Application of flow cytometry for the determination of minimal inhibitory concentration of several antibacterial agents on Mycoplasma hyopneumoniae

Aim: In this study, flow cytometry was evaluated for the determination of the minimal inhibitory concentrations (MICs) of nine antibacterial agents (enrofloxacin, ciprofloxacin, oxytetracycline, chloramphenicol, tylosin, lincomycin, gentamycin, spectinomycin and streptomycin) against M. hyopneumoniae. Methods and Results: Flow cytometry was able to detect Mycoplasma hyopneumoniae inhibition at 12 h postincubation, whereas the results obtained by the traditional method were only obtained at 48 h, when a visible change in the medium had occurred. At 48 h, both methods gave the same result for eight antibacterial agents, whereas flow cytometry gave slightly higher MIC values for one antibacterial agent (tylosin). This was attributed to the fact that the M. hyopneumoniae growth that had occurred in those tubes was not enough to visibly change the colour of the medium. A good relationship was found between the flow cytometry and the traditional method. Conclusion: Flow cytometry was found to be a good method for the determination of antimicrobial MICs in M. hyopneumoniae. Significance and Impact of the Study: The flow cytometric method allows the determination of the response of M. hyopneumoniae to each of the antibacterial agents in near real time, and has potential for the identification and study of resistant subpopulations.