Abstract. The antimicrobial susceptibility of 73 Actinobacillus (Haemophilus) pleuropneumoniae isolates from swine in Missouri was determined with a microdilution minimal inhibitory concentration test system. Serotyping was accomplished by means of co-agglutination. Serotype 1 (39/73) and serotype 5 (30/73) were commonly found, whereas serotype 7 (4/73) was infrequently encountered. Most isolates (MIC,,) were found susceptible to ampicillin (amoxicillin), cephalothin, penicillin, erythromycin, gentamicin, and kanamycin. Marked resistance was found with oxytetracycline, tylosin, and sulfadimethoxine. The data indicate that use of ampicillin (amoxicillin) or penicillin may correlate well with the favorable outcome of treatment.The first case in the United States of Actinobacillus (Haemophilus) pleuropneumoniae was reported in 1963. 9 The microorganism was first named Haemophilus parahemolyticus, then Haemophilus pleuropneumoniae, and now is known as Actinobacillus pleuropneumoniae.9,10 It was first identified by culture in Missouri in 198l. 6 Since then 73 outbreaks have been confirmed by the University of Missouri Veterinary Medical Diagnostic Laboratory (UMC-VMDL), between September 1981 and October 1987. Additional cases may have occurred in the field but were not referred to the UMC-VMDL for diagnosis.Antimicrobial susceptibility tests with A. pleuropneumoniae were first performed using a modification of the standard disk diffusion technique utilizing Eugon chocolatized horse blood agar.l,2,6 However, because the possibility exists that growth inhibition zone sizes may or may not correlate with predicted minimal inhibitory concentration (MIC) values with bacterial isolates of veterinary origin, a microdilution MIC system was utilized. 4 The purpose of this paper is to report the serotypes Presented at the 30th Annual Meeting of the AAVLD, Salt Lake City, UT, October 26-27, 1987.Received for publication October 26, 1987.of and MIC antimicrobial susceptibility data for A.pleuropneumoniae recovered from Missouri swine.
Materials and methods
Bacteriologic culture methods. Actinobacillus pleuropneumoniae was recovered from lungs of pigs referred to theUMC-VMDL by practitioners or recovered from pigs necropsied at the UMC-VMDL from September 1981 to October 1987.Samples were obtained aseptically from affected portions of the lung and inoculated onto 5% defibrinated sheep blood trypticase soy agar (SBA), a brilliant green agar, a MacConkey agar, a and Eugon 10% chocolatized horse blood agar (ECA). a The ECA plate was incubated at 37 C in a humid atmosphere of 95% air-5% CO, for 24-48 hr. All other plates were incubated in a standard incubator at 35 C. A commercial quad plate was used to determine X and V requirements of suspected A. pleuropneumoniae isolates.b Criteria described by Carter were used for final identification, along with serotyping.
3,8Serotyping. A 24-hr growth of A. pleuropneumoniae was recovered from the surface of ECA plates, suspended in 0.3% formalinized saline, and serotyped c using a co-agglutin...