A rapid method to quantify bacterial contamination on hatching eggs. 1. Correlation of optical density with initial bacterial count

Abstract

The use of optical-density (OD) readings after a 6-h incubation period, as a suitable method to quantify the bacterial contamination on hatching eggs, was established by the use of pure cultures of five bacterial isolates found to be the most prevalent on the hatching eggs examined. These isolates were identified as Micrococcus luteus, Staphylococcus gallinarum, Streptococcus epidermidis, Pseudomonas cepacei and Bacillus cereus. It was established that the OD reading was repeatable when the same inoculum was used to inoculate five different cultures, which were incubated for 6 h at 37 °C. This repeatability was not affected by bacterial isolate, or bacterial concentration of the inoculum, or when mixed bacterial cultures were used. A direct relationship was established between the OD reading (at 540 nm) after 6 h and the log of the bacterial concentration at the start of incubation. The OD reading after 6 h of incubation is a repeatable, rapid and simple method to quantify the bacterial concentration at the start of the incubation period.