Molecular identification of maggots captured from forensic cases.

Abstract

Problem/Background : The estimation of the postmortem interval (PMI) is necessary for supporting justice to the dead. During the early stage of death, estimation of PMI of the corpses depends on the changing of muscle contraction and physical conditions, but this method can be used effectively in case of death within 24 hours. Flies are the first organisms which swarm on corpses. Consequently, accuracy of the estimation of PMI using fly larvae collected from corpses depends on identification of the species of flies. However, the macroscopic method using posterior spiracle is not definite for identifying the species of flies. Therefore, the molecular identification is used for solving this problem.

Objective : To demonstrate the application of mitochondrial cytochrome oxidase I (COI) gene in identification of maggot species by using molecular techniques.

Design : Descriptive study

Setting : The Department of Parasitology and the Department of Forensic Medicine, Faculty of Medicine, Chulalongkorn University.

Methods : Six maggot samples were collected from six forensic cases at the Department of Forensic Medicine, King Chulalongkorn Memorial Hospital in 2004 - 2007. Before DNA extraction, posterior spiracles of specimens were morphologically investigated under stereomicroscope. Then, mitochondrial maggot DNA was extracted and amplified for cytochrome oxidase I gene (COI) via polymerase chain reaction (PCR) technique using specific primers. The PCR products were cloned into pGEM^®-T easy vector and further verified by blue/ white screening and selection system. Positive clones were propagated and extracted. Recombinant plasmids harboring PCR insert were analyzed by automated DNA sequencing. Obtained nucleotide sequences were compared with GenBank database using the BLAST N bioinformatics programme.

Results : Sequencing reactions revealed that PCR yielded a single 351 bp in all maggot specimens. Sequence analyses, based on percentage of identity with available data from GenBank, demonstrated that five (83%) specimens and the remaining one (17%) were identified as Sarcophaga ruficornis and Chrysomya rufifacies, respectively.

Conclusions : This is the first report that provides promising data of molecular identification of the maggot species captured from forensic cases in Thailand.