I n a previous paper (MACUCH et al. 1967) we described the transferability of tetracycline resistance in strains of Escherichia coli isolated from a pig farm near Bratislava. However, in a field survey of strains of E . coli from another farm, distant far from the first one, a series of E. coli strains was isolated with certain different properties including defectivity of lactose fermentation in some of them which defect could be used for their differentiation. All strains isolated were tetracycline resistant, but, so far, no strain with transferable tetracycline resistance (out of 39 checked) was isolated from this place. A great deal of these strains was colicinogenic. We studied the properties of T-determinants and of colicinogenic factors and their mutual relations in some collected strains of this series.
Material and methodsStrains: We selected two clones of lactose non-fermenting strains coded 1 H 100 and 1 H 101 as representatives of one group of strains, i. e . those producing colicines. They were signed as Tr (tetracycline-resistant), T F -(transfer factor negative), Col+. The strain 1 H 103 was a representative of colicine non-producing strains and therefore i t was Tr, TF-, Col-. Owing to their tetracycline resistance, the strains were given the symbols 1 H 100 T, etc.As donor or recipient strains in the crosses with the above mentioned strains we used the typical lactose fermenting strains 2 H 101 (Ts, TF+, Col+), 2 H 102 (Ts, TF+, Col-), 2 H 106 (Ts, TF-, Col+) and a strain of E. coli, lactose fermenting, from the above mentioned series of strains, coded 1 H 122 T (Tr, TF-. Col-).I n so called triple-tests, developed by ANDERSON (1965) for the detection of naturally occurring transfer factor (TF) in enterobacteria, following strains were used as interrnediary recipients: Salmonella typhimurium coded 12 H 123 S (TF-) and S. typhimuriutu 12 H 126 K (TF-). They are resistant t o streptomycin and t o canamycin, respectively, but their R-determinants are non transferable (owing to lack of a transfer factor) but mobilizable, i. e. extrachromosomal.The crosses with strains E. coli 1 H 100 etc. were performed exactly according to AKDER-SON and LEWIS (1965). As recipient strains, S. typhimuriunz 12 H 124 Nx (nalidixic acid-resistant), E. coli 12 H 125 Nx and S. typhimurium 12 H 126 K were used alternatively.The production of colicines was estimated according t o ~M A R D A (1965) in the following way: The strain to be tested was inoculated as 4-5 hours broth culture in the middle of each of four plates and grown for additional 24 hours a t 37 "C. The culture was devitalized by chloroform vapours and overflown with 5-7 ml of 0.4% agar to which t,he respective indicator strain was added at 45 "C. After 12 hours incubation t,he plates were read the first time, and the zone of inhibition in the layer of the indicat~or strain was measured in millimeters. The second reading was made after further 12 hours.As indicator strains five colicine-sensitive strains of E. coli were used: KO. 185, No. 2147, I < *
