Rapid detection and evaluation of clinical characteristics of emerging multiple-drug-resistant gram-negative rods carrying the metallo-beta-lactamase gene blaIMP

Abstract

Gram-negative rods (GNR) carrying the transferable carbapenem resistance gene blaIMP, including Pseudomonas aeruginosa and Serratia marcescens, have been isolated from more than 20 hospitals in Japan. Although the emergence of such multiple-drug-resistant bacteria is of utmost clinical concern, little information in regard to the distribution of blaIMP-positive GNR in hospitals and the clinical characteristics of infected patients is available. To address this, a system for the rapid detection of the blaIMP gene with a simple DNA preparation and by enzymatic detection of PCR products was developed. A total of 933 ceftazidime-resistant strains of GNR isolated between 1991 and 1996 at Nagasaki University Hospital, Nagasaki, Japan, were screened for the blaIMP gene; 80 isolates were positive, including 53 P. aeruginosa isolates, 13 other glucose-nonfermenting bacteria, 13 S. marcescens isolates, and 1 Citrobacter freundii isolate. Most of the patients from whom blaIMP-positive organisms were isolated had malignant diseases (53. 8%). The organisms caused urinary tract infections, pneumonia, or other infections in 46.3% of the patients, while they were just colonizing the other patients evaluated. It was possible that blaIMP-positive P. aeruginosa strains contributed to the death of four patients, while the other infections caused by GNR carrying blaIMP were not lethal. DNA fingerprinting analysis by pulsed-field gel electrophoresis suggested the cross transmission of strains within the hospital. The isolates were ceftazidime resistant and were frequently resistant to other antibiotics. Although no particular means of pathogenesis of blaIMP-positive GNR is evident at present, the rapid detection of such strains is necessary to help with infection control practices for the prevention of their dissemination and the transmission of the resistance gene to other pathogenic bacteria.

FIG. 1

Distribution of bla_IMP-positive GNR detected by a combination of heat lysis of bacteria and ED-PCR in Nagasaki University Hospital between 1991 and 1996. ○, P. aeruginosa; •, other GNF bacteria; ⧫, S. marcescens; ◊, C. freundii; ICU, intensive care unit.

FIG. 2

DNA fingerprinting profiles for clinical isolates of bla_IMP-positive P. aeruginosa. Total DNA was prepared for each clinical isolate, digested with SpeI, and then subjected to PFGE. Lanes M, DNA molecular size marker. The strains suggesting typical nosocomial spread (A) and whose profiles are discrepant (B) are shown. (A) Three pairs of isolates showing indistinguishable PFGE profiles isolated on the same ward during a short period in 1991. Four strains isolated within 5 days in 1996. The PFGE profiles could not be distinguished for the strains in lanes PA47 and PA49, while those profiles that were different from each other were found for the strains in lanes PA46 and PA47 isolated on the same day.

FIG. 3

Dendrogram based on computer-assisted comparison of PFGE profiles of 53 isolates of bla_IMP-positive P. aeruginosa and their isolation date, floor, and department.

FIG. 4

DNA fingerprinting profiles for the clinical isolates of bla_IMP-positive S. marcescens. Total DNA was prepared for each clinical isolate, digested with XbaI, and then subjected to PFGE. Lanes M, DNA molecular size marker; S1 to S13, bla_IMP-positive S. marcescens ordered by date of isolation in the 6-year study period. The PFGE profiles of the lanes 3, 4, 6, 7, 10, and 12 suggest that these isolates are genetically related to each other.