Prevalence and Diversity of Leptospires in Different Ecological Niches of Urban and Rural Areas of South Andaman Island.

Leptospirosis is an emerging disease around the globe. South Andaman Island is an endemic region for leptospirosis. We herein compared the prevalence of leptospires in urban and rural areas of South Andaman Island. The PCR detection and isolation of Leptospira revealed that pathogenic leptospires were prevalent in sewage water and household drainage water in urban areas and in paddy fields, vegetable field water, and stream water in rural areas. These results demonstrate that intermediates are ubiquitously present in the environment and may be responsible for asymptomatic infections, and also provide an insight into disease ecology.

Coexistence and survival of pathogenic leptospires by formation of biofilm with Azospirillum.

Pathogenic Leptospira spp. represent one cause of leptospirosis worldwide and have long been regarded as solitary organisms in soil and aquatic environments. However, in the present study, Leptospira interrogans was observed to be associated with environmental biofilms with 21 bacterial isolates belonging to 10 genera. All 21 isolates were examined for their coaggregation and biofilm-forming ability with leptospires in vitro. Among these, Azospirillum brasilense RMRCPB showed maximum interspecies coaggregation with leptospiral strains (>75%, visual score of +4). Other significant coaggregating isolates belonged to the genera Sphingomonas, Micrococcus, Brevundimonas, Acinetobacter and Paracoccus. Biofilms of leptospires in combination with A. brasilense RMRCPB showed high resistance to penicillin G, ampicillin and tetracycline (minimum bactericidal concentration ≥800 µg/mL) and tolerance to UV radiation and high temperature (up to 49°C). This study hypothesized that biofilm formation with A. brasilense protects the pathogenic Leptospira from adverse environmental conditions/stress. This coexistence of pathogenic Leptospira with other bacteria may be the key factor for its persistence and survival. However, the mechanism of biofilm formation by leptospires needs to be explored to help devise an appropriate control strategy and reduce transmission of leptospires.