Abstract
Avian pathogenic Escherichia coli (APEC) strains cause systemic and localized infections in poultry, jointly termed colibacillosis. Avian colibacillosis is responsible for significant economic losses to the poultry industry due to disease treatment, decrease in growth rate and egg production, and mortality. APEC are also considered a potential zoonotic risk for humans. Fully elucidating the virulence and zoonotic potential of APEC is key for designing successful strategies against their infections and their transmission. Herein, we investigated the prevalence of a newly discovered E. coli common pilus (ECP) for the subunit protein of the ECP pilus (ecpA) and ECP expression amongst APEC strains as well as the role of ECP in virulence. A PCR-based ecpA survey of a collection of 167 APEC strains has shown that 76% (127/167) were ecpA+. An immunofluorescence assay using anti-EcpA antibodies, revealed that among the ecpA+ strains, 37.8% (48/127) expressed ECP when grown in DMEM +0.5% Mannose in contact with HeLa cells at 37°C and/or in biofilm at 28°C; 35.4% (17/48) expressed ECP in both conditions and 64.6% (31/48) expressed ECP in biofilm only. We determined that the ecp operon in the APEC strain χ7122 (ecpA+, ECP-) was not truncated; the failure to detect ECP in some strains possessing non-truncated ecp genes might be attributed to differential regulatory mechanisms between strains that respond to specific environmental signals. To evaluate the role of ECP in the virulence of APEC, we generated ecpA and/or ecpD-deficient mutants from the strain χ7503 (ecpA+, ECP+). Deletion of ecpA and/or ecpD abolished ECP synthesis and expression, and reduced biofilm formation and motility in vitro and virulence in vivo. All together our data show that ecpA is highly prevalent among APEC isolates and its expression could be differentially regulated in these strains, and that ECP plays a role in the virulence of APEC.
Highlights
Avian Pathogenic E. coli (APEC), a subgroup of Extraintestinal Pathogenic E. coli (ExPEC), is the etiologic agent of colibacillosis in birds
Results and Discussion ecpA is Highly Prevalent among APEC Isolates E. coli common pilus (ECP), first detected in neonatal meningitis E. coli (NMEC) isolates [4], was found to be common among pathogenic and non-pathogenic E. coli [5]
Recent studies have determined that ecpA, the gene of the major pilin of ECP, was prevalent among the majority of human pathogenic E. coli; it was shown to be highly associated with atypical enteropathogenic E. coli (86%) [10], enteroaggregative E. coli (EAEC) (96%) [7], and enterotoxigenic E. coli (ETEC) (80%) [11] isolates
Summary
Avian Pathogenic E. coli (APEC), a subgroup of Extraintestinal Pathogenic E. coli (ExPEC), is the etiologic agent of colibacillosis in birds. Multiple virulence factors are associated with APEC and are determined to be involved in different steps of their infection and/ or fitness, including colonization (Type 1, P, AC/1, Stg fimbriae, type IV pili, curli, Tsh), invasion (IbeA, Tia), iron acquisition (aerobactin, salmochelin, SitABCD, a heme utilization/transport protein ChuA), serum-complement resistance (TraT, Iss, LPS, K1 capsule), antiphagocytic activity (O and K antigens, SitABCD), and virulence genes regulation (BarA-UvrY, Pts). At different steps of infection, ExPEC, including APEC could use alternative virulence factors. APEC share important virulence traits with human ExPEC, including uropathogenic E. coli (UPEC) and neonatal meningitis E. coli (NMEC), which render them a possible zoonotic risk or a reservoir of virulence genes for human strains [3]
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