Bacteriological studies on egg yolk forms and different formulations of yolk-citrate semen extender

Using a tabular design, the bacteriological profile of egg yolk forms and different formulations of yolk-citrate semen extenders across different storage periods was examined. Twenty-one eggs less than 24 h old were randomly selected from 3 crates of eggs. The yolks were harvested and divided into two equal parts. One part was centrifuged for 1 h at 3500 revolutions per minute (rpm) to get clarified yolk. The remaining part was left whole. Each part was divided into three aliquots, one of which was cultured immediately (pre-storage) on  MacConkey, Chocolate, Deoxycholate Citrate and Sabouraud Dextrose Agars and the other two stored each for 24 and 48 h before culture on the same media. The cultures were incubated for 24 h at 37°C. Left over egg yolks were pooled according to forms and kept frozen (-20°C) before being used to formulate extenders. Four different extenders were prepared using the clarified and whole yolks with or without antibiotics. The extenders were treated as previously described for egg yolk. Plates with apparent colonies were subjected to biochemical tests to identify the isolates and antibiotic susceptibility testing after the colonies were counted. Clarified yolk was less contaminated compared to whole egg yolk. Staphylococcus aureus was isolated from whole egg yolk and it was sensitive to Streptomycin, Amoxicillin, Neomycin, Penicillin and Cefoxitin but resistant to Gentamicin. Extenders with antibiotics were less contaminated than extenders without antibiotics. Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and Salmonella species were isolated from semen extenders without antibiotics. All isolates were sensitive to Gentamicin. In conclusion, clarified yolk and extenders containing clarified yolk with antibiotics had no contamination. Hence, clarified yolk should be used in the preparation of extenders instead of whole yolks. Also, Gentamicin should be included in extender formulations to reduce bacterial contamination. Key words: Egg yolk, whole yolk, clarified yolk, bacterial culture, yolk-citrate extender, antibiotics.