Furthermore, scl-L4, which encodes serine hydroxymethyltransferase (SHMT), has been identified using both SCOTS and STM (Harper et al., 2003). The glyA gene, encoding SHMT, was shown to be essential in E. coli (Yan et al., 2002). It belongs to the pur regulon, which is required for purine synthesis in E. coli (Steiert et al., 1990). The AL393 mutant of P. multocida, which has a probable effect on glyA function, was attenuated only in chickens in STM (Harper et al., SCH772984 chemical structure 2003). Clone scs-L15 corresponds to the gene encoding a polynucleotide phosphorylase (Pnp) that

is involved in the degradation of mRNA. In a previous study using STM, a pnp mutant of P. multocida was identified and found to be attenuated in mice (Fuller et al., 2000). Meanwhile, pnp was found to be required for the expression of plasmid-borne virulence genes in Shigella flexneri, using STM (Tobe et al., 1992). The clone scs-L13, homologous to the fhaB1/fhaB2

gene that encodes filamentous hemagglutinin, harbors a potential virulence factor. Using STM in a model of septicemia in the mouse, the fhaB1 and fhaB2 genes from a case of bovine pneumonia were identified, and an fhaB2 knockout mutant was engineered using a temperature-sensitive plasmid in a well-known virulent strain of P. multocida A: 3 (P-1059) (Fuller et al., 2000). The virulence of the ΔfhaB2 mutant was attenuated in Beltsville white turkeys following intranasal administration, and fhaB2 peptides were evaluated in the

natural host (Tatum et al., 2005). The fhaB1 gene was inserted using see more a kanamicin-resistant gene, and the ΔfhaB1 mutant of P. multocida strain C48-102 was attenuated when administered via intranasal injection (our data). In contrast, some scs-L clones showed homology to the upregulated genes found in other pathogenic bacteria, including those expressed during natural and/or experimental infection or under in vitro growth conditions that mimicked an in vivo environment. Clones scs-L18, scs-L22, and scs-L24 encode cell division protein FtsQ, translation elongation factor EF-Tu (TufA), and ATP-stimulated mitochondrial matrix protein Chlormezanone (Lon protease), respectively. Fittipaldi and colleagues, using SCOTS, identified the ftsQ/divIB gene that is expressed preferentially by S. suis upon interaction with porcine brain microvascular endothelial cells (Fittipaldi et al., 2007). However, FtsQ was downregulated when recovered from the blood of chickens infected with P. multocida (Boyce et al., 2002). FtsQ/divIB is a highly conserved component of the divisome that plays a central role in the assembly of the early and late cell division proteins FtsL and FtsB/DivIC (Robson & King, 2006; Gonzalez et al., 2010). The ftsQ and divIB genes are homologous; ftsQ was essential in E.