Incidence of virulence factors in uropathogenic escherichia coli in two Lebanese hospitals and the evaluation of the CPS ID3 chromogenic medium for urine cultures. (c2007)

Abstract

Urinary tract infections are among the most frequent encountered infections. The vast majority of urinary tract infections are caused by Escberichia coli. The invasion and colonization of the urinary tract by uropathogenic E coli is mediated by its virulence factors. In this study, 160 uropathogenic E coli strains were screened for pilus associated with pyelonephritis (pap), S fimbriae (r/a), afunbriae (qfa), aerobactin (ae!), hemolysin (My), and cytotoxic necrotizing factor 1 (cnf1). The prevalence of these genes al110ng the studied isolates were 33.6, 33.1, 8.8, 45.6, 32.5, and 18.1% for pap, sfa, afa, aer, hly, and cnf, respectively. Genes coding for adherence factors were present in 81 % of the isolates confirming their importance role in tissue targeting and colonization of mucosal sites. Cnf gene was limited to hemolytic strains and was linked in most isolates to adhesins, while sfa was always associated with other virulence factors. Different combinations of genes were detected indicating possible synergisn1 and/ or the fact that the genes coding for these virulence factors are located on the bacterial chromosome. Detection of the virulence factors would be of a great value in understanding pathogenesis. CPS ID3 chromogenic medium was compared to routine media for d1e isolation, and to API system for d1e identification of urinary tract pathogens. Positive predictive values were 100% for all species included in this study except Enterococcus spp. that was 66.7%. False negative results were observe in E. coil and Enterococcus spp. isolates (96% and 92.3% respectively) indicating that additional tests should be performed, particularly when white colonies are recovered. All organisms isolated from urine samples grew on this medium, but not all could be identified based on d1e motphological characteristics of their colonies. However, using this medium had the additional benefit of reducing the time needed for urine analysis when compared to the time needed wid1 routine analysis. The most important advantage attributed to the use of CPS ID3 was d1e prompt identification of E. coil within 24 hours with no need to use additional biochenucal tests. On the other hand, being expensive, having a short shelf life and not covering Staphylococcus saprophyticus were the only important drawbacks of this medium. CPS ID3 enables presumptive identification of a high proportion of urinary tract pathogens through the color of the colony, and even pathogens that were colorless were successfully isolated using this medium. The results of the present study suggest d1at use of chromogenic medium offers a time saving med10d for d1e reliable detection and presumptive identification of urinary tract pad1ogens. Moreover, it also revealed d1at d1e studying of bacterial virulence determinants is an important aspect for the development of strategies to combat urinary tract infection.