FIG 4.

Exacerbation of allergy symptoms by oral administration of Citrobacter. After 1 week of antibiotic-mediated depletion of the endogenous microbiota, ovalbumin (OVA)/alum and phosphate-buffered saline (PBS)/alum mice were orally administered Citrobacter koseri (1 × 10⁹ CFU per animal). Feces were collected 1 and 7 days after administration, and the resulting bacterial isolates were identified to the species level using a Vitek MALDI-TOF MS system. The occupancy rate of C. koseri among the identified fecal bacteria was defined as the survival rate compared with that of the inoculum (A). The severities of OVA-specific allergic responses were compared by determining anaphylactic responses (assessed as the maximum change in rectal temperature following OVA challenge) in OVA/alum mice after the oral administration of C. koseri (B). *, P < 0.05.