J Clin Pathol 1983;36:591-594 A selective medium for Pasteurella multocida and its use with animal and human specimens

tellurite and amphotericin B in 5 % horse-blood agar, allowed unimpaired growth of almost all strains of Pasteurella multocida, and P pneumotropica, while inhibiting other bacteria that might be encountered in upper respiratory tract secretions. With its use, P multocida was readily detected in oral swabs from four of 23 dogs, and 10 of 25 cats, but not detected in oral swabs from 47 human subjects. One of 500 sputum specimens yielded P pneumotropica. Pasteurella multocida is a common commensal of the upper respiratory tracts of domestic and other ani-mals, and also causes disease in many species.I4 It is encountered clinically in man mainly as a cause of acute inflammation in bites and scratches from dogs, cats and other animals,56 and it is also sometimes found as the predominant micro-organism in acute chest infections.7 Many of these cases have no known animal association8 and it has been suggested that there may be long-term carriage by humans. Isolation of P multocida from human respirat6ry tract secretions may be difficult because of over-growth by other bacteria, and because the prevalent Haemophilus strains may readily be confused with pasteurellae. In this investigation, we set out to devise and assess a selective medium which would be effective for such specimens. Material and methods Antibiotics and chemicals that showed differential activity against P multocida strains and other bac-teria commonly encountered in respiratory speci-mens were used alone and in combination in a base of heart infusion agar (Difco) with and without 5% defibrinated horse blood. The media were first tested by streaked inocula of the Pasteurella strain