Identification of Mycobacterium avium subsp. hominissuis Isolated fromDrinking Water and Food

摘要

Mycobacterium avium (MA) is divided into four subspecies based primarily onhost-range and consists of MA subsp. avium (birds), MA subsp. silvaticum (woodpigeons), MA subsp. paratuberculosis (broad, poorly-defined host range), and therecently described MA subsp. hominissuis (humans and swine). MA is ubiquitous in theenvironment and evidence suggests water is a possible source of human exposure.Routes of exposure to waterborne pathogens include ingestion, inhalation of water vapor,and ingestion of produce irrigated or washed with contaminated water. The goal of thisstudy was to determine the specificity of MA subsp. hominissuis to humans bysubspeciating human clinical isolates of MA, and also to determine the proportion of MAisolated from food and water that belongs to this subspecies. Understanding theoccurrence of MA subsp. hominissuis in water and food will aid the U.S. EnvironmentalProtection Agency in assessing the risk of human exposure to these sources.Temperature growth range, IS1245 copy number, sequencing of the 16S-23S internaltranscribed spacer region or hsp65 gene and other methods have been used todifferentiate subspecies hominissuis from the other subspecies. MA subsp. hominissuiscan grow on Lownestein Jensen (LJ) medium supplemented with pyruvate at 45 °Cwhilebird type isolates cannot (Mijs et al., 2002). Clinical and environmental MA isolatesfrom our collection were inoculated on this medium and allowed to incubate for up to 90days. Ninety percent of the isolates grew at 25 °C and 67% grew at 45 °C. Isolates thatgrew at 45 °C also grew at 25 °C. Nearly 100% of the human isolates included in thisstudy grew at 45 °C, suggesting they are strains of MA subsp. hominissuis. In addition,we performed PCR and sequence analysis on the 3′ end of the hsp65 gene as a means toconfirm MA subsp. hominissuis identification. Human isolates had hsp65 sequencesclosely related to hsp65 sequences from MA subspecies hominissuis describedpreviously. Moreover, several hsp65 sequences from environmental isolates wereidentical or very closely related to those of hominissuis. None of the human orenvironmental isolates in our study had hsp65 sequences that clustered with MA subsp.avium or paratuberculosis. These data suggest that the type of MA that is specific tohumans may be more prevalent in the environment than was previously thought.