Drug repurposing against antibiotic resistant bacterial pathogens

The growing prevalence of MDR and XDR bacterial pathogens is posing a critical threat to global health. Traditional antibiotic development paths have encountered significant challenges and are drying up thus necessitating innovative approaches. Drug repurposing, which involves identifying new therapeutic applications for existing drugs, offers a promising alternative to combat resistant pathogens. By leveraging pre-existing safety and efficacy data, drug repurposing accelerates the development of new antimicrobial therapy regimes. This review explores the potential of repurposing existing FDA approved drugs against the ESKAPE and other clinically relevant bacterial pathogens and delves into the identification of suitable drug candidates, their mechanisms of action, and the potential for combination therapies. It also describes clinical trials and patent protection of repurposed drugs, offering perspectives on this evolving realm of therapeutic interventions against drug resistance.

The Prevalence of Multidrug-Resistant and Extensively Drug-Resistant Infections in Respiratory Intensive Care Unit, Causative Microorganisms and Mortality

Aim

This study aims to analyze the incidence of multidrug-resistant (MDR) retrospectively and extensively drug-resistant (XDR) infections, characteristics of patients with these infections, causative microorganisms, and mortality rates in a tertiary respiratory intensive care unit (ICU).

Material and Method

Between 01.01.2022 and 31.12.2023, the data of patients treated in the third-level respiratory ICU were analyzed retrospectively. Adult patients over 18 years of age with MDR and XDR infections were included in the study. Demographic characteristics, age, gender, comorbid systemic diseases, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, Sequential Organ Failure Assessment (SOFA) score, mechanical ventilation support status, duration of ICU stay and prognosis of the patients were analyzed and recorded through the hospital information management system.

Results

The study included 261 patients. Of these patients, 184 (70.5%) were male, 77 (29.5%) were female, and their ages were 65.54 ± 14.43 years. The majority of the patients had chronic diseases such as chronic obstructive pulmonary disease, hypertension, coronary artery disease, malignancy, and diabetes mellitus. There was no statistically significant difference between the resistance status of Klebsiella spp. Pseudomonas spp. and Acinetobacter spp. and the prognosis of the patients (p>0.05). No statistically significant difference was found between MDR and XDR Klebsiella spp. Pseudomonas spp. and Acinetobacter spp. patients in terms of the need for invasive mechanical ventilation, non-invasive mechanical ventilation, respiratory support therapy with high flow, APACHE II score, SOFA score, length of stay in the ICU, and prognosis (p>0.05).

Conclusion

Early detection and close monitoring of MDR, XDR, and PDR bacterial strains are vital to combat antimicrobial resistance. This study shows that MDR and XDR infections are a major health problem in ICUs and that these infections have significant negative effects on patient prognosis.

Transforming microbial pigment into therapeutic revelation: extraction and characterization of pyocyanin from Pseudomonas aeruginosa and its therapeutic potential as an antibacterial and anticancer agent

BACKGROUND

The objectives of the current study were to extract pyocyanin from Pseudomonas aeruginosa clinical isolates, characterize its chemical nature, and assess its biological activity against different bacteria and cancer cells. Due to its diverse bioactive properties, pyocyanin, being one of the virulence factors of P. aeruginosa, holds a promising, safe, and available therapeutic potential.

METHODS

30 clinical P. aeruginosa isolates were collected from different sources of infections and identified by routine methods, the VITEK 2 compact system, and 16 S rRNA. The phenazine-modifying genes (phzM, phzS) were identified using polymerase chain reaction (PCR). Pyocyanin chemical characterization included UV-Vis spectrophotometry, Fourier Transform Infra-Red spectroscopy (FTIR), Gas Chromatography-Mass Spectrometry (GC-MS), and Liquid Chromatography-Mass Spectrometry (LC-MS). The biological activity of pyocyanin was explored by determining the MIC values against different clinical bacterial strains and assessing its anticancer activity against A549, MDA-MB-231, and Caco-2 cancer cell lines using cytotoxicity, wound healing and colony forming assays.

RESULTS

All identified isolates harboured at least one of the phzM or phzS genes. The co-presence of both genes was demonstrated in 13 isolates. The UV-VIS absorbance peaks were maxima at 215, 265, 385, and 520 nm. FTIR could identify the characteristic pyocyanin functional groups, whereas both GC-MS and LC-MS elucidated the chemical formula C11H18N2O2, with a molecular weight 210. The quadri-technical analytical approaches confirmed the chemical nature of the extracted pyocyanin. The extract showed broad-spectrum antibacterial activity, with the greatest activity against Bacillus, Staphylococcus, and Streptococcus species (MICs 31.25-125 µg/mL), followed by E. coli isolates (MICs 250-1000 µg/mL). Regarding the anticancer activity, the pyocyanin extract showed IC50 values against A549, MDA-MB-231, and Caco-2 cancer cell lines of 130, 105, and 187.9 µg/mL, respectively. Furthermore, pyocyanin has markedly suppressed colony formation and migratory abilities in these cells.

CONCLUSIONS

The extracted pyocyanin has demonstrated to be a potentially effective candidate against various bacterial infections and cancers. Hence, the current findings could contribute to producing this natural compound easily through an affordable method. Nonetheless, future studies are required to investigate pyocyanin's effects in vivo and analyse the results of combining it with other traditional antibiotics or anticancer drugs.

Treatment Outcomes for Carbapenem-Resistant and Cephalosporin-Susceptible Pseudomonas aeruginosa Pneumonia

BACKGROUND

Carbapenem-resistant (Car-R) Pseudomonas aeruginosa is an urgent threat. These isolates may remain susceptible to traditional noncarbapenem antipseudomonal β-lactams, but it is unclear if carbapenem resistance impacts the effectiveness of these agents.

OBJECTIVE

The purpose of this study was to compare clinical outcomes in Car-R and cephalosporin-susceptible (Ceph-S) P. aeruginosa pneumonia treated with cefepime versus other susceptible agents.

METHODS

This retrospective cohort study evaluated patients diagnosed with hospital-acquired or ventilator-associated pneumonia who had a respiratory isolate of Car-R Ceph-S P. aeruginosa. Patients were excluded if they had polymicrobial respiratory cultures, other concomitant infections, empyema, death within 3 days of index culture, or received less than 3 days of susceptible therapy. Patients treated with cefepime were compared to other susceptible therapies. The primary endpoint was 30-day in-hospital mortality.

RESULTS

Eighty-seven patients were included: cefepime, n = 61; other susceptible therapies, n = 26. There were no differences in 30-day in-hospital mortality between cefepime and other susceptible therapies (19.6% vs. 19.2%, p value = 0.719). In addition, there were no differences between clinical cure rates (cefepime 65.6% vs. other therapies 72 %, p value = 0.47). In multivariate logistic regression, treatment with cefepime (odds ratio [OR], 0.57; 95% confidence interval [CI], 0.11-2.52) was not independently associated with 30-day in-hospital mortality.

CONCLUSION AND RELEVANCE

For the treatment of Car-R Ceph-S P. aeruginosa pneumonia, cefepime showed similar rates of 30-day in-hospital mortality and clinical outcomes when compared to other susceptible therapies. Cefepime may be utilized to conserve novel β-lactam and β-lactamase inhibitors.

Coexistence of blaIMP-4 and blaSFO-1 in an IncHI5B plasmid harbored by tigecycline-non-susceptible Klebsiella variicola strain

BACKGROUND

Klebsiella variicola is considered a newly emerging human pathogen. Clinical isolates of carbapenemase and broad-spectrum β-lactamase-producing K. variicola remain relatively uncommon. A strain of K. variicola 4253 was isolated from a clinical sample, and was identified to carry the blaIMP-4 and blaSFO-1 genes. This study aims to discern its antibiotic resistance phenotype and genomic characteristics.

METHODS

Species identification was conducted using MALDI-TOF/MS. PCR identification confirmed the presence of the blaIMP-4 and blaSFO-1 genes. Antibiotic resistance phenotype and genomic characteristics were detected by antimicrobial susceptibility testing and whole-genome sequencing. Plasmid characterization was carried out through S1-PFGE, conjugation experiments, Southern blot, and comparative genomic analysis.

RESULTS

K. variicola 4253 belonged to ST347, and demonstrated resistance to broad-spectrum β-lactamase drugs and tigecycline while being insensitive to imipenem and meropenem. The blaIMP-4 and blaSFO-1 genes harbored on the plasmid p4253-imp. The replicon type of p4253-imp was identified as IncHI5B, representing a multidrug-resistant plasmid capable of horizontal transfer and mediating the dissemination of drug resistance. The blaIMP-4 gene was located on the In809-like integrative element (Intl1-blaIMP-4-aacA4-catB3), which circulates in Acinetobacter and Enterobacteriaceae.

CONCLUSIONS

This study reports the presence of a strain of K. variicola, which is insensitive to tigecycline, carrying a plasmid harboring blaIMP-4 and blaSFO-1. It is highly likely that the strain acquired this plasmid through horizontal transfer. The blaIMP-4 array (Intl1-blaIMP-4-aacA4-catB3) is also mobile in Acinetobacter and Enterobacteriaceae. So it is essential to enhance clinical awareness and conduct epidemiological surveillance on multidrug-resistant K. variicola, conjugative plasmids carrying blaIMP-4, and the In809 integrative element.

Deferiprone-Gallium-Protoporphyrin Chitogel Decreases Pseudomonas aeruginosa Biofilm Infection without Impairing Wound Healing

Pseudomonas aeruginosa is one of the most common pathogens encountered in clinical wound infections. Clinical studies have shown that P. aeruginosa infection results in a larger wound area, inhibiting healing, and a high prevalence of antimicrobial resistance. Hydroxypyridinone-derived iron chelator Deferiprone (Def) and heme analogue Gallium-Protoporphyrin (GaPP) in a chitosan-dextran hydrogel (Chitogel) have previously been demonstrated to be effective against PAO1 and clinical isolates of P. aeruginosa in vitro. Moreover, this combination of these two agents has been shown to improve sinus surgery outcomes by quickly reducing bleeding and preventing adhesions. In this study, the efficacy of Def-GaPP Chitogel was investigated in a P. aeruginosa biofilm-infected wound murine model over 6 days. Two concentrations of Def-GaPP Chitogel were investigated: Def-GaPP high dose (10 mM Def + 500 µg/mL GaPP) and Def-GaPP low dose (5 mM Def + 200 µg/mL GaPP). The high-dose Def-GaPP treatment reduced bacterial burden in vivo from day 2, without delaying wound closure. Additionally, Def-GaPP treatment decreased wound inflammation, as demonstrated by reduced neutrophil infiltration and increased anti-inflammatory M2 macrophage presence within the wound bed to drive wound healing progression. Def-GaPP Chitogel treatment shows promising potential in reducing P. aeruginosa cutaneous infection with positive effects observed in the progression of wound healing.

Histone acetyltransferases derived RW20 protects and promotes rapid clearance of Pseudomonas aeruginosa in zebrafish larvae

Pseudomonas is a group of bacteria that can cause a wide range of infections, particularly in people with weakened immune systems, such as those with cystic fibrosis or who are hospitalized. It can also cause infections in the skin and soft tissue, including cellulitis, abscesses and wound infections. Antimicrobial peptides (AMPS) are the alternative strategy due to their broad spectrum of activity and act as effective treatment against multi-drug resistance pathogens. In this study, we have used an AMP, RW20 (1RPVKRKKGWPKGVKRGPPKW20). RW20 peptide is derived from the histone acetyltransferases (HATs) of the freshwater teleost, Channa striatus. The antimicrobial prediction tool has been utilized to identify the RW20 sequence from the HATs sequence. We synthesized the peptide to explore its mechanism of action. In an in vitro assay, RW20 was challenged against P. aeruginosa and we showed that RW20 displayed antibacterial properties and damaged the cell membrane. The mechanism of action of RW20 against P. aeruginosa has been established via field emission scanning electron microscopy (FESEM) as well as fluorescence assisted cell sorter (FACS) analysis. Both these experiments established that RW20 caused bacterial membrane disruption and cell death. Moreover, the impact of RW20, in-vivo, was tested against P. aeruginosa-infected zebrafish larvae. In the infected larvae, RW20 showed protective effect against P. aeruginosa by increasing the larval antioxidant enzymes, reducing the excess oxidative stress and apoptosis. Thus, it is possible that HATs-derived RW20 can be an efficient antimicrobial molecule against P. aeruginosa.

Effect of Graphene Oxide and Silver Nanoparticle Hybrid Composite on Acinetobacter baumannii Strains, Regarding Antibiotic Resistance and Prevalence of AMP-C Production

Background and Objectives: Growing antibiotic resistance among bacteria is a global issue that is becoming harder and more expensive to solve. Traditional treatment options are becoming less effective, causing more fatal outcomes of nosocomial infections. Since the development of new antibiotics has stagnated in the last decade, a novel approach is needed. Materials and Methods: Graphene-based materials are being developed and tested for various applications, and the medical field is no exception. We tested 98 clinical A. baumannii strains for antibiotic resistance, AMP-C production and the effectiveness of a graphene oxide and silver nanoparticle hybrid nanocomposite. The disc diffusion method was used to determine antibiotic susceptibility results. Antibiotic discs containing cefotaxime, cloxacillin and clavulanate were used to detect AMP-C production. The effectiveness of the GO-Ag hybrid nanocomposite was determined by counting colony forming units (CFUs) after a suspension of A. baumannii and the GO-Ag hybrid nanocomposite was plated on MH agar and incubated overnight to grow colonies. Results: In our research, we found that A. baumannii strains are resistant to the majority of commonly used antibiotics. Antibiotic resistance levels and AMP-C production can be factors, indicating the better effectiveness of the graphene oxide and silver nanoparticle hybrid nanocomposite. Conclusions: In this study, a GO-Ag hybrid nanocomposite was shown to have the potential to fight even the most problematic bacteria like A. baumannii.

Carbapenem-Resistant Acinetobacter baumannii Bloodstream Infection in a Ghanaian Patient with Unilateral Diaphragmatic Eventration and HIV Type 1 Infection

Carbapenem-resistant Acinetobacter baumannii infection is a critically prioritized pathogen by the World Health Organization and a cause for growing concern due to increased mortality among hospitalised patients. Phrenic nerve palsy is a rare complication of herpes zoster infection of the C3, C4, and C5 nerve roots. We present a case of bloodstream carbapenem-resistant A. baumannii infection in a Ghanaian patient with HIV type 1 infection and multiple risk factors, including unilateral diaphragmatic eventration with compression atelectasis likely secondary to phrenic nerve palsy due to herpes zoster infection, consequently leading to recurrent hospital and ICU admission. In this case, we emphasize the need for clinicians in LMICs to be aware of CRAB, in order to advocate for the availability of evidence-based medicines in resource-limited settings for appropriate treatment. In addition, we illustrate the importance of a high index of suspicion for infection with carbapenem-resistant organisms such as A. baumannii and highlight a rare and severe complication of herpes zoster infection in the form of phrenic nerve palsy and consequent diaphragmatic eventration.

In vitro activity of the novel Fe-cyclam complex against clinical multidrug-resistant bacterial isolates from Brazil

Aim: To evaluate the effect of a new Fe-cyclam complex on pathogenic bacterial species, including multidrug-resistant clinical specimens. Materials & methods: The complex [Fe(cyclam)ox]PF6 (D2) was tested in cytotoxicity and MIC tests. Clinical and reference strains of Gram-negative and Gram-positive bacteria were used. Considering Staphylococcus aureus strains, the profile of antimicrobial susceptibility and time-kill kinetics for D2 was performed. An in silico analysis for D2 was also performed. Results: D2 showed broad bacterial activity, mainly against specimens of Cutibacterium acnes, S. aureus, Pseudomonas aeruginosa and Acinetobacter baumannii. Low cytotoxicity in human cells was demonstrated. Conclusion: The tested compound proved to be a promising agent against resistant bacterial infections.

Comparison between Colistin and Polymyxin B in the Treatment of Bloodstream Infections Caused by Carbapenem-Resistant Pseudomonas aeruginosa and Acinetobacter baumannii-calcoaceticus Complex

Polymyxins are still widely used for the treatment of carbapenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa bloodstream infections (BSIs). This study seeks to evaluate the impact of polymyxin B versus colistin on mortality and nephrotoxicity in BSI caused by these bacteria. We conducted a retrospective cohort study from 2014 to 2021 in Porto Alegre, Brazil. We included patients aged ≥18 years and excluded patients with polymicrobial infection or treatment for ≤48 h. The 30-day mortality was the primary outcome evaluated through Cox regression. We included 259 patients with BSI episodes: 78.8% caused by A. baumannii and 21.2% caused by P. aeruginosa. Polymyxin B did not impact mortality compared to colistin (adjusted hazard ratio (aHR), 0.82; 95% confidence interval (CI), 0.52-1.30; p = 0.40 (when adjusted for COVID-19 comorbidity, p = 0.05), Pitt bacteremia score, p < 0.01; Charlson comorbidity index, p < 0.001; time to start active antimicrobial therapy, p = 0.02). Results were maintained in the subgroups of BSI caused by A. baumannii (aHR, 0.92; 95% CI, 0.55-1.54; p = 0.74), P. aeruginosa (aHR, 0.47; 95% CI, 0.17-1.32; p = 0.15) and critical care patients (aHR, 0.77; 95% CI, 0.47-1.26; p = 0.30). Treatment with polymyxin B or colistin did not impact 30-day mortality in patients with carbapenem-resistant A. baumannii or P. aeruginosa BSI.

A comparative study of intestinal Pseudomonas aeruginosa in healthy individuals and ICU inpatients

The human intestinal tract is considered the most important reservoir of the opportunistic pathogens, including Pseudomonas aeruginosa, which is often overlooked but critical due to its antimicrobial resistance and virulence. Public health interventions to control this pathogen require a comprehensive understanding of its epidemiology and genomics.  In the current study, we identified P. aeruginosa strains from 2,605 fecal samples collected between 2021 to 2022. Among these samples, 574 were from ICU inpatients in Zhejiang province, while 2,031 were obtained from healthy individuals residing in ten different provinces in China. The prevalence of P. aeruginosa intestinal carriage was found to be higher in ICU inpatients (10.28%, 95% CI: 7.79%-12.76%) than that in healthy individuals (3.99%, 81/2,031, 95% CI: 3.14%-4.84%). Similarly, the prevalence of carbapenem-resistant P. aeruginosa (CRPA) was higher in ICU inpatients (32.2%) compared to healthy individuals (7.41%). The population structure analysis of our isolates revealed a predominantly non-clonal distribution, with 41 distinct sequence types identified among 59 P. aeruginosa isolates from ICU inpatients and 38 different STs among 81 P. aeruginosa isolates from healthy individuals. These findings suggest that the individual acquisition of P. aeruginosa is more frequent than patient-to-patient transmission, as evidenced by the polyclonal population structure. Antimicrobial susceptibility testing and genome analysis indicated that P. aeruginosa strains from ICU inpatients exhibited significantly higher resistance rates to most antimicrobials and harbored a greater number of acquired resistance genes compared to strains from healthy individuals. Notably, in ICU inpatients, we identified three isolates of ST463, all of which shared the conserved Tn3-TnpR-ISKpn8-blaKPC-ISKpn6 genetic context. Additionally, five isolates carrying the qacE gene were also identified, these findings suggest that small-scale transmission events may still occur within the ICU setting, posing significant challenges for clinical management. With regard to virulence factors, we observed similar profiles between the two groups, except for phzA2, phzB2, and pilA, which were statistically higher in isolates from healthy individuals. This may be because the accumulating resistance mutations in ICU-derived P. aeruginosa are linked to a decrease in virulence.

Evaluation of a sterile, filter-based, in-house method for rapid direct bacterial identification and antimicrobial susceptibility testing using positive blood culture

This study aimed to assess the performance of our in-house method for rapid direct bacterial identification (ID) and antimicrobial susceptibility testing (AST) using a positive blood culture (BC) broth. For Gram-negative bacteria, 4 mL of BC broth was aspirated and passed through a Sartorius Minisart syringe filter with a pore size of 5 µm. The filtrate was then centrifuged and washed. A small volume of the pellet was used for ID, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and for AST, using automated broth microdilution. For Gram-positive cocci, 4 mL of BC broth was passed through the Minisart syringe filter. Then, 4 mL of sterile distilled water was injected in the direction opposite to that of the filtration to collect the bacterial residue trapped in the filter. Compared with the conventional method performed with pure colonies on agar plates, 94.0% (234/249) were correctly identified using the in-house method, with rates of 91.4% (127/139) and 97.3% (107/110) for Gram-positive and Gram-negative isolates, respectively. Of 234 correctly identified isolates, 230 were assessed by AST. Categorical agreement and essential agreement were 93.3% and 94.5%, respectively, with a minor error rate of 3.8%, a major error rate of 3.4%, and a very major error rate of 1.6%. Our in-house preparation method showed good performance in rapid direct ID and AST using positive BC broths compared to the conventional method. This simple method can shorten the conventional turnaround time for ID and AST by at least 1 day, potentially contributing to better patient management.

Antimicrobial Therapy Duration for Bloodstream Infections Caused by Pseudomonas aeruginosa or Acinetobacter baumannii-calcoaceticus complex: A Retrospective Cohort Study

Background: Ideal therapy duration for Pseudomonas aeruginosa or Acinetobacter baumannii-calcoaceticus complex (ABC) bloodstream infections (BSI) is not defined, especially in the context of carbapenem resistance. In this study, we compared short- (≤7 days) and long-term (>7 days) antimicrobial therapy duration for these infections. Methods: We performed a retrospective cohort study in two tertiary-care hospitals in Porto Alegre, Brazil, from 2013 to 2019. Eligible patients aged ≥18 years were included and excluded for the following criteria: polymicrobial infections, treatment with non-susceptible antibiotics, complicated infections, or early mortality (<8 days of active antimicrobial therapy). The 30-day mortality risk was evaluated using a Cox regression model. Results: We included 237 BSI episodes, 51.5% caused by ABC and 48.5% by Pseudomonas aeruginosa. Short-term therapy was not associated with 30-day mortality, adjusted hazard ratio 1.01, 95% confidence interval 0.47–2.20, p = 0.98, when adjusted for Pitt score (p = 0.02), Charlson Comorbidity Index score (p < 0.01), and carbapenem resistance (p < 0.01). Among patients who survived, short-term therapy was associated with shorter hospital stay (p < 0.01). Results were maintained in the subgroups of BSI caused by carbapenem-resistant bacteria (p = 0.76), ABC (p = 0.61), and Pseudomonas aeruginosa (p = 0.39). Conclusions: Long-term therapies for non-complicated Pseudomonas aeruginosa and ABC BSI were not superior to short-term therapy for 30-day mortality.

Prevalence of multi-drug resistant <em>Pseudomonas aeruginosa</em> isolated from selected residential sewages in Dutsin-Ma, Katsina State, Nigeria

The global surge in Multidrug resistant (MDR) bacteria is an issue of great concern. Pseudomonas aeruginosa has been impli- cated in several nosocomial infections, where it has caused grave complications in immunocompromised patients. This is the first study to report the prevalence of MDR P. aeruginosa isolated from residential sewage in Dutsin-Ma, Katsina State, Nigeria. Pseudomonads count, isolation, biochemical characterization and antibiogram were carried out using standard microbiological pro- cedures. This study examined sixty (60) samples from selected res- idential sewage in the study site collected at different intervals between July and September 2021. A total of 40 (66.7%) P. aeruginosa were isolated from the analyzed sewage samples. The high- est (2.84x104) pseudomonad count was recorded from sewage samples collected from Kadangaru. Pseudomonas aeruginosa isolates from this sample site showed the highest (100%) resistance to cephalosporins (cefuroxime) and nitrofurantoin. Similarly, isolates from Miami area also demonstrated the highest (95%) resistance to a cephalosporin (ceftazidime). All (100%) isolates used in this study showed MDR resistance to tested antibiotics. The occurrence of MDR P. aeruginosa from a residential sewage site that may con- taminate drinking water sources in the study area is of public health threat to the inhabitants. Surveillance and molecular epi- demiology of antibiotics resistant bacteria are urgently needed in the study area.

Effect of biosynthesized selenium nanoparticles using Nepeta extract against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii

The problems of drug resistance in bacteria have become one of the daily challenges of the clinical treatment of patients, which inevitably forces us to use agents other than common antibiotics. Among these, we can take help from different properties and applications of nanoparticles (NPs). In this work, we evaluate the antibacterial activity of biosynthesized selenium nanoparticles (SeNPs) against standard strains of multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii. The production of biosynthesized SeNPs was proved by ultraviolet-visible, Fourier transform infrared, X-ray diffractometer, Field Emission Scanning Electron Microscopy, Dynamic light scattering, and Zeta potential methods. The cytotoxicity effect of SeNPs was investigated by MTT assay. Disk diffusion agar (DDA) and minimum inhibitory concentration (MIC) tests were performed on the mentioned bacteria using different classes of standard antibiotics and SeNPs separately. The impact of SeNPs combined with the desired antibiotics for better treatment of these infections was evaluated by checkerboard assay to determine the synergism effect. After the confirmation results based on the biosynthesis of SeNPs, both standard bacterial strains were susceptible to SeNPs and had a zone of inhibition using the DDA test. Also, the results of MICs showed that biosynthesized SeNPs in lower concentrations than antibiotics cause no growth of bacteria. On the other hand, according to the checkerboard assay, SeNPs had a synergistic effect with conventional antibiotics. The antibacterial sensitivity tests demonstrated the inhibition of bacterial growth in the presence of lower concentrations of SeNPs than common antibiotics. This property can be exerted in future applications to solve the drug resistance obstacle of microorganisms in bacterial diseases.

Glycyrrhetinic acid protects against Multidrug-resistant Acinetobacter baumannii-induced lung epithelial cells injury by regulating inflammation and oxidative stress

Glycyrrhetinic acid (GA) is a bio-effective component of Licorice. The GA is a monomer and the ingredient is an Oleanane-type pentacyclic triterpenes that has been used as a remedy for years. Due to the abuse of antibiotics, people pay attention to the emergence of Multidrug-resistant Acinetobacter baumannii (MDR-AB). As a conditional pathogen, MDR-AB causes severe infection, endangering human lives. Our previous studies found GA played an important role in Yinhua Pinggan, a Chinese medicine. However, whether GA could protect lung epithelium from MDR-AB-induced cell injury was elusive. Herein, we investigated the effects of GA on MDR-AB-infected A549 cells. The results showed GA had slightly antibacterial activity to MDR-AB in the GA (high concentration) but no impact on drug resistance genes. Notwithstanding, GA could reverse MDR-AB-induced cell apoptosis, hampered adhesion and invasion of MDR-AB to cells, and inhibit pro-inflammatory cytokines expression of IL-1β, IL-6, and TNF. Besides, MDR-AB-induced reactive oxygen species, pro-oxidative protein malonaldehyde, and myeloperoxidase of cells were decreased by GA, while antioxidative proteins were recovered, showing antioxidative capacity of GA might play a critical role. The expressions of toll-like receptor (TLRs) - 1, 2, 4, 5, 6, and 9 were increased by MDR-AB infection, while GA reversed the tendency. Interestingly, GA inhibited MDR-AB induced myeloiddifferentiationfactor88 expression (MYD88), one downstream con-factors of TLRs, but no affection on Interferon regulatory Factor 3 (IRF3), the other one, indicating GA inhibited MDR-AB induced cell injury by impact TLR/MYD88 pathway to attenuate inflammation. Altogether, our results demonstrated that GA protects against MDR-AB-induced cell injury through its antioxidative and anti-inflammatory properties, which deserve further study in the future.

Variation in antibiotic resistance patterns for children and adults treated at 166 non-affiliated US facilities using EHR data

Background

Antibiotic resistance (AR) is a global public health threat. Surveillance of baseline AR and trends and emerging resistance among priority bacterial isolates with respect to the age of the patients and the type of healthcare setting are required due to differences in antimicrobial need and use in these populations.

Methods

We performed a retrospective study using deidentified electronic health record (EHR) data in the Cerner Health Facts™ data warehouse. Antibiotic susceptibility data were extracted for all bacterial isolates of interest at 166 non-affiliated healthcare facilities reporting microbiology susceptibility results of the FDA recommended antibiotics between the years 2012 to 2017. We assessed and visualized the slope coefficient from linear regression to compare changes in resistance over time for the four patient care groups.

Results

The trends in resistance rates to clinically relevant antibiotics were influenced by age and care setting. For example, ertapenem-resistant Enterobacter cloacae isolates from children overall increased significantly compared with adults (0.7% to 9.8%, 2.1% to 2.8%, P = 0.00013) and isolates from children in paediatric facilities increased significantly compared with facilities treating adults and children (0.1% to 27.1%, 0.9% to 3.8%, P = 0.0002).

Conclusions

Large-scale analysis of EHR data from 166 facilities shows that AR patterns for some bug-drug combinations vary by care setting and patient age. We describe novel data visualizations to interpret large-scale EHR data on the prevalence and trends of AR that should influence antimicrobial prescribing and antimicrobial stewardship programme interventions.

Ceftazidime/Avibactam for the Treatment of Carbapenem-Resistant Pseudomonas aeruginosa Infection in Lung Transplant Recipients

Background

Experience of ceftazidime-avibactam (CAZ/AVI) for carbapenem-resistant Pseudomonas aeruginosa (CRPA) infection in recipients after lung transplantation (LT) is relatively limited.

Methods

A retrospective observational study was conducted on lung transplant recipients receiving CAZ/AVI therapy for CRPA infection. The primary outcomes were the 14-day and 30-day mortality. The secondary outcomes were clinical cure and microbiological cure.

Results

Among 183 LT recipients, a total of 15 recipients with CRPA infection who received CAZ/AVI therapy were enrolled in this study. The mean age of recipients was 54 years and 73.3% of recipients were male. The median time from infection onset to initiation of CAZ/AVI treatment was 4 days (IQR, 3-7) and the mean duration of CAZ/AVI therapy was 10 days. CAZ/AVI was mainly administered as monotherapy in LT recipients (80%). Among these eligible recipients, 14-day and 30-day mortality were 6.7% and 13.3%, respectively. The clinical cure and microbiological cure rates of CAZ/AVI therapy were 53.3% and 60%, respectively. Three recipients (20%) experienced recurrent infection. In addition, the mean lengths of ICU stay and hospital stay were 24 days and 35 days, respectively, among LT recipients.

Conclusion

CAZ/AVI may be an alternative and promising regimen for CRPA eradiation in lung transplant recipients.

Prevalence and Trends of Carbapenem-Resistant Pseudomonas aeruginosa and Acinetobacter Species Isolated from Clinical Specimens at the Ethiopian Public Health Institute, Addis Ababa, Ethiopia: A Retrospective Analysis

Purpose

Carbapenem-resistant Acinetobacter species and P. aeruginosa are the leading cause of nosocomial infections. Therefore, the objective of this study was to analyze the prevalence, antimicrobial susceptibility profile, and trends of carbapenem-resistant P. aeruginosa and Acinetobacter species isolated from clinical specimens.

Patients and Methods

This retrospective study included data from Ethiopian Public Health Institute from 2017 to 2021. BD phoenix M50, Vitek 2 compact, and conventional identification methods were used to identify the organisms. The Kirby-Bauer disc diffusion, BD phoenix M50, and Vitek 2 compact methods were used to determine the antimicrobial susceptibility profiles of the isolates. Chi-square for linear trends using Epi Info was employed to test the significance of carbapenem resistance trends over time. The p-values of ≤0.05 were considered statistically significant.

Results

Following data cleaning, 7110 reports were used. Out of this, (N=185, 2.6%) and (N=142, 2%), Acinetobacter species and P. aeruginosa were isolated, respectively. Twenty-four Acinetobacter species and fourteen P. aeruginosa species were omitted because carbapenem antimicrobial agents were not tested for them. The overall prevalence of carbapenem-resistant Acinetobacter species and P. aeruginosa were 61% and 22%, respectively. The prevalence of carbapenem-resistant Acinetobacter species increased significantly from 50% in 2017 to 76.2% in 2021 (p=0.013). The trend of carbapenem-resistant P. aeruginosa was fluctuating (p=0.99). Carbapenem-resistant Acinetobacter had a lower resistance rate to amikacin (44%) and tobramycin (55%); similarly, carbapenem-resistant P. aeruginosa had a lower resistance rate to amikacin (27%) and tobramycin (47%).

Conclusion

This study revealed a high prevalence of carbapenem-resistant Acinetobacter species and P. aeruginosa, both of which showed better sensitivity to amikacin and tobramycin. Furthermore, Acinetobacter species showed a statistically significant increasing trend in carbapenem resistance.

Riparin-B as a Potential Inhibitor of AdeABC Efflux System from Acinetobacter baumannii

Acinetobacter baumannii is an important opportunistic pathogen that causes serious health-related infections, especially in intensive care units. The present study aimed to investigate the antimicrobial activity of Riparin-B (Rip-B) alone and in association with norfloxacin against multidrug-resistant clinical isolates of A. baumannii. For this, the minimum inhibitory concentrations were determined by the microdilution method. For the evaluation of resistance-modulating activity, MIC values for antibiotics were determined in the presence or absence of subinhibitory concentrations of Rip-B or chlorpromazine (CPZ). The AdeABC-AdeRS efflux system genes from these isolates were detected by PCR. Docking studies were also carried out to evaluate the interaction of Riparin-B and the AdeABC-AdeRS efflux system. The study was conducted from 2017 to 2019. The results showed that Rip-B showed weak intrinsic activity against the strains tested. On the other hand, Rip-B was able to modulate norfloxacin's response against A. baumannii strains that express efflux pump-mediated resistance. Docking studies provided projections of the interaction between Rip-B and EtBr with the AdeB protein, suggesting that Rip-B acts by competitive inhibition with the drug. Results found by in vitro and in silico assays suggest that Rip-B, in combination with norfloxacin, has the potential to treat infections caused by multidrug-resistant A. baumanni with efflux pump resistance.

Carbapenem-Resistant Klebsiella pneumoniae: Diversity, Virulence, and Antimicrobial Resistance

Background

Klebsiella pneumoniae (K. pneumoniae) is one of the most important pathogens in nosocomial infections. It has resistance to most antibiotics, even carbapenem, resulting in restricted therapeutic options.

Purpose

We tried to assess the antimicrobial resistance and virulence fitness of carbapenem-resistant K. pneumoniae (CRKP) in addition to their phenotypic and genotypic diversity.

Materials and Methods

The conventional methods, automated Vitek-32 system, and antimicrobial susceptibility pattern were used to detect CRKP isolates. Virulence and resistance genes profiles were created by using PCR technique. The correlation analysis was done by using R-program.

Results

The antimicrobial resistance profile for all our K. pneumoniae isolates was shocking as the MDR and CRKP were the most prominent phenotypes. Unfortunately, high degrees of heterogeneity among our CRKP isolates were recorded, as 97.5% of them were differentiated into different clusters. We found a negative correlation between the existence of virulence and antimicrobial resistance genes. In contrast to sputum and urine CRPK isolates, the blood isolates showed high antimicrobial resistance and low virulence fitness. Finally, K. pneumoniae creates several outbreaks and crises in Egypt owing to the highly heterogeneity and the wide spread of multidrug-resistant (MDR) and multi-virulent CRKP phenotypes.

Conclusion

Our results are significant and alarming to health organizations throughout the world for the severity and heterogeneity of K. pneumoniae infections. Therefore, the traditional method for treatment of CRKP infections must be renewed. Additionally, the treatment protocols must be well correlated with the site of infections, phenotypes, and genotypes of CRKP strains.

A rationale for the unlike potency of avibactam and ETX2514 against OXA-24 β-lactamase

Diazabicyclooctanone inhibitors such as ETX2514 and avibactam have shown enhanced inhibitory performance to fight the antibiotic resistance developed by pathogens. However, avibactam is ineffective against Acinetobacter baumannii infections, unlike ETX2514. The molecular basis for this difference has not been tackled from a molecular approach, precluding the knowledge of relevant information. In this article, the mechanisms involved in the inhibition of OXA-24 by ETX2514 and avibactam are studied theoretically by hybrid QM/MM calculations. The results show that both inhibitors share the same inhibition mechanisms, comprising acylation a deacylation stages. The involved mechanisms include the same number of steps, transition states and intermediates; although they differ in the involved activation barriers. This difference accounts for the dissimilar inhibitory ability of both inhibitors. The molecular reason for this is the endocyclic double bond in the piperidine ring of ETX2514 increasing the ring strain and chemical reactivity on the N6 and C7 atoms, besides the methyl substituent, which enhance the hydrophobic character of the ring. Furthermore, Lys218 and the carboxylated Lys84 of ETX2514, play a crucial role in the mechanism by coordinating their protonation states in an on/off (protonated/deprotonated) manner, favoring the proton transference between the residues and the inhibitor.

Antibacterial, Anticandidal, and Antibiofilm Potential of Fenchone: In Vitro, Molecular Docking and In Silico/ADMET Study

The aim of the present study is to investigate the effective antimicrobial and antibiofilm properties of fenchone, a biologically active bicyclic monoterpene, against infections caused by bacteria and Candida spp. The interactions between fenchone and three distinct proteins from Escherichia coli (β-ketoacyl acyl carrier protein synthase), Candida albicans (1, 3-β−D-glucan synthase), and Pseudomonas aeruginosa (Anthranilate-CoA ligase) were predicted using molecular docking and in silico/ADMET methods. Further, to validate the in-silico prediction, the antibacterial and antifungal potential of fenchone was evaluated against E. coli, P. aeruginosa, and C. albicans by determining minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC), and minimum fungicidal concentration (MFC). The lowest MIC/MBC values of fenchone against E. coli and P. aeruginosa obtained was 8.3 ± 3.6/25 ± 0.0 and 266.6 ± 115.4/533.3 ± 230.9 mg/mL, respectively, whereas the MIC/MFC value for C. albicans was found to be 41.6 ± 14.4/83.3 ± 28.8 mg/mL. It was observed that fenchone has a significant effect on antimicrobial activity (p < 0.05). Our findings demonstrated that fenchone at 1 mg/mL significantly reduced the production of biofilm (p < 0.001) in E. coli, P. aeruginosa, and C. albicans by 70.03, 64.72, and 61.71%, respectively, in a dose-dependent manner when compared to control. Based on these results, it has been suggested that the essential oil from plants can be a great source of pharmaceutical ingredients for developing new antimicrobial drugs.

Genomic and transcriptomic profiling of phoenix colonies

Pseudomonas aeruginosa is a Gram-negative bacterium responsible for numerous human infections. Previously, novel antibiotic tolerant variants known as phoenix colonies as well as variants similar to viable but non-culturable (VBNC) colonies were identified in response to high concentrations of aminoglycosides. In this study, the mechanisms behind phoenix colony and VBNC-like colony emergence were further explored using both whole genome sequencing and RNA sequencing. Phoenix colonies were found to have a single nucleotide polymorphism (SNP) in the PA4673 gene, which is predicted to encode a GTP-binding protein. No SNPs were identified within VBNC-like colonies compared to the founder population. RNA sequencing did not detect change in expression of PA4673 but revealed multiple differentially expressed genes that may play a role in phoenix colony emergence. One of these differentially expressed genes, PA3626, encodes for a tRNA pseudouridine synthase which when knocked out led to a complete lack of phoenix colonies. Although not immediately clear whether the identified genes in this study may have interactions which have not yet been recognized, they may contribute to the understanding of how phoenix colonies are able to emerge and survive in the presence of antibiotic exposure.

Occurrence of antibiotics and bacterial resistance genes in wastewater: resistance mechanisms and antimicrobial resistance control approaches

Antimicrobial pharmaceuticals are classified as emergent micropollutants of concern, implying that even at low concentrations, long-term exposure to the environment can have significant eco-toxicological effects. There is a lack of a standardized regulatory framework governing the permissible antibiotic content for monitoring environmental water quality standards. Therefore, indiscriminate discharge of antimicrobials at potentially active concentrations into urban wastewater treatment facilities is rampant. Antimicrobials may exert selective pressure on bacteria, leading to resistance development and eventual health consequences. The emergence of clinically important multiple antibiotic-resistant bacteria in untreated hospital effluents and wastewater treatment plants (WWTPs) has been linked to the continuous exposure of bacteria to antimicrobials. The levels of environmental exposure to antibiotics and their correlation to the evolution and spread of resistant bacteria need to be elucidated to help in the formulation of mitigation measures. This review explores frequently detected antimicrobials in wastewater and gives a comprehensive coverage of bacterial resistance mechanisms to different antibiotic classes through the expression of a wide variety of antibiotic resistance genes either inherent and/or exchanged among bacteria or acquired from the reservoir of antibiotic resistance genes (ARGs) in wastewater systems. To complement the removal of antibiotics and ARGs from WWTPs, upscaling the implementation of prospective interventions such as vaccines, phage therapy, and natural compounds as alternatives to widespread antibiotic use provides a multifaceted approach to minimize the spread of antimicrobial resistance.

Clinical data from studies involving novel antibiotics to treat multidrug-resistant Gram-negative bacterial infections

Multidrug-resistant (MDR) Gram-negative bacteria (GNB) are a critical threat to healthcare worldwide, worsening outcomes and increasing mortality among infected patients. Carbapenemase- and extended-spectrum β-lactamase-producing Enterobacterales, as well as carbapenemase-producing Pseudomonas and Acinetobacter spp., are common MDR pathogens. To address this threat, new antibiotics and combinations have been developed. Clinical trial findings support several combinations, notably ceftazidime-avibactam (CZA, a cephalosporin-β-lactamase inhibitor combination) which is effective in treating complicated urinary tract infections (cUTI), complicated intra-abdominal infections and hospital-acquired and ventilator-associated pneumonia caused by GNBs. Other clinically effective combinations include meropenem-vaborbactam (MVB), ceftolozane-tazobactam (C/T) and imipenem- relebactam (I-R). Cefiderocol is a recent siderophore β-lactam antibiotic that is useful against cUTIs caused by carbapenem-resistant Enterobacterales (CRE) and is stable against many β-lactamases. CRE are a genetically heterogeneous group that vary in different world regions and are a substantial cause of infections, among which Klebsiella pneumoniae are the most common. Susceptible CRE infections can be treated with fluoroquinolones, aminoglycosides or fosfomycin, but alternatives include CZA, MVB, I-R, cefiderocol, tigecycline and eravacycline. MDR Acinetobacter baumannii and Pseudomonas aeruginosa are increasingly common pathogens producing a range of different carbapenemases, and infections are challenging to treat, often requiring novel antibiotics or combinations. Currently, no single agent can treat all MDR-GNB infections, but new β-lactam-β-lactamase inhibitor combinations are often effective for different infection sites, and, when used appropriately, have the potential to improve outcomes. This article reviews clinical studies investigating novel β-lactam approaches for treatment of MDR-GNB infections.

Synergistic Antimicrobial Effect of Colistin in Combination with Econazole against Multidrug-Resistant Acinetobacter baumannii and Its Persisters

Colistin is a last-line antibiotic which acts by causing membrane permeabilization in Gram-negative bacteria. However, its clinical value has been limited by its toxicity and the emergence of resistant organisms. In this study, we showed that econazole and colistin can act synergistically to produce a strong antimicrobial effect sufficient for eradication of starvation-induced tolerant and multidrug-resistant populations of Acinetobacter baumannii, a notorious pathogen causing recalcitrant infections, both in vitro and in mouse infection models. Investigation of the underlying mechanism showed that, while colistin disrupts the membrane structure, econazole causes the dissipation of proton motive force, eliciting a vicious cycle of membrane structural damages and disruption of membrane protein functions, and eventually cell death. This drug combination therefore achieves our goal of using a much smaller dosage of colistin to produce a much stronger antimicrobial effect to tackle the problems of toxicity and resistance associated with colistin usage. IMPORTANCE Findings described in this study constitute concrete evidence that it is possible to significantly enhance the antimicrobial activity of colistin by using an antifungal drug, econazole, as a colistin adjuvant. We showed that this drug combination can kill not only multidrug-resistant A. baumannii but also the tolerant subpopulation of such strains known as persisters, which may cause chronic and recurrent infections in clinical settings. The synergistic killing effect of the econazole and colistin combination was also observable in mouse infection models at a very low concentration, suggesting that such a drug combination has high potential to be used clinically. Findings in this study therefore have important implications for enhancing its clinical application potential as well as developing new approaches to enhance treatment effectiveness and reduce suffering in patients.

Genomic Characterization of Mutli-Drug Resistant Pseudomonas aeruginosa Clinical Isolates: Evaluation and Determination of Ceftolozane/Tazobactam Activity and Resistance Mechanisms

Resistance to ceftolozane/tazobactam (C/T) in Pseudomonas aeruginosa is a health concern. In this study, we conducted a whole-genome-based molecular characterization to correlate resistance patterns and β-lactamases with C/T resistance among multi-drug resistant P. aeruginosa clinical isolates. Resistance profiles for 25 P. aeruginosa clinical isolates were examined using disk diffusion assay. Minimal inhibitory concentrations (MIC) for C/T were determined by broth microdilution. Whole-genome sequencing was used to check for antimicrobial resistance determinants and reveal their genetic context. The clonal relatedness was evaluated using MLST, PFGE, and serotyping. All the isolates were resistant to C/T. At least two β-lactamases were detected in each with the bla_OXA-4, bla_OXA-10, bla_OXA-50, and bla_OXA-395 being the most common. bla_IMP-15, bla_NDM-1, or bla_VIM-2, metallo-β-lactamases, were associated with C/T MIC >256 μg/mL. Eight AmpC variants were identified, and PDC-3 was the most common. We also determined the clonal relatedness of the isolates and showed that they grouped into 11 sequence types (STs) some corresponding to widespread clonal complexes (ST111, ST233, and ST357). C/T resistance was likely driven by the acquired OXA β-lactamases such as OXA-10, and OXA-50, ESBLs GES-1, GES-15, and VEB-1, and metallo- β-lactamases IMP-15, NDM-1, and VIM-2. Collectively, our results revealed C/T resistance determinants and patterns in multi-drug resistant P. aeruginosa clinical isolates. Surveillance programs should be implemented and maintained to better track and define resistance mechanisms and how they accumulate and interact.

Structure of Pseudomonas aeruginosa spermidine dehydrogenase: a polyamine oxidase with a novel heme-binding fold

The opportunistic pathogen Pseudomonas aeruginosa can utilize polyamines (including putrescine, cadaverine, 4-aminobutyrate, spermidine, and spermine) as its sole source of carbon and nitrogen. Spermidine dehydrogenase (SpdH) is a component of one of the two polyamine utilization pathways identified in P. aeruginosa, but little is known about its structure and function. Here, we report the first crystal structure of SpdH from P. aeruginosa to 1.85 Å resolution. The resulting core structure confirms that SpdH belongs to the polyamine oxidase (PAO) family with flavin-binding and substrate-binding domains. A unique N-terminal extension wraps around the flavin-binding domain of SpdH and is required for heme binding, placing a heme cofactor in close proximity to the FAD cofactor. Structural and mutational analysis reveals that residues in the putative active site at the re side of the FAD isoalloxazine ring form part of the catalytic machinery. PaSpdH features an unusual active site and lacks the conserved lysine that forms part of a lysine-water-flavin N5 atom interaction in other PAO enzymes characterized to date. Mutational analysis further confirms that heme is required for catalytic activity. This work provides an important starting point for understanding the role of SpdH, which occurs universally in P. aeruginosa strains, in polyamine metabolism.

Correlation between Carbapenem Consumption and Carbapenems Susceptibility Profiles of Acinetobacter baumannii and Pseudomonas aeruginosa in an Academic Medical Center in Thailand

The emergent issue of carbapenem-resistant Acinetobacter baumannii (A. baumannii) and Pseudomonas aeruginosa (P. aeruginosa) is a major problem in Thailand. The wide use of carbapenems can increase selective pressure of bacterial resistance. The objective of this study was to determine the relationship between carbapenem consumption and the susceptibility rates of A. baumannii and P. aeruginosa, including multi-drug resistance (MDR) strains. This was a retrospective study. Carbapenem consumption and susceptibility profiles were collected from 2007 to 2013 at the Her Royal Highness Princess Maha Chakri Sirindhorn Medical Center, Thailand. We found that the susceptibility rate of A. baumannii to imipenem and meropenem from the sputum and the bronchoalveolar lavage (BAL) specimens was significantly decreased during the study period, but no significant change was found in the P. aeruginosa data. The relationship between carbapenem consumption and the susceptibility rate of A. baumannii had a clear association with the use of ertapenem. We found a statistically significant negative correlation between ertapenem consumption and the susceptibility rate of A. baumannii to imipenem (r = −0.91; p = 0.004) and meropenem (r = −0.97; p = 0.000) in the data from the non-ICU wards. In addition, imipenem use had a moderate negative correlation with the MDR P. aeruginosa data but no statistical significance (r = −0.714; p > 0.05). In conclusion, our study suggested there is an association between carbapenem use and the susceptibility of A. baumannii and P. aeruginosa. Notwithstanding this, information on ecological factors should be considered for further study. These findings showed the need to optimize the carbapenem prescription policy. Avoiding carbapenem overuse and rethinking the appropriate initial therapy might decrease the rate of resistant organisms.

Five-year Surveillance of Antimicrobial Resistance Changes and Epidemiological Characteristics in Pseudomonas aeruginosa: A Retrospective Study in a Chinese City Hospital

Background: In recent years, the widespread use of antibiotics has resulted in increased rates of antibiotic resistance (ABR). Pseudomonas aeruginosa is one of the most important opportunistic pathogens causing hospital-acquired infections. Pseudomonas aeruginosa has continuously increased resistance to commonly used clinical antimicrobial drugs, bringing great difficulties to clinical treatment. Objectives: This retrospective study investigated the epidemiological characteristics of P. aeruginosa and changes in ABR over a 5-year period at a hospital in Shandong Province, China. Methods: Pseudomonas aeruginosa strains were collected from 2015 to 2019. The antimicrobial susceptibility testing employed the Kirby-Bauer disk diffusion method and the broth microdilution method (VITEK-2 compact system), according to the guidelines by the Clinical and Laboratory Standards Institute. Data were analyzed using WHONET 5.6 and SPSS V. 21.0 software. Results: A total of 3,324 P. aeruginosa strains were isolated from clinical specimens (604, 631, 700, 595, and 794 strains from 2015 to 2019, respectively). The highest P. aeruginosa detection rates were from respiratory tract specimens (72.54%). The highest resistance was seen in aztreonam, followed by ciprofloxacin, levofloxacin, and imipenem. The isolation rates for carbapenem-resistant P. aeruginosa (CRPA) and multidrug-resistant P. aeruginosa (MDRPA) ranged from 15.21 - 18.38% and 17.31 - 27.31%, respectively. Also, the isolation rates for extensively drug-resistant P. aeruginosa (XDRPA) ranged from 1.86 - 3.52%. Conclusions: The main sources of the P. aeruginosa isolates were older adult patients with chronic respiratory diseases. The isolation rates for CRPA, MDRPA, and XDRPA strains decreased over the 5-year period. However, the drug resistance situation remains a serious concern. Hence, continued infection control and antimicrobial stewardship and basic and clinical research on bacterial resistance are essential.

Prevalence, Risk Factors, and Molecular Epidemiology of Intestinal Carbapenem-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa may become multidrug-resistant (MDR) due to multiple inherited and acquired resistance mechanisms. The human gastrointestinal tract is known as a reservoir of P. aeruginosa and its resistance genes. In this study, we collected 76 intestinal carbapenem-resistant P. aeruginosa (CRPA) strains from clinical inpatients admitted to our hospital from 2014 to 2019, together with their medical data. We aim to analyze the clinical risk factors associated with CRPA infection and its molecular features. We found that the prevalence of CRPA in P. aeruginosa strains was 41.3% (95% confidence interval [CI], 34.1 to 48.8%). We also identified four variables associated with intestinal CRPA positivity, prior antibiotic exposure to aminoglycosides or carbapenems, underlying diabetes mellitus, and extraintestinal P. aeruginosa isolation. bla_KPC-2 is the only detected carbapenemase gene, accounting for 21.1% of CRPA strains. The genetic environment showed that the bla_KPC-2 gene was flanked immediately by ISKpn8 and ISKpn6 and several other mobile elements further upstream or downstream. Four sequence types (STs) were identified, with ST463 as the dominant sequence type. In conclusion, screening for P. aeruginosa colonization upon hospital admission could reduce the risk of P. aeruginosa infection and spread of CRPA in the hospital.

IMPORTANCEPseudomonas aeruginosa may become multidrug-resistant (MDR) due to multiple inherited and acquired resistance mechanisms. The human gastrointestinal tract is known as a reservoir of P. aeruginosa and its resistance genes. Risk factor analysis and molecular epidemiology are critical for preventing their potential dissemination. Here, we identified four risk factors associated with intestinal CRPA—prior antibiotic exposure to aminoglycosides or carbapenems, underlying diabetes mellitus, and extraintestinal P. aeruginosa isolation. Further, we found similar genetic environments with several mobile elements surrounding the bla_KPC gene, a carbapenemase gene only detected in intestinal CRPA strains in this study. These findings are of significant public health importance, as the information will facilitate the control of the emergence and spread of CRPA.

The many antibiotic resistance and tolerance strategies of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a bacterial pathogen associated with a wide range of infections and utilizes several strategies to establish and maintain infection including biofilm production, multidrug resistance, and antibiotic tolerance. Multidrug resistance in P. aeruginosa, as well as in all other bacterial pathogens, is a growing concern. Aminoglycoside resistance, in particular, is a major concern in P. aeruginosa infections and must be better understood in order to maintain effective clinical treatment. In this review, the various antibiotic resistance and tolerance mechanisms of Pseudomonas are explored including: classic mutation driven resistance, adaptive resistance, persister cells, small colony variants, phoenix colonies, and biofilms. It is important to further characterize each of these phenotypes and continue to evaluate antibiotic surviving isolates for novel driving mechanisms, so that we are better prepared to combat the rising number of recurrent and recalcitrant infections.

New insights about the EptA protein and its correlation with the pmrC gene in polymyxin resistance in Pseudomonas aeruginosa

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Computational biology.

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Bacterial resistance.

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Pseudomonas aeruginosa.

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Gram-negative bacteria.

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Polymyxin.

Nowadays, clinical and scientific interest in antibiotics, as polymyxin, has increased due to the large number of reports of multiresistant Gram-negative bacteria, as Pseudomonas aeruginosa. The aim of this study was to investigate a related group of proteins for resistance to polymyxins, encoded by P. aeruginosa genome, through in silico analysis. The mobilized colistin resistance 1 (MCR₁) protein from Escherichia coli was used for comparison. Similar sequences to the protein MCR₁ in P. aeruginosa were analysed for physicochemical properties. 31 protein isoforms in P. aeruginosa (EptA) were found able to confer resistance to polymyxin showing protein lengths between 551 and 572 amino acids, with molecular mass values between 61.36 - 62. 80 kDa, isoelectric point between 6.10 to 7.17, instability index between 33.76 to 41.87, aliphatic index between 98.67 to 102.63 and the hydropathyindex between - 0.008 to 0.094. These proteins belong to the DUF₁₇₀₅ superfamily with bit-score values between 559.81 and 629.78. A high degree of similarity between EpTAs in P. aeruginosa was observed in relation to other proteins that confer resistance to polymyxins, present in Gram-negative bacteria species of clinical interest. Although, further studies are needed to identify the actual contribution of EptAs in P. aeruginosa species.

Determination of the prevalence of blaoxa-like gene and ISAba1 elements among extensiveــdrug resistant (XDR) Acinetobacter boumannii isolates

The capacity of Multiـdrug resistant (MDR) Acinetobacter baumannii to survive in any state of affairs concerning the gaining of various gene types of virulence and antimicrobial agent resistance are the main anxiety in the hospital’s environments. So, it is very crucial to determine the prevalence of insertion sequences in A. baumannii. In the hospitals. Detecting the blaoxa-51 gene through the polymerase chain reaction (PCR) was performed to confirm Acinetobacter baumannii and the search for ISAba1 element. Between October 2020 and February 2021, 540 distinct clinical specimens were gathered from five hospitals in Baghdad. Thirty-eight A. baumannii isolates were obtained from various clinical specimens. The isolates were initially identified phenotypically using standard microbiological techniques and by the Vitek2 compact automated machine. Isolates of A. baumannii were identified genotypically by amplification of the blaoxa-51-like gene. Antimicrobials are studied by Kirby-Bauer (disc diffusion) technique on Muller-Hinton agar as specified by the recent clinical and laboratory standard institute (CLSI) guidelines (2020). The actual results of the current study indicated that from total isolated (38) A.baumannii isolates, 23 isolates (61%) were resistant to meropenem and 25 isolates (66%) were resistant to imipenem. The blaoxa-51 gene was identified in all strains examined, ISAba1 was also present in all A. baumannii isolates. ISAba1 has a high predominance between drug-resistant A. baumannii. Identifying these parameters can assist in the control of infection and decreasing the microorganism’s prevalence rate.

Exploration of the Pharmacodynamics for Pseudomonas aeruginosa Biofilm Eradication by Tobramycin

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen which is involved in numerous infections. It is of growing concern within the field of antibiotic resistant and tolerance and often exhibits multi-drug resistance. Previous studies have shown the emergence of antibiotic resistant and tolerant variants within the zone of clearance of a biofilm lawn after exposure to aminoglycosides. As concerning as the tolerant variant emergence is, there was also a zone of killing (ZOK) immediately surrounding the antibiotic source from which no detectable bacteria emerged or were cultured. In this study, the ZOK was analyzed using both in vitro and in silico methods to determine if there was a consistent antibiotic concentration versus time constraint (area under the curve, (AUC)) which is able to completely kill all bacteria in the lawn biofilms in our in vitro model. Our studies revealed that by achieving an average AUC of 4,372.5 μg*hr/mL, complete eradication of biofilms grown on both agar and hydroxyapatite was possible. These findings show that appropriate antibiotic concentrations and treatment duration may be able to treat antibiotic resistant and tolerant biofilm infections.

Propensity Score and Desirability of Outcome Ranking Analysis of Ertapenem for Treatment of Nonsevere Bacteremic Urinary Tract Infections Due to Extended-Spectrum-Beta-Lactamase-Producing Enterobacterales in Kidney Transplant Recipients

There are scarce data on the efficacy of ertapenem in the treatment of bacteremia due to extended-spectrum-beta-lactamase (ESBL)-producing Enterobacterales (ESBL-E) in kidney transplant (KT) recipients. We evaluated the association between treatment with ertapenem or meropenem and clinical cure in KT recipients with nonsevere bacteremic urinary tract infections (B-UTI) caused by ESBL-E. We performed a registered, retrospective, international (29 centers in 14 countries) cohort study (INCREMENT-SOT, NCT02852902). The association between targeted therapy with ertapenem versus meropenem and clinical cure at day 14 (the principal outcome) was studied by logistic regression. Propensity score matching and desirability of outcome ranking (DOOR) analyses were also performed. A total of 201 patients were included; only 1 patient (treated with meropenem) in the cohort died. Clinical cure at day 14 was reached in 45/100 (45%) and 51/101 (50.5%) of patients treated with ertapenem and meropenem, respectively (adjusted OR 1.29; 95% CI 0.51 to 3.22; P = 0.76); the propensity score-matched cohort included 55 pairs (adjusted OR for clinical cure at day 14, 1.18; 95% CI 0.43 to 3.29; P = 0.74). In this cohort, the proportion of cases treated with ertapenem with better DOOR than with meropenem was 49.7% (95% CI, 40.4 to 59.1%) when hospital stay was considered. It ranged from 59 to 67% in different scenarios of a modified (weights-based) DOOR sensitivity analysis when potential ecological advantage or cost was considered in addition to outcome. In conclusion, targeted therapy with ertapenem appears as effective as meropenem to treat nonsevere B-UTI due to ESBL-E in KT recipients and may have some advantages.

Memantine Promotes Bactericidal Effect of Neutrophils Against Infection with Pseudomonas aeruginosa and Its Drug-Resistant Strain, by Improving Reactive Oxygen Species Generation

Pseudomonas aeruginosa is an opportunistic pathogen, which usually presents multiple antibiotic resistance. Host-directed therapy involves modulating the host defense system and the interplay between innate and adaptive immunity is a new strategy for designing anti-infection drugs. Memantine (MEM), a drug used to treat Alzheimer's disease, has a good inhibitory effect on neonatal mice with Escherichia coli-associated bacteremia and meningitis; however, the inhibitory effect and mechanisms of MEM against P. aeruginosa infection remain unclear. Here, we investigated whether MEM could inhibit P. aeruginosa infection and explored the potential mechanisms. MEM significantly promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain. The combination index of MEM and amikacin (AMK) was <1. In vivo experiments showed that the bacteremia and inflammation severities in the MEM-treated group were less than those in the untreated group, and the bacterial load in the organs was significantly less than that in the control group. Combining MEM with the reactive oxygen species (ROS) inhibitor, N-acetyl-l-cysteine, weakened the anti-infective effect of MEM. MEM increased the expression of NADPH p67phox and promoted neutrophilic ROS production. Deleting the p67phox gene significantly weakened the effects of MEM on ROS generation and improving bactericidal effect of neutrophils. In conclusion, MEM promoted the bactericidal effect of neutrophils against P. aeruginosa and its drug-resistant strain, and had a synergistic antibacterial effect when combined with AMK. MEM may exert its anti-infective effects by promoting neutrophilic bactericidal activity via increasing the expression level of p67phox and further stimulating ROS generation.

Management of bacterial and fungal infections in cirrhosis: The MDRO challenge

Bacterial infections are frequent in cirrhotic patients with acute decompensation or acute-on-chronic liver failure and can complicate the clinical course. Delayed diagnosis and inappropriate empirical treatments are associated with poor prognosis and increased mortality. Fungal infections are much less frequent, usually nosocomial and associated with extremely high short-term mortality. Early diagnosis and adequate empirical treatment of infections is therefore key in the management of these patients. In recent decades, antibiotic resistance has become a major worldwide problem in patients with cirrhosis, warranting a more complex approach to antibiotic treatment that includes the use of broad-spectrum antibiotics, new administration strategies, novel drugs and de-escalation policies. Herein, we review epidemiological changes, the main types of multidrug-resistant organisms, mechanisms of resistance, new rapid diagnostic tools and currently available therapeutic options for bacterial and fungal infections in cirrhosis.

Activity of β-lactam/taniborbactam (VNRX-5133) combinations against carbapenem-resistant Gram-negative bacteria

BACKGROUND

Boronates are of growing interest as β-lactamase inhibitors. The only marketed analogue, vaborbactam, principally targets KPC carbapenemases, but taniborbactam (VNRX-5133, Venatorx) has a broader spectrum.

METHODS

MICs of cefepime and meropenem were determined combined with taniborbactam or avibactam for carbapenem-resistant UK isolates. β-Lactamase genes and porin alterations were sought by PCR or sequencing.

RESULTS

Taniborbactam potentiated partner β-lactams against: (i) Enterobacterales with KPC, other class A, OXA-48-like, VIM and NDM (not IMP) carbapenemases; and (ii) Enterobacterales inferred to have combinations of ESBL or AmpC activity and impermeability. Potentiation of cefepime (the partner for clinical development) by taniborbactam was slightly weaker than by avibactam for Enterobacterales with KPC or OXA-48-like carbapenemases, but MICs of cefepime/taniborbactam were similar to those of ceftazidime/avibactam, and the spectrum was wider. MICs of cefepime/taniborbactam nonetheless remained >8 + 4 mg/L for 22%-32% of NDM-producing Enterobacterales. Correlates of raised cefepime/taniborbactam MICs among these NDM Enterobacterales were a cefepime MIC >128 mg/L, particular STs and, for Escherichia coli only: (i) the particular blaNDM variant (even though published data suggest all variants are inhibited similarly); (ii) inserts in PBP3; and (iii) raised aztreonam/avibactam MICs. Little or no potentiation of cefepime or meropenem was seen for Pseudomonas aeruginosa and Acinetobacter baumannii with MBLs, probably reflecting slower uptake or stronger efflux. Potentiation of cefepime was seen for Stenotrophomonas maltophilia and Elizabethkingia meningoseptica, which have both chromosomal ESBLs and MBLs.

CONCLUSIONS

Taniborbactam broadly reversed cefepime or meropenem non-susceptibility in Enterobacterales and, less reliably, in non-fermenters.

In vitro synergy of ceftolozane/tazobactam in combination with fosfomycin or aztreonam against MDR Pseudomonas aeruginosa

OBJECTIVES

Carbapenem-resistant Pseudomonas aeruginosa (CR-PSA) imposes great limitations on empirical therapeutic choices, which are further complicated by metallo-β-lactamase production. This study evaluated in vitro antimicrobial synergy of ceftolozane/tazobactam in combination with aztreonam and fosfomycin against MDR PSA.

METHODS

MICs were determined by broth microdilution and gradient strips. The effect of ceftolozane/tazobactam+aztreonam and ceftolozane/tazobactam+fosfomycin combinations were tested against 27 MDR PSA isolates carrying blaSPM-1 (n = 13), blaIMP (n = 4), blaVIM (n = 3), blaGES-1 (n = 2) and blaCTX-M-like (n = 2), and 3 isolates with no acquired β-lactamase production detected by gradient diffusion strip crossing (GDSC). Six genetically unrelated SPM-1-producing isolates were also evaluated by time-kill analysis (TKA).

RESULTS

All CR-PSA isolates harbouring blaSPM-1, blaGES-1 and blaIMP-1 were categorized as resistant to ceftolozane/tazobactam, meropenem and fosfomycin, with 70% being susceptible to aztreonam. Synergism for ceftolozane/tazobactam+fosfomycin and ceftolozane/tazobactam+aztreonam combinations was observed for 88.9% (24/27) and 18.5% (5/27) of the isolates by GDSC, respectively. A 3- to 9-fold reduction in ceftolozane/tazobactam MICs was observed, depending on the combination. Ceftolozane/tazobactam+fosfomycin was synergistic by TKA against one of six SPM-1-producing isolates, with additional non-synergistic bacterial density reduction for another isolate. Aztreonam peak concentrations alone demonstrated a ≥3 log10 cfu/mL reduction against all six isolates, but all strains were within the susceptible range for the drug. No antagonism was observed.

CONCLUSIONS

In the context of increasing CR-PSA and the genetic diversity of resistance mechanisms, new combinations and stewardship strategies may need to be explored in the face of increasingly difficult to treat pathogens.

Carbapenem resistance in Acinetobacter baumannii, and their importance in hospital-acquired infections: a scientific review

Carbapenem is an important therapy for serious hospital-acquired infections and for the care of patients affected by multidrug-resistant organisms, specifically Acinetobacter baumannii; however, with the global increase of carbapenem-resistant A. baumannii, this pathogen has significantly threatened public health. Thus, there is a pressing need to better understand this pathogen in order to develop novel treatments and control strategies for dealing with A. baumannii. In this review, we discuss an overview of carbapenem, including its discovery, development, classification and biological characteristics, and its importance in hospital medicine especially in critical care units. We also describe the peculiarity of bacterial pathogen, A. baumannii, including its commonly reported virulence factors, environmental persistence and carbapenem resistance mechanisms. In closing, we discuss various control strategies for overcoming carbapenem resistance in hospitals and for limiting outbreaks. With the appearance of strains that resist carbapenem, the aim of this review is to highlight the importance of understanding this increasingly problematic healthcare-associated pathogen that creates significant concern in the field of nosocomial infections and overall public health.

Comprehensive genomic analysis reveals virulence factors and antibiotic resistance genes in Pantoea agglomerans KM1, a potential opportunistic pathogen

Pantoea agglomerans is a Gram-negative facultative anaerobic bacillus causing a wide range of opportunistic infections in humans including septicemia, pneumonia, septic arthritis, wound infections and meningitis. To date, the determinants of virulence, antibiotic resistance, metabolic features conferring survival and host-associated pathogenic potential of this bacterium remain largely underexplored. In this study, we sequenced and assembled the whole-genome of P. agglomerans KM1 isolated from kimchi in South Korea. The genome contained one circular chromosome of 4,039,945 bp, 3 mega plasmids, and 2 prophages. The phage-derived genes encoded integrase, lysozyme and terminase. Six CRISPR loci were identified within the bacterial chromosome. Further in-depth analysis showed that the genome contained 13 antibiotic resistance genes conferring resistance to clinically important antibiotics such as penicillin G, bacitracin, rifampicin, vancomycin, and fosfomycin. Genes involved in adaptations to environmental stress were also identified which included factors providing resistance to osmotic lysis, oxidative stress, as well as heat and cold shock. The genomic analysis of virulence factors led to identification of a type VI secretion system, hemolysin, filamentous hemagglutinin, and genes involved in iron uptake and sequestration. Finally, the data provided here show that, the KM1 isolate exerted strong immunostimulatory properties on RAW 264.7 macrophages in vitro. Stimulated cells produced Nitric Oxide (NO) and pro-inflammatory cytokines TNF-α, IL-6 and the anti-inflammatory cytokine IL-10. The upstream signaling for production of TNF-α, IL-6, IL-10, and NO depended on TLR4 and TLR1/2. While production of TNF-α, IL-6 and NO involved solely activation of the NF-κB, IL-10 secretion was largely dependent on NF-κB and to a lesser extent on MAPK Kinases. Taken together, the analysis of the whole-genome and immunostimulatory properties provided in-depth characterization of the P. agglomerans KM1 isolate shedding a new light on determinants of virulence that drive its interactions with the environment, other microorganisms and eukaryotic hosts

Rational Drug Design for Pseudomonas aeruginosa PqsA Enzyme: An in silico Guided Study to Block Biofilm Formation

Pseudomonas aeruginosa is an opportunistic gram-negative bacterium implicated in acute and chronic nosocomial infections and a leading cause of patient mortality. Such infections occur owing to biofilm formation that confers multidrug resistance and enhanced pathogenesis to the bacterium. In this study, we used a rational drug design strategy to inhibit the quorum signaling system of P. aeruginosa by designing potent inhibitory lead molecules against anthranilate-CoA ligase enzyme encoded by the pqsA gene. This enzyme produces autoinducers for cell-to-cell communication, which result in biofilm formation, and thus plays a pivotal role in the virulence of P. aeruginosa. A library of potential drug molecules was prepared by performing ligand-based screening using an available set of enzyme inhibitors. Subsequently, structure-based virtual screening was performed to identify compounds showing the best binding conformation with the target enzyme and forming a stable complex. The two hit compounds interact with the binding site of the enzyme through multiple short-range hydrophilic and hydrophobic interactions. Molecular dynamic simulation and MM-PBSA/GBSA results to calculate the affinity and stability of the hit compounds with the PqsA enzyme further confirmed their strong interactions. The hit compounds might be useful in tackling the resistant phenotypes of this pathogen.

Evaluation of in vitro activity of ceftazidime/avibactam and ceftolozane/tazobactam against MDR Pseudomonas aeruginosa isolates from Qatar

OBJECTIVES

To investigate the in vitro activity of ceftazidime/avibactam and ceftolozane/tazobactam against clinical isolates of MDR Pseudomonas aeruginosa from Qatar, as well as the mechanisms of resistance.

METHODS

MDR P. aeruginosa isolated between October 2014 and September 2015 from all public hospitals in Qatar were included. The BD PhoenixTM system was used for identification and initial antimicrobial susceptibility testing, while Liofilchem MIC Test Strips (Liofilchem, Roseto degli Abruzzi, Italy) were used for confirmation of ceftazidime/avibactam and ceftolozane/tazobactam susceptibility. Ten ceftazidime/avibactam- and/or ceftolozane/tazobactam-resistant isolates were randomly selected for WGS.

RESULTS

A total of 205 MDR P. aeruginosa isolates were included. Of these, 141 (68.8%) were susceptible to ceftazidime/avibactam, 129 (62.9%) were susceptible to ceftolozane/tazobactam, 121 (59.0%) were susceptible to both and 56 (27.3%) were susceptible to neither. Twenty (9.8%) isolates were susceptible to ceftazidime/avibactam but not to ceftolozane/tazobactam and only 8 (3.9%) were susceptible to ceftolozane/tazobactam but not to ceftazidime/avibactam. Less than 50% of XDR isolates were susceptible to ceftazidime/avibactam or ceftolozane/tazobactam. The 10 sequenced isolates belonged to six different STs and all produced AmpC and OXA enzymes; 5 (50%) produced ESBL and 4 (40%) produced VIM enzymes.

CONCLUSIONS

MDR P. aeruginosa susceptibility rates to ceftazidime/avibactam and ceftolozane/tazobactam were higher than those to all existing antipseudomonal agents, except colistin, but were less than 50% in extremely resistant isolates. Non-susceptibility to ceftazidime/avibactam and ceftolozane/tazobactam was largely due to the production of ESBL and VIM enzymes. Ceftazidime/avibactam and ceftolozane/tazobactam are possible options for some patients with MDR P. aeruginosa in Qatar.

Novel Aminoglycoside-Tolerant Phoenix Colony Variants of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterial pathogen and is known to produce biofilms. We previously showed the emergence of colony variants in the presence of tobramycin-loaded calcium sulfate beads. In this study, we characterized the variant colonies, which survived the antibiotic treatment, and identified three distinct phenotypes-classically resistant colonies, viable but nonculturable colonies (VBNC), and phoenix colonies. Phoenix colonies, described here for the first time, grow out of the zone of clearance of antibiotic-loaded beads from lawn biofilms while there are still very high concentrations of antibiotic present, suggesting an antibiotic-resistant phenotype. However, upon subculturing of these isolates, phoenix colonies return to wild-type levels of antibiotic susceptibility. Compared with the wild type, phoenix colonies are morphologically similar aside from a deficiency in green pigmentation. Phoenix colonies do not recapitulate the phenotype of any previously described mechanisms of resistance, tolerance, or persistence and, thus, form a novel group with their own phenotype. Growth under anaerobic conditions suggests that an alternative metabolism could lead to the formation of phoenix colonies. These findings suggest that phoenix colonies could emerge in response to antibiotic therapies and lead to recurrent or persistent infections, particularly within biofilms where microaerobic or anaerobic environments are present.