Mechanisms Underlying Contact Lens-Related Keratitis Caused by Pseudomonas aeruginosa.

ABSTRACT: Infectious keratitis is a severe complication associated with contact lens (CL) wear, and can progress rapidly with suppurative infiltration, resulting in the loss of vision. Contact lens wearers with poor and improper care are susceptible to develop infectious keratitis. Gram-negative bacilli such as Pseudomonas aeruginosa, have an ability to form biofilms on CL cases and CLs. Moreover, P. aeruginosa has various virulence factors such as type III secretion system (TTSS) which is an important factor for pathogenicity in keratitis. The effector proteins of TTSS have been identified, namely ExoU, ExoS, ExoT, and ExoY. Pseudomonas aeruginosa strains with ExoU show resistance to disinfection. The strains isolated from CL-related keratitis have higher ExoU gene positivity. Expression of elastase and swarming motility of P. aeruginosa isolates significantly correlates with focus size of keratitis. In addition to education of lens care for the CL wearer, development of CL cleaning solutions targeting suppression of virulence factors are needed for prevention of CL-related keratitis in the future.

Investigation of antimicrobial resistance patterns and molecular typing of Pseudomonas aeruginosa isolates among Coronavirus disease-19 patients.

BACKGROUND: Pseudomonas aeruginosa is a common co-infecting pathogen recognized among COVID-19 patients. We aimed to investigate the antimicrobial resistance patterns and molecular typing of Pseudomonas aeruginosa isolates among Coronavirus disease-19 patients. METHODS: Between December 2020 and July 2021, 15 Pseudomonas aeruginosa were isolated from COVID-19 patients in the intensive care unit at Sina Hospital in Hamadan, west of Iran. The antimicrobial resistance of the isolates was determined by disk diffusion and broth microdilution methods. The double-disk synergy method, Modified Hodge test, and polymerase chain reaction were utilized to detect Pseudomonas aeruginosa extended spectrum beta-lactamase and carbapenemase producers. Microtiter plate assay was performed to evaluate the biofilm formation ability of the isolates. The isolates phylogenetic relatedness was revealed using the multilocus variable-number tandem-repeat analysis method. RESULTS: The results showed Pseudomonas aeruginosa isolates had the most elevated resistance to imipenem (93.3%), trimethoprim-sulfamethoxazole (93.3%), ceftriaxone (80%), ceftazidime (80%), gentamicin (60%), levofloxacin (60%), ciprofloxacin (60%), and cefepime (60%). In the broth microdilution method, 100%, 100%, 20%, and 13.3% of isolates showed resistance to imipenem, meropenem, polymyxin B, and colistin, respectively. Ten (66.6%) isolates were identified as multiple drug resistance. Carbapenemase enzymes and extended spectrum beta-lactamases were identified in 66.6% and 20% of the isolates, respectively and the biofilm formation was detected in 100% of the isolates. The blaOXA-48, blaTEM, blaIMP, blaSPM, blaPER, blaVEB, blaNDM, blaSHV, and blaCTX-M genes were detected in 100%, 86.6%, 86.6%, 40%, 20%, 20%, 13.3%, 6.6%, and 6.6% of the isolates, respectively. The blaVIM, blaGIM, blaGES, and blaMCR-1 genes were not identified in any of the isolates. The MLVA typing technique showed 11 types and seven main clusters and most isolates belong to cluster I, V and VII. CONCLUSION: Due to the high rate of antimicrobial resistance, as well as the genetic diversity of Pseudomonas aeruginosa isolates from COVID-19 patients, it is indispensable to monitor the antimicrobial resistance pattern and epidemiology of the isolates on a regular basis.

Isolation of Pseudomonas aeruginosa from Persistent Bacterial Coinfection of a COVID-19 Patients with Molecular Detection of Antibiotics Resistance Genes.

Pseudomonas aeruginosa (P. aeruginosa) have a considerable risk to public health in the world, due to its high ability to develop resistance to different classes of antibiotics. It has been discovered as a prevalent coinfection pathogen that causes sickness exacerbation in COVID-19 patients. This study aimed to determine the prevalence of P. aeruginosa from COVID-19 patients in Al Diwaniyah province, Iraq and to identify its genetic resistance pattern. 70 clinical samples were obtained from severe cases of patients (RT-PCR positive for SARS-COV-2 on a nasopharyngeal swab) who attended Al Diwaniyah Academic Hospital. 50 P. aeruginosa bacterial isolates were detected via microscopic examination, routine cultured and biochemical testing, then validated by the VITEK-2 compact system. VITEK reported 30 positive results, which later confirmed through molecular detection using 16s RNA specific for detection and a phylogenetic tree.20 isolates had positive PCR findings and 5 isolates submitted to GenBank with accession numbers OL314557.1, OL314556.1, OL314555.1, OL314554.1, OL314553.1.For antibiotic resistance genes, the number of the isolates containing blaOXA-1 and blaCTX-M 18 (90 percent) and 16 (80 percent) respectively. To study its adaptation in a SARS-CoV-2 infected environment, genomic sequencing investigations were undertaken with phenotypic validation. In conclusion, we demonstrate that multidrug resistant P. aeruginosa play an important role in in vivo colonization in COVID-19 patients and could be one of the causes of death of these patients which indicates the great challenge to clinicians in the facing of this serious disease.

Coexistence of COVID-19, Pseudomonas, and thoracic actinomycosis in a cystic bronchiectasis case.

Actinomycosis often leads to cervicofacial infections, but thoracic involvement may also occur. However, the development of empyema is rare. While being followed up with the diagnosis of asthma and bronchiectasis, our case was hospitalized for infected bronchiectasis. As empyema developed in the follow-up, the pleural effusion was drained by tube thoracostomy. Actinomycosis was diagnosed through pleural effusion cytology. Growth of Pseudomonas aeruginosa was observed in sputum culture, and SARS-CoV2 RT-PCR was also positive in nasopharyngeal sampling. Polymicrobial agents can often be detected in actinomycosis. Actinomycosis cases have also been reported in the post-COVID period. Our case is presented since it would be the first in the literature regarding the coexistence of COVID-19, Pseudomonas, and thoracic Actinomycosis (empyema).

Acquisition of T6SS Effector TseL Contributes to the Emerging of Novel Epidemic Strains of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen with multiple strategies to interact with other microbes and host cells, gaining fitness in complicated infection sites. The contact-dependent type VI secretion system (T6SS) is one critical secretion apparatus involved in both interbacterial competition and pathogenesis. To date, only limited numbers of T6SS-effectors have been clearly characterized in P. aeruginosa laboratory strains, and the importance of T6SS diversity in the evolution of clinical P. aeruginosa remains unclear. Recently, we characterized a P. aeruginosa clinical strain LYSZa7 from a COVID-19 patient, which adopted complex genetic adaptations toward chronic infections. Bioinformatic analysis has revealed a putative type VI secretion system (T6SS) dependent lipase effector in LYSZa7, which is a homologue of TseL in Vibrio cholerae and is widely distributed in pathogens. We experimentally validated that this TseL homologue belongs to the Tle2, a subfamily of T6SS-lipase effectors; thereby, we name this effector TseL (TseLPA in this work). Further, we showed the lipase-dependent bacterial toxicity of TseLPA, which primarily targets bacterial periplasm. The toxicity of TseLPA can be neutralized by two immunity proteins, TsiP1 and TsiP2, which are encoded upstream of tseL. In addition, we proved this TseLPA contributes to bacterial pathogenesis by promoting bacterial internalization into host cells. Our study suggests that clinical bacterial strains employ a diversified group of T6SS effectors for interbacterial competition and might contribute to emerging of new epidemic clonal lineages. IMPORTANCE Pseudomonas aeruginosa is one predominant pathogen that causes hospital-acquired infections and is one of the commonest coinfecting bacteria in immunocompromised patients and chronic wounds. This bacterium harbors a diverse accessory genome with a high frequency of gene recombination, rendering its population highly heterogeneous. Numerous Pa lineages coexist in the biofilm, where successful epidemic clonal lineage or strain-specific type commonly acquires genes to increase its fitness over the other organisms. Current studies of Pa genomic diversity commonly focused on antibiotic resistant genes and novel phages, overlooking the contribution of type VI secretion system (T6SS). We characterized a Pa clinical strain LYSZa7 from a COVID-19 patient, which adopted complex genetic adaptations toward chronic infections. We report, in this study, a novel T6SS-lipase effector that is broadly distributed in Pa clinical isolates and other predominant pathogens. The study suggests that hospital transmission may raise the emergence of new epidemic clonal lineages with specified T6SS effectors.

Pseudomonas aeruginosa countrywide outbreak in hospitals linked to pre-moistened non-sterile washcloths, Norway, October 2021 to April 2022.

In November 2021, a clonal outbreak of Pseudomonas aeruginosa of novel sequence type ST3875 was detected in three patients who died of bloodstream infections in one hospital. By 25 April 2022, the outbreak included 339 cases from 38 hospitals across Norway. Initial hospital reports indicate Pseudomonas infection as the main contributing cause in seven deaths. In March 2022, the outbreak strain was identified in non-sterile pre-moistened disposable washcloths, used to clean patients, from three lots from the same international manufacturer.

Personalized bacteriophage therapy to treat pandrug-resistant spinal Pseudomonas aeruginosa infection.

Bone and joint infections (BJI) are one of the most difficult-to-treat bacterial infection, especially in the era of antimicrobial resistance. Lytic bacteriophages (phages for short) are natural viruses that can selectively target and kill bacteria. They are considered to have a high therapeutic potential for the treatment of severe bacterial infections and especially BJI, as they also target biofilms. Here we report on the management of a patient with a pandrug-resistant Pseudomonas aeruginosa spinal abscess who was treated with surgery and a personalized combination of phage therapy that was added to antibiotics. As the infecting P. aeruginosa strain was resistant to the phages developed by private companies that were contacted, we set up a unique European academic collaboration to find, produce and administer a personalized phage cocktail to the patient in due time. After two surgeries, despite bacterial persistence with expression of small colony variants, the patient healed with local and intravenous injections of purified phages as adjuvant therapy.

Pseudomonas aeruginosa: pathogenesis, virulence factors, antibiotic resistance, interaction with host, technology advances and emerging therapeutics.

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen that infects patients with cystic fibrosis, burn wounds, immunodeficiency, chronic obstructive pulmonary disorder (COPD), cancer, and severe infection requiring ventilation, such as COVID-19. P. aeruginosa is also a widely-used model bacterium for all biological areas. In addition to continued, intense efforts in understanding bacterial pathogenesis of P. aeruginosa including virulence factors (LPS, quorum sensing, two-component systems, 6 type secretion systems, outer membrane vesicles (OMVs), CRISPR-Cas and their regulation), rapid progress has been made in further studying host-pathogen interaction, particularly host immune networks involving autophagy, inflammasome, non-coding RNAs, cGAS, etc. Furthermore, numerous technologic advances, such as bioinformatics, metabolomics, scRNA-seq, nanoparticles, drug screening, and phage therapy, have been used to improve our understanding of P. aeruginosa pathogenesis and host defense. Nevertheless, much remains to be uncovered about interactions between P. aeruginosa and host immune responses, including mechanisms of drug resistance by known or unannotated bacterial virulence factors as well as mammalian cell signaling pathways. The widespread use of antibiotics and the slow development of effective antimicrobials present daunting challenges and necessitate new theoretical and practical platforms to screen and develop mechanism-tested novel drugs to treat intractable infections, especially those caused by multi-drug resistance strains. Benefited from has advancing in research tools and technology, dissecting this pathogen's feature has entered into molecular and mechanistic details as well as dynamic and holistic views. Herein, we comprehensively review the progress and discuss the current status of P. aeruginosa biophysical traits, behaviors, virulence factors, invasive regulators, and host defense patterns against its infection, which point out new directions for future investigation and add to the design of novel and/or alternative therapeutics to combat this clinically significant pathogen.

Comparative outcomes of combined corticosteroid and remdesivir therapy with corticosteroid monotherapy in ventilated COVID-19 patients.

Remdesivir (RDV) reduces time to clinical improvement in hospitalized COVID -19 patients requiring supplemental oxygen. Dexamethasone improves survival in those requiring oxygen support. Data is lacking on the efficacy of combination therapy in patients on mechanical ventilation. We analyzed for comparative outcomes between Corticosteroid (CS) therapy with combined Corticosteroid and Remdesivir (CS-RDV) therapy. We conducted an observational cohort study of patients aged 18 to 90 with COVID-19 requiring ventilatory support using TriNetX (COVID-19 Research Network) between January 20, 2020, and February 9, 2021. We compared patients who received at least 48 hours of CS-RDV combination therapy to CS monotherapy. The primary outcome was 28-day all-cause mortality rates in propensity-matched (PSM) cohorts. Secondary outcomes were Length of Stay (LOS), Secondary Bacterial Infections (SBI), and MRSA (Methicillin-Resistant Staphylococcus aureus), and Pseudomonas infections. We used univariate and multivariate Cox proportional hazards models and stratified log-rank tests. Of 388 patients included, 91 (23.5%) received CS-RDV therapy, and 297 (76.5%) received CS monotherapy. After propensity score matching, with 74 patients in each cohort, all-cause mortality was 36.4% and 29.7% in the CS-RDV and CS therapy, respectively (P = 0.38). We used a Kaplan-Meier with a log-rank test on follow up period (P = 0.23), and a Hazards Ratio model (P = 0.26). SBI incidence was higher in the CS group (13.5% vs. 35.1%, P = 0.02) with a similar LOS (13.4 days vs. 13.4 days, P = 1.00) and similar incidence of MRSA/Pseudomonas infections (13.5% vs. 13.5%, P = 1.00) in both the groups. Therefore, CS-RDV therapy is non-inferior to CS therapy in reducing 28-day all-cause in-hospital mortality but associated with a significant decrease in the incidence of SBI in critically ill COVID-19 patients.

Recombinant Myeloperoxidase as a New Class of Antimicrobial Agents.

Heme-containing peroxidases are widely distributed in the animal and plant kingdoms and play an important role in host defense by generating potent oxidants. Myeloperoxidase (MPO), the prototype of heme-containing peroxidases, exists in neutrophils and monocytes. MPO has a broad spectrum of microbial killing. The difficulty of producing MPO at a large scale hinders its study and utilization. This study aimed to overexpress recombinant human MPO and characterize its microbicidal activities in vitro and in vivo. A human HEK293 cell line stably expressing recombinant MPO (rMPO) was established as a component of this study. rMPO was overexpressed and purified for studies on its biochemical and enzymatic properties, as well as its microbicidal activities. In this study, rMPO was secreted into culture medium as a monomer. rMPO revealed enzymatic activity similar to that of native MPO. rMPO, like native MPO, was capable of killing a broad spectrum of microorganisms, including Gram-negative and -positive bacteria and fungi, at low nM levels. Interestingly, rMPO could kill antibiotic-resistant bacteria, making it very useful for treatment of nosocomial infections and mixed infections. The administration of rMPO significantly reduced the morbidity and mortality of murine lung infections induced by Pseudomonas aeruginosa or methicillin-resistant Staphylococcus aureus. In animal safety tests, the administration of 100 nM rMPO via tail vein did not result in any sign of toxic effects. Taken together, the data suggest that rMPO purified from a stably expressing human cell line is a new class of antimicrobial agents with the ability to kill a broad spectrum of pathogens, including bacteria and fungi with or without drug resistance. IMPORTANCE Over the past 2 decades, more than 20 new infectious diseases have emerged. Unfortunately, novel antimicrobial therapeutics are discovered at much lower rates. Infections caused by resistant microorganisms often fail to respond to conventional treatment, resulting in prolonged illness, greater risk of death, and high health care costs. Currently, this is best seen with the lack of a cure for coronavirus disease 2019 (COVID-19). To combat such untreatable microorganisms, there is an urgent need to discover new classes of antimicrobial agents. Myeloperoxidase (MPO) plays an important role in host defense. The difficulty of producing MPO on a large scale hinders its study and utilization. We have produced recombinant MPO at a large scale and have characterized its antimicrobial activities. Most importantly, recombinant MPO significantly reduced the morbidity and mortality of murine pneumonia induced by Pseudomonas aeruginosa or methicillin-resistant Staphylococcus aureus. Our data suggest that recombinant MPO from human cells is a new class of antimicrobials with a broad spectrum of activity.

Clinical characteristics, appropriateness of empiric antibiotic therapy, and outcome of Pseudomonas aeruginosa bacteremia across multiple community hospitals.

There is relatively little contemporary information regarding clinical characteristics of patients with Pseudomonas aeruginosa bacteremia (PAB) in the community hospital setting. This was a retrospective, observational cohort study examining the clinical characteristics of patients with PAB across several community hospitals in the USA with a focus on the appropriateness of initial empirical therapy and impact on patient outcomes. Cases of PAB occurring between 2016 and 2019 were pulled from 8 community medical centers. Patients were classified as having either positive or negative outcome at hospital discharge. Several variables including receipt of active empiric therapy (AET) and the time to receiving AET were collected. Variables with a p value of < 0.05 in univariate analyses were included in a multivariable logistic regression model. Two hundred and eleven episodes of PAB were included in the analysis. AET was given to 81.5% of patients and there was no difference in regard to outcome (p = 0.62). There was no difference in the median time to AET in patients with a positive or negative outcome (p = 0.53). After controlling for other variables, age, Pitt bacteremia score ≥ 4, and septic shock were independently associated with a negative outcome. A high proportion of patients received timely, active antimicrobial therapy for PAB and time to AET did not have a significant impact on patient outcome.

Flagellin From Pseudomonas aeruginosa Modulates SARS-CoV-2 Infectivity in Cystic Fibrosis Airway Epithelial Cells by Increasing TMPRSS2 Expression.

In the coronavirus disease 2019 (COVID-19) health crisis, one major challenge is to identify the susceptibility factors of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) in order to adapt the recommendations for populations, as well as to reduce the risk of COVID-19 development in the most vulnerable people, especially patients with chronic respiratory diseases such as cystic fibrosis (CF). Airway epithelial cells (AECs) play a critical role in the modulation of both immune responses and COVID-19 severity. SARS-CoV-2 infects the airway through the receptor angiotensin-converting enzyme 2, and a host protease, transmembrane serine protease 2 (TMPRSS2), plays a major role in SARS-CoV-2 infectivity. Here, we show that Pseudomonas aeruginosa increases TMPRSS2 expression, notably in primary AECs with deficiency of the ion channel CF transmembrane conductance regulator (CFTR). Further, we show that the main component of P. aeruginosa flagella, the protein flagellin, increases TMPRSS2 expression in primary AECs and Calu-3 cells, through activation of Toll-like receptor-5 and p38 MAPK. This increase is particularly seen in Calu-3 cells deficient for CFTR and is associated with an intracellular increased level of SARS-CoV-2 infection, however, with no effect on the amount of virus particles released. Considering the urgency of the COVID-19 health crisis, this result may be of clinical significance for CF patients, who are frequently infected with and colonized by P. aeruginosa during the course of CF and might develop COVID-19.

Inhibitors of bacterial H2S biogenesis targeting antibiotic resistance and tolerance.

Emergent resistance to all clinical antibiotics calls for the next generation of therapeutics. Here we report an effective antimicrobial strategy targeting the bacterial hydrogen sulfide (H2S)-mediated defense system. We identified cystathionine γ-lyase (CSE) as the primary generator of H2S in two major human pathogens, Staphylococcus aureus and Pseudomonas aeruginosa, and discovered small molecules that inhibit bacterial CSE. These inhibitors potentiate bactericidal antibiotics against both pathogens in vitro and in mouse models of infection. CSE inhibitors also suppress bacterial tolerance, disrupting biofilm formation and substantially reducing the number of persister bacteria that survive antibiotic treatment. Our results establish bacterial H2S as a multifunctional defense factor and CSE as a drug target for versatile antibiotic enhancers.

Protective effect of SARS-CoV-2 preventive measures against ESKAPE and Escherichia coli infections.

BACKGROUND/OBJECTIVES: We investigated whether behavioral precautions adopted during Coronavirus disease (COVID-19) pandemic also influenced the spreading and multidrug resistance (MDR) of ESKAPEEc (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii [AB], Pseudomonas aeruginosa, Enterobacter spp and Escherichia Coli, [EC]) among Intensive Care Unit (ICU) patients. SUBJECTS/METHODS: We performed a single-center retrospective study in adult patients admitted to our COVID-19-free surgical ICU. Only patients staying in ICU for more than 48 hours were included. The ESKAPEEc infections recorded during the COVID-19 period (June 1, 2020 - February 28, 2021) and in the corresponding pre-pandemic period (June 1, 2019 - February 28, 2020) were compared. An interrupted time series analysis was performed to rule out possible confounders. RESULTS: Overall, 173 patients in the COVID-19 period and 132 in the pre-COVID-19 period were investigated. The ESKAPEEc infections were documented in 23 (13.3%) and 35 (26.5%) patients in the pandemic and the pre-pandemic periods, respectively (p = 0.005). Demographics, diagnosis, comorbidities, type of surgery, Simplified Acute Physiology Score II, length of mechanical ventilation, hospital and ICU length of stay, ICU death rate, and 28-day hospital mortality were similar in the two groups. In comparison with the pre-pandemic period, no AB was recorded during COVID-19 period, (p = 0.017), while extended-spectrum beta-lactamase-producing EC infections significantly decreased (p = 0.017). Overall, the ESKAPEEc isolates during pandemic less frequently exhibited multidrug-resistant (p = 0.014). CONCLUSIONS: These findings suggest that a robust adherence to hygiene measures together with human contact restrictions in a COVID-19 free ICU might also restrain the transmission of ESKAPEEc pathogens.

Antimicrobial susceptibility patterns of respiratory Gram-negative bacterial isolates from COVID-19 patients in Switzerland.

BACKGROUND: Bacterial superinfections associated with COVID-19 are common in ventilated ICU patients and impact morbidity and lethality. However, the contribution of antimicrobial resistance to the manifestation of bacterial infections in these patients has yet to be elucidated. METHODS: We collected 70 Gram-negative bacterial strains, isolated from the lower respiratory tract of ventilated COVID-19 patients in Zurich, Switzerland between March and May 2020. Species identification was performed using MALDI-TOF; antibiotic susceptibility profiles were determined by EUCAST disk diffusion and CLSI broth microdilution assays. Selected Pseudomonas aeruginosa isolates were analyzed by whole-genome sequencing. RESULTS: Pseudomonas aeruginosa (46%) and Enterobacterales (36%) comprised the two largest etiologic groups. Drug resistance in P. aeruginosa isolates was high for piperacillin/tazobactam (65.6%), cefepime (56.3%), ceftazidime (46.9%) and meropenem (50.0%). Enterobacterales isolates showed slightly lower levels of resistance to piperacillin/tazobactam (32%), ceftriaxone (32%), and ceftazidime (36%). All P. aeruginosa isolates and 96% of Enterobacterales isolates were susceptible to aminoglycosides, with apramycin found to provide best-in-class coverage. Genotypic analysis of consecutive P. aeruginosa isolates in one patient revealed a frameshift mutation in the transcriptional regulator nalC that coincided with a phenotypic shift in susceptibility to ß-lactams and quinolones. CONCLUSIONS: Considerable levels of antimicrobial resistance may have contributed to the manifestation of bacterial superinfections in ventilated COVID-19 patients, and may in some cases mandate consecutive adaptation of antibiotic therapy. High susceptibility to amikacin and apramycin suggests that aminoglycosides may remain an effective second-line treatment of ventilator-associated bacterial pneumonia, provided efficacious drug exposure in lungs can be achieved.

Acute SARS-CoV-2 infection is associated with an increased abundance of bacterial pathogens, including Pseudomonas aeruginosa in the nose.

Research conducted on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogenesis and coronavirus disease 2019 (COVID-19) generally focuses on the systemic host response, especially that generated by severely ill patients, with few studies investigating the impact of acute SARS-CoV-2 at the site of infection. We show that the nasal microbiome of SARS-CoV-2-positive patients (CoV+, n = 68) at the time of diagnosis is unique when compared to CoV- healthcare workers (n = 45) and CoV- outpatients (n = 21). This shift is marked by an increased abundance of bacterial pathogens, including Pseudomonas aeruginosa, which is also positively associated with viral RNA load. Additionally, we observe a robust host transcriptional response in the nasal epithelia of CoV+ patients, indicative of an antiviral innate immune response and neuronal damage. These data suggest that the inflammatory response caused by SARS-CoV-2 infection is associated with an increased abundance of bacterial pathogens in the nasal cavity that could contribute to increased incidence of secondary bacterial infections.

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.