Microbicidal activity of monochloramine and chloramine T compared

SummaryChloramine T (CAT) and monochloramine (NH2Cl) are active chlorine compounds and well-known biocides. CAT has stronger oxidative activity than NH2Cl, which is a smaller, more lipophilic molecule. The question arises whether lower oxidative activity can be compensated by higher lipophilicity. To address this problem, we investigated the bactericidal and fungicidal activity of pure NH2Cl compared to CAT. Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillus fumigatus, A. flavus, and Candida albicans were subjected to quantitative killing assays at 20 °C and pH 7.1 in equimolar solutions of CAT or NH2Cl. NH2Cl was superior to CAT against all test strains at all test concentrations. At a concentration of 0.036 mM, NH2Cl reduced the count of E. coli (S. aureus) by 3 log10 within 1 min (5 min), whereas CAT needed 120 min (30 min) for the same effect. At 0.107 mM NH2Cl, a 3 log10 reduction of P. aeruginosa was achieved after 5 min compared to 20 min using CAT. NH2Cl (0.355 mM) caused a 2 log10 reduction of C. albicans within 30 s, whereas 60 min were necessary for the same reduction with 0.355 mM CAT. The difference between the antiseptics was even more pronounced when tested on aspergilli. NH2Cl had a significantly stronger bactericidal and fungicidal activity than CAT despite its lower oxidative activity. This phenomenon can be attributed to its lipophilicity and smaller bulk, and it should be taken into account when developing and using chloramine antiseptics.