Abstract
The increasing resistance to antibiotics is compromising the empirical treatment of infections caused by resistant bacteria. Rapid, efficient, and clinically applicable phenotypic methods are needed for their detection. This study examines the phenotypic behavior of β-lactam-resistant Gram-negative bacteria grown on ChromID ESBL medium with ertapenem, cefoxitin, and cefepime disks, reports on the coloration of colonies, and establishes a halo diameter breakpoint for the detection of carbapenemase-producing bacteria. We studied 186 β-lactam-resistant Gram-negative microorganisms (77 with extended spectrum beta lactamase (ESBL), 97 with carbapenemases, and 12 with AmpC β-lactamases (AmpC)). Susceptibility profiles of Gram-negative bacteria that produced ESBL, AmpC, and carbapenemases were similar to the expected profiles, with some differences in the response to cefepime of ESBL-producing microorganisms. Coloration values did not differ from those described by the manufacturer of ChromID ESBL medium. In the screening of carbapenemase production, inhibition halo diameter breakpoints for antibiotic resistance were 18 mm for Enterobacterales and ertapenem, 18 mm for Pseudomonas and cefepime, and 16 mm for Acinetobacter baumannii and cefepime. This innovative phenotypic approach is highly relevant to clinical laboratories, combining susceptibility profiles with detection by coloration of high-priority resistant microorganisms such as carbapenemase-producing A. baumannii, carbapenemase-producing Pseudomonas spp., and ESBL and/or carbapenemase-producing Enterobacterales.
Highlights
The increasing resistance to antibiotics is a major worldwide health problem, and the WHO has highlighted the threat posed by extended-spectrum β-lactamase (ESBL)-producingEnterobacteriaceae and carbapenemase-producing Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae [1]
We studied 71 isolates: 31 (43.7%) were carbapenemase-producing A.baumannii, with halos between 5 and 15 mm (12.45 ± 2.142) for FEP, and 40 were non-carbapenemase-producing microorganisms (2 A. baumannii, 14 P. aeruginosa, and 24 Enterobacterales), with halos between 14 and mm for FEP (29.61 ± 6.727), as control group
This study highlights the usefulness of ChromID ESBL medium with the placement of antibiotic disks to screen for resistant
Summary
The increasing resistance to antibiotics is a major worldwide health problem, and the WHO has highlighted the threat posed by extended-spectrum β-lactamase (ESBL)-producingEnterobacteriaceae and carbapenemase-producing Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae [1]. Techniques to detect ESBL-producing enterobacteria colonies include the utilization of CHROMID. The inclusion of cefoxitin (FOX), cefepime (FEP), and imipenem disks on CHROMID ESBL medium has been proposed to identify ESBL- and/or carbapenemase-producing microorganisms resistant to these antibiotics, a halo diameter breakpoint of 15 mm did not prove diagnostically useful [5]. The diagnostic performance may be improved by considering a higher halo breakpoint (16 mm) and replacing imipenem with ertapenem (ERT). Carbapenemase or ESBL production is frequently studied in episodes of colonization by multi-resistant Gram-negative bacteria, and the addition of ERT, FOX, and FEP disks to this medium may offer a simple and effective method. ERT has a higher activity against ESBL-producing Enterobacterales but a lower activity against carbapenemase-producing
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