Increased sporulation rate of epidemic Clostridium difficile Type 027/NAP1

Abstract

Clostridium difficile PCR ribotype 027 comprised 0.2% of a collection of Swedish isolates in 1997-2001 (3 of 1,325 isolates). These isolates had lower moxifloxacin MICs than the epidemic type 027 isolates, but they had the same tcdC sequence and toxin yield. Type 027 produced 3- to 13-fold more toxin than did major Swedish types. One epidemic strain (027/NAP1a) sporulated more than did other type 027 isolates, a feature that should contribute to its survival and spread.

FIG. 1.

Toxin yields of 24-h C. difficile cultures. Isolates T-378, Ö99-1670, A177:1, US1067, and US1165 are type SE10, i.e., PCR ribotype 027. Isolates representing major Swedish PCR ribotypes, CCUG 37783 (SE20, i.e., PCR ribotype 001), Ö99-1751 (SE30), Ö99-0304 (SE21), and two high-level toxin producing reference strains, VPI 10463 (SE20c) and 8864 (SE10b), were included for comparison. Values are averages of duplicate cultures, and bars indicate standard errors. Statistics were calculated using logarithmic average values of total toxin for “All SE10,” CCUG 37783, Ö99-1751, Ö99-0304, VPI 10463, and 8864 by using analysis of variance and Bonferroni post hoc compensation for multiple comparisons (the P value for the comparison of “All SE10” and strain Ö99-1751 is shown).

FIG. 2.

Sporulation frequencies of C. difficile cultures. For further explanation of strains, see the legend for Fig. 1. Bars indicate standard errors. Statistics were calculated by using analysis of variance and Bonferroni post hoc compensation for multiple comparisons. The P value for the comparison of US1067 and US1165 is indicated. As T-378 formed doublet cells, the total frequency scored (filled and hatched areas) and an estimate of the true sporulation frequency per unit cell (filled area) are shown. For details, see the text.