Bacteriome in Ticks Collected from Domestic Livestock in Kenya

Abstract

Background: Metagenomics approaches are increasingly being utilized as “dipstick” for microbial carriage. In this study, 16S rRNA metagenomics was used to probe for microbial community that resides in the ticks, those they pick from the environment, wildlife and livestock and to identify potential tick borne zoonoses. Methods: Tick DNA from 463 tick pools collected from domestic animals between 2007 and 2008 were amplified with primers that target the 16S rRNA V3-V4 domain and then sequenced on Illumina Miseq platform using 300 cycles version 3 kits. Ticks were pooled according to species and animal from which they were collected. A non-target control was used to track laboratory contaminants. Sequence data were analyzed using Mothur v1.3 pipeline and R v3.3.1 software and taxonomy determined using SILVA rRNA database. Shannon diversity index was used to compute bacterial diversity in each tick species before computing the means. Results: A total of 645 bacteria genera grouped into 27 phyla were identified. Four phyla contributed 97.4% of the 36,973,934 total sequences. Proteobacteria contributed 61.2% of these sequences that tarried to 33.8% genera, compared to 15.9% (23.4% genera) for Firmicutes, 15.6% (20% genera) for Actinobacteria and 4.7% (11.6% genera) for Bacteroidetes. The remaining 23 phyla only contributed 2.6% of the sequence reads (11.2% genera). Amongst the 645 genera, three groups were discernible, with the biggest group comprised commensals/symbionts that contributed 93.6% of the genera, but their individual sequence contribution was very low. Group two comprised genera that are known to contain pathogenic species, with C oxiella contributing 15,445,204 (41.8%) sequences, Corynebacterium (13.6%), Acinetobacter (4.3%), Staphylococcus (3.9%), Bacillus (2.7%) and Porphyromonas (1.6%), Ralstonia (1.5%), Streptococcus (1.3%), Moraxella (1.3%), amongst others. Group three comprised genera known to contain tick borne zoonotic pathogens (TBZ): Rickettsiae, Anaplasma, Francisella, Ehrlichia, Bartonella and Borrelia . Individually the TBZ contributed <1% of the sequences. By Shannon diversity index, Amblyomma variegatum carried the least diverse bacteria (mean Shannon diversity index of 2.69 ± 0.92) compared to 3.79 ± 1.10 for A. gemma , 3.71 ± 1.32 for A. hebraeum , 4.15 ± 1.08 for other Amblyomma spp, 3.79 ± 1.37 for Hyalomma truncatum , 3.67 ± 1.38 for other Hyalomma spp, 3.86 ± 1.27 for Rhipicephalus annulatus , 3.56 ± 1.21 for Rh. appendiculatus , and 3.65 ± 1.30 for Rh. Pulchellus , but the difference was not significant (p = 0.443). Conclusion: This study illustrates the utility of 16S rRNA metagenomics in revealing the complexity of bacteria communities that reside and/or transit through the tick having been picked from the environment, livestock and/or wild animals, some with potential to cause zoonoses.