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...
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. 7,10 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), a 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 2 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) a MacConkey agar (supplemented with 1% dextrose) b and a selective Columbia Blood Inhibitory agar. 2 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. a,c,d The plates were streaked for isolation and incubated aerobically at 35 C for 24-48 hours. Bacterial growth was identified by standard methods. 3 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. 4 Microdilution antimicrobial susceptibility testing was accomplished using Ca++-and Mg++-supplemented Mueller-Hinton (MH) broth and a 96-well customized Sensititre microdilution tray. e 5 The antimicrobial agents and concentration ranges (&ml) are listed as follows: ampicillin 0.25-32, trimethoprim/sulfamethoxazole 0.25/4.75-32/608, cephalothin 0.5-64, penicillin 0.125-l6, spectinomycin 0.75-96, sulfachlorpyridazine 12.5-400, sulfadimethoxine 12.5-400, oxytetracycline 0.25-32, tylosin 0.31-40, erythromycin 0.125-16, gentamicin 0.25-16, and kanamycin 0.5-32.Several colonies of P. multocida were picked to trypticase soy broth a and incubated at 35 C to achieve a nephelometer reading (API standardized reader) f of 0.5 (McFarland scale). A 10-µ1 inoculum was then transferred to 10 ml of Ca++ Mg++ supplemented MH broth and mixed. e An au...
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