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Chinook salmon, Oncorhynchus tshawytscha (Walbaum), and rainbow trout, Salmo gairdneri Richardson, were used to determine if sublethal copper exposure would increase their susceptibility to Vibrio anguillarum infection. Fish were pretreated with copper at fractional levels of the 96 h copper LC50 before exposure to the pathogen. Mortality by vibriosis was greater among fish exposed to 9% of the copper LC50 for 96 h than unexposed fish. Peak susceptibility to vibriosis depended in part on the interaction of exposure time and copper concentration. The higher copper concentrations produced peak susceptibility to infection in shorter time periods. After the peak of susceptibility, sensitivity to infection declined to near control levels in those fish where exposure was continued. Rainbow trout stressed by copper required about 50% fewer pathogens to induce a fatal infection than non-copper exposed fish. [ABSTRACT FROM AUTHOR]

The transmission of Yersinia ruckeri has been investigated in steelhead trout using asymptomatic carriers of the causative bacterium of enteric redmouth disease. It was found that unstressed carrier fish did not transmit the bacterium to recipient fish to cause either an epizootic or produce new carrier fish, However, when the carriers were stressed with heat, the bacterium was transmitted from the carrier to recipient fish producing a lower intestinal carrier state but no deaths. Examination of experimentally infected fish to determine the number of carriers among the survivors indicated that the frequency varied as a function of time following infection. When immunized fish were challenged with Y. ruckeri they became temporary carriers of the bacterium for up to 3 days; but were not able to transmit the infection to healthy recipient fish. [ABSTRACT FROM AUTHOR]

This article discusses the effect of water temperature on the infection of rainbow trout Salmo gairdneri Richardson with infectious haematopoietic. Water temperature is known to be an important factor influencing bacterial infections of salmonid fish however, very little information is available as to its effect on viral disease. If the virus was demonstrable in infected fish before their shift to 18°C, the increase in temperature was ineffective and in fact the course of the disease was even heightened.

The phenotypic and nucleic acid properties of Klebsiella pneumoniae have been studied on cultures obtained from six different habitats (humans, vegetables, seeds, trees, rivers, and pulp mills). The 19 cultural reactions of 107 isolates varied significantly only in tryptophanase activity and dulcitol fermentation. The percentage of guanine plus cytosine base composition of 41 isolates varied from 53.9 to 59.2%. The range of percentage of guanine plus cytosine base composition for environmental klebsiellas was broader than that for the cultures of human origin. The range of deoxyribonucleic acid relative reassociation (homology) to the human K. pneumoniae reference strain extended from 5% to 100% and the chromosome molecular weights ranged from 2,200 x 10(6) to 3,000 x 10(6). The species of K. pneumoniae is thus molecularly more heterogeneous than previously thought and most isolates of human, pulp mill, and river origin are genetically indistinguishable. The presence of K. pneumoniae therefore represents a deterioration of the microbiological quality of the environment and should be considered of public health significance. At the present time the health significance of the molecularly more divergent strains, primarily of vegetable and seed origin, their relationship to klebsiellas of human origin, or to other genera of the Enterobacteriaceae is unclear.

Exposure of rainbow trout to sublethal levels of copper in water increased their susceptibility to infectious hematopoietic necrosis virus. In most instances, the percent mortality was twice as great in the stressed groups compared with those groups which were not stressed but received the same virus dose. Although the level of copper in the water influenced the mortality rates, the length of exposure did not prove to be critical, as similar results were obtained after 1, 3, 5, 7, or 9 days of exposure. When different virus challenges were employed, the percent mortalities were again greater in the stressed fish at all virus doses tested, and at one dose level mortalities were noted in the stressed group but not in the untreated group.

Growth, survival, and pathogenicity of Klebsiella growing in and on environmental foci were examined. Total coliforms present in raw wastes from pulp mills were in excess of 10(5)/ml, and 60 to 80% were Klebsiella. Fecal coliform counts ranged from 10(1) to 10(5)/ml. Klebsiella isolates from industrial effluents and a variety of human and bovine mastitis origins multiplied in pulp waste and commonly exceeded 10(6) cells per ml. Pathogenic isolates also multiplied in dilute aqueous extracts of sawdust to comparable levels. Klebsiella strains from vegetable surfaces and human infections grew rapidly on the surfaces of potatoes and lettuce and exceeded 10(3) organisms per g of surface peel and leaf after a 24h incubation at room temperature. After 7 weeks on potatoes stored at 5 degrees C, some 10 to 30% of the day 1 Klebsiella counts were recoverable. Three Klebsiella isolates of pathogenic origin were passed 45 times through sterile pulp effluent (270 generations), and mean lethal dose levels in mice were periodically monitored. In two instances, a significant decrease in virulence was noted after 15 to 26 passes (90 to 156 generations). The third culture, of bovine mastitis origin, retained its original mean lethal dose value. Botanical milieu provided suitable habitats for the multiplication and colonization of Klebsiella isolates of disease origins in the same manner as indigenous isolates. Aquatic environments polluted with botanical material served as potential reservoirs for perpetuating the growth and spread of opportunistic Klebsiella pathogens that may ultimately colonize animals, humans, and aquatic organisms.