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M Achtman

Publications and source records attributed to M Achtman.

At least 91 records · Page 5Linked to original sources
PubMed1985

Antibodies to O-antigen of lipopolysaccharide are protective against neonatal infection with Escherichia coli K1.

Monoclonal IgM specific for the O18 antigen conferred passive protection to 1-week-old rats against bacteremia and killing after oral challenge with O18:K1 Escherichia coli. Specific protection of the pups was also achieved by immunizing the pregnant rats with purified O18 lipopolysaccharide. We suppose that most human newborns that are colonized by potentially invasive K1 E. coli are protected by the transplacental transfer of anti-lipopolysaccharide immunoglobulin G, and we suggest that treatment with such antibodies might in the future be considered a therapeutic option. Rat serum from 1-week-old animals had only about one-third of the complement hemolytic activity of adult rat serum. This low level of hemolytic activity correlated with a relatively poor bactericidal activity in antibody-dependent and antibody-independent bactericidal in vitro assays. Monoclonal anti-O18 immunoglobulin M, although protective in vivo and bactericidal when added to adult rat serum, only poorly inhibited the multiplication of O18:K1 cells in serum from 1-week-old rats. This suggests that other elements of host defense besides complement participate in antibody-mediated in vivo protection.

Agglutination Tests↗
PubMed1984

Lipopolysaccharide, capsule, and fimbriae as virulence factors among O1, O7, O16, O18, or O75 and K1, K5, or K100 Escherichia coli.

K1, K5, and K100 Escherichia coli isolates of the lipopolysaccharide antigen types O1, O7, O16, O18, or O75, which had formerly been assigned to clonal groupings were compared with K? E. coli isolates and with laboratory-derived mutants defective in capsule or lipopolysaccharide synthesis. The amount of K1 capsule, the length distribution of the lipopolysaccharide, and the expression of type I and P fimbriae were determined. The clonal groupings were uniform with regard to these properties within each group but different from each other. Many of the K? strains differed from the clonal representatives. The results are interpreted with regard to the different diseases caused by each of these bacterial groups.

Cell Membrane↗
PubMed1984

Degree of antibody-independent activation of the classical complement pathway by K1 Escherichia coli differs with O antigen type and correlates with virulence of meningitis in newborns.

A total of 95 K1 Escherichia coli strains of the O (lipopolysaccharide) serotypes O1, O7, or O18 had been analyzed previously for the ability to cause bacteremia after colonizing the gut of newborn rats. In this study, these strains were tested for their resistance to the bactericidal activity of rat serum. All strains that had caused bacteremia in a high percentage of the inoculated rats were able to survive for several hours in 90% adult rat serum. With only a few exceptions, O7:K1 and O18:K1 strains were serum resistant and virulent, whereas O1:K1 strains were serum sensitive and avirulent. Serum sensitivity was due to the classical complement pathway. K1 strains of all three O serotypes were resistant to the alternative complement pathway. O7:K1 and O18:K1 cells were killed efficiently after the classical pathway was triggered by specific antilipopolysaccharide antibodies. However, killing of O1:K1 bacteria by the classical pathway system did not require antibodies. Isolated O1-lipopolysaccharide fixed complement more efficiently than did isolated O7- or O18-lipopolysaccharide, suggesting that the differences in the chemical structure of the O antigens are responsible for the observed differences in complement sensitivity. In combination with epidemiological data, the results indicate that antibody-independent classical pathway activation provides an important defense mechanism for newborns against certain gram-negative infections.

Antigens, Bacterial↗
PubMed1984

Conservation of plasmids among Escherichia coli K1 isolates of diverse origins.

Escherichia coli K1 isolates of various O types were previously assigned to different clonal groups. Members of the two clones defined by membrane pattern 9 (MP9) and serotypes O18:K1 and O1:K1 had been found to be very similar to each other. The plasmid contents of these bacteria confirmed this conclusion. Both groups carried a self-transmissible plasmid of the FI incompatibility group that coded for colicin production and a major outer membrane protein called the plasmid-coded protein (PCP). The size of this plasmid varied from 76 to 96 megadaltons, but restriction endonuclease digestion and DNA heteroduplex analysis revealed that these plasmids were highly related. O18:K1 bacteria of MP6 had previously been determined to represent a subclone, related to but different from O18:K1 MP9 bacteria. These MP6 bacteria carried a different, smaller IncFI plasmid which did not code for colicin production or the PCP protein. This smaller plasmid was primarily related to the larger plasmid within the regions of DNA encoding incompatibility, replication, and conjugation. O1:K1 bacteria of MP5 contained other unrelated plasmids in agreement with the previous conclusion that they are unrelated to O1:K1 bacteria of MP9. The bacteria examined had been isolated from two continents over a time span of 38 years, and the results attest to conservative inheritance of plasmids within bacteria of common descent.

DNA Restriction Enzymes↗
PubMed1983

Escherichia coli strains binding neuraminyl alpha 2-3 galactosides.

A total of 46 E. coli strains showing mannose-resistant, P-blood-group independent hemagglutination of human erythrocytes were tested for binding to neuraminic acid. Nine of the strains completely lost their hemagglutination activity after the erythrocytes were treated with neuraminidase. To characterize the receptor structure, different neuraminic acid containing glycoproteins, their desialylated derivatives and neuraminyl oligosaccharides were tested for hemagglutination inhibition. These studies showed that the nine strains had binding specificity for alpha 2-3 linked neuraminic acid.

Carbohydrate Conformation↗
PubMed1983

Six widespread bacterial clones among Escherichia coli K1 isolates.

Variable properties among Escherichia coli isolates include serotype, electrophoretic migration of major outer membrane proteins, metabolic properties, production of hemolysin or colicin or both, and plasmid content. These characteristics were compared in E. coli strains of capsular types K1, K5, K92, and K100 and in non-encapsulated isolates. The 234 bacterial strains from the United States and Europe which we studied had been isolated from healthy or diseased individuals recently or as long ago as 1941. Regardless of source, most O7:K1, O16:K1, and O75:K100 isolates could be assigned to three unique, serotype-specific groups, which were interpreted as representing three bacterial clones. Two bacterial (sub)clones each were discerned among the O18:K1 and O18:K5 isolates, and two further, distinct clones were discerned among the O1:K1 isolates. The implications of these results for epidemiological analyses and for virulence are discussed.

Cell Membrane↗
PubMed1983

Induction of bacteremia in newborn rats by Escherichia coli K1 is correlated with only certain O (lipopolysaccharide) antigen types.

A total of 95 Escherichia coli strains (O1:K1, O7:K1, or O18:K1), obtained from different sources of human infections and from healthy individuals, were analyzed for the ability to cause bacteremia after colonizing the gut of newborn rats. Strains of all three serotypes were able to multiply extensively in the gut after oral inoculation and to translocate (in small numbers) to the mesenteric lymph nodes. With only few exceptions, O7:K1 and O18:K1 strains were able to cause bacteremia, while O1:K1 strains could not. Mixed-infection experiments revealed that the bacteria present in the blood during a case of bacteremia are in most cases the descendants of one cell that has multiplied extraintestinally after translocation to the mesenteric lymph nodes. It appears that virulent O7:K1 and O18:K1, but not avirulent O1:K1, bacteria are able to multiply directly in the bloodstream of the newborn rats. No correlation between virulence and the source of isolation of the different strains was observed. Disease isolates thus do not seem to differ from fecal isolates of the same serotype in special virulence properties. The differences in virulence among different O serotypes of K1 E. coli observed in the rat model were comparable to their relative frequency of isolation from meningitis in newborn children.

Animals↗
PubMed1983

Role of the capsule and the O antigen in resistance of O18:K1 Escherichia coli to complement-mediated killing.

Epidemiological data show that O18:K1 Escherichia coli is a common cause of neonatal bacteremia and meningitis. These bacteria were capable of multiplying in the bloodstream of newborn rats and were resistant to the bactericidal effects of complement in the absence of specific antibodies. The roles played by the O antigen and the K antigen in complement resistance were analyzed by comparing the bactericidal effects of normal sera and of sera deficient in various complement components or in immunoglobulins. These sera were tested on O18:K1 bacteria and on mutants lacking either the lipopolysaccharide O antigen or the K1 capsular polysaccharide. In addition, O1:K1 cells, which can cause pyelonephritis but which are rare in newborn meningitis and which do not multiply in the bloodstream of newborn rats, were also examined. Different mechanisms of protection against the alternative and classical pathways were recognized: K1-positive cells were resistant to the bactericidal activity of sera deficient in classical complement pathway components, whereas K1-negative cells were sensitive to these sera. Based on these results and on those from complement fixation assays, the K1 sialic acid polysaccharide impedes the activation of, and thus protects the bacteria against, the alternative complement pathway. Not only the K1-negative mutant cells but also O1:K1 bacteria and mutants lacking the O18 oligosaccharide repeating units of the lipopolysaccharide were sensitive to the classical complement pathway. These bactericidal effects were observed even in the absence of specific antibodies. It is proposed that both the K1 capsule and the O18 oligosaccharide restrict antibody-independent classical pathway activation by shielding deeper structures on the cell membrane that are capable of activating this pathway.

Animals↗
PubMed1982

Analysis of the promoter-distal region of the tra operon of the F sex factor of Escherichia coli K-12 encoded by EcoRI restriction fragments f17, f19, and f2.

The promoter-distal region of the tra operon of the F sex factor Escherichia coli K-12 was analyzed, using the chimeric plasmid pRS31, which contains the F EcoRI restriction fragments f17, f19, and f2 cloned into the EcoRI site of pSC101. A series of deletion plasmids of pRS31, extending increasing distances from a site in f17 through f19 and ending in f2, were isolated. These plasmids were examined by heteroduplex analysis with the parent DNA, and a restriction map of this region of DNA was constructed. A series of Tn5 insertion derivatives of pRS31 were also isolated and mapped, using both heteroduplex analysis and restriction mapping. Both the insertion and deletion mutants were tested in minicells for the synthesis of radioactively labeled proteins. This allowed the identification of the individual gene products and mapping of the genes. The result is a saturated physical map of this region of DNA from fragment f17 through to the IS3 insertion sequence near the promoter-distal end of f2.

Bacterial Proteins↗
PubMed1982

Promoter-distal region of the tra operon of F-like sex factor R100 in Escherichia coli K-12.

The distal region of the tra (transfer) operon of F-like plasmid R100 was investigated, using small plasmids derived from R100, primarily the plasmid pSM6. The transposon Tn5 (which confers kanamycin resistance) was inserted at different positions into pSM6, and the transposition derivatives were tested for ability to complement defined tra mutants of the F sex factor. Thus, the tra genes traH, G, T, and D were localized on the plasmid R100. A restriction map of pSM6 was constructed, and the locations of the insertions were mapped, using restriction endonuclease digestion of the plasmid DNA and exploiting the fact that several restriction sites are localized in the inverted repeat regions of the transposon. The gene products of the genes traG, S, T, and D were identified by radioactive labeling of proteins synthesized in minicells carrying the various insertion plasmids followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The presence of another transfer gene, traI, was inferred from these data. Another protein, the r2-A protein, was also identified, and its gene was mapped. On the basis of the data, a best-fit physical map of this region of the tra operon of R100 was constructed. The results confirmed that the general order and size of the distal transfer genes is as in the F sex factor, but showed that differences exist with respect to all of the gene products. The significance of these differences are discussed in the light of the genetic and physical homology (Manning et al., J. Bacteriol. 150:76-88) of the transfer regions.

Bacterial Proteins↗
PubMed1981

traG protein of the F sex factor of Escherichia coli K-12 and its role in conjugation.

The traG protein of the F sex factor is an inner membrane protein with a molecular weight of 116,000. Mutants in traG (or in traN) are able to trigger conjugal DNA replication even though they cannot efficiently form stable mating aggregates with F(-) cells. The traG protein (and the traN protein) probably acts in the donor at the stabilization stage of conjugation.

Bacterial Proteins↗
PubMed1981

sfrA and sfrB products of Escherichia coli K-12 are transcriptional control factors.

The mechanisms whereby mutations in Escherichia coli K-12 genes sfrA and sfrB reduce expression of the transfer functions of sex factor F have been examined by assaying the levels of tra messenger ribonucleic acid and of tra proteins. The sfrA product was necessary for efficient transcription of the control gene traJ and, directly or indirectly, for transcription of the traY leads to Z operon. In the absence of sfrA, reduced levels of the traJ and traT proteins were observed in the outer membrane. The sfrB product was needed to prevent premature transcription at one or more rho-dependent termination sites. sfrB mutations also reduced synthesis of full-length lipopolysaccharide molecules, of several chromosomally determined outer membrane proteins, and of functional flagella. Thus, the sfrB product may act as an antiterminator in transcription of several operons encording cell envelope components.

Bacterial Proteins↗
PubMed1980

Outer membrane of Escherichia coli: properties of the F sex factor traT protein which is involved in surface exclusion.

The traT protein (TraTp) of the F sex factor is the product of one of the two genes involved in surface exclusion. Several detergents were examined under different conditions in order to determine their ability to solubilize TraTp from membrane vesicles. These experiments showed that TraTp behaved similar to a number of peptidoglycan-associated outer membrane proteins and that it existed in multimeric aggregates within the membrane. However, unlike other major outer membrane proteins, the amount of TraTp incorporated into the membrane was not affected by lipopolysaccharide-deficient mutants, even when mutants totally lacking the neutral sugars in their lipopolysaccharide backbone were used. TraTp wqs also examined by two-dimensional gel electrophoresis, where it ran as a discrete spot with a very basic isoelectric point. By coupling cyanogen bromide-activated dextran onto whole cells and by labeling whole cells with 125I (via lactoperoxidase), it was shown that TraTp was exposed on the cell surface. TraTp in a membrane environment was also insensitive to proteolytic attack by trypsin.

Bacterial Proteins↗
PubMed1979

The control region of the F sex factor DNA transfer cistrons: physical mapping by deletion analysis.

A technique has been developed which allows the isolation of random deletions extending from unique restriction enzyme sites in plasmid DNA molecules. The method involves transformation of E. coli cells with linear plasmid DNAs generated by restriction enzyme cleavage. We have used this technique to map DNA transfer genes in the tra control region of F sex factor DNA. Deletions within EcoRI fragment f6 of F DNA have been isolated and used to assign physical locations to tra genes by a combination of genetic complementation tests, restriction enzyme analysis, DNA heteroduplexing and the analysis of the proteins synthesised in minicells and in vitro. Deletion analysis has also allowed the identification of the traK gene product.

Bacterial Proteins↗
PubMed1979

Export without proteolytic processing of inner and outer membrane proteins encoded by F sex factor tra cistrons in Escherichia coli minicells.

Most tra proteins encoded by the Escherichia coli F sex factor are incorporated into the minicell envelope. We have now assigned the tra proteins to cytoplasm (TraIp and 2b), inner membrane (TraEp, TraMp, and TraSp), and outer membrane (6e, TraAp, TraBp, TraJp, TraKp, TraLp, and TraTp). two proteins, TraDp and 6d, were associated with both inner and outer membranes. The proteins exported to the inner or outer membranes did not undergo proteolytic cleavage (processing) whereas beta-lactamase was processed normally.

Cell Membrane↗