Escherichia coli O157:H7 facilitates the penetration of Staphylococcus aureus into table eggs.

Fresh eggshells collected from a local farm were subjected to different levels of surface contamination with feces containing different levels (3 to 5 log₁₀) of Escherichia coli O157:H7 or Staphylococcus aureus and incubated at 3 different temperatures (10, 25, and 32 °C). The penetration rates of contaminating bacteria were followed throughout the incubation period by tracing bacterial presence in shell, shell membranes, albumen, and yolk. The study revealed the ability of both E. coli O157:H7 and enterotoxigenic S. aureus to grow on shell in feces, penetrate the shell, and move and multiply within egg contents at different rates and periods depending on bacterial type and incubation conditions. High temperatures (25 and 32 °C) increased penetration rate, whereas storage at 10 °C decreased significantly the rate of penetration. High levels of contamination with E. coli O157:H7 also shortened the time needed for the penetration process. Results showed that when eggshells were contaminated with both organisms simultaneously, the penetration of E. coli O157:H7 preceded that of S. aureus and facilitated the invasion of the latter bacteria.