GAS Survive Intracellularly in Monocytes and Macrophages

<div><p>A) Frequency of cells containing viable intracellular bacteria 4 and 12 h postinfection with strains 8157 and 5448, respectively. Bars denote mean ± SEM of four or five experiments performed using monocytes or macrophages, respectively.</p> <p>(B) A confocal image of a representative macrophage harboring intracellular GAS (viable in green and dead in red) as assessed by staining with a bacterial viability kit. (C) Resurgence of intracellular bacteria (8157 and 5448) in the medium. At 12 h postinfection, antibiotic-free medium was added, and extracellular growth was monitored in the medium over time. The figure shows one representative out of four experiments performed. Control experiments lacking live human cells failed to support growth after antibiotic removal (unpublished data).</p> <p>(D) Comparison of frequencies of cells harboring viable GAS after infection with either 5448 wild-type (WT) strain or its isogenic ΔSpeB knockout (SpeB ko). Infected cells were stained with a live/dead BacLight bacterial viability kit, at 4 and 12 h postinfection, and the frequencies of cells containing viable bacteria in relation to the total number of cells were determined. Mean ± SEM of five experiments performed is shown. Significant difference in survival over time was determined by a Mann-Whitney test, and the <i>p</i>-value is indicated.</p>