3.6.2. Determination of antibiotic susceptibility testing by the disc diffusion method

The disc diffusion method of antibiotic susceptibility testing is the most practical method for determining antibiotic susceptibility/resistance of microorganisms to different antimicrobial agents. The accuracy and reproducibility of this test are dependent on maintaining standard procedures. As there are no CLSI (formerly NCCLS) (www.clsi.org) nor EUCAST (www.eucast.org) recommendations for the determination of susceptibility/resistance of P. larvae by the disc diffusion method, a method developed for this species is described below.

For determining tetracycline resistance, the agar diffusion procedure can be employed, using MYPGP agar (see section 3.1. for recipe) and 5 µg tetracycline discs (OxoidÒ or BBLÒ). The discs can also be prepared in the laboratory by using S & SÒ or similar sterile discs (6 mm in diameter) impregnated with 5 µg tetracycline per disc. Determination of resistance/susceptibility