Pseudomonas aeruginosa is an opportunistic gram-negative human pathogen that causes a wide range of infections, including nosocomial infections. Aside from the intrinsic and acquired antimicrobial resistance against many classes of antibiotics, P. aeruginosa can produce an extracellular polymeric matrix called “biofilm” that protects bacteria from antibiotics and harmful factors. Biofilm enables P. aeruginosa to develop chronic infections. This study assessed the inhibitory action of ZnO-nanoparticles against biofilms formed by multidrug-resistant P. aeruginosa strains. A collection of 24 clinical strains of P. aeruginosa were tested for their antimicrobial resistance against different antibiotics using the disk diffusion method. The antibiofilm activity of ZnO-NPs was assessed using the microtiter plate biofilm assay. The application of ZnO-NPs dramatically modulated the resistance profile and biofilm activity of P. aeruginosa. The combination of ZnO-NPs and meropenem showed synergistic antipseudomonal activity with lower MICs. The scanning electron microscope (SEM) micrographs revealed complete inhibition of biofilms treated with the meropenem–ZnO-NPs combination. Reduced expression of biofilm regulating genes lasR, pslA, and fliC was detected, reflecting the enhanced antibiofilm effect of ZnO-NPs. In vivo application of this antimicrobial mixture completely cured P. aeruginosa-induced keratitis in rats. Our findings represent a dual enhancement of antibacterial and antibiofilm activity via the use of meropenem–ZnO-NPs combination against carbapenem-resistant P. aeruginosa infections.

Multidrug-resistant (MDR) bacteria are one of the major public health threats facing humanity. Infections with MDR strains are difficult or impossible to treat with standard antibiotics leading to severe illnesses and even deaths. The spread of MDR bacteria has necessitated the search for alternative approaches that tackle MDR pathogens. Natural plants can be utilized as alternative therapeutic agents against the rise of MDR bacteria. In this study, we aimed to assess the antimicrobial activity of pomegranate peel extracts (PPE) against MDR clinical isolates. A total of 9 clinical isolates (8 MDR and 1 non-MDR clinical isolates) were collected and examined for their susceptibility to PPE. Using the zone of inhibition assay, 4 isolates (S. aureus, three MRSA isolates, Vancomycin-resistant Enterococci (VRE), and Acinetobacter baumannii) were sensitive to PPE. In Broth assay, 4 mg/ml PPE significantly reduced the growth (S. aureus, three MRSA isolates, Vancomycin-resistant Enterococci (VRE), and Acinetobacter baumannii), while 40 mg/ml PPE either significantly reduced or completely inhibited the growth of the isolates. The minimum bactericidal concentration (MBC) of PPE against S. aureus and MRSA-88 was 10 mg/ml. This study showed the potential of PPE as an alternative compound for treating infections caused by PPE-sensitive MDR bacteria.

Aim This study is aimed at characterization of both antimicrobial and anti‐biofilm activity of R‐pyocin from clinical Pseudomonas aeruginosa against Gram‐positive pathogens including Staphylococcus aureus. Methods and Results Pyocinogenic P. aeruginosa was detected using reverse‐side method and pyocinogeny typing was confirmed using revised‐spotting method. Transmission electron microscopy (TEM) was used for morphological characterization of R‐pyocin and for detection of changes in membrane of R‐pyocin‐treated S. aureus. SDS‐PAGE analysis was used for detection of the molecular weight of R‐pyocin protein‐subunits and Poisson‐killing‐distribution assay for burst‐size calculation. Lipotechoic‐acid (LTA) adsorption‐assay was used to confirm whether LTA in Gram‐positive bacteria served as R‐pyocin receptor. Moreover, R‐pyocin production at 10‐60 °C was assessed herein. Host‐range of activity of R‐pyocin was tested against antimicrobial resistant (AMR) pathogens. The anti‐biofilm activity of R‐pyocin was detected against sensitive bacterial strains. Chemical, enzymatic, pH and thermo‐stability of R‐pyocin were evaluated. TEM micrographs revealed a typical morphology of myotailocins indicating the production of R‐pyocin designated as RPU15. TEM revealed pores‐formation in S. aureus membrane and bacteriophage‐like plaques were obvious on plates of R‐pyocin‐treated S. aureus. R‐pyocin activity was neutralized by LTA of S. aureus and Listeria monocytogenes. P. aeruginosa PU15 produced ~428 non‐inducible R‐pyocin particles. RPU15 sheath and tube protein‐subunits exhibited a molecular weight of 38 and 23 kDa respectively. RPU15 possessed activity against S. aureus, L. monocytogenes, Bacillus cereus and Candida albicans and reduced biofilm‐biomasses of tested AMR strains. Conclusion Our results showing the potential therapeutic use of R‐pyocin due to its effectiveness on tested bacterial biofilms. Significance and Impact of Study This is the first study that investigates antimicrobial and anti‐biofilm activity of R‐pyocin activity against S. aureus. R‐pyocin shows new phenomenon of bacteriophage‐like plaques. Our findings represent a future therapeutic agent targeting both Methicillin resistant and Vancomycin resistant S. aureus.