In Vitro Antimicrobial Activity of Clove Oil against Gram Negative Bacteria Isolated from Chickens

Abstract

The use of antibiotics as growth promotors to enhance animal production is banned in many countries around the world due to antimicrobial resistance. There is a need therefore, for new alternatives to anti- biotics in medicine and veterinary medicine practices. The antibacterial activity of clove oil and some antibiotics were tested in vitro against three isolates of E. coli {1 avian pathogenic (E. coli 6.2) and 2 non-pathogenic (E. coli 6.1 and E. coli X)}, Salmonella enter- itidis and Salmonella spp., by disk diffusion and minimum inhibitory concentration (MIC) methods. All bacteria tested showed intermediate susceptibility to clove oil using disk diffusion method except the non-pathogenic E.coli 6.1. The inhibition zones measured were 0mm, 12mm, 13mm, 15mm and 15mm for E. coli 6.1, E. coli 6.2, E. coli X, Salmonella enteritidis and Salmonella spp., respectively. E. coli 6.1 was resistant to Ampicillin, and Lincomycin with multi antibiotic resistance (MAR) index of 0.2. E. coli 6.2 was resistant to Ampicillin, Doxycyclin and Lincomycin with MAR index of 0.3. E. coli X was resistant to Am- picillin and Colistin with MAR index of 0.2. Salmonella enteritidis was resistant to Amoxycillin/Clavulinic acid, Ampicillin and Lincomycin with MAR index of 0.3. Salmonella spp was susceptible only to Neomycin but was resistant to 9 out of 10 antibiotics with very high MAR index of 0.9. The MICs of clove oil were 6.25mg/ml for the avian pathogenic E. coli and 3.12mg/ml for non-pathogenic E. coli and Salmonella spp. and 12.5mg/ml for Salmonella enteritidis. It is concluded that clove oil has promising antibacterial activ- ity and more studies are needed to investigate its in vivo activity as alternative to antibiotics in poultry production. However, the mechanism of resistance of non-pathogenic E. coli 6.1 needs more investigation.