Modification and evaluation of the Triton Hodge test for screening carbapenemase-producing Enterobacteriaceae

Evaluation of Disk carbapenemase test using improved disks for rapid detection and differentiation of clinical isolates of carbapenemase-producing Enterobacterales

OBJECTIVES

Rapid detection of carbapenemase-producing Enterobacterales (CPE) is important to control spread of the resistance. We previously reported that imipenem disks prepared from injectable imipenem-cilastatin could rapidly detect KPC- and NDM-type carbapenemases. In the present study, we evaluated performance of disks of IPM and combined disks of imipenem-tazobactam and imipenem-EDTA, which were prepared from powders of imipenem and inhibitors.

METHODS

Isolates of Enterobacterales were recovered from specimens of patients at a tertiary care hospital in Korea during January 2017 and March 2018. Routine CPE detection was performed by the CPE surveillance personnel whereas evaluation of the Disk carbapenemase test (DCT) was performed by the other personnel without knowing the results of surveillance. The DCT was carried out by pressing disks on to colonies and rehydrating in Petri plates and observing color change.

RESULTS

The DCT differentiated 688 of 694 (sensitivity 99.1%) carbapenemase-producing isolates in 2.5-20 min: 630 with KPC, 51 with NDM, three with IMP, one with VIM, two with KPC and IMP, and one with NDM and OXA-181. The DCT failed to detect six OXA- 48-like enzyme-producing isolates, but the modified method using 96-well flat-bottom microplates with mineral oil cover detected all 29 OXA-48-like enzyme-producing isolates in 20-120 min. The DCT was negative for all 440 ertapenem-nonsusceptible, carbapenemase gene-negative isolates (specificity 100%).

CONCLUSION

The procedure of DCT is simple and can differentiate isolates of Enterobacterales with KPC-, NDM-, IMP- and VIM-type carbapenemases rapidly, and the modified DCT can detect isolates with OXA-48-like enzymes rapidly.

High-Speed Quenching Probe-Polymerase Chain Reaction Assay for the Rapid Detection of Carbapenemase-Producing Gene Using GENECUBE: A Fully Automatic Gene Analyzer

BACKGROUND

The prevalence of carbapenemase-producing organisms (CPOs) globally poses a public health threat; however, detecting carbapenemases is a challenge because of their variety.

METHODS

GENECUBE, a fully automated gene analyzer, detects a target gene in a short time and simultaneously detects its single nucleotide polymorphism. We used this property to develop for the first time a rapid assay for detecting CPOs from cultured bacteria using GENECUBE. The original primer-probe sets were used to detect bla_KPC, bla_IMP, bla_VIM, bla_NDM, and bla_OXA-48-like from 149 CPOs (nine types) and 61 non-CPOs.

RESULTS

The sensitivity, specificity, and positive and negative predictions of the GENECUBE assay were 100%. This assay detected carbapenemase single-producers and carbapenemase co-producers with 100% accuracy. The time required for detects of four types of carbapenemase at one run was about 30 min, but it took about 1 h to detect all five types. In addition, this assay performed the rapid detection and classification of bla_OXA-48, bla_OXA-181, bla_OXA-232, and bla_OXA-244 simultaneously.

CONCLUSIONS

The GENECUBE assay is a promising tool for controlling the spread of CPOs and helping to select accurate and rapid antibiotic therapies.

Application Value of Triton X-100 to Modified Hodge Test and Carbapenem Inactivation Method in the Detection of Acinetobacter baumannii Carbapenemase

Aim

To compare the sensitivity and specificity before and after the addition of Triton X-100 in the modified Hodge test (MHT) and carbapenem inactivation method (CIM) for the detection of carbapenemase in Acinetobacter baumannii.

Materials and Methods

A total of 135 isolates of A. baumannii (83 carbapenem-resistant and 52 carbapenem-sensitive) were selected and the carbapenemase genotypes were detected using PCR. Carbapenemase phenotypes were tested using the MHT, Triton-MHT (THT), CIM, modified CIM (mCIM), and Triton-CIM (TCIM). Different concentrations (0.05, 0.1, 0.25, and 0.5% v/v) of Triton X-100 were used in the TCIM.

Results

The sensitivity was determined to be 59.03% (MHT), 100% (THT), 6.02% (CIM), 8.43% (mCIM), 71.08% (TCIM 0.05%), 100% (TCIM 0.1%), 97.59% (TCIM 0.25%), and 96.38% (TCIM 0.5%) in 83 carbapenemase-producing isolates, and the specificity for each of these methods was 100%.

Conclusion

The addition of Triton X-100 while using the MHT and CIM could significantly improve the sensitivity in the detection of A. baumannii carbapenemase with a specificity of 100%. A concentration of 0.1% v/v Triton X-100 showed the best results in TCIM.