A new serotype of Bacillus thuringiensis from Colombia toxic to mosquito larvae

During a survey conducted in Colombia a new isolate of Bacillus thuringiensis that showed toxicity toward Culex quinquefasciatus, Cx. pipiens, Aedes aegypti, and Anopheles stephensi larvae was isolated. Parasporal crystals were spherical in shape and showed a great degree of similarity with those produced by the reference strain of Bacillus thuringiensis subsp. israelensis. Supernatant fraction of the whole culture was not toxic, and heat-stable exotoxin production was negative. Catalase, urease, arginine dihydrolase, amylase, lecithinase, acetyl-methyl-carbinol, and gelatinase production were positive. Hemolysis on sheep blood agar was alpha-type. The isolate 163-131 showed natural resistance to azolocillin and was sensible to cephoperazone, cephalotin, nalidixic acid, and trimetoprin sulfametoxazole. Flagellar agglutination showed a specific H 30 antigen which allows individualization of this strain as a new serotype and the subspecies name of medellin is proposed.