Single-Step Capsular Transformation and Acquisition of Penicillin Resistance inStreptococcus pneumoniae

Abstract

The capsule (cps) locus of Streptococcus pneumoniae is flanked by the pbp2x and pbp1a genes, coding for penicillin-binding proteins, enzymes involved in cell wall synthesis that are targets for ␤-lactams. This linkage suggested to us that selection for ␤-lactam resistance might coselect for capsular transformants. The recombination event would then involve PBP genes, as well as the cps operon, and would change both the serotype and the resistance profile of the strain. We transformed ␤-lactam-susceptible strain TIGR4 by using whole genomic DNA extracted from multidrug-resistant strain GA71, a serotype 19F variant of pneumococcal clone Spain 23F -1, and selected ␤-lactam-resistant transformants. Smooth colonies appearing on selective plates were subcultured, serotyped by the Quellung reaction, and genotyped to confirm the presence of the GA71 pbp2x-cps19-pbp1a locus in the TIGR4 genetic background by restriction fragment length polymorphism analysis of the whole locus and its flanking regions. The results showed that a new serotype, combined with resistance to ␤-lactams, could emerge in a susceptible strain via a single transformation event. Quantitative analysis showed that transfer of the cps locus had occurred at an elevated rate in ␤-lactam-selected transformants. This suggests that in natural settings selection by host immunity and selection by antibiotics may be interrelated because of "hitchhiking" effects due to linkage of resistance determinants and the capsule locus.

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

“…The first account of pneumococcal serotype switching was described in 1928 (157), leading to the discovery of the transforming substance in 1944 (158). Through transforming a sensitive strain with chromosomal DNA from a resistant strain and selecting for ␤-lactam resistance, another hitchhiking effect was observed: the cotransfer of the large cps locus and the closely flanking pbp1a and pbp2x genes (159). This experiment demonstrated the potential for the appearance of serotype-switching events through selection for ␤-lactam resistance.…”

Evolution of Clonal and Susceptibility Profiles of Serotype 19A Streptococcus pneumoniae among Invasive Isolates from Children in Spain, 1990 to 2008

“…In this sense, eight STs (ST81, ST172, ST199, ST276, ST320, ST663, ST2012, and ST2013) express serotypes 19A or 19F, three STs (ST63, ST199, and ST2074) express serotype 19A or serogroup 15, ST93 expresses serotype 21 or 19A, and ST695 expresses serotype 19A or 4. Interestingly, capsular switching and acquisition of antibiotic resistance may occur through a single transformation event, as suggested by the proximity of the 19A-type capsular locus and the flanking pbp1a and pbp2x sequences (17,29), linking the ability of pneumococci to exchange DNA to the success of some serotypes in colonizing and sharing the same ecologic niche.…”

Emergence of Multidrug-Resistant Pneumococcal Serotype 35B among Children in the United States

“…As a result, novel combinations of serotype and ST are generated which allow established circulating clones to adapt to the postvaccine environment by switching their serotype to a nonvaccine serotype (21). Capsular switching may include recombination of cps flanking regions like penicillin binding protein-encoding genes pbp1A and pbp2X, which can be altered and, thus, lead to penicillin resistance (23,24).…”