Molecular epidemiological and antimicrobial-resistant mechanisms analysis of prolonged collection between 1971 and 2005 in Japan.

OBJECTIVES

As antimicrobial-resistant (AMR) strains have emerged, humans have adjusted the antimicrobials used to treat infections. We identified shifts in the population and the determinants of AMR strains isolated during the recurring emergence of resistant strains and changes in antimicrobial therapies.

METHODS

We examined 243 strains corrected at the Kanagawa Prefectural Institute of Public Health, Kanagawa, Japan, these isolated in 1971-2005. We performed multilocus sequence typing and AMR determinants (, , , , 23S rRNA, and ) mainly using high-throughput genotyping methods together with draft whole-genome sequencing on the MiSeq (Illumina) platform.

RESULTS

All 243 strains were divided into 83 STs. ST1901 ( = 17) was predominant and first identified after 2001. Forty-two STs were isolated in the 1970s, 34 in the 1980s, 22 in the 1990s and 13 in the 2000s, indicating a decline in ST diversity over these decades. Among the 29 strains isolated after 2001, 28 were highly resistant to ciprofloxacin (MIC ≥ 8 mg/L) with two or more amino-acid substitutions in quinolone-resistance-determining regions. Seven strains belonging to ST7363 ( = 3), ST1596 ( = 3) and ST1901 ( = 1) were not susceptible to cefixime, and six strains carried alleles with mosaic-like penicillin-binding protein 2 (PBP2; 10.001 and 10.016) or PBP2 substitutions A501V and A517G.

CONCLUSIONS

We observed a significant reduction in the diversity of over 35 years in Japan. Since 2001, ST1901, which is resistant to ciprofloxacin, has superseded previous strains, becoming the predominant ST population.