Background: Due to increasing antibiotic resistance, it is important to identify the antimicrobial activity of herbs. This experimental study aimed to evaluate the antimicrobial activity of herbal extracts of common hop (Humulus lupulus) and oak (Quercus castaneifolia) against several microbial standard strains.

Materials and Methods: The alcoholic and aqueous extracts of H. lupulus and Q. castaneifolia were extracted. The inhibitory effects of herbal extracts were evaluated against the microbial standard strains (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans) by both agar diffusion and macrobroth dilution methods. In the agar diffusion method, concentrations of extracts were 125, 250, 500 and 1000 mg/ml. In order to determine the MIC, serial dilutions were prepared with a range from 1 to 512 mg/ml.

Results: Alcoholic extract of both hop and oak showed higher inhibitory effect against microbial standard strains, compared to the aqueous extract. Staphylococcus aureus ATCC 29213 and Candida albicans ATCC 76615 showed higher susceptibility to both alcoholic and aqueous extracts compared to Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. Statistically significant difference was found on the MIC of alcoholic and aqueous extracts (p<0.05).

Conclusion: This study revealed the considerable inhibitory effects of herbal hop and oak extracts on the various microorganisms, including bacteria and fungi. Although more research is needed in this field, they can be used as new antimicrobials in medicine.

Abstract

Background: Prevalence extension of antibiotic resistant bacteria has raised concerns about control of infections especially nosocomial infections. Many attempts have been done to replace antibiotics or limit their use. The use of antimicrobial agents produced by bacteria as antibiotic replacement has been promising in recent years. The goal of this study was to isolate Bacillus strains and evaluate their antimicrobial activity against some standard pathogens and clinical antibiotic resistant strains.

Materials and Methods: In the present study, Bacillus strains were isolated from various resources and identified by 16S rDNA PCR method. Then, the phylogenetic tree of the isolates was constructed and antimicrobial activity of the isolates was investigated against some standard pathogens and clinical antibiotic resistant strains using spotting and well diffusion methods.

Results: Eight Bacillus strains were isolated from 15 different samples. Based on the molecular identification, the isolates were identified as B.pumilus, B.coagulans, B.licheniformis, B.endophitycus and B.amiloliquefaciens. The results showed that isolates have antimicrobial activity against meticilin-resistant Staphylococcus aureus, vancomycin resistant enterococci, Klebsiella, Acinetobacter, Salmonella, Shigella, Listeria, Streptococcus and Escherichia coli.

Conclusion: In this study, isolated Bacillus strains produced antimicrobial agents against pathogens and antibiotic resistant strains and inhibited their growth.