Effect of osmotic stabilizers on radiometric detection of cell wall-damaged bacteria

The effect of osmotic stabilizers on the 14CO2-dependent radiometric detection of cell wall-damaged Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa was studied in BACTEC 14C-labeled blood culture medium. The organisms were previously exposed to cefamandole or carbenicillin at 63 to 80% of the minimum inhibitory concentrations. The addition of 10% sucrose, 2.2% glycerol, and 2.2% ethylene glycol to the medium failed to reduce the time required for detection and diminished the amounts of 14CO2 released by the growing cultures. Viable counts made after 4 to 7 h of incubation showed a decreased culture density in osmotically stabilized media as compared with saline or Ficoll controls. Sucrose and Ficoll had little or no inhibitory effect on 14CO2 evolution by P. aeruginosa. The osmotic stabilizers tested did not seem to improve the survival of the bacterial inoculum and failed to increase the sensitivity of the radiometric system of detection.