Glutaraldehyde sporicidal activity

A number of aldehydes possess antimicrobial properties, including sporicidal activity however, only two, formaldehyde and glutaraldehyde, are used for disinfection. Both these aldehydes are highly effective biocides and their use as chemosterilants reflect this. 

The degree of ionization of acidic and basic antimicrobial agents depends on pH. Some compounds are active only in the unionized state (e.g., phenolics) whereas others are preferentially active as either the anion or cation. It therefore follows that the activity of a particular concentration of an agent will be enhanced at a pH that favors the formation of the active species. Thus, cationic antibacterials such as acridines and quaternary ammonium compounds are more active under alkaline conditions. Conversely, phenols and benzoic acid are more active in an acid medium. Chlorbutol is less active above pH 5 and unstable above pH 6. Phenylmercuric nitrate is only active at above pH 6 whereas thiomersal is more active under acid conditions. The sporicidal activity of glutaraldehyde is considerably enhanced under alkaline conditions whereas hypochlorites are virtually ineffective at above pH 8. 

In the liquid phase, time-survival curves of bacterial spores treated with formaldehyde have been reported to show initial shoulders, irrespective of whether aqueous or alcoholic solutions are used [62, 74], although this phenomenon has not been observed by other workers [75]. Various alcohols have also been shown to reduce the sporicidal activity of glutaraldehyde [62, 63]. 

Theis and Leder (1993) demonstrated in aerobic biofilm experiments with an oil field isolate of aerobic bacteria, containing predominantly Pseudomonas species, that OPA is more effective than formaldehyde (FA, 2.1a.) or glutaraldehyde (GA, 2.5.) in killing or inhibiting the growth of sessile microorganisms (see Table 16). OPA is effective without activation and is able to inactivate GA-restistant strains of Mycobacterium chelonae. On the other hand OPA unlike GA acts not sporicidal at its in-use concentration of 0.5% (w/v) and normal pH (6.5.). 

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