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Persistence of Streptococcus pyogenes in the lysosomal environment (836.9)

Streptococcus pyogenes is a bacterial pathogen that can cause a range of infections from pharyngitis to necrotizing fasciitis. During an infection, the phagocytes of the host engulf the bacteria and fuse the phagosome with a lysosome to degrade the bacteria and prevent further infection. Previous experiments using a pH‐sensitive GFP construct demonstrated that while bacteria are localized to the lysosomal compartment of THP‐1 monocytes, the construct was not degraded. Because we determined the GFP construct was indeed pH‐sensitive, one possible explanation is that S. pyogenes is able to survive the low pH conditions of a lysosome. We tested the growth of S. pyogenes in different pH medias, ranging from pH = 4 ‐ 7. Our results indicated that within the pH range of a lysosome, bacteria persisted, but did not proliferate. Upon more detailed examination of the bacteria in a narrower pH range (pH = 4 ‐ 5), we found that bacteria were able to survive at pH = 4.5 ‐ 4.7. These results were corroborated with fluorescence microscopy of pH‐sensitive GFP‐expressing bacteria incubated in low pH media. Thus, S. pyogenes can survive the low pH‐environment of the lysosome. Our data do not however exclude the possibility that S. pyogenes can also prevent the acidification of the lysosome and future experiments will be aimed at measuring the pH of the lysosome in an infected cell as well as elucidating bacterial factors involved in pH resistance.