Prospective evaluation of an easy and reliable work flow for the screening of OXA-48-producing Klebsiella pneumoniae in endemic settings

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Summary

Background

Carbapenemase-producing Enterobacterales (CPE) represent a serious threat to public health. Clinical microbiology laboratories (CMLs) need effective protocols for screening and confirmation of CPE.

Aim

To prospectively evaluate an algorithm for the screening of carbapenemase-producing Klebsiella pneumoniae in an OXA-48 endemic hospital.

Methods

The algorithm was based on a disc diffusion assay using ertapenem and temocillin, which also served as a purity check for routine automated antimicrobial susceptibility testing. All isolates with minimal inhibitory concentrations >0.5 mg/L or zone inhibition diameters <25 mm for ertapenem (Criterion 1) and <12 mm for temocillin (Criterion 2) were tested sequentially by an OXA-48 lateral flow immunochromatographic assay and a multiplex polymerase chain reaction targeting VIM, KPC and OXA-48. If neither test was positive, the modified Hodge test or CARBA NP test was used.

Findings

Over 2 years, 2487 K. pneumoniae were assessed by the algorithm proposed, and 378 (15.20%) met both criteria. Of these, 98.68% (373/378) were either confirmed as OXA-48 producers or originated from patients with a previous CPE isolate that maintained the same resistance phenotype over time. The remaining three K. pneumoniae were VIM producers. Only two of the 378 isolates (0.53%) did not produce carbapenemase, despite meeting Criteria 1 and 2.

Conclusion

The algorithm described combined the most sensitive carbapenem for CPE detection with a cut-off for temocillin that was highly specific for detection of OXA-48. It is reliable and easy to apply in routine CML work flow, allowing rapid detection of CPE isolates and hence prompt implementation of infection control measures and targeted antimicrobial regimens.

Introduction

Over the last decade, decreased susceptibility to carbapenems has been increasing worldwide in Gram-negative clinical isolates, mainly in Enterobacterales [1]. The mechanisms conferring reduced susceptibility to carbapenems in Enterobacterales are mainly divided into two groups: (i) hyperproduction of AmpC or extended-spectrum β-lactamases (ESBLs) combined with altered membrane permeability; and (ii) production of carbapenemases [carbapenemase-producing Enterobacterales (CPE)] [[2], [3], [4]]. The potential for spread of carbapenem resistance among Gram-negative bacterial species, and the multi-drug-resistant phenotype usually expressed by CPE isolates, mean that these bacteria are of particular concern as they represent a serious threat from a public health perspective [1,4]. Despite efforts to control their spread over recent years, CPE have disseminated and established in several countries worldwide, becoming endemic in many healthcare institutions [5]. Among them, Klebsiella pneumoniae is by far the most frequently encountered species worldwide, and OXA-48 is the most common carbapenemase reported in Spain and other countries in Europe, the Middle East and North Africa [5,6]. Rapid detection of CPE is the most important step to implement prompt infection control measures in order to initiate appropriate antimicrobial therapy and to prevent further dissemination [7]. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines recommend the detection of carbapenemase producers among all Enterobacterales with minimum inhibitory concentrations (MICs) of ertapenem or meropenem ≥0.125 mg/L or disc diffusion zone diameters <25 mm and <28 mm, respectively [8]. In this context, several methods for carbapenemase detection have been developed, including phenotypic tests such as the combination disc test, colorimetric assays based on carbapenem hydrolysis, and lateral flow assays. Molecular tests based on polymerase chain reaction (PCR), which are still the reference standard, are also available [4]. Nonetheless, the phenotypic detection of carbapenemase producers with a low level of carbapenem hydrolysis, such as those positive for OXA-48, remains challenging [4,9]. As such, several authors have proposed temocillin resistance as a surrogate marker for detection of OXA-48 producers [1,4,7,9,10]. The increase of Enterobacterales with reduced susceptibility to carbapenems, CPE and non-CPE makes it necessary to implement algorithms for CPE detection in clinical microbiology laboratory (CML) work flows, providing prompt and accurate results with minimal cost and labour input. The aim of this study was to describe and evaluate an algorithm which incorporates testing of temocillin resistance for the screening and confirmation of carbapenemase-producing K. pneumoniae, performed in an OXA-48 endemic hospital [11].

Section snippets

Methods

All K. pneumoniae isolates recovered from clinical samples of patients admitted to the Hospital Universitario Central de Asturias, Spain, from June 2017 to June 2019 were collected prospectively. The isolates were first identified with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (Microflex; Bruker Daltonik GmbH, Bremen, Germany), and antimicrobial susceptibility testing (AST) was performed subsequently using the MicroScan system (Beckman Coulter, Pasadena, CA,

Results and discussion

Over the study period, 2487 K. pneumoniae isolates were recovered from inpatients from the study hospital, and 378 (15.20%) met the two criteria. Of these, 373 (98.68%) were confirmed as OXA-48 producers (N=250) or were recovered from patients in whom OXA-48-producing isolates had been detected in the previous 6 months (N=123). These isolates were assumed to be OXA-48 producers if their resistance phenotype did not change over time. Two hundred and fifty-five isolates were subsequently analysed

Conflict of interest statement

None declared.

Funding sources

This work was supported, in part, by Project FIS PI17-00728 (Fondo de Investigación Sanitaria, Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Spain), co-funded by the European Regional Development Fund of the European Union: a Way to Making Europe.

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