Avian colibacillosis is the most significant infectious bacterial disease of poultry worldwide. Many antimicrobial-resistant
Escherichia coli pathogens are increased due to drug overusing in veterinary medicine and animals feed. The objective of
this study was to observe the in vitro inhibitory effect of garlic (Allium sativum) as alternative natural agent against
Escherichia coli isolates and their virulence genes expression. The antimicrobial effects of aqueous and ethanolic garlic
extracts against multidrug-resistant (MDR) E. coli isolates were studied using agar well-diffusion method as well as the
minimum inhibitory concentration (MIC) of garlic and consequently their subinhibitory concentration (SIC) (the
concentration of garlic that did not inhibit E. coli growth after 24 hr. incubation at 37ºC) were calculated by a modification
of broth macrodilution method. The E. coli virulence was assessed via mRNA expression of their genes such as increased
serum survival (iss), verotoxine (vt2e) and intimin (eaeA) before and after garlic treatment using reverse transcriptase real
time PCR. One hundred and thirteen (46.12%) of 245 isolates were identified as E. coli that were highly recorded in
intestinal samples as 64.60% followed by liver 24.77% then heart 10.6%. The most chemotherapeutic resistant 14 E. coli
isolates showed high garlic susceptibility rates mainly for aqueous extract and had nine different serotypes, the most
predominant one was O146 of 21.42%. The complete inhibition of and downregulating of eaeA and vt2e genes expression
were proved respectively in the E. coli treated isolates with garlic SIC (1%). In conclusion, the garlic supplementation
through feed can reduce infection by E. coli via decrescent their toxin production and may be the adhesion ability to the
intestinal mucosa of the host either animal or human