Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a major drug-resistant bacterium known for its high genetic and epidemiological diversity. MRSA is found worlwide and can cause hospital-, community-, and livestock-asscociated infections. The objective of this research was to study the evolution and epidemiology of MRSA strains, focusing on the incidence of infection and the distribution of MRSA clones among patients at Maharaj Nakhon Chiang Mai Hospital. Additionally, the study investigated the pattern of antimicrobial susceptibility and the presence of virulence factors. Whole genome sequencing (WGS) technology and bioinformatics analysis of MRSA collected from 2018 to 2019 and 2021 to 2022 were employed, along with the analysis of laboratory and epidemiological data. A total of 115 S. aureus isolates (MRSA = 54, MSSA = 61) were studied. Among MRSA-infected patients, the average age was 58.52±19.43 years, with the majority being male (62.5%) and experiencing complications (75.9%). Additionally, a higher proportion of patients were inpatients compared to outpatients (77.8% vs. 23.2%). Most MRSA isolates were detected from sputum specimens (38.9%) and caused skin and tissue infections (44.4%). Additionally, 27.8% were classified as community onset infections (COI). The length of hospital stay ranged from 3 to 128 days, with a cure rate of 64.8% among patients. Using the t-test and Fisher's Exact test, factors that were significantly different between the groups of MSSA and MRSA infections were found, including admission to the inpatient department (p = 0.001), hospital-onset infection (HOI) (p = 0.007), length of hospital stay (p = 0.043), and drug susceptibility to co-trimoxazole (p = 0.001) and clindamycin (p = 0.001). In addition, susceptibility testing of 12 antimicrobial agents revealed that all MRSA isolates were resistant to oxacillin but susceptible to vancomycin, teicoplanin, daptomycin, and linezolid though they exhibited high resistance rates to erythromycin, amoxicillin, and clindamycin at at 87.0%, 81.5% and 79.6%, respectively. WGS data analysis was performed on 40 MRSA isolates, comprising 36 isolates collected between 2018-2019 and 2021-2022, and 4 isolates collected in 2011-2012. The latter are known to be a clone associated with infection in livestock and 20 MRSA clones were classified. Among the 36 MRSA isolates, the most frequently identified clone was CC8-ST8-IV-t008 (19.4%), followed by ST9-IX-t337 (13.89%), CC8-ST239-III-t037 (11.1%), and CC5-ST764-II-t045 (8.3%). Additionally, MRSA isolates possessing multiple SCCmec types were detected, including ST398-V, XII-t034, and SCCmec II, III-t037. The evolutionary relationship among the 40 MRSA strains and 7 reference MRSA strains was elucidated using Maximum Likelihood estimation. Six clades of MRSA were clustered with HA-MRSA, CA-MRSA, and LA-MRSA clones reported worldwide, suggesting the potential for MRSA transmission between community, livestock, and hospital settings, as well as between countries across different continents. However, it is important to note that this study represents a preliminary investigation based on a limited sample size of only 40 MRSA isolates from a single hospital. The results solely encompass the genetic information, structure, and distribution of specific MRSA clones in the study samples. Therefore, it is not possible to ascertain the prevalence of the clones and strains detected. The majority of the MRSA clones studied were found to be multidrug resistant (92.5%), with a high prevalence of antibiotic resistance genes detected, consistent with the results of susceptibility testing. Moreover, a total of 12 drug resistance patterns were identified. Twenty-eight virulence genes were detected, and the most common virulence genes were aur, hlgA, hlgB, and hlgC, found in all isolates (100%). Twnety-five virulence genotypes were identified, with the most common being aur, splA, splB, splE, hlgA, hlgB, hlgC, lukD, lukE, lukF-PV, lukS-PV, sek, seq, ACME, sak, scn (17.5%). Genes encoding the PVL toxin were detected in MRSA clones CC8-ST8-IV-t008 and ST1232-V-t034. These clones were identified as community-onset infections (COI) and were the main cause of infections in outpatient departments. Notably, this finding has not been reported previously in Chiang Mai Province. Therefore, continuous study of the genetic characteristics and epidemiology of MRSA is crucial for surveillance and monitoring of evolutionary and epidemiological changes among MRSA clones originating from different sources. This knowledge is essential for addressing the emergence and spread of potentially highly severe strains and for preparing to combat the public health issues that may arise in the future.
