DOES ACANTHAMOEBA SERVE AS AN INTRACELLULAR ECOLOGICAL NICHE FOR SALMONELLA TYPHI

Abstract

Intro: Acanthamoeba spp. is known to harbor bacterial endosymbionts and this mechanism is linked to intracellular survival of at least two pathogens in the environment – Legionella and Burkholderia cepacia. This study was undertaken with the hypothesis that “Acanthamoeba in the environment harbour intracellular S.Typhi, thereby conferring these strains a survival advantage in the environment”. Methods: 160 drinking water samples were collected from households in a periurban site in Vellore, India; isolation/characterization of Acanthamoeba in these samples by culture and subsequent detection of internalized S. Typhi in the isolates were carried out by lysis followed by culture and fluorescent imaging. The common genotypes of Acanthamoeba spp. isolated from the environmental samples were co-cultured with environmental strains and clinical isolates (MDR, H58 clade and CT-18) of S. Typhi in order to measure intracellular viability of Typhi and survivability of Acanthamoeba in such an environment. Findings: Acanthamoeba was isolated from 62/160 samples(38.75%) by culture. No intracellular typhi bacilli were identified in these isolates. T2(A.polypahaga) and T4(A.castellani) were the two most common genotypes isolated. S. Typhi was recovered from six samples, two of which were positive for Acanthamoeba spp. Though both Acanthamoeba and Typhi had improved viable counts (∼ 10X) when cultured together as opposed to when cultured singly, the co-culture experiments did not show a significant deviation in the dynamics and degree of survivability between the different strains of S.Typhi. All strains of the Typhi bacilli were more capable of internalising and maintaining its viability in the T2 genotype when compared to T4.