Varsha Unni

Enteroaggregative Escherichia coli (EAEC) is a neglected, though emerging, bacterial pathogen associated with gastrointestinal illnesses worldwide. Recently, a surprising surge in the multi-drug resistance pattern among EAEC strains has been observed on a global scale; hence, emphasis has been given to adjuvant therapies to combat this nagging public health threat. This study assessed the antibacterial efficacy of ZnO NPs synthesised using the aqueous extract of Piper longum catkin against multi-drug resistant (MDR) strains of EAEC. Initially, the synthesis of ZnO NPs was confirmed via UV-Vis spectroscopy and Fourier transform infra-red spectroscopy (FTIR) analysis. The thermal stability of ZnO NPs was evidenced by TGA/DTA, while PXRD analysis revealed a hexagonal wurtzite crystalline structure, which was then confirmed by electron microscopy. The minimum inhibitory concentration and minimum bactericidal concentration of the bio-fabricated ZnO NPs, determined via microbroth dilution technique against MDR-EAEC (n = 3) strains, was revealed to be 125 μg/mL and 250 μg/mL, respectively. In addition, the ZnO NPs were found to be variably stable and safe. The green synthesised ZnO NPs exhibited a concentration-dependent antioxidant activity and inhibited the biofilm forming ability of the tested MDR-EAEC strains. Overall, this study revealed an eco-friendly one-pot synthesis of ZnO NPs, which could be used as a fruitful antimicrobial substitute against MDR-EAEC strains.

Enteroaggregative Escherichia coli (EAEC) has been widely recognized as one of the leading causes of infantile diarrhoea and nutrient malabsorption in developing as well as developed countries. In recent years, drug resistance, particularly multi-drug resistance (MDR), among the EAEC strains has been widely documented and could result in a therapeutic stumble. Antimicrobial alternatives are widely employed to curb this emerging public health crisis. In the present study, a facile one-pot synthesis of silver/zinc oxide nanocomposites (Ag/ZnO NCs) using a methanolic extract of stem and leaves of Curcuma longa was performed. The synthesis of Ag/ZnO NCs was confirmed using UV-vis spectroscopy and Fourier transform infrared spectroscopy, while the thermal stability was ascertained by thermogravimetric analysis with differential thermogravimetric analyses, and crystallinity was determined using powder X-ray diffraction. The shape and size of the green synthesized Ag/ZnO NCs, determined using field-emission–scanning-electron microscopy and transmission electron microscopy, revealed an irregular polycrystalline morphology with a size of 31.34 ± 1.27 nm. Later, the antibacterial potential of the green synthesized Ag/ZnO NCs evaluated against MDR- EAEC strains revealed a minimum inhibitory concentration of 31.25 μg/mL and a minimum bactericidal concentration ranging from 62.50 to 125 μg/mL. Moreover, the green synthesized Ag/ZnO NCs inhibited the biofilm-forming ability of the tested strains of MDR-EAEC. Furthermore, concentration-dependent antioxidant activity was exhibited by the green synthesized Ag/ZnO NCs, as evidenced by the ABTS assay and reducing power assay. Overall, this study demonstrated the antibacterial potential of Ag/ZnO NCs synthesized using C. longa extracts with antifouling as well as antioxidant properties, which could be used as an alternative therapeutic candidate.

The global emergence of antimicrobial resistance (AMR) needs no emphasis. In this study, the in vitro stability, safety, and antimicrobial efficacy of nanosilver-entrapped cinnamaldehyde (AgC) against multi-drug-resistant (MDR) strains of enteroaggregative Escherichia coli (EAEC) were investigated. Further, the in vivo antibacterial efficacy of AgC against MDR-EAEC was also assessed in Galleria mellonella larval model. In brief, UV-Vis and Fourier transform infrared (FTIR) spectroscopy confirmed effective entrapment of cinnamaldehyde with nanosilver, and the loading efficiency was estimated to be 29.50 ± 0.56%. The AgC was of crystalline form as determined by the X-ray diffractogram with a mono-dispersed spherical morphology of 9.243 ± 1.83 nm in electron microscopy. AgC exhibited a minimum inhibitory concentration (MIC) of 0.008–0.016 mg/mL and a minimum bactericidal concentration (MBC) of 0.008–0.032 mg/mL against MDR- EAEC strains. Furthermore, AgC was stable (high-end temperatures, proteases, cationic salts, pH, and host sera) and tested safe for sheep erythrocytes as well as secondary cell lines (RAW 264.7 and HEp-2) with no negative effects on the commensal gut lactobacilli. in vitro, time-kill assays revealed that MBC levels of AgC could eliminate MDR-EAEC infection in 120 min. In G. mellonella larvae, AgC (MBC values) increased survival, decreased MDR-EAEC counts (p < 0.001), had an enhanced immunomodulatory effect, and was tested safe to the host. These findings infer that entrapment enhanced the efficacy of cinnamaldehyde and AgNPs, overcoming their limitations when used individually, indicating AgC as a promising alternative antimicrobial candidate. However, further investigation in appropriate animal models is required to declare its application against MDR pathogens.