Joyce C. de Azavedo

BACKGROUND: Fluoroquinolones are now recommended for the treatment of respiratory tract infections due to Streptococcus pneumoniae, particularly when the isolates are resistant to beta-lactam antibiotics. Although pneumococci with reduced susceptibility to fluoroquinolones have been identified, their prevalence has not been determined in a defined population. METHODS: We performed susceptibility testing on 7551 isolates of S. pneumoniae obtained from surveillance in Canada in 1988 and from 1993 to 1998. Pneumococci with reduced susceptibility to fluoroquinolones (defined as a minimal inhibitory concentration of ciprofloxacin of at least 4 microg per milliliter) were further characterized. We also examined antibiotic prescriptions dispensed in Canadian retail pharmacies. RESULTS: Between 1988 and 1997, fluoroquinolone prescriptions increased from 0.8 to 5.5 per 100 persons per year. The prevalence of pneumococci with reduced susceptibility to fluoroquinolones increased from 0 percent in 1993 to 1.7 percent in 1997 and 1998 (P=0.01). Among adults, the prevalence increased from 1.5 percent in 1993 and 1994 combined to 2.9 percent in 1997 and 1998 combined. The prevalence was higher in isolates from older patients (2.6 percent among those 65 years of age or older vs. 1.0 percent among those 15 to 64 years of age, P<0.001) and among those from Ontario (1.5 percent, vs. 0.4 percent among those from the rest of Canada; P< 0.001). Fluoroquinolone use was greatest among the elderly and in Ontario. The 75 isolates (17 serotypes) of pneumococci with reduced susceptibility to fluoroquinolones were submitted by 40 laboratories in eight provinces. Reduced susceptibility to fluoroquinolones was associated with resistance to penicillin. CONCLUSIONS: The prevalence of pneumococci with reduced susceptibility to fluoroquinolones is increasing in Canada, probably as a result of selective pressure from the increased use of fluoroquinolones.

Of a total of 147 erythromycin-resistant Streptococcus pneumoniae isolates, 64 (43.5%) were resistant to erythromycin, clindamycin, and streptogramin B (MLSB phenotype), 57 of which possessed the ermB gene. Eighty-two (55.8%) were resistant to erythromycin alone (M phenotype), 81 of which possessed the mefE gene. One was erythromycin and streptogramin B resistant but susceptible to clindamycin (MS phenotype) and possessed neither the erm gene nor the mefE gene.

In enteropathogenic Escherichia coli, the eaeA gene produces a 94-kDa outer membrane protein called intimin which has been shown to be necessary but not sufficient to produce the attaching-and-effacing lesion. The purpose of this study was to characterize the intimin specified by the eaeA allele of the enterohemorrhagic E. coli (EHEC) serotype O157:H7 strain CL8 and to determine its role in adherence. The carboxyl-terminal 266 amino acids of the CL8 intimin were expressed as a protein fusion with glutathione S-transferase, which was used to raise antiserum in rabbits. The antiserum reacted in Western immunoblots with a 97-kDa outer membrane protein of EHEC strains of serogroups O5, O26, O111, and O157 and enteropathogenic E. coli strains of serogroups O55 and O127. Surface labelling of CL8 with 125I showed that intimin was surface exposed. An eaeA insertional inactivation mutant of CL8 was produced and was designated CL8-KO1. Total adherence of CL8-KO1 to HEp-2 cells was not significantly different from that of CL8, but CL8-KO1 gave a negative result in the fluorescent actin staining test. The eaeA gene expressed alone in E. coli HB101 also gave a negative fluorescent actin staining test result. The eaeA gene of CL8 was able to complement the eaeA deletion mutation in CVD206. We conclude that the product of the EHEC eaeA gene is a 97-kDa surface-exposed protein and propose that it be designated intiminO157. Sherman et al. described a 94-kDa outer membrane protein which played an important role in adherence of E. coli O157:H7 (Infect. Immun. 59:890-899, 1991). Western immunoblotting and indirect fluorescent antibody studies showed that the protein described by Sherman et al. is not intimin.

Toxic shock syndrome (TSS) toxin 1 (TSST1) is produced by strains of Staphylococcus aureus associated with TSS. Purified TSST1 induces in rabbits a shock-like illness with many features similar to TSS in humans. These symptoms were also induced by TSST1-producing bacteria in diffusion chambers implanted in the rabbit uterus. Naturally occurring TSST1+ strains and a TSST1- strain harboring a pE194-derived plasmid carrying the cloned TSST1 determinant tst gave the same symptoms. TSST1- strains and a TSST1- strain carrying a pE194-tst plasmid with a deletion of the tst gene had no effect in rabbits. The results with the plasmid-carrying TSST1+ and TSST1- strains, which were isogenic apart from tst, show that the toxin is responsible for the illness in rabbits and suggest that it is a major factor in the pathogenesis of TSS.

Strains of Staphylococcus aureus associated with toxic shock syndrome produce toxic shock syndrome toxin 1 (TSST 1), which is lethal to conventional rabbits and acts synergistically with gram-negative lipopolysaccharide. The lethal effect of TSST 1 was examined in specific-pathogen-free rabbits on the basis that these rabbits, being less colonized by gram-negative bacteria, would be less susceptible than conventional animals. Although there was no significant difference in mortality between specific-pathogen-free and conventional rabbits in response to 100 micrograms of TSST 1, there was a difference in response between Dutch belted rabbits and New Zealand white rabbits. Both specific-pathogen-free and conventional New Zealand white rabbits were more susceptible to TSST 1 than the Dutch belted strain. Pretreatment of conventional New Zealand white rabbits with polymyxin B neutralized the lethal effect of TSST 1.