The influence of antibiotics and sulfa drugs on Bacillus larvae, cause of American foulbrood of the honeybee, in vitro and in vivo.

American foulbrood is a disease of the larvae of the honeybee caused by a sporeforming organism, Bacillus larvae White (1920), and is considered the most serious of all bee diseases. The unusual resistance of the spores to heat and disinfectants (White, 1920; Sturtevant, 1926; Burnside, 1940) has resulted in the development of a variety of methods for control based on their effectiveness in destroying these spores. The burning of diseased and contaminated material has been univerally accepted as the most efficacious of these methods, although it is a costly procedure. For this reason the recent announcement of the use of sulfa drugs in controlling American foulbrood (Haseman and Childers, 1944) was of great interest to beekeepers. These drugs not only prevented the development of the disease but also resulted in strengthening colony morale to the extent that the bees cleaned out all evidence of the disease (dead larvae, scale) from the hive. However, when feeding of the drugs was discontinued, the disease recurred (Eckert, 1947; Johnson, 1947, 1948; Johnson and Stadel, 1946; Milne, 1947; Reinhardt, 1947). This raised many problems concerning the effect of sulfa drugs on the vegetative cells and spores of Bacillus larvae. Attempts to use antibiotics such as penicillin to control American foulbrood in the apiary have not been on the whole successful (Johnson, 1947; Katznelson and Gooderham, 1949). Experiments with antibiotics and sulfa drugs were therefore initiated to determine their bacteriostatic effect on Bacillus larvae, in vitro and in the apiary, and to obtain some information as to the mode of action of the drugs in the larva. It has already been demonstrated by Katznelson and Gooderham (1949) that para-aminobenzoic acid reverses the effect of sulfathiazole in the apiary. No attempt will be made to review the literature on the influence of sulfa drugs and antibiotics on bacteria as this has already been done exhaustively (Henry, 1943; Northey, 1948; Waksman, 1947).