Testing antimicrobial susceptibility against Mycoplasma hyopneumoniae in vitro

Methods: Isolates were cultured directly from porcine lung sections and positively identified as M. hyopneumoniae using an indirect-fluorescent antibody (IFA) method. A Sensititre® plate broth microdilution technique was used to determine the minimum inhibitory concentrations (MICs) of each of the antimicrobials. Inocula concentrations were determined by serial tenfold dilutions of the 14 M. hyopneumoniae isolates. An inoculum density of 103 CCU per mL was chosen as the target concentration of M. hyopneumoniae. Each well of a Sensititre® plate, prepared with the 12 antimicrobials, was inoculated with 50 μL of diluted culture and incubated at 37°C, then growth was monitored for 3–5 days. The MIC was recorded as the lowest concentration of each antimicrobial to inhibit visible color change.