The impact of chlortetracycline on Drosophila melanogaster and Aedes aegypti

Microbial symbionts of insects have been demonstrated to play an important role in the nutrition and protection of the host; these include aphids and tsetse. Studies often use antibiotics to eliminate the symbionts but the deleterious impact of using these antibiotics is not commonly addressed. The impact of chlortetracycline treatment on Aedes aegypti and Drosophila melanogaster was investigated by assessing life-span, fecundity, development time, survival, nutrition and metabolism. The impact on microbial numbers and diversity was also determined. With Drosophila, treatment with 50 µg ml-1 and above showed a significant extension in development time and life-span, reduction in fecundity and change in nutritional content. Microbial numbers were significantly reduced at 50 µg ml-1 and above. Culturable techniques and 454 pyrosequencing, demonstrated that the microbial diversity of Drosophila was predominantly Acetobacter. Bacterial elimination through egg dechorionation yielded some similar results to chlortetracycline treatment. However, fecundity and life-span was not significantly affected. Microarray analysis established a significant reduction in the abundance of transcripts associated with immunity, particularly antimicrobial peptides. With Aedes aegypti, treatment significantly reduced the survival and also affected the life-span and nutrition of the insect. Microbial numbers of mosquito larvae were reduced at 30 and 100 µg ml-1. Colonies grew on plates supplemented with 50 µg ml-1 of chlortetracycline, indicating that the larvae bore chlortetracycline-resistant bacteria. 454 pyrosequencing demonstrated a change in diversity of bacteria found in mosquitoes +/- chlortetracycline, switching from Elizabethkingia meningoseptica to Raoultella sp with chlortetracycline. It is concluded that chlortetracycline significantly impacts the performance of the 2 insects through bacterial depletion, changes to bacterial diversity and toxicity. Nevertheless, different responses were observed with Aedes aegypti and Drosophila melanogaster. Moreover, experiments with Drosophila using egg dechorionation, emphasised the toxic impact of using antibiotics to eliminate microbes in the insect host.