In vitro activity of β-lactams in combination with avibactam against multidrug-resistant Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Achromobacter xylosoxidans isolates from patients with cystic fibrosis

The in vitro synergistic and antibiofilm activity of Ceftazidime/avibactam against Achromobacter species recovered from respiratory samples of cystic fibrosis patients

PURPOSE

Achromobacter spp. may form biofilm in patients' respiratory tracts and cause serious infections. This research examined the bactericidal and synergistic effects of ceftazidime/avibactam (CZA) alone and in combination with different antibiotics against Achromobacter spp.

METHODS

MICs of 52 Achromobacter spp. were determined by broth microdilution. In-vitro time-kill curve experiments assessed CZA's bactericidal and synergistic properties alone and in combination with other antibiotics. Moreover, the antibiofilm activity of CZA alone or in combination with the antibiotics was assessed with using microplate method.

RESULTS

Based on MIC90 values, CZA exhibited four times greater in-vitro activity against tested strains than ceftazidime. The most effective agent was meropenem, with a 92% susceptibility level on the tested strains. On the other hand, ciprofloxacin was found to be bactericidal at both 1 × and 4xMIC concentrations. CZA, chloramphenicol and meropenem were observed to have bactericidal effects alone at 4xMIC concentrations against the tested isolates. CZA + CS and CZA + MEM showed synergy in three out of five and two out of five strains tested at 1xMIC, respectively. Furthermore, the pairing of CZA with colistin, CZA with meropenem and CZA with ciprofloxacin exhibited a synergistic impact at 4xMIC. Moreover, combination therapy CZA with the tested antibiotics showed reduced biofilm formation in a concentration-dependent manner at 24 h.

CONCLUSION

The outcomes of this research also suggest that CZA plus colistin, meropenem, or ciprofloxacin were more productive against Achromobacter strains. To our knowledge, this is the first article to evaluate the synergistic and antibiofilm activities of CZA alone or in combination with different agents against Achromobacter species.

Clinical and microbiological features of positive blood culture episodes caused by non-fermenting gram-negative bacilli other than Pseudomonas and Acinetobacter species (2020-2023)

INTRODUCTION

Non-fermenting Gram-negative bacilli (NFGNB) other than Pseudomonas aeruginosa and Acinetobacter baumannii complex are pathogens of interest due to their ability to cause health-care associated infections and display complex drug resistance phenotypes. However, their clinical and microbiological landscape is still poorly characterized.

METHODS

Observational retrospective study including all hospitalized patients presenting with a positive positive blood culture (BC) episode caused by less common NFGNB over a four-year period (January 2020-December 2023). Clinical-microbiological features and factors associated with mortality were investigated.

RESULTS

Sixty-six less common NFGNB isolates other than Pseudomonas and Acinetobacter species causing 63 positive BC episodes were recovered from 60 patients. Positive BC episodes were predominantly sustained by Stenotrophomonas maltophilia (49.2%) followed by Achromobacter species (15.9%) that exhibited the most complex resistance phenotype. Positive BC episodes had bloodstream infection criteria in 95.2% of cases (60 out 63), being intravascular device (30.2%) and respiratory tract (19.1%) the main sources of infection. Fourteen-day, 30-day, and in-hospital mortality rates were 6.4%, 9.5%, and 15.9%, respectively. The longer time from admission to the positive BC episode, older age, diabetes, admission due to sepsis, and higher Charlson Comorbidity Index were identified as the main predictors of in-hospital mortality.

CONCLUSIONS

Positive BC episodes sustained by NFGNB other than Pseudomonas and Acinetobacter species were predominantly sustained by Stenotrophomonas maltophilia and Achromobacter species, having bloodstream infection criteria in the vast majority of cases. Factors that have emerged to be associated with mortality highlighted how these species may have more room in prolonged hospitalisation and at the end of life for patients with chronic organ diseases.

Multicenter evaluation of activity of aztreonam in combination with avibactam, relebactam, and vaborbactam against metallo-β-lactamase-producing carbapenem-resistant gram-negative bacilli

Treatment options for carbapenem-resistant gram-negative bacilli (CR-GNB), especially metallo-β-lactamase (MBL)-producing CR-GNB, are limited. Aztreonam (ATM) in combination with avibactam (AVI) has shown potential for treating MBL-producing carbapenem-resistant Enterobacterales (CREs) and Stenotrophomonas maltophilia. However, data on ATM in combination with other β-lactamase inhibitors (BLIs) are limited. We performed a multicenter study to evaluate the in vitro activities of ATM in combination with AVI, vaborbactam (VAB), relebactam (REL), tazobactam (TAZ) as well as with their commercially available formulations against CREs and S. maltophilia using broth microdilution. AVI restored ATM activity for MBL-producing CREs (ATM: 9.8% vs ATM-AVI: 78.0%) and S. maltophilia (ATM: 0% vs ATM-AVI: 93.3%). REL also moderately restored activity of ATM in MBL-producing CREs (ATM: 9.8% vs ATM-REL: 42.7%) and S. maltophilia (ATM: 0% vs ATM-REL: 68.9%). VAB and TAZ demonstrated very limited effect on the activity of ATM against CR-GNB evaluated. The combination of ATM with ceftazidime-AVI (CAZ-AVI) demonstrated maximum activity against CREs. Although ATM-CAZ-AVI is the most potent regimen available for CREs and S. maltophilia, ATM-IMI-REL might be a reasonable alternative.

Comparative in vitro activities of eravacycline in combination with colistin, meropenem, or ceftazidime against various Achromobacter spp. strains isolated from patients with cystic fibrosis

The Achromobacter species is an emerging pathogen causing chronic bacterial infections in patients with certain conditions, such as cystic fibrosis (CF), hematologic and solid organ malignancies, renal failure, and certain immune deficiencies. In the present study, we assessed the in vitro bactericidal activities of eravacycline, either alone or in combination with colistin, meropenem, or ceftazidime, using 50 Achromobacter spp. strains isolated from CF patients. We also investigated the synergistic interactions of these combinations using microbroth dilutions against 50 strains of Achromobacter spp. Bactericidal, and we assessed the synergistic effects of the tested antibiotic combinations using the time-kill curve (TKC) technique. Our studies show that meropenem alone is the most effective antibiotic of those tested. Based on the TKCs, we found that eravacycline-colistin combinations display both bactericidal and synergistic activities for 24 h against 5 of the 6 Achromobacter spp. strains, including colistin-resistant ones, at 4xMIC of colistin. Although we did not observe synergistic interactions with eravacycline-meropenem or eravacycline-ceftazidime combinations, we did not observe antagonism with any combination tested.This study's findings could have important implications for antimicrobial therapy with tested antibiotics.

A Review of the Resistance Mechanisms for β-Lactams, Macrolides and Fluoroquinolones among Streptococcus pneumoniae

Streptococcus pneumoniae (S. pneumoniae) is a bacterial species often associated with the occurrence of community-acquired pneumonia (CAP). CAP refers to a specific kind of pneumonia that occurs in individuals who acquire the infection outside of a healthcare setting. It represents the leading cause of both death and morbidity on a global scale. Moreover, the declaration of S. pneumoniae as one of the 12 leading pathogens was made by the World Health Organization (WHO) in 2017. Antibiotics like β-lactams, macrolides, and fluoroquinolones are the primary classes of antimicrobial medicines used for the treatment of S. pneumoniae infections. Nevertheless, the efficacy of these antibiotics is diminishing as a result of the establishment of resistance in S. pneumoniae against these antimicrobial agents. In 2019, the WHO declared that antibiotic resistance was among the top 10 hazards to worldwide health. It is believed that penicillin-binding protein genetic alteration causes β-lactam antibiotic resistance. Ribosomal target site alterations and active efflux pumps cause macrolide resistance. Numerous factors, including the accumulation of mutations, enhanced efflux mechanisms, and plasmid gene acquisition, cause fluoroquinolone resistance. Furthermore, despite the advancements in pneumococcal vaccinations and artificial intelligence (AI), it is not feasible for individuals to rely on them indefinitely. The ongoing development of AI for combating antimicrobial resistance necessitates more research and development efforts. A few strategies can be performed to curb this resistance issue, including providing educational initiatives and guidelines, conducting surveillance, and establishing new antibiotics targeting another part of the bacteria. Hence, understanding the resistance mechanism of S. pneumoniae may aid researchers in developing a more efficacious antibiotic in future endeavors.

Antimicrobial Treatment Options for Difficult-to-Treat Resistant Gram-Negative Bacteria Causing Cystitis, Pyelonephritis, and Prostatitis: A Narrative Review

Urinary tract infections, including cystitis, acute pyelonephritis, and prostatitis, are among the most common diagnoses prompting antibiotic prescribing. The rise in antimicrobial resistance over the past decades has led to the increasing challenge of urinary tract infections because of multidrug-resistant and "difficult-to-treat resistance" among Gram-negative bacteria. Recent advances in pharmacotherapy and medical microbiology are modernizing how these urinary tract infections are treated. Advances in pharmacotherapy have included not only the development and approval of novel antibiotics, such as ceftazidime/avibactam, meropenem/vaborbactam, imipenem/relebactam, ceftolozane/tazobactam, cefiderocol, plazomicin, and glycylcyclines, but also the re-examination of the potential role of legacy antibiotics, including older aminoglycosides and tetracyclines. Recent advances in medical microbiology allow phenotypic and molecular mechanism of resistance testing, and thus antibiotic prescribing can be tailored to the mechanism of resistance in the infecting pathogen. Here, we provide a narrative review on the clinical and pre-clinical studies of drugs that can be used for difficult-to-treat resistant Gram-negative bacteria, with a particular focus on data relevant to the urinary tract. We also offer a pragmatic framework for antibiotic selection when encountering urinary tract infections due to difficult-to-treat resistant Gram-negative bacteria based on the organism and its mechanism of resistance.

Evaluation of the Whole Proteome of Achromobacter xylosoxidans to Identify Vaccine Targets for mRNA and Peptides-Based Vaccine Designing Against the Emerging Respiratory and Lung Cancer-Causing Bacteria

Achromobacter xylosoxidans is a rod-shaped Gram-negative bacterium linked with causing several infections which mostly includes hematological malignancies. It has been recently reported to be associated with the development and progression of lung cancer and is an emerging respiratory disease-causing bacterium. The treatment of individuals infected with A. xylosoxidans bacteremia is difficult due to the fact that this pathogen has both intrinsic and acquired resistance mechanisms, typically resulting in a phenotype of multidrug resistance (MDR). Efforts are needed to design effective therapeutic strategies to curtail the emergence of this bacterium. Computational vaccine designing has proven its effectiveness, specificity, safety, and stability compared to conventional approaches of vaccine development. Therefore, the whole proteome of A. xylosoxidans was screened for the characterization of potential vaccine targets through subtractive proteomics pipeline for therapeutics design. Annotation of the whole proteome confirmed the three immunogenic vaccine targets, such as (E3HHR6), (E3HH04), and (E3HWA2), which were used to map the putative immune epitopes. The shortlisted epitopes, specific against Cytotoxic T Lymphocytes, Helper T-cell Lymphocytes, and linear B-Cell, were used to design the mRNA and multi-epitopes vaccine (MEVC). Initial validations confirmed the antigenic and non-allergenic properties of these constructs, followed by docking with the immune receptor, TLR-5, which resulted in robust interactions. The interaction pattern that followed in the docking complex included formation of 5 hydrogen bonds, 2 salt bridges, and 165 non-bonded contacts. This stronger binding affinity was also assessed through using the mmGBSA approach, showing a total of free binding energy of -34.64 kcal/mol. Further validations based on in silico cloning revealed a CAI score of 0.98 and an optimal percentage of GC contents (54.4%) indicated a putatively higher expression of the vaccine construct in Escherichia coli. Moreover, immune simulation revealed strong antibodies production upon the injection of the designed MEVC that resulted in the highest peaks of IgM+ IgG production (>3,500) between 10 and 15 days. In conclusion the current study provide basis for vaccine designing against the emerging A. xylosoxidans, which demands further experimental studies for in vitro and in vivo validations.

Antimicrobial Treatment Strategies for Stenotrophomonas maltophilia: A Focus on Novel Therapies

Stenotrophomonas maltophilia is an urgent global threat due to its increasing incidence and intrinsic antibiotic resistance. Antibiotic development has focused on carbapenem-resistant Enterobacteriaceae, Pseudomonas, and Acinetobacter, with approved antibiotics in recent years having limited activity for Stenotrophomonas. Accordingly, novel treatment strategies for Stenotrophomonas are desperately needed. We conducted a systemic literature review and offer recommendations based on current evidence for a treatment strategy of Stenotrophomonas infection.

Advances in the Microbiology of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Achromobacter Infections and Treatment Options

Achromobacter is a genus of nonfermenting Gram-negative bacteria under order Burkholderiales Although primarily isolated from respiratory tract of people with cystic fibrosis, Achromobacter spp. can cause a broad range of infections in hosts with other underlying conditions. Their rare occurrence and ever-changing taxonomy hinder defining their clinical features, risk factors for acquisition and adverse outcomes, and optimal treatment. Achromobacter spp. are intrinsically resistant to several antibiotics (e.g., most cephalosporins, aztreonam, and aminoglycosides), and are increasingly acquiring resistance to carbapenems. Carbapenem resistance is mainly caused by multidrug efflux pumps and metallo-β-lactamases, which are not expected to be overcome by new β-lactamase inhibitors. Among the other new antibiotics, cefiderocol, and eravacycline were used as salvage therapy for a limited number of patients with Achromobacter infections. In this article, we aim to give an overview of the antimicrobial resistance in Achromobacter species, highlighting the possible place of new antibiotics in their treatment.

Comparative in vitro activities of meropenem in combination with colistin, levofloxacin, or chloramphenicol against Achromobacter xylosoxidans strains isolated from patients with cystic fibrosis

OBJECTIVES

Achromobacter xylosoxidans is an emerging pathogen in cystic fibrosis (CF). Relatively little is known about its clinical impact and optimal management. In the present study, the in vitro bactericidal activities of meropenem, either alone or in combination with colistin, levofloxacin, or chloramphenicol, were assessed using A. xylosoxidans strains isolated from CF patients. The synergistic interactions of these combinations were also investigated.

METHODS

Minimal inhibitory concentrations (MICs) were determined by microbroth dilution. Bactericidal and synergistic effects of the tested antibiotic combinations were assessed by using the time-kill curve technique.

RESULTS

Based on the time-kill curves, we found that meropenem-colistin combinations have bactericidal and synergistic activities for 24 h against A. xylosoxidans strains, both at 1 × MIC and 4 × MIC. Although synergistic interactions were seen with meropenem-levofloxacin combinations, no bactericidal interactions were observed. Additionally, the meropenem-chloramphenicol combinations were found to be neither bactericidal nor synergistic. No antagonism was observed with any combination tested.

CONCLUSIONS

This study's findings could have important implications for empirical or combination antimicrobial therapy with tested antibiotics.