Methicillin-resistant Staphylococcus aureus in China: a multicentre longitudinal study and whole-genome sequencing

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.

Phenotypic and genomic analysis of the hypervirulent methicillin-resistant Staphylococcus aureus ST630 clone in China

Methicillin-resistant Staphylococcus aureus (MRSA) sequence type 630 (ST630) is a rarely reported lineage worldwide. This study aimed to trace the dissemination of the emerging MRSA ST630 clones in China and investigate their virulence potential. We collected 22 ST630-MRSA isolates from across China and performed whole-genome sequencing analysis and virulence characterization on these isolates. Epidemiological results showed that MRSA ST630 isolates were primarily isolated from pus/wound secretions, mainly originating from Jiangxi province, and carried diverse virulence and drug resistance genes. Staphylococcal cassette chromosome mec type V (SCCmec V) predominated (11/22, 50.0%) among the MRSA ST630 isolates. Interestingly, nearly half (45.5%) of the 22 ST630-MRSA isolates tested lacked intact SCCmec elements. Phylogenetic analysis demonstrated that ST630-MRSA could be divided into two distinct clades, with widespread dissemination mainly in Chinese regions. Five representative isolates were selected for phenotypic assays, including hemolysin activity, real-time fluorescence quantitative PCR, western blot analysis, hydrogen peroxide killing assay, blood killing assay, cell adhesion and invasion assay, and mouse skin abscess model. The results showed that, compared to the USA300-LAC strain, ST630 isolates exhibited particularly strong invasiveness and virulence in the aforementioned phenotypic assays. This study described the emergence of a highly virulent ST630-MRSA lineage and improved our insight into the molecular epidemiology of ST630 clones in China.IMPORTANCEMethicillin-resistant Staphylococcus aureus (MRSA) sequence type 630 (ST630) is an emerging clone with an increasing isolation rate in China. This study raises awareness of the hypervirulent MRSA ST630 clones in China and alerts people to their widespread dissemination. ST630-staphylococcal cassette chromosome mec V is a noteworthy clone in China, and we present the first comprehensive genetic and phenotypic analysis of this lineage. Our findings provide valuable insights for the prevention and control of infections caused by this emerging MRSA clone.

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.

Antibiotic Resistance Profiles and MLST Typing of Staphylococcus Aureus Clone Associated with Skin and Soft Tissue Infections in a Hospital of China

Objective

To analyze the antibiotic resistance profile, virulence genes, and molecular typing of Staphylococcus aureus (S. aureus) strains isolated in skin and soft tissue infections at the First Affiliated Hospital, Gannan Medical University, to better understand the molecular epidemiological characteristics of S. aureus.

Methods

In 2023, 65 S. aureus strains were isolated from patients with skin and soft tissue infections. Strain identification and susceptibility tests were performed using VITEK 2 and gram-positive bacteria identification cards. DNA was extracted using a DNA extraction kit, and all genes were amplified using polymerase chain reaction. Multilocus sequence typing (MLST) was used for molecular typing.

Results

In this study, of the 65 S. aureus strains were tested for their susceptibility to 16 antibiotics, the highest resistance rate to penicillin G was 95.4%. None of the staphylococcal isolates showed resistance to ceftaroline, daptomycin, linezolid, tigecycline, teicoplanin, or vancomycin. fnbA was the most prevalent virulence gene (100%) in S. aureus strains isolated in skin and soft tissue infections, followed by arcA (98.5%). Statistical analyses showed that the resistance rates of methicillin-resistant S. aureus isolates to various antibiotics were significantly higher than those of methicillin-susceptible S. aureus isolates. Fifty sequence types (STs), including 44 new ones, were identified by MLST.

Conclusion

In this study, the high resistance rate to penicillin G and the high carrying rate of virulence gene fnbA and arcA of S.aureus were determine, and 44 new STs were identified, which may be associated with the geographical location of southern Jiangxi and local trends in antibiotic use. The study of the clonal lineage and evolutionary relationships of S. aureus in these regions may help in understanding the molecular epidemiology and provide the experimental basis for pathogenic bacteria prevention and treatment.

Antibiotic resistance, biofilm formation, and molecular epidemiology of Staphylococcus aureus in a tertiary hospital in Xiangyang, China

Staphylococcus aureus is a common clinical pathogen that causes various human infections. The aim of this study was to investigate the antibiotic susceptibility pattern, molecular epidemiological characteristics, and biofilm formation ability of S. aureus isolates from clinical specimens in Xiangyang and to analyze the correlation among them. A total of 111 non-duplicate S. aureus isolates were collected from the Affiliated Hospital of Hubei University of Arts and Science. All isolates were tested for antibacterial susceptibility. Methicillin-resistant S. aureus (MRSA) was identified by the mecA gene PCR amplification. All isolates were analyzed to determine their biofilm-forming ability using the microplate method. The biofilm-related gene was determined using PCR. SCCmec, MLST, and spa types of MRSA strains were performed to ascertain the molecular characteristics. Among the 111 S. aureus isolates, 45 (40.5%) and 66 (59.5%) were MRSA and MSSA, respectively. The resistance of MRSA strains to the tested antibiotics was significantly stronger than that of MSSA strains. All isolates were able to produce biofilm with levels ranging from strong (28.9%, 18.2%), moderate (62.2%, 62.1%), to weak (8.9%, 19.7%). Strong biofilm formation was observed in MRSA strains than in MSSA strains, based on percentages. There were dynamic changes in molecular epidemic characteristics of MRSA isolates in Xiangyang. SCCmecIVa-ST22-t309, SCCmecIVa-ST59-t437, and SCCmecIVa-ST5-t2460 were currently the main epidemic clones in this region. SCCmecIVa-ST5-t2460 and SCCmecIVa/III-ST22-t309 have stronger antibiotic resistance than SCCmecIVa-ST59-t437 strains, with resistance to 6 ~ 8 detected non-β-lactam antibiotics. The molecular epidemic and resistance attributes of S. aureus should be timely monitored, and effective measures should be adopted to control the clinical infection and spread of the bacteria.

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.

Demographic fluctuations in bloodstream Staphylococcus aureus lineages configure the mobile gene pool and antimicrobial resistance

Staphylococcus aureus in the bloodstream causes high morbidity and mortality, exacerbated by the spread of multidrug-resistant and methicillin-resistant S. aureus (MRSA). We aimed to characterize the circulating lineages of S. aureus from bloodstream infections and the contribution of individual lineages to resistance over time. Here, we generated 852 high-quality short-read draft genome sequences of S. aureus isolates from patient blood cultures in a single hospital from 2010 to 2022. A total of 80 previously recognized sequence types (ST) and five major clonal complexes are present in the population. Two frequently detected lineages, ST5 and ST8 exhibited fluctuating demographic structures throughout their histories. The rise and fall in their population growth coincided with the acquisition of antimicrobial resistance, mobile genetic elements, and superantigen genes, thus shaping the accessory genome structure across the entire population. These results reflect undetected selective events and changing ecology of multidrug-resistant S. aureus in the bloodstream.

Genome-based surveillance reveals cross-transmission of MRSA ST59 between humans and retail livestock products in Hanzhong, China

Methicillin-resistant Staphylococcus aureus (MRSA) has been recognized in hospitals, community and livestock animals and the epidemiology of MRSA is undergoing a major evolution among humans and animals in the last decade. This study investigated the prevalence of MRSA isolates from ground pork, retail whole chicken, and patient samples in Hanzhong, China. The further characterization was performed by antimicrobial susceptibility testing and in-depth genome-based analysis to identify the resistant determinants and their phylogenetic relationship. A total of 93 MRSA isolates were recovered from patients (n = 67) and retail livestock products (n = 26) in Hanzhong, China. 83.9% (78/93) MRSA isolates showed multiple drug resistant phenotype. Three dominant livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) sequence types were identified: ST59-t437 (n = 47), ST9-t899 (n = 10) and ST398 (n = 7). There was a wide variation among sequence types in the distribution of tetracycline-resistance, scn-negative livestock markers and virulence genes. A previous major human MRSA ST59 became the predominant interspecies MRSA sequence type among humans and retail livestock products. A few LA-MRSA isolates from patients and livestock products showed close genetic similarity. The spreading of MRSA ST59 among livestock products deserving special attention and active surveillance should be enacted for the further epidemic spread of MRSA ST59 in China. Data generated from this study will contribute to formulation of new strategies for combating spread of MRSA.

Genomic characterization and outbreak investigations of methicillin-resistant Staphylococcus aureus in a county-level hospital in China

Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen contributing to healthcare-associated infections, which can result in multiple sites infections. The epidemiological characteristics of MRSA exhibit variability among distinct regions and healthcare facilities. The aim of this study was to investigate the molecular epidemiology and nosocomial outbreak characteristics of MRSA in a county-level hospital in China. A total of 130 non-repetitive MRSA strains were collected from December 2020 to November 2021. Whole-genome sequencing (WGS) was performed to identify antimicrobial resistance and virulence factors. Phylogenetic analysis was conducted to ascertain genetic diversity and phylogenetic relationships. Independent transmission scenarios were determined by the phylogeny derived from single nucleotide polymorphisms (SNPs) within the core genome. All the MRSA isolates were collected from the intensive care unit (30.00%, 39/130), the department of otorhinolaryngology (10.00%, 13/130) and the department of burn unit (9.23%, 12/130). The clinical samples mainly included phlegm (53.85%, 70/130), purulent fluid (24.62%, 32/130), and secretions (8.46%, 11/130). The resistance rates to erythromycin, clindamycin and ciprofloxacin were 75.38, 40.00, and 39.23%, respectively. All the isolates belonged to 11 clonal complexes (CCs), with the major prevalent types were CC5, CC59, and CC398, accounting for 30.00% (39/130), 29.23% (38/130), and 16.92% (22/130), respectively. Twenty sequence types (STs) were identified, and ST59 (25.38%, 33/130) was the dominant lineage, followed by ST5 (23.84%, 31/130) and ST398 (16.92%, 22/130). Three different SCCmec types were investigated, most of isolates were type IV (33.85%, 44/130), followed by type II (27.69%, 36/130) and type III (0.77%, 1/130). The common clonal structures included CC5-ST5-t2460-SCCmec IIa, CC59-ST59-t437-SCCmec IV and CC398-ST398-t034-SCCmec (-), with rates of 16.92% (22/130), 14.62% (19/130), and 13.84% (18/130), respectively. Only 12 panton-valentine leucocidin (PVL) positive strains were identified. Two independent clonal outbreaks were detected, one consisting of 22 PVL-negative strains belongs to CC5-ST5-t2460-SCCmec IIa and the other consisting of 8 PVL-negative strains belongs to CC5-ST5-t311-SCCmec IIa. Overall, our study indicated that the CC5 lineage emerged as the predominant epidemic clone of MRSA, responsible for nosocomial outbreaks and transmission within a county-level hospital in China, highlighting the necessity to strengthen infection control measures for MRSA in such healthcare facilities.

High prevalence of ST5-SCCmec II-t311 clone of methicillin-resistant Staphylococcus aureus isolated from bloodstream infections in East China

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a challenging global health threat, resulting in significant morbidity and mortality worldwide. This study aims to determine the molecular characteristics and antimicrobial susceptibility of 263 MRSA isolates in Zhejiang Province, east China.

METHODS

From 2014 to 2019, a total of 263 MRSA isolates from bloodstream infections (BSIs) were collected from 6 hospitals in 4 cities in Zhejiang province, east China. Antimicrobial susceptibility tests were conducted according to the guidelines set forth by the Clinical and Laboratory Standards Institute (CLSI). To characterize and analyze these isolates, multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing and virulence genes gene profiles were performed.

RESULTS

The most predominant clone was ST5-SCCmec II-t311, which accounted for 41.8% (110/263), followed by ST59 (44/263, 16.7%). Compared with non-ST5-II-t311 isolates, ST5-II-t311 isolates were more resistant to erythromycin, tetracycline, levofloxacin, moxifloxacin, and ciprofloxacin, but more susceptible to clindamycin. Moreover, the rates of multidrug resistance were higher in ST5-II-t311 isolates compared to the non-ST5-II-t311 isolates. In comparison to the non-ST5-II-t311 isolates, ST5-II-t311 isolates showed no significant difference in virulence genes detected.

CONCLUSIONS

MRSA ST5-II-t311 clone has become the most predominant clone in Zhejiang Province, east China and has higher rates of multidrug resistance than other isolates, that should be kept in mind when treating BSI. Moreover, MRSA ST59 clone shows an upward trend and has begun to spread into hospitals. Our findings highlight the importance of epidemiological studies of S. aureus carriage in the eastern region.

Global genetic diversity and Asian clades evolution: a phylogeographic study of Staphylococcus aureus sequence type 5

Staphylococcus aureus sequence type (ST) 5 has spread worldwide; however, phylogeographic studies on the evolution of global phylogenetic and Asian clades of ST5 are lacking. This study included 368 ST5 genome sequences, including 111 newly generated sequences. Primary phylogenetic analysis suggested that there are five clades, and geographical clustering of ST5 methicillin-resistant S. aureus (MRSA) was linked to the acquisition of S. aureus pathogenicity islands (SaPIs; enterotoxin gene island) and integration of the prophage φSa3. The most recent common ancestor of global S. aureus ST5 dates back to the mid-1940s, coinciding with the clinical introduction of penicillin. Bayesian phylogeographic inference allowed to ancestrally trace the Asian ST5 MRSA clade to Japan, which may have spread to major cities in China and Korea in the 1990s. Based on a pan-genome-wide association study, the emergence of Asian ST5 clades was attributed to the gain of prophages, SaPIs, and plasmids, as well as the coevolution of resistance genes. Clade IV displayed greater genomic diversity than the Asian MRSA clades. Collectively, our study provides in-depth insights into the global evolution of S. aureus ST5 mainly in China and the United States and reveals that different S. aureus ST5 clades have arisen independently in different parts of the world, with limited geographic dispersal across continents.

Novel small-molecule compound YH7 inhibits the biofilm formation of Staphylococcus aureus in a sarX-dependent manner

The emergence of antibiotic-resistant and biofilm-producing Staphylococcus aureus isolates presents major challenges for treating staphylococcal infections. Biofilm inhibition is an important anti-virulence strategy. In this study, a novel maleimide-diselenide hybrid compound (YH7) was synthesized and demonstrated remarkable antimicrobial activity against methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in both planktonic cultures and biofilms. The minimum inhibitory concentration (MIC) of YH7 for S. aureus isolates was 16 µg/mL. Quantification of biofilms demonstrated that the sub-MIC (4 µg/mL) of YH7 significantly inhibits biofilm formation in both MSSA and MRSA. Confocal laser scanning microscopy analysis further confirmed the biofilm inhibitory potential of YH7. YH7 also significantly suppressed bacterial adherence to A549 cells. Moreover, YH7 treatment significantly inhibited S. aureus colonization in nasal tissue of mice. Preliminary mechanistic studies revealed that YH7 exerted potent biofilm-suppressing effects by inhibiting polysaccharide intercellular adhesin (PIA) synthesis, rather than suppressing bacterial autolysis. Real-time quantitative PCR data indicated that YH7 downregulated biofilm formation-related genes (clfA, fnbA, icaA, and icaD) and the global regulatory gene sarX, which promotes PIA synthesis. The sarX-dependent antibiofilm potential of YH7 was validated by constructing S. aureus NCTC8325 sarX knockout and complementation strains. Importantly, YH7 demonstrated a low potential to induce drug resistance in S. aureus and exhibited non-toxic to rabbit erythrocytes, A549, and BEAS-2B cells at antibacterial concentrations. In vivo toxicity assays conducted on Galleria mellonella further confirmed that YH7 is biocompatible. Overall, YH7 demonstrated potent antibiofilm activity supports its potential as an antimicrobial agent against S. aureus biofilm-related infections. IMPORTANCE Biofilm-associated infections, characterized by antibiotic resistance and persistence, present a formidable challenge in healthcare. Traditional antibacterial agents prove inadequate against biofilms. In this study, the novel compound YH7 demonstrates potent antibiofilm properties by impeding the adhesion and the polysaccharide intercellular adhesin production of Staphylococcus aureus. Notably, its exceptional efficacy against both methicillin-resistant and methicillin-susceptible strains highlights its broad applicability. This study highlights the potential of YH7 as a novel therapeutic agent to address the pressing issue of biofilm-driven infections.

Different evolution of S. aureus methicillin-resistant and methicillin-susceptible infections, Argentina

Staphylococcus aureus-(SA) is widespread among healthcare-associated-(HA) and the community-associated-(CA) infections. However, the contributions of MRSA and MSSA to the SA overall burden remain unclear. In a nationally-representative-survey conducted in Argentina, 668 SA clinical isolates from 61 hospitals were examined in a prospective, cross-sectional, multicenter study in April 2015. The study aimed to analyze MRSA molecular epidemiology, estimate overall SA infection incidence (MSSA, MRSA, and genotypes) in community-onset (CO: HACO, Healthcare-Associated-CO and CACO, Community-Associated-CO) and healthcare-onset (HO: HAHO, Healthcare-associated-HO) infections, stratified by age groups. Additionally temporal evolution was estimated by comparing this study's (2015) incidence values with a previous study (2009) in the same region. Erythromycin-resistant-MSSA and all MRSA strains were genetically typed. The SA total-infections (TI) overall-incidence was 49.1/100,000 monthly-visits, 25.1 and 24.0 for MRSA and MSSA respectively (P = 0.5889), in April 2015. In adults with invasive-infections (INVI), MSSA was 15.7 and MRSA was 11.8 (P = 0.0288), 1.3-fold higher. HA SA infections, both MSSA and MRSA, surpassed CA infections by over threefold. During 2009-2015, there was a significant 23.4 % increase in the SA infections overall-incidence, mainly driven by MSSA, notably a 54.2 % increase in INVI among adults, while MRSA infection rates remained stable. The MSSA rise was accompanied by increased antimicrobial resistance, particularly to erythromycin, linked to MSSA-CC398-t1451-ermT + -IEC+-pvl- emergence. The SA-infections rise was primarily attributed to community-onset-infections (37.3 % and 62.4 % increase for TI and INVI, respectively), particularly HACO-MSSA and HACO-MRSA in adults, as well as CACO-MSSA. The main CA-MRSA-PFGE-typeN-ST30-SCCmecIVc-PVL+/- clone along with other clones (USA300-ST8-IV-LV-PVL+/-, PFGE-typeDD-ST97-IV- PVL-) added to rather than replaced CA-MRSA-PFGE-typeI-ST5-SCCmecIVa-PVL+/- clone in HA invasive-infections. They also displaced clone HA-MRSA-PFGE-typeA-ST5-SCCmecI, mainly in HAHO infections. The overall-burden of SA infections is rising in Argentina, driven primarily by community-onset MSSA, particularly in adults, linked to increased erythromycin-resistance and MSSA-CC398-t1451-ermT + -IEC+-pvl- emergence. Novel knowledge and transmission-control strategies are required for MSSA.

The Prevalence, Epidemiological, and Molecular Characterization of Methicillin-Resistant Staphylococcus aureus (MRSA) in Macau (2017-2022)

Macau, recognized as a global tourism hub and the world's most densely populated region, provides a unique environment conducive to methicillin-resistant Staphylococcus aureus (MRSA) transmission in healthcare and community settings, posing a significant public health concern both locally and globally. The epidemiology and molecular characteristics of MRSA in the distinct city of Macau remain largely unelucidated. This five-year longitudinal study (2017-2022) examined the local prevalence and molecular typing of MRSA in Macau, with future MRSA type distribution predicted through ARIMA modeling. We subsequently analyzed the epidemiological characteristics of MRSA, including specimen source, clinical department, collection year, season, patient age, sex, and the annual number of tourists. Comprehensive antibiotic resistance profiles of the strains were also assessed. Of 504 clinically isolated S. aureus strains, 183 (36.3%) were identified as MRSA by the cefoxitin disk diffusion method and validated through multi-locus sequence typing (MLST). The MRSA detection rate showed an upward trend, increasing from 30.1% in 2017 to 45.7% in 2022. SCCmec type IV was predominant (28.9%), followed by types II (25.4%), III (22.1%), and V (22.1%). The primary sources of MRSA isolates were sputum (39.2%) and secretions (25.6%). Older age emerged as a risk factor for MRSA infection, whereas no significant associations were found with seasonal variations, gender, or the annual number of tourists. Despite displaying universal resistance to cefoxitin, oxacillin, and benzylpenicillin, MRSA isolates in Macau remained fully sensitive to vancomycin, tigecycline, quinupristin, nitrofurantoin, and linezolid. Continuous surveillance and analysis of MRSA distribution in Macau could provide invaluable insights for the effective management of MRSA prevention and control measures within healthcare settings.

Comparative efficacy of vancomycin in treating ST5 and ST764 methicillin-resistant Staphylococcus aureus infections in adult patients

IMPORTANCE

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that is resistant to multiple drugs and can cause serious infections. In recent years, one of the most widespread strains of MRSA worldwide has been the clonal complex 5 (CC5) type. Sequence type 5 (ST5) and ST764 are two prevalent CC5 strains. Although ST5 and ST764 are genotypically identical, ST764 is classified as a hybrid variant of ST5 with characteristics of community-associated MRSA (CA-MRSA). In contrast to ST5, ST764 lacks the tst and sec genes but carries the staphylococcal enterotoxin B (seb) gene. Vancomycin is commonly used as the first-line treatment for MRSA infections. However, it is currently unclear whether the genetic differences between the ST5 and ST764 strains have any impact on the efficacy of vancomycin in treating MRSA infections. We conducted a prospective observational study comparing the efficacy of vancomycin against ST5-MRSA and ST764-MRSA in five hospitals in China. There were significant differences in bacteriological efficacy between the two groups, with virulence genes, such as the tst gene, being a risk factor for bacterial persistence (adjusted odds ratio, 4.509; 95% confidence interval, 1.216 to 16.724; P = 0.024). In the future, it may be necessary to consider personalized vancomycin treatment strategies based on the genetic characteristics of MRSA isolates.

Phylogenetic analysis and virulence characteristics of methicillin-resistant Staphylococcus aureus ST764-SCCmec II: an emerging hypervirulent clone ST764-t1084 in China

Previous studies have shown that the increased prevalent ST764 clone in China, Japan, and other Asian areas. However, the knowledge of the genetic features and virulence characteristics of methicillin-resistant Staphylococcus aureus (MRSA) ST764 in China is still limited. In this study, we identified 52 ST764-SCCmec type II isolates collected from five cities in China between 2014 and 2021. Whole genome sequencing showed that the most common staphylococcal protein A (spa) types of ST764 in China were t002 (55.78%) and t1084 (40.38%). Virulence assays showed that ST764-t1084 isolates had high haemolytic activity and α-toxin levels. Of the critical regulatory factors affecting α-toxin production, only the SaeRS was highly expressed in ST764-t1084 isolates. Mouse abscess model indicated that the virulence of ST764-t1084 isolates was comparable to that of S. aureus USA300-LAC famous for its hypervirulence. Interestingly, ST764-t002 isolates exhibited stronger biofilm formation and cell adhesion capacities than ST764-t1084 isolates. This seems to explain why ST764-t002 subclone has become more prevalent in China in recent years. Phylogenetic analysis suggested that all ST764 isolates from China in Clade III were closely related to KUN1163 (an isolate from Japan). Notably, genomic analysis revealed that the 52 ST764 isolates did not carry arginine catabolic mobile element (ACME), which differed from ST764 isolates in Japan. Additionally, most ST764 isolates (69.23%) harboured an obvious deletion of approximately 5 kb in the SCCmec II cassette region compared to KUN1163. Our findings shed light on the potential global transmission and genotypic as well as phenotypic characteristics of ST764 lineage.

Prevalence, drug resistance, molecular typing and comparative genomics analysis of MRSA strains from a tertiary A hospital in Shanxi Province, China

Staphylococcus aureus (S. aureus) is an important zoonotic pathogen that causes a high incidence rate and mortality worldwide. This study investigated the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains in a tertiary A hospital in Shanxi Province, China, in order to determine the major epidemic clones as well as their antibiotic resistance and virulence characteristics. A total of 212 S. aureus strains were collected in this hospital, and were subjected to antimicrobial susceptibility testing, detection of virulence genes, resistance genes, and efflux pump genes. Among them, 38 MRSA strains were further subjected to detection of biofilm genes, assessment of biofilm formation ability, MLST, spa typing, SCCmec typing, and phylogenetic analysis. The majority of S. aureus strains came from the neonatology department, with secretions and purulent fluid being the main source of samples. The strains showed high resistance to penicillin (98.11%), erythromycin (64.62%) and clindamycin (59.91%), while being sensitive to vancomycin and linezolid. The detection rates of efflux pump genes and resistance genes were high, and there was a significant correlation between resistance gene types and phenotypes, with mecA showing a close correlation with oxacillin. The detection rates of virulence genes and the toxin gene profiles of MSSA and MRSA strains showed significant differences. And the detection rate of biofilm genes in MRSA strains was relatively high, with 13.16% of MRSA strains showing strong biofilm formation ability. The most common epidemic clone of MRSA was ST59-SCCmecIV-t437, followed by ST59-SCCmecV-t437. The former had a higher detection rate of resistance genes and a stronger biofilm formation ability, while the latter had a higher positive rate for pvl gene and stronger pathogenicity, making it more likely to cause systemic infections. Phylogenetic analysis showed that all MRSA strains in this study clustered into three major branches, with distinct differences in antibiotic resistance and virulence characteristics among the branches. ST59-MRSA strains from different species showed consistency and inter-species transmission, but there were differences among ST59-MRSA strains from different geographical locations. In general, most MSSA and MRSA strains exhibited multidrug resistance and carried multiple resistance genes, virulence genes, and biofilm formation genes, warranting further research to elucidate the mechanisms of drug resistance and pathogenesis.

Molecular typing and characterization of Staphylococcus aureus isolates from burn wound infections in Fujian, China

Background

Staphylococcus aureus (S. aureus) is the most common causative agent of burn wound infection, that often leads to high morbidity and mortality. However, there is not enough knowledge about the molecular epidemiology and antimicrobial susceptibility of S. aureus isolates from burn wound infections in Fujian, China.

Methods

Between 2016 and 2021, 90 S. aureus isolates were collected from burn wound infections in Fujian, China, including 59 methicillin-resistant (MRSA) strains and 31 methicillin-susceptible (MSSA) strains. These were investigated for molecular characteristics, virulence genes, biofilms, and antimicrobial susceptibility. All the isolates were genotyped by multilocus sequence typing (MLST), spa typing, agr typing, and SCCmec typing. Conventional PCR was performed for the detection of virulence genes. Biofilm formation capacity was assessed by tissue culture plate assay (TCP). The antimicrobial susceptibility of the isolates was evaluated using the dilution method.

Results

In total, 37 sequence types (ST) and 34 Staphylococcal protein A (spa) types (including a new type named spa-t20720) were identified based on multilocus sequence typing (MLST) and spa typing, respectively. CC8-ST239-t030-agrI-SCCmecIII (57.6%,34/59) and CC7-ST7-t091-agrI (16.1%, 5/31) represented the main clone of MRSA and MSSA isolates, respectively. Antibiotic susceptibility testing identified a significant difference in resistance rates between ST239 and non-ST239 isolates (p < 0.05). Twelve virulence genes were detected, of which the most common were icaA and icaD (both 100%), followed by icaB and icaC (both 96.7%), icaR (95.6%), lukED (81.1%), lukAB (62.2%), pvl (50%), hlgBC (26.7%), and eta (4.4%). Moreover, lukAB, hlgBC, agrI, and agrIII were significantly correlated with burn severity (p < 0.05). MRSA isolates were less likely, compared with MSSA isolates, to carry pvl, lukAB, and hlgBC (p < 0.05). A new spa type, t20720, was identified that contains pvl, lukED, lukAB, hlgBC, icaA, icaB, icaC, icaD, and icaR genes and has strong biofilm formation ability.

Conclusion

CC8-ST239-t030-agrI-SCCmecIII and CC7-ST-7-t091-agrI were the prevalent molecular signatures of MRSA and MSSA isolates from burn wound infections in Fujian, China, respectively. The newly identified spa-t20720 isolate, which carries a wide range of virulence genes and has strong biofilm formation ability, requires special clinical attention.

Molecular Surveillance of MRSA in Raw Milk Provides Insight into MRSA Cross Species Evolution

Methicillin-resistant Staphylococcus aureus (MRSA) in foods has been associated with severe infections in humans and animals worldwide. In the present study, the molecular characteristics of livestock-associated MRSA (LA-MRSA) and human-associated MRSA (hMRSA) isolates obtained in China, as well as MRSA isolates obtained from raw milk in 2018, were investigated. In total, 343 (20.38%; 343/1,683) S. aureus isolates were obtained from 1,683 raw milk samples from 100 dairy farms in 11 provinces across China. Among these, 49 (2.91%; 49/1,683) were mecA-positive MRSA. All LA-MRSA isolates were resistant to penicillin and highly resistant to erythromycin, sulfisoxazole, and clindamycin. Bioinformatic analysis the 49 genomes of LA-MRSA and 71 previously published hMRSA genomes isolated from Chinese individuals in 2018 indicated that blaZ, erm, ant(6)-Ia, aph(3')-III, tet(K), cat, and aph(2″)-Ia were more prevalent in MRSA from raw milk (P < 0.05) compared to hMRSA. Additionally, hMRSA isolates were more significantly associated with ST5 (P < 0.01) compared to LA-MRSA; in contrast, ST338 was more prevalent among LA-MRSA isolates (P < 0.01). Likewise, the SCCmec type II was only detected in hMRSA isolates, whereas SCCmec type V and IV were more prevalent among LA-MRSA (P < 0.01). Furthermore, core-genome phylogenetic analysis showed the endemic characteristics of LA-MRSA in local provinces, as well as the close evolutionary relationships between MRSA from cattle and humans. Finally, homology analysis of mecA and blaZ genetic contexts revealed a high possibility of horizontal transmission of MRSA resistance genes among raw milk-associated and hMRSA strains, which increases the risk for public health. IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is considered a public health concern as it is resistant to multiple antibiotics, thus being in zoonotic transmission of antibiotic resistance genes. MRSA causes serious public health issues and leads to hard-to-treat infections in humans and animals; therefore, it was meaningful to determine the prevalence of MRSA in raw milk samples and investigate phenotype and genotype of antimicrobial resistance and molecular characteristics in livestock-associated MRSA (LA-MRSA) and human-associated MRSA (hMRSA) in China, which could provide a theoretical basis for preventing and controlling the spread of MRSA between livestock and humans.

Dynamics of the MRSA Population in a Chilean Hospital: a Phylogenomic Analysis (2000-2016)

The global dissemination of methicillin-resistant Staphylococcus aureus (MRSA) is associated with the emergence and establishment of clones in specific geographic areas. The Chilean-Cordobes clone (ChC) (ST5-SCCmecI) has been the predominant MRSA clone in Chile since its first description in 1998, despite the report of other emerging MRSA clones in recent years. Here, we characterize the evolutionary history of MRSA from 2000 to 2016 in a Chilean tertiary health care center using phylogenomic analyses. We sequenced 469 MRSA isolates collected between 2000 and 2016. We evaluated the temporal trends of the circulating clones and performed a phylogenomic reconstruction to characterize the clonal dynamics. We found a significant increase in the diversity and richness of sequence types (STs; Spearman r = 0.8748, P < 0.0001) with a Shannon diversity index increasing from 0.221 in the year 2000 to 1.33 in 2016, and an effective diversity (Hill number; q = 2) increasing from 1.12 to 2.71. The temporal trend analysis revealed that in the period 2000 to 2003 most of the isolates (94.2%; n = 98) belonged to the ChC clone. However, since then, the frequency of the ChC clone has decreased over time, accounting for 52% of the collection in the 2013 to 2016 period. This decline was accompanied by the rise of two emerging MRSA lineages, ST105-SCCmecII and ST72-SCCmecVI. In conclusion, the ChC clone remains the most frequent MRSA lineage, but this lineage is gradually being replaced by several emerging clones, the most important of which is clone ST105-SCCmecII. To the best of our knowledge, this is the largest study of MRSA clonal dynamics performed in South America. IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is a major public health pathogen that disseminates through the emergence of successful dominant clones in specific geographic regions. Knowledge of the dissemination and molecular epidemiology of MRSA in Latin America is scarce and is largely based on small studies or more limited typing techniques that lack the resolution to represent an accurate description of the genomic landscape. We used whole-genome sequencing to study 469 MRSA isolates collected between 2000 and 2016 in Chile providing the largest and most detailed study of clonal dynamics of MRSA in South America to date. We found a significant increase in the diversity of MRSA clones circulating over the 17-year study period. Additionally, we describe the emergence of two novel clones (ST105-SCCmecII and ST72-SCCmecVI), which have been gradually increasing in frequency over time. Our results drastically improve our understanding of the dissemination and update our knowledge about MRSA in Latin America.

From Hospital to Community: Exploring Antibiotic Resistance and Genes Associated with Virulence Factor Diversity of Coagulase-Positive Staphylococci

Coagulase-positive staphylococcus (CoPS), including methicillin-resistant Staphylococcus aureus (MRSA), poses a global threat. The increasing prevalence of MRSA in Saudi Arabia emphasizes the need for effective management. This study explores the prevalence of virulence-associated genes and antibiotic resistance patterns in CoPS. Nasal swabs from 200 individuals were collected, and standard protocols were used for the isolation, identification, and characterization of CoPS and coagulase-negative staphylococci (CoNS). Additionally, antimicrobial susceptibility testing and PCR were conducted. Bacterial growth was observed in 58.5% of participants, with 12% positive for CoPS and 30% positive for CoNS. Hospital personnel carriers showed a significantly higher proportion of CoNS compared with non-hospital personnel carriers. Non-hospital personnel CoPS strains displayed higher sensitivity to oxacillin than hospital personnel strains. Cefoxitin exhibited the highest sensitivity among β-lactam antibiotics. All isolates were sensitive to trimethoprim/sulfamethoxazole, rifampin, and quinupristin. Polymerase chain reaction analysis detected methicillin resistance genes in both non-hospital and hospital personnel MRSA strains. The coa and spa genes were prevalent in MRSA isolates, while the Luk-PV gene was not detected. A high prevalence of CoPS and CoNS was observed in both non-hospital and hospital personnel carriers. Occupational risk factors may contribute to the differences in the strain distribution. Varying antibiotic susceptibility patterns indicate the effectiveness of oxacillin and cefoxitin. Urgent management strategies are needed due to methicillin resistance. Further research is necessary to explore additional virulence-associated genes and develop comprehensive approaches for CoPS infection prevention and treatment in Saudi Arabia.

Prevalence of Culturable Bacteria and Yeasts in the Nasopharynx Microbiota during the Physiological Course of Pregnancy

The aim of the study was to compare the prevalence of the nasopharyngeal carriage of culturable microorganisms in the microbiota of asymptomatic women with a physiological pregnancy (PW) and nonpregnant women (NPW). Nasopharyngeal swabs were collected from 53 PW and 30 NPW to detect bacterial and fungal colonization. Isolates were identified using the culture method and the MALDI-TOF MS technique. The nasopharyngeal microbiota (NPM) partially differed between PW and NPW. These differences in the frequency of nasopharyngeal colonization between the PW and NPW groups were not statistically significant (p > 0.05); all cases were colonized by bacteria and only two cases in the PW group were colonized by yeasts, namely, Rhodotorula spp. High levels of staphylococcal colonization, including predominantly coagulase-negative staphylococci and S. aureus in the nasopharyngeal sample, were present in both groups. The reduced number of Gram-negative rods colonized in the cases studied was seen in samples from the NPW group, particularly with Enterobacterales, and anaerobic Cutibacterium spp. were isolated only in the PW group (p < 0.05). Moreover, a higher carriage rate of Enterobacter aerogenes colonization was statistically significant (p < 0.05) and correlated with the NPW group. Pregnancy may disturb the composition of the NPM represented by commensals and opportunistic bacteria and promote yeast colonization as compared to nonpregnant women.

Characteristics of Virulent ST5-SCCmec II Methicillin-Resistant Staphylococcus aureus Prevalent in a Surgery Ward

Objective

To investigate the transmission pathway of a MRSA prevalence in a pancreatic surgery ward in a Chinese teaching hospital.

Methods

Molecular epidemiology investigations were carried out combined PFGE, MLST, SCCmec typing and whole-genome sequencing for 20 successive MRSA isolates (2 isolates from the ward environment). Resistance and virulence genes were detected using specific PCR. Bacterial identification and AST were performed using the Vitek 2 Compact System. Clinical data of enrolled cases were retrieved from electronic case records.

Results

From January 2020 to May 2020, successive isolated 20 MRSA strains were clarified to 2 PFGE patterns (A = 19, B = 1) in the ward. Both isolates from environment and patients belonged to sequence type ST5-SCCmec II-spa type t311. MRSA-related resistance genes mecA, blaZ, ermA, ant(4')-Ia and norA were found in each clone. All 20 isolates carried tst, hlg, hla, eta, eap, fnbA and seo virulence genes, other virulence genes such as sea, sec, seb, seg, sei, sem, sen, ebpS and fnbB were also found in partial stains. All patients had fever symptom, 27.8% were accompanied by diarrhea, 88.9% had undergone surgery or invasive procedures within 30 days. Finally, 94.4% of these patients recovered.

Conclusion

This study confirmed a prevalence of ST5-MRSA-II-t311 clone in a surgery ward, indicated MRSA is a risk factor for post-surgery nosocomial infection and hand hygiene and environmental surveillance should not be ignored.

Progress in the Prevalence, Classification and Drug Resistance Mechanisms of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is a common human pathogen with a variety of virulence factors, which can cause multiple infectious diseases. In recent decades, due to the constant evolution and the abuse of antibiotics, Staphylococcus aureus was becoming more resistant, the infection rate of MRSA remained high, and clinical treatment of MRSA became more difficult. The genetic diversity of MRSA was mainly represented by the continuous emergence of epidemic strains, resulting in the constant changes of epidemic clones. Different classes of MRSA resulted in different epidemics and resistance characteristics, which could affect the clinical symptoms and treatments. MRSA had also spread from traditional hospitals to community and livestock environments, and the new clones established a relationship between animals and humans, promoting further evolution of MRSA. Since the resistance mechanism of MRSA is very complex, it is important to clarify these resistance mechanisms at the molecular level for the treatment of infectious diseases. We firstly described the diversity of SCCmec elements, and discussed the types of SCCmec, its drug resistance mechanisms and expression regulations. Then, we described how the vanA operon makes Staphylococcus aureus resistant to vancomycin and its expression regulation. Finally, a brief introduction was given to the drug resistance mechanisms of biofilms and efflux pump systems. Analyzing the resistance mechanism of MRSA can help study new anti-infective drugs and alleviate the evolution of MRSA. At the end of the review, we summarized the treatment strategies for MRSA infection, including antibiotics, anti-biofilm agents and efflux pump inhibitors. To sum up, here we reviewed the epidemic characteristics of Staphylococcus aureus, summarized its classifications, drug resistance mechanisms of MRSA (SCCmec element, vanA operon, biofilm and active efflux pump system) and novel therapy strategies, so as to provide a theoretical basis for the treatment of MRSA infection.

Staphylococcal Resistance Patterns, blaZ and SCCmec Cassette Genes in the Nasopharyngeal Microbiota of Pregnant Women

Antimicrobial resistance in Staphylococcus spp. colonising the nasopharynx can create risk factors of therapeutic treatment failure or prophylaxis in pregnant women. Resistance is mostly encoded on plasmids (e.g., blaZ gene for penicillinase synthesis) or chromosomes (e.g., mecA and mecC for methicillin resistance). The mecA gene is part of the chromosomal mec gene cassette (SCCmec), which is also located on the plasmid. The disc diffusion method for the selected drugs (beta-lactams, fluoroquinolones, streptogramins, aminoglicosides, macrolides, oxasolidinones, tetracyclines and other groups) was used. PCR for blaZ, mecA and mecC genes and SCCmec cassette detection and typing were performed. S. aureus (54.4%) and S. epidermidis (27.9%) were the most prevalent and showed the highest diversity of resistance profiles. The blaZ, mecA and mecC genes were reported in 95.6%, 20.6% and 1.5% of isolates, respectively. The highest resistance was found to beta-lactams, commonly used during pregnancy. Resistance to a variety of antimicrobials, including benzylpenicillin resistance in blaZ-positive isolates, and the existence of a very high diversity of SCCmec cassette structures in all staphylococci selected from the nasopharyngeal microbiota of pregnant women were observed for the first time. Knowledge of the prevalence of antimicrobial-resistant staphylococci in the nasopharynx of pregnant women may be important for the appropriate treatment or prophylaxis of this group of patients.

Decrease in vancomycin MICs and prevalence of hGISA in MRSA and MSSA isolates from a German pediatric tertiary care center

PURPOSE

Resistance of Staphylococcus aureus to vancomycin includes a general increase of minimal inhibitory concentrations (MIC) within the susceptible range over time (Vancomycin MIC Creep) and the presence of a subset of the bacterial population that expresses resistance (heterogeneous glycopeptide-intermediate S. aureus; hGISA). Increased MICs have been associated with adverse clinical outcomes. However, the vancomycin MIC creep is not a uniform trend suggesting the importance of regional surveys.

METHODS

We performed a retrospective analysis at a German pediatric tertiary care hospital. Isolates from 2002 to 2017 were selected which were newly identified methicillin-resistant S. aureus (MRSA) or samples from invasive methicillin-susceptible S. aureus (MSSA) or MRSA infections. Vancomycin and oxacillin MICs as well as GISA/hGISA were measured using MIC test strips and resistance was evaluated over time.

RESULTS

A total of 540 samples were tested, 200 from the early (2002-2009) and 340 from the later period (2010-2017). All samples were vancomycin susceptible, but the MIC was higher for the earlier samples as compared to the later ones (1.11 vs 0.99; p < 0.001). 14% of the samples were hGISA, GISA strains were not detected. Again, vancomycin resistance decreased over time with 28 vs. 6% hGISA (p < 0.001). There was no significant difference between MRSA and MSSA samples with respect to vancomycin MIC and hGISA prevalence.

CONCLUSION

This study shows a decreasing trend for both MIC values and presence of hGISA strains highlighting the importance of monitoring local susceptibilities. Vancomycin remains a first-line treatment option for suspected severe infection with Gram-positive cocci and proven infection with MRSA.

Molecular Characteristics of Methicillin-Resistant and Susceptible Staphylococcus aureus from Pediatric Patients in Eastern China

Staphylococcus aureus is an opportunistic pathogen that causes invasive infections in humans. In recent years, increasing studies have focused on the prevalence of S. aureus infections in adults; however, the epidemiology and molecular characteristics of S. aureus from Chinese pediatric patients remain unknown. The present study examined the population structure, antimicrobial resistance, and virulent factors of methicillin-resistant and -susceptible S. aureus isolated from Chinese pediatric patients from one medical center in eastern China. A total of 81 cases were screened with positive S. aureus infections among 864 pediatric patients between 2016 and 2022 in eastern China. Molecular analysis showed that ST22 (28.4%) and ST59 (13.6%) were the most typical strains, and associations between different clonal complex (CC) types/serotype types (ST) and the age of pediatric patients were observed in this study. CC398 was the predominant type in neonates under 1 month of age, while CC22 was mainly found in term-infant (under 1 year of age) and toddlers (over 1 year of age). Additionally, 17 S. aureus isolates were resistant to at least three antimicrobials and majority of them belonged to CC59. The blaZ gene was found in 59 isolates and mecA gene was present in 26 strains identified as methicillin-resistant. Numerous virulent factors were detected in S. aureus isolated from present pediatric patients. Remarkably, lukF-PV and lukS-PV were dominantly carried by CC22, tsst-1 genes were detected in CC188, CC7, and CC15, while exfoliative toxin genes were found only in CC121. Only 41.98% of the S. aureus isolates possessed scn gene, indicating that the sources of infections in pediatric patients may include both human-to-human transmissions as well as environmental and nosocomial infections. Together, the present study provided a phylogenetic and genotypic comparison of S. aureus from Chinese pediatric patients in Suzhou city. Our results suggested that the colonization of multi-drug resistant isolates of S. aureus may raise concern among pediatric patients, at least from the present medical center in eastern China.

Prevalence and molecular characteristics of community-associated methicillin-resistant Staphylococcus aureus in the respiratory tracts of Chinese adults with community-acquired pneumonia

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is an important pathogen causing healthcare-associated infections. In recent years, an increasing number of CA-MRSA clones have emerged and rapidly spread in the community and hospital settings in China.

OBJECTIVES

To investigate the molecular epidemiology and resistance of CA-MRSA in the respiratory tracts of Chinese adults with community-acquired pneumonia (CAP).

METHODS

A total of 243 sputum samples were collected from adult patients with CAP at the Nantong Hospital in China between 2018 and 2021. S. aureus was identified using PCR, and its susceptibility to 14 antimicrobials was tested using the broth dilution method. Genomic characterization of respiratory CA-MRSA and our previously collected intestinal CA-MRSA isolates was performed using whole-genome sequencing, and the evolutionary relationships of these isolates were assessed using phylogenetic analysis.

RESULTS

The CA-MRSA colonization rate among adults with CAP in China was 7.8 % (19/243). Antimicrobial resistance analysis revealed that the proportion of multidrug-resistant respiratory CA-MRSA isolates (100 %) was higher than that of intestinal CA-MRSA isolates (6.3 %). Among the 35 CA-MRSA isolates, 10 MLST types were identified and clustered into five clone complexes (CCs). CC5 (48.6 %) and CC88 (20 %) were predominant CA-MRSA clones. Notably, the CC5 clone ST764/ST6292-MRSA-II-t002 was identified as the major lineage causing respiratory tract infections in Chinese adults with CAP.

CONCLUSIONS

The prevalence of CA-MRSA among Chinese adults with CAP is high and often involves ST764/ST6292-MRSA-II-t002 as the causal pathogen.

Phylogenetic Analysis and Virulence Characteristics of Methicillin-Resistant Staphylococcus aureus ST45 in China: a Hyper-Virulent Clone Associated with Bloodstream Infections

Methicillin-resistant Staphylococcus aureus (MRSA) sequence type 45 (ST45) was rarely found in China. This study was conducted to trace the transmission and evolution of emerging MRSA ST45 strains in mainland China and explore its virulence. A total of 27 ST45 isolates were included for whole-genome sequencing and genetic characteristic analysis. Epidemiological results showed that MRSA ST45 isolates were often obtained from blood, primarily originated in Guangzhou, and carried diverse virulence and drug resistance genes. Staphylococcal cassette chromosome mec type IV (SCCmec IV) dominated in MRSA ST45 (23/27, 85.2%). ST45-SCCmec V was located on a phylogenetic clade distinct from the SCCmec IV cluster. We selected two representative isolates, MR370 (ST45-SCCmec IV) and MR387 (ST45-SCCmec V), and performed hemolysin activity, a blood killing assay, a Galleria mellonella infection model, and a mouse bacteremia model, as well as real-time fluorescence quantitative PCR. MR370 was proved to have extreme virulence in the phenotypic assays and at the mRNA level compared with ST59, ST5, and USA300 MRSA strains. MR387 was comparable to USA300-LAC on the phenotype and was verified to have higher expression of scn, chp, sak, saeR, agrA, and RNAIII than USA300-LAC. The results emphasized the extraordinary performance of MR370 and the good potential of MR387 in virulence causing bloodstream infection. Meanwhile, we conclude that China MRSA ST45 showed two different clonotypes, which may be widespread in the future. The entire study is valuable as a timely reminder and reports virulence phenotypes of China MRSA ST45 for the first time. IMPORTANCE Methicillin-resistant Staphylococcus aureus ST45 is epidemic worldwide. This study contributed to the awareness of the Chinese hyper-virulent MRSA ST45 strains and served as a timely reminder of its wide dissemination of clonotypes. Further, we provide novel insights for prevention from the perspective of bloodstream infections. ST45-SCCmec V is a clonotype deserving special attention in China, and we performed genetic and phenotypic analyses for the first time on it.

Genomic Epidemiology and Phenotypic Characterization of Staphylococcus aureus from a Tertiary Hospital in Tianjin Municipality, Northern China

Staphylococcus aureus remains a dangerous pathogen and poses a great threat to public health worldwide. The prevalence of the S. aureus clonotype is temporally and geographically variable. The genomic and phenotypic characteristics of S. aureus isolates in Tianjin, which is among the four big municipalities in China, are unclear. In the present study, 201 nonduplicate S. aureus isolates, including 70 methicillin-resistant S. aureus (MRSA) and 131 methicillin-susceptible S. aureus (MSSA), were collected from 2015 to 2021 in a tertiary hospital in Tianjin. Whole-genome sequencing of S. aureus isolates was carried out to investigate bacterial molecular characteristics, genomic phylogeny, antimicrobial resistance (AMR) gene carriage, and virulence factor gene distribution. The antibiotic resistance profiles, hemolytic activities, and biofilm formation abilities of the S. aureus isolates were also determined. In total, 31 distinct sequence types (STs) and 68 spa types were identified. ST59 (15.9%, 32/201) was the predominant clonotype, followed by ST398 (14.9%, 30/201) and several other major STs (ST1, ST5, ST6, ST22, ST25, ST188, and the newly emerging ST5527). ST59 and ST5527 mainly included MRSA isolates, while ST398 and the other major STs mainly included MSSA isolates. The unique characteristics of the S. aureus isolates belonging to the major STs were determined. ST59 isolates exhibited strong hemolytic activity, and ST398 strains had high biofilm formation capacity, while ST5527 isolates presented the greatest AMR. The genomic epidemiology and phenotypic characteristics of S. aureus isolates determined in this study will help in disease control in nosocomial environments. IMPORTANCE Staphylococcus aureus is an important bacterium pathogen in tertiary hospitals, which provide rich medical resources. Tianjin is one of the four municipalities in China with a population of more than 13 million. However, the epidemiology and molecular characteristics of S. aureus isolates in Tianjin are unknown. In this study, the genomic and phenotypic analyses were performed to investigate 201 S. aureus isolates collected from a tertiary hospital in Tianjin over a time span of 6 years. The refined analysis of predominant clones ST59, ST398, the newly emerging clone ST5527, as well as other major clones, will undoubtedly aid in the control and prevention of infections caused by S. aureus in tertiary hospitals.

Dissemination of Methicillin-Resistant Staphylococcus aureus Sequence Type 764 Isolates with Mupirocin Resistance in China

Mupirocin, a topical antimicrobial agent, is an important component in the eradication of methicillin-resistant Staphylococcus aureus (MRSA) colonization. The molecular characteristics of 46 mupirocin-resistant MRSA (MR-MRSA) clinical isolates were analyzed by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec element (SCCmec) typing, spa typing, and analysis of virulence genes. All 26 MRSA isolates with low-level mupirocin resistance possessed a V588F mutation in ileS. Among 20 MRSA isolates with high-level resistance to mupirocin, all carried mupA; 2 isolates also possessed the V588F mutation in ileS, and 1 possessed the V631F mutation in ileS (isoleucyl-tRNA synthetase). The majority of MR-MRSA isolates were resistant to erythromycin, clindamycin, tetracycline, ciprofloxacin, and gentamicin, but the rates of resistance to rifampin and fusidic acid were 8.7% and 6.5%, respectively. Eight sequence types (STs) were found among the 46 MR-MRSA isolates, of which ST764 was the most prevalent (76.1%). The most frequent spa type identified was t1084 (52.2%). The SCCmec type most frequently found was type II (80.4%). The most common clone among low-level MR-MRSA isolates was ST764-MRSA-SCCmec type II-t1084 (23 isolates), while ST764-MRSA-SCCmec type II-t002 (9 isolates) was the most common clone among high-level MR-MRSA isolates. Additionally, all toxin genes except the seb gene were not identified among ST764 isolates. Among clonal complex 5 (CC5) isolates, immune evasion cluster (IEC)-associated genes (chp, sak, and scn) and seb were present in ST764 but absent in ST5, while sec, sel1, tsst-1, and hlb genes were identified in ST5 but absent in ST764. In conclusion, the spread of CC5 clones, especially a novel ST764-MRSA-SCCmec type II-t1084 clone with high-level resistance to mupirocin, was responsible for the increase in mupirocin resistance. These findings indicated that the emergence of the ST764 MR-MRSA clone involves a therapeutic challenge for treating serious MRSA infections. IMPORTANCE Mupirocin, a topical antibiotic that is commonly used for the nasal decolonization of MRSA and methicillin-sensitive Staphylococcus aureus in hospital settings and nursing homes, was introduced as a highly effective antibiotic against MRSA. Mupirocin acts by competitively binding isoleucyl-tRNA synthetase, thereby disrupting protein synthesis. This drug shows bacteriostatic and bactericidal activity at low and high concentrations, respectively. However, with the increase in mupirocin use, low-level and high-level resistance during nasal mupirocin treatment has been reported. In a previous study, the proportion of MRSA strains with high-level mupirocin resistance in a Canadian hospital increased from 1.6% in the first 5 years of surveillance (1995 to 1999) to 7.0% (2000 to 2004).

Dynamics of the MRSA Population in A Chilean Hospital: A Phylogenomic Analysis (2000-2016)

The global dissemination of methicillin-resistant Staphylococcus aureus (MRSA) is associated with the emergence and establishment of clones in specific geographic areas. The Chilean-Cordobes clone (ChC) (ST5-SCC mec I) has been the predominant MRSA clone in Chile since its first description in 1998, despite the report of other emerging MRSA clones in the last years. Here, we characterize the evolutionary history of MRSA from 2000 to 2016 in a Chilean tertiary healthcare center using phylogenomic analyses. We sequenced 469 MRSA isolates collected between 2000-2016 in a tertiary healthcare center in Chile. We evaluated the temporal trends of the circulating clones and performed a phylogenomic reconstruction to characterize the clonal dynamics. We found a significant increase in the diversity and richness of sequence types (STs; Spearman r=0.8748, p<0.0001) with a Shannon diversity index increasing from 0.221 in the year 2000 to 1.33 in 2016. The temporal trend analysis revealed that in the period 2000-2003 most of the isolates (94.2%; n=98) belonged to the ChC clone. However, since then, the frequency of the ChC clone has decreased over time, accounting for 52% of the collection in the 2013-2016 period. This decline was accompanied by the rise of two emerging MRSA lineages, ST105-SCC mec II and ST72-SCC mec VI. In conclusion, the ChC clone remains the most frequent MRSA lineage in Chile. However, this lineage is gradually being replaced by several emerging clones, the most important of which is clone ST105-SCC mec II. To the best of our knowledge, this is the largest study of MRSA clonal dynamics performed in South America.

Importance

Methicillin-resistant Staphylococcus aureus (MRSA) is a major public health pathogen that disseminates through the emergence of successful dominant clones in specific geographic regions. Knowledge of the dissemination and molecular epidemiology of MRSA in Latin America is scarce and is largely based on small studies or classical typing techniques with several limitations to depict an accurate description of their genomic landscape. We used whole-genome sequencing to study 469 MRSA isolates collected between 2000-2016 in Chile to provide the largest and most detailed study of clonal dynamics of MRSA carried out in South America to date. We found a significant increase in the diversity of MRSA clones circulating over the 17-year study period. Additionally, we describe the emergence of two novel clones (ST105-SCCmecII and ST72-SCCmecVI), which have been gradually increasing their frequency over time. Our results drastically improve our understanding of the dissemination and update our knowledge about MRSA in Latin America.

Resistance and Molecular Characteristics of Methicillin-Resistant Staphylococcus aureus and Heterogeneous Vancomycin-Intermediate Staphylococcus aureus

Objective

To investigate the molecular epidemiology of Staphylococcus aureus (S. aureus) isolated from patients in the Yellow River Delta region and to construct antibiotic resistance profiles in different genetic backgrounds.

Methods

Antibiotics susceptibility testing, staphylococcal protein A (spa) typing and accessory gene regulator (agr) typing were performed for all the 204 strains. Isolates with the positive mecA gene and heterogeneous vancomycin-intermediate S. aureus (hVISA) were subjected to multilocus sequence typing (MLST) and Staphylococcal chromosomal cassettes mec (SCCmec) typing.

Results

Thirty-nine MRSA strains were identified by mecA gene. Twenty-two hVISA isolates including 9 MRSA and 13 methicillin-sensitive S. aureus (MSSA) strains were confirmed, the rest isolates (n = 182) were vancomycin-susceptible S. aureus (VSSA). 94.9% of MRSA and 63.6% of hVISA belonged to agrI. Fifty-seven distinct spa types including 5 novel types were mainly t309 (30.9%), t078 (11.8%) and t437 (11.8%). Fourteen sequence types (STs) containing 3 new STs were classified into 3 clone complexes (CCs) and 7 singletons among MRSA and hVISA isolates. Most MRSA isolates (87.2%) belonged to type Ⅳ SCCmec.

Conclusion

The predominant genotype among MRSA population was ST59-t437-agrI-IVa (53.8%), followed by ST72-t2431-agrI-IVF (15.4%). ST72 and CC5 (ST5/965/7197) were the most common hVISA clones. Both CC59 (ST59/7437) and ST72 clones were resistant to erythromycin and clindamycin among MRSA population. Strains of MSSA with phenotypic hVISA (MS-hVISA) exhibited a striking genetic diversity accompanied by the diversification of drug resistance patterns.

MRSA compendium of epidemiology, transmission, pathophysiology, treatment, and prevention within one health framework

Staphylococcus aureus is recognized as commensal as well as opportunistic pathogen of humans and animals. Methicillin resistant strain of S. aureus (MRSA) has emerged as a major pathogen in hospitals, community and veterinary settings that compromises the public health and livestock production. MRSA basically emerged from MSSA after acquiring SCCmec element through gene transfer containing mecA gene responsible for encoding PBP-2α. This protein renders the MRSA resistant to most of the β-lactam antibiotics. Due to the continuous increasing prevalence and transmission of MRSA in hospitals, community and veterinary settings posing a major threat to public health. Furthermore, high pathogenicity of MRSA due to a number of virulence factors produced by S. aureus along with antibiotic resistance help to breach the immunity of host and responsible for causing severe infections in humans and animals. The clinical manifestations of MRSA consist of skin and soft tissues infection to bacteremia, septicemia, toxic shock, and scalded skin syndrome. Moreover, due to the increasing resistance of MRSA to number of antibiotics, there is need to approach alternatives ways to overcome economic as well as human losses. This review is going to discuss various aspects of MRSA starting from emergence, transmission, epidemiology, pathophysiology, disease patterns in hosts, novel treatment, and control strategies.

Molecular Epidemiology of Community-Acquired Methicillin-Resistant Staphylococcus aureus and Clinical Characteristics of Different Sites of Infection

Purpose

Since community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) was recognized, the molecular epidemiology of CA-MRSA in China has been diverse. It is unclear whether different sites of CA-MRSA infection differ in antimicrobial resistance and clinical characteristics. The purpose of this study was to identify the molecular types, virulence factors and antimicrobial resistance of CA-MRSA strains and to analyze the clinical characteristics of different sites of CA-MRSA infection.

Methods

26 CA-MRSA strains were screened from Beijing Chao-Yang Hospital from 2014 to 2022. SCCmec type, MLST type, spa type, Panton-Valentine leukocidin (PVL), hemolysin α (Hla), phenolic soluble regulatory protein α (PSMα), toxic shock syndrome toxin-1 (TSST-1), and enterotoxin (SE) A to E were detected by PCR and gene sequencing. Antimicrobial susceptibility tests and the clinical features of CA-MRSA infection cases were collected for statistical analysis.

Results

The predominant type of CA-MRSA was ST59-t437-IV. New non-epidemic types, SCCmec VII, were also found. PVL was seen in 65.4% of CA-MRSA strains and TSST-1 was only be detected in 3.8% of CA-MRSA strain which caused poor prognosis. There were three types of infections: pneumonia (61.5%), infective endocarditis (7.7%), and skin and soft tissue infections (SSTIs) (30.8%). CA-MRSA pneumonia cases were secondary to influenza infection (37.5%). Patients with CA-MRSA-associated infective endocarditis were more likely to have underlying cardiac diseases. Patients with CA-MRSA-associated SSTIs were more likely to have a history of diabetes mellitus, and strains in this group were more susceptible to erythromycin and clindamycin.

Conclusion

ST59-t437-IV was the primary CA-MRSA type in our research and in China. We proposed that TSST-1 might be one of the indicators to predict the severity and prognosis of CA-MRSA infection. Different sites of CA-MRSA infection had difference in antibiotics susceptibility testing and underlying diseases of patients. It could provide a new perspective on treating different types of CA-MRSA infection.

Vancomycin Resistance in Enterococcus and Staphylococcus aureus

Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus are both common commensals and major opportunistic human pathogens. In recent decades, these bacteria have acquired broad resistance to several major classes of antibiotics, including commonly employed glycopeptides. Exemplified by resistance to vancomycin, glycopeptide resistance is mediated through intrinsic gene mutations, and/or transferrable van resistance gene cassette-carrying mobile genetic elements. Here, this review will discuss the epidemiology of vancomycin-resistant Enterococcus and S. aureus in healthcare, community, and agricultural settings, explore vancomycin resistance in the context of van and non-van mediated resistance development and provide insights into alternative therapeutic approaches aimed at treating drug-resistant Enterococcus and S. aureus infections.

Phenotypic and Genomic Comparison of Staphylococcus aureus Highlight Virulence and Host Adaptation Favoring the Success of Epidemic Clones

Methicillin-resistant Staphylococcus aureus (MRSA) of the sequence type 59 (ST59) and ST398 lineages has emerged in hospitals and displayed a higher virulent potential than its counterparts ST5 and ST239. However, the mechanism of the host cell-pathogen interaction and specific determinates that contribute to the success of epidemic clones remain incompletely understood. In the present study, 142 S. aureus strains (ST59, ST398, ST239, and ST5) were selected from our 7-year national surveillance of S. aureus bloodstream infections (n = 983). We revealed that ST59 and ST398 had a higher prevalence of the protease-associated genes hysA^VSaβ, paiB, and cfim and enhanced proteolytic activity than the other lineages. ST59 and ST398 showed a higher expression of RNAIII and psmα and greater proficiency at causing cell lysis than other lineages. Furthermore, ST59 and ST398 were strongly recognized by human neutrophils and caused more cell apoptosis and neutrophil extracellular trap degradation than the other lineages. In addition, these strains differed substantially in their repertoire and composition of intact adhesion genes. Moreover, ST398 displayed higher adaptability to human epidermal keratinocytes and a unique genetic arrangement inside the oligopeptide ABC transport system, indicating functional variations. Overall, our study revealed some potential genomic traits associated with virulence and fitness that might account for the success of epidemic clones. IMPORTANCE Considerable efforts have been exerted to identify factors contributing to the success of epidemic Staphylococcus aureus clones, however, comparative phenotypic studies lack representation owing to the small number of strains. Large-scale strain collections focused on the description of genomic characteristics. Moreover, methicillin-resistant S. aureus infections constitute 30% to 40% of S. aureus bloodstream infections, and recent research has elucidated highly virulent methicillin-susceptible S. aureus strains. However, comprehensive research on the factors contributing to the success of epidemic S. aureus clones is lacking. In this study, 142 S. aureus strains were selected from our 7-year national surveillance of S. aureus bloodstream infections (n = 983) accompanied by a rigorous strain selection process. A combination of host cell-pathogen interactions and genomic analyses was applied to the represented strains. We revealed some potential genomic traits associated with virulence and fitness that might account for the success of epidemic clones.

Genotypes of Staphylococcus aureus Clinical Isolates Are Associated with Phenol-Soluble Modulin (PSM) Production

Phenol-soluble modulins (PSMs) are important S. aureus virulence factors that cause cytolysis, mast cell degranulation, and stimulate inflammatory responses. In this study, PSM production by S. aureus clinical isolates was measured by liquid chromatography/mass spectrometry (LC-MS) and correlated with staphylococcal protein A (spa) type and staphylococcal cassette chromosome mec (SCCmec) type. Of 106 S. aureus clinical isolates, 50 (47.2%) corresponded to methicillin-susceptible S. aureus (MSSA) and 56 (52.8%) to methicillin-resistant S. aureus (MRSA). LC-MS analysis revealed no significant difference in average PSMα3, PSMα4, PSMβ2, and δ-toxin production between MSSA and MRSA isolates, but PSMα1, PSMα2, and PSMβ1 production were higher in MSSA than MRSA. This study demonstrated that average PSMα1–α4, PSMβ1–β2, and δ-toxin production by SCCmec type II strains was significantly lower than the IV, IVA, and V strains. Most of the SCCmec type II strains (n = 17/25; 68.0%) did not produce δ-toxin, suggesting a dysfunctional Agr system. The spa type t111 (except one strain) and t2460 (except one strain producing PSM α1–α4) did not produce PSMα1–α4 and δ-toxin, while average PSM production was higher among the t126 and t1784 strains. This study showed that the genotype of S. aureus, specifically the spa and SCCmec types, is important in characterizing the production of PSMs.

Molecular Mechanisms of Drug Resistance in Staphylococcus aureus

This paper discusses the mechanisms of S. aureus drug resistance including: (1) introduction. (2) resistance to beta-lactam antibiotics, with particular emphasis on the mec genes found in the Staphylococcaceae family, the structure and occurrence of SCCmec cassettes, as well as differences in the presence of some virulence genes and its expression in major epidemiological types and clones of HA-MRSA, CA-MRSA, and LA-MRSA strains. Other mechanisms of resistance to beta-lactam antibiotics will also be discussed, such as mutations in the gdpP gene, BORSA or MODSA phenotypes, as well as resistance to ceftobiprole and ceftaroline. (3) Resistance to glycopeptides (VRSA, VISA, hVISA strains, vancomycin tolerance). (4) Resistance to oxazolidinones (mutational and enzymatic resistance to linezolid). (5) Resistance to MLS-B (macrolides, lincosamides, ketolides, and streptogramin B). (6) Aminoglycosides and spectinomicin, including resistance genes, their regulation and localization (plasmids, transposons, class I integrons, SCCmec), and types and spectrum of enzymes that inactivate aminoglycosides. (7). Fluoroquinolones (8) Tetracyclines, including the mechanisms of active protection of the drug target site and active efflux of the drug from the bacterial cell. (9) Mupirocin. (10) Fusidic acid. (11) Daptomycin. (12) Resistance to other antibiotics and chemioterapeutics (e.g., streptogramins A, quinupristin/dalfopristin, chloramphenicol, rifampicin, fosfomycin, trimethoprim) (13) Molecular epidemiology of MRSA.