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Biomedical subjects

S Falkow

Publications and source records attributed to S Falkow.

At least 289 records · Page 16Linked to original sources
PubMed1978

Replication of the nonconjugative plasmid RSF1010 in Escherichia coli K-12.

Replicating DNA molecules of the nonconjugative R plasmid RSF1010 (Smr Sur) were cleaved with the EcoRI restriction endonuclease and examined with the electron microscope. Results of this analysis indicated that replication is initiated from an origin located at about 19% of total genome size from one of the EcoRI ends. Replication proceeded either unidirectionally or bidirectionally with equal frequency. Results of the analysis of replicative intermediates of RSF1010 containing the Apr-transposable sequence (Tn) are also presented.

DNA Replication↗
PubMed1978

Analysis of sequences transposed by complementation of two classes of transposition-deficient mutants of Tn3.

The Tn1 and Tn3 elements are closely related transposons which carry the structural gene for ampicillin resistance. Two classes of deletion mutants of the plasmid pMB8::Tn3 (RSF1050) are unable to transpose ampicillin resistance but can be complemented in trans by a coresident Tn1 or Tn3 element. The analysis of the sequences transposed upon complementation of one class of mutants (type I) showed that the mutant element had undergone bona fide transposition. Complementation of the type II mutants led to the transposition of a sequence analogous to bacteriophage mu-promoted integration of non-mu DNA. The transposed sequence consisted of two Tn3 elements which flanked a single copy of the pMB8 portion of the RSF1050 genome. Complementation data indicated that the type II mutants are defective in at least one trans-acting function which must be supplied for transposition to occur. The nature of sequence transposed from the type II mutant is the consequence of a defective cis-acting function (or site). In addition, the type II mutants were defective in a trans-acting function which regulated the frequency of transposition.

Base Sequence↗
PubMed1978

beta-lactamases and R-plasmids of Haemophilus influenzae.

The emergence of resistance to ampicillin and other antibiotics in Haemophilus influenzae has been a relatively recent event. In contrast, drug resistance has been rampant in the Enterobacteriaceae for many years. Ampicillin-resistance in H. influenzae is almost invariably attributable to possession of the TEM (Type III a)beta-lactamase. As is common in other bacteria the gene specifying this enzyme is plasmid-borne in Haemophilus. Some ampicillin-resistant strains of H. influenzae can transfer the TEM beta-lactamase gene to other strains of Haemophilus, to Escherichia coli and to Pseudomonas aeruginosa. The features of such transfer are unusual and lead for example, to the induction of adenine requirement in recipient strains of P. aeruginosa. Crypticity measurements of beta-lactamase activity show that in comparison to P. aeruginosa or E. coli, the outer membrane of H. influenzae affords only a weak penetration barrier to beta-lactam antibiotics. This may have consequences for the stability and distribution of beta-lactamase production in Haemophilus spp. which are discussed. A comparison of the molecular properties of R-plasmids determining a variety of resistances and carried by strains of H. influenzae isolated in diverse geographical locations has revealed unexpected homologies. A series of such plasmids of similar molecular weights (about 30 X 10(6)) differ substantially only in the transposable resistance genes that they carry. A model based on these findings is presented to explain the acquisition of ampicillin- and other resistances by Haemophilus.

Amidohydrolases↗
PubMed1978

In vivo transfer of an Escherichia coli enterotoxin plasmid possessing genes for drug resistance.

Experiments were conducted to study transfer of an enterotoxin (Ent) plasmid from a porcine enteropathogenic Escherichia coli to an E coli K12 strain in the intestine of newly weaned pigs. The Ent plasmid carried genes for resistance to tetracycline, streptomycin, and sulfonamides, thereby permitting a selection for tetracycline-resistant exconjugants in the feces of the pigs. In vivo transfer of the Ent plasmid was demonstrated to occur when the pigs were given large oral inocula of donor and recipient cultures, 1 hour apart. Differences in extent of transfer were not detected in pigs given antibiotic-free feed compared with littermates on feed containing oxytetracycline at 50 g/ton. In one experiment, tetracycline-resistant Ent- exconjugants were found which appeared to have received an R plasmid from an enteropathogenic type of E coli resident in the intestine.

Animals↗
PubMed1977

Deletions affecting the transposition of an antibiotic resistance gene.

The structural gene for plasmid-mediated ampicillin resistance resides upon a 3.2 X 10(6) dalton transposable sequence (TnA) flanked by short inverted repeated sequences that accompany its insertion. TnA was transposed to pMB8, a 1.8 X 10(6) dalton derivative of the colicingenic plasmid ColE1. Random deletions were introduced in the resultant 5 X 10(6) dalton recombinant plasmid by a combination of nuclease treatments in vitro. From this set of deletions a subset was isolated that contained deletions affecting the transposition of TnA. The deletions were mapped by digestion with restriction nucleases and electron microscopic analysis of DNA hetero-duplexes and were found to include one of the inverted repeated sequences or lie in the central portion of TnA. Complementation experiments were attempted between these plasmids and another compatible plasmid carrying a deletion in TnA that abolished its ampicillin resistance. The results of the deletion data indicate that approximately 2 X 10(6) daltons of TnA is required for transposition; the complementation experiments suggest that the terminal inverted repetition and the central region of TnA play different essential roles in TnA transposition.

Crosses, Genetic↗
PubMed1977

Plasmid-mediated beta-lactamase production in Neisseria gonorrhoeae.

Several beta-lactamase-producing, penicillin-resistant strains of Neisseria gonorrhoeae were examined for R plasmids. Penicillin-resistant strains isolated from men returning from the Far East and their contacts contained a 4.4 x 10(6)-dalton plasmid in common. Transformation studies and the isolation of a spontaneous penicillin-susceptible segregant showed that the structural gene for beta-lactamase was part of the 4.4 x 10(6)-dalton plasmid. An additional penicillin-resistant gonococcal strain isolated in London was found to harbor a 3.2 x 10(6)-dalton R plasmid. Deoxyribonucleic acid (DNA)-DNA duplex studies revealed that the penicillin-resistant gonococcal isolates contained a significant portion (about 40%) of the transposable DNA sequence, TnA, which includes the beta-lactamase gene commonly found on R plasmids of the Enterobacteriaceae and Haemophilus influenzae.

DNA, Bacterial↗
PubMed1977

Genetic studies on Neisseria gonorrhoeae from disseminated gonococcal infections.

Isolates from uncomplicated and disseminated gonococcal infections were analyzed by using deoxyribonucleic acid-mediated transformation. Most pairs of auxotrophs could recombine, producing independent transformants. When the constellation of arginine (Arg), hypoxanthine (Hyx), and uracil (Ura) requirements was present in donor and recipient, no recombination for these traits could be detected. Except for Arg to Hyx, no linkage between Arg, Hyx, Ura, penicillin G sensitivity, and serum resistance could be demonstrated. Some distant linkage of Ura to nalidixic acid and rifampin resistances was found. The data show that the traits associated with disseminated gonococcal infection strains are not closely linked but are identical in all strains, indicating a common origin.

Arginine↗
PubMed1977

Evidence for plasmid contribution to the virulence of fish pathogen Vibrio anguillarum.

Analysis of the plasmid deoxyribonucleic acid complement of high- and low- virulent strains of the fish pathogen Vibrio anguillarum showed a correlation between enhanced virulence and the presence of a 50-megadalton plasmid class. All 50-megadalton plasmids isolated from different high-virulent V. anguillarum strains were homologous as judged by the analysis of plasmid deoxyribonucleic acid-deoxyribonucleic acid hybridization. The 50-megadalton plasmid class did not have polynucleotide sequences in common with plasmids of different incompatibility groups.

Base Sequence↗
PubMed1977

Transposition of a plasmid deoxyribonucleic acid sequence that mediates ampicillin resistance: identity of laboratory-constructed plasmids and clinical isolates.

The structural gene for ampicillin resistance resides upon a 3.2 X 10(6)-dalton sequence of deoxyribonucleic acid, TnA that can be transposed from replicon to replicon in laboratory experiments. TnA was transposed from a large conjugative plasmid to a small nonconjugative plasmid, RSF1010. Several RSF1010::TnA plasmids isolated in these laboratory experiments have been shown to be identical to plasmids found in clinical isolates. These data provide direct support to the theory that transposition of drug resistance genes play a key role in the evolution of R plasmids.

Ampicillin↗
PubMed1977

Relationships among some R plasmids found in Haemophilus influenzae.

Tetracycline resistance in a strain of Haemophilus influenzae isolated in the United Kingdom was found to be determined by an apparently non-selftransmissible plasmid of 31 X 10(6) daltons (31 MDal), designated pUB701. Deoxyribonucleic acid hybridization studies indicated that pUB701 shares about 70% base sequence homology with the 30-MDal ampicillin resistance R plasmid RSF007 isolated in the United States from H. influenzae, and 64% sequence homology with the 38-MDal tetracycline and chloramphenicol resistance R plasmid pRI234, isolated in the Netherlands. Heteroduplex studies between RSF007 and pUB701 confirmed the fact that these plasmids were largely homologous, except that pUB701 contained the tetracycline resistance transposon TnD, whereas RSF007 contained the ampicillin resistance transposon TnA. A strain of H. parainfluenzae resistant to both chloramphenicol and tetracycline carried two species of plasmid deoxyribonucleic acid of 2.7 and 0.75 MDal. We were unable to prove that either resistance was plasmid-borne in this strain. Hybridization studies with a [3H]thymine-labeled tetracycline resistance enteric plasmid suggested that the tetracycline transposon was integrated into the chromosome of H. parainfluenzae UB2832. We conclude either that the strains we studied received R factors of the same incompatibility group bearing different resistance genes, or that different resistance genes were translocated to a commom resident plasmid of H. influenzae.

Ampicillin↗
PubMed1977

Molecular characterization of two beta-lactamase-specifying plasmids isolated from Neisseria gonorrhoeae.

The molecular nature of two distinct gonococcal R plasmids, 4.4 X 10(6) and 3.2 X 10(6) daltons, encoding beta-lactamase activity were examined. Both plasmids contained about 40% of the transposable ampicillin resistance sequence Tn2. Deoxyribonucleic acid-deoxyribonucleic acid polynucleotide sequence studies have shown that the two gonococcal plasmids share about 70% of their sequences and are closely related to RSF0885, a 4.1 X 10(6)-dalton plasmid found in a beta-lactamase-producing strain of Haemophilus influenzae. All three of these R plasmids possess a guanine-plus-cytosine content of 0.40 to 0.41 mol fraction and are present as multicopy gene pools in their bacterial hosts.

Base Sequence↗
PubMed1977

Construction and characterization of new cloning vehicles. II. A multipurpose cloning system.

In vitro recombination techniques were used to construct a new cloning vehicle, pBR322. This plasmid, derived from pBR313, is a relaxed replicating plasmid, does not produce and is sensitive to colicin E1, and carries resistance genes to the antibiotics ampicillin (Ap) and tetracycline (Tc). The antibiotic-resistant genes on pBR322 are not transposable. The vector pBR322 was constructed in order to have a plasmid with a single PstI site, located in the ampicillin-resistant gene (Apr), in addition to four unique restriction sites, EcoRI, HindIII, BamHI and SalI. Survival of Escherichia coli strain X1776 containing pBR313 and pBR322 as a function of thymine and diaminopimelic acid (DAP) starvation and sensitivity to bile salts was found to be equivalent to the non-plasmid containing strain. Conjugal transfer of these plasmids in bi- and triparental matings were significantly reduced or undetectable relative to the plasmid ColE1.

Ampicillin↗
PubMed1976

Increased survival in calves of Escherichia coli K-12 carrying an Ent plasmid.

Escherichia coli K-12 strains with and without an Ent plasmid were fed to calves, and the survival of each was monitored by viable bacterial counts of the feces. The E. coli K-12 strain carrying the Ent plasmid survived in the calves at significantly higher levels and for a longer period of time than the E. coli F(-) stain.

Animals↗
PubMed1976

Plasmid-mediated properties of a heat-stable enterotoxin-producing Escherichia coli associated with infantile diarrhea.

The plasmid mediation and transmissibility of heat-stable enterotoxin production and multiple antibiotic resistance have been demonstrated for Escherichia coli O78:K80:H12 epidemiologically incriminated in a hospital outbreak of infantile diarrhea. The conjugal transfer of a 67 X 10(6) - and a 30 X 10(6)-dalton plasmid was associated with the transfer of resistances and enterotoxin production, respectively. Using antibiotics to select E. coli K-12 transconjugants from a one-step bacterial cross, all of the monitored resistances were transferred concurrently, and 36% of the resistant transconjugants produced enterotoxin.

Animals↗
PubMed1976

Molecular nature of two beta-lactamase-specifying plasmids isolated from Haemophilus influenzae type b.

The molecular nature of two beta-lactamase-specifying plasmids isolated from two separate ampicillin-resistant Haemophilus influenzae type b strains was examined. A 30 X 10(6)-dalton (30-Mdal) plasmid (RSF007) had a copy number of approximately 3 per chromosomal equivalent and a mole fraction guanine plus cytosine content of 0.39. By heteroduplex analysis the 30-Mdal plasmid was found to contain the entire ampicillin translocation DNA segment (TnA) found on R factors of enteric origin. A 3.0-Mdal plasmid (RSF0885) was found as a multicopy pool of approximately 28 copies per chromosomal equivalent, had a mole fraction guanine plus cytosine content of 0.40, and contained only about one-third of the transposable TnA sequence. RSF007 and RSF0885 appeared to be unrelated plasmids in that they share base sequence homology only within the confines of the TnA segment. The 3.0-Mdal Haemophilus plasmid was used to transform E. coli to ampicillin resistance but was found to be unstable in this host in the absence of antibiotic. The possibility that R-plasmids arose in Haemophilus by the translocation of TnA from a donor R-factor onto an indigenous H. influenzae plasmid is discussed.

Ampicillin↗