STARVATION-SURVIVAL PROCESSES OF THE BACTERIAL FISH PATHOGEN YERSINIA-RUCKERI

The fish pathogen Yersinia ruckeri survived for more than three months in the environments studied (river, lake and estuary). The three stra ins showed similar survival dynamics, regardless of their origin or se rotype. The number of culturable cells increased in the first 15 days from 1 (water microcosms) to 3-log-unit (sediment microcosms), and the n declined during a 100-day period. Persistence of culturable cells wa s greater in sediments than in waters, as well as at 6 degrees C than at 18 degrees C. Therefore, while a situation of long term survival co uld be stated in all sediments at both temperatures and in river water at 6 degrees C, in estuary and lake waters situations of non-culturab ility were observed. In addition, measurement of the cellular metaboli c activity showed decreases in the respiratory rates to 60-70% of the original values in the cases of sediments and river water, and to 10-1 5% when the cells became non-culturable. However, in all the microcosm s, the acridine orange direct counts (AODC) remained nearly constant d uring the experimental period at values of about 10(6) cell/ml in wate r and 10(8) cell/ml in sediments. These findings demonstrated that Y. ruckeri may undergo a dormant state under certain starvation condition s. Non-culturable cells showed marked changes in morphology and size. Slight changes in LPS patterns of dormant cells were also detected, bu t not in membrane proteins or plasmid profiles. Moreover, maintenance of virulence during the non-culturability state was demonstrated. Dorm ant cells were easily resuscitated by addition of fresh medium to the microcosms, showing the resuscitated cells levels of metabolic activit y and plate counts similar to those seen prior the start of the experi ment.