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Screening of Disinfectants Against Bacillus Thuringiensis Var. Kurstaki

A.Nahar
Bangladesh Sericulture Research and training Institute (BSRTI), Rajshahi.

T.O Sashidharan
Central Sericulture Research & Training Institute (CSRTI), Mysore.

M.A.Rashid
Bangladesh Sericulture Board.

Abstract/ Executive Summary:

Disinfectants act differently on micro¬organisms bringing about destruction of cells. Since the time of Pasteur, the methods of testing disinfectants have evolved along two parallel and complementary lines: developments of in vitro tests (specific activity of the product) and development of methods that simulate in the laboratory conditions of practical use. The Rideal Walker test stipulates the efficacy of a disinfectant to be evaluated in relation to that of phenol and thus the phenol coefficient of the tested product is determined (Block, 1983). The culture of Bacillus thuringiensis was maintained on nutrient agar by periodical sub culturing. Sterilized molten nutrient agar medium was seeded with the bacterial spores. Out of the ten disinfectants tested, formalin (3%) was found to be most effective against Bacillus thuringiensis var. Kurstaki followed by Paraformaldehyde (3%), Asiphor and steridol (both lodophores) were found to be only moderately effective even at 3% concentration.

Keywords: Bacillus thuringiensis var. Kurstaki, Screening, Disinfectant

Location: Bangladesh Sericulture Research and Training Institute

Start Date:

End Date:

Program Area: Pest Management

Commodity: Diseases

Objectives:

To see 10( Ten) different disinfectant’s bactericidal effectiveness against Bacillus thuringiensis var. in virto culture.

Methodology:

In the case of Bacillus thuringiensis infections, certain chemicals are reported to destroy the toxin produced by the organism. Detoxification of crystal toxin of Bacillus thuringiensis strains has been reported by Barjac et. al. (1968). Disinfactants like sodium hypochlorite have been reported to influence the infectivity of several Bacillus Sp. (Ignoffo and Dutky, 1963). Nakajima (1939) studied the effect of feeding certain chemicals along with leaves and reported prevention of flacherie disease. Several workers have attempted enrichment of mulberry leaves with small quantities of different antibiotics to improve rearing and prevent incidence of flacherie (Murthy et al. 1951; Sharada and Bhat, 1956; Shyamala et al. 1962; Verma and Atwal, 1963 and Radha et al. 1981). In the present study, ten disinfectants were used to see their bactericidal effectiveness against Bacillus thuringiensis var. Kurstaki, in virto culture. The culture of Bacillus thuringiensis was maintained on nutrient agar by periodical sub culturing. Sterilized molten nutrient agar medium was seeded with the bacterial spores. The seeded medium was poured into petri-dishes. After solidifying, small filter paper disc (8 mm diameter), cut and prepared from Whatman No. 1 filter paper were dipped in different concentrations of the disinfectants to be tested (detail indicated below) and placed on the seeded media of the petri-dishes. The inhibition zones formed with these disinfectants were measured to assess the degree of efficacy of the disinfectants. The measurements were taken after 24 hours and 48 hours of placing the discs. The plates were incubated at room temperature during this period.

Source of Information: Bulletin of Sericulture Research. 2000-2004 Vol.11: 99-101 published by Bangladesh Sericulture Research and Training Institute.

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Out of the 10 ten disinfectants tested, formalin (3%) was found to be most effective against Bacillus thuringiensis var. Kurstaki followed by Paraformaldehyde (3%), Asiphor and steridol (both lodophores) were found to be only moderately effective even at 3% concentration. They were not effective below 2% concentration, lodophors are lose complexes of elemental iodine or triodide with a carrier that serves not only to increase the solubility of the iodine but also provide a sustained release reservoir of iodine. Germfree which is a quaternary ammonium compound, was not found to be effective against the bacterium even at 3% concentration. Samson (1987) also observed that formalin was best effective against two isolates of Bacillus thuringiensis viz, B.t. var. thuringiensis and B.t. var. dendrolimus. He reported that disinfectants like sodium hypochlorite was ineffective against these two strains of B.t. even at a concentration of 4% phenol. Lime and Captaf were also not effective against B.t. var. Kurstaki when tested at 1%, 2% or 3% concentration. Aldepol which is a Benzalkonium chloride Gluteraldehyde compound, however, was observed to be moderately effective against B.t. var. kurstaki. Gluteraldehyde has a broad spectrum of activity and rapid rate of killing. Borick (1968) reported that vegetative bacteria, including the more resistant species, are destroyed within 1 minute and most viruses within 10 minutes and bacterial spores within 3 hours by Gluteraldehyde. Benzalkonium chloride is a quaternary ammonium salt which also has been reported to inhibit bacterial strains like Siaphylococcus aureuss and Pseudomonas aeruginosa (Hugbo, 1976).

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