A 16S rRNA gene oligonucleotide probe for identification of Bacillus thuringiensis isolates from sheep fleece

Larvae of the Australian sheep blowfly Lucilia cuprina are susceptible to some strains of Bacillus thuringiensis, including some isolates from sheep fleeces from South Australia and Western Australia. Larvicidal strains of B. thuringiensis include var. thuringiensis, tolworthi, darmstadiensis, morrisoni, and toumanoffi. As part of an ecological study, a large number of B. thuringiensis fleece isolates from untreated sheep and sheep previously treated with larvicidal B. thuringiensis were screened for larvicidal activity. A ribotyping method to distinguish larvicidal B. thuringiensis jetted (sprayed) onto sheep from the natural B. thuringiensis flora of the fleece was developed. A cloned fragment of the 16S rRNA gene used as a probe for B. thuringiensis DNA digested with restriction endonucleases enables separation of B. thuringiensis serovars and separation within the serovars thuringiensis, tolworthi, and kurstaki. The 16S gene probe method is useful for distinguishing between reisolates of larvicidal B. thuringiensis jetted onto sheep and the background B. thuringiensis population present prior to jetting.