It will not become a grave menace to the poultry industry and human health. Several studies have tested using live E. coli as vaccines against colibacillosis (22, 23, 25). In almost all selleck screening library cases, live bacteria were delivered by spray, allowing stimulation of eye-, conjunctiva-, and bronchus-associated

lymphoid tissue. Use of fine sprays, which penetrate deep into the lower respiratory system, lungs, and air sacs, may result in a stronger immune response than coarse sprays, which do not penetrate as deeply into the respiratory system (43). In the current study, we observed that AESN1331 administered via fine spray colonized the avian respiratory tract, but disappeared within a few days. Administration of AESN1331 by fine spray, coarse spray, Selleck Navitoclax or eye drop induced equivalent protection against challenge with an APEC wild strain. These results show that the AESN1331 strain is attenuated and safe, yet immunogenic and extremely effective against avian colibacillosis. We also demonstrated that AESN1331 partially protected chickens that had been immunized as 19-day-old embryonated eggs. Our mutant provided protection without impairing hatching or chick survival, although a small number of the challenge strain was recovered from some in ovo-immunized chickens that had survived exposure to challenge. Given that the poultry industry is moving towards greater use of in ovo vaccination, administration

of the mutant via this route may be of value. We did not detect the

major virulence-associated genes in AESN1331, as is true for J29. AESN1331 remained susceptible to all tested antibiotics except for nalidixic acid. These properties are appropriate for a live vaccine candidate, since field usage of such a mutant would not spread virulence-associated or drug resistance-encoding genes to wild APEC. Emergence of drug resistance (4, 5, 8–12) and costs associated with administration of drugs have led to increased medical costs worldwide. Ozawa et al. (11) reported APEC isolates in Japan have moderate- or high-level check details resistance to many antimicrobials, including fluoroquinolones. Antimicrobial susceptibility is critical for the adequate treatment of colibacillosis. AESN1331 is resistant only to nalidixic acid. This resistance resulted from the construction of AESN1331; it was introduced by the amino acid change at position 87 (Asp to Gly) on the gyrA gene of chromosomal DNA. Unlike quinolone resistance caused by qnr plasmid, this resistance will not disseminate to APEC wild strains and other Enterobacteriaceae. Resistance to nalidixic acid, a drug that is not commonly used to treat colibacillosis in the poultry industry, is not a serious obstacle to the treatment, elimination and prevention of colibacillosis. Administration of the AESN1331 strain via various routes evoked an effective immune response that protected against a virulent, wild-type E. coli O78 APEC isolate.