STUDIES ON AMERICAN FOUL BROOD OF BEES: THE RELATIVE PATHOGENICITY OF VEGETATIVE CELLS AND ENDOSPORES OF BACILLUS LARVAE FOR THE BROOD OF THE BEE

Abstract

THE discovery that American foul brood was a distinct disease caused by a spore-forming bacillus was first made by White (B), though Maassen (4), working independently, came to the same conclusion shortly afterwards. White termed the causal organism Bacillus larvae, and this designation was subsequently accepted by Maassen. Maassen (4) produced American foul brood in colonies of bees by feeding them pure cultures of B.larvae, but it is not clear whether his cultures contained only the vegetative cells of this organism or the spores as well. Later@) he found that B. larvae rapidly loses virulence and ability to form spores when cultivated for some time on laboratory media. w h i t e ( 1 3 ) produced American foul brood by feeding spore-containing brood filtrate or eggagar cultures of B. larvae to the bees of healthy colonies, but he does not record that disease was produced by feeding the vegetative cells of this organism alone. He also found that direct inoculation of larvae with cultures of the causal organism rarely produced the disease. In France, Toumanoff(ll) failed in his attempts to produce American foul brood by individual feeding of the young larvae of a healthy colony of bees with large numbers of the vegetative cells of B. larvae, and Chalmers(1) also experienced difficulty in infecting colonies with pure cultures of this organism. Sturtevant(7) showed that, normally, a healthy colony of bees will not contract American foul brood unless the bees are fed at least 50 million spores of B. larvae, obtained from the scales of dead larvae, in 1 litre of sugar syrup. In his experiments individual larvae did not contract the disease unIess they were fed 10 million or more spores of this organism in 0.01 C.C. of a p p .When considered collectively, the above results indicate that the vegetative cells of B. Zurvae do not cause American foul brood readily, if at all; that the spores of this species are effective in producing the disease only when introduced in large numbers into healthy colonies; that the

Medium Promoting Sporulation of Bacillus larvae and Metabolism of Medium Components

“…About 3% of all bee colonies inspected in the United States are infected with B. larvae (20). It was recognized early (22) that only spores are able to transmit the disease. The spores germinate in the midgut of the bee larvae, and the resulting vegetative cells invade the hemocoel, where they grow in the hemolymph to very large populations (1,17,18,24).…”

Growth Factor Requirements ofBacillus larvae, White

“…Later, Lochhead (1937) found an otherwise similar medium, in which turnip extract is used instead of carrot extract, to support rather better growth of B. larvae in the routine examination of suspected combs for this organism. Tarr (1937) found a modification of the brood filtrate medium more satisfactory for obtaining large numbers of spores than other media on which B. larvae sporulates with difficulty. He (1938) also devised a chicken embryo medium which proved suitable for the germination of the spores of B. larvae.…”

Bacillus larvae: its Cultivation in vitro and its Growth in vivo

“…The vegetative forms of B. larvae that reached the gut epithelium were unable to penetrate the tissues, a t least of the larvae that were not ejected by nurse bees, and most of them were probably voided in the faeces when the larvae pupated. These vegetative forms are of no further consequence because they cannot infect more larvae (Tarr, 1937) even if they could survive desiccation in the larval faeces. A few organisms presumablyremain in the gut and invade the aerobic tissues where they can multiply and sporulate, probably when the gut epithelium changes to the adult type during pupation.…”

“…Extract of larval honey-bees (White, 1907), unheated egg yolk (White, 1920) and egg yolk +yeast + carrot-extract + peptone (Sturtevant, 1932) are usually fairly suitable media but only when inoculated with many million spores (Tarr, 1937). A medium containing glucose, peptone and thiamine with trace elements (Lochhead, 1942) is sometimes satisfactory and becomes more reliable with added soluble starch or after treatment with activated charcoal (Foster, Hardwick & Guirard, 1950).…”