Assesssment of sporicidal efficacy

On the basis of their activity against bacterial spores, chemical agents can be divided into two groups: Group A contains chemicals that are bactericidal and sporistatic but not sporicidal, e.g. phenols, cresols, parabens, quaternary ammonium compounds and biguanides; Group B contains those, such as glutaraldehyde, chloride-releasing agents, ethylene oxide and hydrogen peroxide, that show both bactericidal and sporicidal activity, although much higher concentrations may be needed to achieve the latter effect. Sporistatic activity can be examined by various methods, e.g. (i) determining minimum inhibitory concentrations, (ii) detecting by phase-contrast microscopy the concentrations needed to inhibit germination or outgrowth, (iii) measuring spectrophotometrically effects on germination or outgrowth. Information thereby obtained is of considerable importance in food microbiology. Sporicidal efficacy can be tested against spores in liquid medium or suspended on appropriate carriers. Factors influencing activity such as concentration, pH, temperature and the presence of organic matter need to be assessed. The principles of evaluating sporicidal activity are essentially the same as for determining bactericidal activity. The main difference is that a treated spore has to pass through complex stages (germination and outgrowth) before a vegetative cell, and eventually a colony, is produced, if a conventional counting method is employed. It is essential that adequate quenching of residual activity is achieved and that recovery conditions are such as to permit viable but damaged spores the opportunity to revive. A recently developed procedure utilises bioluminescence as a means of determining sporicidal efficacy.