No abstract

Differences in severity among STEC infections could not be explained by stx2, suggesting that additional factors are important in STEC virulence.

Erythromycin treatment failures and in vitro resistance of Bordetella pertussis have been reported on several occasions in the past few years, but the mechanism of resistance has not been described. One potential mechanism, genetic modification of the erythromycin-binding site on the 23S rRNA of the 50S ribosomal subunit, has been observed in other bacteria. To explore this possibility, we amplified the portion of the 23S rRNA gene encoding the central loop of domain V. DNA sequencing and restriction fragment length polymorphism of the PCR products showed that each of the four erythromycin-resistant B. pertussis strains tested contained an A-to-G transition mutation at position 2058 (Escherichia coli numbering) of the 23S rRNA gene. The mutation was not found in seven erythromycin-susceptible isolates tested. Two of the resistant isolates were heterozygous, containing at least one mutant copy and one wild-type copy of the 23S rRNA gene. These results indicate that erythromycin resistance in these strains is likely due to a mutation of the erythromycinbinding site in the 23S rRNA gene. Identification of the resistance mechanism will facilitate development of molecular susceptibility testing methods that can be used directly on clinical specimens in the absence of an isolate.

According to population-based invasive pneumococcal surveillance in the United States during 2007, 898 (26%) of 3,511 isolates were penicillin nonsusceptible. Non-7-valent pneumococcal conjugate vaccine (PCV7) serotypes other than 19A accounted for 40% of these penicillin-nonsusceptible isolates; of these, serotypes 15A (11%), 23A (8%), 35B (8%), and 6C (5%) were most common (cumulatively 32% of penicillin-nonsusceptible isolates). Each except 6C represented a single serotype and clonal complex combination that predated the introduction of PCV7. We evaluated the genetic characteristics and nonsusceptibility to penicillin of non- PCV7 serotypes, and we found increased proportions of specific penicillin-nonsusceptible clones in serotypes 15A, 23A, 35B, and 6C, which potentially indicates a basic change of population structure within these individual serotypes.

During a nosocomial outbreak of infection due to vancomycin-resistant enterococci (VRE), rectal swabs that were collected weekly were used to identify and isolate VRE carriers. Over 6 months, 1,458 stool specimens from 724 high-risk patients were cultured, and 187 VRE isolates were recovered from 61 patients; 96% of the isolates were Enterococcus faecium. VRE tended to be isolated from clinical specimens from patients identified as VRE carriers by stool surveillance (P < .01). However, isolation of VRE from surveillance cultures preceded clinical isolation for only approximately 50% of the patients from whom a clinical VRE isolate was recovered. Mortality was greater (P < .05) among patients from whom a clinical VRE isolate was recovered than among patients from whom VRE was isolated only by stool surveillance. The mortality (1[17%] of 6) among patients for whom VRE was isolated from blood was similar to that (10 [27%] of 37) among patients for whom vancomycin-susceptible enterococcus was isolated from blood (P = .97). Despite prompt initiation of contact precautions for VRE carriers, the incidence of fecal carriage of VRE remained approximately 8% among this patient population for the 6-month period of the study.