Prevalence of the carbapenem-heteroresistant phenotype among ESBL-producing Escherichia coli and Klebsiella pneumoniae clinical isolates

Resilience of tigecycline heteroresistance phenotype in Acinetobacter baumannii

BACKGROUND

Heteroresistance, frequently observed in diverse bacterial species, imposes clinical challenges. For this study, we investigated the stability and resilience of tigecycline heteroresistance in Acinetobacter baumannii.

METHODS

Four tigecycline-heteroresistant (HR) A. baumannii strains and resistant populations (RPs) obtained from them were subjected to laboratory evolution assays for 30 days in antibiotic-free media. The heteroresistance phenotype was determined using a population analysis. Bacterial growth curves and in vitro competitiveness were determined to investigate the fitness cost of heteroresistance. Tigecycline efficacy was evaluated using an in vitro time-killing assay. Genetic mutations were identified using whole genome sequencing, and expression of genes in the two-component systems was also evaluated.

RESULTS

Tigecycline heteroresistance was preserved even in antibiotic-free media, and tigecycline-RPs reverted to heteroresistance during serial culture without tigecycline pressure. The tigecycline-RPs showed a higher fitness cost than their respective HR strains, and the HR strains exhibited a survival advantage upon tigecycline treatment. Although the AdeABC efflux pump was overexpressed in the tigecycline-RPs, it was down-regulated in the HR strains.

CONCLUSIONS

Our data indicate that tigecycline heteroresistance is a highly resilient phenotype in A. baumannii that gives a high fitness advantage to bacteria in terms of competitiveness and response to antibiotic pressure.

The Prevalence of Multidrug-Resistant Escherichia coli Producing ESBL among Male and Female Patients with Urinary Tract Infections in Riyadh Region, Saudi Arabia

The Escherichia coli that produces extended-spectrum lactamases (ESBL-E. coli) can develop resistance to many antibiotics. The control of ESBL-E. coli disorders is challenging due to their restricted therapeutic approaches, so this study aims to determine the prevalence and pattern of the antibiotic resistance of ESBL-E. coli among male and female patients with urinary tract infections in Riyadh, Saudi Arabia. During the period of 2019 to 2020 at King Fahd Medical City, Riyadh, 2250 urine samples from patients with urinary tract infections (UTIs) were collected, and microbial species were cultured and identified using standard biochemical techniques. A double-disc synergy test was used to identify ESBL-producing strains of E. coli, and an in vitro method and the clinical laboratory standard institute (CLSI) criteria were employed to determine the resistance of these strains to antimicrobial drugs. ESBL-E. coli was detected in 510 (33.49%) of the 1523 E. coli isolates, 67.27% of which were recovered from women and 33.7% of which were recovered from men. A total of 284 (55.69%) ESBL-E. coli isolates were found in patients under 50 years of age, and 226 (44.31%) were found in patients over 50 years of age. Nearly all the isolates of ESBL-E. coli were resistant to cephalosporins (ceftriaxone, cefotaxime, cefepime, cefuroxime, and cephalothin) and penicillin (ampicillin), whereas the majority of the isolates were sensitive to several carbapenems (imipenem, meropenem, and ertapenem), aminoglycosides (amikacin), and nitrofurantoins. The development of antibiotic resistance by ESBL-E. coli, the most frequent pathogen linked to urinary tract infections, plays a crucial role in determining which antibiotic therapy is appropriate.

Impact of Carbapenem Heteroresistance Among Multidrug-Resistant ESBL/AmpC-Producing Klebsiella pneumoniae Clinical Isolates on Antibiotic Treatment in Experimentally Infected Mice

Purpose

Antibiotic resistance is a growing health crisis that is further complicated by treatment failures caused by bacteria that exhibit heterogeneous susceptibility to antibiotics. The aim of this study was to describe imipenem (IPM)-heteroresistant strains among multidrug-resistant (MDR) ESBL/AmpC-producing Klebsiella pneumoniae clinical isolates, investigate their molecular phenotypic characteristics, and elucidate the outcome of antibiotic treatment in mice infected with the heteroresistant isolates.

Materials and Methods

Antimicrobial susceptibility of K. pneumoniae isolates was determined by the disk diffusion and E-test methods. Heteroresistance to IPM was confirmed by population analysis profile (PAP) assays. PCR and sequencing were employed to detect MDR determinants. Molecular differences between the susceptible and resistant subpopulations were evaluated by sequencing and quantitative real-time reverse transcription PCR (qRT-PCR) analysis. The effect of the carbapenem-heteroresistant strains on antibiotic treatment was assessed using a mouse model of peritonitis with heteroresistant K. pneumoniae and subsequent treatment with IPM.

Results

In total, 37 MDR ESBL/AmpC-producing clinical isolates of K. pneumoniae were identified between September 2018 and December 2019. These strains were notably resistant to conventional antimicrobials other than carbapenems. Among the isolates, three strains exhibited heteroresistance to IPM and carried several ESBL and/or AmpC genes. Mice infected with a lethal dose of any of the three heteroresistant isolates were unable to survive in the presence of IPM treatment, as the percentage of the IPM-resistant subpopulation of each strain was increased in the peritoneum of these mice at 24 h after infection. The resistant subpopulation of the strains presented pulsed-field gel electrophoresis (PFGE) profiles that were identical to those of the susceptible subpopulation, but ompK36 porin showed a reduction in gene expression (0.09- to 0.50-fold) in the resistant subpopulation.

Conclusion

Carbapenem-heteroresistant strains were present among the MDR K. pneumoniae isolates producing ESBL/AmpC β-lactamases, and these heteroresistant strains failed IPM therapy in experimentally infected mice.

Antibiotic Resistance Pattern of Extended Spectrum Beta Lactamase Producing Escherichia coli Isolated From Patients With Urinary Tract Infection in Morocco

Extended-spectrum β-lactamases producing Escherichia coli (ESBL-EC) lend resistance to most β-lactam antibiotics. Because of limited treatment options, ESBL-EC infections are generally more difficult to treat, leading to higher hospital costs, reduced rates of microbiological and clinical responses, and a threat to the patient’s life. This study aimed to determine the antibiotic resistance pattern of ESBL-EC isolated from patients with urinary tract infection in Morocco. This retrospective laboratory-based study was conducted at Cheikh Khalifa International University Hospital, Casablanca, from January 2016 to June 2019. A total of 670 urine samples were collected from urinary tract infection patients and processed by standard microbiological methods. In vitro susceptibility testing to different antibiotics of all identified isolates of Escherichia coli (E. coli) was performed following Kirby–Bauer’s disc diffusion method on Mueller–Hinton Agar according to the EUCAST standards. The reviewing of ESBL-EC was confirmed by the appearance of a characteristically shaped zone referred to as a “champagne cork” using the Combined Disk Test. Among a total of 438 E. coli isolated from nonrepetitive urine samples, two hundred fifty-nine (59%) were ESBL-EC, of which 200 (77%) were isolated from adult patients (over the age of 50) and the majority were female. All ESBL-EC isolates were resistant to third-generation cephalosporin and quinolones and sensitive to carbapenem and fosfomycin. Knowledge of antimicrobial resistance patterns in ESBL-EC, the major pathogen associated with urinary tract infection, is indispensable as a guide in choosing empirical antimicrobial treatment.

Enhanced Carbapenem Resistance through Multimerization of Plasmids Carrying Carbapenemase Genes

The worldwide dissemination of carbapenem-resistant Enterobacteriaceae (CRE) poses a critical human health issue by limiting the range of antibiotics that are usable in the treatment of common bacterial infections. Along with CRE, carbapenem heteroresistance has disseminated worldwide, which is described as different levels of carbapenem resistance within a seemingly isogenic bacterial population. Unstable carbapenem resistance will likely lead to unexpected treatment failure due to the enhanced resistance after initiation of treatment, contradicting antimicrobial susceptibility test results. Porin mutation and tandem amplification of the carbapenemase gene have been reported as mechanisms underlying enhanced carbapenem resistance. In this study, we identified multimerization of plasmids carrying carbapenemase genes, by using Southern blotting, whole-genome sequencing, and quantitative PCR (qPCR) analysis for the CRE isolates obtained in our previous surveillance in Osaka, Japan. Plasmids harboring a carbapenemase gene were multimerized by recA, likely through recombination at two consecutive sets of transposase genes of the IS91 family, thereby producing various plasmids of discrete sizes in a single bacterial cell of an Escherichia coli isolate. This multimerization resulted in increased copy numbers of carbapenemase genes, leading to enhanced gene transcription as well as carbapenem resistance. Prior exposure to meropenem further increased the copy number of carbapenemase genes, readily resulting in enhancement of carbapenem resistance. This mechanism may lead to clinical treatment failure by sifting antimicrobial resistance after the treatment initiation.

Detection of colistin-resistant populations prior to antibiotic exposure in KPC-2-producing Klebsiella pneumoniae clinical isolates

Although colistin is frequently regarded as the antibiotic of last resort in treating carbapenem-resistant Klebsiella pneumoniae, colistin heteroresistance may in part be associated with antibiotic treatment failure. However, we do not know how widespread the colistin heteroresistance is in carbapenem-resistant K. pneumoniae isolates. In this study, we performed colistin disc diffusion assays, E-tests, and population analysis profiling for KPC-2-producing K. pneumoniae isolates to identify colistin heteroresistance. Although no colistin-resistant colonies were detected by the disc diffusion test and E-test, a colistin-resistant subpopulation was identified in population analysis profiling in all colistin-susceptible, KPC-2-producing K. pneumoniae isolates. Colistin-resistant subpopulations were also identified even when isolates had no colistin exposure. The ratio of colistin-resistant subpopulations to the total population increased as the exposure concentration of colistin increased. In in vitro time-kill assays, regrowth was observed in all isolates after 2 h upon exposure to colistin. We identified common amino acid alterations in PhoQ, PhoP, and PmrB in colistin-resistant subpopulations from some isolates, but no substitutions were found in most resistant subpopulations from other isolates. In all colistin-resistant subpopulations, overexpression of PhoQ and PbgP was observed. In this study, we demonstrated that colistin heteroresistance may be common in KPC-2-producing K. pneumoniae isolates, which could not be detected in the disc diffusion method and E-test. Colistin heteroresistance may cause colistin treatment failure in part and may evolve into resistance. Thus, development of more reliable diagnostic methods is required to detect colistin heteroresistance.

Risk factors and outcome associated with infection or colonization due to carbapenem-heteroresistant Escherichia coli

Background

Up to 32% of ESBL-producing Enterobacterales strains display a carbapenem-heteroresistant (cHR) phenotype but its clinical relevance is unknown.

Objectives

To determine risk factors and clinical outcome associated with infection due to cHR ESBL-producing Escherichia coli (ESBL-EC).

Methods

A retrospective, case–control study was conducted on patients from whom a pair of clonally related E. coli strains were isolated during separate healthcare encounters with (case) or without (control) development of cHR phenotype in the latter strain. Study groups were compared for host and microbial characteristics and carbapenem exposure. Outcome measures included ICU admission, length of hospitalization, and mortality.

Results

Study patients (15 cases, 10 controls) were elderly (median age: 74 years) with half admitted from home (52%), most (80%) having ≥3 comorbid conditions and severe functional impairment. Case patients were more likely to have ‘index’ ESBL-EC isolating from blood (27% versus 0%; P = 0.125) and have greater cumulative amount and duration of carbapenem exposure than controls. All control ‘subsequent’ isolates were from urine whereas five cHR case isolates were from blood or respiratory sources. More hospitalized case patients required ICU admission (23% versus 0%; P = 0.257) and prolonged hospital stay (>7 days) than controls (62% versus 38%%; P = 0.387).

Conclusions

Our findings deserve confirmation with a larger study population and call attention to the potential for increased morbidity with cHR ESBL-EC infections, which underscores the need to screen for cHR phenotype in patients with repeated growth of ESBL-EC, particularly from systemic sites and patients that have had extensive carbapenem exposure.

Multidrug Resistance (MDR) and Collateral Sensitivity in Bacteria, with Special Attention to Genetic and Evolutionary Aspects and to the Perspectives of Antimicrobial Peptides-A Review

Antibiotic poly-resistance (multidrug-, extreme-, and pan-drug resistance) is controlled by adaptive evolution. Darwinian and Lamarckian interpretations of resistance evolution are discussed. Arguments for, and against, pessimistic forecasts on a fatal “post-antibiotic era” are evaluated. In commensal niches, the appearance of a new antibiotic resistance often reduces fitness, but compensatory mutations may counteract this tendency. The appearance of new antibiotic resistance is frequently accompanied by a collateral sensitivity to other resistances. Organisms with an expanding open pan-genome, such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, can withstand an increased number of resistances by exploiting their evolutionary plasticity and disseminating clonally or poly-clonally. Multidrug-resistant pathogen clones can become predominant under antibiotic stress conditions but, under the influence of negative frequency-dependent selection, are prevented from rising to dominance in a population in a commensal niche. Antimicrobial peptides have a great potential to combat multidrug resistance, since antibiotic-resistant bacteria have shown a high frequency of collateral sensitivity to antimicrobial peptides. In addition, the mobility patterns of antibiotic resistance, and antimicrobial peptide resistance, genes are completely different. The integron trade in commensal niches is fortunately limited by the species-specificity of resistance genes. Hence, we theorize that the suggested post-antibiotic era has not yet come, and indeed might never come.