Role of acid responsive genes in the susceptibility of Escherichia coli to ciclopirox

EvgS/EvgA, the unorthodox two-component system regulating bacterial multiple resistance

IMPORTANCE

EvgS/EvgA, one of the five unorthodox two-component systems in Escherichia coli, plays an essential role in adjusting bacterial behaviors to adapt to the changing environment. Multiple resistance regulated by EvgS/EvgA endows bacteria to survive in adverse conditions such as acidic pH, multidrug, and heat. In this minireview, we summarize the specific structures and regulation mechanisms of EvgS/EvgA and its multiple resistance. By discussing several unresolved issues and proposing our speculations, this review will be helpful and enlightening for future directions about EvgS/EvgA.

Plastic wastes and surface antibiotic resistance genes pollution in mangrove environments

Mangroves are located at the intersection of land and sea and are also heavily affected by plastic wastes. Biofilms of plastic wastes in mangroves are reservoirs for antibiotic resistance genes (ARGs). In this study, plastic wastes and ARG pollution were investigated from three typical mangrove areas in Zhanjiang, South China. Transparent was the dominant colors of plastic wastes in three mangroves. Fragment and film shape accounted for 57.73-88.23% of plastic waste samples in mangroves. In addition, 39.50% of plastic wastes in protected area mangroves are PS. The metagenomic results shows that the 175 ARGs were found on plastic wastes of the three mangroves, the abundance accounting for 91.11% of the total ARGs. The abundance of Vibrio accounted for 2.31% of the total bacteria genera in aquaculture pond area mangrove. Correlation analysis shows that a microbe can carry multiple ARGs that may improve resistance to antibiotics. Microbes are the potential hosts of most ARGs, suggesting that ARGs can be transmitted by microbes. Because the mangroves are closely related to human activities and the high abundance of ARGs on plastic increases the ecological risks, people should improve plastic waste management and prevent the spread of ARGs by reducing plastic pollution.

Repurposing of Ciclopirox to Overcome the Limitations of Zidovudine (Azidothymidine) against Multidrug-Resistant Gram-Negative Bacteria

Multidrug-resistant (MDR) Gram-negative bacteria are the top-priority pathogens to be eradicated. Drug repurposing (e.g., the use of non-antibiotics to treat bacterial infections) may be helpful to overcome the limitations of current antibiotics. Zidovudine (azidothymidine, AZT), a licensed oral antiviral agent, is a leading repurposed drug against MDR Gram-negative bacterial infections. However, the rapid emergence of bacterial resistance due to long-term exposure, overuse, or misuse limits its application, making it necessary to develop new alternatives. In this study, we investigated the efficacy of ciclopirox (CPX) as an alternative to AZT. The minimum inhibitory concentrations of AZT and CPX against MDR Gram-negative bacteria were determined; CPX appeared more active against β-lactamase-producing Escherichia coli, whereas AZT displayed no selectivity for any antibiotic-resistant strain. Motility assays revealed that β-lactamase-producing Escherichia coli strains were less motile in nature and more strongly affected by CPX than a parental strain. Resistance against CPX was not observed in E. coli even after 25 days of growth, whereas AZT resistance was observed in less than 2 days. Moreover, CPX effectively killed AZT-resistant strains with different resistance mechanisms. Our findings indicate that CPX may be utilized as an alternative or supplement to AZT-based medications to treat opportunistic Gram-negative bacterial infections.

Sugar and iron: Toward understanding the antibacterial effect of ciclopirox in Escherichia coli

New antibiotics are needed against antibiotic-resistant gram-negative bacteria. The repurposed antifungal drug, ciclopirox, equally blocks antibiotic-susceptible or multidrug-resistant Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae clinical isolates, indicating that it is not affected by existing resistance mechanisms. Toward understanding how ciclopirox blocks growth, we screened E. coli mutant strains and found that disruption of genes encoding products involved in galactose salvage, enterobacterial common antigen synthesis, and transport of the iron binding siderophore, enterobactin, lowered the minimum inhibitory concentration of ciclopirox needed to block growth of the mutant compared to the isogenic parent strain. We found that ciclopirox induced enterobactin production and that this effect is strongly affected by the deletion of the galactose salvage genes encoding UDP-galactose 4-epimerase, galE, or galactose-1-phosphate uridylyltransferase, galT. As disruption of ECA synthesis activates the regulation of capsular synthesis (Rcs) phosphorelay, which inhibits bacterial swarming and promotes biofilm development, we test whether ciclopirox prevents activation of the Rcs pathway. Sub-inhibitory concentrations of ciclopirox increased swarming of the E. coli laboratory K12 strain BW25113 but had widely varying effects on swarming or surface motility of clinical isolate E. coli, A. baumannii, and K. pneumoniae. There was no effect of ciclopirox on biofilm production, suggesting it does not target Rcs. Altogether, our data suggest ciclopirox-mediated alteration of lipopolysaccharides stimulates enterobactin production and affects bacterial swarming.