Ultrastructural and molecular characterization of Balantidium coli isolated in the Philippines.

Balantidium coli is a ciliated protozoon inhabiting the colon of swine, rodents, horses, nonhuman primates and humans. In association with disease triggered by other infectious agents, B. coli may become a pathogenic opportunist. This study describes the isolation, cultivation, morphological as well as molecular characterization of B. coli isolated from the large intestine of a pig in the Philippines. Based on scanning and transmission electron microscopy, this protozoon presents a dense ciliation in the oral structure and somatic cilia that are arranged in a more transverse field. Oral and somatic monokinetids were identified in the cortex of the organism. The presence of heterokaryotic nuclear condition is evident, and the cell body of the ciliate shows numerous mucocysts, several food vacuoles, mitochondria, endoplasmic reticulum, and contractile vacuoles. Polymerase chain reaction and phylogenetic analysis based on the small subunit ribosomal RNA gene were performed in order to compare our isolate with other previously reported B. coli isolates. The full-length sequence of the SSU rRNA gene of the isolate showed 99% similarity to other B. coli isolates reported in the GenBank. Phylogenetic analysis revealed that the isolate clustered with previously reported B. coli isolates from gorillas, pig, and ostrich. To date, no studies on the ultrastructure and phylogeny of B. coli isolated in the Philippines have been reported. Results from this study may serve as a baseline data for further ultrastructural and phylogenetic studies on this organism. This study also suggests that morphological characteristics along with molecular identification are essential for validating and identifying species of Balantidium.