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.
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