minor (70%). The role of this protein in infection is unclear; however, because of the large increase in expression in vivo, and the possible surface localization, it may be antigenic and a potential vaccine candidate. Twenty-seven genes that were differentially expressed had lower

expression levels in vivo. Many of these genes were involved in energy metabolism (11/27). These include a number of genes involved in electron transport. This could reflect a lower energy requirement during this stage of infection. Some of the genes identified in this study showed similar expression patterns in previous studies. For example, torC, frdB, and frdC all had lower expression in A. pleuropneumoniae and M. hemolytica A1 cultured in vitro under iron-restricted conditions (Deslandes et al., 2007; Roehrig et al., 2007). As iron restriction High Content Screening causes a decrease in growth rate, the similar results to ours may not be iron-specific. It is possible that Ivacaftor in vivo in both systems an increase doubling time may account for decreased in energy requirements. Mannheimia hemolytica A1 genes encoding proteins involved in amino acid transport and metabolism and cell envelope biogenesis also had lower expression. Again, similar results were reported in A. pleuropneumoniae grown in vivo and M. hemolytica A1 grown in vitro under iron-restricted conditions (Roehrig et al., 2007; Deslandes et al., 2010).

Actinobacillus pleuropneumoniae from a pneumonic lung also exhibited lower

expression of genes involved in cell envelope biogenesis (Deslandes et al., 2010). The lower expression of genes involved in energy metabolism, cell envelope biogenesis, and amino acid transport and metabolism observed in this study may be due Ureohydrolase to the in vivo samples being derived from the lung washings of calves at 6 days after challenge where bacterial growth may be slower. The gene encoding glutamate dehydrogenase, gdhA, had the lowest level of expression in this study (27-fold lower), when compared with the in vitro levels. The aspC gene, encoding aspartate transaminase, was also severely lower (−11 fold). In contrast, in vivo studies of Pasteurella multocida obtained from blood of infected chickens demonstrated that both aspC and gdhA had higher expression in vivo. As GdhA is key to nitrogen assimilation by converting ammonia to glutamate and AspC converts glutamate to aspartate, this may indicate that amino acid pool is sufficient at this stage of infection. Two of the virulence-associated genes (lktA and nmaA) that we have previously analyzed by RT-PCR and qPCR (Lo et al., 2006; S. Sathiamoorthy et al., manuscript submitted) were differentially expressed in this study. Both genes showed greater than eightfold lower expression in lung washings obtained from both calves. qRT-PCR analysis of lktA expression during the earlier time points of infection showed that the expression was higher in vivo than in vitro.