558 



FISHERY BULLETIN OF THE FISH ANID WILDLIFE SERVICE 



Table 3. — Morlalily of brown troul foUnwing treatment 

 with sulfonamides and chloramphenicol — Con. 



B. TREATMENT WITH CHLORAMPHENICOL 



[Fish surviving treatment with sulfonamides (3-A) used in this experiment; 

 weight of fish per lot (trough). 1,500 gm.; mean weight per fish, 31 gm.; 

 mean number of fish per lot (trough), 48; no additional infection, with 

 treatment started Sept. 7, 1955; mortality expressed as percent of fish at 

 beginning of each period) 



Period 



Sept. 6-10 



Sept. 11-15 



Sept. 16-20 



Sept. 21-26 



Sept. 26-30 



Total mortality 



Average, total 

 mortality 



Mortality under treat- 

 ment in— 



Lot A Lot C Lot E 



10.0 

 2.2 

 

 

 



12.0 



1.6 











1.6 



1.6 



4.8 



3.3 





 

 

 



Mortality in controls 



Lot B Lot D Lot r 



13 4 



8.9 

 

 

 



21.0 







6.1 

 6 4 

 

 2.3 



6.7 

 6.1 



29.5 



While the results obtained in the treatment of 

 furunculosis caused by sulfonamide-resistant but 

 chloramphenicol -sensitive strains of A. salmonicida 

 are of considerable interest in their own merit, 

 they are presented in this paper chiefly as back- 

 ground information for the history of the majority 

 of the strains of this bacterium which were used 

 in the in-vitro sensitivity tests. Summary 



Table 4. — Sensitivity of 84 strains of A. salmonicitia to 

 stdfonamides tested with sodium sulfadiazine in buffered 

 nutrient broth 



' Cultures in which there was no growth within 24 hours in buffered nu- 

 trient broth having a pH of 8.0 and containing sodium sulfadiazine in the 

 concentration of 1:1,600. 



' Cultures in which there was undiminished growth in nutrient broth 

 containing sodium sulfadiazine in the concentration of 1:100. 



information on the cultures used for testing of 

 the drug sensitivity is presented in table 4. 



Sensitivity tests with antibiotics 



Tests of the sensitivity of Aeromonas salmonicida 

 to various antibiotics were performed with 47 

 strains of the pathogen that were isolated during 

 the summer of 1955 from fingerling brook trout 

 known to be either susceptible or resistant to 

 furunculosis and from fingerling brown trout. 

 Trout from wliicli the bacteria were isolated liad 

 been treated with sulfonamides or chloramphe- 

 nicol, or had served as controls (table 4). Cul- 

 tures of tliese strains were grown on the Leetown 

 standard furunculosis medium on which 6-tipped 

 sensitivity disks containing various antibiotics 

 had been placed (table 5 and fig. 1). All strains 

 of A. salmonicida that were tested were found to 

 be uniform in their response to disks containing 

 antibiotics. No correlation between the sensitiv- 

 ity to antibiotics and sulfonamides was apparent. 



Table 5. — Sensitivity of .\eromonas salmonicida to selected 

 antibiotics as determined with MuUidisks 



Chloromycetin ' 

 Terramycin 2__. 

 Tetracycline... 

 Aureomycin 3.. 

 Erythromycin.. 

 Streptomycin. . 



Neomycin 



Penicillin 



Carbomycin 



Bacitracin 



Polymyxin B. . 



Viomycin 



Furadantin *.,. 



Quantity of antibiotic in 

 disk 



10 ng 



do ... 



do... 



do... 



do... 



do... 



do ... 



1.5 units.. 



6 »ig 



5 units .. 



10 units.. 



10 Mg 



50 (ig 



Width of 

 zones of 

 growth 



inhibition 

 (mm.) 



14-19 



12-14 



10-13 



10-12 



5- 8 



4- 6 



1- 2 



0- 1 



















8-10 



' Chloramphenicol. 



2 Oxvtetracveline. 



3 Chlortctraivi'line. 



< Nitri.fur;inhHn; related to furacin, which has possibilities in the treat- 

 ment of furuiu-ulosis (Outsell 1948). 



Sensitivity tests with sulfonamides 



Tests were run in liquid and solid media. The 

 first liquid substrate tested was the standard 

 furunculosis medium containing serial dilutions of 

 sodium sulfamerazine. The pH of the medium was 

 6.8 to 7.0 and the sulfonamide concentrations 

 ranged from 1 : 100 to 1 : 10,000. Thirty resistant 

 and 10 sensitive strains of A. salmonicida were 

 used. The results were not satisfactory because 

 sensitive strains of A. salmonicida grew as well as 

 the resistant strains. Crystals of sulfamerazine 

 appeared in test tubes with the higher drug con- 

 centrations. Therefore, other liquid media such 



