Thoughts of the medical microbiologist on the use of antimicrobial drugs in animals.

The restriction in feed-antibiotics as carried out in our country so far did not lead to the expected decrease of R-factors in the faecal flora of the animals staying in stable. Possible explanations on this subject are given in this report. The question arises whether the best solution to the problem would not be a complex separation of antibiotics used in human medicine from those used in veterinary medicine, as already discussed in the Swann report. A further spreading of plasmids and transposons should be stopped because their influence on the microcosmos is not presumable for the future, especially because R-factors get more and more genes for rising the virulence of their host bacteria.

[Nutritive antibiotic additives in animal feeding stuffs--a further form of environmental pollution (author's transl)]. / Nutritive antibiotika-Zusätze im Tierfutter--eine weitere Form der Umweltverschmutzung.

Feeding domestic animals with mycelia, a by-product of vitamine production, gave rise to the side effect of markedly improved utilization of the fodder. This effect is not due to the vitamine and protein content but to the antibiotic content of this waste product. The nutritive effect was brought about by a larger number of different antibiotics in concentrations which were considerably lower than the therapeutically required doses. Therefore we speak, in this connection, of a nutritive addition of antibiotics to animal fodder. Since at the time of introducing this feeding method only the mutational resistance to antibiotics of pathogens was known and since the nutritive dosaging cannot select such therapeutically relevant degrees of resistance of the germs, no importance was attached to the development of the resistance and its effect on human medicine. However, during the last decade it has been found that the feeding of antibiotics is indeed capable of selecting the plasmidic resistance to antibiotics of the gram-negative intestinal bacteria in the faeces of the animals. For pigs, calves and hens--to quote only the most important animals--now contain a coliflora almost completely studded with R-factors. Owing to the transmissibility of the plasmids and the epidemiologically short path from animal to man, dangers emerge for the human medicine from this nutritive selection. Therefore the use of all antibiotics which select resistance plasmids, should be avoided in animal feed stuffs. It would be best, if antibiotics used in human medicine were not used in veterinary practice.

[Significance of plasmid virulence factors for transmission of nosocomial infection]. / Die Bedeutung plasmidischer Virulenzfaktoren für die Ausbreitung nosokomialer infektionen.

The genetical basis of germ change especially for the gain of the resistance, and virulence plasmids have been treated not only with regard to clinical consequences but also have been classified in their evolutionary importance. Mechanisms of virulence have been illustrated on example of origin of siderophors, the increase of virulence through cytotoxical damage, on the obtained ability of adhesion and colonisation as well as by enhancement of equipment with enzyms. The patient with reduced resistance has been put out as selection condition.

The development of chromosomally coded beta-lactamase production by Escherichia coli after in vitro selection with ampicillin, cefoxitin and ceftriaxone.

Subclones of Escherichia coli K12 921 which produced a chromosomal beta-lactamase were naturally selected in vitro with ampicillin, cefoxitin and ceftriaxone. The selected subclones were identical with respect to beta-lactamase production, resistance spectrum and resistance level, regardless of the selection agent. A ceftriaxone selection following an ampicillin selection led to higher ceftriaxone resistance. The beta-lactamase which was formed hydrolysed ceftriaxone to a measurable extent. After incubation of ceftriaxone with the beta-lactamase, the hydrolysed degradation product was demonstrated by thin-layer chromatography.

R-selection of subbacteriostatic tetracyclin-concentrations.

We investigated the smallest R-factor selecting tetracyclin concentration in a chemostat. All experiments were performed with a miscellaneous culture of three clones of the E. coli K12 921 strain. The first clone was plasmid-free, the second one harboured the R270 (Tc, Su) Inc F II rep and the third one the F'lac-plasmid Inc F I derep. The influence of different tetracyclin concentrations on the development of the viable count of these three clones was investigated in batch and in steady state culture phase. The steady state was kept for about three hours. It served to enforce the selection effect of the antibiotic. A selection effect was already stated with 0.25 microgram Tc/ml. That is to say with 1/10 of the MIC (2.5 micrograms Tc/ml) of the clones used. The importance of these results will be discussed.

[Verification of nosocomial infection chains with Pseudomonas aeruginosa (author's transl)]. / Zur Erfassung nosokomialer Infektketten mit Pseudomonas aeruginosa.

With all 3 typing methods (sero, lyso, pyocin type) errors can arise. The pyocin test following heat curing can be expected to give the least erroneous results. This was demonstrated by a test of 200 non-selected strains which were grown within 4 weeks. The possibility exists that a single patient discharges several different strains simultaneously or in succession. These results must be considered when efforts are made to detect infection chains in a hospital.

Combined effect of intercalating agents and antibiotics on R-factor carrying bacteria in broth culture.

Growth of Salmonella typhimurium LT2 and Escherichia coli K12 bearing any of four R-factors of the fi+ and fi- group in repressed and derepressed form was not inhibited by a combination of ethidium bromide with ampicillin and kanamycin.

[Classification of R-factors. Possible errors and their elimination]. / Klassifizierung von R-Faktoren. Fehlermöglichkeiten und deren Beseitigung.

The necessity for classifying plasmids is emphasized. From our results the uniformity of a nosocomial infectious outbreak is only given by the R-factor and not by the infectious agent. Determination of the appropriate pilus groups by sexphages using the HFRT-system and identification of incompatibility as a further means of subdividing the pilus groups into incompatibility groups is described. A distinction is made between incoming- and resident incompatibility. To eliminate possible errors in plasmid classification the following points are considered: 1. Testing in recombination deficient rec A- -strains of E. coli K12 to avoid any recombination of the plasmids. 2. Trypsin addition to remove the possibility of plasmid coded colicin production. 3. A proper choice of the indicator plasmids. 4. Consideration of the spontaneous loss of the indicator plasmid and also an occurrence of transposons coding for an additional pilus type.

[Hygiene at the treatment area in the dental office]. / Untersuchung zur Hygiene am Patientenstuhl in der Zahnarztpraxis

The state of hygiene in a dental office in the canton of Bern was examined. 22 bacteriological tests were made on the surfaces around the treatment area. Also, the water from the sprays and the most important instruments were tested. Before cleaning and disinfection the test objects showed an average of 110 microorganisms per 100 cm2. The species are enumerated. Particularly infected were polishing brushes, "slurry-water", dentures polished and cleaned with water, also the water from the dental unit. The results show that improvement is badly in need. Also a warning is given for the possible transmission of hepatitis. Female dentists and dental assistants are cautioned to get a german measles vaccination.

[Selection of R plasmid-carrying E. coli pathogens in a mixed population by subinhibitory antibiotic concentrations]. / Selektion R-Plasmid-tragender E. coli-Keime in einer Mischpopulation durch subinhibitorische Antibiotika-Konzentrationen.

The effect of subinhibitory concentrations of tetracyclin, chloramphenicol, gentamicin and ampicillin in a mixed culture of E. coli was investigated in a chemostat in order to determine minimal selection concentration of these drugs. The mixed culture consisted of three clones of E. coli K12 921. One of these clones was plasmid free, one harboured the F'lac plasmid and the third one an R-factor. The antibiotics tetracyclin, chloramphenicol and gentamicin selected the antibiotic resistant R-factor bearing strain at a concentration of 1/10 of the minimal inhibition concentration. Subinhibitory concentrations of ampicillin failed to select the R-factor bearing strain because this strain produced a secreted betalactamase.

A method for typing Listeria monocytogenes strains by classification of listeriocins and phage receptors.

A method for typing Listeria monocytogenes (L.m.) strains was developed which is based on two different approaches. First, strains were classified according to the phage receptors specific to their mitomycin-induced prophages. The frequency of lysogenic strains ranged between 63 and 80%, depending on the serotype. For non-lysogenic strains, a reversed phage-receptor analysis was applied based on the susceptibility of the strains to be typed against bacteriophages from selected, inducible indicator strains. As a second method, typing of mitomycin-induced listeriocins was shown to be practicable as well. By this approach, it was possible to distinguish 11 different listeriocins when using a set of 7 selected indicator strains. Only two of these listeriocins were probably produced by L.m. strains of serotype 4b. A combination of the two approaches described raises the number of types. When applied to 20 human isolates of L.m. belonging to serotype 4b, 17 different types were demonstrated. 46 L.m. strains of serotype 1/2b could be differentiated into 38 types of which 18 clinical isolates represented 17 different types. 26 L.m. strains of serotype 1/2a isolated from various food products showed a large heterogeneity, with 22 different types. The power of discrimination of the method outlined recommends its application in epidemiological investigations.

Haemolytic activity and characteristics of plasmid and chromosomally borne hly genes isolated from E. coli of different origin.

20 hly plasmids of different origin and source and 8 recombinant plasmids containing either chromosomally or plasmid encoded hly determinants were characterized with emphasis on their haemolytic activity. Remarkable differences among the hly genes tested were found in their haemolytic activity and in the regulation of the haemolytic activity by the extracellular iron concentration. Under iron-limiting growth conditions the haemolysin secretion encoded by 6 hly plasmids, but not by the remaining 14 hly plasmids and the chromosomal hly genes, was significantly induced. The 6 plasmids all derived from human isolates, belonged to the incompatibility groups FIV and FVI and showed similar restriction patterns. Two hly determinants, encoding an inducible haemolysin secretion, cloned from plasmids isolated in Berne and Paris, respectively, showed identical restriction maps, indicating a common origin. Compared to the hly determinant of a plasmid encoding a noninducible haemolysin secretion, distinct differences, mainly in the flanking regions, were observed.