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A 56-year-old woman with systemic lupus erythematosus had bacteremia due to multidrug-resistant Pseudomonas aeruginosa (MDRP). She was initially treated with imipenem-cilastatin, tobramycin, and aztreonam; however, MDRP was still detected intermittently in her plasma. Multidrug-susceptibility tests demonstrated that MDRP was susceptible only to colistin. Therefore, in addition to these antibiotics, the administration of intravenous colistin methanesulfonate, a prodrug formula of colistin, was started at a daily dose of 2.5 mg/kg (as colistin base activity). The initial dose setting was based on the patient's renal function (baseline creatinine clearance 32.7 mL/min). After initiating colistin, the patient's C-reactive protein levels gradually decreased. Blood cultures showed no evidence of MDRP on days 8, 14, and 22 after colistin initiation. However, the patient's renal function went from bad to worse owing to septic shock induced by methicillin-resistant Staphylococcus aureus (MRSA) infection. A few days later, the trough plasma levels of colistin were 7.88 mg/L, which appeared to be higher than expected. After decreasing the colistin dose, the patient's renal function gradually improved. On the final day of colistin treatment, the plasma levels decreased to 0.60 mg/L. MDRP could not be detected in blood culture after colistin treatment. Therefore, we successfully treated a case of bloodstream infection due to MDRP by therapeutic drug monitoring (TDM) of colistin. It is suggested that the monitoring of blood colistin levels by liquid chromatography-tandem mass spectrometry can contribute to safer, more effective antimicrobial therapy of MDRP because TDM facilitates quick decisions on dose adjustments.

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Cell recognition plays a central part in the sexual process. Although cell‐surface molecules involved in gamete recognition have been identified in several organisms, our knowledge of the molecular basis of sexual cell recognition is still limited. We have been studying molecular mechanisms of sexual cell fusion using the lower eukaryote Dictyostelium discoideum. There are homothallic, heterothallic, bisexual and asexual strains in D. discoideum, and how they distinguish between each other to find out proper partners is an interesting and important question. However, analytical studies of sexuality in D. discoideum have been carried out mostly on heterothallic strains, and the polymorphism of the mating system has not yet been thoroughly investigated. In the present study, we extended our analysis to the bisexual mating phenomenon paying special attention to the mechanism of self‐incompatibility. We showed that a bisexual strain WS2162 was self‐incompatible at the step of sexual cell fusion. Results of antibody inhibition of cell fusion and detection of gp138, a cell‐fusion‐related protein found in heterothallic strains, suggest that a molecular basis for bisexual and heterothallic mating are common. We propose two models to clarify the mechanisms of self‐ and non‐self discrimination in bisexual mating patterns of D. discoideum.

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