB, ST8/USA300 MRSAB patients had more diabetes mellitus (50.0%), more admitted from long-term care facility residents (25.0%), had more skin ad soft tissue infection as primary focus (25.0%), and had fewer vascular devices (26.9%) at MRSAB onset. On multivariable analysis, isolates with vancomycin MIC were significantly associated with mortality in the dose-response relationship, rather than STs. This report depicts the clinical features of ST8/USA300 MRSAB and clonal shift from prior endemic clones to ST8/USA300. Our data strongly support long-term surveillance to ascertain whether ST8/USA300 will successfully disseminate and demonstrate its pathogenicity on clinical outcomes.

A Longitudinal Study of Adult Patients with Staphylococcus aureus Bacteremia over 11 Years in Korea

BACKGROUND

The temporal changes in the Staphylococcus aureus genotypes causing S. aureus bacteremia (SAB) and the corresponding clinical changes over the last decade in South Korea are rarely investigated.

METHODS

A longitudinal study of adult SAB patients was conducted in a large referral hospital in Seoul, South Korea. Adult monomicrobial SAB patients were enrolled between August 2008 and December 2018. Genotyping was performed by multilocus sequence typing (MLST) and staphylococcal protein A (spa) typing. Trends in changes were identified by linear regression analysis.

RESULTS

Of 1782 adult SAB patients, the blood isolates of 1,778 (99.8%) and 1,634 (91.7%) were determined to be MLST and spa type, respectively. ST5 (-2.626%/year) and ST239 (-0.354%/year) decreased during the study period (P < 0.001 for both), but ST72 (2.009%/yr)-and ST8 (0.567%/yr) increased (P < 0.001 for both). The most common genotype was changed from ST5 in 2008 (44.9%) to ST72 in 2018 (36.3%). Panton-Valentine leukocidin-positive spa-t008-MRSA (USA300) was found in 28.6%. Central venous catheter (CVC)-related SAB (-2.440%/yr) and persistent SAB (-1.016%/yr) decreased, but mortality and recurrence rates were unchanged.

CONCLUSION

Over the last decade, the hospital clones ST5 and ST239 have been replaced by community genotype ST72. This was associated with decreased CVC-related and persistent SAB. Increased USA300 was observed in community and hospital settings. Further research is required to identify the reasons for the ST72 epidemic and predict the impending epidemic of ST8 strains, including USA300.

A Novel Surface-Exposed Polypeptide Is Successfully Employed as a Target for Developing a Prototype One-Step Immunochromatographic Strip for Specific and Sensitive Direct Detection of Staphylococcus aureus Causing Neonatal Sepsis

Neonatal sepsis is a life-threatening condition and Staphylococcus aureus is one of its major causes. However, to date, no rapid and sensitive diagnostic tool has been developed for its direct detection. Bioinformatics analyses identified a surface-exposed 112-amino acid polypeptide of the cell wall protein NWMN_1649, a surface protein involved in cell aggregation and biofilm formation, as being a species-specific and highly conserved moiety. The polypeptide was cloned, purified, and used to immunize mice to raise specific immunoglobulins. The purified antibodies were conjugated to gold nano-particles and used to assemble an immunochromatographic strip (ICS). The developed prototype ICS detected as low as 5 µg purified polypeptide and 102 CFU/mL S. aureus within 15 min. The strip showed superior ability to directly detect S. aureus in neonatal sepsis blood specimens without prior sample processing. Moreover, it showed no cross-reaction in specimens infected with two other major causes of neonatal sepsis; coagulase-negative staphylococci and Klebsiella pneumoniae. The selected NWMN_1649-derived polypeptide demonstrates success as a promising biomolecule upon which a prototype ICS has been developed. This ICS provides a rapid, direct, sensitive, and specific option for the detection of S. aureus causing neonatal sepsis. Such a tool is urgently needed especially in resources-limited countries.

Clinical characteristics and molecular analysis of USA300 and ST 764 methicillin-resistant Staphylococcus aureus isolates from outpatients in Japan by PCR-Based open reading frame typing

INTRODUCTION

USA300 is the most common community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strain. Sequence type (ST) 764 MRSA is a new local variant of the ST 5 lineage. The objective of this study was to determine the clinical characteristics of USA300 and ST 764 infections among outpatients in Japan.

METHODS

We obtained MRSA isolates from 132 outpatients who visited our hospital from January 2016 to December 2017 and compared USA300 infection group to ST 764 infection group. Molecular analysis, including that of various toxins and other virulence factors, of the MRSA isolates were performed. In particular, we investigated the relationships among PCR-based open reading frame typing (POT) scores, MRSA clones, and virulence factors.

RESULTS

Twenty-seven USA300 isolates (20.5%) and 16 ST 764 isolates (12.1%) were identified. Although USA300 and ST 764 had lower rates of risk factors, their infection rates were higher. USA300-infected patients had higher rates of deep skin and soft tissue infections compared with the non-USA300 CA-MRSA-infected patients. Notably, the USA300 and ST 764 isolates had unique POT scores.

CONCLUSIONS

Our results indicated that USA300 MRSA was spreading in an area 120 km west of Tokyo, Japan. We observed multiple cases of ST 764 MRSA infection, raising concerns about the antimicrobial resistance of ST 764, as it limits the choices of antibiotics to treat infection. The POT score can predict the presence of toxins and virulence factors, as well as the clone identity of MRSA with high accuracy.

Molecular Characteristics, Virulence Gene and Wall Teichoic Acid Glycosyltransferase Profiles of Staphylococcus aureus: A Multicenter Study in China

Staphylococcus aureus (S. aureus) constantly evolves under host and environment pressures. The monitoring network is essential in assessing the epidemiology of S. aureus infections. A total of 555 S. aureus isolates were collected from five hospitals in three different geographical regions of China for the investigation of molecular characteristics, antibiotic resistance, virulence gene, and wall teichoic acid (WTA) glycosyltransferase gene profiles. 233 (42.0%) isolates were identified as MRSA, and 323 (58.2%) were defined as multidrug-resistant (MDR) isolates. MRSA prevalence showed no significant difference among the three regions. In contrast, the MDR prevalence was significantly higher in central China than that in northern China (63.5% vs. 50.8%, P < 0.05). Thirty-eight sequence types (STs) belonging to 17 clone complexes (CCs) and 126 distinct spa-types were identified. The most prevalent clone was ST59-t437 (9.7%, 54/555), followed by ST22-t309 (7.6%, 42/555) and ST5-t2460 (7.2%, 40/555). Most ST59-t437 and ST5-t2460 were MRSA isolates, whereas most ST22-t309 was MSSA isolates. The predominant clones varied in different geographical areas. The distribution of the pvl, etb, tsst, clfb, sdrC, sdrD, hlg, fnbA, and hla genes showed significant differences among different regions. We found five WTA glycosyltransferase gene profiles, with tarP-/tarS+/tarM-/tagN- being the most common combination. Remarkably, the tarP gene was identified in more CCs than just CC5 and CC398. All of 16 tarP-positive isolates also contained the tarS. Moreover, tarS was present in almost all S. aureus isolates except 10 ST630 isolates. The tagN gene was only detected in 10 of 12 ST630 S. aureus isolates without tarS. The tarM gene was absent in CC5 and CC398. In brief, there were regional differences among molecular characteristics, antibiotic resistance, and virulence gene profiles. The tarS-negative ST630 lineage carried the tagN, which was never found before, indicating that it may be capable of expressing GroP-α-GalNAc WTA and exchanging mobile genetic elements with coagulase-negative staphylococci (CoNS).

Staphylococcus aureus Glucose-Induced Biofilm Accessory Protein A (GbaA) Is a Monothiol-Dependent Electrophile Sensor

Staphylococcus aureus is a commensal pathogen that has evolved to protect itself from unfavorable conditions by forming complex community structures termed biofilms. The regulation of the formation of these structures is multifactorial and in S. aureus involves a number of transcriptional regulators. GbaA (glucose-induced biofilm accessory protein A) is a tetracycline repressor (TetR) family regulator that harbors two conserved Cys residues (C55 and C104) and impacts the regulation of formation of poly-N-acetylglucosamine-based biofilms in many methicillin-resistant S. aureus (MRSA) strains. Here, we show that GbaA-regulated transcription of a divergently transcribed operon in a MRSA strain can be induced by potent electrophiles, N-ethylmaleimide and methylglyoxal. Strikingly, induction of transcription in cells requires C55 or C104, but not both. These findings are consistent with in vitro small-angle X-ray scattering, chemical modification, and DNA operator binding experiments, which reveal that both reduced and intraprotomer (C55-C104) disulfide forms of GbaA have very similar overall structures and each exhibits a high affinity for the DNA operator, while DNA binding is strongly inhibited by derivatization of one or the other Cys residues via formation of a mixed disulfide with bacillithiol disulfide or a monothiol derivatization adduct with NEM. While both Cys residues are reactive toward electrophiles, C104 in the regulatory domain is the more reactive thiolate. These characteristics enhance the inducer specificity of GbaA and would preclude sensing of generalized cellular oxidative stress via disulfide bond formation. The implications of the findings for GbaA function in MRSA strains are discussed.

Diversity of staphylococcal species in food producing animals in Spain, with detection of PVL-positive MRSA ST8 (USA300)

This work aimed to determine the prevalence, diversity, antibiotic-resistance phenotype/genotype and virulence factors in staphylococci of farm-animals. Nasal samples of 117 farm-animals (calve: 72; lamb: 37; goat: 8) were collected from one slaughterhouse in La Rioja/Spain and cultured for staphylococci and methicillin-resistant Staphylococcus (MRS) recovery. Identification was performed by MALDI-TOF. Antimicrobial resistance phenotype/genotype was determined by susceptibility testing and specific PCRs. Molecular typing (spa-typing, multilocus-sequence-typing, agr-typing, SCCmec), and detection of 12 virulence genes and human Immune-evasive-cluster (IEC) genes were performed by PCR/sequencing in S. aureus. Two marker genes of arginine catabolic mobile element (ACME) were determined by PCR (USA300-MRSA detection). Staphylococci were identified in 50%, 54% and 21% of goat, lamb and calve samples, respectively. Among the 13 S. aureus isolates recovered, 11 were susceptible to all antimicrobials tested, and two were multidrug-resistant-MRSA [beta-lactams (blaZ, mecA), macrolides [(msr(A)/msr(B)] and fluoroquinolones]. The MSSA harboured either tst or enterotoxin genes, while the MRSA harboured the lukF/lukS-PV genes. Five sequence-types were detected. The two MRSA strains (from lamb and goat) were typed as t5173/ST8/agr-I/SCCmec-IVa/ACME-positive, corresponding to USA300 clone, and were IEC-B-positive. Among the 47 coagulase-negative staphylococci (CoNS), six species were identified, predominating S. simulans (n = 25) and S. sciuri (n = 11). Fifty-three percent of CoNS showed resistance to at least one antimicrobial agent (six multidrug-resistant strains), and the following resistance phenotypes/genotypes were detected: streptomycin [27.6%; ant(6)-Ia, str], tetracycline [23.4%; tet(M), tet(L), tet(K)], clindamycin [19.1%; lnu(A), vgaA], erythromycin [10.6%; erm(C), msr(A)/msr(B)], chloramphenicol (8.5%; fexA), tobramycin (6.4%), penicillin-cefoxitin (4.3%; blaZ, mecA), and SXT (2.1%). The detection of the MRSA-USA300 lineage in food animals is worrisome and should be further monitored.

Impact of Community-Onset Methicillin-Resistant Staphylococcus aureus on Staphylococcus aureus Bacteremia in a Central Korea Veterans Health Service Hospital

BACKGROUND

No study has examined the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in Korean veterans' hospitals. We investigated the microbiological and clinical epidemiology of S. aureus bacteremia at the central Veterans Health Services (VHS) hospital in Korea.

METHODS

Patients with S. aureus bacteremia were consecutively enrolled from February to August 2015. Bacteremia was classified as hospital-acquired (HA), community-onset healthcare-associated (COHA), or community-acquired (CA). MRSA bacteremia risk factors were analyzed. Species identification, antimicrobial susceptibility, and presence of luk and tst were tested. Staphylococcal cassette chromosome mec (SCCmec) typing, spa sequence typing agr polymorphism typing, and multilocus sequence typing were performed. Biofilm production and δ-hemolysin activity were measured to determine agr function.

RESULTS

In total, 60 patients were enrolled (30 HA, 23 COHA, and seven CA bacteremia); 44 (73.3%) had MRSA bacteremia (26 HA, 16 COHA, and two CA). MRSA bacteremia occurred more frequently in non-CA patients and those who had received antibiotic treatment within the past month (P<0.05). The major MRSA strains comprised 24 ST5-agr2-SCCmecII, 11 ST72-agr 1-SCCmecIV, and five ST8-agr1-SCCmecIV strains. Of 26 agr2-SCCmecII strains, including two MSSA strains, 25 were multidrug-resistant, 18 were tst-positive, and 13 were agr-defective, whereas only five of the 18 agr1-SCCmecIV strains were multidrug-resistant, and all were tst-negative and agr-intact. agr1-SCCmecIV and ST8-agr1-SCCmecIV strains were more likely than agr2-SCCmecII strains to be COHA.

CONCLUSIONS

MRSA was highly prevalent in both COHA and HA bacteremia. The introduction of virulent CA-MRSA strains may be an important cause of increased HA-MRSA bacteremia in VHS hospitals.

Clinical and Molecular Characterization of Panton-Valentine Leukocidin-Positive Invasive Staphylococcus aureus Infections in Korea

AIM

Panton-Valentine leukocidin (PVL) is a virulent cytotoxin and an indicator of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection. In this study, we evaluated the prevalence and clinical and molecular characteristics of PVL-positive invasive S. aureus (ISA) infections in Korea.

RESULTS

A collection of 1,962 nonduplicate clinical isolates were screened for multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec), accessory gene regulator typing, major toxins, and antimicrobial susceptibility. Twenty-eight (1.4%) PVL-positive S. aureus samples were found; of them 19 (67.9%) were MRSA (8 CA and 11 healthcare-associated infections). Seventeen patients (60.7%) were men (median age: 63 years; range: 13-93 years) and 12 patients (42.9%) had no underlying comorbidities. The most common infections were skin and skin structure infection (SSSI) and pneumonia. The 30-day mortality rate was 37.0%. The most common PVL-positive MRSA clones were ST8-SCCmec IVa and ST30-SCCmec IVc along with their single-locus variants. Antimicrobial susceptibility and toxin-gene profile differed according to the clone.

CONCLUSIONS

ISA infections caused by PVL-positive strains are rare in Korea, with the two most common infections being SSSI and pneumonia. Our findings indicated that several PVL-positive MRSA clones, predominantly ST8-SCCmecIVa and ST30-SCCmecIVc, were circulating and causing sporadic cases of ISA infections in the community and hospital settings.

Methicillin-resistant Staphylococcus aureus nasal carriage in international medical conference attendees

BACKGROUND

Carriage of methicillin-resistant Staphylococcus aureus (MRSA) is associated with its transmission. International travels and massive gatherings may accelerate such transmission. MRSA carriage was surveyed among the attendees of two international medical conferences held in Taipei in 2010.

METHODS

A total of 209 attendees from 23 countries were recruited. Nasal specimens were collected from each volunteer and subjected to polymerase chain reaction (PCR) detection for MRSA. Molecular analysis, including pulsed-field gel electrophoresis, multilocus sequence typing (MLST), typing of staphylococcal cassette chromosome mec (SCCmec) and staphylococcal protein A (spa) genes, and detection of Panton-Valentine leukocidin (PVL) and sasX genes, was performed.

RESULTS

MRSA carriage was detected in 10 (4.8%) attendees from Vietnam (3/8, 37.5%), Korea (2/6, 33.3%), Japan (2/41, 4.9%), Philippines (2/52, 3.8%), and Bangladesh (1/4, 25.0%). The proportion of MRSA colonizers was significantly higher in the local hospital group compared to those from the other groups (3/17 vs. 7/192, p < 0.05). Six MRSA isolates were available for molecular analysis. They all carried a type IV SCCmec gene. Five pulsotypes were identified; four genotypes, respectively, were identified by MLST and spa typing. None of the isolates carried either PVL or sasX genes. None of common molecular characteristics was shared by isolates from different countries. Most of these isolates were local endemic community clone in each country.

CONCLUSIONS

As healthcare workers, a certain proportion of international medical conference attendees harbored MRSA in their nares, mostly local endemic community clones in each country, which has the potential of spread among attendees.

Arginine Catabolic Mobile Elements in Livestock-Associated Methicillin-Resistant Staphylococcal Isolates From Bovine Mastitic Milk in China

The arginine catabolic mobile element (ACME) facilitates colonization of staphylococci on skin and mucous membranes by improving their tolerances to polyamines and acidic conditions. ACME is inserted in tandem with the SCCmec element and Staphylococcus epidermidis has been proposed to be a reservoir of ACME for other staphylococci. In this study, we investigated the existence of ACME in 146 staphylococcal isolates from mastitic milk and found 21 of them carried ACME. Almost half of the investigated S. epidermidis isolates contained the element. The whole genome of a S. epidermidis strain Y24 with ACME was further sequenced and the ACME-SCCmec composite island was assembled. This composite island is 81.3 kb long and consisted of 77 ORFs including a methicillin resistance gene mecA, a type II’ ACME gene cluster, a virulence gene pls and eight heavy metal tolerance genes. Wide existence of ACME in livestock-associated staphylococci from this study and a potential risk of spreading ACME among different staphylococcal species warrant close monitoring and further studies.

Characterization of SCCmec type IV methicillin-resistant Staphylococcus aureus clones increased in Japanese hospitals

Recently, the prevalence of staphylococcal cassette chromosome mec (SCCmec) type IV isolates, which are the major community-acquired methicillin-resistant Staphylococcus aureus (MRSA), have increased in Japanese hospitals. The aim of this study was to elucidate the detailed molecular epidemiological features of the SCCmec type IV clones in Japanese hospitals. When 2589 MRSA isolated from four hospitals in Tokyo, Japan between 2010 and 2014 were analysed, the proportion of SCCmec type IV overtook that of type II, which was the major type of hospital-acquired MRSA in 2014. Multilocus sequence typing showed that CC1 was the most predominant clone in the SCCmec type IV isolates. The clinical departments that the patients belonged to, pulsed-field gel electrophoresis analysis and antimicrobial susceptibility profiles suggested that the origin of the CC1-SCCmec type IV (CC1-IV) clone was a community setting. Our data show that the CC1-IV clone is becoming a predominant MRSA clone in Japanese hospitals.

Emergence, transmission and phylogeny of meticillin-resistant Staphylococcus aureus sequence type 8 (USA300) in Taiwan

Twenty-seven (0.51%) USA300 isolates were identified from a pool of 5308 meticillin-resistant Staphylococcus aureus (MRSA) isolates collected in Taiwan between 1995 and October 2015, including 12 infecting isolates from 10 patients. The first two isolates were identified in 2005, and 23 isolates have been collected since 2010. Phylogenetic analysis revealed that all the local isolates were closely related to those in North America, and there was a clade consisting of 13 local isolates from 10 patients. MRSA USA300 existed in Taiwan in 2005 or earlier, with increasing identification since 2010. Local transmission of USA300 has occurred in Taiwan after importation from North America.

Origin, evolution, and global transmission of community-acquired Staphylococcus aureus ST8

USA300 is a hypervirulent, community-acquired, multidrug-resistant Staphylococcus aureus clone that started to spread in the United States around 17 years ago. Many studies detected it also in South America, Europe, and the Asia-Pacific region. In this study, we show that USA300 is also circulating in sub-Saharan Africa. Locating the temporal and spatial origin of clonal lineages is important with respect to epidemiology and molecular evolution of pathogens. We show that USA300 evolved from a less virulent and less resistant ancestor circulating in Central Europe around 160 years ago. Constant surveillance of pathogen transmission routes is vital to prevent and control potential outbreaks. Whole genome sequencing proved to be a useful tool for epidemiological surveillance.

USA300 is a pandemic clonal lineage of hypervirulent, community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) with specific molecular characteristics. Despite its high clinical relevance, the evolutionary origin of USA300 remained unclear. We used comparative genomics of 224 temporal and spatial diverse S. aureus isolates of multilocus sequence type (ST) 8 to reconstruct the molecular evolution and global dissemination of ST8, including USA300. Analyses of core SNP diversity and accessory genome variations showed that the ancestor of all ST8 S. aureus most likely emerged in Central Europe in the mid-19th century. From here, ST8 was exported to North America in the early 20th century and progressively acquired the USA300 characteristics Panton–Valentine leukocidin (PVL), SCCmec IVa, the arginine catabolic mobile element (ACME), and a specific mutation in capsular polysaccharide gene cap5E. Although the PVL-encoding phage ϕSa2USA was introduced into the ST8 background only once, various SCCmec types were introduced to ST8 at different times and places. Starting from North America, USA300 spread globally, including Africa. African USA300 isolates have aberrant spa-types (t112, t121) and form a monophyletic group within the clade of North American USA300. Large parts of ST8 methicillin-susceptible S. aureus (MSSA) isolated in Africa represent a symplesiomorphic group of ST8 (i.e., a group representing the characteristics of the ancestor), which are rarely found in other world regions. Isolates previously discussed as USA300 ancestors, including USA500 and a “historic” CA-MRSA from Western Australia, were shown to be only distantly related to recent USA300 clones.

Diagnosis and management of Panton-Valentine leukocidin toxin associated Staphylococcus aureus infection: an update

The incidence of invasive Staphylococcus aureus (SA) infection has increased in the past decade and is associated with poor outcomes and high mortality rates. Of all the virulence factors, Panton-Valentine Leukocidin (PVL) has received the greatest attention. PVL producing SA strains are more likely to produce severe skin and soft tissue infections (SSTIs) and necrotizing pneumonia. This review focuses on the current evidence on PVL-SA virulence, epidemiology, clinical disease and treatment with relevance to healthcare in India.

Changing epidemiology of community-associated methicillin-resistant Staphylococcus aureus in the Asia-Pacific region

INTRODUCTION

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become an important threat to public health in the Asia-Pacific region, which is characterized by a large population and relatively insufficient resources. Better understanding on the current status of CA-MRSA in the region is of paramount importance. Areas covered: This article reviews the published literatures on the prevalence, molecular epidemiology, colonization, and hospital spread of CA-MRSA. Expert commentary: The burden of CA-MRSA has been increasing in the past two decades. The molecular epidemiology of CA-MRSA in the Asia-Pacific region shows a marked diversity in each country. Still, some strains - multilocus sequence type (MLST) ST59, ST30, ST72, ST8, and ST772 - are unique clones that have successfully established themselves as predominant, often spreading into nosocomial settings. More coordinated and comprehensive surveillance to understand the true epidemiology of CA-MRSA in the Asia-Pacific region is urgently needed.