Oxygen status of lung granulomas in Mycobacterium tuberculosis‐infected mice

Abstract

It is often assumed that Mycobacterium tuberculosis (Mtb)-induced granulomatous lesions, particularly those undergoing central caseation, are anoxic, and that the survival of Mtb in these lesions requires the integrity of its non-oxidative respiratory pathways. Using the hypoxia marker pimonidazole, we now provide immunohistochemical evidence that in the most frequently used animal model system of inbred mice Mtb-induced granulomas, even after more than one year of aerogenic infection, are not severely hypoxic. In contrast, chronic aerosol infection with M. avium strain TMC724 was associated with hypoxia surrounding necrotizing granuloma centres. Direct measurements of oxygen tension with a flexible microelectrode in mouse lungs chronically infected with Mtb disclosed a wide range of oxygen partial pressures in different parts of the lungs which, however, rarely approached the anoxic conditions consistently found in necrotizing tumours. We further show that an Mtb mutant, defective in nitrate reductase (narG) necessary for survival under anaerobic conditions in vitro, can persist in the lungs of chronically infected mice to a similar extent as wild-type Mtb. These findings have important implications for the use of the mouse model of Mtb infection in developing eradication chemotherapy and for evaluating putative mechanisms of chronic persistence and latency of Mtb.

Multifunctional essentiality of succinate metabolism in adaptation to hypoxia in Mycobacterium tuberculosis

“…However, growing evidence has revealed that the extent of hypoxia associated within a given host varies widely based on the size, location, and composition of the microenvironment (31)(32)(33). Our studies modeled quiescent M. tuberculosis using an O 2 environment of 1%, but the metabolic principle revealed may have broader significance, namely, the ability of succinate to serve as a biochemical bridge between oxidative and fermentative metabolic states.…”

Nitrite produced byMycobacterium tuberculosisin human macrophages in physiologic oxygen impacts bacterial ATP consumption and gene expression

“…To determine whether Mtb might be the source, we infected macrophages with a strain of Mtb lacking narG. The mutant strain grows normally in aerobic culture and is as virulent as WT Mtb in mice (17,19) but cannot respire nitrate. Macrophage cultures infected with ΔnarG Mtb accumulated no nitrite, whereas infection with a mutant strain complemented with the WT narG allele led to accumulation of as much nitrite as infection with WT Mtb (Fig.…”

“…In the host, Mtb is thought to survive over decades in hypoxic sites (17,18). When oxygen is scarce, Mtb reduces nitrate (NO 3 − ) to nitrite (NO 2 − ) as a means to maintain redox homeostasis and energy production (19).…”

The Pathology ofMycobacterium tuberculosisInfection

“…138 The caseum is predominantly composed of host-derived lipids, and a recent analysis of gene regulation in the immediately surrounding cells shows Mtb-driven dysregulation of host lipid metabolism. 117 The granuloma environment is considered hypoxic in guinea pigs, rabbits, nonhuman primates, and human beings, 5,213 which is an important consideration for mycobacterial metabolism and antibiotic therapy efficacy. It was previously believed that Mtb were sparse in the caseum, based on Ziehl-Neelsen acid-fast staining, with most of the detectable bacilli persisting at the periphery.…”