Abstract
Polyhexamethylene biguanide hydrochloride (PHMB), an antimicrobial agent, has been widely used as a disinfectant in medical industries and public facilities. However, long-term use of any antimicrobial agent increases the risk of the microorganisms developing resistance. We aimed to examine the presence of microorganisms highly resistant to PHMB to address potential medical safety and public health concerns and devise strategies to prevent resistance development. We isolated and characterized a fungus from a 20% aqueous solution of PHMB and compared its microbiological characteristics and resistance profile with those of other major antimicrobial agents. Additionally, we sequenced the genome of the isolate to predict PHMB resistance-related genes. Based on the internal transcribed spacer (ITS) region of ribosomal DNA, the fungus was identified as Purpureocillium lilacinum. Although the P. lilacinum type and resistant strains showed similar morphology, the latter had extremely low PHMB susceptibility and was able to grow in the 20% aqueous solution of PHMB, which killed the type strain. Additionally, the minimum inhibitory concentration (MIC) of PHMB against the resistant strain was approximately four times higher than that against the type strain. In contrast, the MICs of four other antimicrobial agents and seven antifungal agents against the resistant strain were either less than or equal to those against the type strain. Furthermore, MICs of PHMB against four pathogenic filamentous fungi and two yeasts were significantly lower than those against the resistant strain. Despite its specific high resistance to PHMB, no gene homologous to fungal PHMB-resistant gene was found in the genome of the resistant strain. In summary, P. lilacinum was found to be significantly more resistant to PHMB than previously reported, suggesting an unidentified novel mechanism underlying drug resistance in the fungi.
Isolation and Characterization of the Polyhexamethylene Biguanide Hydrochloride-Resistant Fungus, Purpureocillium lilacinum
