Development of a rapid and inexpensive assay for the nonspecific detectionof antimicrobial residues in chicken egg yolks and neonatal yolk sacs

Competitive exclusion of intestinal pathogens by administration of benefici al and defined cultures of normal intestinal microflora is a safe and effec tive means of reducing the incidence and severity of chick infections with Salmonella and other intestinal pathogens. It is important that competitive exclusion cultures not carry genetic material (e.g., plasmids), which coul d transfer antibiotic resistance to other microflora, including pathogens. As such, safe and effective competitive exclusion cultures must be sensitiv e to commonly used antimicrobial agents. By necessity, intentional or accid ental exposure of these beneficial microflora to antibiotics will reduce or eliminate the protection provided by competitive exclusion culture establi shment. As antibiotic residues can be present from embryonic, hatchling, or maternal administration, a rapid and sensitive assay for the nonspecific d etection of residues, which could interfere with competitive exclusion cult ure establishment, is needed. This study was conducted to develop a rapid a nd inexpensive bioassay to detect multiple antimicrobial residues in egg yo lk and neonatal yolk sacs. Aerobic bacterial strains with known sensitivity to several antibiotics used by the poultry industry were selected and indi vidually compared for sensitivity to enrofloxacin, gentamicin, tetracycline , ceftiofur, and tylosin concentrations in egg yolks. This assay was found to be relatively sensitive for the detection of these antimicrobials, and d etection of residues was associated with reduced competitive exclusion cult ure (PREEMPT) establishment in one experiment. Importantly, this assay can be implemented with minimal training or equipment under commercial hatchery practices and could be used to determine embryo groups, in advance of hatc h, that are not suitable candidates for competitive exclusion treatment in the hatchery.