Abstract
•
ZnO-NPs showed strong antagonism against
E. coli
causing avian colibacillosis disease.
•
The 90 mg/ml of ZnO-NPs was more effective.
•
A combination of ZnO-NPs and
Pseudomonas
sp
.
show higher antagonism.
•
Docking analysis exhibited that ZnO binds with PBP 6 protein receptor like other ligands.
Avian colibacillosis caused by the zoonotic pathogen
Escherichia coli
is a common bacterial infection that causes major losses in the poultry sector. Extracts of different medicinal plants and antibiotics have been used against poultry bacterial pathogens. However, overuse of antibiotics and extracts against pathogenic strains leads to the proliferation of multi-drug resistant bacteria
.
Due to their environmentally friendly nature, nanotechnology and beneficial bacterial strains can be used as effective strategies against poultry infections. Green synthesis of zinc oxide nanoparticles (ZnO-NPs) from
Eucalyptus globulus
leaves was carried out in this study. Their characterization was done by UV–vis spectroscopy, X-ray diffraction (XRD), and Fourier transmission infrared spectroscopy (FT-IR) which confirmed their synthesis, structure, and size.
In vitro,
antimicrobial activities of plant leaf extract, ZnO-NPs, and plant growth-promoting rhizobacteria (PGPR) were checked against
E. coli
using well diffusion as well as disc diffusion method. Results proved that the antimicrobial activity of ZnO-NPs and PGPR strains was more enhanced when compared to eucalyptus leaf extract at 36 h. The maximum relative inhibition shown by ZnO-NPs, PGPR strains and eucalyptus leaf extracts was 88%, 67% and 58%, respectively. The effectiveness of ZnO-NPs was also increased with an increase in particle dose and treatment time. The 90 mg/ml of ZnO-NPs was more effective
.
PGPR strains from all over the tested strains,
Pseudomonas
sp
.
(HY8N) exhibited a strong antagonism against the
E. coli
strain as compared to other PGPR strains used in this study. However, combined application of PGPR (
Pseudomonas
sp
.
(HY8N)) and ZnO-NPs augment antagonistic effects and showed maximum 69% antagonism. The study intends to investigate the binding affinity of ZnO-NPs with the suitable receptor of the bacterial pathogen by
in silico
methods. The binding site conformations showed that the ligand ZnO binds with conserved binding site of penicillin-binding protein 6 (PBP 6) receptor. According to the interactions, ZnO-NPs form the same interaction pattern with respect to other reported ligands, hence it can play a significant role in the inhibition of PBP 6. This research also found that combining ZnO-NPs with
Pseudomonas
sp. (HY8N) was a novel and effective technique for treating pathogenic bacteria, including multidrug-resistant bacteria.