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The hemagglutination activity and morphology of antigen K 99 in enterotoxic E. coli strains isolated from calves was studied. It was proven that antigen K 99 is produced not at 18 degrees C, but at 37 degrees C. All K 99+ E. coli strains react with absorbed anti K 99 serum, showing various anti-agglutination titers. The hemagglutination activity of K 99+ E. coli strains is inhibited by absorbed K 99 antiserum. In immunodiffuse tests all K 99+ E. coli strains react by producing a single precipitation line. It is proven electronmicroscopically that on the surface of the bacterial cell of K 99+ E. coli strains is observed a filamentous structure, consisting of numerous fine fibers which give it a fibriform outlook. No such morphological structures are observed in K 99- E. coli strains.

Studied were a total of 220 samples of material taken from the respiratory tract of calves and from fetuses of cows that miscarried for the presence of Haemophilus bacteria. Haemophilus somnus was isolated for the first time in this country from the respiratory tract of calves (10.1 per cent) and from fetuses of cows with abortions (6.2 per cent). Haemophilus somnus was found in calves that had contracted respiratory diseases in 13 per cent of the cases, and in clinically normal calves--in 3.5 per cent of the cases. It was isolated both in pure culture and in mixed culture with P. multocida, M. bovirhinis, M. arginini, V. fetus, and C. pyogenes. As many as 21 strains of Haemophilus somnus were isolated, having the same morphologic, cultural, and biochemical properties characteristic of the species.

Antistrain sera were obtained against cytopathic rotavirus strains isolated from calves as well as against reference rotavirus strains, belonging to I and II serotype of the bovine rotaviruses with which cross antigenic studies were carried out. It was found that the isolated DS 39/82 and TR 248/82 strains belonged to I serotype of the bovine rotaviruses. Data was obtained speaking of some minor antigenic differences between strain TR 248/82 and strain DS 39/82 as well as between strain TR 248/82 and the reference rotavirus strain Lincoln (I serotype), which showed that there existed serologic variants between the strains of this serotype.

The study of 30 strains of Escherichia coli, isolated from calves on various farms of the district of Haskovo, revealed that 70.0% of them manifested resistance to drugs. The capacity of calf E. coli organisms of being donors of resistance factors pointed to the episomal nature of their polyresistance. The comparatively readily effected transmission of drug resistance from E. coli isolated from calves was shown to be potential clinical and epizootic hazard. Such animals proved to be carriers and a source of R+ Escherichia coli organisms. It was found that the transmission of drug resistance was not coupled with the transmission of chromosomal inheritance. A high frequency of the drug-resistance transmission phenomenon was established.

Studied was the dynamic of antibiotic resistance of Escherichia coli strains as isolated from fecal samples taken from 5-day-old calves that had not been offered antibacterial means. The resistance manifested was compared to that of E. coli organisms isolated from calves that had been given antibacterial agents in the course of 36 months as well as to the resistance of E. coli strains isolated from calves at 1, 3, and 5 months of age and from dam cows in the last 12 months of the experiment. A varying period was established for receding of the signs of resistance of the strains to antibiotics--6 months for E. coli to kanamycin and furazolidone, 9 months to tetracycline, chloramphenicol, and gentamycin, and 15 months to streptomycin. Strains isolated from newborn calves on farms with no records of infection were shown to be susceptible to all antibiotics, while those isolated from calves on farms where enteritis was recorded remained polyresistant up to 36 months. No correlation was found between the antibiotic resistance of fecal E. coli strains from the dams and their calves.

A total of five strains of Bacteroides nodosus were isolated from cattle with interdigital dermatitis on a number of farms. With regard to their cultural and morphologic properties and response to carbohydrates these strains did not differ from B. nodosus strains that caused foot rot in sheep. However, their K-antigen was different from the one of the B. nodosus strains isolated from sheep with foot rot as established via the hemagglutination test. No antigenic variations were found with the strains isolated from cattle. The tests with the proteolytic activity of the isolated strains showed that it was considerably lower than the activity of the strains isolated from sheep.

A total of 66 Pseudomonas aeruginosa strains isolated from frozen bull semen were studied with regard to their sensitivity to antibiotics, sulfamides, and furazolidone with the employment of the disk method after Anderson. All strains were found resistant to penicillin, erythromycin, tetracycline, novobiocin, neomycin, kanamycin, chloramphenicol, streptomycin, oleandomycin, spectam, furazolidone, borgal, tylan, oxacillin, and sulfathiazole. Experiments are carried out to find antibiotics that would have good activity against this species of bacteria. The attention is focused on gentamycin, carbenicillin, and rimactan which inhibit the growth of these strains at a minimal suppressive concentration ranging from 1.5 up to 50 microgram/cm3. Regressive lines have been drawn for these antibiotics. It is suggested to use the graphs of the same lines in the rapid determination of the minimal suppressive concentration of gentamycin, carbenicillin, and rimactan against Ps. aeruginosa strains contaminating the semen of bulls.

A study of the psychrotrophic and coliform microflora over the udders of cows was carried out. It was proved that the way and means of cleaning them exercise a great influence on the composition of the psychrotrophic and coliform microflora. The psychrotrophic flora over the udders consisted of 46.9% of specimens of p. Micrococcus, 8.7%-p. Streptococcus, 8.2% Staphylococcus, 7.4%-Corynebacterium, 2.8%-Saccharomyces, 10%-coliform bacteria, 12.5%-psychrophils, mainly of p. Pseudomonas and p. Flavobacterium. The coliform microflora over the udders consisted of 55.4% of p. Escherichia, 20.8%-p. Citrobacter, 16.8%-Klebsiella and 6.9%-p. Enterobacter.

Studied were a total of 58 samples, containing intestinal content of calves that had died of enteritis as well as fecal samples and samples from clinically normal calves. Campylobacter spp. were isolated in 8.8 per cent of the cases. The isolated 5 strains was determined as Campylobacter fetus subsp. intestinalis. This is the first communication on the isolation of Campylobacter spp. in this country.

The study on vaginal mucous secretion in cows with metritis and vaginitis, on fetuses and placentae of cows that had miscarried as well as on preputial secretion of bulls revealed the presence of Mycoplasma organisms associated with V. fetus and other bacterial species. By their reaction to cholesterol, digitonin, sodium polyanetol sulfonate as well as their serum and temperature requirements, the formation of films and spots, their phosphatase activity and biochemical and serologic behaviour the mycoplasmas isolated from the genital tract of cows were specified as A. laidlawii and A. axanthum. From both cows and bulls T-forms of mycoplasmas were isolated. The strains determined as A. laidlawi showed deviations from the species characteristics by the fermentation of glucose, hydrolysis of esculine, and reduction of 2,3,5-triphenyl-tetrazolium chloride.

Electron-microscopic studies were carried out on a concentrated and purified adenovirus type I. It was found that its morphologic aspects were characteristic of the adenovirus group. In the preparations of this virus there were large amounts of incomplete virions and soluble components--hexons, groups of hexons and pentons. Some of the virions were grouped in p-crystal structures or were released as grouped in cell vacuoles. The hexons presented a six-angle contour and a central cavity. The pentons possessed fibre components that were comparatively long. The presence of free pentons spoke of the existence of incomplete hemagglutinins.

Studies were carried out to establish the carrier status and the topographic distribution of Salmonella bacteria in the carcass and organs of healthy pigs and calves. A total of 3980 samples were subjected to investigation (m. gracilis, lymphonodus subilicus, lymphonodus praescapularis, lymphonodi mesenterici, liver bile duct, gallbladder, lymphonodi hepatici, and spleen and samples from caecum content taken from 560 slaughtered normal pigs), and a total of 2400 samples (m. gracilis, caput longum of m. triceps brachii, lymphonodus praescapularis, lymphonodus subilicus lymphonodi hepatic, lymphonodi mesenterici, gallbladder, spleen, heart, and kidney and samples from the caecum content taken from 200 slaughtered normal calves. The investigations were carried out with methods routinely employed in the microbiological science and practice with special reference to Salmonella bacteria. It was found that 4.29 per cent of the slaughtered healthy pigs were carriers of Salmonella organisms, 10 serotypes of the groups B, C1, C2, D and E1 of Salmonellae being isolated. Most frequently isolated serotypes in a descending order were: S. anatus, 7 strains; S. cholerae suis, 6 strains; S. derby, 5 strains; S. agona, 4 strains; S thompson and S. dublin, 2 strains; and S. essen, S. lille, S. kottbus, and S. enteritidis, 1 strain. The highest percent of Salmonellae in the slaughtered normal pigs was found in the caecum content (3,75%). No Salmonellae were found in the samples from the slaughtered 200 normal calves and the muscle and carcass lymph node a samples taken from the investigated 560 pigs.

A study was carried out on E. coli strains eliminated in the Pleven District. It was proved that 19.4% of the strains were enteropathogenic. The enteropathogenic E. coli provoked dilatation of the ligated intestinal segments. All enteropathogenic E. coli proved positive for K 99 antigen. For the non-enteropathogenic E. coli K 99 antigen was not proved. The enteropathogenic E. coli strains referred to the serotypes O 101, O 8, O 9 and O 11, whereas the non-enteropathogenic ones referred to the serotypes O 78, O 35, O 117, O 26, O 111 and O 86. The strains under consideration were not haemolytic. The prevailing part were sensitive to kanamycin, ampicillin, spectam, medium sensitive to streptomycin and slightly sensitive to furazolin and erythran. No differences were proved with regard to sensitivity both of enteropathogenic and nonenteropathogenic E. coli strains to antibiotics.

Etiological, clinical, and epizootiological studies were carried out with newborn calves on two cow complexes of 500 animals each, raised under industrial conditions. Virologic and bacteriologic investigations of a total of 300 fecal samples taken from both calves and dams on the day of calving up to the 10th day as well as on the 20th and 30th day revealed that in 90 per cent of the cases there were rotaviruses. With calves that remained with the cows up to the 72nd hour 30 to 50 per cent of the rotaviruses were found from the second to the tenth day, and with calves that were separated from their dams immediately after calving rotaviruses were found at more advanced age too. Bacteriologically, as many as 92 strains of Escherichia coli were established as isolated from the fecal samples studied. Antigen K99 was demonstrated with 3.26 per cent of the strains. It was concluded that both with regard to the numbers of the E. coli strains isolated and to the period during which these were found the bacterium prevailed in calves that did not suck directly from their dams in the first days following calving.

The manose-resistant hemagglutination activity of 272 E. coli strains isolated from calves sick or dead of colibacteriosis, 43 of which were enteropathogenic, was assessed. Strain enteropathogeneity was determined after the method of Smith and Halls (1967). It was established that 38 (88.3%) of the 43 enteropathogenic strains cause full or partial hemagglutination of horse or pig erythrocytes. Manose-resistant hemagglutination was not observed in the non-enteropathogenic E. coli strains. Manose-resistant hemagglutination of enterotoxic E. coli strains is in relation with their enteropathogeneity.

Investigated was the microflora of various objects contributing to the contamination of veal during the process of its production. It was found that the main sources of primary contamination of the carcass surface with microorganisms are the hair coat, residual mud on the hoofs, intestinal contents of the calves for slaughter, the slaughter premise itself (walls, floor, air), tools used in slaughter (knives, axes for cutting open), clothing for work as well as the hands of the workers. The microbial contamination of the objects studied during work proved strong, in some cases the log value of the total count of organisms for some of them reaching up to 8.90, of the psychrophiles--up to 7.91, of the coliform bacteria--up to 7.04, of the moulds and yeasts--up to 6.08. Disinfection with 1 per cent water solution of Vosfasteril lowered the contamination of the objects studied by more than 99 per cent. The detergent used produced a high bactericidal effect and could successfully be employed at the meat producing enterprises throughout the country.

Escherichia coli strains were isolated from calves and were biochemically and serologically identified in terms of their sensitivity to antibiotics. An exclusively high frequency of sensitivity was established to sulfonamides (100 per cent), tetracicline, erythromycin, oleandomycin (86.6 per cent) ampicillin, and streptomycin (70 per cent). Well expressed was their sensitivity to nitrofurans, canamycin, neomycin, and polymyxin. It was demonstrated through serial dilutions that there exists a high level of resistance to sulfanilamides, oleandomycin, erytromycin, tetracycline, streptomycin, chloramphenicol (more than 512 mug/cm3). The prevalence of such polyresistand E. coli strains in calves is the reason for concern in the district of Haskovo.