COLUMNARIS DISEASE OF FISHES

Columnaris disease is an acute to chronic bacterial infection that affects anadromous salmonids and virtually all species of warmwater fishes. Davis (1922), who first described the disease, named it columnaris because the causal bacterial cells seen in wet mounts of affected gills and fins were arranged in columnar aggregations. Ordal and Rucker (1944) were the first to isolate the causal organism and, based on cellular morphology, identified it as a myxobacterium. Organisms classified in the order Myxobacterales are long, thin gram-negative rods that are motile on agar media by a creeping or flexing motion. They have a life cycle composed of vegetative cells, microcysts (resting cells), and fruiting bodies, or only vegetative cells and microcysts. Ordal and Rucker (1944) reported that the myxobacterium from columnaris disease produced both fruiting bodies and microcysts and named the organism Chondrococcus columnaris. Garnjobst (1945) studied strains of the columnaris bacterium and reported that microcysts were present but not fruiting bodies. Because fruiting bodies could not be demonstrated, she placed the organism in the genus Cytophaga and suggested Cytophaga columnaris. However, in the eighth edition of Bergey\u27s Manual of Determinative Bacteriology (Buchanan and Gibbons 1974), it was stated that the columnaris bacterium produced neither fruiting bodies nor microcysts. Therefore it was removed from the Myxobacterales, placed in the order Cytophagales, and renamed Flexibacter columnaris

Stability of antibiotics under growth conditions for thermophilic anaerobes.

It was shown that the inhibitory effect of kanamycin and streptomycin in a growing culture of Clostridium thermohydrosulfuricum JW 102 is of limited duration. To screen a large number of antibiotics, their stability during incubation under the growth conditions of thermophilic clostridia was determined at 72 and 50 degrees C by using a 0.2% yeast extract-amended prereduced mineral medium with a pH of 7.3 or 5.0. Half-lives were determined in a modified MIC test with Escherichia coli, Staphylococcus aureus, and Bacillus megaterium as indicator strains. All compounds tested were similar at the two temperatures or more stable at 50 than at 72 degrees C. The half-life (t1/2) at pH 7.3 and 72 degrees C ranged from 3.3 h (k = 7.26 day-1, where k [degradation constant] = 1/t1/2) for ampicillin to no detectable loss of activity for kanamycin, neomycin, and other antibiotics. Apparently some compounds (e.g., lasalocid and neomycin) became more potent during incubation (k greater than 0). A change to pH 5.0 caused some compounds to become more labile (e.g., kanamycin) and others (e.g., streptomycin) to become more stable than at pH 7.3

Comparison of plasmids isolated from romet-30-resistant edwardsiella ictaluri and tribrissen-resistant escherichia coli

Edwardsiella ictaluri, the etiological agent of enteric septicemia of channel catfish (ESC), is the leading cause of bacterial disease in commercially raised channel catfish Ictalurus punctatus. The only drug approved by U.S. Food and Drug Administration for use against ESC is Romet-30. Recently, several isolates were obtained that had a naturally occurring resistance to Romet-30. On further characterization these isolates were shown to possess a 55-kilobase (kb) plasmid that encodes resistance to the drug. We compared Romet-30-resistant E. ictaluri and a Tribrissen-resistant strain of Escherichia coli (strain 1898) isolated from equine cystitis. Antimicrobial profiles, plasmid screening, restriction digest, and Southern blot analysis indicated that the two plasmids are very similar. The resistance afforded to the E. coli was encoded by a 55-kb plasmid. Each of the R plasmids conferred resistance to Romet-30, tetracycline, and Terramycin (oxytetracycline). The R plasmid from E. coli strain 1898 was transferred to Romet-30-sensitive isolates of E. ictaluri by single-step conjugation, rendering the transconjugates resistant to Romet-30, tetracycline, and Terramycin. Each plasmid was cleaved into fragments by restriction enzymes, then electrophoresed in an agarose gel and transferred to nitrocellulose. A labeled probe prepared from the R plasmid of E. ictaluri isolate 5-90-156, one of the original Romet-30-resistant E. ictaluri isolates, was added. Restriction enzyme digestion resulted in an equal number of fragments of equal mobility for the two plasmids, and the probe hybridized with the same fragments of each plasmid. These results indicate that the R plasmids of E. ictaluri and E. coli are similar, if not identical. © by the American Fisheries Society 1993