2011 Volume 26 Issue 6 Pages 392-400
The present study investigated the relationships between antimicrobial use density (AUD) and drug susceptibility, as well as cross-resistance, for a total of 6587 strains of Pseudomonas aeruginosa clinically isolated from April 2003 to March 2010 (previous 7 fiscal years, FY). During the investigation period, a total of 22 metallo-β-lactamase (MBL)-producing strains (0.33%) were isolated, and a total of 3 multidrug-resistant P. aeruginosa (MDRP) strains were isolated from urine in FY 2007. Isolation of MBL-producing strains was concentrated from FY 2004 to FY 2006, with 4 (0.4%), 8 (0.8%) and 6 (0.7%) strains being isolated in FY 2004, FY 2005 and FY 2006, respectively. The total AUD of carbapenem, aminoglycoside and new quinolone antibiotics increased annually, and increases in AUD were particularly marked for meropenem (MEPM), amikacin (AMK) and ciprofloxacin (CPFX). Drug susceptibility was classified as susceptible, intermediate or resistant, and AUD and susceptibility were compared between the 3-year periods before and after FY 2006. For all antibiotics other than AMK, imipenem/cilastatin (IPM/CS), and MEPM, the number of resistant strains increased significantly with AUD. In the case of IPM/CS and MEPM, the number of intermediate strains increased significantly with AUD, but no increases were observed in the number of resistant strains. With regard to CPFX, the number of resistant strains increased significantly with AUD, but no increases were observed in the number of intermediate strains. However, for AMK, neither resistant nor intermediate strains increased, despite increased AUD. Although the proportion of MEPM-resistant strains exhibiting cross-resistance with IPM/CS-resistant and intermediate strains had been 100% from FY 2003 to FY 2006, strains showing no cross-resistance were isolated from samples collected in FY 2007 and later, probably due to the effects of increased AUD of MEPM. These findings suggest that the susceptibility of P. aeruginosa to most antibiotics is closely related to AUD, and that AUD is important in the long-term monitoring of susceptibility.
