Serratia marcescens and Enterobacter cloacae exhibit differential population dynamics in Anopheles gambiae s.l after sugar and blood feeding

Background Serratia marcescens and Enterobacter cloacae are associated with Anopheles gambiae mosquitoes and have been found to possess anti-plasmodial properties, making them suitable candidates to explore for bacteria-mediated disease/vector control. Their natural growth trends in the mosquito particularly after the host has fed on sugar and blood is required to deepen our understanding of how they can be effectively utilized in vector/disease control. Methods In this study, we employed a time-course experiment to investigate the dynamics of S. marcescen s and E. cloacae in An. gambiae s.l mosquitoes over a 48-hour period after feeding. Absolute bacterial counts were estimated using quantitative PCR (qPCR) on cDNA obtained from total RNA extracted from mosquito samples and, with standard curves from bacterial isolates. A generalized additive mixed model (GAMM) was employed to investigate the effects of feeding and time on the bacteria trends while accounting for non-linear trends and repeated measures (random effects for ID). Results We show that E. cloacae are ~ 2000-fold more abundant than S. marcescens in mosquitoes 30 min after sugar-feeding ( p  < 0.0001). This difference drops to ~ 860-fold at the same time point in blood-fed mosquitoes due to an initial increase in S. marcescens . While E. cloacae remain remarkably stable at 10 ⁶ CFU/mL over 48 hours in sugar- and blood-fed mosquitoes, S. marcescens demonstrates non-linear growth dynamics ( p  = 0.02), dipping at 2 hours (3.4×10 ³ CFU/mL) and rising steeply to a peak of 1.3×10 ⁶ CFU/mL at 12 hours post–blood meal, representing ~ 200-fold increase in its abundance post-feeding. Conclusion Contrary to the general perception that members of Enterobacteriaceae increase after the mosquito blood feeds, our results provide evidence that Serratia but not Enterobacter naturally proliferates following a blood meal. This highlights that the choice of microbes for disease/vector biocontrol strategies must be informed by the specific growth kinetics of the candidate species. This work also hints on a multi-species consortium approach as a robust strategy for biocontrol.