R plasmids with thermosensitive transferability in Salmonella strains isolated from humans.

Temperature dependence of transfer was examined with ten R plasmids originating from clinical isolates of Salmonella. Six of the plasmids were thermosensitive upon transfer, five of which were originally harbored in S. typhimurium and the remaining one in S. derby. One of these plasmids, pNR502, which conferred resistance to kanamycin, streptomycin (Sm) and tetracycline (Tc) on its host was stably maintained both in Salmonella and Escherichia coli at either 30, 37, or 43 C. Another plasmid, pNR516, which was resistant to chloramphenicol, sulfathiazole, Sm and Tc, was slightly unstable only at 43 C. The remaining four plasmids, pNR503, pNR510, pNR512 and pNR514, conferred resistance to Sm and Tc. Of these plasmids, the former two were stably maintained at both 30 and 37 C, but were unstable at 43 C. The latter two were slightly unstable at the lower temperatures and considerably unstable at 43 C. Kinetics of the transfer of the plasmid pNR503 revealed that the efficiency of transfer of the plasmid between E. coli strains was affected not only by the temperature of the conjugation but also by the preincubation temperature of the donor culture before the conjugation.     

Conjugative R plasmids isolated from hospital strains of Pseudomonas aeruginosa]

It was shown that Pseudomonas aeruginosa hospital strains isolated from patients and environment in the Republican Centre of Burns in Tbilisi contained conjugative R plasmids. The plasmids were marked pM15 and pM19, respectively. The plasmid pM15 determined resistance to carbenicillin, kanamycin and tetracycline and plasmid pM19 determined resistance to carbenicillin, kanamycin, tetracycline, chloramphenicol, gentamicin and streptomycin. Plasmid pM15 had a molecular weight of 45.8 MD and seven sites for EcoRI, six sites for HindIII and five sites for Hpa-I-restrictase. This plasmid, as others, belongs to the Inc-P1 incompatibility group.     

Drug resistance and R plasmids in Escherichia coli strains isolated from broilers

In 1978, 1,021 Escherichia coli strains were isolated from 105 field broilers (F) and 1,058 strains from 106 broilers in a zootechnical experiment station (Z), and their drug-resistance patterns and the presence of conjugative R plasmids were compared. The resistance markers examined were tetracycline (TC), chloramphenicol (CM), streptomycin (SM), sulfonamides (SA), kanamycin (KM), and ampicillin (APC). The populations of individuals that excreted resistant strains were 100% in F and 58% in Z. Frequencies of isolation of drug-resistant strains among the total isolates were 93% in F and 36% in Z, indicating that the resistant strains are a rather high proportion of the intestinal flora in F but are slightly less prevalent in Z. The resistance pattern to (TC.SM.SA.KM) was seen at the highest frequency in both groups. Conjugative R plasmids were demonstrated more frequently in field broilers (F). The results reflect the wide use of antibiotics in the livestock industry, resulting in the appearance of drug-resistant strains mostly due to the presence of R plasmids.     

Properties of the R plasmids of Sh. flexneri strains isolated in Bulgaria]

The study of 3,237 Sh. flexneri strains isolated in Bulgaria revealed that 50.72% of them were resistant to antibiotics. 95.88% of the antibiotic-resistant strains were found to have R factor of incompatibility groups F, I or N. The plasmids of incompatibility group F had the property fin+, and the plasmids of groups I and N had the property fin-. R plasmids were divided into 4 groups by their ability for phage restriction.     

IncH plasmids in Escherichia coli strains isolated from broiler chicken carcasses.

Plasmids conferring tellurite resistance were transferred at low temperature (27 degrees C) from Escherichia coli strains isolated from chicken carcasses at the time of slaughter and after storage. They belonged to group IncH, as evidenced by their large molecular weight and incompatibility with plasmid pIP233. E. coli strains contaminating chickens meat can thus represent a source of IncH plasmids in the food chain of humans.     

Cryptic plasmids in Lactobacillus strains isolated from the murine gastrointestinal tract.

Ten of twenty Lactobacillus strains isolated from the gastrointestinal tracts of animals of several species contained plasmids of 80 to 90 megadaltons or less than 2.6 megadaltons in size, as analyzed by agarose gel electrophoresis. The large plasmids were found only in strains originally isolated from the keratinized epithelium of the murine stomach.     

Mobilization of the Proteus morganii chromosome by R plasmids

Mutants of Pseudomonas aeruginosa PAC1 which could grow on L-threonine were isolated. These mutants, like the parent strain, synthesized a biosynthetic threonine deaminase, but its apparent Km value for threonine was higher than that of the enzyme from strain PAC1. These mutants also synthesized an inducible NAD-dependent threonine dehydrogenase, which was not present in the parent strain. No threonine aldolase activity could be detected. The results suggest that the threonine deaminase with lowered affinity for L-threonine, together with L-threonine dehydrogenase, enabled these mutants to utilize L-threonine as the sole source of carbon for growth.     

Conjugal transfer of R plasmids to and from Enterobacteriaceae isolated from sewage.

The potential of the transfer of natural plasmids between sewage strains has been studied. In vitro transfer was conducted at 37 degrees C in tryptone soya broth and sterile raw sewage as mating media. In situ transfer was carried out in sterile raw sewage within membrane diffusion chambers at 10.6 degrees C. When the recipient was a laboratory strain of Escherichia coli K-12, the in situ frequency values were significantly lower (P less than 0.001) than those obtained in vitro for the same mating pair. When the laboratory recipient was replaced with recipients from the same sewage source, frequency values decreased progressively from the optimum conditions to the most adverse. However, in situ frequency values were higher than those for the same donors mated with a laboratory recipient.     

Patterns of mobilization of the Proteus mirabilis chromosome by R plasmids.

R plasmids R40a, Rip69, R447b, R769 belonging to incompatibility groups A-C, M, N, V, respectively, were investigated for chromosomal mobilizing ability in Proteus mirabilis. Plasmids R40a, Rip69 and R447b mediated polarized transfer of markers in a clockwise direction from origins near tyr-1, metF and ser-2, respectively, on the linkage map. The recovery frequency per donor cell of proximal markers approached 1 x 10(-4) for these three plasmids and the efficiency of chromosomal transfer was higher than that of the previously studied plasmid D. The plasmid-guided chromosomal trajectories overlap and it was possible to complement results obtained with plasmid D to assemble a time-of-entry chromosomal map and directly establish the circularity of the linkage group. The map comprises a length of 93 min in terms of transfer time. Plasmid R769 had a different pattern of chromosome transfer. This plasmid produced recombinants for all markers at frequencies of about 4 x 10(-6) per donor. It effected multiple and more or less simultaneous entry of markers and produced recombination over lengths of chromosome rarely corresponding to more than 10 min on the linkage map.     

Hemagglutinating properties of Proteus mirabilis strains isolated from clinical specimens

Haemagglutinating properties of 345 P. mirabilis strains isolated from various clinical samples were determined. Red blood cells of different origin as human group 0, bovine, horse, sheep and rat were used for the study. For the detection of MS and MR/P haemagglutinins the haemagglutination reaction was run with and without D-mannose. On the other hand, for the detection of type MR/K haemagglutinins tanned human and bovine erythrocytes were used. The majority of tested strains (90.14%) was polyhaemagglutinating i.e. showed simultaneously the presence of two or three haemagglutinins. Only three strains of P. mirabilis (0.87%) did not agglutinate any of the erythrocytes used for the study. The majority of strains (95.83-100%) in specific groups of clinical materials showed the presence of MR/K+ while MR/P+ 45.45-93.75% of strains and MS+ 45.83-73.1% of tested strains. Out of P. mirabilis strains isolated from urine, faeces and blood the highest percentage possessed at the same time all three haemagglutinin types (MS+, MR/K+, MR/P+) or pattern MR/K+, MR/P+. Bronchial isolates had usually pattern MR/K+ (31.82%) and strains isolated from skin possessed haemagglutinins of pattern MR/K+, MR/P+ (50%) and MS+, MR/K+, MR/P+ (43.75%). Among strains expressing MR/P+ at 37 degrees C a great differentiation of spectrum activity against tested erythrocytes was seen. Undoubtedly, the majority of MR/P+ strains from specific groups of clinical materials (with the exception of urine) agglutinated sheep and horse erythrocytes with and without D-mannose. The majority of strains isolated from urine agglutinated sheep and bovine erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

R plasmids in environmental Vibrio cholerae non-O1 strains.

The occurrence of drug resistance and its plasmid-mediated transferability was investigated in 140 environmental strains of Vibrio cholerae non-O1 and 6 strains of Vibrio cholerae, both O1 and non-O1, of clinical origin. Of the 146 strains tested, 93% were resistant to at least one drug and 74% were resistant to two or more antibiotics. The O1 strains were susceptible to all antibiotics used. A total of 26 of 28 selected resistant wild strains carried R plasmids that were transferable by intraspecific and intergeneric matings. The most common transmissible R factor determined resistance to ampicillin, amoxicillin, and sulfanilamide (30%), followed by resistance to ampicillin and amoxicillin (13%) and resistance to ampicillin, amoxicillin, phosphomycin, and sulfanilamide (9%). Comparison of the three methods of plasmid analysis showed that the method of Birnboim and Doly (Nucleic Acids Res. 7:1513-1523, 1979) without EDTA and lysozyme was optimal for isolation of both large and small plasmids in environmental V. cholerae strains. Most strains harbored more than one plasmid, and the molecular sizes ranged from 1.1 to 74.8 megadaltons. The plasmids of high molecular size (around 74 megadaltons) were responsible for the resistance pattern transferred and were maintained with high stability in the hosts.     

Urinary pathogenicity of Proteus mirabilis strains isolated from faeces or urine

Urinary and faecal isolares of Proteus mirabilis were studied with respect to a number of bacterial properties as possible virulence factors in the pathogenesis of urinary tract infections: experimental virulence in a mouse model, haemolysin production, haemagglutinating properties, hydrophobicity of the bacterial surface, sensitivity to the bactericidal effect of human serum, serotype and cell invasiveness. Urinary isolates were slightly more virulent than faecal isolates in the mouse model. No other significant differences were found between both groups. So urinary strains seem to be selected from the faecal reservoir mainly on the basis of their prevalence in the faeces and not on the basis of the possession of particular virulence factors.     

Molecular comparisons of plasmids isolated from colicinogenic strains of Escherichia coli

The plasmid content of 14 colicinogenic strains of Escherichia coli has been examined. Four strains contained miniplasmids (1.2-2.0 kb). Small plasmids (4-7 kb) were detected in all the strains specifying group A colicins (colicins A, E1, E2, E3 and K; group I plasmids). Larger plasmids (55-130 kb) were detected in seven out of nine strains specifying group B colicins (colicins B, H, Ia, Ib, M, V and S1; group II plasmids). DNA-DNA hybridization with group II plasmids showed a wide variation in the degree of DNA sequence homology among its members. In contrast little (if any) DNA sequence homology was detected with the group I plasmids when the same group II plasmid DNAs were used as hybridization probes. The results of DNA-DNA hybridization studies with the two small group II plasmids (pcolG-CA46 and pcolD-CA23) suggested that these plasmids are equivalent to deleted forms of larger group II plasmids. Our hybridization data thus support the division of colicin plasmids into the two groups (I and II) that have been previously defined from genetic and physiological studies.     

Cryptic plasmids in Lactobacillus strains isolated from the murine gastrointestinal tract

Ten of twenty Lactobacillus strains isolated from the gastrointestinal tracts of animals of several species contained plasmids of 80 to 90 megadaltons or less than 2.6 megadaltons in size, as analyzed by agarose gel electrophoresis. The large plasmids were found only in strains originally isolated from the keratinized epithelium of the murine stomach.     

IncH plasmids in Escherichia coli strains isolated from broiler chicken carcasses

Plasmids conferring tellurite resistance were transferred at low temperature (27 degrees C) from Escherichia coli strains isolated from chicken carcasses at the time of slaughter and after storage. They belonged to group IncH, as evidenced by their large molecular weight and incompatibility with plasmid pIP233. E. coli strains contaminating chickens meat can thus represent a source of IncH plasmids in the food chain of humans.     

Influence of plasmids on bacterial susceptibility to the bactericidal activity of sera. I. Characteristic of R plasmids of enteropathogenic strains of Escherichia coli isolated from clinical cases

The 47 enteropathogenic Escherichia coli strains isolated from the cases of infant diarrhoea were characterized from the point of view of antigenic structures and drug resistance. Six R plasmids were obtained from these strains and were tested for protective activity of E. coli K12 W 1485 against lethal action of sera. Out of three sera tested, the investigated plasmids showed the most evident protective activity upon lethal action of neonatal serum. One of the plasmids appeared even more efficient than R100.1.     

Conjugal transfer of R plasmids to and from Enterobacteriaceae isolated from sewage

A. FERNANDEZ-ASTORGA, A. FERNANDEZ DE ARANGUIZ, M. POCINO, A. UMARAN AND R. CISTERNA. 1992. The potential of the transfer of natural plasmids between sewage strains has been studied. In vitro transfer was conducted at 37°C in tryptone soya broth and sterile raw sewage as mating media. In situ transfer was carried out in sterile raw sewage within membrane diffusion chambers at 10.6°C. When the recipient was a laboratory strain of Escherichia coli K-12, the in situ frequency values were significantly lower ( P < 0.001) than those obtained in vitro for the same mating pair. When the laboratory recipient was replaced with recipients from the same sewage source, frequency values decreased progressively from the optimum conditions to the most adverse. However, in situ frequency values were higher than those for the same donors mated with a laboratory recipient.     

Cryptic plasmids isolated from Campylobacter strains represent multiple, novel incompatibility groups

Three small, cryptic plasmids from the multi-drug-resistant (MDR) Campylobacter coli strain RM2228 and one small, cryptic plasmid from the MDR Campylobacter jejuni strain RM1170 were sequenced and characterized. pCC2228-1 has some similarity to Firmicutes RepL family plasmids that replicate via a rolling-circle mechanism. pCC2228-2 is a theta-replicating, iteron-containing plasmid (ICP) that is a member of the same incompatibility (Inc) group as previously described Campylobacter shuttle vectors. The other two ICPs, pCC2228-3 and pCJ1170, represent a second novel Inc group. Comparison of the four plasmids described in this study with other characterized plasmids from C. jejuni, C. coli, C. lari, and C. hyointestinalis suggests that cryptic plasmids in Campylobacter may be classified into as many as nine Inc groups. The plasmids characterized in this study have several unique features suitable for the construction of novel Campylobacter shuttle vectors, e.g., small size, absence of many common multiple-cloning site restriction sites, and Inc groups not represented by current Campylobacter shuttle plasmids. Thus, these plasmids may be used to construct a new generation of Campylobacter shuttle vectors that would permit transformation of environmental Campylobacter isolates with an existing repertoire of native plasmids.