Clonal Expansion of Macrolide-Resistant Sequence Type 3 Mycoplasma pneumoniae, South Korea

Abstract

To investigate the genetic background for the emergence of macrolide resistance, we characterized the genetic features of Mycoplasma pneumoniae using multilocus sequence typing. Of the 146 M. pneumoniae strains collected during the 5 consecutive outbreaks of M. pneumoniae pneumonia during 2000-2016 in South Korea, macrolide resistance increased from 0% in the first outbreak to 84.4% in the fifth. Among the 8 sequence types (STs) identified, ST3 (74.7%) was the most prevalent, followed by ST14 (15.1%). Macrolide-susceptible strains comprised 8 different STs, and all macrolide-resistant strains were ST3 (98.3%) except 1 with ST14. The proportion of macrolide-resistant strains in ST3 remained 2.2% (1/46) until the 2006-2007 outbreak and then markedly increased to 82.6% (19/23) during the 2010-2012 outbreak and 95.0% (38/40) during the 2014-2016 outbreak. The findings demonstrated that clonal expansion of ST3 M. pneumoniae was associated with the increase in macrolide resistance in South Korea.

Keywords: Mycoplasma pneumoniae; South Korea; antimicrobial resistance; bacteria; drug resistance; macrolides; multilocus sequence typing.

Figure 1

Macrolide resistance of Mycoplasma pneumoniae, South Korea, 2000–2016. Each number on the bar graph indicates the macrolide-resistancet of each epidemic year. The proportion of macrolide resistance strains by each outbreak were as follows: 0% (2000 and 2003–2004), 3.4% (2006–2007), 54.1% (2010–2012), and 84.4% (2014–2016).

Figure 2

Mycoplasma pneumoniae ST distribution by each outbreak and macrolide resistance within specific STs, South Korea, 2000–2016. Each number of the box indicates proportion of each ST. (R) designates macrolide resistance. ST, sequence type.

Figure 3

Mycoplasma pneumoniae sequence type (ST) relationship of 146 strains by eBURST analysis (http://eburst.mlst.net/), South Korea, 2000–2016. Two main CCs were defined without any singleton. ST3 and ST2 were the predicted founder of each CC. Numbers on the diagram correspond to STs. The size of each circle correlates with the number of isolates of each ST. CC, clonal complex.