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. 2022 Jul 11;9:945632. doi: 10.3389/fvets.2022.945632

Figure 2.

Figure 2

A large potentiation effect of serum on in vitro potency of gamithromycin against S. suis. (A) Porcine serum disrupts the plasma membrane of S. suis cells by measuring fluorescence intensity of 1-N-phenylnaphthylamine (NPN) after 4 h of incubation. (B) Serum-induced NPN uptake of S. suis strains. Bacterial cells were exposed to increasing proportions of porcine serum from 25 to 75%. NPN uptake (%) represents fluorescence intensity divided by the value observed in 100% serum. (C) Intracellular accumulations of gamithromycin in S. suis strains after exposure to 0.5 mg/L gamithromycin for 30 min in Mueller-Hinton broth (MHB) and serum matrix. Data shown are the means of three independent biological replicates, *P < 0.05 and **P < 0.005. (D) A concentration-dependent decrease in gamithromycin MICs for S. suis strains in the presence of increasing proportions of serum from 25 to 75%. Data shown are the log2-transformed MIC values.