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E. coli strains isolated from urinary specimens of patients suffering from pyelonephritis can be defined as uropathogenic by the following entities: production of hemolysins, adhesins and hydroxamates, serum resistance, capsule formation and specific O: H antigenes. The presence of these properties do not coincide with the carriage of specific plasmids encoding these functions. Moreover, using the plasmid pattern analysis identical uropathogenic clones distributed among the patients investigated could not be detected. These data point to the facts that in spite of specific marker combinations which give rise to uropathogenicity, a full range of different biological qualified strains occur. The clinical significance of these strains remain to be elucidated.

The formation of IncM plasmid encoded pili is dependent on the incubation temperature of the corresponding host strains. By labelling the short, rigid M pili with the donor specific bacteriophage luminal diameter M, the presence of pili at 30 degrees C but not at 37 degrees C incubation temperature could be demonstrated for E. coli K12 substrains carrying different IncM group plasmids. In contrast, such a temperature dependence of M pilus formation is not observed in S. typhimurium substrains.

The streptothricin resistance transposons Tn1825 and Tn1826 are closely related, based on physical and genetic characteristics, to the trimethoprim resistance transposon Tn7. These transposons may be considered to be members of a transposon family sharing in common the transposition functions and a basic streptomycin/spectinomycin resistance determinant but differing from one another with respect to particular additional resistance genes inserted to the left of the aadA gene.

The determination of clonal identity of bacterial isolates of Salmonella, in particular epidemiological important serovars of Salmonella, is an unequivocal prerequisite for the study of the epidemic process of salmonellosis. This is demonstrated for the serovar S. typhimurium by means of classical as well as molecular methods for epidemiological subdifferentiation.

More than 30 conjugative R plasmids between 60 and 70 Md in size were identified in wild type strains of Enterobacteriaceae isolated in German Democratic Republic, Bulgaria, Mongolia, Poland, Ethiopia, Iraque, and Soviet Union. They have been characterized by means of several genetic and molecular techniques as members of a new incompatibility group, termed IncZ. The properties of these plasmids including digestion pattern after EcoRI treatment demonstrate a phylogenetic relatedness.

14 conjugative plasmids originated from different bacterial hosts and geographical sources were identified as members of the incompatibility group IncX with R6K as the reference plasmid. In spite of their close genetic relatedness (transfer and incompatibility properties), their molecular sizes ranged between 39 and 77 kb and DNA fingerprinting with endonucleases such as EcoRI, EcoRV, BamHI, BglI, BglII, PstI and SalI revealed a great variety of fragment patterns.

The diagnostically and in regard to surveillance rather comprehensively recorded salmonellosis bear the character of a model of zoonotic diarrhoeal diseases. Whereas those serovars predominantly adapted to human beings or animal species are without any importance in this connection, such serovars with own epizootic processes in different animal species with or without causing illness are able to be transferred to human beings via foods of animal origin and to act as etiological agents of gastroenteritis. Some strains of them equipped by special properties often encoded by plasmids can be transferred from man to man, too. In GDR in 1987 S. enteritidis (34.0%), S. typhimurium (17.9%), S. manhattan (7.7%) and S. agona (7.4%) amounted to two thirds of all the salmonella isolates in connection with human enteritis. For analyzing epizootic-epidemic processes in the case of rare serovars the identity of serovars is sufficient in first approximation, in the case of frequently isolated serovars the complex typing of the concerned strains by using epidemiological laboratory methods is required.

Following the employment of trimethoprim/sulfonamid and gentamicin in the general clinical praxis transferable plasmids with respective resistance function were identified at first in enteric bacteria from sewage before they could be detected in patient strains. Whereas the trimethoprim resistance plasmids represent different incompatibility groups (C, FII, I5, K, M, N, S, U) the gentamicin resistance plasmids are very similar IncM members of 62 MD in size. Therefore a clonal distribution of a particular gentamicin resistance plasmid has to be taken into consideration.

The spread of particular clones of S. sonnei throughout the territory of the German Democratic Republic within one year was evaluated by means of plasmid pattern analysis of the bacterial isolates. Such epidemic clones are described by their "clone formulae" comprising the phage type, biotype, colicinogenotype, antibiogram and the plasmid pattern type. They were not observed before 1982, but potential progenitor strains could be identified as having occurred sporadically in the years before. The additional application of plasmid pattern analysis revealed a better discrimination of the epidemic distribution of distinct bacterial clones than the use of conventional methods such as phage-typing, biotyping and colicinogenotyping only.

The analysis of heteroduplexes between EcoRI digested DNA derived from IncM plasmids in the transfer-off and in the transfer-on state revealed an internal loop of about 1 kbp on a distinct large EcoRI fragment. The presence of an invertible element (Min) is suggested which enables the formation of conjugative pili at 30 degrees C, but switches off the pilus formation at 37 degrees C incubation temperature.

Natural isolates of Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, and Providencia stuartii were analysed to determine their plasmid content. This data allowed the identification of nosocomial strains of K. pneumoniae and P. stuartii and helped in the differentiation of epidemic strains of E. coli 0111 and S. typhimurium. Phenotypically similar isolates of S. typhimurium could be shown to be of independent origin using plasmid pattern analysis. The dissemination of a particular plasmid through different strains of S. typhimurium resulted in a simulation of a very widely distributed epidemic strain, because the plasmid interfered with the phage type of its host strain in addition to determining resistance properties. Plasmid pattern analysis disclosed two independently existing but interacting epidemic processes: a bacterial 'epidemic' strain may become disseminated over a large territory and may predominate there for a long time; a single plasmid, however, may also become distributed through many different bacterial strains and may spread over a large territory. Plasmid pattern analysis provides a valuable and universal epidemiological laboratory method.

Salmonella typhimurium strains isolated in the German Democratic Republic between 1972 and 1980 mainly belong to phage type n.c.1/72/n.c. and biochemotype b. Nearly all of these strains are characterized by an identical basic plasmid pattern. Thus, they may be considered to be independent isolates of the same epidemic strain. Moreover, some multiple drug resistant offsprings of that epidemic strain have been characterized by their carriage of an additional IncH-1 R plasmid. However, a few strains of phage type n.c.1/72/n.c. were found to differ fundamentally in their plasmid patterns from that of the epidemic strain. The phage pattern of these strains is determined by a conjugative R plasmid belonging to the incompatibility group IncI4. Despite of the same phage- and biochemotype these strains must be considered non-related with the epidemic strain, therefore. The analysing of the plasmid pattern of bacterial strains turns out to be an important contribution to the investigation of epidemic processes.

Five conjugative plasmids governing different antibiotic resistance patterns were identified in wild strains of enteric bacteria isolated in Czechoslovakia and the G.D.R. between 1976 and 1979. They have been characterized as members of the new incompatibility group IncU (reference plasmid RA3 from Japan). The molecular sizes of the IncU plasmids ranged between 18 and 37 megadaltons; their restriction fragment patterns indicated them to be distinct types.

In 50 Escherichia coli strains obtained from the bladder puncture urine of patients with chronic pyelonephritis, determinations of virulence properties were performed. All of the E. coli strains isolated from 26 acute episodes of pyelonephritis were found in the smooth form. 30% possessed K 1 antigen, 77% showed the ability to form hemolysin and 30% produced colicin V (aerobactin). Fimbriae (detected by mannose-resistant hemagglutination) were registered in 81%, and plasmids ranging between 50 and 70 Md were demonstrated in 70% of the bacteria. In contrast to this, only 70% of the E. coli strains isolated from 24 patients at an inactive stage of pyelonephritis were found in the smooth form; 10% of these encoded K 1 antigen, 20% hemolysin and 10% colicin V. Plasmids in the range 50 to 70 Md could be found in 30%. On the basis of multivariate analysis of variance and discriminant analysis, it was confirmed that uropathogenic strains possess several virulence properties, mannose-resistant hemagglutination being of particular importance.

A total of 1800 S. typhimurium strains isolated in different regions of the USSR in 1968-1979 were studied. Of these strains, 68.6% were resistant to 6-8 antibiotics, 7.8% were resistant to 2-5 antibiotics, and 23.6% proved to be resistant to all antibiotics. The number of multiresistant strains sharply increased during the last 10 years. The strains isolated from different sources and in different epidemic situations considerably differed in their sensitivity to the action of antibiotics. The infective agents isolated from the hospital foci of salmonellosis were found to possess the maximum multiresistance. The study of the genetic nature of multiresistance showed that the multiresistance strains had a conjugative R-plasmid with resistance determinants CmTc, type Fin+, incompatibility group F1me. The phage typing of the strains with phages from the collection of the Tbilisi Research Institute for Vaccines and Sera revealed that these strains belonged to phagotype 2. The problems of the relationship between the biological properties of causative agents and the character of the epidemic process of the diseases caused by these agents are discussed.