Reactive oxygen species generated by the phagocyte NADPH oxidase have an essential role in the control of B. pseudomallei infection

in C57BL/6 bone marrow derived macrophages [16]. Type I of all 5 B. pseudomallei isolates tested here had the greatest resistance to H2O2, followed by types II and III, respectively, suggesting that type I has the greatest potential to scavenge or degrade H2O2 molecules. This may explain the finding that type I had the highest replication after uptake by the macrophage cell line. Type III switched to type I or II during culture in medium containing H2O2, indicated that type III had a survival disadvantage under such conditions that required switching to a more H2O2 resistant type. One of the mechanisms by which B. pseudomallei escapes macrophage killing is by repressing inducible nitric Dabrafenib clinical trial oxide synthase (iNOS) by activating the expression of two negative regulators, a suppressor of cytokine signaling 3(SOC3) and cytokione-inducible src homology2-containing protein (CIS) [17]. It is unknown whether there are variation between strains and isogenic morphotypes in the ability to interfere with iNOS induction. However, colony morphology differences did not influence resistance to RNI. B.

pseudomallei is protected Deforolimus solubility dmso from RNI by the production of alkyl hydroperoxide reductase (AhpC) protein and depends on OxyR regulator and a compensatory KatG expression [18]. These mechanisms may not be associated with colony morphology variability. B. pseudomallei survive in the phagolysosome [10] which are acidified environments containing lysozymes, proteins and antimicrobial peptides that destroy pathogen. There was no difference in growth for the 3 isogenic morphotypes of B. pseudomallei

derived from all five isolates at all pH levels tested above 4.0, but a pH of 4.0 was universally bactericidal, suggesting that morphotype switching did not provide a survival advantage against acid conditions. All morphotypes of B. pseudomallei were highly resistance to lysozyme and lactoferrin. Lysozyme functions to dissolve cell walls of bacteria. Lactoferrin is a competitor that works by binding iron and preventing uptake by the bacteria. Common Tolmetin structures for resistance to these factors such as capsule and LPS [8] were present in all isogenic morphotypes [11]. An alternative explanation is that B. pseudomallei may produce a morphotype-independent lysozyme inhibitor that counteracts the action of lysozyme and lactoferrin. Antimicrobial peptides are efficient at killing a broad range of organisms. They are distributed in variety tissues, and in neutrophils and macrophages [12, 13]. All 3 isogenic B. pseudomallei morphotypes were resistant to α-defensin HNP-1 and β-defensin HBD-2, but were susceptible to LL-37. In contrast to sensitivity to H2O2, type III was more resistant than type I or II to LL-37.