Perturbation of Alphavirus and Flavivirus Infectivity by Components of the Bacterial Cell Wall

During the past decades, the world has experienced a vast increase in epidemics of alphavirus and flavivirus infections. These viruses can cause severe diseases, such as hemorrhagic fever, encephalitis, and arthritis. The impact of the host microbiota on arbovirus infections is currently not well understood. Arboviruses are viruses transmitted through the bites of infected arthropods, predominantly mosquitoes or ticks. The first site of arbovirus inoculation is the biting site in the host skin, which is colonized by a complex microbial community that could possibly influence arbovirus infection. We demonstrated that preincubation of arboviruses with certain components of the bacterial cell wall, including lipopolysaccharides (LPS) of some Gram-negative bacteria and lipoteichoic acids or peptidoglycan of certain Gram-positive bacteria, significantly reduced arbovirus infectivity in vitro. This inhibitory effect was observed for arboviruses of different virus families, including chikungunya virus of the Alphavirus genus and Zika virus of the Flavivirus genus, showing that this is a broad phenomenon. A modest inhibitory effect was observed following incubation with a panel of heat-inactivated bacteria, including bacteria residing on the skin. No viral inhibition was observed after preincubation of cells with LPS. Furthermore, a virucidal effect of LPS on viral particles was noticed by electron microscopy. Therefore, the main inhibitory mechanism seems to be due to a direct effect on the virus particles. Together, these results suggest that bacteria are able to decrease the infectivity of alphaviruses and flaviviruses. IMPORTANCE During the past decades, the world has experienced a vast increase in epidemics of alphavirus and flavivirus infections. These viruses can cause severe diseases, such as hemorrhagic fever, encephalitis, and arthritis. Several alpha- and flaviviruses, such as chikungunya virus, Zika virus, and dengue virus, are significant global health threats because of their high disease burden, their widespread (re-)emergence, and the lack of (good) anti-arboviral strategies. Despite the clear health burden, alphavirus and flavivirus infection and disease are not fully understood. A knowledge gap in the interplay between the host and the arbovirus is the potential interaction with host skin bacteria. Therefore, we studied the effect of (skin) bacteria and bacterial cell wall components on alphavirus and flavivirus infectivity in cell culture. Our results show that certain bacterial cell wall components markedly reduced viral infectivity by interacting directly with the virus particle.