Chlorine covers on living bacteria: the initial step in antimicrobial action of active chlorine compounds.
OBJECTIVE
Although active chlorine compounds are well-known antimicrobial agents in human medicine, their initial steps of action have not been completely clarified. Using N-chlorotaurine (NCT), an endogenous mild representative, we observed persisting oxidation capacity affixed to bacteria. It was the aim of this study to investigate this 'chlorine cover'.


METHODS
Pathogens were incubated in NCT, which was subsequently washed off. The oxidation capacity on the bacterial surface was measured photometrically.


RESULTS
Superficial chlorination in the form of covalent N-Cl bonds to Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa and Candida albicans could be attached before killing took place. For S. aureus, 3 min incubation with NCT produced a cover of 3.3 x 10(-16) mol Cl(+)/cfu, while the cfu count was reduced by only 26%. The kind of microorganism, coating time, pH, buffer system and, basically, the chlorine compound, influenced the cover strength. The relative cover strength on S. aureus by NCT, chloramine T, sodium dichloro-isocyanurate or N,N-dichlorotaurine was 1:15.7:38.7:0.24. Chlorine covers were surprisingly stable and could be detected for 3 h at 20 degrees C (>8 h at 1 degrees C), even without a reduction of cfu. However, addition of 5% ammonium chloride caused a rapid loss of viability, explained by formation of highly bactericidal NH(2)Cl, an effect that resembles the ignition of a time-bomb.


CONCLUSIONS
The chlorine cover can be regarded as the first sign of interaction between chlorinating agent and microorganism, and may explain the non-lethal features of postantibiotic effect and attenuation of bacterial virulence. Furthermore, it may be a decisive step in bacterial inactivation by the myeloperoxidase-hypochlorite system in innate immunity.
Gottardi
Waldemar
W
Department of Hygiene, Microbiology and Social Medicine, Division of Hygiene and Medical Microbiology, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria. waldemar.gottardi@uibk.ac.at
Nagl
Markus
M
D001419:Bacteria / Q000187:drug effects*; D002700:Chloramines / Q000494:pharmacology; D002713:Chlorine; D017606:Chlorine Compounds / Q000737:chemistry / Q000494:pharmacology*; D004202:Disinfectants / Q000737:chemistry / Q000494:pharmacology*; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013499:Surface Properties; D013654:Taurine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors; D014105:Tosyl Compounds / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology
D002700:Chloramines; D017606:Chlorine Compounds; D004202:Disinfectants; D014105:Tosyl Compounds; D014227:Triazines; C016300:chloramine-T; D013654:Taurine; D002713:Chlorine; C043410:N-chlorotaurine; C011765:troclosene