An investigation on fruit fly mortality and the carrier state in disease transmission with the bacterium Serratia marcescens.




Mohamed, Fulanat
Jones, Dr. Crosby

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This study focused on the bacterium Serratia marcescens; specifically to assay its effect on fruit fly mortality, its ability to use the fruit fly as a living reservoir, and its transmissibility between fruit flies. It was hypothesized that this insect pathogen would kill susceptible fruit flies leaving those more resistant in a carrier state capable of transmitting the bacteria to uninfected flies. One unique property of the bacterium is its ability to produce a distinct red pigment that can be used to trace its presence. Experimental methods involved infecting fruit flies with the bacterium by allowing them to ingest the bacterium mixed with their food supply. More susceptible flies developed an infection and died. Fruit flies that survived were tested for the presence of S. marcescens in and on their bodies. Survivors were then successfully used to transmit the bacterium to fresh uninfected flies. This study is important because: [1] it represents an animal model for studying innate immunity to infectious agents (S. marcescens is capable of causing human infections) and [2] it provides a relatively safe, inexpensive classroom exercise to demonstrate the significance of the carrier state in transmission of infectious disease.


HYPOTHESES AND OBJECTIVES We have hypothesized the following concerning the interaction of D. melanogaster and S. marcescens: [1] This insect pathogen will cause the morality of fruit flies which are more susceptible to infection. [2] some more resistant fruit flies will survive [3] possible carriers will be able to communicate the infection when exposed to new uninfected fruit flies. The fruit fly immune system is comparable to humans, therefore conclusions relevant to our immune system can be reached. This study could be a useful exercise to emphasize the importance of the carrier state in disease transmission.


Serratia marcescens, bacteria, carrier state, disease transmission, fruit fly mortality, innate immunity