Higher inoculum levels of 10 cfu/ml, which here translate to adding 10,000 cells per leaf, well over the lesion coalescence threshold, may therefore mask changes in virulence of up to a thousand-fold.
Further studies are needed to understand how amastigote metabolism is regulated in the absence of significant gene-specific transcriptional regulation, while the identification of key steps in carbon metabolism that are essential for amastigote virulence opens up new opportunities for the development of novel anti-microbial strategies.
Although there were a limited number of genes encoding putative or proven virulence molecules up-regulated during culture in blood, transcripts encoding gamma-hemolysin (hlgA, hlgB, and hlgC) were among the most highly up-regulated USA300 genes over a 2-h culture period in human blood.
We previously applied the gene discovery methodology, known as in vivo-induced antigen technology (IVIAT), to identify B. abortus virulence genes up-regulated during infection in elk (Cervis elaphus), and as a result have identified ten loci with gene products potentially important to survival of the pathogen in this host [20].
Whereas major metabolic pathways including cell division, nutrient transport and regulatory processes were drastically down-regulated, numerous genes involved in iron scavenging and virulence were up-regulated.
Four of the 148 C. albicans genes that have been shown to contribute to virulence were up-regulated in the rabbit kidney lesions.
The HlyX regulon was characterized recently, and iron-regulated protein B (FrpB) was identified as a potentially important virulence factor up-regulated when A. pleuropneumoniae is grown in oxygen-deprived environments [ 20].
Results reported in this study show that, as opposed to swarm center cells, tendril tip populations of a swarming colony displays general down-regulation of genes associated with virulence and up-regulation of genes involved in energy metabolism.
A number of putative cytoplasmic, inner membrane and periplasmic proteins, as well as proteins from several characterized operons (e.g., ssa, sse, and inv) that contain known virulence genes make up this third category.
Such scenarios may intensify disease impacts on populations, because a diverse parasite community can greatly constrain a host's life history strategies and ultimately fitness by imposing a larger antigenic variation for the host's immune system [21], and perhaps by boosting up virulence as a consequence of within-host competition among closely related parasites [22].
