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Abstract
Escherichia coli is a Gram-negative facultative anaerobe bacillus that colonizes the intestine of humans and warm-blooded animals rarely causing disease. However, some strains have become pathogenic to humans and animals via acquisition of virulence factors that make them able to colonize niches outside of the host intestines and cause extra-intestinal infections. These strains are defined as ExPEC and they include, among others, the subjects of this study: avian pathogenic E. coli (APEC), and neonatal meningitis E. coli (NMEC). APEC cause extra-intestinal infections in birds known as colibacillosis, that is one of the leading causes of economic losses worldwide in poultry and turkey production industry. NMEC is the second most common cause of neonatal sepsis and meningitis leading to mortality and morbidity rates up to 30%. To cause disease, ExPEC strains must produce virulence factors required for adherence and invasion, iron uptake, resistance to host serum and may also contain genes encoding toxins and invasins. Although many virulence factors associated with the pathogenicity of APEC and NMEC are described, their pathogenesis is not completely understood, and the role of protein secretion in their virulence remains to be defined. Type 6 Secretion System (T6SS) has gained attention as a factor involved in pathogenicity and fitness traits of different bacterial species. In APEC and NMEC, current information on the role of T6SS in virulence is limited and warrants further investigation. The aim of this study was to perform an epidemiological analysis and characterization of APEC strains isolated from turkeys as well as the investigation of the role of T6SS genes in the virulence of APEC and NMEC strains. The epidemiological analysis of E. coli isolates from turkeys highlights the role of APEC in turkey cellulitis. In relation to the T6SS, we found that components of the system are involved in different virulence traits employed by APEC and NMEC to cause disease. The main contribution of this work was to be the first one to extensively characterize a large collection of E. coli originated from turkeys and to demonstrate that the T6SS plays an important role in the virulence of APECO18 and NMEC 15.