SPI1 and infection: To explore the relationships between sipA, sipC, hilA, and hns mRNA expression levels, real-time reverse transcription polymerase chain reaction (qRT-PCR) was performed using total RNA from WT cells cultured under aerobic and anaerobic conditions, since SPI-1 T3SS expression is known to be up-regulated during Salmonella growth under low oxygen conditions and during host cell infection [27,53].