EFFECT OF PASSAGE THROUGH THE INTESTINAL-TRACT OF DETRITIVORE EARTHWORMS (LUMBRICUS SPP) ON THE NUMBER OF SELECTED GRAM-NEGATIVE AND TOTAL BACTERIA

Laboratory experiments were carried out to investigate the fate of bac teria during and after passage through the intestinal tract of detriti vore earthworms. Earthworms (Lumbricus spp.) were fed with cattle dung inoculated 7 days previously with one of five different Gram-negative bacteria. Bacterial concentrations were determined 2 days later in du ng and soil, and in gut material from different parts of the earthworm intestinal tract. A high percentage (28-82%) of the total bacteria (e pifluorescence direct counts) in the earthworm gut content was cultura ble. The concentration of total heterotrophic aerobic bacteria did not vary significantly among the five different bacterial additions and t he non-inoculated control. In earthworm casts the number of total hete rotrophs per gram dry matter (2.1 x 10(9)) was higher than in soil (1. 7 x 10(8)), but lower than in the dung (1.5 x 10(10)). The test-bacter ia, however, showed different survival patterns along the earthworm in testinal tract. The concentrations of Escherichia coli BJ18 and Pseudo monas putida MM1 and MM11 in earthworm casts were lower than in the in gested dung, while concentrations of Enterobacter cloacae A107 and Aer omonas hydrophila DMU115 in dung and casts were similar. Ent. cloacae, and to a minor extent E. coli, were reduced in numbers by several ord ers of magnitude in the pharynx and/or crop. In the hind gut, however, the concentration of Ent. cloacae had increased to the same level as in the ingested dung, while the concentration of E coli remained low. Our observations indicate that the bacterial flora of ingested food ma terials changes qualitatively and quantitatively during gut transit.