coli found. Cook et al. (2001) studied the presence of several virulence factors among 50 strains of E. coli causing vaginitis in nonpregnant women, with findings similar to ours. However, both studies differed considerably compared with the

results of Birõsováet al. (2004), who found higher percentages of the virulence factors studied (hly, cnf, pap, sfa, iucD genes) Roscovitine molecular weight among E. coli isolates from vaginal samples of nonpregnant and pregnant women than in our study. Obata-Yasuoka et al. (2002) compared E. coli isolates from pregnant women with isolates from nonpregnant women, with different results. The hly, cnf and pap genes, all associated with PAIs, were significantly more frequent among strains from pregnant women presenting a higher percentage of nalidixic acid-susceptible

strains. In spite of the lack of significant differences in the levels of nalidixic acid resistance between E. coli strains from pregnant and nonpregnant women, statistically significant differences were found in the frequency of several virulence factors among nalidixic acid-resistant and -susceptible strains. The lower frequency of the hly, cnf1 and pap genes among the nalidixic acid-resistant isolates could be explained by the partial loss of PAI associated with acquisition of quinolone find more resistance, as has been demonstrated in a previous study carried out in our laboratory (Soto et al., 2006), in which a quinolone-susceptible E. coli strain was grown in culture media with subinhibitory concentrations of ciprofloxacin, observing the loss of the hly and cnf1 genes. In urinary tract infections, P-fimbriae mediate the specific attachment many of uropathogenic E. coli to kidney tissue and elicit a cytokine response in these cells

(Johnson, 1991; Johnson, 2005). Nevertheless, the role of P-fimbriae in genital tract infection remains unknown. Notably, 60% of isolates from pregnant women belonged to phylogenetic group B2, considered the most virulent, and a high percentage of nonpregnant isolates were phylogenetic group A, considered as commensal, thereby confirming the greater virulence of E. coli isolates from pregnant women. In summary, E. coli strains isolated from vaginal and/or endocervical samples of pregnant women are more virulent than those from nonpregnant women. The presence of hemolysin, cytotoxic necrotizing factor and P-fimbriae, all in a PAI, may allow the bacteria to cause severe infections during pregnancy, thereby increasing the possibility of neonatal sepsis. Further studies are needed in order to analyze the role of each virulence factor in the transmission of microorganisms between mother and baby. Thanks are due to Quique Bassat (CRESIB) for the revision and suggestions.