Co-occurrence of the cephalosporinase cepA and carbapenemase cfiA genes in a Bacteroides fragilis division II strain, an unexpected finding.

BACKGROUND: Bacteroides fragilis, an anaerobic gut bacterium and opportunistic pathogen, comprises two genetically divergent groups (or divisions) at the species level. Differences exist both in the core and accessory genomes and the beta-lactamase genes, with the cephalosporinase gene cepA represented only in division I and the carbapenemase gene cfiA only in division II. METHODS: Multidrug resistance in a clinical B. fragilis strain was examined by whole-genome sequencing. RESULTS: Strain CNM20200260 carried the antimicrobial resistance genes cepA, cfiA2, ant(6'), erm(F), mef(En2), est(T), tet(Q) and cat(A), along with 82-Phe mutation in gyrA (together with 47 amino acid changes in gyrA/B and parC/parE). bexA/B and other efflux pump genes were also observed. None of the detected insertion sequences was located upstream of cfiA2. The genome-based taxonomy coefficients (average nucleotide identity, DNA-DNA hybridization similarity and difference in genomic G + C%) with respect to genomes of the strains of B. fragilis division II and the novel species Bacteroides hominis (both cfiA-positive) met the criteria for CNM20200260 to belong to either species (>95%, >70% and <1%, respectively). No such similarity was seen with type strain NCTC 9343 or the representative genome FDAARGOS 1225 of B. fragilis (division I, cfiA-negative). Strain CNM20200260 harboured four out of nine Kyoto Encyclopedia of Genes and Genomes orthologues defined for division I and one of two defined for division II. CONCLUSIONS: This is the first description of the co-occurrence of cepA and cfiA in a Bacteroides strain, confirming the complexity of the taxonomy of this species.

Extensively Drug-Resistant Pseudomonas aeruginosa Outbreak Associated With Artificial Tears.

BACKGROUND: Carbapenemase-producing, carbapenem-resistant Pseudomonas aeruginosa (CP-CRPA) are extensively drug-resistant bacteria. We investigated the source of a multistate CP-CRPA outbreak. METHODS: Cases were defined as a US patient's first isolation of P. aeruginosa sequence type 1203 with carbapenemase gene blaVIM-80 and cephalosporinase gene blaGES-9 from any specimen source collected and reported to the Centers for Disease Control and Prevention during 1 January 2022-15 May 2023. We conducted a 1:1 matched case-control study at the post-acute care facility with the most cases, assessed exposures associated with case status for all case-patients, and tested products for bacterial contamination. RESULTS: We identified 81 case-patients from 18 states, 27 of whom were identified through surveillance cultures. Four (7%) of 54 case-patients with clinical cultures died within 30 days of culture collection, and 4 (22%) of 18 with eye infections underwent enucleation. In the case-control study, case-patients had increased odds of receiving artificial tears versus controls (crude matched OR, 5.0; 95% CI, 1.1-22.8). Overall, artificial tears use was reported by 61 (87%) of 70 case-patients with information; 43 (77%) of 56 case-patients with brand information reported use of Brand A, an imported, preservative-free, over-the-counter (OTC) product. Bacteria isolated from opened and unopened bottles of Brand A were genetically related to patient isolates. Food and Drug Administration inspection of the manufacturing plant identified likely sources of contamination. CONCLUSIONS: A manufactured medical product serving as the vehicle for carbapenemase-producing organisms is unprecedented in the United States. The clinical impacts from this outbreak underscore the need for improved requirements for US OTC product importers.

Enhancing the activity of ß-lactamase inhibitory protein-II with cell-penetrating peptide against KPC-2-carrying Klebsiella pneumoniae.

Carbapenem-resistant Enterobacterales (CRE) is considered a paramount threat due to its rapid spread and high mortality rate. Klebsiella pneumoniae carbapenemases (KPCs), specifically KPC-2, are prevalent enzymes responsible for carbapenem resistance in many countries. While combinations of antibiotics are commonly used, they must be tailored to match the remaining susceptibility of the infecting strains. Therefore, there is a need to develop the ß-lactamase inhibitor to effectively address this issue. ß-lactamase inhibitor protein (BLIP) and its variants, BLIP-I and BLIP-II, have demonstrated the ability to inhibit class A ß-lactamases. In particular, BLIP-II shows strong binding to the KPC-2 carbapenemase, making it a potential candidate for inhibition. To improve the intracellular penetration of BLIP-II, a cell-penetrating peptide (CPP) was employed. In this study, a KRK-rich peptide was introduced at either the N-terminal or C-terminal region of tBLIP-II, excluding the signal sequence of the BLIP-II protein. tBLIP-II, tBLIP-II-CPP, and CPP-BLIP-II were successfully expressed, and the chimeric proteins retained inhibitory activity compared to tBLIP-II alone. It is apparent that homology modeling demonstrated neither the poly-histidine tag nor the CPP interfered with the essential interaction residues of tBLIP-II. Interestingly, BLIP-II-CPP exhibited the highest inhibitory activity, reducing the minimal inhibitory concentration (MIC) of meropenem by 8 folds. Moreover, the combination of tBLIP-CPP with meropenem significantly decreased the viable bacterial cell count compared to the combination of tBLIP-II with meropenem or meropenem alone. These findings suggest that tBLIP-CPP is a promising candidate for restoring carbapenem susceptibility against CRE and provides a valuable therapeutic option for infections caused by CRE.

Filling knowledge gaps related to AmpC-dependent ß-lactam resistance in Enterobacter cloacae.

Enterobacter cloacae starred different pioneer studies that enabled the development of a widely accepted model for the peptidoglycan metabolism-linked regulation of intrinsic class C cephalosporinases, highly conserved in different Gram-negatives. However, some mechanistic and fitness/virulence-related aspects of E. cloacae choromosomal AmpC-dependent resistance are not completely understood. The present study including knockout mutants, ß-lactamase cloning, gene expression analysis, characterization of resistance phenotypes, and the Galleria mellonella infection model fills these gaps demonstrating that: (i) AmpC enzyme does not show any collateral activity impacting fitness/virulence; (ii) AmpC hyperproduction mediated by ampD inactivation does not entail any biological cost; (iii) alteration of peptidoglycan recycling alone or combined with AmpC hyperproduction causes no attenuation of E. cloacae virulence in contrast to other species; (iv) derepression of E. cloacae AmpC does not follow a stepwise dynamics linked to the sequential inactivation of AmpD amidase homologues as happens in Pseudomonas aeruginosa; (v) the enigmatic additional putative AmpC-type ß-lactamase generally present in E. cloacae does not contribute to the classical cephalosporinase hyperproduction-based resistance, having a negligible impact on phenotypes even when hyperproduced from multicopy vector. This study reveals interesting particularities in the chromosomal AmpC-related behavior of E. cloacae that complete the knowledge on this top resistance mechanism.

Natural protein engineering in the Ω-loop: the role of Y221 in ceftazidime and ceftolozane resistance in Pseudomonas-derived cephalosporinase.

A wide variety of clinically observed single amino acid substitutions in the Ω-loop region have been associated with increased minimum inhibitory concentrations and resistance to ceftazidime (CAZ) and ceftolozane (TOL) in Pseudomonas-derived cephalosporinase and other class C ß-lactamases. Herein, we demonstrate the naturally occurring tyrosine to histidine substitution of amino acid 221 (Y221H) in Pseudomonas-derived cephalosporinase (PDC) enables CAZ and TOL hydrolysis, leading to similar kinetic profiles (k cat = 2.3 ± 0.2 µM and 2.6 ± 0.1 µM, respectively). Mass spectrometry of PDC-3 establishes the formation of stable adducts consistent with the formation of an acyl enzyme complex, while spectra of E219K (a well-characterized, CAZ- and TOL-resistant comparator) and Y221H are consistent with more rapid turnover. Thermal denaturation experiments reveal decreased stability of the variants. Importantly, PDC-3, E219K, and Y221H are all inhibited by avibactam and the boronic acid transition state inhibitors (BATSIs) LP06 and S02030 with nanomolar IC50 values and the BATSIs stabilize all three enzymes. Crystal structures of PDC-3 and Y221H as apo enzymes and complexed with LP06 and S02030 (1.35-2.10 Å resolution) demonstrate ligand-induced conformational changes, including a significant shift in the position of the sidechain of residue 221 in Y221H (as predicted by enhanced sampling well-tempered metadynamics simulations) and extensive hydrogen bonding between the enzymes and BATSIs. The shift of residue 221 leads to the expansion of the active site pocket, and molecular docking suggests substrates orientate differently and make different intermolecular interactions in the enlarged active site compared to the wild-type enzyme.

Synthesis of a Novel Boronic Acid Transition State Inhibitor, MB076: A Heterocyclic Triazole Effectively Inhibits Acinetobacter-Derived Cephalosporinase Variants with an Expanded-Substrate Spectrum.

Class C Acinetobacter-derived cephalosporinases (ADCs) represent an important target for inhibition in the multidrug-resistant pathogen Acinetobacter baumannii. Many ADC variants have emerged, and characterization of their structural and functional differences is essential. Equally as important is the development of compounds that inhibit all prevalent ADCs despite these differences. The boronic acid transition state inhibitor, MB076, a novel heterocyclic triazole with improved plasma stability, was synthesized and inhibits seven different ADC ß-lactamase variants with Ki values <1 µM. MB076 acted synergistically in combination with multiple cephalosporins to restore susceptibility. ADC variants containing an alanine duplication in the Ω-loop, specifically ADC-33, exhibited increased activity for larger cephalosporins, such as ceftazidime, cefiderocol, and ceftolozane. X-ray crystal structures of ADC variants in this study provide a structural context for substrate profile differences and show that the inhibitor adopts a similar conformation in all ADC variants, despite small changes near their active sites.

Antimicrobial resistance of Pseudomonas aeruginosa in a cystic fibrosis population after introduction of a novel cephalosporin/ß-lactamase inhibitor combination.

Ceftolozane-tazobactam is a new ß-lactam/ß-lactamase inhibitor combination approved by the U.S. Food and Drug Administration in 2019 for the treatment of hospital-acquired and ventilator-associated pneumonia. The combination is a particularly potent inhibitor of penicillin-binding proteins with higher affinity than other ß-lactam agents. Persons with cystic fibrosis (pwCF) often harbour resistant Gram-negative bacteria in the airways and need antibiotics to prevent declining lung function. To test whether the introduction of ceftolozane-tazobactam in the period 2015-2020 led to a bacterial population level increase in cephalosporin resistance in a Danish CF population. In vitro, activity of ceftolozane-tazobactam was evaluated by susceptibility testing of clinical Pseudomonas aeruginosa isolated from pwCF from January 1, 2015, to June 1, 2020. Six thousand three hundred thirty two isolates collected from 210 adult pwCF were included. Thirty pwCF were treated with ceftolozane-tazobactam at least once. Ceftolozane-tazobactam exposure did not increase cephalosporin resistance on an individual or population level. However, resistance to ceftolozane-tazobactam was recorded despite no prior exposure in four pwCF. Compared to ceftazidime, ceftolozane-tazobactam had a better in vitro activity on P. aeruginosa. The percentage of non-mucoid P. aeruginosa isolates susceptible to ceftolozane-tazobactam were higher or equal to 5 other ß-lactams. Ceftolozane-tazobactam expands the armamentaria against P. aeruginosa with acceptable levels for a selection of drug resistance.

LY2183240 regioisomers act as competitive and selective inhibitors of class C ß-lactamases.

The regioisomers of the anandamide-acting drug LY2183240 exhibited specific potent and competitive inhibitory activities against class C ß-lactamases. More explicitly, the 1,5- and 2,5-regioisomers inhibited AmpC from Enterobacter hormaechei (formerly Enterobacter cloacae) with inhibitor binding affinity values of 1.8 µM and 2.45 µM, respectively. Structural molecular modelling studies revealed the interaction of the regioisomers with the relevant residues of the catalytic site of cephalosporinase from E. hormaechei P99, which included Tyr150, Lys315 and Thr316.

Simultaneous and divergent evolution of resistance to cephalosporin/ß-lactamase inhibitor combinations and imipenem/relebactam following ceftazidime/avibactam treatment of MDR Pseudomonas aeruginosa infections.

OBJECTIVES: To describe and characterize the emergence of resistance to ceftolozane/tazobactam, ceftazidime/avibactam and imipenem/relebactam in a patient receiving ceftazidime/avibactam treatment for an MDR Pseudomonas aeruginosa CNS infection. METHODS: One baseline (PA1) and two post-exposure (PA2 and PA3) isolates obtained before and during treatment of a nosocomial P. aeruginosa meningoventriculitis were evaluated. MICs were determined by broth microdilution. Mutational changes were investigated through WGS. The impact on ß-lactam resistance of mutations in blaPDC and mexR was determined through cloning experiments and complementation assays. RESULTS: Isolate PA1 showed baseline resistance mutations in DacB (I354A) and OprD (N142fs) conferring resistance to conventional antipseudomonals but susceptibility to ceftazidime/avibactam, ceftolozane/tazobactam and imipenem/relebactam. Post-exposure isolates showed two divergent ceftazidime/avibactam-resistant phenotypes associated with distinctive mutations affecting the intrinsic P PDC ß-lactamase (S254Ins) (PA2: ceftolozane/tazobactam and ceftazidime/avibactam-resistant) or MexAB-OprM negative regulator MexR in combination with modification of PBP3 (PA3: ceftazidime/avibactam and imipenem/relebactam-relebactam-resistant). Cloning experiments demonstrated the role of PDC modification in resistance to ceftolozane/tazobactam and ceftazidime/avibactam. Complementation with a functional copy of the mexR gene in isolate PA3 restored imipenem/relebactam susceptibility. CONCLUSIONS: We demonstrated how P. aeruginosa may simultaneously develop resistance and compromise the activity of new ß-lactam/ß-lactamase inhibitor combinations when exposed to ceftazidime/avibactam through selection of mutations leading to PDC modification and up-regulation of MexAB-OprM-mediated efflux.

Evaluation of the BL-RED (Beta-Lactamase Rapid Electrochemical Detection) test for the rapid detection of resistance to third-generation cephalosporins in Enterobacteriaceae.

The sensitivity of NG-test CTX-M Multi assay and BL-RED test incubated 10 min for the detection of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae was 80.6% and 90.3% respectively. Using an extended 60 min incubation with the BL-RED test, its sensitivity was increased to 100% and 60.9% for ESBL-producing and cephalosporinase-overexpressing Enterobacteriaceae respectively.

Role of Enzymatic Activity in the Biological Cost Associated with the Production of AmpC ß-Lactamases in Pseudomonas aeruginosa.

In the current scenario of growing antibiotic resistance, understanding the interplay between resistance mechanisms and biological costs is crucial for designing therapeutic strategies. In this regard, intrinsic AmpC ß-lactamase hyperproduction is probably the most important resistance mechanism of Pseudomonas aeruginosa, proven to entail important biological burdens that attenuate virulence mostly under peptidoglycan recycling alterations. P. aeruginosa can acquire resistance to new ß-lactam-ß-lactamase inhibitor combinations (ceftazidime-avibactam and ceftolozane-tazobactam) through mutations affecting ampC and its regulatory genes, but the impact of these mutations on the associated biological cost and the role that ß-lactamase activity plays per se in contributing to the above-mentioned virulence attenuation are unknown. The same questions remain unsolved for plasmid-encoded AmpC-type ß-lactamases such as FOX enzymes, some of which also provide resistance to new ß-lactam-ß-lactamase inhibitor combinations. Here, we assessed from different perspectives the effects of changes in the active center and, thus, in the hydrolytic spectrum resistance to inhibitors of AmpC-type ß-lactamases on the fitness and virulence of P. aeruginosa, using site-directed mutagenesis; the previously described AmpC variants T96I, G183D, and ΔG229-E247; and, finally, blaFOX-4 versus blaFOX-8. Our results indicate the essential role of AmpC activity per se in causing the reported full virulence attenuation (in terms of growth, motility, cytotoxicity, and Galleria mellonella larvae killing), although the biological cost of the above-mentioned AmpC-type variants was similar to that of the wild-type enzymes. This suggests that there is not an important biological burden that may limit the selection/spread of these variants, which could progressively compromise the future effectiveness of the above-mentioned drug combinations. IMPORTANCE The growing antibiotic resistance of the top nosocomial pathogen Pseudomonas aeruginosa pushes research to explore new therapeutic strategies, for which the resistance-versus-virulence balance is a promising source of targets. While resistance often entails significant biological costs, little is known about the bases of the virulence attenuations associated with a resistance mechanism as extraordinarily relevant as ß-lactamase production. We demonstrate that besides potential energy and cell wall alterations, the enzymatic activity of the P. aeruginosa cephalosporinase AmpC is essential for causing the full attenuation associated with its hyperproduction by affecting different features related to pathogenesis, a fact exploitable from the antivirulence perspective. Less encouraging, we also show that the production of different chromosomal/plasmid-encoded AmpC derivatives conferring resistance to some of the newest antibiotic combinations causes no significantly increased biological burdens, which suggests a free way for the selection/spread of these types of variants, potentially compromising the future effectiveness of these antipseudomonal therapies.

Longitudinal Evolution of the Pseudomonas-Derived Cephalosporinase (PDC) Structure and Activity in a Cystic Fibrosis Patient Treated with ß-Lactams.

Traditional studies on the evolution of antibiotic resistance development use approaches that can range from laboratory-based experimental studies, to epidemiological surveillance, to sequencing of clinical isolates. However, evolutionary trajectories also depend on the environment in which selection takes place, compelling the need to more deeply investigate the impact of environmental complexities and their dynamics over time. Herein, we explored the within-patient adaptive long-term evolution of a Pseudomonas aeruginosa hypermutator lineage in the airways of a cystic fibrosis (CF) patient by performing a chronological tracking of mutations that occurred in different subpopulations; our results demonstrated parallel evolution events in the chromosomally encoded class C ß-lactamase (blaPDC). These multiple mutations within blaPDC shaped diverse coexisting alleles, whose frequency dynamics responded to the changing antibiotic selective pressures for more than 26 years of chronic infection. Importantly, the combination of the cumulative mutations in blaPDC provided structural and functional protein changes that resulted in a continuous enhancement of its catalytic efficiency and high level of cephalosporin resistance. This evolution was linked to the persistent treatment with ceftazidime, which we demonstrated selected for variants with robust catalytic activity against this expanded-spectrum cephalosporin. A "gain of function" of collateral resistance toward ceftolozane, a more recently introduced cephalosporin that was not prescribed to this patient, was also observed, and the biochemical basis of this cross-resistance phenomenon was elucidated. This work unveils the evolutionary trajectories paved by bacteria toward a multidrug-resistant phenotype, driven by decades of antibiotic treatment in the natural CF environmental setting. IMPORTANCE Antibiotics are becoming increasingly ineffective to treat bacterial infections. It has been consequently predicted that infectious diseases will become the biggest challenge to human health in the near future. Pseudomonas aeruginosa is considered a paradigm in antimicrobial resistance as it exploits intrinsic and acquired resistance mechanisms to resist virtually all antibiotics known. AmpC ß-lactamase is the main mechanism driving resistance in this notorious pathogen to ß-lactams, one of the most widely used classes of antibiotics for cystic fibrosis infections. Here, we focus on the ß-lactamase gene as a model resistance determinant and unveil the trajectory P. aeruginosa undertakes on the path toward a multidrug-resistant phenotype during the course of two and a half decades of chronic infection in the airways of a cystic fibrosis patient. Integrating genetic and biochemical studies in the natural environment where evolution occurs, we provide a unique perspective on this challenging landscape, addressing fundamental molecular mechanisms of resistance.

Functional and Structural Characterization of OXA-935, a Novel OXA-10-Family ß-Lactamase from Pseudomonas aeruginosa.

Resistance to antipseudomonal penicillins and cephalosporins is often driven by the overproduction of the intrinsic ß-lactamase AmpC. However, OXA-10-family ß-lactamases are a rich source of resistance in Pseudomonas aeruginosa. OXA ß-lactamases have a propensity for mutation that leads to extended spectrum cephalosporinase and carbapenemase activity. In this study, we identified isolates from a subclade of the multidrug-resistant (MDR) high risk P. aeruginosa clonal complex CC446 with a resistance to ceftazidime. A genomic analysis revealed that these isolates harbored a plasmid containing a novel allele of blaOXA-10, named blaOXA-935, which was predicted to produce an OXA-10 variant with two amino acid substitutions: an aspartic acid instead of a glycine at position 157 and a serine instead of a phenylalanine at position 153. The G157D mutation, present in OXA-14, is associated with the resistance of P. aeruginosa to ceftazidime. Compared to OXA-14, OXA-935 showed increased catalytic efficiency for ceftazidime. The deletion of blaOXA-935 restored the sensitivity to ceftazidime, and susceptibility profiling of P. aeruginosa laboratory strains expressing blaOXA-935 revealed that OXA-935 conferred ceftazidime resistance. To better understand the impacts of the variant amino acids, we determined the crystal structures of OXA-14 and OXA-935. Compared to OXA-14, the F153S mutation in OXA-935 conferred increased flexibility in the omega (Ω) loop. Amino acid changes that confer extended spectrum cephalosporinase activity to OXA-10-family ß-lactamases are concerning, given the rising reliance on novel ß-lactam/ß-lactamase inhibitor combinations, such as ceftolozane-tazobactam and ceftazidime-avibactam, to treat MDR P. aeruginosa infections.

Rapid Identification and Classification of Pathogens That Produce Carbapenemases and Cephalosporinases with a Colorimetric Paper-Based Multisensor.

Infections caused by bacteria that produce ß-lactamases (BLs) are a major problem in hospital settings. The phenotypic detection of these bacterial strains requires culturing samples prior to analysis. This procedure may take up to 72 h, and therefore it cannot be used to guide the administration of the first antibiotic regimen. Here, we propose a multisensor for identifying pathogens bearing different types of ß-lactamases above the infectious dose threshold within 90 min that does not require culturing samples. Instead, bacterial cells are preconcentrated in the cellulose scaffold of a paper-based multisensor. Then, 12 assays are performed in parallel to identify whether the pathogens produce carbapenemases and/or cephalosporinases, including metallo-ß-lactamases, extended-spectrum ß-lactamases (ESBLs), and AmpC enzymes. The multisensor generates an array of colored spots that can be quantified with image processing software and whose interpretation leads to the detection of the different enzymes depending on their specificity toward the hydrolysis of certain antibiotics, and/or their pattern of inhibition or cofactor activation. The test was validated for the diagnosis of urinary tract infections. The inexpensive paper platform along with the uncomplicated colorimetric readout makes the proposed prototypes promising for developing fully automated platforms for streamlined clinical diagnosis.

Colonization of White-Tailed Deer (Odocoileus virginianus) from Urban and Suburban Environments with Cephalosporinase- and Carbapenemase-Producing Enterobacterales.

Wildlife play a role in the acquisition, maintenance, and dissemination of antimicrobial resistance (AMR). This is especially true at the human-domestic animal-wildlife interface, like urbanized areas, where interactions occur that can promote the cross-over of AMR bacteria and genes. We conducted a 2-year fecal surveillance (n = 783) of a white-tailed deer (WTD) herd from an urban park system in Ohio to identify and characterize cephalosporin-resistant and carbapenemase-producing bacteria using selective enrichment. Using generalized linear mixed models we found that older (OR = 2.3, P < 0.001), male (OR = 1.8, P = 0.001) deer from urbanized habitats (OR = 1.4, P = 0.001) were more likely to harbor extended-spectrum cephalosporin-resistant Enterobacterales. In addition, we isolated two carbapenemase-producing Enterobacterales (CPE), a Klebsiella quasipneumoniae harboring blaKPC-2 and an Escherichia coli harboring blaNDM-5, from two deer from urban habitats. The genetic landscape of the plasmid carrying blaKPC-2 was unique, not clustering with other reported plasmids encoding KPC-2, and only sharing 78% of its sequence with its nearest match. While the plasmid carrying blaNDM-5 shared sequence similarity with other reported plasmids encoding NDM-5, the intact IS26 mobile genetic elements surrounding multiple drug resistant regions, including the blaNDM-5, has been reported infrequently. Both carbapenemase genes were successfully conjugated to a J53 recipient conferring a carbapenem-resistant phenotype. Our findings highlight that urban environments play a significant role on the transmission of AMR bacteria and genes to wildlife and suggest WTD may play a role in the dissemination of clinically and epidemiologically relevant antimicrobial resistant bacteria. IMPORTANCE The role of wildlife in the spread of antimicrobial resistance is not fully characterized. Some wildlife, including white-tailed deer (WTD), can thrive in suburban and urban environments. This may result in the exchange of antimicrobial resistant bacteria and resistance genes between humans and wildlife, and lead to their spread in the environment. We found that WTD living in an urban park system carried antimicrobial resistant bacteria that were important to human health and resistant to antibiotics used to treat serious bacterial infections. This included two deer that carried bacteria resistant to carbapenem antibiotics which are critically important for treatment of life-threatening infections. These two bacteria had the ability to transfer their AMR resistance genes to other bacteria, making them a threat to public health. Our results suggest that WTD may contribute to the spread of antimicrobial resistant bacteria in the environment.

In vitro activity of imipenem/relebactam plus aztreonam against metallo-ß-lactamase-producing, OprD-deficient Pseudomonas aeruginosa with varying levels of Pseudomonas-derived cephalosporinase production.

BACKGROUND: Treatment options for metallo-ß-lactamase (MBL)-producing Pseudomonas aeruginosa infections are limited. Imipenem/relebactam (I/R) plus aztreonam (ATM) may be an option. METHODS: Ten OprD(-) P. aeruginosa isolates (3 parent strains; 7 MBL-producers) were evaluated using checkerboard methodology and Fractional Inhibitory Concentration Index (FICI). Isolates exhibiting synergy in checkerboard studies (FICI ≤0.5) were evaluated using 24-h static concentration time-kill. Bacteria in late log-phase growth were diluted to 1 × 106 cfu/mL and incubated at 37°C for 24 h. Samples were drawn at 0, 2, 4, 6 and 24 h. Physiological fCmax, fCss,avg and fCmin of imipenem (26.7, 5.6, 0.5 mg/L), relebactam (REL; 13.1, 4, 0.8 mg/L) and ATM (62, 29, 8 mg/L) were used. Synergy in time-kill studies was defined as >2 log10 cfu/mL reduction compared with the most active individual agent. RESULTS: Synergy was observed in five isolates in checkerboard studies, including three of seven MBL-producing isolates. Isolates that were OprD(-) and harbored inducible Pseudomonas-derived cephalosporinases (PDCs) did not show synergy as defined by FICI; however, ATM minimum inhibitory concentrations (MICs) were significantly reduced with the combination. In time-kill studies, ATM alone was as active as combination regimens for MBL-producing isolates with deleted or inducible PDC production. For strains exhibiting constitutive PDC production, I/R plus ATM was synergistic at fCss,avg concentrations but exhibited similar activity to ATM at fCmin and fCmax concentrations. CONCLUSIONS: I/R plus ATM appears to exhibit synergy for some MBL-producing P. aeruginosa at physiological concentrations. Further study of the effect of dynamic concentrations is needed to fully understand the utility of this combination.

Impact of Peptidoglycan Recycling Blockade and Expression of Horizontally Acquired ß-Lactamases on Pseudomonas aeruginosa Virulence.

In the current scenario of antibiotic resistance magnification, new weapons against top nosocomial pathogens like Pseudomonas aeruginosa are urgently needed. The interplay between ß-lactam resistance and virulence is considered a promising source of targets to be attacked by antivirulence therapies, and in this regard, we previously showed that a peptidoglycan recycling blockade dramatically attenuated the pathogenic power of P. aeruginosa strains hyperproducing the chromosomal ß-lactamase AmpC. Here, we sought to ascertain whether this observation could be applicable to other ß-lactamases. To do so, P. aeruginosa wild-type or peptidoglycan recycling-defective strains (ΔampG and ΔnagZ) harboring different cloned ß-lactamases (transferable GES, VIM, and OXA types) were used to assess their virulence in Galleria mellonella larvae by determining 50% lethal doses (LD50s). A mild yet significant LD50 increase was observed after peptidoglycan recycling disruption per se, whereas the expression of class A and B enzymes did not impact virulence. While the production of the narrow-spectrum class D OXA-2 entailed a slight attenuation, its extended-spectrum derivatives OXA-226 (W159R [bearing a change of W to R at position 159]), OXA-161 (N148D), and principally, OXA-539 (D149 duplication) were associated with outstanding virulence impairments, especially in recycling-defective backgrounds (with some LD50s being >1,000-fold that of the wild type). Although their exact molecular bases remain to be deciphered, these results suggest that mutations affecting the catalytic center and, therefore, the hydrolytic spectrum of OXA-2-derived enzymes also drastically impact the pathogenic power of P. aeruginosa. This work provides new and relevant knowledge to the complex topic of the interplay between the production of ß-lactamases and virulence that could be useful to build future therapeutic strategies against P. aeruginosa. IMPORTANCE Pseudomonas aeruginosa is one of the leading nosocomial pathogens whose growing resistance makes the development of therapeutic options extremely urgent. The resistance-virulence interplay has classically aroused researchers' interest as a source of therapeutic targets. In this regard, we describe a wide array of virulence attenuations associated with different transferable ß-lactamases, among which the production of OXA-2-derived extended-spectrum ß-lactamases stood out as a dramatic handicap for pathogenesis, likely as a side effect of mutations causing the expansion of their hydrolytic spectrums. Moreover, our results confirm the validity of disturbing peptidoglycan recycling as a weapon to attenuate P. aeruginosa virulence in class C and D ß-lactamase production backgrounds. In the current scenario of dissemination of horizontally acquired ß-lactamases, this work brings out new data on the complex interplay between the production of specific enzymes and virulence attenuation that, if complemented with the characterization of the underlying mechanisms, will likely be exploitable to develop future virulence-targeting antipseudomonal strategies.

Emergence of Resistance to Novel Cephalosporin-ß-Lactamase Inhibitor Combinations through the Modification of the Pseudomonas aeruginosa MexCD-OprJ Efflux Pump.

A ceftolozane-tazobactam- and ceftazime-avibactam-resistant Pseudomonas aeruginosa isolate was recovered after treatment (including azithromycin, meropenem, and ceftolozane-tazobactam) from a patient that had developed ventilator-associated pneumonia after COVID-19 infection. Whole-genome sequencing revealed that the strain, belonging to ST274, had acquired a nonsense mutation leading to truncated carbapenem porin OprD (W277X), a 7-bp deletion (nt213Δ7) in NfxB (negative regulator of the efflux pump MexCD-OprJ), and two missense mutations (Q178R and S133G) located within the first large periplasmic loop of MexD. Through the construction of mexD mutants and complementation assays with wild-type nfxB, it was evidenced that resistance to the novel cephalosporin-ß-lactamase inhibitor combinations was caused by the modification of MexD substrate specificity.

Emergence of Resistance to Ceftazidime-Avibactam in a Pseudomonas aeruginosa Isolate Producing Derepressed blaPDC in a Hollow-Fiber Infection Model.

Ceftazidime (CAZ)-avibactam (AVI) is a ß-lactam/ß-lactamase inhibitor combination with activity against type A and type C ß-lactamases. Resistance emergence has been seen, with multiple mechanisms accounting for the resistance. We performed four experiments in the dynamic hollow-fiber infection model, delineating the linkage between drug exposure and both the rate of bacterial kill and resistance emergence by all mechanisms. The Pseudomonas aeruginosa isolate had MICs of 1.0 mg/liter (CAZ) and 4 mg/liter (AVI). We demonstrated that the time at ≥4.0 mg/liter AVI was linked to the rate of bacterial kill. Linkage to resistance emergence/suppression was more complex. In one experiment in which CAZ and AVI administration was intermittent and continuous, respectively, and in which AVI was given in unitary steps from 1 to 8 mg/liter, AVI at up to 3 mg/liter allowed resistance emergence, whereas higher values did not. The threshold value was 3.72 mg/liter as a continuous infusion to counterselect resistance (AVI area under the concentration-time curve [AUC] of 89.3 mg · h/liter). The mechanism involved a 7-amino-acid deletion in the Ω-loop region of the Pseudomonas-derived cephalosporinase (PDC) ß-lactamase. Further experiments in which CAZ and AVI were both administered intermittently with regimens above and below the AUC of 89.3 mg · h/liter resulted in resistance in the lower-exposure groups. Deletion mutants were not identified. Finally, in an experiment in which paired exposures as both continuous and intermittent infusions were performed, the lower value of 25 mg · h/liter by both profiles allowed selection of deletion mutants. Of the five instances in which these mutants were recovered, four had a continuous-infusion profile. Both continuous-infusion administration and low AVI AUC exposures have a role in selection of this mutation.

Screening and identification of bioactive components resistant to metallo-beta-lactamase from Schisandra chinensis (Turcz.) Baill. by metalloenzyme-immobilized affinity chromatography.

The screening and identification of bioactive components, which are effectively resistant to metallo-beta-lactamase (MßL), were studied in the alcohol extract of Schisandra chinensis (Turcz.) Baill. by metalloenzyme-immobilized affinity chromatography. Taking bizinc metalloenzyme beta-lactamase II from Bacillus cereus (Bc II) and monozinc metalloenzyme CphA from aeromonas hydrophila (CphA) as examples, we studied the feasibility of this scheme based on the construction of metalloenzyme-immobilized chromatographic model. It was found that the Bc II- and CphA-immobilized chromatographic column could be used not only to explore the interaction between the MßL and their specific ligands, but also to screen the bioactive components from traditional Chinese medicine. The Bc II-and CphA-immobilized columns were used to screen the bioactive components from the alcohol extract of Schisandra chinensis (Turcz.) Baill. Time-of-flight tandem mass spectrometry analysis and molecular docking revealed that isobutyl 3-O-sulfo-ß-D-galactopyranoside is the effective bioactive components that could bind with metalloenzyme Bc II. It is believed that our current work may provide a methodological reference for screening MßL inhibitors from traditional Chinese medicine.