Comparing Antimicrobial Susceptibilities among Mycoplasma pneumoniae Isolates from Pediatric Patients in Japan between Two Recent Epidemic Periods

We compared the antimicrobial susceptibility of Mycoplasma pneumoniae isolates from pediatric patients in Japan in 2011–2012 and 2015–2016, when epidemics occurred. The antimicrobial activity of macrolides and tetracyclines against M. pneumoniae infection tended to be restored in 2015–2016.

Pediatricians at the facilities collected samples from patients with suspected M. pneumoniae infections. Informed consent was obtained from the parents of all patients. The Ethics Committee at Kawasaki Medical School, Kurashiki, Japan, approved the study protocol on 15 October 2018 (no. 3119-1).
The MICs of antimicrobial agents for the isolated strains were determined with microdilution methods (8). Briefly, medium containing 10 5 to 10 6 CFU/ml of M. pneumoniae was added to 96-well microplates and incubated at 37°C for 6 to 8 days.
MIC was defined as the lowest concentration of antimicrobial agent at which the metabolism of the organism was inhibited, which was evidenced by the lack of a color change in the medium 3 days after the drug-free control first showed a color change. The reference strain FH was used as a drug-susceptible control. The antimicrobial agents used for MIC determination were erythromycin, clarithromycin, azithromycin, clindamycin, minocycline, tetracycline, tosufloxacin, garenoxacin, and levofloxacin.    (6).
We considered two reasons for recovery of the sensitivity to macrolides. One is the appropriate use of tosufloxacin for treating M. pneumoniae infection, and the other is a shift in the P1 type.
First, tosufloxacin was approved in 2010 in Japan as treatment for pediatric patients and is recommended for use in patients with suspected MR M. pneumoniae infection as a second-line drug under various guidelines (2). Specifically, tosufloxacin is recommended for cases with M. pneumoniae infection in which fevers are not reduced by 48 to 72 h after the initiation of macrolide treatment. Ouchi et al. (10) reported that tosufloxacin was significantly more effective than clarithromycin in eradicating MR M. pneumoniae. Additionally, total oral antimicrobial use of macrolides decreased, whereas that of quinolones, including tosufloxacin, increased from 2011 to 2013 in children (age, 0 to 14 years), based on analysis of health insurance claim data in the national database (11). Miyashita et al. (12) reported lower macrolide resistance rates of M. pneumoniae infection in adults to whom macrolides, tetracyclines, or respiratory quinolones were commonly administered than in children to whom only macrolides or tetracyclines were administered in 2008 to 2011. Thus, because tosufloxacin was used appropriately for M. pneumoniae infections, the development of MR M. pneumoniae was prevented.
Second, a type shift in p1 may explain the recovery of sensitivity to macrolides. At the surface of the attachment organelle is the 170-kDa adhesin protein P1, which is densely clustered and plays a major role in binding to the receptor molecule of host epithelial cells (13). Two major subtypes of p1 (subtypes 1 and 2) are known that form some minor variants (subtype 1, 2a, 2b, and 2c).
A type-shift phenomenon occurs in Japan every 8 to 10 years. A major subtype of p1 was subtype 2 in 1995 to 2001. Thereafter, subtype 1 reached a level of 90% in 2005, whereas subtype 2 decreased from 2001 to 2005. Recently, it was reported that a type shift from subtype 1 to subtype 2 occurred in 2013 to 2015 in Yamagata Prefecture, Japan (14). It was presumed that because this subtype had few opportunities to be exposed to macrolides since 2000, isolates of subtype 2 may have been more sensitive to macrolides than isolates of subtype 1. Furthermore, correlations of P1 with multilocus variable-number tandem-repeat analysis (MLVA), which is one of the methods for typing, have been described (15,16). As revealed by a previous MLVA-4 analysis, almost all isolates of 4/5/7/2 or 4/5/7/3 strains belonged to subtype 1 of p1, whereas almost all of the 3/5/6/2 or 3/6/6/2 strains belonged to subtype 2 of p1. We did not perform MLVA, and we hope to address this aspect in the future. Next