Effects of the order of exposure to antimicrobials on the incidence of multidrug-resistant Pseudomonas aeruginosa.

Multidrug-resistant Pseudomonas aeruginosa (MDRP) is one of the most important pathogens in clinical practice. To clarify the mechanisms contributing to its emergence, we isolated MDRPs using the P. aeruginosa PAO1, the whole genome sequence of which has already been elucidated. Mutant strains resistant to carbapenems, aminoglycosides, and new quinolones, which are used to treat P. aeruginosa infections, were isolated; however, none met the criteria for MDRPs. Then, PAO1 strains were exposed to these antimicrobial agents in various orders and the appearance rate of MDRP varied depending on the order of exposure; MDRPs more frequently appeared when gentamicin was applied before ciprofloxacin, but were rarely isolated when ciprofloxacin was applied first. Exposure to ciprofloxacin followed by gentamicin increased the expression of MexCD-OprJ, an RND-type multidrug efflux pump, due to the NfxB mutation. In contrast, exposure to gentamicin followed by ciprofloxacin resulted in more mutations in DNA gyrase. These results suggest that the type of quinolone resistance mechanism is related to the frequency of MDRP and that the risk of MDRP incidence is highly dependent on the order of exposure to gentamicin and ciprofloxacin.

Genome Mining-Based Discovery of Fungal Macrolides Modified by glycosylphosphatidylinositol (GPI)-Ethanolamine Phosphate Transferase Homologues.

Through genome mining for fungal macrolide natural products, we discovered a characteristic family of putative macrolide biosynthetic gene clusters that contain a glycosylphosphatidylinositol-ethanolamine phosphate transferase (GPI-EPT) homologue. Through the heterologous expression of two clusters from Aspergillus kawachii and Colletotrichum incanum, new macrolides, including those with phosphoethanolamine or phosphocholine moieties, were formed. This study is the first demonstration of the tailoring steps catalyzed by GPI-EPT homologues in natural product biosynthesis, and it uncovers a new gene resource for phospholipid-resembling fungal macrolides.