Salmonella Typhimurium Infection and Excretion Following Sublethal Exposure to Insecticidal Bait in the German Cockroach Vector.

The German cockroach, Blattella germanica, is a widespread indoor pest and a vector of enteric human pathogens, including Salmonella enterica serovar Typhimurium (S. Typhimurium). Insecticidal baits are the most commonly used tools to control these cockroaches in built environments. Sublethal exposure to insecticidal baits has been a major driver of adaptive evolution, leading to physiological resistance to insecticides and behavioral aversion to glucose in some cockroach populations. Here, we conducted the first study investigating the effects of sublethal bait exposure on human pathogen biology in B. germanica. Our results show that a sublethal exposure to bait containing the common insecticide indoxacarb can increase susceptibility to subsequent infection by ingested S. Typhimurium in surviving cockroaches within the same generation. Interestingly, increased susceptibility to infection after sublethal bait exposure was cockroach strain dependent and did not increase the rate of shedding of the pathogen in excreta. These findings establish for the first time a potential link between a common anthropogenic intervention used to control this prevalent indoor pest and its capacity to maintain pathogens. In doing so, our work reveals a possible unintended consequence of failed pest control efforts. That is, some cockroach populations may become inadvertently more adept at maintaining pathogens due to sublethal exposure to baits stemming from existing insecticide resistance. Additional studies should further investigate this phenomenon to determine its extent and impact.