Antimicrobial Susceptibility of Pasteurella Multocida Type D from Missouri Swine

Abstract

Atrophic rhinitis (AR) is a significant disease and management problem to swine producers worldwide. 1,9 For some time, Bordetella bronchiseptica was considered to be the primary etiologic agent of AR. However, current evidence indicates that toxigenic strains of Pasteurella multocida type D may also play a role in this disease process. 1,9 Pasteurella multocida type D is a fastidious microorganism, and often, when taken from turbinates, it will not initially grow on standard blood agar (trypticase soy with 5% defibrinated sheep blood), thus requiring mouse inoculation to recover the isolate. Because Bordetella bronchiseptica is readily recovered from swine with AR and P. multocida is not, the role of P. multocida has not been fully appreciated. The use of a selective medium has greatly enhanced the recovery of P. multocida type D from nasal turbinates without the necessity of mouse inoculation. The purpose of this paper is to report the antimicrobial susceptibility of P. multocida type D from Missouri swine as determined by a microdilution test procedure+ Pasteurella multocida type D was isolated from the nasal turbinates of pigs referred to the University of Missouri Veterinary Medical Diagnostic Laboratory from November 1986 to April 1988. Samples were obtained aseptically from affected portions of the turbinates after sectioning of the snouts. Swabs were inoculated to SBA (trypticase soy agar-5% defribrinated sheep blood) MacConkey agar (supplemented with 1% dextrose) and a selective Columbia Blood Inhibitory agar. Briefly, the medium was prepared with Columbia blood agar base supplemented with 5% defibrinated sheep blood, and it contained a final concentration of 2 μg/ml neomycin and 3.5 μg/ ml of bacitracin. The plates were streaked for isolation and incubated aerobically at 35 C for 24-48 hours. Bacterial growth was identified by standard methods. Pasteurella multocida type D was determined by cross-streaking the subcultured isolate on fresh trypticase soy blood agar with Staphylococcus aureus and observing for the presence or absence of capsule formation. Isolates resistant to hyaluronidase activity of the S. aureus were classified as P. multocida type D. Microdilution antimicrobial susceptibility testing was accomplished using Ca++and Mg++-supplemented Mueller-Hinton (MH) broth and a 96-well customized Sensititre