Changing molecular epidemiology and characteristics of methicillin-resistant Staphylococcus aureus isolated from bloodstream infections: nationwide surveillance in Japan in 2019

Abstract

ObjectivesSome single-center studies have reported that methicillin-resistant Staphylococcus aureus (MRSA) carrying the staphylococcal cassette chromosome mec (SCCmec) type IV has been increasing in bloodstream infections (BSIs) in Japan. Therefore, we conducted nationwide surveillance for MRSA BSI to verify that there is a change all over Japan.MethodsWe recruited 51 Japanese hospitals from the Japanese Association for Infectious Diseases. MRSA strains, which were detected in two or more sets of blood, were collected between January and September 2019. They were analyzed by antimicrobial susceptibility testing at Nagasaki University Hospital. Whole-genome sequencing was also performed to determine SCCmec typing and multilocus typing and detect drug-resistance and virulence genes.Results270 MRSA strains were collected from 45 hospitals. The major clones were ST8 with SCCmec type IV (ST8-IV) (30.7%), ST1-IV (29.6%), ST2725-IV (9.5%), ST764-II (8.1%), and ST5-II (7.8%). However, there were regional differences among the most major clones. The most common clones in western, eastern, and northern Japan were ST1-IV, ST8-IV, and ST5-II, respectively. ST8-IV, ST1-IV, and ST2725-IV exhibited lower drug resistance against clindamycin and minocycline than ST764-II and ST5-II, but erm(A) was detected in 93.8% and 100% of ST1-IV and ST2725-IV, respectively. Based on drug-resistance and virulence genes, characteristics of ST8-IV were different from those of ST1-IV and ST2725. In addition, the two major types were expected to be ST8-IV.ConclusionsThis study revealed that SCCmec type IV clones replaced SCCmec type II in MRSA BSI. In addition, three main types of SCCmec type IV clones have spread throughout Japan.