Masao Kuwabara

Increased resistance to cationic antimicrobial peptide LL-37 in methicillin-resistant strains of Staphylococcus aureus.

OBJECTIVES The susceptibility of clinical isolates of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), to host-derived cationic antimicrobial peptides was investigated. METHODS We examined the susceptibility of 190 clinical strains of methicillin-susceptible S. aureus (MSSA) and 304 strains of MRSA to two different classes of cationic antimicrobial peptides: LL-37 and human beta-defensin-3 (hBD3). Out of the total 494 clinical strains, a random selection of 54 S. aureus strains was examined to establish the relationship between the net charge, or zeta potential, of each strain and its susceptibility to hBD3 or LL-37. To further confirm bacterial susceptibility to either hBD3 or LL-37, we concurrently measured: (i) percentage survival after in vitro bacterial exposure and (ii) MBCs for both MRSA and MSSA strains. RESULTS Of the 54 randomly selected S. aureus strains, those MRSA strains resistant to LL-37 showed significantly higher zeta potentials than those susceptible to LL-37 (P < 0.05). In contrast, there was no difference in bacterial zeta potentials for MRSA strains that showed either resistance or susceptibility to hBD3. In addition, resistance to LL-37, but not to hBD3, as determined by either percentage survival or MBC, was significantly elevated in highly methicillin-resistant strains of S. aureus when compared with MSSA strains (P < 0.01). CONCLUSIONS Clinical strains of MRSA, but not MSSA, that demonstrated an increased net charge also showed elevated resistance to LL-37, but not to hBD3.

Molecular characterization of imipenem-resistant Pseudomonas aeruginosa in Hiroshima, Japan.

Pseudomonas aeruginosa showing resistance to imipenem were found in 100 of 1,058 strains (9.5%) from six hospitals (a–f) in Hiroshima City, Japan. Of the 100 strains, 14 (14%) were double disk synergy test positive using sodium mercaptoacetic acid disks, and 18 (18%) were blaIMP‐1 or blaVIM‐2 allele positive by polymerase chain reaction (PCR). Among 100 imipenem‐resistant strains, 32 were categorized into multi‐drug resistant strains, in which 13 were positive for the metallo‐β‐lactamase gene. Fifty‐one strains (51%) among the 100 imipenem‐resistant strains had elevated RND efflux pump activity against levofloxacin. But only 6 of 51 strains were classified as multi‐drug resistant strains. The pulsed field gel electrophoresis analysis of the SpeI‐digested DNA from the 100 isolates suggested not only clonal spread but spread of heterogeneous clones started to contribute to the prevalence of metallo‐β‐lactamase producing P. aeruginosa strains in Japanese hospitals.

Pharmacokinetic-pharmacodynamic target attainment analysis of biapenem in adult patients: a dosing strategy.

Background: A pharmacokinetic-pharmacodynamic (PK-PD) target attainment analysis to build a dosing strategy for biapenem in adult patients has not been conducted. Methods: A total of 321 plasma concentration samples from 68 adult patients (1–6 samples per patient) were assayed biologically and chromatographically, and used for a population PK modeling and Monte Carlo simulation to assess the probability of attaining the PK-PD target (40% of the time above the minimum inhibitory concentration). Results: The population PK model was based on the standard two-compartment model, and creatinine clearance (Clcr) was the most significant covariate that affected the drug clearance. The Monte Carlo simulation demonstrated that the dosages up to 600 mg Q12H (0.5-h infusions) achieved a PK-PD target attainment probability of ≧90%, which varied with Clcr of the patient and susceptibility of the tested bacterium; however, higher dosage with prolonged infusion time (600 mg Q8H, 3 h infusion) was required for a high probability against Pseudomonas aeruginosa and Haemophilus influenzae isolates in the case of Clcr = 90 ml/min. Conclusion: These results provide guidance for constructing a PK-PD-based strategy for tailoring biapenem regimens in adult patients.

Purification of Staphylococcal Exfoliative Toxin by High Pressure Liquid Chromatography

Exfoliative toxin (ET) isolated from a clinical strain of Staphylococcus aureus was purified to homogeneity, using a 3-step HPLC system. NH2-terminal 20 amino residues of purified ET was found to be identical with ETA of S. aureus TA (7), S. aureus TC16 (9) and S. aureus ZM (10), but stability of purified ET was completely different from that of ETA. This purification system gave a high yield of pure ET, which exhibited higher purity than specimens purified by more complicated and time-consuming procedures. It is useful for small-scale purification for the comparative study of ET and easy to scale up for preparative purification.