ANTIBACTERIAL ABILITIES OF INTESTINAL MICROFLORA OF THE RIVER FISH

Bacterial strains were isolated from the intestinal tract of river fis h and the environmental water and sediment, and examined for their ant ibacterial abilities against Aeromonas hydrophila ATCC 7966, A. salmon icida ATCC 33658, Escherichia coli IAM 1264 and Staphylococcus aureus ATCC 25923 using a double agar-layer method. A total of 940 isolates i ncluding aerobic and anaerobic bacteria were classified into 13 taxono mic groups. Almost all specimens of carp and crucian carp harbored Aer omonas, Enterobacteriaceae and Bacteroidaceae (including Bacteroides t ype A) as predominant intestinal microflora. All fish specimens harbor ed the bacteria with antibacterial abilities. An average of 2.1% of te sted strains exhibited antibacterial activity against the four target strains, but the activity varied with fish species, intestinal segment s and sampling times, along with taxonomic groups of tested bacteria. The target strains were inhibited mainly by the predominant microflora of fish intestines: 3.2-10.3% of strains belonging to Bacteroides typ e A and other Bacteroidaceae inhibited the growth of A. salmonicida AT CC 33658 while 3.1-7.4% of strains of genus Aeromonas exhibited the in hibitory effect against E. coli IAM 1264 and S. aureus ATCC 25923. The se results may suggest that these bacteria affect the composition of i ntestinal microflora of river fish, to some extent, by producing antib acterial substances.