Avidumicin, a novel cyclic bacteriocin, produced by Cutibacterium avidum shows anti-Cutibacterium acnes activity.

The prevalence of antimicrobial-resistant Cutibacterium acnes in acne patients has increased owing to inappropriate antimicrobial use. Commensal skin bacteria may play an important role in maintaining the balance of the skin microbiome by producing antimicrobial substances. Inhibition of Cu. acnes overgrowth can prevent the development and exacerbation of acne vulgaris. Here, we evaluated skin bacteria with anti-Cu. acnes activity. Growth inhibition activity against Cu. acnes was tested using 122 strains isolated from the skin of healthy volunteers and acne patients. Comparative genomic analysis of the bacterium with or without anti-Cu. acnes activity was conducted. The anti-Cu. acnes activity was confirmed by cloning an identified gene cluster and chemically synthesized peptides. Cu. avidum ATCC25577 and 89.7% of the Cu. avidum clinical isolates (26/29 strains) inhibited Cu. acnes growth. The growth inhibition activity was also found against other Cutibacterium, Lactiplantibacillus, and Corynebacterium species, but not against Staphylococcus species. The genome sequence of Cu. avidum showed a gene cluster encoding a novel bacteriocin named avidumicin. The precursor protein encoded by avdA undergoes post-translational modifications, supposedly becoming a circular bacteriocin. The anti-Cu. acnes activity of avidumicin was confirmed by Lactococcus lactis MG1363 carrying avdA. The C-terminal region of the avidumicin may be essential for anti-Cu. acnes activity. A commensal skin bacterium, Cu. avidum, producing avidumicin has anti-Cu. acnes activity. Therefore, avidumicin is a novel cyclic bacteriocin with a narrow antimicrobial spectrum. These findings suggest that Cu. avidum and avidumicin represent potential alternative agents in antimicrobial therapy for acne vulgaris.

Increased Prevalence of Minocycline-Resistant Staphylococcus epidermidis with tet(M) by Tetracycline Use for Acne Treatment.

Staphylococcus epidermidis, a major skin bacterium, can cause opportunistic infections. Use of antimicrobial agents against Cutibacterium acnes for acne treatment becomes a risk factor for emergence of antimicrobial-resistant skin bacteria. In this study, the impact of antimicrobial treatment of acne vulgaris on S. epidermidis antimicrobial resistance was assessed. A total of 344 S. epidermidis strains isolated from patients with acne vulgaris who visited hospital (165 strains) and dermatological clinics (179 strains), respectively, were analyzed. Except for doxycycline, the resistance rates were higher in strains isolated from patients who had used antimicrobials for acne treatment than in those isolated from patients who had not used antimicrobials. The prevalence rates of strains with erm(C) from patients who used macrolides and clindamycin (hospital, 78.0%; clinics, 61.3%) and those of strains with tet(M) from patients who used tetracyclines (hospital, 27.5%; clinics, 42.4%) were significantly higher than those of strains from patients who did not use antimicrobials (p < 0.05). All strains with erm(A) (8/8) and 91.7% strains with erm(C) (156/170) showed high-level resistance to macrolides and clindamycin (MIC ≥256 µg/mL). Furthermore, almost all strains with tet(M) showed resistance to minocycline. Our results showed that the use of antimicrobials for acne treatment may lead to an increased prevalence of antimicrobial-resistant S. epidermidis. In particular, the emergence of minocycline-resistant strains with tet(M) owing to the use of tetracyclines (doxycycline and minocycline) is a critical issue. Appropriate antimicrobial use for acne treatment may be an important strategy to prevent the emergence of antimicrobial-resistant skin bacteria.

Chinese herbal medicines and nutraceuticals inhibit Pseudomonas aeruginosa biofilm formation.

Pseudomonas aeruginosa is a major biofilm-forming, opportunistic pathogen. Tolerance to antimicrobial agents due to biofilm formation may lead to the emergence of antimicrobial-resistant bacterial strains. Thus, adjunctive agents that can inhibit biofilm formation are necessary to enhance the therapeutic efficacy of antimicrobial agents. In this study, we evaluated the anti-biofilm formation activity of selected Chinese herbal medicines and nutraceuticals, which are commercially available in Japan. Among the eight agents evaluated for their potential to inhibit biofilm formation, Eiekikaryu S, Iribakuga and Hyakujunro significantly reduced P. aeruginosa biofilm formation (P <0.05) without inhibiting bacterial growth. Additionally, the expression of biofilm-associated genes (rhlR, rhlA and lasB) in P. aeruginosa was significantly suppressed by Eiekikaryu S, Iribakuga and Hyakujunro (P <0.001). Our findings indicate that some Chinese herbal medicines and nutraceuticals can be potential adjunctive agents for antimicrobial therapy against P. aeruginosa .

Cutibacterium acnes phylogenetic type IC and II isolated from patients with non-acne diseases exhibit high-level biofilm formation.

Cutibacterium (formerly Propionibacterium) acnes is an important for not only exacerbating factor of acne vulgaris but also pathogen of surgical site infections (SSIs) in orthopedics and plastic surgery. Although biofilm-forming (BF) C. acnes are associated with intractable SSI, characteristics of these strains were still unknown. Here, we explored detailed molecular epidemiological features of BF C. acnes isolated as causative pathogen of infectious diseases. Phylogenetic types of 205 C. acnes strains isolated between 2013 and 2018 from 18 clinical departments of a university hospital in Japan were determined by single-locus sequence type (SLST). Clade H (traditional type IC) and K (type II) which are less relevant with healthy skin and acne vulgaris, were detected in 26.8% (55/205) and 16.1% (33/205) of the strains, respectively. The incidence of them was significantly higher than that of acne patients (H and K, each 2.9%, P < 0.05). In addition, SLST distribution of C. acnes strains differed by each department and isolation site. When biofilm formation was quantified, 51 strains (24.9%) were defined as high-BF strains. Notably, most high-BF strains were classified into the strains of clade H (56.4%, 31/55) and clade K (54.4%, 18/33), and these strains were frequently found in the strains isolated from patients of medical emergency center and plastic surgery. Similarly, high-BF strains were frequently found among the isolates from blood (35.7%) and catheters (30.0%), with a high proportion belonging to clades H and K. Compared to C. acnes strains isolated from acne patients, antimicrobial-resistant strains were less identified in non-acne patients. Our findings showed that pathogenicity of C. acnes strains differs by their phylogenetic types. Furthermore, we showed clade H and K have the ability of high biofilm formation and suggest that these strains have potential to become a risk factor for SSI.

Comparison of the bactericidal effects of quinolones against low-susceptible Haemophilus influenzae.

The increasing incidence of Haemophilus influenzae with decreased susceptibility to quinolones (quinolone low-susceptible H. influenzae) in Japan has raised concerns about therapeutic failure. Thus, assessment of effective antimicrobial agents is necessary to establish an effective therapeutic strategy against resulting infections. In this study, in vitro bactericidal effects of quinolones on low-susceptible H. influenzae strains were evaluated using time-kill curve analysis. For tosufloxacin, log reduction values for low-susceptible strains were significantly lower than those for susceptible strains at both Cmax and 1/2 Cmax. Conversely, although the log reduction values were lower for susceptible strains, the Cmax of levofloxacin and ß-lactams (amoxicillin and cefditoren) indicated bactericidal effects. In addition, higher concentrations of tosufloxacin at 2×Cmax and 4×Cmax had bactericidal effects on not only susceptible but also low-susceptible strains. These data strongly suggest that we should consider the presence of low-susceptible strains and reconsider the appropriate dosage of tosufloxacin for treatment, especially for paediatric patients.

In vitro growth-inhibitory effects of Portulaca oleracea L. formulation on intestinal pathogens.

INTRODUCTION: Empirical evidence suggests that Portulaca oleracea L. treats enteric infections, including dysentery, cholera, and acute infectious gastroenteritis. AIM: The aim of this study is to clarify the growth-inhibitory effects of Portulaca oleracea L. extract against 56 strains of intestinal pathogens. METHODOLOGY: 'Gogyo-so-cha (GSC)' was used as the P. oleracea L. formulation. A growth curve analysis was used to measure the growth-inhibitory effects of GSC, and Shiga toxin induction was measured using the latex agglutination test. RESULTS: GSC demonstrated strong bactericidal effects against Shigella dysenteriae and Vibrio cholerae strains from various isolates. GSC demonstrated weak or no bactericidal effects against intestinal commensal bacteria, including Enterococcus spp. and Escherichia coli . GSC did not induce Shigella toxins. CONCLUSION: GSC significantly inhibited the growth of intestinal pathogens, including S. dysenteriae and V. cholerae , without adversely affecting the intestinal flora, supporting the usage of GSC in traditional Chinese medicine. Taken together, GSC would be of immense value in the developing world, where diarrhoeal infectious diseases continue to pose a major health risk.

Increased prevalence of doxycycline low-susceptible Cutibacterium acnes isolated from acne patients in Japan caused by antimicrobial use and diversification of tetracycline resistance factors.

The prevalence of antimicrobial-resistant Cutibacterium acnes is an important concern for the antimicrobial treatment of acne vulgaris. We hypothesized that antimicrobial treatment regimens for acne vulgaris would change following the revisions in the Japanese acne treatment guidelines, which added a statement regarding appropriate antimicrobial usage. Here, we studied the changes in antimicrobial use and antimicrobial-resistant C. acnes isolated from acne patients. A total of 127 C. acnes isolates collected from 212 patients with acne between 2013 and 2018 were used. Roxithromycin and clindamycin resistance rates were approximately 50% and 40%, respectively. In contrast, the prevalence of low doxycycline-susceptible strains (minimum inhibitory concentration [MIC] ≥8 µg/mL) in 2018 (17.4%) was 5.6-fold higher than that in 2013 (3.1%). Although the number of patients with severe and moderate acne did not change, the number of patients with a history of oral tetracycline use increased. The incidence of low doxycycline-susceptible strains was high in patients with a history of oral tetracycline use. The prevalence of strains with a 16S rRNA mutation, which confers reduced susceptibility to tetracyclines, increased by 8.6-fold (12.1%) from 2016 to 2018 in comparison with the previously revised guidelines (1.4%). Furthermore, the prevalence of low susceptibility strains with two resistance factors, 16S rRNA mutation and ribosomal S10 protein substitution, also increased. Approximately 10% of strains had the exogenous resistance gene, tet(W) (2013 to 2015, 10.1%; 2016 to 2018, 8.6%), and these strains showed different susceptibility to doxycycline dependent on the expression of tet(W) (MIC range 0.5-8 µg/mL). Our data show that the antimicrobial resistance pattern in C. acnes changes according to the trend of antimicrobial usage for acne treatment. Therefore, we should pay heed to the rapid dissemination of tetracycline resistance in C. acnes owing to acquisition of 16S rRNA mutation and tet(W).

Dissemination of quinolone low-susceptible Haemophilus influenzae ST422 in Tokyo, Japan.

INTRODUCTION: Haemophilus influenzae with a reduced susceptibility to quinolones (quinolone low-susceptible H. influenzae) has recently emerged in Japan. In addition, the regional outbreak of the quinolone low-susceptible H. influenzae ST422 clone has been reported. In this study, we isolated this clone from an acute care hospital located in a geographically different area from the previous outbreak and characterised the nature of this clone. METHODS: Eighty-nine H. influenzae isolated between 2017 and 2019 were tested. The antimicrobial susceptibility was determined by the broth dilution method. The genetic background was analysed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Growth ability and ß-lactamase acquisition were evaluated by growth curve analysis and conjugative transfer experiments, respectively. RESULTS: Quinolone low-susceptible isolates accounted for 4.2% (1/24) in 2018 and 13.9% (5/36) in 2019. Most of the quinolone low-susceptible strains (83.3%) were classified as ST422 and had amino acid substitutions in quinolone resistance-determining regions in both GyrA and ParC. The patients' backgrounds were highly diverse. In addition, these isolates showed the same PFGE pattern as outbreak strains. The growth of ST422 clone was relatively faster than other clones. Furthermore, ST422 clone was able to acquire ß-lactamase from a ß-lactamase positive strain by horizontal transfer, becoming highly resistant to ß-lactams. CONCLUSION: Our study indicated that the quinolone low-susceptible H. influenzae ST422 clone has been spreading in the community undetected. In addition, this clone has the potential to grow faster and become more resistant through exogenous gene transfer. Therefore, ST422 clone should be monitored attention throughout Japan.

Antimicrobial activity and additive effect of the modified Gingyo-san with antimicrobials against Helicobacter pylori.

INTRODUCTION: Helicobacter pylori is an important factor in the development of gastroduodenal ulcers and gastric cancer. Although H. pylori eradication therapy has been employed, the eradication rate has decreased in recent years owing to an increase in clarithromycin-resistant strains. We previously reported the anti-infective effect of herbal medicines against several bacterial species. Here, we evaluated the growth inhibitory activity of herbal medicines alone and in combination with antimicrobials against H. pylori. METHODS AND RESULTS: Nine of 37 herbal medicines inhibited the growth of H. pylori ATCC700392. In particular, modified Gingyo-san showed the strongest growth inhibitory activity with a minimum inhibitory concentration (MIC) of 512 µg/ml for not only ATCC700392 but also clarithromycin-resistant strains having a 23 S rRNA mutation. Results of Time-Kill Kinetics Assay showed that 1 mg/mL modified Gingyo-san treatment for one hour killed 50% of the H. pylori population. Furthermore, modified Gingyo-san showed additive effects with clarithromycin, amoxicillin, and metronidazole against H. pylori ATCC700392 and clarithromycin-resistant strains. CONCLUSIONS: Our findings showed that modified Gingyo-san inhibits the growth of H. pylori and improves antimicrobial susceptibility when used in combination. Therefore, modified Gingyo-san has the potential to enhance the eradication rate of clarithromycin-resistant H. pylori.

[Antimicrobial Resistance and Infection Control for Gram-positive Bacteria].

Antimicrobial resistance (AMR) is a serious problem worldwide. We searched for the AMR determinants of various bacteria isolated from clinical settings and studied their resistance mechanisms and molecular epidemiology. This review focuses on the AMR of Staphylococcus aureus, a major gram-positive pathogen, which has the ability to acquire resistance to antimicrobials. The resistance factors of S. aureus are frequently found on mobile elements, including plasmids and transposons. We determined the complete DNA sequence of the tetracycline-resistance plasmid and found that the inducible expression of tetK in S. aureus was regulated by a post-transcriptional attenuation mechanism. Furthermore, outbreaks of methicillin-resistant S. aureus (MRSA) in hospitals and communities have led us to study infection controls, including the antiseptic susceptibility evaluation and molecular epidemiology of MRSA. Various antiseptic resistance determinants, such as qacA/B and smr, were identified on plasmids and characterized. We demonstrated that the plasmid-mediated efflux pump QacB variant QacIII confers fluoroquinolone efflux ability to S. aureus. Studies on MRSA epidemiology had shown that community-acquired MRSA (CA-MRSA) was disseminated into hospitals and that an increased use of alcohol-based rubs could reduce the incidence of MRSA infections in such institutions. Additionally, the study of CA-MRSA collected from communities and hospitals showed an increase in Panton-Valentine leucocidin (PVL)-positive CA-MRSA, causing severe skin and soft tissue infections. Moreover, various PVL-positive CA-MRSA clones have disseminated in Japan, whereas the USA300 LV/J clone evolved in that country. Our study provides important information regarding MRSA infection control.

[Evaluation of the Antimicrobial Effects of a Novel Visible Light-driven Photocatalyst in Vitro and in the Environment].

Environmental microorganisms can cause several infections in humans, especially in compromised hosts. Since there are many compromised hosts in a hospital setting, it is important to control environmental pathogens in such scenarios. To disinfect the environment, photocatalysts that produce reactive oxygen in response to light have attracted attention. In the present study, the effects of a visible-light-driven antimicrobial photocatalyst, silver (I) iodide and benzalkonium complex, on bacteria, viruses, and fungi were evaluated in vitro. In addition, uncoated panels and panels coated with the photocatalyst were set up at 11 points in a university campus for 6 months, and the adherent bacteria and fungi were measured. Bacteria, bacterial spores, viruses, and fungi were completely inactivated within 45 min on the photocatalyst-coated surface exposed to approximately 700-lux fluorescent light. In the university setting, there were fewer viable adherent bacteria and fungi on the coated plates. Our findings indicate that the silver (I) iodide and benzalkonium complex photocatalyst can decrease environmental bacteria in vitro and in actual environmental settings, and thus highlight its potential in controlling and disinfecting environmental pathogens.

Prevalence of antimicrobial-resistant staphylococci in nares and affected sites of pet dogs with superficial pyoderma.

Currently, antimicrobial-resistant staphylococci, particularly methicillin-resistant Staphylococcus pseudintermedius (MRSP), are frequently isolated from canine superficial pyoderma in Japan. However, little is known regarding the nasal prevalence of MRSP in pet dogs. Here, we determined the prevalence of antimicrobial-resistant staphylococci in nares and affected sites of pet dogs with superficial pyoderma. Of the 125 nares and 108 affected sites of pet dogs with superficial pyoderma, 107 (13 species) and 110 (eight species) staphylococci strains, respectively, were isolated. The isolation rate of S. pseudintermedius from pyoderma sites (82/110 strains, 74.5%) was significantly higher than that from nares (57/107 strains, 53.3%) (P<0.01). Notably, the prevalence of MRSP (18/57 strains, 31.6%) in nares was equivalent to that in pyoderma sites (28/82 strains, 34.1%). Furthermore, the phenotypes and genotypes of antimicrobial resistance in MRSP strains from nares were similar to those from pyoderma sites. Our findings revealed that the prevalence of antimicrobial-resistant staphylococci in the nares of pet dogs with superficial pyoderma is the same level as that in affected sites. Therefore, considerable attention should be paid to the antimicrobial resistance of commensal staphylococci in companion animals.

In vitro anti-biofilm effect of anti-methicillin-resistant Staphylococcus aureus (anti-MRSA) agents against the USA300 clone.

OBJECTIVES: Infection with a typical community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), the USA300 clone, has become a worldwide epidemic. Biofilm formation at the site of infection is one of the reasons for the development of intractable infectious diseases resulting from this clone. Here we evaluated the in vitro antibiofilm effects of anti-MRSA agents to identify the most effective agent against the USA300 clone embedded in biofilms. METHODS: Vancomycin, linezolid, teicoplanin, daptomycin, arbekacin and tigecycline were used as anti-MRSA agents. The biofilm permeability of the anti-MRSA agents was assessed using a biofilm-coated Transwell®. Morphological and compositional effects of anti-MRSA agents against biofilms were analysed based on the distribution of fluorescence intensity using confocal laser microscopy. Bactericidal activities of the anti-MRSA agents against biofilm-embedded S. aureus were compared. RESULTS: The permeability rates of linezolid (93.1%), daptomycin (91.3%), arbekacin (87.1%) and tigecycline (99.7%) for biofilms formed by the USA300 clone were found to be significantly higher than those of vancomycin (64.9%) and teicoplanin (62.3%) (P < 0.01). Confocal microscopic analysis showed that daptomycin greatly altered the biofilm morphology (decreased thickness and increased roughness) and markedly reduced the area occupied by the biofilm. Furthermore, daptomycin effectively reduced the extracellular DNA of biofilms and showed the highest bactericidal activity against biofilm-embedded USA300 clone among the anti-MRSA agents. CONCLUSION: The findings from this study demonstrate that, of the tested anti-MRSA agents, daptomycin is the most effective against biofilm-embedded USA300 clone in vitro.

Possible Dissemination of a Panton-Valentine Leukocidin-Positive Livestock-Associated Methicillin-Resistant Staphylococcus aureus CC398 Clone in Tokyo, Japan.

In the last decade, methicillin-resistant Staphylococcus aureus (MRSA) has been identified in livestock animals, such as swine, poultry, and veal calves, and has been termed livestock-associated MRSA (LA-MRSA). LA-MRSA sequence type (ST) 398 strains can effectively infect and colonize humans, with subsequent human-to-human transmission in both community and hospital settings. Unlike other countries, LA-MRSA had not been reported in Japanese patients until 2019. However, we recently reported a case of intractable arthritis caused by an LA-MRSA CC398 (ST1232) clone, which is a single-locus variant of ST398, in a patient in Tokyo, Japan, with no animal contact (Nakaminami H, et al. Emerg Infect Dis. 2020; 26: 795-7.). Uniquely, the strain was positive for Panton-Valentine leukocidin. Here, we report the second such case in Japan. To prevent the dissemination of LA-MRSA in the Japanese community, the prevalence of the CC398 MRSA clone should be closely monitored in the future.

First Report of Fatal Infection Caused by Community-acquired Methicillin-resistant Staphylococcus aureus USA300 Clone in a Collegiate Athlete.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is prevalent around the world and is a causative agent of skin and soft tissue infections in healthy individuals. Particularly, Panton-Valentine leukocidin (PVL)-positive CA-MRSA strains occasionally cause life-threatening infections, such as septic pulmonary emboli (SPE) and infectious endocarditis. However, severe infections caused by PVL-positive CA-MRSA strains have rarely been reported in Japan. For the first time, this study reports the case of a 20-year-old Japanese college athlete with life-threatening PVL-positive CA-MRSA USA300 clone infection, including sepsis, SPE, and skin and soft tissue infections with iliofemoral deep venous thrombosis.

First isolation of an IMP-1 metallo-ß-lactamase-producing Kluyvera ascorbata in Japan.

OBJECTIVES: The emergence of carbapenemase-producing Enterobacterales has been increasing globally, causing growing concerns. Although Kluyvera ascorbata is not known as a metallo-ß-lactamase (MBL)-producer, in the present study we isolated a K. ascorbata strain producing IMP-1 MBL from catheter-associated urine of a paediatric patient and performed whole-genome analysis to elucidate the features of this strain and the origin of IMP-1. METHODS: Carbapenemase production was confirmed by a modified carbapenemase inactivation method. Whole-genome sequencing was performed using NovaSeq 6000 and GridION. Conjugation ability was evaluated using Escherichia coli ML1410 by a broth mating assay. RESULTS: TheblaIMP-1 gene was located on a 149 316-bp transferable plasmid (pKATP2) and formed a class 1 integron structure. In addition, this plasmid had two types of repA genes as well as astA encoding a putative heat-stable enterotoxin. Comparison with other plasmids from Enterobacterales and Pseudomonas aeruginosa suggested that this plasmid might have originated by the integration of multiple plasmids. In addition, pKATP2 harboured conjugation-associated genes and was transferable. CONCLUSION: This is the first report of MBL-producing K. ascorbata. Therefore, our findings suggest that species which do not typically produce MBL could acquire the corresponding genes, attracting attention as potential MBL-producing pathogens.

Phosphatidylinositol-specific phospholipase C enhances epidermal penetration by Staphylococcus aureus.

Staphylococcus aureus (S. aureus) commonly colonizes the human skin and nostrils. However, it is also associated with a wide variety of diseases. S. aureus is frequently isolated from the skin of patients with atopic dermatitis (AD), and is linked to increased disease severity. S. aureus impairs the skin barrier and triggers inflammation through the secretion of various virulence factors. S. aureus secretes phosphatidylinositol-specific phospholipase C (PI-PLC), which hydrolyses phosphatidylinositol and cleaves glycosylphosphatidylinositol-anchored proteins. However, the role of S. aureus PI-PLC in the pathogenesis of skin diseases, including AD, remains unclear. In this study, we sought to determine the role of S. aureus PI-PLC in the pathogenesis of skin diseases. PI-PLC was observed to enhance the invasion and persistence of S. aureus in keratinocytes. Besides, PI-PLC promoted the penetration of S. aureus through the epidermal barrier in a mouse model of AD and the human organotypic epidermal equivalent. Furthermore, the loss of PI-PLC attenuated epidermal hyperplasia and the infiltration of Gr-1+ cells and CD4+ cells induced by S. aureus infection in the mouse model of AD. Collectively, these results indicate that PI-PLC eases the entry of S. aureus into the dermis and aggravates acanthosis and immune cell infiltration in infected skin.

Current status of Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus isolated from patients with skin and soft tissue infections in Japan.

The USA300 clone, which produces Panton-Valentine leukocidin (PVL), is a major pathogenic community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) clone that causes intractable skin infections. Recently, PVL-positive CA-MRSA, including USA300 clones, have emerged in both communities and hospitals in Japan. To prevent an outbreak of PVL-positive MRSA, infected patients should be treated with effective antimicrobial agents at community clinics. Herein, we investigate molecular epidemiological characteristics of PVL-positive MRSA isolated from outpatients with skin and soft tissue infections (SSTI), which are common community-onset infectious diseases. The detection rate of MRSA was 24.9% (362 strains) out of 1455 S. aureus strains isolated between 2013 and 2017. Among the MRSA strains, 15.5% (56 strains) were PVL-positive strains and associated with deep-seated skin infections. Molecular epidemiological analyses of PVL-positive MRSA showed that USA300 was the predominant clone (53.6%, 30 strains) and was identified in Kanto (18 strains), Kagawa (nine strains), Tohoku (two strains) and Hokkaido (one strain). Notably, minocycline and fusidic acid were effective against all PVL-positive MRSA strains. Hence, our data reveals the current status of PVL-positive MRSA isolated from patients with SSTI in Japan. Continuous surveillance of CA-MRSA is necessary to monitor latest prevalence rates and identify effective antimicrobial agents for PVL-positive MRSA strains.

A novel community-acquired MRSA clone, USA300-LV/J, uniquely evolved in Japan.

BACKGROUND: USA300 [ST8-staphylococcal cassette chromosome mec type IVa (ST8-IVa)/arginine catabolic mobile element (ACME) positive] is a major Panton-Valentine leucocidin (PVL)-positive community-acquired MRSA (CA-MRSA) clone. In Japan, we identified USA300-like strains with characteristics (ST8-IVc/ACME negative) similar to those of USA300. OBJECTIVES: To reveal the evolution of the USA300-like strains. METHODS: The whole-genome sequence of a USA300-like strain was determined and genome analysis was performed using Type Strain Genome Server, MUSCLE and progressiveMauve. RESULTS: Genome-based phylogenetic analysis showed that the USA300-like strain is more similar to the USA300-Latin American variant (USA300-LV), which is a PVL-positive CA-MRSA clone identified in South America, than to USA300. Instead of the ACME, copper and mercury resistance mobile elements were located on the genome of the USA300-like strain. In addition, the USA300-like strain possessed a unique mobile genetic element, ICE6013. Therefore, we named this novel USA300-LV variant identified in Japan as USA300-LV/J. CONCLUSIONS: Our findings strongly suggest that a PVL-positive CA-MRSA USA300-LV/J clone originating from abroad has uniquely evolved and disseminated in Japan.