Plasma albumin contributes to early Yersinia pestis survival at the onset of flea infection.

The plague bacillus, Yersinia pestis, encounters a hostile oxidative environment upon entering the flea gut, a barrier it must overcome to initiate biofilm formation for transmission. This resilience has been attributed mainly to bacterial defenses, yet we show that host plasma proteins act as transient allies, consistent with a role in mitigating oxidative stress immediately after the blood meal. These findings reframe blood not only as nutrition but also as an active modulator of vector competence.