Mycobacterium avium resists exposure to the acidic conditions of the stomach

• Published in: FEMS microbiology letters Vol. 182; no. 1; pp. 45 - 49
• Main Authors: Bodmer, Thomas, Miltner, Elizabeth, Bermudez, Luiz E.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.2000; Blackwell; Oxford University Press
• Subjects: Acid resistance; Acid tolerance; Acids; Acquired immune deficiency syndrome; Action of physical and chemical agents on bacteria; Adaptation; Adaptation, Physiological; AIDS; AIDS/HIV; Amikacin - pharmacology; Bacteria; Bacterial Proteins - biosynthesis; Bacteriology; Biological and medical sciences; Clinical isolates; Colony Count, Microbial; Culture Media; Exposure; Fundamental and applied biological sciences. Psychology; Gastric Acid; Gastrointestinal system; Gastrointestinal tract; Humans; Hydrogen-Ion Concentration; Microbiology; Mycobacterium avium; Mycobacterium avium Complex - growth & development; Mycobacterium avium Complex - metabolism; Pathogens; pH effects; Protein biosynthesis; Protein synthesis; Saline solutions; Stationary phase; Stomach; Stomach - chemistry; Stomach - microbiology; Virulence; Water; Acid tolerance; AIDS; Sensitivity resistance; Mycobacteriales; Acid-fastness; Mycobacteriaceae; Mycobacterium avium; pH; Bacteria; Environmental factor; Actinomycetes; Acid medium; Survival
• DOI: 10.1111/j.1574-6968.2000.tb08871.x
• ISSN: 0378-1097

Abstract Organisms of the Mycobacterium avium complex are common pathogens in immunosuppressed patients such as individuals with AIDS. There is evidence that in AIDS patients, the main route for M. avium infection is the gastrointestinal tract. The stomach is a formidable barrier to pathogens and the ability to resist exposure to pH lower than 3 has been shown to be a virulence determinant of enteric pathogens. Incubation of three clinical isolates of M. avium under acidic pH revealed resistance of M. avium grown both to the exponential and stationary phase at pH 2.2 for 2 h. Inhibition of protein synthesis had no effect on the acid tolerance. When the duration of the incubation at pH 2.2 was extended to 24 h, bacteria grown to the stationary phase had a significantly greater tolerance to acid than exponential phase bacteria. M. avium incubated with acid in the presence of water was significantly more resistant to pH 2.2 than M. avium in the presence of buffer. Pre-adaptation in water prior to exposure to acidic conditions was also associated with increased resistance to pH 2.2. Isoosmolarity of Hank's balanced salt solution appears to be responsible for the impaired resistance to acid between 2 and 24 h of incubation. These findings indicate that M. avium is naturally tolerant to pH<3 and that pre-adaptation under conditions similar to the conditions where M. avium is found in the environment results in increased acid resistance.