Revealing the Mosaic Nature of Salmonella Genomes Using Microarrays

The accumulation of whole genome sequences has truly brought forth the strength of microarray technology. Thereby, DNA microarray technologies have gained the ability to generate and provide efficient access to vast genetic information suited not only for comparative genomics, but also for the identification and subclassification of microbes. Furthermore, DNA-microarrays have opened the possibility to probe bacterial transcriptomes at a whole genome level. This review describes the application of DNA microarrays to define the genome content within the genus Salmonella. Also, the review will discuss the diagnostic potential of the array technology in terms of use in routine reference laboratory for seroand genotyping. Introduction In 1880 Eberth observed Salmonella as human pathogen through examination of histological sections of spleen and mesenteric lymph nodes obtained from a patient that had died from typhoid fever. Subsequently the “typhoid bacillus” was cultivated in 1884 by Gaffky (Grimont et al, 2000). Since then, the “typhoid bacillus” has been placed into the genus Salmonella, an apparently large collection of closely related Gram-negative bacterial species. Yet, more recent biochemical and DNA-hybridization-based studies have established that the genus Salmonella comprises two species, S. enterica and S. bongori (Crosa et al., 1973; Le Minor et al., 1982a; Le Minor et al, 1982b; 1986). S. enterica is further divided into 7 subspecies: enterica, salamae, arizonae, diarizonae, indica and houtenae, or respectively into subspecies I, II, IIIa, IIIb, IV, VI, and VII (Le Minor and Popoff, 1987). Furthermore, the White-Kauffmann-Le Minor (WKL) scheme divides Salmonella into 2449 serovars, of which only 20 occur in S. bongori. Of the remaining serovars 1443 are contained in S. enterica subspecies enterica, 488 in subspecies salamae, 94 in subspecies arizonae, 70 in subspecies houtenae and 11 in subspecies indica (Popoff et al., 1998). In spite of this wide variety within Salmonella, only serovars included into subspecies I are associated with disease in warm-blooded animals, and furthermore only a small fraction of the serovars within subspecies I are enteric pathogens. In fact, the 12 most prevalent Salmonella serovars are responsible for more than 70% of all human Salmonella infections (Centre for Disease Control and Prevention, 2001; http://www.cdc.gov/ncidod/bdmd/phlisdata/Salmonella.htm). For the selected serovars of S. enterica subspecies I that inhabits the intestinal tracts of humans and warm-blooded anicaister.com/bacteriology