Antibiotic-mediated weight loss is correlated with activation of the acute-phase response. Mice were infected for 30 d, and their transmission status was identified. Superspreaders (black circles) and nonsuperspreaders (red squares) were treated with 5 mg of antibiotic via oral gavage. Superspreaders and nonsuperspreaders were treated with streptomycin and sacrificed 6 d after antibiotic treatment. Data shown are representative of two experiments with a total of 8–10 mice in each condition. (A and B) Serum (A) and intestinal cytokine (B) levels were measured by ELISA. Each point represents an individual mouse, and data are representative of two experiments with 10–15 mice per group. Nonsuperspreader hosts that lost >20% of their total body weight are represented by filled squares (Inset). (C) Fecal samples from streptomycin-treated superspreaders and nonsuperspreaders were processed, and host-derived proteins were identified by using mass spectrometry. Data show normalized spectral counts from the 17 identified proteins in the acute-phase response pathway depicted in a heat map where intensity was normalized within each protein and warmer colors represent increased spectral counts as depicted in the key. Host weight was normalized from red to blue with warmer colors depicting increased host weight. All proteins were correlated to host weight loss using Spearman’s correlation. *Significant correlations. (D) Host weight data from C is quantified, and significance is calculated by using the two-tailed Mann–Whitney test. **P < 0.005.

Antibiotic-treated nonsuperspreaders have increased inflammatory myeloid cells in the spleen, but not the gut. Mice were infected for 30 d, and their shedding status was identified. Superspreaders (black) and nonsuperspreaders (red) were treated with 5 mg of antibiotic via oral gavage. (A and B) Splenic cells were collected from streptomycin-treated superspreaders and nonsuperspreaders 6 d after antibiotic treatment. (A) Representative FACS plot shows frequency of CD11b⁺ Ly6C⁺ inflammatory myeloid cells gated on nonlymphocytes. (B) Total frequency of myeloid inflammatory cells expressed as a percentage of nonlymphocytes. (C and D) Ceca were fixed, and hematoxylin/eosin-stained sections were scored for histopathological changes. A representative figure of a cecal section from each group is displayed in C, and histopathological scores are represented in D. (E) Bars represent colonic neutrophils measured as a frequency of CD11b⁺ cells 6 d after streptomycin treatment. *P < 0.05.

CD4 T cells contribute to antibiotic-induced morbidity but not superspreader tolerance. Mice were infected for 30 d, and their shedding status was identified. Superspreaders (black circles) and nonsuperspreaders (red squares) were treated with 5 mg of streptomycin via oral gavage. Mice were treated with CD4-neutralizing antibodies or the isotype control (n = 4 or 5 in each group) 1 d before antibiotic treatment and at 2 and 4 d after antibiotic treatment. (A) Each point represents an individual mouse, and the weight data were collected daily. (B) Splenocytes were collected and representative cell populations were enumerated. In the isotype group, a single mouse was excluded due to morbidity. (C) Splenic Salmonella burden was quantified. *P < 0.05; **P < 0.005.