Differential susceptibility of presumptive cultivable eggshell bacterial groups to rosemary essential oil in Japanese quail (Coturnix coturnix japonica).

This study investigated the antimicrobial activity of rosemary essential oil (REO) as a natural alternative to conventional disinfectants for Japanese quail hatching egg sanitization, focusing on the differential susceptibility of presumptive cultivable bacterial groups associated with eggshell contamination. Following previous findings demonstrating that REO reduces total microbial load and improves hatchability and chick performance, the present study aimed to characterize the response of specific cultivable bacterial groups to REO treatment. Eggs were divided into four groups: untreated control (C-), 70% alcohol-treated (C+ A), quaternary ammonium-treated (C+ Q), and REO-treated at 10 µL/mL. Cultivable bacterial populations were assessed using serial dilutions and selective culture media targeting specific Gram-positive and Gram-negative bacterial groups. Presumptive identification based on culture and morphological characteristics suggested the presence of Lactobacillus spp., Bacillus spp., Acinetobacter spp., Staphylococcus spp., Escherichia coli, and Enterobacter spp. REO treatment reduced several cultivable eggshell bacterial groups, with the greatest reduction observed for presumptive Escherichia coli, whereas presumptive Lactobacillus spp. were comparatively less affected. The response to REO therefore varied among the bacterial groups evaluated. In comparison, conventional sanitizers produced greater reductions in some bacterial groups, particularly presumptive Lactobacillus spp. These findings indicate that REO exhibits a differential antimicrobial profile against cultivable eggshell bacterial populations and highlight its potential as a natural alternative for hatching egg sanitization. Under the conditions investigated, the 10 µL/mL concentration may provide a favorable balance between antimicrobial activity and embryonic safety.