Evaluation of "floc" as a Replica Plating Material for Bacteria.

and spread during the summer to widely separated locations. In addition to white perch (Roccus americanus), striped bass (R. saxatilis) were involved to a lesser degree. Carefully selected moribund specimens were collected and delivered to the laboratory. Microscopy disclosed an abundance of polarly staining gram-negative rods in blood and organs of diseased fish. First isolations of these bacteria were carried out on media enriched with blood, because it was suspected that bacteria were fastidious; later, agar media with 1 to 3% sodium chloride, or half-strength seawater, were used. Thirty cultures of this bacterium were isolated from internal organs of 17 white perch and 5 striped bass. The bacterium was isolated in pure culture from perch, but a Vibrio, and other unidentified gram-negative rods, were also isolated from some of the bass. Since the polarly staining rod was implicated in the epizootic, owing to its presence in large numbers and in pure culture in the perch, its characteristics were determined in cultures grown at 20 and 30 C. No growth occurred at 37 C. The cells were gram-negative, nonmotile, polarly stained rods. From fish tissues, they measured 1.5 by 1.0 ,u. On agar media with salt, colonies were regular, convex, and viscid, and the cells were capsulated. Striking pleomorphism of cells was noted on several media, and was influenced by sodium chloride concentration. Growth was observed in nutrient broth with 0.5 to 5.0% sodium chloride. Levels above 5.0% were not investigated. The isolate was negative in respect to production of indole, hydrogen sulfide, gelatinase, urease, and amylase, and to reduction of nitrates and methyl red. A trace of acetyl-methyl-carbinol was detected (Page, J. Bacteriol. 84:772, 1962). The cytochrome oxidase test (Ewing and Johnson, Intern. Bull. Bacteriol. Nomenclature Taxon. 10:223, 1960) was positive. From 17 carbohydrates tested, dextrose, maltose, fructose, and sucrose were anaerogenically fermented. Because of its strong polar-staining nature and many physiological reactions, this bacterium was placed in the genus Pasteurella. No attempt at speciation was made. So far as we know, this is the first time a representative of the genus Pasteurella was isolated from a fish epizootic.