B. Spanggaard et al., ANTIBIOTIC-RESISTANCE IN BACTERIA ISOLATED FROM 3 FRESH-WATER FISH FARMS AND AN UNPOLLUTED STREAM IN DENMARK, Aquaculture, 115(3-4), 1993, pp. 195-207
Resistance profiles against two antibiotics, oxytetracycline and oxoli
nic acid, were determined for 296 bacterial strains isolated from thre
e fish farms (202 strains) and from an unpolluted stream (94 strains)
in Denmark. Resistance against oxytetracycline (25 mug/ml) was seen am
ongst 15% (29 strains) from fish farms and for 6% (6 strains) from an
unpolluted stream. Oxolinic acid resistance was also more prevalent am
ongst fish farm strains where 27% (53 strains) grew in the presence of
12.5 mug/ml oxolinic acid. Only 16% (15 strains) of isolates from the
unpolluted stream were resistant against oxolinic acid. Bacteria from
the fish farms may spread with the water circulation and, although th
e resistance frequencies found in this study were not statistically di
fferent, the use of chemotherapeutics may add to the environmental res
istance pool. Two types of inhibition curves were observed. One showed
instant inhibition at a given concentration of antibiotic. The other
curve showed a slow decrease in growth with increasing concentration o
f antibiotic. Six percent (13 strains) and 4% (4 strains) from fish fa
rms and an unpolluted stream were resistant to both antibiotics. The i
solates from the fish farms and the unpolluted stream were identified
as Vibrionaceae, Enterobacteriaceae, Alcaligenes spp., Acinetobacter s
pp., Pseudomonas spp., Moraxella spp., Moraxella-like and Shewanella p
utrefaciens. Fifteen percent were Gram-positive organisms of which one
half were resistant to oxolinic acid. Resistance profiles for the Gra
m-negative bacteria were, in general, independant of species or groups
and no difference was seen between isolates from three different trou
t farms exposed to different environmental stress.