Enterobacter cloacae on various media was compared after disinfection. This was done to examine the effects of monochloramine and chlorine on the enumeration of coliforms. The media used were TLY (nonselective; 5.5% tryptic soy broth, 0.3% yeast extract, 1.0% lactose, and 1.5% Bacto-Agar), m-T7 (selective; developed to recover injured coliforms), m-Endo (selective; contains sodium sulfite), TLYS (TLY with sodium sulfite), and m-T7S (m-T7 with sodium sulfite). Sodium sulfite in any medium improved the recovery of chloramine-treated E. cloacae. However, sodium sulfite in TLYS and m-T7S did not significantly improve the detection of chlorine-treated E. cloacae, and m-Endo was the least effective medium for recovering chlorinated bacteria. Differences in recovery of chlorineand chloramine-treated E. cloacae are consistent with mechanistic differences between the disinfectants.

A Pseudomonas cepacia population was isolated which had reduced susceptibility to iodine and maintained resistance when subcultured several times in phosphate buffer. This population was also resistant to iodine after growth in a minimal medium containing glycerol but not glucose. Addition of cAMP to glucose-grown cells caused increased resistance to iodine. Iodine-resistant cultures also demonstrated reduced susceptibility to chlorination but not to heat or metals (Cu/Ag). The results indicate that halogen resistance can be expressed in varying degrees, dependent on the carbon source, and cAMP may promote this expression. Thus, a catabolite repression-like mechanism may cause resistant cultures grown in some media to become more sensitive to halogens.

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