Expansion and evolution of the Streptococcus pneumoniae Spain9V-ST156 clonal complex in Poland

Abstract

In this study, we analyzed 118 penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) isolates (MICs, >or=0.12 microg/ml) recovered in Poland in 2003 to 2005 from patients with respiratory tract diseases and invasive infections. Seven different serotypes (14, 9V, 23F, 19F, 6B, 19A, and 6A, in order of descending frequency), seven alleles of the murM gene (murMA, murMB6, and the new murMB12 to -16 alleles), and 31 multilocus sequence types (STs) were observed. The vast majority of the PNSP isolates (90.7%) belonged to the international multiresistant clones, and among these, the Spain(9V)-ST156 clonal complex was the most prevalent (56 isolates) and was significantly overrepresented in invasive infections. The clone has been evolving rapidly, as demonstrated by the observed number of STs, the diversity in multiple-locus variable-number-tandem-repeat analysis (MLVA) types, and the polymorphism of pbp and pspA genes (coding for penicillin-binding proteins and the pneumococcal surface protein A, respectively). The presence and structure of the rlrA islet (encoding the pneumococcal pilus) were very well conserved. The Spain(9V)-ST156 clonal complex has been largely responsible for a decreasing susceptibility to penicillin among pneumococci in Poland in recent years, in spite of a relatively moderate antimicrobial use.

FIG. 1.

Distributions of numbers of isolates according to their MIC values for amoxicillin (AMX), ceftriaxone (CXM), cefepime (FEP), and meropenem (MEM). White and gray arrows indicate breakpoints for nonsusceptible nonmeningeal and meningeal isolates, respectively.

FIG. 2.

MLST-based population structure of Polish PNSP isolates obtained in 2003 to 2005, constructed using eBURST analysis. STs (symbolized by circles) typical for the PMEN multiresistant clones and characteristic of sporadic isolates are grouped on the left and right sides of the figure, respectively. The size of the circle corresponds to the number of isolates belonging to an ST. Single-locus variant and double-locus variant links are represented by solid and dotted lines, respectively.

FIG. 3.

MLVA-based relationships within the Spain^9V-ST156 clonal complex. Solid circles represent MTs. The size of a circle is proportional to the number of isolates with a given MT. Single-locus variant links between MTs are symbolized by lines; open circles include all MTs with a particular ST.