EFFECT OF VOLUME OF LIQUID ENRICHMENT MEDIUM CONTAINING OXYRASE® ON GROWTH OF CAMPYLOBACTER JEJUNI1

Abstract

The effect of volume of liquid medium (Hunt broth) supplemented with Oxyrase® on growth of Campylobacter jejuni was evaluated by using four sizes of containers and two concentrations of Oxyrase® (0.15 units/mL and 0.6 units/mL). We used 13×100 mm screw-capped tubes containing 1, 3, and 6 mL of medium; 18x150 mm screw-capped tubes containing 1, 5, 10, and 20 mL of medium; 45x45x120 mm bottles containing 25, 50, and 100 mL of medium; and Stomacher® 400 bags containing 250 mL of medium. Counts of four strains of C. jejuni were determined on blood agar plates at 0, 6, 12, 20, and 28 h of incubation. For 13×100 mm tubes, 3 mL of broth resulted the highest bacterial counts with increases of 4–5 log CFU/mL at 12 h and 7–8 log CFU/mL at 20 h. For 18x150 mm tubes, 10 mL and 20 ml of broth both provided increases of 3–4 log CFU/mL and of 6–7 log CFU/mL at 12 h and 20 h, respectively. Increases of 3.5 log CFU/mL at 12 h and of 7–8 log CFU/mL at 20 h were found in bottles containing 100 mL of broth. Overall, 0.15 units/mL Oxyrase® enhanced Campylobacter growth as effectively as 0.6 units/mL in all containers with no significant differences (p>0.05). However, supplementation with 0.6 units/mL of Oxyrase® gave slightly higher bacterial counts than addition of 0.15 units/mL in containers with high ratios of head space volume to medium volume (H:M). Ratios between 1.0 and 3.0 generally gave better results with all strains. The dissolved oxygen levels in each container were lower with high medium volume than with low medium volume. This study positively supported the efficiency of using Oxyrase® for recovery of C. jejuni under normal atmospheric conditions. In addition, various sizes of containers could be used for culturing campylobacters by maintaining the H:M ratio between 1.0 and 3.0.