Samples of hatchery air (hatcher and processing room), Marek's disease vaccine suspensions and injection needles collected during chick processing, revealed variable levels (< 500 to 10(6) colony forming units (cfu)/m(3) air, < 10 to 10(6) cfu/ml vaccine suspension, and 9500 to 61000 cfu/needle) of Enterococcus faecalis contamination. This observation suggests a possible infection route in 1-day-old chickens through intramuscular vaccination of Marek's disease vaccine contaminated with arthropathic and amyloidogenic E. faecalis, which could lead to amyloid arthropathy. Pulsed-field gel electrophoresis (PFGE) DNA restriction endonuclease fragment analysis of E. faecalis strains obtained from two hatcheries revealed a predominant PFGE pattern in one hatchery, while one isolate with an almost identical PFGE pattern to an amyloid arthropathy inducing isolate was found.