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J Hacker

Publications and source records attributed to J Hacker.

At least 235 records · Page 13Linked to original sources
PubMed1983

Spontaneous deletions and flanking regions of the chromosomally inherited hemolysin determinant of an Escherichia coli O6 strain.

The hemolytic Escherichia coli strain 536 (O6) propagates spontaneous hemolysin-negative mutants at relatively high rates (10(-3) to 10(-4)). One type of mutant (type I) lacks both secreted (external) and periplasmic (internal) hemolysin activity (Hlyex-/Hlyin-) and in addition shows no mannose-resistant hemagglutination (Mrh-), whereas the other type (type II) is Hlyex-/Hlyin+ and Mrh+. The genetic determinants for hemolysin production (hly) and for mannose-resistant hemagglutination (mrh) of this strain are located on the chromosome. Hybridization experiments with DNA probes specific for various parts of the hly determinant reveal that mutants of type I have lost the total hly determinant, whereas those of type II lack only part of the hlyB that is essential for transport of hemolysin across the outer membrane. Using a probe that contains the end sequence of the plasmid pHly152-encoded hly determinant (adjacent to hlyB), we determined that a related sequence flanks also the hlyB-distal end of the chromosomal hly determinant of E. coli 536. In addition several other similar or even identical sequences are found in the vicinity of the hlyC- and the hlyB-distal ends of both the chromosomal and the plasmid hly determinants.

Base Sequence↗
PubMed1983

Hemolytic Escherichia coli strains in the human fecal flora as potential urinary pathogens.

Hemolysin production is presumed to be a virulence factor in extraintestinal, e.g. urinary tract, infections caused by Escherichia coli. In order to investigate its incidence among the fecal flora, particularly in combination with other presumptive virulence factors, 369 and 373 fecal isolates from Würzburg, FRG and Lima, Peru respectively were examined. 12% of the former and 4% of the latter were hemolytic (Hly+) compared to 33% of 249 E. coli strains isolated from urinary tract infections in Würzburg. In comparison to those which were non hemolytic (Hly-), Hly+ fecal E. coli isolates were associated to a far greater extent with other factors implicated in urinary tract virulence. 41% of these Hly+ strains (cf. 8% Hly-) possessed mannose resistant hemagglutination (MRHA types V, VI, VII). In addition they belonged to the "common O serogroups" O1, O2, O4, O6, O7, O8, O18, O25, O75 in 61% of cases (cf. 25% Hly-) and they possessed K5 antigen in 13% of instances (cf. 2.5% Hly-). The occurrence of these three virulence factors among Hly+ fecal E. coli strains is very similar to that observed among E. coli urinary isolates. One may conclude that these Hly+ fecal strains constitute a "pool" of potential urinary tract pathogens.

Adult↗
PubMed1982

Genetics and pathogenic role of Escherichia coli haemolysin.

While clear evidence exists for the direct involvement of cytolysins in the pathogenesis of Gram-positive bacteria, the significance of Gram-negative haemolysins remains unclear. This paper presents briefly data indicating a role for haemolysin production in infections caused by Escherichia coli and also experiments which have allowed an analysis of the molecular basis of the haemolysis among pathogenic and non-pathogenic strains of this species.

DNA Restriction Enzymes↗
PubMed1982

Cloning of the chromosomal determinants encoding hemolysin production and mannose-resistant hemagglutination in Escherichia coli.

We have cloned the chromosomal hemolysin determinants from Escherichia coli strains belonging to the four O-serotypes O4, O6, O18, and O75. The hemolysin-producing clones were isolated from gene banks of these strains which were constructed by inserting partial Sau3A fragments of chromosomal DNA into the cosmid pJC74. The hemolytic cosmid clones were relatively stable. The inserts were further subcloned either as SalI fragments in pACYC184 or as BamHI-SalI fragments in a recombinant plasmid (pANN202) containing cistron C (hlyC) of the plasmid-encoded hemolysin determinant. Detailed restriction maps of each of these determinants were constructed, and it was found that, despite sharing overall homology, the determinants exhibited minor specific differences in their structure. These appeared to be restricted to cistron A (hlyA), which is the structural gene for hemolysin. In the gene banks of two of these hemolytic strains, we could also identify clones which carried the genetic determinants for the mannose-resistant hemagglutination antigens Vb and VIc. Both of these fimbrial antigens were expressed in the E. coli K-12 clones to an extent similar to that observed in the wild-type strains. These recombinant cosmids were rather unstable, and, in the absence of selection, segregated at a high frequency.

Base Sequence↗
PubMed1978

Total support of the circulation of a patient with post-cardiotomy stone-heart syndrome by a partial artificial heart (ALVAD) for 5 days followed by heart and kidney transplantation.

A patient with acute bacterial endocarditis in whom ischaemic contracture of the left ventricle (stone-heart syndrome) developed during aortic and mitral valve replacement had an emergency implantation of an intracorporeal partial artificial heart (an abdominal left-ventricular assist device of ALVAD). This device functioned as a total artificial heart for nearly 6 days, while a donor heart for transplantation was sought. The ALVAD was then removed, and the patient received allografts of a heart and a kidney. The transplanted heart functioned well, but the patient died 15 days later from gram-negative sepsis. There was no evidence of cardiac or renal allograft rejection.

Acute Disease↗
PubMedDate not supplied

Comparative therapeutic activities of ciprofloxacin, amoxicillin, ceftriaxone and co-trimoxazole in a new model of experimental infection with Escherichia coli.

A new mouse model for systemic infection with Escherichia coli is presented. Whereas in other models 10(7)-10(8) bacteria have to be injected into an animal to induce toxic effects resulting in death within 24 hours, now, only 10(3)-10(4) bacteria of an appropriate strain are required to produce a genuine infection characterized by an increase in the bacterial load over several days. The quantitative determination of bacterial counts per liver allows a more sensitive measurement than recording death rates. Furthermore, few animals are required for a definite result in contrast to the LD50 determination of other models. The salient point regarding this new model is that conditioning of animals has to be achieved by incorporating the inoculum into agar which is injected subcutaneously. The resulting infection is completely dependent on the E. coli strain used. Whereas a hemolytic, uropathogenic strain is so virulent that an overwhelming infection develops within 48 hours after the injection of 10(3) bacterial cells, a non-hemolytic variant of this strain is completely avirulent, being unable to multiply in spite of the potentiating agar. The hemolytic E. coli strain ATCC 25922 is intermediate in virulence. The bacterial counts per liver increase steadily until death occurs five to seven days after the injection of 10(4) bacteria. This bacterial infection can be therapeutically influenced by daily treatment with various drugs. Ciprofloxacin, ceftriaxone and co-trimoxazole are able to cure the infection, whereas amoxicillin given orally is only moderately active against this ATCC strain, which is relatively resistant to amoxicillin.

Amoxicillin↗
PubMedDate not supplied

S-fimbriae mediated adhesion of Escherichia coli to human buccal epithelial cells is age independent.

S-fimbriated Escherichia coli, which cause sepsis and meningitis in the newborn, bind to sialic acid-containing glycoprotein structures on the surface of human buccal epithelial cells. The dependence of this binding on host age was examined. S-fimbriated E. coli adhered in comparable numbers to cells in newborns, infants, children and adults (23.0 +/- 8.6; 23.1 +/- 11.5; 24.7 +/- 7.9; 28.9 +/- 8.8). Thus, the increased susceptibility of neonates to infections caused by S-fimbriated E. coli cannot be explained by enhanced adhesion to epithelial cells.

Age Factors↗
PubMedDate not supplied

Properties of Escherichia coli strains of serotype O6.

Escherichia coli isolates of serotype O6 show a broad spectrum of virulence: virulent strains often cause urinary tract infections; other strains are considered nonpathogenic. In order to analyze the properties of E. coli O6 strains, different phenotypic and genotypic test systems were used. Our data indicate that O6 strains represent a rather heterogenous group of bacteria, which differ in the genotypic presence as well as in the phenotypic expression of virulence factors. In contrast to the isolates 536 (O6:K15) and RZ 475 (O6:K5) the strain DSm 6601, belonging to serotype O6:K5:H1, produces neither toxins nor mannose-resistant hemagglutinating (MRHA) adhesins. However, the strain possesses chromosomally located gene clusters coding for F1C (foc) and type I fimbriae (fim). In addition, the strain secrets the iron-uptake substances aerobactin and enterobactin and produces at least one microcin. The strain is serum-sensitive and is less virulent in in vivo animal tests.

Bacterial Proteins↗
PubMedDate not supplied

The role of macrophages in primary and secondary infection of mice with Salmonella typhimurium.

Elimination of macrophages with high-molecular dextran sulphate (DS) markedly impairs resistance of mice to primary infection with smooth, virulent strains of Salmonella typhimurium, whereas stimulation of this system by killed Bordetella pertussis organisms increases resistance. In infection with rough, avirulent strains of S. typhimurium the elimination of macrophages was not followed by an essential loss of resistance, and it appears that other non-specific defence mechanisms, for example the complement system, may have compensated for the lack of macrophages. Macrophages, therefore, play an important role in defence during primary infection with virulent strains. In immunity to challenge infection with S. typhimurium, macrophages play an even more significant role. Treatment with DS completely removes immunity, and both humoral and cell-mediated immune mechanisms seem to require the participation of macrophages.

Animals↗
PubMedDate not supplied

Nucleotide sequence of the genes coding for minor fimbrial subunits of the F1C fimbriae of Escherichia coli.

F1C fimbriae allow uropathogenic Escherichia coli to adhere to specific epithelial surfaces. This adhesive property is probably due to the presence of minor fimbrial components in F1C fimbriae. The foc gene cluster encoding F1C fimbriae has been cloned, as described previously. Here we present the nucleotide sequence (2081 bp) coding for the F1C minor fimbrial subunits. The structural genes code for polypeptides of 175 (FocF), 166 (FocG), and 300 (FocH) amino acids. The deduced amino acids of the F1C minor subunits were compared with the reported sequences of the minor subunits of other types of fimbriae. The data show that the Foc minor subunits are highly homologous to the corresponding Sfa proteins, whereas homology to the minor subunits of type 1 and P fimbriae is much lower.

Bacterial Adhesion↗
PubMedDate not supplied

Salmonella typhimurium strains carrying haemolysin plasmids and cloned haemolysin genes from Escherichia coli.

Like all other Salmonella typhimurium strains examined, the smooth variants SF1397 (LT2) and 1366 and also their semi-rough and rough derivatives are non-haemolytic. Nevertheless, two haemolysin (Hly) plasmids of E. coli belonging to the inc groups incFIII,IV (pSU316) and incI2 (pHly152) were able to be introduced into these strains by conjugation and stably maintained. A considerable percentage of the Hly+ transconjugants obtained had lost parts of their O-side chains, a result of selection for the better recipient capability of "semi-rough" variants rather than the direct influence of the Hly+ plasmids themselves. In contrast to the incFIII,IV plasmid pSU316, which exhibited higher conjugation rates with rough recipients, the incI2 plasmid pHly152 was accepted best by smooth strains. Transformation with cloned E. coli haemolysin (hly) determinant was inefficient (less than 10(-6)) for smooth strains, but 10(2) - 10(3) times higher for rough recipients, and was increased by the use of Salmonella-modified DNA. The transformants and transconjugants were relatively stable and showed the same haemolytic activity as the E. coli donor strains. The virulence of the Hly+ smooth, semi-rough and rough S. typhimurium strains was tested in two mouse models, and neither the mortality rate nor the ability to multiply within the mouse spleen was influenced by the hly determinants.

Animals↗
PubMedDate not supplied

Molecular analysis of bacterial cytolysins.

Results of molecular and pathogenic studies of three different bacterial hemolysins (cytolysins) are presented. These exoproteins derive from the two gram-negative bacteria Escherichia coli and Aeromonas hydrophila and from the gram-positive pathogen Listeria monocytogenes. The hemolysin of E. coli is determined by an 8-kilobase (kb) region that includes four clustered genes (hlyC, hlyA, hlyB, and hlyD). This hemolysin determinant is part either of large transmissible plasmids or of the chromosome. The genes located chromosomally are found predominantly in E. coli strains that can cause pyelonephritis and/or other extraintestinal infections. A detailed analysis of the chromosomal hyl determinants of one nephropathogenic E. coli strain revealed the existence of specific, large chromosomal insertions 75 kb and 100 kb in size that carry the hly genes but that also influence the expression of other virulence properties, i.e., adhesion and serum resistance. The direct involvement of E. coli hemolysin in virulence could be demonstrated in several model systems. The genetic determinants for hemolysin (cytolysin) formation in A. hydrophila (aerolysin) and L. monocytogenes (listeriolysin) are less complex. Both cytolysins seem to be encoded by single genes, although two loci (aerB and aerC) that affect the expression and activity of aerolysin have been identified distal and proximal to the structural gene for aerolysin (aerA). Cytolysin-negative mutants of both bacteria were obtained by site-specific deletion and/or transposon mutagenesis. These mutants show a drastic reduction in the virulence of the respective bacteria.

Aeromonas↗