Nitrogen-fixing heterotrophic bacteria and presumptive coliforms in sewage treatment plants and irrigation reservoirs in Libya.

Monitoring of heterotrophic nitrogen-fixing bacteria and presumptive coliforms in two Libyan sewage treatment plants showed that tertiary treatment of effluents by chlorination killed these bacteria. However, the irrigation reservoirs which received the treated effluent contained large numbers of both types of bacteria. As the proportion of nitrogen-fixers to presumptive coliforms was much less in the sewage than in the irrigation reservoirs it is probable that the irrigation water became contaminated by a source other than sewage

Culturability, injury and morphological dynamics of thermophilic Campylobacter spp. within a laboratory-based aquatic model system.

AIMS: To study the survival processes of thermophilic Campylobacter spp. within a modelled aquatic system and particularly the involvement and survival potential of viable but non-culturable forms. METHODS AND RESULTS: The survival and morphological characteristics of populations of thermophilic Campylobacter species exposed to simulated aquatic conditions were examined using a combination of cultural and microscopic techniques. Populations underwent progressive decay when exposed to simulated aquatic conditions. The rates of population decay were observed to be significantly greater at the higher temperature (20 degrees C) with a rapid transition of the dominant sub-populations from non-stressed to dead cells occurred within 3 days. At 10 degrees C the rate of culturability loss was much reduced with substantial development (approx. 80% of total population) of viable but non-culturable (VBNC) populations by all species within 3 days, declining to represent approximately 5-25% of the total population at day 60. Significant differences (P < 0.001) were identified between decay rates as a consequence of different species, sub-populations and temperature but not between sub-populations of different species. Morphological variants including spiral, elongated spirals and rods, short rods and coccoid forms were identified. The endpoints of morphological transition were temperature-independent and isolate-specific yet the rate of morphological transition was directly related to temperature and approximately equivalent between species. CONCLUSION: The VBNC state is a transitory stage in the degeneration of Campylobacter population within the aquatic environments simulated during this study. SIGNIFICANCE AND IMPACT OF THE STUDY: VBNC cells form the most persistent, viable, potentially pathogenic sub-population of Campylobacter populations exposed to aquatic stress conditions