Effects of storage in an anaerobic transport system on bacteria in known polymicrobial mixtures and in clinical specimens

Abstract

An anaerobic transport system (ATS) which provides for catalytic removal of oxygen was evaluated by using in vitro-prepared polymicrobial mixtures of logphase bacteria and clinical specimens. Inoculated swabs were stored at room temperature in (i) aerobic, (ii) anaerobic glove box, and (iii) ATS environments, and bacteria were quantitated after 2, 24, 48, and 72 h. Bacteria in a three-part mixture of Bacteroides fragilis, Peptostreptococcus anaerobius, and Escherichia coli and in a five-part mixture of B. fragilis, P. anaerobius, Fusobacterium nucleatum, Staphylococcus epidermidis, and Pseudomonas aeruginosa survived 72 h of storage in the ATS and anaerobic glove box environments, but the anaerobic species were inactivated in the aerobic storage except for B. fragilis in pure culture or in the three-part mixture. Changes in relative proportions among the species in a mixture were least in the ATS and anaerobic glove box environments and greatest during the aerobic storage, particularly in the five-part mixture. Bacteria present in pure or mixed culture in clinical specimens generally survived 72 h of storage in the ATS. These data indicate that changes in relative proportions occur with prolonged storage even under anaerobic conditions, but that the ATS would be most effective for preserving anaerobic bacteria and preventing drastic concentration changes and overgrowth of facultative and aerobic bacteria.