Activity of imipenem/relebactam against Enterobacterales and Pseudomonas aeruginosa in Spain. SMART 2016-2020

OBJECTIVE

To determine susceptibility to the novel β-lactam/β-lactamase inhibitor combination imipenem/relebactam in clinical isolates recovered from intra-abdominal (IAI), urinary (UTI), respiratory (RTI) and bloodstream (BSI) infections in the SMART (Study for Monitoring Antimicrobial Resistance Trends) study in SPAIN during 2016 - 2020.

METHODS

Broth microdilution MICs for imipenem/relebactam and comparators were determined by a central laboratory against isolates of Enterobacterales and Pseudomonas aeruginosa. MICs were interpreted using EUCAST-2021 breakpoints.

RESULTS

In total, 5,210 Enterobacterales and 1,418 P. aeruginosa clinical isolates were analyzed. Imipenem/relebactam inhibited 98.8% of Enterobacterales. Distinguishing by source of infection susceptibility was 99.1% in BSI, 99.2% in IAI, 97.9% in RTI, and 99.2% in UTI. Of intensive care unit isolates (ICU) 97.4% were susceptible and of non-ICU isolates 99.2% were susceptible. In Enterobacterales, activity against Class A, Class B and Class D carbapenemases was 96.2%, 15.4% and 73.2%, respectively. In P. aeruginosa, imipenem/relebactam was active in 92.2% of isolates. By source of infection it was 94.8% in BSI, 92.9% in IAI, 91.7% in RTI, and 93.1% in UTI. An 88.7% of ICU isolates and 93.6% of non-ICU isolates were susceptible to imipenem/relebactam. Imipenem/relebactam remained active against P. aeruginosa ceftazidime-resistant (76.3%), cefepime-resistant (73.6%), imipenem-resistant (71.5%) and piperacillin-resistant (78.7%) isolates. Of all multidrug-resistant or difficult-to-treat resistance P. aeruginosa isolates, 75.1% and 46.2%, respectively, were susceptible to imipenem/relebactam.

CONCLUSIONS

Imipenem/relebactam showed high rates of susceptibility in Enterobacterales and P. aeruginosa isolates from different sources of infection as well as depending on patients' location (ICU or non-ICU scenarios).

Are GES carbapenemases underdiagnosed? An allelic discrimination assay for their accurate detection and differentiation

GES (Guiana Extended Spectrum) carbapenemases belong to "minor class A carbapenemases" and its prevalence could be underestimated due to the lack of specific tests. The aim of this study was to develop an easy PCR method to differentiate between GES β-lactamases with or without carbapenemase activity, based on an allelic discrimination system of SNPs that encode E104K and G170S mutations, without need of sequencing. Two pair of primers and Affinity Plus probes, labeled with different fluorophores; FAM/IBFQ and YAK/IBFQ, were designed for each one of the SNPs. This allelic discrimination assay allows to detect in real time the presence of all type of GES- β-lactamases, being able to differentiate between carbapenemases and extended-spectrum β-lactamase (ESBL), through a quick PCR test that avoid costly sequencing approaches and could help to decrease the current underdiagnosis of minor carbapenemases that scape of phenotypic screenings.

Usefulness of EUCAST rapid antibiotic susceptibility breakpoints and screening cut-off values directly from blood cultures for the inference of β-lactam resistance mechanisms in Enterobacterales

Background

Reducing the turnaround time for reporting antimicrobial susceptibility testing (AST) results is important for adjusting empirical treatments and may impact clinical outcomes of septic patients, particularly in settings with high antimicrobial resistance. Disc diffusion could be useful for inferring β-lactam resistance mechanisms.

Objectives

To evaluate the usefulness of EUCAST rapid AST (RAST) disc diffusion breakpoints for the screening of resistance mechanisms (sRAST) and interpretive reading of resistance phenotypes to infer ESBL and carbapenemases production in Enterobacterales.

Methods

Blood cultures were artificially spiked with Enterobacterales clinical isolates with well-characterized β-lactam resistance mechanisms (n = 93), WT phenotypes (n = 26) and ATCC strains (n = 8). AST was performed by disc diffusion directly from blood cultures and inhibition zones were manually measured at 4, 6 and 8 h. To infer the presence of resistance mechanisms, EUCAST RAST breakpoints and screening cut-off values (sRAST) combined with the double-disc synergy test (DDS) for ESBLs or aztreonam susceptibility for carbapenemases detection were used.

Results

DDS together with sRAST detected all ESBL producers as early as at 4 h incubation. Cefotaxime was the antibiotic with the highest discriminatory power. The suspicion of carbapenemase production by sRAST at 8 h was possible in 73% of Klebsiella pneumoniae and in 100% of Escherichia coli carbapenemase-producing isolates. Phenotypic analysis improves the detection of some low hydrolytic carbapenemases (OXA-48 or KPC-3 mutants).

Conclusions

Early detection of β-lactam resistance mechanisms directly from positive blood cultures was possible using sRAST together with the interpretive reading of antibiotic resistance phenotypes. Some carbapenemase types such as OXA-48 might be difficult to infer. Screening-positive isolates should be confirmed using an alternative technique.

New insights regarding HLA-B27 diversity in the Asian population

A polymerase chain reaction-sequence-specific primer (PCR-SSP) method which distinguishes all B27 alleles described at present (B*2701-23) has been developed. The distribution of B27 alleles was characterised in six different Asian populations. HLA-B*2705, 02, 04, 07, 22 (formerly B*2706) subtypes found in Asian populations differ in their ethnic distribution, which may be the result of different genetic and geographic origins. Furthermore, two novel B27 alleles were found in this study. B*2714 was identified in two Siberians, one of whom was a patient with ankylosing spondylitis. B*2715 was found in two patients with ankylosing spondylitis in Thais. These associations have not previously been reported in either ethnic group.

Genetic variability, molecular evolution, and geographic diversity of HLA-B27

HLA-B27 represents a family of 23 closely related alleles (B*2701-23) that differ at 24 amino acid positions. The pattern of polymorphisms of B27 was studied, with special reference to synonymous (Ks) and nonsynonymous (Ka) divergence among alleles. B27 alleles are characterized by the enhanced rate of nonsynonymous nucleotide substitution in the peptide-binding region (PBR). The percentage of substitutions between each of the B27 pairs ranges from 0.2%-3% in exons 2-3 to 1.8%-20.1% in the PBR. A phylogenetic analysis of all B27 alleles is described in order to identify subtypes with a common evolutionary history. These results, together with the phylogenetic trees obtained from the comparison between exons 2-3 and PBR indicate that polymorphism of B27 is selectively maintained. Most of the differences are clustered in the C/F pocket affecting the specific binding of antigenic peptides. Gene conversion and point mutation are the most important mechanisms responsible for B27 diversification. The interaction of selection, genetic drift, and recombination events is important for generating polymorphism at B27 alleles. We analyzed a large extended B27 positive population from different parts of the world. Our results indicate that B27 subtypes differ in their ethnic distribution, which may be the result of different genetic and geographical origins. Different factors such as genetic drift, bottleneck effect, and admixture among populations could contribute to the genetic constitution of B27. The striking correlation between the structural features of B27 and the ethnic distribution of these subtypes suggests a model of strong directional evolution, in which the subtypes could have arisen from B*2705.