Antimicrobial resistance in clinical isolates of Neisseria subflava from the oral cavities of a Japanese population

A recent study indicated that Neisseria subflava, one of the commensal Neisseria species, may play an important role in the emergence of Neisseria gonorrhoeae strains with chromosomally mediated resistance to penicillin or cephalosporin by the horizontal genetic exchange of penA genes encoding the target site for penicillin or cephalosporin. The present investigation examined the antimicrobial susceptibility of 45 isolates of N. subflava from the oral cavities of Japanese men and women to various agents used for the treatment of gonococcal infections. Of the 45 isolates, 40 (88.9%) and 4 (8.8%) were intermediately resistant and resistant to penicillin, respectively, with the minimal inhibitory concentration (MIC)₅₀ and MIC₉₀ of penicillin being 0.5 mg/l and 1 mg/l, respectively. Of the 45 isolates, 13 (28.9%) and 14 (31.1%) were resistant to tetracycline and ciprofloxacin, respectively, and 3 (6.7%) showed reduced susceptibility to cefixime (although the susceptibility category was not determined). These results indicate that several isolates of N. subflava have acquired resistance or intermediate resistance to various antimicrobial agents, including penicillin, cephalosporin, tetracycline, and ciprofloxacin. The present study may thus confirm that N. subflava may be involved in the emergence of N. gonorrhoeae strains with either intermediate or total resistance to penicillin or cephalosporin by the horizontal genetic exchange of the penA gene.     

Differences in antimicrobial susceptibility breakpoints for <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>, isolated from blood cultures,set by the Clinical and Laboratory Standards Institute (CLSI) and the Japanese Society of Chemotherapy

A study was made of the antimicrobial susceptibility to and efficacy of various kinds of antimicrobial agents against 179 strains of Pseudomonas aeruginosa that were isolated from blood cultures at Kansai Medical University Hospital from 1990 through 2004. The annual detection rate was highest in 1994, at 22 strains (6.5%). There were 9 multidrug resistant strains of Pseudomonas aeruginosa (5.0%). Among 14 antimicrobial agents tested for measurements, ciprofloxacin (CPFX) showed the best minimum inhibitory concentration (MIC) 50 value, of 0.25 μg/ml, followed by pazufloxacin (PZFX) and biapenem (BIPM), each at 0.5 μg/ml. When the period of 15 years was divided into three stages, the MIC50 value for each antimicrobial agent was highest in the middle stage (1995 to 1999). Assuming that the percentage of sensitive strains according to the breakpoints set by the Clinical and Laboratory Standards Institute (CLSI) represents the antimicrobial susceptibility rate, amikacin (AMK) showed the best value, of 85.5%. According to the sepsis breakpoint set by the Japanese Society of Chemotherapy (JSC), the efficacy of CPFX showed the highest rate (77.1%) of all the antimicrobial agents tested. Among β-lactams, BIPM showed the highest efficacy rate, of 67.0%. When the efficacy rates were compared with each other, the difference in efficacy rate between the breakpoint set by the CLSI and the sepsis breakpoint set by the JSC was large for β-lactams. Comparisons made based on the CLSI criteria showed no difference in cross-resistance rates between CPFX, meropenem (MEPM), and BIPM. However, when comparisons were made using the JSC sepsis breakpoint, MEPM showed a cross-resistance rate of 87.8%, while the rate for BIPM was lower, at 56.1%, with the χ² test showing a significant difference, at P = 0.0014. In accordance with the pharmacokinetics/pharmacodynamics theory that has been advocated, breakpoints which are more suitable for the clinical setting in Japan should be set so that more effective and more appropriate treatment can be carried out.