S-Pyocins as potential antimicrobial agents for eradicating pseudomonas aeruginosa biofilms

Pseudomonas aeruginosa (Pa) is a gram-negative opportunistic pathogen associated with life-threatening hospital-acquired and community-acquired infections affecting urinary tract, skin, eye, ear, and lungs. Antipseudomonal antibiotics are the most potent arsenals to treat Pa infections. However, Pa infections are still common and stubborn bacterial infections due to elevated resistance levels against most of the antibiotics used in clinics. Treating Pa infections becomes even harder especially if antibiotic resistant Pa strains form biofilms and cystic structures in human body. In such cases, drug doses for treating bacterial infections can be up to one thousand fold higher than the necessary dose for treating infections caused by planktonic bacteria. Thus, there is an obvious need for novel therapies for fighting against Pa infections and Pa biofilms. Recently, several studies performed on pyocins, proteinaceous bacterial toxins produced by Pa, to explore the potential of pyocins as novel antibiotics to treat Pa infections. Similar to other members of the bacteriocin family, pyocins mostly kill strains of the related species. There are three types of pyocins: S, R, and F pyocins. S-type pyocins are high molecular weight proteins and RF-type pyocins resemble bacteriophage tails. In this study, we applied four S-pyocins (S1, S2, S3, AP41) on Pa biofilms separately and in combination with six commonly used antibiotics (Tobramycin, Gentamicin, Colistin, Piperacillin, Ceftazidime, Ciprofloxacin) to determine the efficacy of S-pyocins in eradicating Pa biofilms and interactions between S-pyocins and antibiotics. We created Pa biofilms using Calgary Biofilm Device (CBD) to determine minimum biofilm eradication concentration (MBEC) of each antibiotics and S-pyocins separately and in combination. This study aims to explore the potential use of S-pyocins as alternative drugs for eradicating biofilms where Pa biofilms show high resistance to antibiotics. Our preliminary results suggest wild type pyocins have a slight effect on Pa biofilms but there is an antagonism between pyocin AP41 and drugs Ciprofloxacin, and Colistin which can be used for selecting against drug resistant Pa strains

Strength of selection pressure is an important parameter contributing to the complexity of antibiotic resistance evolution

Revealing the genetic changes responsible for antibiotic resistance can be critical for developing novel antibiotic therapies. However, systematic studies correlating genotype to phenotype in the context of antibiotic resistance have been missing. In order to fill in this gap, we evolved 88 isogenic Escherichia coli populations against 22 antibiotics for 3 weeks. For every drug, two populations were evolved under strong selection and two populations were evolved under mild selection. By quantifying evolved populations' resistances against all 22 drugs, we constructed two separate cross-resistance networks for strongly and mildly selected populations. Subsequently, we sequenced representative colonies isolated from evolved populations for revealing the genetic basis for novel phenotypes. Bacterial populations that evolved resistance against antibiotics under strong selection acquired high levels of cross-resistance against several antibiotics, whereas other bacterial populations evolved under milder selection acquired relatively weaker cross-resistance. In addition, we found that strongly selected strains against aminoglycosides became more susceptible to five other drug classes compared with their wild-type ancestor as a result of a point mutation on TrkH, an ion transporter protein. Our findings suggest that selection strength is an important parameter contributing to the complexity of antibiotic resistance problem and use of high doses of antibiotics to clear infections has the potential to promote increase of cross-resistance in clinics