Risk factors and the resistance mechanisms involved in Pseudomonas aeruginosa mutation in critically ill patients

Stability Studies of Antipseudomonal Beta Lactam Agents for Outpatient Therapy

Outpatient parenteral antimicrobial therapy (OPAT) is a useful treatment strategy against Pseudomonas aeruginosa and other multidrug-resistant bacteria. However, it is hindered by the lack of stability data for the administration of antibiotics under OPAT conditions. Our objective was to investigate the stability of nine antipseudomonal and broad-spectrum beta lactam antibiotics (aztreonam, cefepime, cefiderocol, ceftazidime, ceftazidime/avibactam, ceftolozane/tazobactam, meropenem, meropenem/vaborbactam, and piperacillin/tazobactam) to allow the spread of OPAT programs. All the antibiotics were diluted in 500 mL 0.9% sodium chloride and stored at 4, 25, 32, and 37 °C for 72 h in two different devices (infusion bags and elastomeric pumps). The solutions were considered stable if the color, clearness, and pH remained unchanged and if the percentage of intact drug was ≥90%. All the antimicrobials remained stable 72 h under refrigerated conditions and at least 30 h at 25 °C. At 32 °C, all the antibiotics except for meropenem and meropenem/vaborbactam remained stable for 24 h or more. At 37 °C, only aztreonam, piperacillin/tazobactam, cefepime, cefiderocol, and ceftolozane/tazobactam were stable for at least 24 h. The stability results were the same in the two devices tested. All the antibiotics studied are actual alternatives for the treatment of antipseudomonal or multidrug-resistant infections in OPAT programs, although the temperature of the devices is crucial to ensure antibiotic stability.

Survival Comes at a Cost: A Coevolution of Phage and Its Host Leads to Phage Resistance and Antibiotic Sensitivity of Pseudomonas aeruginosa Multidrug Resistant Strains

The increasing ineffectiveness of traditional antibiotics and the rise of multidrug resistant (MDR) bacteria have necessitated the revival of bacteriophage (phage) therapy. However, bacteria might also evolve resistance against phages. Phages and their bacterial hosts coexist in nature, resulting in a continuous coevolutionary competition for survival. We have isolated several clinical strains of Pseudomonas aeruginosa and phages that infect them. Among these, the PIAS (Phage Induced Antibiotic Sensitivity) phage belonging to the Myoviridae family can induce multistep genomic deletion in drug-resistant clinical strains of P. aeruginosa, producing a compromised drug efflux system in the bacterial host. We identified two types of mutant lines in the process: green mutants with SNPs (single nucleotide polymorphisms) and smaller deletions and brown mutants with large (∼250 kbp) genomic deletion. We demonstrated that PIAS used the MexXY-OprM system to initiate the infection. P. aeruginosa clogged PIAS phage infection by either modifying or deleting these receptors. The green mutant gaining phage resistance by SNPs could be overcome by evolved PIASs (E-PIASs) with a mutation in its tail-fiber protein. Characterization of the mutant phages will provide a deeper understanding of phage-host interaction. The coevolutionary process continued with large deletions in the same regions of the bacterial genomes to block the (E-)PIAS infection. These mutants gained phage resistance via either complete loss or substantial modifications of the phage receptor, MexXY-OprM, negating its essential role in antibiotic resistance. In vitro and in vivo studies indicated that combined use of PIAS and antibiotics could effectively inhibit P. aeruginosa growth. The phage can either eradicate bacteria or induce antibiotic sensitivity in MDR-resistant clinical strains. We have explored the potential use of combination therapy as an alternative approach against MDR P. aeruginosa infection.

Multidrug-Resistant and Extensively Drug-Resistant Enterobacteriaceae: Prevalence, Treatments, and Outcomes - A Retrospective Cohort Study

Background

Drug-resistant gram-negative bacteria (GNB) are a global public health threat, especially in intensive care units (ICU). This study explored the prevalence of drug-resistant Enterobacteriaceae infections in an ICU in Saudi Arabia. The appropriateness of the antibiotic therapies used and their ability to improve the clinical outcomes were also assessed.

Methods

A retrospective study was conducted from 2015 to 2018 in the different ICUs of a tertiary-care hospital in Saudi Arabia. Positive cultures for multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) Enterobacteriaceae, including Klebsiella pneumoniae, Escherichia coli, and Enterobacter sp., were included. The primary outcomes involved microbiological cure and 30 days in-hospital mortality rate, while the secondary outcome included the length of hospital stay (LOS). Regression models were used to assess the relationship between appropriateness of the antibiotic therapy and clinical outcomes.

Results

Of the 227 Enterobacteriaceae cultures included in this study, 60% were either MDR (n= 130) or XDR (n= 8) infections; no PDR Enterobacteriaceae cultures were identified. Majority of the patients were female (54%), and the average age was 60.1 ± 17.7 years. MDR/XDR cultures primarily comprised E. coli (51.4%), followed by K. pneumoniae (33%) and Enterobacter sp. (16%). Most commonly used antibiotics were piperacillin/tazobactam (53%), carbapenems (47%), and cephalosporins (21.3%). Antibiotic therapy was considered appropriate in only 85 of 138 (61.59%) patients. Microbiological cure rate was achieved in 40% of the cases, and in-hospital death rate was 84%. The average LOS was 27 days. Appropriateness of the antibiotic therapy prescribed could not predict any of the study outcomes.

Conclusion

The study revealed a high prevalence of drug-resistant Enterobacteriaceae infections, which were associated with a high mortality rate. Therefore, it is essential to assess the effectiveness of antimicrobial stewardship program and infection prevention and control practices, particularly in critically ill patients.