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STUDIES ON THE USE OF AMPICILLIN-DEXTRIN AGAR ASAS AEROMONAS RECOVERY MEDIUM
Citation:
Rodgers, M R., L. Shadix, AND M. A. Feige. STUDIES ON THE USE OF AMPICILLIN-DEXTRIN AGAR ASAS AEROMONAS RECOVERY MEDIUM. Presented at Water Technology Conference, Salt Lake City, UT, November 5-9, 2000.
Impact/Purpose:
Investigate the occurrence of Aeromonas bacteria in potable water derived from both surface and ground water sources. Develop improved method(s) for the detection of culturable H. pylori in environmental samples and investigate the occurrence of H. pylori in potable waters.
Description:
The Contaminant Candidate List (CCL) includes the unregulated chemical and microbiological contaminants the EPA has identified as possibly posing a significant public risk to consumers if present in drinking water (1). There are three bacterial species listed in the CCL (Aeromonas hydrophila, Mycobacterium avium and Helicobacter pylori) and more information is needed on the occurrence of all of these species in drinking water in the U.S. Aeromonas are Gram negative, facultatively anaerobic, rod shaped bacteria in the family Aeromonadaceae, that occur ubiquitously in surface waters. These bacteria are considered to be human pathogens, although there is a disagreement as to the specific spectrum of disease caused by Aeromonas. While there are documented cases of Aeromonas septicemia, it is less clear whether Aeromonas are causative agents of gastroenteritis (2). It is generally agreed upon that of the 15 different recognized groups/species in this genus, only three, A. hydrophila, A. caviae and A. veronii biotype sobria, can be considered to be major human pathogens (2).
Many methods have been published for the recovery of Aeromonas bacteria from environmental waters. Havelaar et.al. developed such a method using ampicillin dextrin agar (ADA), in 1987 and several reports subsequently showed it to be one of the best media for recovery of Aeromonas bacteria (3,4,5). ADA employs both antibiotic, ampicillin, and a detergent, deoxycholate, as selective agents. Most Aeromonas are intrinsically resistant to ampicillin and deoxycholate. This medium also contains dextrin as a fermentable sugar and bromthymol blue as a pH indicator. Since all aeromonads ferment dextrin, producing acid by-products, they appear on ADA as yellow colonies. Other non-dextrin fermenting bacteria appear green or colorless on ADA. ADA is compatible with a membrane filtration procedure, allowing the bacteria from large volumes of water to be concentrated and grown on membrane filters.