The New Zealand National Antimicrobial Susceptibility Testing Committee (NZ NAC) was formed in late 2017 to provide expert advice to New Zealand diagnostic laboratories and to further the collaboration and sharing of skill development in the area of antimicrobial susceptibility testing within New Zealand.
This document provides a minimum requirement for the laboratory detection of CPE in New Zealand with the aim of ensuring that laboratories take a consistent approach to screening high-risk patients for CPE. Details are given so that laboratories can identify when confirmatory testing, referral of CPE isolates, and notification to clinical and infection prevention teams is required.
The 2019 update for this document contains new paragraphs on the detection of carbapenamase enzymes in Acinetobacter baumanni and Pseudomonas aeruginosa as well as identifying temocillin as a sensitive, but not specific, marker for OXA-48 producers. Laboratories are encouraged to read the document and implement the recommendations.
In August 2018, the NZ NAC introduced guidelines for the detection of CPE from clinical samples and screening specimens. As part of an annual review process to identify any shortfalls in the document, and to assess compliance to the standards, 3 isolates and a questionnaire were sent to each laboratory in June 2019. Overall, laboratories performed very well, with most being able to comply with the minimum standards guidelines, identifying the presence or possibility of a carbapenemase in each isolate. The most challenging isolate was an OXA-48-producing E. coli, which coproduced an ESBL, had only low-level resistance to meropenem, and was a weak carbapenem hydrolyser. Temocillin is a sensitive, but not specific, marker for OXA-48, and might be a useful addition to routine screens for resistance mechanism detection, particularly when testing E. coli. The updated guidelines for the detection of CPE from clinical samples and screening specimens are available here [PDF, 328 KB].
EUCAST have issued a warning regarding the poor performance of disc diffusion, MIC gradient strips and automated systems for reliably detecting colistin resistance in Gram-negative bacilli. The issues include the poor diffusion of colistin molecules into the agar, drug powder composition and heteroresistance. The discovery of a readily transferable, plasmid-mediated gene, mcr-1, has further complicated detection of resistance. As such, EUCAST currently recommends broth microdilution (BMD) as the only valid method to determine colistin susceptibility. The NZ NAC group conducted a small study to evaluate a variety of commercial methods for the detection of colistin resistance, including Liofilchem colistin MIC Test Strips, BD Phoenix NMIC-404, Rapid Polymyxin NP, Liofilchem SensiTest Colistin BMD, and Trek Sensititre EURGNCOL BMD.
Several laboratories have indicated an increase of β-lactamase-negative ampicillin-resistant (BLNAR) H. influenzae, after switching from CLSI to EUCAST. A recent study looking at 100 H. influenzae clinical isolates; measuring penicillin, ampicillin and cefuroxime disc zone sizes, as well as ampicillin MICs, using EUCAST guidelines has been carried out. Analysis of ftsI gene mutations (PBP3 substitutions) was also performed. The study found an excellent correlation between the EUCAST recommended screening method of penicillin 1 unit disc and ftsI gene mutations, predominantly affecting cephalosporins rather than ampicillin.
Newsletter 1 - October 2018 [PDF, 418 KB]
Newsletter 2 - December 2019 [PDF, 490 KB]
Guidance for standardisation of laboratory antibiogram data has been published here [PDF, 531 KB] by the NZ NAC. The recommendations in this document are based on those in the 2013 specification for hospital cumulative antibiograms(external link) by the Australian Commission on Safety and Quality in Healthcare. Suggested templates for laboratory antibiograms are given below and these can be adapted to suit individual laboratories.
Antimicrobial Reference Laboratory reference and confirmatory testing services: Specialist Testing | ESR(external link)
ESR antimicrobial resistance surveillance reports: Antimicrobial Resistance Surveillance Reports(external link)
All communications and enquiries to the NZ NAC should be through the NZ NAC administrator, Sarah Underwood