I was also wondering about this! We use MacConkey agar to kill gram positives/select for gram negatives, but if bile disrupts lipids it would seem that gram negatives would be more vulnerable via their outer membrane. I would like to hear from true experts, but I did find this article useful-- it does seem that bile exerts its antimicrobial effects through proteins, not lipids:

Article Bile salts act as effective protein-unfolding agents and ins...