Oxygen tolerance of fresh clinical anaerobic bacteria

The oxygen tolerance and sensitivity of 57 freshly isolated anaerobic bacteria from clinical specimens was studied. All the organisms tolerated 8 h or more of exposure to oxygen in room air. Growth of the isolates in increasing oxygen concentrations demonstrated that the 57 isolates varied in oxygen sensitivity from strict to aerotolerant anaerobes. Comparison of the oxygen tolerance and sensitivity showed that the most tolerant organisms (best survival after prolonged exposure) included anaerobes capable of growth at only 0.4% or less O2 (strict) as well as those able to grow in as much as 10% O2. The least tolerant were predominately strict anaerobes. Decrease in the inoculum size from a concentration of 10(8) to 10(6) colony-forming units per ml had only a minor effect. The data indicate that the brief oxygen exposure with bench techniques in clinical laboratories would not be deleterious to the anaerobic bacteria present in clinical specimens.