A nitrocefin disc supplemented with ertapenem for rapid screening of carbapenemase-producing Enterobacteriaceae

Antibacterial activity of colistin is resurrected by Stephania suberosa Forman extract against colistin-resistant Enterobacter cloacae

To resurrect antibacterial efficacy of colistin (CLT), ceftazidime (CAZ) and cefotaxime (CTX), Stephania suberosa extract (SSE) was combined with these particular antibiotics to combat CLT-resistant Enterobacter cloacae (CREC) isolates. Disc diffusion assay showed that SSE inhibited E. cloacae strains with the dose-dependent manner. Minimum inhibitory concentrations (MICs) of SSE against all tested strains were 2000 µg ml^-1 . CREC DMST 37480 and 19719 were found to be resistant to CLT with MICs of 64 and 4 µg ml^-1 , respectively, and also resistant to CAZ. These strains showed a minimum bactericidal concentration (MBC) of SSE at 8000 µg ml^-1 . Checkerboard assay showed that CLT resistance was synergistically reversed by SSE against CREC DMST 37480 and 19719 with a fractional inhibitory concentration (FIC) indices of 0·253 and 0·265, respectively. Time-killing assay confirmed synergistic interaction by a decline in the viability combined treated group compared to an individual. CREC DMST 19719 was found to produce AmpC β-lactamase. SSE cannot resurrect CAZ in an AmpC producer. The scanning electron microscopy showed that SSE and CLT induced cell damages at different sites. GC-MS analysis identified 25 known Phyto-compounds. SSE and CLT combination could be further developed as a novel agent for treating multidrug-resistant CREC. SIGNIFICANCE AND IMPACT OF THE STUDY: Resistance to colistin (CLT), an alternative agent for treating multiple drug-resistant Enterobacter cloacae, is among the most serious, life-threatening issues. This study utilizes Stephania suberosa extract (SSE) to revive the antibacterial activity of colistin that has lost its antibacterial effectiveness in inhibiting E. cloacae. The findings support the development of the combined agent between SSE and colistin to conquer colistin-resistant E. cloacae.

Nitro-Carba test, a novel and simple chromogenic phenotypic method for rapid screening of carbapenemase-producing Enterobacteriaceae

OBJECTIVES

In this study, a rapid and simple chromogenic method for screening of carbapenemase-producing Enterobacteriaceae (CPE), namely the Nitro-Carba test (NCT), was developed.

METHODS

The NCT was validated using a total of 31 carbapenemase-producing isolates [9 Klebsiella pneumoniae carbapenemase (KPC), 11 metallo-β-lactamase (MBL) and 11 OXA-48] and 56 non-carbapenemase-producing isolates. The assay relies on the hydrolysis of nitrocefin by carbapenemases in the presence of carbapenem antibiotics. Carbapenemases were extracted with lysis buffer prior to addition to wells with and without imipenem (IPM), meropenem (MEM) and ertapenem (ETP). Following addition of nitrocefin, a change in colour from yellow to red, indicating carbapenemase production, was observed within 20min. The susceptibility profiles of each bacterial isolate were also investigated.

RESULTS

The NCT detected all 31 CPE within a timeframe of only 10s to 12min. All carbapenemase-producers hydrolysed nitrocefin in all wells. No colour change in wells with carbapenems was observed in non-carbapenemase-producers. The sensitivity for all three carbapenems was 100%, whilst the specificity of IPM, MEM and ETP was 64.3%, 91.1% and 100%, respectively. IPM, MEM and ETP had minimum inhibitory concentrations (MICs) against all carbapenemase-producing strains ranging from 0.5μg/mL to ≥256μg/mL, 0.25μg/mL to ≥256μg/mL and 1μg/mL to ≥256μg/mL, respectively. OXA-48-producing isolates showed lower MICs compared with MBL- and KPC-producing isolates.

CONCLUSION

This assay is a promising method for detecting CPE rapidly. The NCT is a simple and reliable method capable of detecting CPE even in carbapenem-susceptible strains.