Abstract
To trace the linkage between Japanese healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) strains in the early 1980s and the 2000s onward, we performed molecular characterizations using mainly whole-genome sequencing. Among the 194 S. aureus strains isolated, 20 mecA-positive MRSA (10.3%), 8 mecA-negative MRSA (4.1%) and 3 mecA-positive methicillin-susceptible S. aureus (MSSA) (1.5%) strains were identified. The most frequent sequence type (ST) was ST30 (n = 11), followed by ST5 (n = 8), ST81 (n = 4), and ST247 (n = 3). Rates of staphylococcal cassette chromosome mec (SCCmec) types I, II, and IV composed 65.2%, 13.0%, and 17.4% of isolates, respectively. Notably, 73.3% of SCCmec type I strains were susceptible to imipenem unlike SCCmec type II strains (0%). ST30-SCCmec I (n = 7) and ST5-SCCmec I (n = 5) predominated, whereas only two strains exhibited imipenem-resistance and were tst-positive ST5-SCCmec II, which is the current Japanese HA-MRSA genotype. All ST30 strains shared the common ancestor strain 55/2053, which caused the global pandemic of Panton-Valentine leukocidin-positive MSSA in Europe and the United States in the 1950s. Conspicuously more heterogeneous, the population of HA-MRSA clones observed in the 1980s, including the ST30-SCCmec I clone, has shifted to the current homogeneous population of imipenem-resistant ST5-SCCmec II clones, probably due to the introduction of new antimicrobials.
Highlights
Staphylococcus aureus (S. aureus) is a major opportunistic pathogen that can cause various life-threatening infections, and approximately 20% of healthy human individuals are persistent carriers of this bacterial species[1]
The aims of this study were to retrospectively review the population structure of Japanese healthcare-associated methicillin-resistant Staphylococcus aureus (HA-methicillin-resistant S. aureus (MRSA)) strains isolated in the early 1980s using multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing and phylogenetic analysis based on whole-genome single nucleotide polymorphisms (SNPs), and to compare the population structure with that of strains isolated in recent years
32.1% of MRSA strains (9 of 28 strains) showed resistance to imipenem, which was unavailable in Japan during the period under study, whereas all methicillin-susceptible S. aureus (MSSA) strains were susceptible to imipenem
Summary
Staphylococcus aureus (S. aureus) is a major opportunistic pathogen that can cause various life-threatening infections, and approximately 20% of healthy human individuals are persistent carriers of this bacterial species[1]. MRSA is generated when methicillin-susceptible S. aureus (MSSA) acquires the exogenous mecA gene encoding the penicillin-binding protein 2′ (PBP2′), which is carried on a mobile genetic element designated staphylococcal cassette chromosome mec (SCCmec)[8]. There have been few reports on molecular epidemiology of MRSA isolates collected before . Epidemiological tracking of drug-resistant bacteria using molecular typing tools over time can provide crucial insights into infection control and appropriate use of antimicrobials in clinical practice[19]. The aims of this study were to retrospectively review the population structure of Japanese HA-MRSA strains isolated in the early 1980s using MLST, SCCmec typing and phylogenetic analysis based on whole-genome single nucleotide polymorphisms (SNPs), and to compare the population structure with that of strains isolated in recent years. Our data shows that in the 1980s, the population structure of Japanese HA-MRSA was remarkably polyclonal, including representative clones that are rarely found
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