Usefulness of inclusion of ertapenem and temocillin screening breakpoints in the EUCAST rapid antimicrobial susceptibility testing (RAST) for rapid detection of OXA-48-producing Klebsiella pneumoniae directly from positive blood cultures.

OBJECTIVES

The aims of this study were: (i) to assess the ability of the meropenem screening breakpoint as part of the screening rapid antimicrobial susceptibility testing (sRAST) of EUCAST for the detection of OXA-48 carbapenemase-producing Klebsiella pneumoniae directly from positive blood cultures (BCs); and (ii) to evaluate the inclusion of ertapenem and temocillin discs into the sRAST to enhance the detection of OXA-48-producing isolates.

METHODS

BC bottles were spiked with a total of 117 K. pneumoniae isolates, including 77 previously characterized OXA-48 producers and 40 non-OXA-48 producers. Disc diffusion assays were directly performed from positive BCs with meropenem (10 µg), ertapenem (10 µg) and temocillin (30 µg) discs, and inhibition zones were manually measured after 4, 6 and 8 h of incubation. The screening cut-off values of sRAST were applied to evaluate their capability in detecting OXA-48-producing isolates. Receiver operating characteristic curves were constructed to illustrate the performance efficacy of the disc diffusion assays to detect OXA-48 producers.

RESULTS

The meropenem cut-off values of sRAST only detected 90.91% of the OXA-48-producing isolates after 6 and 8 h of incubation. With the proposed cut-off points for ertapenem [<19 mm (4/6 h) and <20 mm (8 h)] and temocillin [<10 mm (4 h) and <11 mm (6/8 h)], all OXA-48-positive isolates were detected without any false-positive results at any reading time.

CONCLUSIONS

In healthcare settings with a high prevalence of OXA-48 producers, the inclusion of ertapenem and temocillin discs in the sRAST procedure may improve the detection of OXA-48-producing K. pneumoniae isolates directly from positive BCs, providing reliable results after only a 4 h incubation period.