[Antimicrobial activities and mechanisms of carbapenem resistance in clinical isolates of carbapenem-resistant Pseudomonas aeruginosa and Acinetobacter spp]

Risk of transmission of imipenem-resistantPseudomonas aeruginosa through use of mobile bathing service

OBJECTIVES

The demand for mobile bathing service (MBS) is increasing in the Japanese society. Therefore, we assessed the risk of MBS-associated infection in MBS clients and their caregivers by examining the bacterial colonization of MBS equipment and utensils.

METHODS

Bacterial isolates collected by the stamp agar culture method were examined by disk diffusion assay for their susceptibility to the following drugs: imipenem, ciprofloxacin, amikacin, azutreonam, ceftazidim, meropenem, piperacillin, tobramycin, ofloxacin and cefoperazone. Furthermore, these isolates were subtyped bySpeI-pulsed field gel electrophoresis (SpeI-PFGE).

RESULTS

Fifty-fourP. aeruginosa isolates were recovered from different sampling sites, and of these, 26 (47.3%) were isolated from pillows. Eighteen isolates (33.3%) were imipenem (IPM) resistant. The minimum inhibitory concentrations (MICs) of 17 isolates were between 16 and 32 μg/ml, and the MIC of one isolate was greater than 32 μg/ml. TheSpeI-PFGE typing of IPM-resistant isolates revealed that 13 of the 18 isolates were closely related (F=1.0-0.87).

CONCLUSION

Our findings suggest that MBS equipment and utensils, particularly pillows, are the primary sources of bacterial contamination and transmission and that there is a risk of MBS-mediated infection among MBS clients and their caregivers.

Detection of metallo-β-lactamase–producing Pseudomonas aeruginosa strains isolated from burn patients in Ahwaz, Iran

The antimicrobial activities of 6 common antimicrobial agents including carbapenems were tested against 100 clinical Pseudomonas aeruginosa isolates using a disk diffusion method. All imipenem (IPM)-resistant isolates were screened for metallo-beta-lactamase (MBL) production by Etest assay and were subsequently subjected to polymerase chain reaction (PCR) analysis with the bla(IMP) and bla(VIM) genes. Of 41 IPM-nonsusceptible isolates detected, 8 (19.51%) appeared to produce MBL, as determined by Etest. Using PCR assay, these isolates were positive for bla(VIM) genes, whereas none were positive for bla(IMP) genes.

Spread of novel aminoglycoside resistance gene aac(6')-Iad among Acinetobacter clinical isolates in Japan

A novel aminoglycoside resistance gene, aac(6')-Iad, encoding aminoglycoside 6'-N-acetyltransferase, was identified in Acinetobacter genospecies 3 strain A-51. The gene encoded a 144-amino-acid protein, which shared modest identity (up to 36.7%) with some of the aminoglycoside 6'-N-acetyltransferases. The results of high-pressure liquid chromatography assays confirmed that the protein is a functional aminoglycoside 6'-N-acetyltransferase. The enzyme conferred resistance to amikacin, tobramycin, sisomicin, and isepamicin but not to gentamicin. The prevalence of this gene among Acinetobacter clinical isolates in Japan was then investigated. Of 264 Acinetobacter sp. strains isolated from geographically diverse areas in Japan in 2002, 16 were not susceptible to amikacin, and aac(6')-Iad was detected in 7. Five of the producers of aminoglycoside 6'-N-acetyltransferase type Iad were identified as Acinetobacter baumannii, and two were identified as Acinetobacter genospecies 3. These results suggest that aac(6')-Iad plays a substantial role in amikacin resistance among Acinetobacter spp. in Japan.

Evaluation of the Hodge test and the imipenem-EDTA double-disk synergy test for differentiating metallo-beta-lactamase-producing isolates of Pseudomonas spp. and Acinetobacter spp

Gram-negative bacilli with acquired metallo-beta-lactamase (MBL) production have been increasingly reported in some countries, necessitating their detection. The aim of this study was to evaluate the performance of the Hodge test and those of the imipenem (IPM)-EDTA, ceftazidime (CAZ)-mercaptopropionic acid (MPA), and CAZ-sodium mercaptoacetic acid (SMA) double-disk synergy tests (DDSTs). The efficiencies of testing CAZ-resistant and IPM-nonsusceptible isolates were also compared. Strains used for the evaluation were known IMP-1 and VIM-2 MBL-producing isolates and consecutive and CAZ-nonsusceptible isolates of pseudomonads and acinetobacters. The performance of the Hodge test was improved by addition of zinc sulfate (140 microg/disk) to an IPM disk. In DDSTs, EDTA (ca. 1,900 microg) disks were better at detecting MBL-producing strains among pseudomonads, while MPA (3 microl) and SMA (3 mg) disks performed better for acinetobacters. EDTA (ca. 750 microg)-plus-SMA (ca. 2 mg) disks performed better than EDTA, MPA, or SMA disks with both organisms. CAZ-SMA DDSTs failed to detect 22 of 80 (28%) MBL-producing acinetobacters. In conclusion, use of an IPM disk and an EDTA (750 microg)-plus-SMA (2 mg) disk improves performance, and testing IPM-nonsusceptible isolates rather than CAZ-resistant isolates could reduce screening work. Further evaluation of the test is required for the detection of other types of MBL-producing gram-negative bacilli.