Shotaro Izumi

Relationship between gyrA Mutations and Quinolone Resistance in Flavobacterium psychrophilum Isolates

ABSTRACT Flavobacterium psychrophilum is the causative agent of the fish diseases called bacterial cold-water disease and rainbow trout fry syndrome. It has been reported that some isolates of F. psychrophilum are resistant to quinolones; however, the mechanism of this quinolone resistance has been unexplained. In this study, we examined the quinolone susceptibility patterns of 27 F. psychrophilum strains isolated in Japan and the United States. Out of 27 isolates, 14 were resistant to both nalidixic acid (NA) and oxolinic acid (OXA), and the others were susceptible to NA and OXA. When amino acid sequences deduced from gyrA nucleotide sequences of all isolates tested were analyzed, two amino acid substitutions (a threonine residue replaced by an alanine or isoleucine residue in position 83 of GyrA [Escherichia coli numbering] and an aspartic acid residue replaced by a tyrosine residue in position 87) were observed in the 14 quinolone-resistant isolates. These results strongly suggest that, as in other gram-negative bacteria, DNA gyrase is an important target for quinolones in F. psychrophilum.

Plasmid Profiling of Japanese Flavobacterium psychrophilum Isolates

Abstract Flavobacterium psychrophilum is the causative agent of bacterial coldwater disease and rainbow trout fry syndrome in salmonids, cyprinids, and ayu Plecoglossus altivelis. To investigate genetic variability of this bacterium, plasmid profiling analysis was undertaken in 104 isolates of F. psychrophilum from Japan (n = 92), Europe (n = 9) and the USA (n = 3). Plasmids were isolated by a simple and inexpensive procedure using silica particles and then analyzed by agarose gel electrophoresis. Seventy-two of 104 isolates (69.2%) possessed plasmids, which were distributed at 2.8 kilobases (kb) (n = 33), 3.4 kb (n = 15), 4.1 kb (n = 23), and 5.2 kb (n = 1). The type strain of F. psychrophilum possessed a 2.8-kb plasmid, and a 3.4-kb plasmid was found mainly in isolates from rainbow trout O. mykiss. The 4.1-kb and 5.2-kb plasmids were found in Japanese isolates. Although the functions of these plasmids remain cryptic, no plasmids were associated with antibiotic resistance to ampicillin, sodium nifurstyre...