The cytochrome bd-I respiratory oxidase augments survival of multidrug-resistant Escherichia coli during infection

Abstract

Nitric oxide (NO) is a toxic free radical produced by neutrophils and macrophages in response to infection. Uropathogenic Escherichia coli (UPEC) induces a variety of defence mechanisms in response to NO, including direct NO detoxification (Hmp, NorVW, NrfA), iron-sulphur cluster repair (YtfE), and the expression of the NO-tolerant cytochrome bd-I respiratory oxidase (CydAB). The current study quantifies the relative contribution of these systems to UPEC growth and survival during infection. Loss of the flavohemoglobin Hmp and cytochrome bd-I elicit the greatest sensitivity to NO-mediated growth inhibition, whereas all but the periplasmic nitrite reductase NrfA provide protection against neutrophil killing and promote survival within activated macrophages. Intriguingly, the cytochrome bd-I respiratory oxidase was the only system that augmented UPEC survival in a mouse model after 2 days, suggesting that maintaining aerobic respiration under conditions of nitrosative stress is a key factor for host colonisation. These findings suggest that while UPEC have acquired a host of specialized mechanisms to evade nitrosative stresses, the cytochrome bd-I respiratory oxidase is the main contributor to NO tolerance and host colonisation under microaerobic conditions. This respiratory complex is therefore of major importance for the accumulation of high bacterial loads during infection of the urinary tract.

Iron-sulfur cluster repair contributes to Y. pseudotuberculosis survival within deep tissues

“…Similarly, despite the lowered fitness of the Δ hmp Δ ytfE strain in spleens relative to Δ hmp , the Δ hmp Δ ytfE strain was not significantly more sensitive than the Δ hmp mutant strain to the presence of acidified nitrite during growth in culture (Figure 5A; compare +NO 2 samples). This is consistent with previous reports in other organisms (36, 37), perhaps due to the presence of other backup repair pathways that are active in the absence of Hmp or because YftE plays a role in protection from other stress species.…”

“…The absence of ytfE also did not significantly alter the sensitivity of strains to the NO donor compound, DETANONOate, during growth in minimal media (Figure 4B). This is consistent with previous reports in other organisms (38, 39), perhaps due to the presence of other backup repair pathways that are active in the absence of Hmp or because YtfE plays a role in protection from other stress species.…”

“…NO alone was not sufficient to limit the growth of Δ ytfE bacteria in bacteriological media, consistent with previous studies that indicated the uropathogenic E. coli (UPEC) Δ ytfE strain had reduced intracellular survival within host cells, but was not sensitive to exogenous NO alone (39). Presumably, the Δ ytfE strain is sensitive to other antimicrobial compounds generated within host tissues, possibly by the generation of a variety of reactive nitrogen species (RNS) as a consequence of NO reaction with reactive oxygen species (ROS) or other compounds.…”

Metal homeostasis and resistance in bacteria

“…Genetic evidence from E. coli 116 , S. coelicolor 117 , and B. subtilis 119 suggests specific inhibition of the major aerobic cytochrome oxidase as bacteria upregulate the relatively Zn(II)-insensitive cytochrome bd quinol oxidase under conditions of Zn(II) intoxication conditions. This may be of particular importance for host-pathogen interactions because induction of the cytochrome bd system also confers tolerance to nitric oxide 120,121 and hydrogen sulfide 122 , which can be abundant in the host environment.…”

Invasion of Host Cells and Tissues by Uropathogenic Bacteria

“…The altered morphology and surface characteristics of filamentous UPEC forms render these bacteria resistant to phagocytosis by neutrophils (23, 157). However, even if phagocytosis cannot be avoided, some UPEC strains can survive for some time within the phagosomal compartments of neutrophils and macrophages (61, 158–160). Transcriptional profiling recently identified 22 bacterial genes that seem to promote UPEC survival within macrophages (161).…”