Multiresistant ST59-SCCmec IV-t437 clone with strong biofilm-forming capacity was identified predominantly in MRSA isolated from Chinese children

ESKAPE in China: epidemiology and characteristics of antibiotic resistance

The escalation of antibiotic resistance and the diminishing antimicrobial pipeline have emerged as significant threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria, demanding urgently effective therapies. Despite the introduction of various new antibiotics and antibiotic adjuvants, such as innovative β-lactamase inhibitors, these organisms continue to pose substantial therapeutic challenges. People's Republic of China, as a country facing a severe bacterial resistance situation, has undergone a series of changes and findings in recent years in terms of the prevalence, transmission characteristics and resistance mechanisms of antibiotic resistant bacteria. The increasing levels of population mobility have not only shaped the unique characteristics of antibiotic resistance prevalence and transmission within People's Republic of China but have also indirectly reflected global patterns of antibiotic-resistant dissemination. What's more, as a vast nation, People's Republic of China exhibits significant variations in the levels of antibiotic resistance and the prevalence characteristics of antibiotic resistant bacteria across different provinces and regions. In this review, we examine the current epidemiology and characteristics of this important group of bacterial pathogens, delving into relevant mechanisms of resistance to recently introduced antibiotics that impact their clinical utility in China.

Cell-wall-anchored proteins affect invasive host colonization and biofilm formation in Staphylococcus aureus

As a major human and animal pathogen, Staphylococcus aureus can attach to medical implants (abiotic surface) or host tissues (biotic surface), and further establish robust biofilms which enhances resistance and persistence to host immune system and antibiotics. Cell-wall-anchored proteins (CWAPs) covalently link to peptidoglycan, and largely facilitate the colonization of S. aureus on various surfaces (including adhesion and biofilm formation) and invasion into host cells (including adhesion, immune evasion, iron acquisition and biofilm formation). During biofilm formation, CWAPs function in adhesion, aggregation, collagen-like fiber network formation, and consortia formation. In this review, we firstly focus on the structural features of CWAPs, including their intracellular function and interactions with host cells, as well as the functions and ligand binding of CWAPs in different stages of S. aureus biofilm formation. Then, the roles of CWAPs in different biofilm processes with regards in development of therapeutic approaches are clarified, followed by the association between CWAPs genes and clonal lineages. By touching upon these aspects, we hope to provide comprehensive knowledge and clearer understanding on the CWAPs of S. aureus and their roles in biofilm formation, which may further aid in prevention and treatment infection and vaccine development.

Biofilm-producing ability of methicillin-resistant Staphylococcus aureus clinically isolated in China

BACKGROUND

Staphylococcus aureus, a commensal bacterium, colonizes the skin and mucous membranes of approximately 30% of the human population. Apart from conventional resistance mechanisms, one of the pathogenic features of S. aureus is its ability to survive in a biofilm state on both biotic and abiotic surfaces. Due to this characteristic, S. aureus is a major cause of human infections, with Methicillin-Resistant Staphylococcus aureus (MRSA) being a significant contributor to both community-acquired and hospital-acquired infections.

RESULTS

Analyzing non-repetitive clinical isolates of MRSA collected from seven provinces and cities in China between 2014 and 2020, it was observed that 53.2% of the MRSA isolates exhibited varying degrees of ability to produce biofilm. The biofilm positivity rate was notably high in MRSA isolates from Guangdong, Jiangxi, and Hubei. The predominant MRSA strains collected in this study were of sequence types ST59, ST5, and ST239, with the biofilm-producing capability mainly distributed among moderate and weak biofilm producers within these ST types. Notably, certain sequence types, such as ST88, exhibited a high prevalence of strong biofilm-producing strains. The study found that SCCmec IV was the predominant type among biofilm-positive MRSA, followed by SCCmec II. Comparing strains with weak and strong biofilm production capabilities, the positive rates of the sdrD and sdrE were higher in strong biofilm producers. The genetic determinants ebp, icaA, icaB, icaC, icaD, icaR, and sdrE were associated with strong biofilm production in MRSA. Additionally, biofilm-negative MRSA isolates showed higher sensitivity rates to cefalotin (94.8%), daptomycin (94.5%), mupirocin (86.5%), teicoplanin (94.5%), fusidic acid (81.0%), and dalbavancin (94.5%) compared to biofilm-positive MRSA isolates. The biofilm positivity rate was consistently above 50% in all collected specimen types.

CONCLUSIONS

MRSA strains with biofilm production capability warrant increased vigilance.

Emerging threats of high biofilm formation and antibiotic resistance in clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates from Pakistan

OBJECTIVES

This multicenter study, conducted from a One Health perspective, aimed to comprehensively examine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections and their biofilm-forming capabilities in Pakistan. Phylogenetic analysis of the study isolates was also performed.

METHODS

A total of 150 MRSA isolates were screened from various clinical samples using Cefoxitin antibiotic discs. Genotypic confirmation was conducted through mecA, S. aureus-specific nuc, and 16S rRNA genes. Biofilm formation was assessed using Congo red agar (CRA) and slime layer quantification methods. The intercellular adhesion (ica) operon genes, specifically icaA and icaD, were detected. Phylogenetic analysis utilized the 16S rRNA sequences. Statistical associations between various parameters were determined using chi-square analysis.

RESULTS

The presence of the mecA gene was observed in 131 out of 150 isolates (87.3%). CRA identified 28% and 40% of isolates as strong and moderate biofilm producers, respectively, while 9.3% were classified as non-biofilm producers. The slime layer assay exhibited higher sensitivity, classifying only 4.7% of isolates as non-biofilm producers. Biofilm-forming genes icaA and icaD were detected in 85.3% and 86.7% of the isolates, respectively. Antibiotic resistance was more prevalent among biofilm-forming isolates, particularly against ciprofloxacin, levofloxacin, erythromycin, trimethoprim-sulfamethoxazole, and fosfomycin. Ceftaroline demonstrated efficacy irrespective of biofilm-forming abilities. Conversely, non-biofilm producers exhibited complete susceptibility to clarithromycin and tigecycline.

CONCLUSIONS

Clinical MRSA strains exhibit a substantial potential for biofilm formation, contributing to a resistant phenotype. Routine antibiotic testing in clinical settings that overlook the biofilm aspect may lead to the failure of empiric antibiotic therapy.

Prevalence and characterization of community-associated Staphylococcus aureus isolates from human mastitis in Beijing, China

OBJECTIVES

Staphylococcus aureus (S. aureus) spreads worldwide and occurrence of mastitis caused by it holds significant implications for public health. We aim to reveal the molecular typing, antibiotic resistance and virulence gene profile of S. aureus causing mastitis through investigation.

METHODS

A total of 200 isolates of S. aureus were collected from outpatients infected with mastitis in a hospital in Beijing from 2020.7 to 2021.7. The molecular characteristics were analyzed by MLST and spa typing, virulence genes were screened by PCR, antibiotic susceptible test was performed by VITEK® 2 Compact system and phylogenetic analysis was performed by MEGA11 and iTOL.

RESULTS

Nineteen sequence types (STs) belonging to 9 clone complexes (CCs) were identified. ST22 was the most dominant clone (77.0%, 154/200). MRSA accounted for 19.0% (38/200) and 89.5% (34/38) of MRSA isolates belonged to CC22 and CC59. The isolates had relatively low levels of antibiotic resistance, with the exception of β-lactams and macrolides with resistance rates above 50.0%. The carrying rate of pvl in the ST22-MRSA strains were 84.2% and the detection rates of seb and pvl in the MRSA isolates were significantly higher than those in the MSSA isolates, while the hlg, fnbA and sdrD showed opposite results. Whole genome sequenced specimens of MRSA strains X4 and B5 show the same evolutionary origin as ST22 EMRSA-15 (HE681097), which is popular in Europe.

CONCLUSIONS

The method based on molecular epidemiology is an important tool for tracking the spread of S. aureus infections. We need to be alert to the major MRSA clones CC22 and CC59 in the region and be vigilant to the possible pandemic and spread of ST22 EMRSA-15.

Global epidemiology of asymptomatic colonisation of methicillin-resistant Staphylococcus aureus in the upper respiratory tract of young children: a systematic review and meta-analysis

OBJECTIVE

To estimate the global prevalence of asymptomatic colonisation, and determine the associated risk factors, antibiotic resistance and genotypes of methicillin-resistant Staphylococcus aureus (MRSA) in the upper respiratory tract of young children.

DESIGN

Four bibliometric databases were searched for publications between 2010 and 2022 according to the protocol registered in PROSPERO. Cross-sectional or cohort studies describing the prevalence of asymptomatic colonisation of S. aureus and MRSA in young children were included. Data extraction and analysis were carried out by two reviewers independently according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement. Pooled prevalence was estimated using a random effects model.

SETTING AND STUDIES

We included studies where children without respiratory tract infection or Staphylococcal infection were recruited from the community, children's institutions (ie, nurseries, kindergartens, daycare centres and preschools) and healthcare centre visits and assessed for asymptomatic colonisation with S. aureus and MRSA.

MAIN OUTCOME MEASURES

The pooled prevalence of asymptomatic colonisation of S. aureus and MRSA of young children globally.

RESULTS

In this systematic review and meta-analysis of 21 416 young children, the pooled global prevalence of asymptomatic S. aureus colonisation was 25.1% (95% CI 21.4 to 28.8) and MRSA colonisation was 3.4% (95% CI 2.8 to 4.1). The clones of MRSA strains included healthcare-associated MRSA, community-associated MRSA and livestock-associated MRSA.

CONCLUSION

This study provides evidence of increased MRSA colonisation globally among young children, underlining the critical role of asymptomatic carriers in MRSA transmission and the need for control measures.

PROSPERO REGISTRATION NUMBER

CRD 42022328385.

Resistance phenotype and genetic features of a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus strain from an immunocompromised patient

Strain C1 was successfully isolated from an immunosuppressed patient with persistent bacteremia, who had not previously been exposed to glycopeptide antibiotics. This strain was found to be a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus (hVISA). It is noteworthy that, following a brief period of vancomycin treatment, strains C6, C8, and C9, which were obtained from blood and other body parts, exhibited a significant reduction in heterogeneity as determined by population analysis profile-area under the curve (PAP-AUC) detection. Genotyping analysis revealed that these bacterial strains belonged to the same SCCmecIVa-ST59-t437-agrI genotype and shared the same virulome and resistome. In this study, a comparative genomics analysis was conducted between strain C1 and strain N315 to identify potential hVISA-associated mutations. Ultimately, a total of 205 mutation sites in 19 candidate genes, likely associated with the hVISA phenotype, were identified.

Prevalence and molecular characteristics of heterogeneous vancomycin intermediate Staphylococcus aureus in a tertiary care center of northern China

The use of glycopeptide medications may decline in line with the annual decline in methicillin-resistant Staphylococcus aureus (MRSA) detection rates in China. The rate of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA)detection may be impacted by this. However, there is currently a dearth of information on the incidence of hVISA in China. This study aims to analyze the recent epidemiology and molecular characteristics of hVISA strains in Beijing, China. A total of 175 non-duplicate MRSA strains from various infection sites were collected from a medical center between January 2018 and May 2023 and underwent molecular typing and susceptibility testing (Vitek2). Vancomycin and teicoplanin MICs were also evaluated by standard broth microdilution method and agar dilution method, respectively. Isolates growing on screening agar (BHIV4 and BHIT5, brain heart infusion agar containing 4 μg/ml vancomycin and 5 μg/ml teicoplanin, respectively) were characterized further by analysis of macro-Etest (MET) and population analysis profiling with area under the curve (PAP-AUC). The proportion of hVISA among MRSA isolates was 8.6 %. BHIT5 could select all hVISA strains while BHIV4 and MET only selected two hVISA strains. Compared with vancomycin- susceptible Staphylococcus aureus (VSSA), hVISA isolates were less susceptible to erythromycin and clindamycin. In addition, hVISA frequency was MIC-independent despite using different detection methods. In total, 11 types of STs, 28 types of spa typing, four types of SCCmec typing, and two types of agr typing were identified and the predominant type in both MRSA and hVISA isolates was ST239-t030-SCCmecIII-agr I. The analysis of biofilm formation, growth, and virulence genes in hVISA strains revealed sparse information. The dataset presented in this study provided the prevalence and molecular characteristics of hVISA in hospital settings and the combination of BHIT5 and PAP-AUC may identify hVISA efficiently. The result of genotyping suggested the genotype of hVISA was mainly consistent with that of local MRSA. Additional studies on the characteristics of hVISA strains were necessary.

Genotypic diversity of staphylococcal enterotoxin B gene (seb) and its association with molecular characterization and antimicrobial resistance of Staphylococcus aureus from retail food

To investigate the expression pattern of staphylococcal enterotoxin B (SEB) in food and the genotypic diversity of SEB-encoding gene in association with molecular characteristics and antimicrobial resistance of S. aureus, 498 isolates from retail food were screened for seb gene and detected for SEB production in S. aureus. In addition, the seb nucleotide sequences, virulence genes, resistance genes, antimicrobial susceptibility and molecular characteristics of S. aureus were examined. A total of 45 (9.0 %) seb-positive S. aureus strains were identified, all of which expressed SEB. The detection rate of SEB-production strains was significantly higher from dairy-related sources than those from other sources (P < 0.05). In vitro simulations showed that S. aureus could grow and express SEB in both milk and pork, with SEB expression exceeding 20 ng/g after 1 day of storage at room temperature. There were 2 distinct SEB genotyping (SEB1 and SEB2) in the SEB amino acid sequences of the 45 isolates, including 4 amino acid differences (Ala-13Val, Ser14Ala, Asn192Ser, and Met222Leu). There was no significant difference (P > 0.05) in SEB production between SEB1 and SEB2 genotyping strains. Based on MLST clustering analysis, the same molecular type strains were found to have the same SEB genotyping, virulence gene profile, resistance gene profile and drug resistance profile. Among them, the dominant molecular types of SEB1 and SEB2 strains were CC1-ST188-t189 and CC59-ST59-t437, respectively. Compared to the CC1-ST188-t189 clonal strain, the CC59-ST59-t437 clonal strain carried a higher number of virulence and resistance genes and exhibited a broader resistance profile. Therefore, understanding the characteristics of the strains and their expression patterns in food can be effective in preventing food poisoning incidents.

Clinical and molecular characteristics of methicillin-resistant Staphylococcus aureus in bone and joint infection among children

OBJECTIVE

To investigate the characteristics of Methicillin-Resistant Staphylococcus aureus (MRSA) in bone and joint infection (BJI) among children.

METHODS

A total of 338 patients diagnosed with BJI from 2013 to 2022 in Children's Hospital of Fudan University were enrolled. Demographic information, microbiology culture results and laboratory findings, including white blood counts (WBC), C-reactive protein (CRP), procalcitonin (PCT), interleukin-6 (IL-6), and erythrocyte sedimentation rate (ESR) were collected and analyzed. MRSA was confirmed by antimicrobial susceptibility testing. Other MRSA-caused infections were randomly selected for comparison. Twenty-three virulence and antimicrobial resistance (AMR) genes were screened for MRSA strains. Multilocus sequence typing (MLST) and Staphylococcal protein A (spa) typing were performed using PCR amplification and sequencing.

RESULTS

Of the identified pathogens in BJI, MRSA accounted for 21.0% (47/224). Patients with BJI had high levels of initial CRP, white blood cell count (WBC) and IL-6. ST59 (43.9%) and t437 (37.6%) were the main MRSA subtypes isolated from the children. The major genotypes in BJI were ST59-t437 (29.8%) and ST22-t309 (14.9%), with high carriage of hemolysins including hla (94.4-100%), hlb (66.2-93.3%), and hld (100%). Notably, Panton-Valentine leukocidin (pvl) had a high prevalence (53.3%) in ST22-t309-MRSA. Other virulence genes including tst, seg and sei were more commonly detected in ST22-t309-MRSA (40.0-46.7%) than in ST59-t437-MRSA (4.2-9.9%). High-carriage AMR genes in MRSA included aph(3')/III (66.7-80%), ermB (57.5-73.3%) and ermC (66.7-78.9%). MRSA presented high-resistance to erythromycin (52.0-100%) and clindamycin (48.0-92.5%), different genotypes displayed variation in their susceptibilities to antibiotics.

CONCLUSIONS

The major MRSA genotype in BJI was ST59-t437, followed by ST22-t309, with a higher prevalence of the pvl gene. Continuous surveillance of pvl-positive ST22-t309-MRSA in pediatric BJI infections is thus required.

Hospital-Related Lineage of USA300 Methicillin-Resistant Staphylococcus aureus (MRSA) to Cause Bacteremia in Iran

Staphylococcus aureus is an important pathogen that causes bloodstream infections. This study is aimed at assessing the genotypic characteristics of S. aureus strains responsible for bloodstream infections. An epidemiological study was conducted using 85 S. aureus strains isolated from bloodstream infections. Susceptibility was tested using the broth microdilution method and disk diffusion. All detected methicillin-resistant S. aureus (MRSA) isolates were confirmed by mecA PCR assays. S. aureus isolated from bacteremia were characterized using SCCmec, spa, and multilocus sequence typing methods. The prevalence of S. aureus strains responsible for bloodstream infections was 38.8%. All isolates were MRSA. Multidrug resistance (MDR) was present in 84.7% of isolates. MRSA isolated categorized within six clonal complexes including CC8 (60%), CC22 (22.4%), CC5 (5.9%), CC30 (4.7%), CC45 (4.7%), and CC59 (2.3%). The main lineages found were USA300/CC8-MRSA-IV/t008 (41.2%), followed by ST22-SCCmecIV/t790 (9.4%), ST239-SCCmecIII/t037 (7.1%), ST22-SCCmecIV/t032 (7.1%), ST239-SCCmecIII/t631 (5.9%), ST239-SCCmecIII/t860 (5.9%), ST22-SCCmecIV/t852 (5.9%), ST5-SCCmecIV/t002 (4.7%), ST45-SCCmecIV/t038 (4.7%), ST30-SCCmecIV/t318 (4.7%), ST59-SCCmecIV/t437 (2.3%), and ST225-SCCmecII/t045 (1.1%). Resistance to vancomycin amounted to 5.9% of isolates that belonged to ST239-SCCmecIII/t037 (80%) and ST8-SCCmecIV/t008 (20%). The emergence of USA300 strains in bloodstream infections in our country is a serious alarm and highlights the significant invasion of this lineage into the healthcare system. MDR patterns among these strains appear to be becoming the biggest problem in healthcare treatment.

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.

Current molecular approach for diagnosis of MRSA: a meta-narrative review

Introduction:

Detection and diagnosis of methicillin-resistant Staphylococcus aureus (MRSA) are important in ensuring a correct and effective treatment, further reducing its spread. A wide range of molecular approaches has been used for the diagnosis of antimicrobial resistance (AMR) in MRSA. This review aims to study and appraise widely used molecular diagnostic methods for detecting MRSA.

Methods:

This meta-narrative review was performed by searching PubMed using the following search terms: (molecular diagnosis) AND (antimicrobial resistance) AND (methicillin-resistant Staphylococcus aureus). Studies using molecular diagnostic techniques for the detection of MRSA were included, while non-English language, duplicates and non-article studies were excluded. After reviewing the libraries and a further manual search, 20 studies were included in this article. RAMESES publication standard for narrative reviews was used for this synthesis.

Results:

A total of 20 full papers were reviewed and appraised in this synthesis, consisting of PCR technique (n = 7), deoxyribonucleic acid (DNA) Microarray (n = 1), DNA sequencing (n = 2), Xpert MRSA/SA BC assay (n = 2), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) (n = 2), MLST (n = 4), SCCmec typing (n = 1) and GENECUBE (n = 1).

Discussion:

Different diagnostic methods used to diagnose MRSA have been studied in this review. This study concludes that PCR has been extensively used due to its higher sensitivity and cost-effectiveness in the past five years

The FnBPA from methicillin-resistant Staphylococcus aureus promoted development of oral squamous cell carcinoma

Background

Oral squamous cell carcinoma (OSCC) is the most common tumor in the oral cavity. Methicillin-resistant Staphylococcus aureus (MRSA) were highly detected in OSCC patients; however, the interactions and mechanisms between drug-resistant bacteria (MRSA) and OSCC are not clear.

Aim

The aim of this study was to investigate the promotion of MRSA on the development of OSCC.

Methods

MRSA and MSSA (methicillin-susceptible) strains were employed to investigate the effect on the proliferation of OSCC in vitro and vivo.

Results

All of the MRSA strains significantly increased the proliferation of OSCC cells and MRSA arrested the cell cycles of OSCC cells in the S phase. MRSA activated the expression of TLR-4, NF-κB and c-fos in OSCC cells. MRSA also promoted the development of squamous cell carcinoma in vivo. The virulence factor fnbpA gene was significantly upregulated in all MRSA strains. By neutralizing FnBPA, the promotions of MRSA on OSCC cell proliferation and development of squamous cell carcinoma were significantly decreased. Meanwhile, the activation of c-fos and NF-κB by MRSA was also significantly decreased by FnBPA antibody.

Conclusion

MRSA promoted development of OSCC, and the FnBPA protein was the critical virulence factor. Targeting virulence factors is a new method to block the interaction between a drug-resistant pathogen and development of tumors.

Molecular characterization and virulence gene profiling of methicillin-resistant Staphylococcus aureus associated with bloodstream infections in southern China

Methicillin-resistant Staphylococcus aureus (MRSA) causes an enormous illness burden, including skin and soft tissue infections (SSTIs), pneumonia, bloodstream infections (BSI), and sepsis. BSI are associated with significant patient morbidity and mortality worldwide. However, limited information is available on MRSA-related BSI in China. This study aimed to investigate the molecular characterization of 77 MRSA isolates recovered from hospitalized patients with BSI between 2012 and 2020 at three first-class tertiary hospitals in southern China based on multilocus sequence typing (MLST), spa typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Overall, 13 clonal complexes (CCs) were identified, with CC59 and CC5 being the largest clusters, indicating high genetic diversity among BSI-causing MRSA isolates. ST59 was the most prevalent MLST type (22.1%). ST5/ST764-MRSA SCCmec II was the predominant adult MRSA clone, whereas ST59-MRSA SCCmec IV was the most common pediatric MRSA clone. ST5-t2460, ST764-t1084, and ST59-t437 were the most common types of adult MRSA isolates, whereas ST59-t437 and ST59-t172 were the predominant types of children’s MRSA isolates. ST59-SCCmec IV/V represented the most common clone among community acquired-MRSA isolates. ST5/ST764-SCCmec II was the most common type of hospital-associated MRSA isolate. The most prevalent toxin-encoding genes detected were hla, hld, icaA, and clfA (96.1–100%). Forty-three (100%, 43/43) isolates harbored more than 18 of the tested virulence genes in adults and eight virulence genes (23.5%, 8/34) in children. Virulence gene analysis revealed diversity among different clones: the positivity rates for the Panton-Valentine leukocidin (PVL) gene were 55.8 and 35.3% in adult and pediatric MRSA isolates, respectively; the genes seb–sei were present in all adult strains; seb–seg–sei–seo were present in all ST5, ST59, ST15, ST45, and ST22 adult strains; and seg–sei–sem–sen–seo were present in different clones, including ST15, ST45, and ST22 adult MRSA isolates and ST25, ST30, ST546, and ST72 children’s MRSA isolates. Adult MRSA isolates had significantly higher antibiotic resistance rates and virulence gene prevalence than pediatric MRSA isolates. For 8 years, this study provided epidemiological data on the molecular characteristics and virulence genes in different groups of MRSA BSI in China. Our findings may provide critical information for a better understanding of MRSA BSI.

Clonality, virulence genes, and antibiotic resistance of Staphylococcus aureus isolated from blood in Shandong, China

BACKGROUND

Bloodstream infection (BSI) caused by Staphylococcus aureus (S. aureus) can be life-threatening and pose a great challenge to infection control and clinical treatment. However, little information exists regarding the characterization of S. aureus in BSI patients in Shandong, China. To identify the clonality, virulence genes, and antibiotic resistance of S. aureus in blood, a total of 101 nonrepetitive blood isolates were collected. The antibiotic resistance phenotypes were determined, and virulence genes were analyzed with polymerase chain reaction (PCR). Finally, the genetic relatedness was investigated with Staphylococcus chromosomal cassette mec (SCCmec) typing for methicillin-resistant S. aureus (MRSA) isolates, Staphylococcal protein A (spa), and multilocus sequence typing (MLST) for all of 101 isolates.

RESULTS

Of the 101 S. aureus isolates, 24 MRSA isolates and 77 methicillin-susceptible S. aureus (MSSA) isolates were identified. Overall, MRSA isolates had higher resistance rates than MSSA isolates when exposed to any of the 15 antibiotics tested in this study except for trimethoprim/sulfamethoxazole. Among the 17 virulence genes tested in this study, hla, hld, and hlg could be detected in all isolates. MRSA isolates were more likely to carry seb and hlb genes, while MSSA isolates were more likely to carry seg and sei genes. Thirty-five sequence types (STs) and 49 spa types were identified, of which ST59-t437 and ST398-t571 were the most abundant. These two genotypes were also the most abundant ST-spa types in MRSA and MSSA isolates, but their abundances shifted over time, with ST398-t571 being the predominant genotype from 2016 to 2017, and ST59-t437 from 2018 to 2020. Besides, all the ST59-t437 isolates harbored hlgb gene, whereas most (88.9%) ST398-t571 did not. In addition, twenty-four MRSA isolates were subject to SCCmec typing. SCCmec IVa was the most prevalent SCCmec type, and all the ST59-t437 MRSA isolates were SCCmec IVa. We also observed 15 new STs, and some of them were MRSA.

CONCLUSION

These findings provide additional observations and epidemiological data for blood S. aureus isolates, which can improve future infection-control measures and aid in potential clinical treatments in hospitals and other clinical settings.

Increased biofilm formation by Staphylococcus aureus clinical isolates on surfaces covered with plasma proteins

Introduction. Biofilm formation is a major virulence factor associated with Staphylococcus aureus infections. However, the influence of plasma proteins on biofilm formation of clinical isolates in vitro remains unclear.Hypotheses. We hypothesized that coating surfaces with plasma proteins might induce biofilm formation by S. aureus of different clonal lineages.Aim. To evaluate biofilm production by clinical S. aureus isolates of different clonal lineages isolated in Rio de Janeiro hospitals and investigated the presence of biofilm-associated genes.Methodology. This study assessed biofilm production of 60 S. aureus isolates in polystyrene microtitre plates with and without fibrinogen or fibronectin. The biochemical composition of the biofilm matrices was determined and the biofilm formation on fibrinogen-coated surfaces was also evaluated by confocal laser scanning microscopy. The presence of biofilm-related genes was detected by PCR, and the typing and functionality of agr operon was also evaluated.Results. Most of the isolates (45 %) were weak biofilm producers or non-producers. However, most of them presented a significant increase in biofilm production on plates covered with plasma proteins. There was no significant difference in biofilm formation between methicillin-resistant and -susceptible S. aureus isolates, or between different clonal lineages, except for ST30-IV (weak producers) and ST239-III (strong producers). The fnbB gene was associated with higher biofilm production.Conclusion. An increase in biofilm production in the presence of plasma proteins highlights the importance of investigating biofilm formation by S. aureus clinical isolates under different conditions since this virulence factor contributes to persistent infections and increased resistance to antimicrobials.

Biofilm Formation of Multidrug-Resistant MRSA Strains Isolated from Different Types of Human Infections

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main pathogens causing chronic infections, mainly due to its capacity to form biofilms. However, the mechanisms underlying the biofilm formation of MRSA strains from different types of human infections are not fully understood. MRSA strains isolated from distinct human infections were characterized aiming to determine their biofilm-forming capacity, the biofilm resistance to conventional antibiotics and the prevalence of biofilm-related genes, including, icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, cna, eno, ebpS, fib and bbp. Eighty-three clinical MRSA strains recovered from bacteremia episodes, osteomyelitis and diabetic foot ulcers were used. The biofilm-forming capacity was evaluated by the microtiter biofilm assay and the biofilm structure was analyzed via confocal scanning laser microscopy. The antimicrobial susceptibility of 24-h-old biofilms was assessed against three antibiotics and the biomass reduction was measured. The metabolic activity of biofilms was evaluated by the XTT assay. The presence of biofilm-related genes was investigated by whole-genome sequencing and by PCR. Despite different intensities, all strains showed the capacity to form biofilms. Most strains had also a large number of biofilm-related genes. However, strains isolated from osteomyelitis showed a lower capacity to form biofilms and also a lower prevalence of biofilm-associated genes. There was a significant reduction in the biofilm biomass of some strains tested against antibiotics. Our results provide important information on the biofilm-forming capacity of clinical MRSA strains, which may be essential to understand the influence of different types of infections on biofilm production and chronic infections.

Prevalence and characterization of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus isolated from retail yak butter in Tibet, China

This study aimed to investigate the prevalence, molecular characteristics and antibiotic resistance of Staphylococcus aureus isolates from yak butter in Tibet, China. A total of 218 yak butter samples were collected from retail stores in Tibet and screened for Staph. aureus. Furthermore, the virulence genes, resistance genes, antimicrobial susceptibility, and molecular typing [pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, and staphylococcal protein A (spa) typing] of Staph. aureus isolates were detected. The results showed that 12.4% of yak butter samples were contaminated with Staph. aureus, including 5 samples positive for methicillin-resistant Staph. aureus (MRSA). Among all isolates, 96.3% harbored one or more virulence genes, including classical (sea and sec), novel enterotoxin-encoding genes (seh, sek, sel, and seq), and hemolysin genes (hla and hld). All isolates were resistant to at least 2 different antibiotic classes, and the isolates were most commonly resistant to sulfonamides, β-lactams, and erythromycin. For resistance genes, blaZ (74.1%) was most frequently detected, followed by dfrG (51.9%), erm(B) (22.2%), mecA (18.5%), tet(K) (14.8%), aph(2″)-Ia, aph(3')-III, and ant(6)-Ia (11.1% for each), and erm(C) (7.4%). We detected 8 spa types, 6 sequence types (ST), and 5 clonal complex (CC) types. In addition, 1 isolate of Staph. aureus was nontypeable. We found that CC1-ST1-t559 (55.6%) was the most predominant clone, followed by CC59-ST59-t437 (11.1%), CC5-ST5-t002 (7.4%), CC1-ST1, CC1-ST1-t114, CC1-ST573-t4938, CC1-ST573-t8915, CC30-ST30-t021, and CC25-ST25-t167 (3.7% for each). For PFGE typing, a total of 5 clusters and 15 pulsotypes were generated, and some isolates from different samples showed indistinguishable pulsotypes. Our findings suggest that yak butter produced in Tibet, China, could be contaminated by Staph. aureus strains, including MRSA strains, carrying various virulence and resistance genes, representing multiple antimicrobial resistance phenotypes. The presence of potentially virulent and antibiotic-resistant Staph. aureus strains in yak butter poses a potential threat to consumers, and appropriate measures need to be taken in the production chain to reduce the occurrence of Staph. aureus in yak butter.

Identification of Methicillin-Resistant Staphylococcus Aureus From Methicillin-Sensitive Staphylococcus Aureus and Molecular Characterization in Quanzhou, China

To distinguish Methicillin-Resistant Staphylococcus aureus (MRSA) from Methicillin-Sensitive Staphylococcus aureus (MSSA) in the protein sequences level, test the susceptibility to antibiotic of all Staphylococcus aureus isolates from Quanzhou hospitals, define the virulence factor and molecular characteristics of the MRSA isolates. MRSA and MSSA Pfam protein sequences were used to extract feature vectors of 188D, n-gram and 400D. Weka software was applied to classify the two Staphylococcus aureus and performance effect was evaluated. Antibiotic susceptibility testing of the 81 Staphylococcus aureus was performed by the Mérieux Microbial Analysis Instrument. The 65 MRSA isolates were characterized by Panton-Valentine leukocidin (PVL), X polymorphic region of Protein A (spa), multilocus sequence typing test (MLST), staphylococcus chromosomal cassette mec (SCCmec) typing. After comparing the results of Weka six classifiers, the highest correctly classified rates were 91.94, 70.16, and 62.90% from 188D, n-gram and 400D, respectively. Antimicrobial susceptibility test of the 81 Staphylococcus aureus: Penicillin-resistant rate was 100%. No resistance to teicoplanin, linezolid, and vancomycin. The resistance rate of the MRSA isolates to clindamycin, erythromycin and tetracycline was higher than that of the MSSAs. Among the 65 MRSA isolates, the positive rate of PVL gene was 47.7% (31/65). Seventeen sequence types (STs) were identified among the 65 isolates, and ST59 was the most prevalent. SCCmec type III and IV were observed at 24.6 and 72.3%, respectively. Two isolates did not be typed. Twenty-one spa types were identified, spa t437 (34/65, 52.3%) was the most predominant type. MRSA major clone type of molecular typing was CC59-ST59-spa t437-IV (28/65, 43.1%). Overall, 188D feature vectors can be applied to successfully distinguish MRSA from MSSA. In Quanzhou, the detection rate of PVL virulence factor was high, suggesting a high pathogenic risk of MRSA infection. The cross-infection of CA-MRSA and HA-MRSA was presented, the molecular characteristics were increasingly blurred, HA-MRSA with typical CA-MRSA molecular characteristics has become an important cause of healthcare-related infections. CC59-ST59-spa t437-IV was the main clone type in Quanzhou, which was rare in other parts of mainland China.

Genetic analysis of methicillin‐susceptible Staphylococcus aureus clinical isolates: High prevalence of multidrug‐resistant ST239 with strong biofilm‐production ability

Background

The distributions of methicillin‐susceptible Staphylococcus aureus (MSSA) are divers geographically with different genetic backgrounds. Data related to molecular characteristics of MSSA compare to methicillin‐resistant Staphylococcus aureus (MRSA) is sparse.

Methods

In this cross‐sectional study, antimicrobial susceptibility testing, virulence genes analysis, biofilm formation, accessory gene regulator (agr) typing, and multilocus sequence typing (MLST) characterized on 75 MSSA isolates.

Results

Multidrug‐resistance MSSA was found to be 84%. Forty‐eight (64%) isolates were toxinogenic with 34 and 14 isolates carrying pvl and tst representing 45.3% and 18.7%. The most common SE genes were sed (20%), sec (16%), and sea (16%). Fifty‐five (73.3%) isolates were confirmed as biofilm producer with a markedly high prevalence of fnbA (93.3%), fnbB (86.7%), icaA (65.3%), icaD (53.3%), can (24%), ebp (10.7%), and bap (1.3%). A total of 3 agr types (I, 73.3%; III, 16%; II, 10.7%) and 4 clonal complexes (CCs) and sequence types (STs), namely CC8/ST293 (45.3%), CC/ST22 (28%), CC/ST30 (16%), and CC/ST5 (10.7%) were detected in this study. All the high and low‐level mupirocin resistance strains belonged to ST239 and ST22 strains, respectively. All the fusidic acid‐resistant isolates carried fusC and belonged to ST30.

Conclusions

These findings indicated that ST239 with strong biofilm production ability is the most common type in MSSA strains isolated from patients. It seems that the antimicrobial resistance profiles, toxin, and biofilm formation were closely associated with specific STs. Further studies are required to identify and control of these clonal lineages in our area.

Molecular characteristics and antimicrobial susceptibility of Staphylococcus aureus among children with respiratory tract infections in southwest China

BACKGROUND

The molecular characteristics and antimicrobial susceptibility of Staphylococcus aureus (S. aureus) in general pediatric wards and county-level hospitals were rarely reported in China.

METHODS

Staphylococcus aureus was isolated from children hospitalized with respiratory tract infection (RTI) in Zhongjiang and Youyang counties in 2015. All isolates were typed by multilocus sequence, staphylococcal protein A, accessory gene regulator (agr), and staphylococcal cassette chromosome mec [SCCmec, for methicillin-resistant S. aureus (MRSA) only]. Polymerase chain reaction was used to screen 21 super-antigen (SAg) genes and panton-valentine leukocidin (pvl). Antimicrobial susceptibility testing was performed by E test.

RESULTS

A total of 2136 children were enrolled. Overall, 125 (5.9%) children carried S. aureus, among which MRSA accounted for 42.4%. ST59-SCCmec type IV-t437-agr group I (58.5%) was the most prevalent genotype in MRSA, and ST188-t189-agr group I (22.2%) was the top genotype in methicillin-sensitive S. aureus (MSSA). The pvl carriage rate in MRSA and MSSA was 15.1% and 9.7%, respectively (P = 0.4112). About 96.8% of S. aureus isolates were positive for at least one SAg gene. The most common SAg gene profile in the dominant ST59 clone was seb-sek-seq (42.8%). All S. aureus isolates were resistant to penicillin and erythromycin (minimum inhibitory concentration 90 was > 32 and 256 mg/L to penicillin and erythromycin, respectively), but usually susceptible to other tested non-β-lactam antimicrobials.

CONCLUSIONS

Staphylococcus aureus and MRSA were detected with a high frequency in children with RTI in county-level hospitals of China. ST59-SCCmec type IV-t437-agr group I was the dominant MRSA clone. The S. aureus isolates exhibited high resistance to penicillin and erythromycin.

Biofilm Production Ability, Virulence and Antimicrobial Resistance Genes in Staphylococcus aureus from Various Veterinary Hospitals

: Staphylococcus aureus (S. aureus) is one of the most clinically important zoonotic pathogens, but an understanding of the prevalence, biofilm formulation ability, virulence, and antimicrobial resistance genes of S. aureus from veterinary hospitals is lacking. By characterizing S. aureus in different origins of veterinary hospitals in Guangzhou, China, in 2019, we identified with the presence of S. aureus in pets (17.1%), veterinarians (31.7%), airborne dust (19.1%), environmental surfaces (4.3%), and medical device surfaces (10.8%). Multilocus sequence typing (MLST) and Staphylococcus protein A (spa) typing analyses demonstrated methicillin-sensitive S. aureus (MSSA) ST398-t571, MSSA ST188-t189, and methicillin-resistant S. aureus (MRSA) ST59-t437 were the most prevalent lineage. S. aureus with similar pulsed-field gel electrophoresis (PFGE) types distributed widely in different kinds of samples. The crystal violet straining assays revealed 100% (3/3) of MRSA ST59 and 81.8% (9/11) of MSSA ST188 showed strong biofilm formulation ability, whereas other STs (ST1, ST5, ST7, ST15, ST88, ST398, ST3154 and ST5353) showed weak biofilm production ability. Polymerase chain reaction (PCR) confirmed the most prevalent leucocidin, staphylococcal enterotoxins, ica operon, and adhesion genes were lukD-lukE (49.0%), sec-sel (15.7%), icaA-icaB-icaC-icaR (100.0%), and fnbB-cidA-fib-ebps-eno (100.0%), respectively. Our study showed that the isolates with strong biofilm production ability had a higher prevalence in clfA, clfB, fnbA and sdrC genes compared to the isolates with weak biofilm production ability. Furthermore, 2 ST1-MRSA isolates with tst gene and 1 ST88-MSSA isolate with lukS/F-PV gene were detected. In conclusion, the clonal dissemination of S. aureus of different origins in veterinary hospitals may have occurred; the biofilm production capacity of S. aureus is strongly correlated with ST types; some adhesion genes such as clfA, clfB, fnbA, and sdrC may pose an influence on biofilm production ability and the emergence of lukS/F-PV and tst genes in S. aureus from veterinary hospitals should raise our vigilance.

Investigation of biofilm production and its association with genetic and phenotypic characteristics of OM (osteomyelitis) and non-OM orthopedic Staphylococcus aureus

Background

Staphylococcus aureus is a primary pathogen of orthopedic infections. By mediating antimicrobial resistance, S. aureus biofilm plays an important role in the recalcitrance of orthopedic infections, especially for the intractable osteomyelitis (OM). This study investigated the relationship between biofilm production and various genetic or phenotypic characteristics among orthopedic S. aureus strains.

Methods

A total of 137 orthopedic S. aureus isolates were enrolled and divided into OM and non-OM groups. Biofilm production was evaluated using the crystal violet assay. Genetic and phenotypic characteristics including MRSA identification, MLST and spa typing, carriage of virulence genes, drug resistance, and patients’ inflammatory responses indicators were characterized. The relationship between biofilm production and above-mentioned features was respectively analyzed among all isolates and compared between OM and non-OM isolates.

Results

Biofilm production presented no significant difference between OM (including 9 MRSA isolates) and non-OM (including 21 MRSA isolates) strains. We found that ST88, t377 and ST630-MSSA-t377 strains produced very strong biofilms, while MLST types of ST15, ST25, ST398, ST5, ST59 and spa types of t002, t2325, t437 tended to produce weaker biofilms. Strains with the following profiles produced stronger biofilms: fib(+)-hlgv(+)-lukED(+)-sei(-)-sem(-)-seo(-) for all isolates, sei(-)-sem(-)-seo(-) for OM isolates, and cna (+)-fib (+)-hlgv (+)-lukED (+)-seb(-)-sed(-) for non-OM isolates. In addition, not any single drug resistance was found to be related to biofilm production. We also observed that, among OM patients, strains with stronger biofilms caused weaker inflammatory responses.

Conclusion

Some genetic or phenotypic characteristics of orthopedic strains were associated with biofilm production, and this association could be different among OM and non-OM strains. The results are of great significance for better understanding, evaluating and managing different kinds of biofilm-associated orthopedic infections, and provide potential targets for biofilm clearance.

The Genomic Context for the Evolution and Transmission of Community-Associated Staphylococcus aureus ST59 Through the Food Chain

Sequence type 59 (ST59) is a predominant clonal lineage of community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) in Asia. Despite its increasing clinical relevance in China, the evolution and geographic expansion of ST59 has been relatively uncared for. Previous study has shown that ST59 was the predominant clone in food-related MRSA in China. This study compared the genomes of 87 clonal complex (CC) 59 S. aureus isolates sourced from food chain and infection cases to reconstruct the molecular evolution and geographical spread of ST59. Accordingly, three major sub-clades of ST59 were identified and these did not correlate with isolation source or location. Phylogenetic analysis estimated that ST59 in mainland China diverged from a most common recent ancestor around 1974, and most of the cases of cross-country transmission occurred between 1987 and 2000. Notably, two recent events of cross-country transmission through the food chain were observed, the isolates from these events diverged within relatively short time intervals. These isolates also showed high similarity in terms of their core genome, accessory genes, and antibiotic resistance patterns. These findings provide a valuable insight into the potential route of ST59 expansion in China and indicate a need for robust food chain surveillance to prevent the spread of this pathogen.

Global Evolution of Pathogenic Bacteria With Extensive Use of Fluoroquinolone Agents

It is well-established that the spread of many multidrug-resistant (MDR) bacteria is predominantly clonal. Interestingly the international clones/sequence types (STs) of most pathogens emerged and disseminated during the last three decades. Strong experimental evidence from multiple laboratories indicate that diverse fitness cost associated with high-level resistance to fluoroquinolones contributed to the selection and promotion of the international clones/STs of hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA), extended-spectrum β-lactamase-(ESBL)-producing Klebsiella pneumoniae, ESBL-producing Escherichia coli and Clostridioides difficile. The overwhelming part of the literature investigating the epidemiology of the pathogens as a function of fluoroquinolone use remain in concordence with these findings. Moreover, recent in vitro data clearly show the potential of fluoroquinolone exposure to shape the clonal evolution of Salmonella Enteritidis. The success of the international clones/STs in all these species was linked to the strains' unique ability to evolve multiple energetically beneficial gyrase and topoisomerase IV mutations conferring high-level resistance to fluorquinolones and concomittantly permitting the acquisition of an extra resistance gene load without evoking appreciable fitness cost. Furthermore, by analyzing the clonality of multiple species, the review highlights, that in environments under high antibiotic exposure virulence factors play only a subsidiary role in the clonal dynamics of bacteria relative to multidrug-resistance coupled with favorable fitness (greater speed of replication). Though other groups of antibiotics should also be involved in selecting clones of bacterial pathogens the role of fluoroquinolones due to their peculiar fitness effect remains unique. It is suggested that probably no bacteria remain immune to the influence of fluoroquinolones in shaping their evolutionary dynamics. Consequently a more judicious use of fluoroquinolones, attuned to the proportion of international clone/ST isolates among local pathogens, would not only decrease resistance rates against this group of antibiotics but should also ameliorate the overall antibiotic resistance landscape.

Screening of genes encoding adhesion factors and biofilm production in methicillin resistant strains of Staphylococcus aureus isolated from Palestinian patients

BACKGROUND

Intercellular adhesion and biofilm production by Staphylococcus aureus makes these bacteria resistant to antimicrobial therapy. Here, Methicillin-resistant Staphylococcus aureus (MRSA) strains were characterized and the prevalence of genes encoding adhesion factors and biofilm formation was determined.

RESULTS

All 248 MRSA isolates identified by cefoxitin disc diffusion were positive for the mecA gene. SCCmec-IV was the most frequently detected genotype (92.7%) and SCCmec-IVa was also very prevalent (84.3%). The quantitative microtiter plate assay showed that all the isolates were able to produce biofilm with levels ranging from high (21%) to moderate (46.4%) to low (32.7%). All the strains possessed the icaD/icaA genes and produced biofilm (P < 0.05). None of the isolates possessed the bap gene. Furthermore, 94.8% of the isolates were positive for eno, 80.2% for clfA and for clfB, 78.2% for fnbA, 76.2% for ebps, 62.2% for fib, 39.9% for cna and 29.0% for fnbB. Also, nearly 69.8% of the isolates were positive for the gene sarA. All four agr groups were present: agr group 1 was predominant with 39.5%; agr group 3. agr group 2 and 3 strains carried more toxin-producing genes, and frequently produced more toxin. Sixty-six (26.6%) of the strains were multidrug resistant. All were vancomycin sensitive. Agr group I is more resistant to ciprofloxacin and gentamicin while agr group III is more resistant to erythromycin. Maximum sensitivity was to gentamicin and SXT, and they could be considered drugs of choice for controlling MRSA mediated infections in this region.

CONCLUSIONS

Biofilm development in MRSA might be an ica dependent and one needs to investigate the involvement of other global regulators, agr and sarA, and their contribution to the biofilm phenotype, as the high rate of biofilm production among the studied strains of S. aureus.

Exoproteome Heterogeneity among Closely Related Staphylococcus aureus t437 Isolates and Possible Implications for Virulence

Staphylococcus aureus with spa-type t437 has been identified as a predominant community-associated methicillin-resistant S. aureus clone from Asia, which is also encountered in Europe. Molecular typing has previously shown that t437 isolates are highly similar regardless of geographical regions or host environments. The present study was aimed at assessing to what extent this high similarity is actually reflected in the production of secreted virulence factors. We therefore profiled the extracellular proteome, representing the main reservoir of virulence factors, of 20 representative clinical isolates by mass spectrometry. The results show that these isolates can be divided into three groups and nine subgroups based on exoproteome abundance signatures. This implies that S. aureus t437 isolates show substantial exoproteome heterogeneity. Nonetheless, 30 highly conserved extracellular proteins, of which about 50% have a predicted role in pathogenesis, were dominantly identified. To approximate the virulence of the 20 investigated isolates, we employed infection models based on Galleria mellonella and HeLa cells. The results show that the grouping of clinical isolates based on their exoproteome profile can be related to virulence. We consider this outcome important as our approach provides a tool to pinpoint differences in virulence among seemingly highly similar clinical isolates of S. aureus.

Accessory gene regulator (agr) dysfunction was unusual in Staphylococcus aureus isolated from Chinese children

Background

Staphylococcus aureus (S. aureus) with accessory gene regulator (agr) dysfunction occurs in health care settings. This study evaluated the prevalence and the molecular and drug resistance characteristics of S. aureus with dysfunctional agr in a pediatric population in Beijing, China.

Results

A total of 269 nonduplicate S. aureus clinical isolates were isolated from Beijing Children’s Hospital, including 211 methicillin-resistant S. aureus (MRSA) from September 2010–2017 and 58 methicillin-sensitive S. aureus (MSSA) from February 2016–2017. Only 8 MRSA and 2 MSSA isolates were identified as agr dysfunction, and the overall prevalence rate was 3.7%. For MRSA isolates, ST59-SCCmec IV and ST239-SCCmec III were the most common clones, and the prevalence rate of agr dysfunction in ST239-SCCmec III isolates (17.39%) was significantly higher than in ST59-SCCmec IV (1.69%) and other genotype strains (P = 0.006). Among the agr dysfunctional isolates, only one MRSA ST59 isolate and one MSSA ST22 isolate harbored pvl. No significant difference was detected between agr dysfunction and agr functional isolates regarding the biofilm formation ability (P = 0.4972); however, 9/10 agr dysfunctional isolates could effectuate strong biofilm formation and multidrug resistance. Among MRSA, the non-susceptibility rates to ciprofloxacin, gentamicin, and trimethoprim-sulfamethoxazole were significantly higher in agr dysfunctional isolates than in isolates with functional agr (P < 0.05). Two isolates belonging to ST239 had no mutations in agr locus, but a synonymous mutation was found in agrA in another ST239 isolate. The inactivating mutations were detected in other seven agr dysfunctional isolates. The variants were characterized by non-synonymous changes (n = 5) and frameshift mutations (insertions, n = 2), which mainly occurred in agrC and agrA.

Conclusions

The results showed that agr dysfunctional S. aureus was not common in Chinese children, and ST59-SCCmec IV was associated with lower prevalence of agr dysfunction as compared to ST239-SCCmec III isolates. The agr dysfunctional isolates were healthcare-associated, multidrug resistant and form strong biofilm, which suggested that agr dysfunction might offer potential advantages for S. aureus to survive in a medical environment.

Genomic analysis of Staphylococcus aureus along a pork production chain and in the community, Shandong Province, China

Livestock-associated meticillin-resistant Staphylococcus aureus (LA-MRSA) is an increasingly important public health concern worldwide; however, data on LA-MRSA from Asian countries is scarce. As such, a comprehensive molecular epidemiological survey of S. aureus along a pork production chain and in the community was undertaken in Shandong Province, China. spa typing and whole-genome sequencing were used to survey the occurrence and potential transmission of S. aureus in various sectors, including 899 porcine samples (snout or skin swabs, carcass swabs and pork portions), 845 human nasal samples and 239 environmental samples from commercial farms, a slaughterhouse, a pork wholesale market and the surrounding community. MRSA was detected in higher frequencies in samples from two commercial pig farms (pigs, 49%; farm workers, 64%; environmental samples, 16%) than in samples from the slaughterhouse (fatteners, 8.2%; carcasses, 1.1%; operation workers, 0%; environmental samples, 3.8%), the pork wholesale market (pork, 14%; sellers, 0%) and individuals in the community (6.8%). There were significant differences in population structures, antimicrobial susceptibility profiles, and the presence of resistance and virulence genes between human- and pig-associated isolates. The phylogenetic analysis confirmed the dissemination of LA-MRSA between various segments along the pork production chain. However, MRSA of the same sequence type was not found to be disseminated between the commercial farms and the surrounding communities. Furthermore, one MRSA ST398 was observed, and a novel CC9 variant ST3597 was detected within the chain. The high MRSA carriage rates and the emergence of a new MRSA CC9 variant identified in this study highlight the need for MRSA surveillance.

Antimicrobial resistance, virulence genes profiling and molecular relatedness of methicillin-resistant Staphylococcus aureus strains isolated from hospitalized patients in Guangdong Province, China

Purpose

The main objective of this study was to decipher the prevalence, antimicrobial resistance, major virulence genes and the molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) isolated from different clinical sources in southern China.

Materials and methods

The present study was performed on 187 non-duplicate S. aureus clinical isolates collected from three tertiary hospitals in Guangdong Province, China, 2010–2016. Antimicrobial susceptibility testing was performed by the disk diffusion method and by measuring the minimum inhibitory concentration. Screening for resistance and virulence genes was performed. Clonal relatedness was determined using various molecular typing methods such as multilocus sequence typing, spa and staphylococcal chromosomal cassette mec (SCCmec) typing. Whole genome sequencing was performed for three selected isolates.

Results

Out of 187 isolates, 103 (55%) were identified as MRSA. The highest prevalence rate was found among the skin and soft tissue infection (SSTI) samples (58/103), followed by sputum samples (25/103), blood stream infection samples (15/103) and others (5/103). Antimicrobial susceptibility results revealed high resistance rates for erythromycin (64.1%), clindamycin (48.5%), gentamicin (36.9%) and ciprofloxacin (33.98%). All isolates were susceptible to vancomycin. Resistance genes and mutation detected were as follows: aac(6’)-aph(2”) (24.3%), dfrG (10.7%), rpoB (21.4%), cfr (0%), fexA (1.94%), gyrA (35.92%), gyrB (0.97%), grlA (20.4%), grlB (10.68%), ermA (21.4%), ermB (18.44%), ermC (21.4%) and lnuA (18.44%). Profiling of virulence genes revealed the following: sea (11.7%), seb (21.4%), sec (0.97%), sed (0.97%), hla (86.41%), hlb (17.48%), hlg (10.68%), hld (53.4%), Tsst-1 (3.9%) and pvl (27.2%). Clonal relatedness showed that ST239-SCCmecA III-t37 clone was the most prevalent clone.

Conclusion

Our study elucidated the prevalence, antibiotic resistance, pathogenicity and molecular characteristics of MRSA isolated from various clinical sources in Guangdong, China. We found that the infectious rate of MRSA was higher among SSTI than other sources. The most predominant genotype was ST239-SCCmecA III-t37 clone, indicating that ST239-t30 clone which was previously predominant had been replaced by a new clone.

Prevalence and Characterization of Food-Related Methicillin-Resistant Staphylococcus aureus (MRSA) in China

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging pathogen that is difficult to treat due to the multiresistance of the bacteria upon infection. From 2011 to 2016, 1581 S. aureus strains were isolated from 4300 samples from retail foods covering most provincial capitals in China. To determine the prevalence of food-related MRSA and its genetic background in China, antibiotic resistance, staphylococcal toxin genes, staphylococcal cassette chromosome mec (SCCmec) typing, spa-typing and MLST were carried out in this study. In total, 108 (7.4%) isolates were confirmed for MRSA by phenotyping (cefoxitin) and genotyping (mecA/mecC gene). A total of 52.8% (57/108) of the MRSA isolates belonged to clonal complex 59 (CC59) (ST59, ST338, and ST3355), which was the predominant clone in this study. These CC59 isolates carried SCCmec elements of type IV, V, or III and exhibited spa type t437, t441, t543, t163, t1785, or t3485, and half of them carried major virulence genes, such as the Panton-Valentine leucocidin (PVL) gene. The secondary clones belonged to ST9 (15.7%, 17/108) with a type of t899-SCCmec III and showed a broader range of antimicrobial resistance. The remaining MRSA isolates (31.5%, 34/108) were distributed in 12 different STs and 18 different spa types. All isolates harbored at least one of the enterotoxin genes, whereas only 4 isolates (3.70%) were positive for the toxic shock syndrome toxin tsst alleles. For antibiotic susceptibility testing, all isolates were resistant to more than three antibiotics, and 79.6% of the isolates were resistant to more than 10 antibiotics. Amoxycillin/clavulanic acid, ampicillin, cefoxitin, penicillin, ceftazidime, kanamycin, streptomycin, clindamycin, and telithromycin was the most common antibiotic resistance profile (55.6%, 60/108) in the study. In summary, the results of this study implied that the major food-related MRSA isolate in China was closer to community-associated MRSA, and some of the remaining isolates (ST9-t899-SCCmec III) were supposed to livestock-associated MRSA. In addition, most MRSA isolates showed resistance to multiple drugs and harbored staphylococcal toxin genes. Thus, the pathogenic potential of these isolates cannot be ignored. In addition, further studies are needed to elucidate the transmission routes of MRSA in relation to retail foods and to determine how to prevent the spread of MRSA.

Staphylococcus aureus Isolated From Retail Meat and Meat Products in China: Incidence, Antibiotic Resistance and Genetic Diversity

This study was to estimate the prevalence and characteristics of Staphylococcus aureus from 1,850 retail meat and meat products in China during July 2011 to June 2016. The samples were collected covering most provincial capitals in China, including 604 raw meat, 601 quick-frozen meat, and 645 ready-to-eat meat. Using the qualitative and quantitative methods, all 39 cities had S. aureus-positive samples, and S. aureus was detected in 35.0% (647/1,850) of the samples. The levels of S. aureus in retail meat showed that the MPN value of the majority of the positive samples ranged from 0.3 to 100 MPN/g. Twenty-four antibiotics were used to test all 868 S. aureus isolates for antibiotic susceptibility. Only 11 isolates (1.26%) were susceptible to all antibiotics, whereas most isolates (821/868, 94.6%) showed resistance or intermediary resistance to more than three or more antibiotics. Of these strains, 104 (12.0%) were resistant to more than 10 antibiotics. However, the most frequent resistance was observed to ampicillin (85.4%), followed by penicillin (84.6%), erythromycin (52.7%), tetracycline (49.3%), kanamycin (45.3%), telithromycin (30.1%), clindamycin (29.6%), streptomycin (21.1%), norfloxacin (20.4%), gentamicin (19.4%), fusidic acid (18.4%), ciprofloxacin (16.9%), chloramphenicol (13.1%), amoxycillin/clavulanic acid (11.0%), and others (<10%). 7.4% of isolates (62/868) were confirmed as methicillin-resistance S. aureus (MRSA). By molecular typing analysis, there were 164 spa types and 111 STs were identified, including 15 novel spa types and 65 newly STs by multilocus sequence typing (MLST) and spa typing. Despite the wide genetic diversity observed among the 868 isolates, a great proportion of the population belonged to finite number of major clones: ST1-t127 (93/868, 10.7%) and ST7-t091 (92/868, 10.6%), ST5-t002 (42/868, 4.8%), ST398-t034 (40/868, 4.6%), ST188-t034 (38/868, 4.4%), ST59-t437 (30/868, 3.5%), ST6-t701 (29/868, 3.3%), and ST9-t899 (27/868, 3.1%) in China. This study reflects S. aureus was readily detected in Chinese retail meat and meat products but the level were not very excessive. In this study, the high antibiotic resistance is alarming and raising public health concern. In additions, most of molecular types of isolates have been linked to human infections around the world, indicating that these types of S. aureus in China have a theoretical pathogenic potential.