Analysis of multidrug-resistant Pseudomonas aeruginosa in a hospital with a dominant population of geriatric inpatients

Bacterial resistance and opportunistic human pathogens have become serious problems in hospitals, particularly those in which the dominant population consists of immunocompromised elderly inpatients. Pseudomonas aeruginosa is a prevalent opportunistic human pathogen that causes acute pneumonia, cystic fibrosis, and septicemia, and it is also known to possess various mechanisms of natural and acquired resistance to antibiotics. Carbapenems have been used to treat infections caused by β-lactamase-producing gramnegative bacteria including P. aeruginosa, but metallo-β-lactamase (MBL) can render carbapenems ineffective, and so action is required to prevent the development of strains that produce MBL. Between September 2010 and August 2011, 8 multidrug-resistant P. aeruginosa (MDRP) strains were isolated from pressure ulcer, urine, or expectoration or aspiration sputum samples of patients with different infections in a hospital in Osaka Prefecture, Japan. After confirming MBL production, we identified 5 strains that produced IMP-type MBL. The strain variations of isolated MDRP were determined by multiplelocus variable-number tandem repeat analysis. Because the 5 IMP-type MBL-producing strains were of the same genotype, it was suggested that the infection had spread within the wards. The remaining non-MBL-producing MDRP strains were also of the same genotype, but antimicrobial breakpoint tests revealed that they were not exactly the same, and the wards from which they had been isolated were not close to each other. Therefore, more accurate typing of the non-MBL-producing genotype group is required to determine whether diffusion between the wards had occurred.