A variant of the TIGR4:19F strain, SpnYL101, showed impaired colonization in a mouse model of multi-strain nasopharyngeal carriage and lower resistance to surface phagocytosis in vitro.
(A) In a mouse colonization model, five TIGR4 capsular variants (TIGR4:1, TIGR4:4, TIGR4:14, TIGR4:19A, TIGR4:23F) were mixed with either TIGR4:19F (solid circle) or SpnYL101 (open circle) at equal amount (~106 CFU each) and were used to intranasally challenge C57BL/6 mice. Nasal wash samples were obtained on days 1 and 7 post challenge, and the frequency of the serotype 19 F variant in each sample was determined by qPCR. The competitive index of the TIGR4:19F or SpnYL101 in each sample is shown. Horizontal bars are medians. p-values are derived from Mann–Whitney tests. (B) Survival rate of the TIGR4:19F and the SpnYL101 measured in a non-opsonic neutrophil-mediated killing assay. Error bars represent SEM. The p-value is derived from t-test (n = 10 for each group). (C) Cell-associated type 19 F capsular polysaccharide (Ps) measured by an inhibition ELISA assay. Error bars represent SEM from two independent experiments. The p-value is derived from t-test. (D) Single-strain colonization of C57BL/6 mice by either TIGR4:19F or SpnYL101. Colonization densities as measured by total CFU/nasal wash on day 1 and day 4 are shown. Horizontal bars are medians. p-values are derived from Mann–Whitney tests.