In accordance with the concept that bacterial microorganisms can be divided with respect to pathogenicity at least into three groups (nonpathogenic, facultative pathogenic, and obligate pathogenic) there is not always a close correlation between a given species and its pathogenicity potential. Thus, identification of the bacterial species using surrogate biochemical and immunological markers may not be sufficient to characterize the virulence properties. Virulence traits, which are frequently encoded by plasmids, phage, integrons, and other horizontally transferred vectors, are conferred independently of the surrogate chromosomal markers and extensively determine the pathogenicity of bacteria [47]. Microarray analysis of microbial virulence factors appears to be very useful for automated identification and characterization of bacterial pathogens [5, 52] (Fig. 22.1). For instance, an E. coli pathoarray carrying different target genes can be used to differentiate E.coli strains causing urinary tract infections or septicemia (Table 22.2). Multiple specific genes can be used to identify each organism, thus turning microbial identification into a pattern recognition process, a process that is amenable to automated, computer-based analysis. Previously developed techniques, such as multiplex PCR, can be rapidly adapted to take advantage of the specificity and speed of pathoarray analysis.

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