Date of Award
Master of Science
Veterinary Microbiology and Preventive Medicine
Swine mycoplasmas are a common contributor to economic losses and adverse health in the pig industry (Sibila, 2009). Although several swine–specific mycoplasmas exist, only four are currently considered pathogenic. Mycoplasma hyosynoviae, Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, and Mycoplasma suis are among the species that impact pigs clinically. This thesis will focus on M. hyosynoviae and M. hyopneumoniae, specifically. Although not understood to initiate disease alone, when combined with a primary viral or bacterial infection, both species trigger serious clinical disease in herds worldwide (Thacker, 2012).
Mycoplasma hyosynoviae is a common cause of clinical arthritis in growing pigs. Carried in the tonsils, a stress event typically facilitates the systemic spread of the organism to the joints, with a predisposition for the stifle(s). Once in the joints, M. hyosynoviae is capable of causing a painful arthritis inducing anorexia-driven weight loss. Although antibiotic therapies are consistently used to treat mycoplasma–induced arthritis, both MICs and breakpoints for these antibiotics have not yet been established due to the fastidious nature of Mycoplasma hyosynoviae. Instituting breakpoint values for any bacteria requires a large number of isolates and subsequent in vitro MIC testing, neither of which has been performed due to the burdensome MIC testing techniques available (Turnridge, 2007). Judicious use of antibiotics continues to be a major concern in food–producing animals, and the push for rational drug use begins with in vitro antibiotic sensitivity testing. Although several methodologies exist for determining antimycoplasmal activity of antibiotics, most diagnostic laboratories do not offer sensitivity testing of mycoplasma isolates. However, a more user–friendly, reproducible procedure was adapted from a previous study concerning Mycoplasma hyopneumoniae minimum inhibitory concentrations (Tanner, 1993). Both Tanner's research and the original work presented in this thesis utilized a commercially–available product that allowed for a large number of isolates to be tested, with minimal preparation, yielding reportable results in less than one week.
Mycoplasma hyopneumoniae is a common component of the Porcine Respiratory Disease Complex and the etiologic agent of enzootic pneumonia in pigs. Although several intervention strategies are available, the pork industry still struggles with economic loss and decreased animal welfare due to the disease. Previous research has optimized both sample techniques and detection methods for Mycoplasma hyopneumoniae, however, the combination has not been utilized to assess herd prevalence of M. hyopneumoniae in the United States. Therefore, the prevalence of M. hyopneumoniae in the weaned pig population from four sow farms across Iowa was measured utilizing a novel tracheobronchial mucous collection technique and real–time polymerase chain reaction.
The two capabilities of antemortem isolation of mycoplasmas and determination of in vitro antimicrobial susceptibility provide the necessary tools for development of clinical–breakpoints for pathogenic mycoplasma. Breakpoint values are established by correlating the clinical outcome of a disease process after administration of a specific drug concentration. Depending on resolution of clinical signs, the isolate is interpreted as susceptible, intermediate, or resistant. The interpretive criteria allow for swine practitioners to make well–informed decisions on antimicrobial therapy specific for that isolate. The work reported here demonstrates that the potential for antemortem isolation of M. hyopneumoniae is improved with the use of tracheobronchial mucous collection. Combining this method with antibiotic susceptibility testing methods described by Tanner and Wu (1993), creating breakpoints for M. hyopneumoniae is possible.
Antemortem joint fluid collection is an effective way to isolate Mycoplasma hyosynoviae (Holt, in publication), however only cumbersome antimicrobial susceptibility assays are described for M. hyosynoviae. With the use of the susceptibility test described in Chapter 3 of this thesis, the institution of breakpoints for M. hyosynoviae is achievable.
In conclusion, the use of the antemortem diagnostic tests developed in this thesis is valuable for treatment of diseases caused by swine mycoplasmas. Possible benefits to the swine industry include early, guided therapeutic intervention leading to more prudent usage of antibiotics in swine herds nationally.
Kimberly Kay Crawford
Crawford, Kimberly Kay, "Optimization of antemortem diagnostic evaluations to guide the judicious use of antimicrobial therapy in diseases caused by swine mycoplasmas" (2013). Graduate Theses and Dissertations. 13569.