Observed Differences in Virulence-Associated Phenotypes between a Human Clinical Isolate and a Veterinary Isolate ofMycobacterium avium

Abstract

Mycobacterium avium, the most common opportunistic pathogen in patients with AIDS, is frequently isolated from a variety of environmental sources, but rarely can these environmental isolates be epidemiologically linked with isolates known to cause human disease. Using a number of in vitro tissue culture assays, we found significant pathogenic differences between a serotype 4 human clinicalM. avium isolate and a serotype 2 veterinary isolate. Cell association of the patient strain with a human intestinal cell line was 1.7 times that of the veterinary strain. Growth of this clinical strain in human peripheral blood mononuclear cell-derived macrophages increased from 12-fold higher than that of the veterinary isolate after 2 days to 200-fold higher after 4 days. By the conclusion of each experiment, lysis of all examined host cell types and accumulation of cell debris were observed in infections with the human isolate, but monolayers remained relatively intact in the presence of the animal isolate. The two strains also differed in the ability to stimulate human immunodeficiency virus replication in coinfected host cells, with p24 antigen levels after 6 days threefold higher in the cells coinfected with the clinical strain than in those infected with the veterinary strain. If the genetic differences responsible for the phenotypes observed in these assays can be identified and characterized, it may be possible to determine which M. avium strains in the environment are potential human pathogens.

Genetic variation/evolution and differential host responses resulting from in-patient adaptation ofMycobacterium avium

“…We tested intracellular growth within murine macrophages and observed that though all isolates managed to survive within the macrophage, the last isolates collected from two patients (9 and 13) survived better than initial isolates from the same patient. This increased survival of certain isolates could either be due to their increased multiplication rate or impaired ability of the macrophages to eradicate the bug (5, 24, 43, 44). In our experiments, we measured reduced levels of pro-inflammatory cytokines like IL-6 and IL-1β when macrophages were infected with later isolates compared to the initial isolate from a patient.…”

Involvement of the autophagy pathway in trafficking ofMycobacterium tuberculosisbacilli through cultured human type II epithelial cells

“…Although much research has been devoted to examining M. tuberculosis interaction with phagocytic cells, some recent studies have focused on the type II pneumocytes and how they might contribute to the pathogenesis associated with M. tuberculosis respiratory infections (McDonough and Kress, ; Birkness et al ., ,b; Wickremasinghe et al ., ; Debbabi et al ., ). Several investigators have shown that internalization of mycobacteria in human A549 cells and murine primary lung epithelial cells is mediated by actin‐dependent mechanisms (Bermudez and Goodman, ; Kumari and Saxena, ).…”

An in vitro model of the leukocyte interactions associated with granuloma formation in Mycobacterium tuberculosis infection

“…Cultures were adjusted to an OD 600 of 0.5 (∼10 7 CFU/ml) and stored at −70°C.Bacteria were plated for viable counts on Middlebrook 7H10 agar (BBL, Cockeysville, MD, USA). M. avium serotype 4, strain PL47, a human clinical isolate from an AIDS patient, 33 was grown in Middlebrook 7H9 broth supplemented with albumin, dextrose, catalase and 0.2% glycerol. Stock cultures were stored at −70°C in growth medium plus 20% glycerol.…”

“…Cultures were adjusted to an OD 600 of 0.5 (B10 7 CFU/ml) and stored at À701C.Bacteria were plated for viable counts on Middlebrook 7H10 agar (BBL, Cockeysville, MD, USA). M. avium serotype 4, strain PL47, a human clinical isolate from an AIDS patient, 33…”