Origin and Impact of Nitric Oxide in Pseudomonas aeruginosa Biofilms

Anesthetic agents, neurodevelopmental risk and the connection to bacterial infections

This short communication identifies a significant flaw in research investigating the neurodevelopmental consequences of general anesthesia exposure. We have identified that chronic environmental exposure to pervasive air pollutants that are also widely used as anesthetic agents, specifically nitrous oxide (N₂O), may contribute to the rising prevalence of neurodevelopmental disorders. Consistent with the emerging link between microbes and psychiatric illness risk, this epidemiological analysis extends our prior conclusions by proposing that such exposures may alter host immunity so as to enhance vulnerability to certain pathogenic microbes that have been implicated in neurodevelopmental disorders, including Pseudomonas aeruginosa and Clostridium difficile.

Ciprofloxacin-nitroxide hybrids with potential for biofilm control

As bacterial biofilms display extreme tolerance to conventional antibiotic treatments, it has become imperative to develop new antibacterial strategies with alternative mechanisms of action. Herein, we report the synthesis of a series of ciprofloxacin-nitroxide conjugates and their corresponding methoxyamine derivatives in high yield. This was achieved by linking various nitroxides or methoxyamines to the secondary amine of the piperazine ring of ciprofloxacin using amide bond coupling. Biological evaluation of the prepared compounds on preformed P. aeruginosa biofilms in flow cells revealed substantial dispersal with ciprofloxacin-nitroxide hybrid 25, and virtually complete killing and removal (94%) of established biofilms in the presence of ciprofloxacin-nitroxide hybrid 27. Compounds 25-28 were shown to be non-toxic in both human embryonic kidney 293 (HEK 293) cells and human muscle rhabdomyosarcoma (RD) cells at concentrations up to 40 μM. Significantly, these hybrids demonstrate the potential of antimicrobial-nitroxide agents to overcome the resistance of biofilms to antimicrobials via stimulation of biofilm dispersal or through direct cell killing.

Haem-Based Sensors of O2: Lessons and Perspectives

Haem-based sensors have emerged during the last 15 years as being a large family of proteins that occur in all kingdoms of life. These sensors are responsible mainly for detecting binding of O₂, CO and NO and reporting the ligation status to an output domain with an enzymatic or macromolecule-binding property. A myriad of biological functions have been associated with these sensors, which are involved in vasodilation, bacterial symbiosis, chemotaxis and biofilm formation, among others. Here, we critically review several bacterial systems for O₂ sensing that are extensively studied in many respects, focusing on the lessons that are important to advance the field.

Synthesis and Evaluation of Ciprofloxacin-Nitroxide Conjugates as Anti-Biofilm Agents

As bacterial biofilms are often refractory to conventional antimicrobials, the need for alternative and/or novel strategies for the treatment of biofilm related infections has become of paramount importance. Herein, we report the synthesis of novel hybrid molecules comprised of two different hindered nitroxides linked to the piperazinyl secondary amine of ciprofloxacin via a tertiary amine linker achieved utilising reductive amination. The corresponding methoxyamine derivatives were prepared alongside their radical-containing counterparts as controls. Subsequent biological evaluation of the hybrid compounds on preformed P. aeruginosa flow cell biofilms divulged significant dispersal and eradication abilities for ciprofloxacin-nitroxide hybrid compound 10 (up to 95% eradication of mature biofilms at 40 μM). Importantly, these hybrids represent the first dual-action antimicrobial-nitroxide agents, which harness the dispersal properties of the nitroxide moiety to circumvent the well-known resistance of biofilms to treatment with antimicrobial agents.

Response to Gaseous NO2 Air Pollutant of P. fluorescens Airborne Strain MFAF76a and Clinical Strain MFN1032

Human exposure to nitrogen dioxide (NO₂), an air pollutant of increasing interest in biology, results in several toxic effects to human health and also to the air microbiota. The aim of this study was to investigate the bacterial response to gaseous NO₂. Two Pseudomonas fluorescens strains, namely the airborne strain MFAF76a and the clinical strain MFN1032 were exposed to 0.1, 5, or 45 ppm concentrations of NO₂, and their effects on bacteria were evaluated in terms of motility, biofilm formation, antibiotic resistance, as well as expression of several chosen target genes. While 0.1 and 5 ppm of NO₂did not lead to any detectable modification in the studied phenotypes of the two bacteria, several alterations were observed when the bacteria were exposed to 45 ppm of gaseous NO₂. We thus chose to focus on this high concentration. NO₂-exposed P. fluorescens strains showed reduced swimming motility, and decreased swarming in case of the strain MFN1032. Biofilm formed by NO₂-treated airborne strain MFAF76a showed increased maximum thickness compared to non-treated cells, while NO₂ had no apparent effect on the clinical MFN1032 biofilm structure. It is well known that biofilm and motility are inversely regulated by intracellular c-di-GMP level. The c-di-GMP level was however not affected in response to NO₂ treatment. Finally, NO₂-exposed P. fluorescens strains were found to be more resistant to ciprofloxacin and chloramphenicol. Accordingly, the resistance nodulation cell division (RND) MexEF-OprN efflux pump encoding genes were highly upregulated in the two P. fluorescens strains. Noticeably, similar phenotypes had been previously observed following a NO treatment. Interestingly, an hmp-homolog gene in P. fluorescens strains MFAF76a and MFN1032 encodes a NO dioxygenase that is involved in NO detoxification into nitrites. Its expression was upregulated in response to NO₂, suggesting a possible common pathway between NO and NO₂ detoxification. Taken together, our study provides evidences for the bacterial response to NO₂ toxicity.