scholarly journals Bacterial killing in gastric juice – effect of pH and pepsin on Escherichia coli and Helicobacter pylori

2006 ◽  
Vol 55 (9) ◽  
pp. 1265-1270 ◽  
Author(s):  
H. Zhu ◽  
C. A. Hart ◽  
D. Sales ◽  
N. B. Roberts

The susceptibility of Escherichia coli and Helicobacter pylori to pH and the effect of pepsin-mediated proteolysis were investigated. This was to establish the relative importance of their bacterial killing properties in gastric juice. Solutions in the pH range 1.5–7.4 with or without pig pepsin A were used, together with seven gastric juice samples obtained from patients undergoing routine gastric collection. Escherichia coli C690 (a capsulate strain), E. coli K-12 (a rough mutant) and Helicobacter pylori E5 were selected as the test organisms. Suspensions of bacteria (1×106 E. coli ml−1 and 1×108 H. pylori ml−1) were pre-incubated with test solutions at 37 °C for up to 2 h, and then cultured to establish the effect on subsequent growth. Survival of bacteria was diminished at pHs of less than 3.5, whereas killing required a pH of less than 2.5. Pre-incubation with pig pepsin at 0.5, 1.0 and 2.0 mg ml−1 at pH 3.5 reduced viable counts by 100 % for E. coli 690 and E. coli K-12 after 100 min incubation. With H. pylori, the viable counts decreased to 50 % of the control after 20 min incubation in 1 mg pepsin ml−1 at pH 2.5, 3.0 and 3.5. The gastric juices showed bactericidal activity at pH 3.5, and the rate of killing was juice dependent, with complete death of E. coli 690 occurring between 5 and 40 min post-incubation. Thus, killing of E. coli and H. pylori occurs optimally at pHs of less than 2.5. At pH 3.5, little effect is observed, whereas addition of pepsin alone or in gastric juice causes a marked increase in bacterial susceptibility, suggesting an important role for proteolysis in the killing of bacteria.

2018 ◽  
Vol 13 (7) ◽  
pp. 1934578X1801300 ◽  
Author(s):  
Subrat Kumar Bhattamisra ◽  
Chew Hui Kuean ◽  
Lee Boon Chieh ◽  
Vivian Lee Yean Yan ◽  
Chin Koh Lee ◽  
...  

The antibacterial activity of geraniol and its effect in combination with ampicillin, amoxicillin and clarithromycin against Staphylococcus aureus, Escherichia coli and Helicobacter pylori was tested. The minimum inhibitory concentrations (MICs) and combinatory effects of geraniol against the bacteria were assessed by using the modified broth microdilution and checkerboard assay, respectively. The combinatory effect is expressed as fractional inhibitory concentration index (FICI). The MIC of geraniol against S. aureus, E. coli and H. pylori was found to be 11200, 5600, and 7325 μg/mL, respectively. A significant synergistic effect was observed with geraniol and ampicillin against S. aureus with FICI in the range 0.19 to 0.32. Geraniol and ampicillin exhibited a partial synergistic effect against E. coli. A similar effect was observed with geraniol and clarithromycin against S. aureus. A partial synergistic effect was observed with clarithromycin and geraniol against H. pylori with the FICI value in the range 0.86 to 0.89. An additive effect was observed with geraniol and amoxicillin combination against H. pylori. However, the amoxicillin and clarithromycin dose was reduced by thirty-two fold when combined with geraniol against H. pylori. The anti- H. pylori effect of geraniol with clarithromycin and amoxicillin could be of potential interest in the treatment of H. pylori infection and associated ulcers in humans. Further, geraniol, in combination with other antibiotics, has substantial therapeutic potential against S. aureus and E.coli infection.


2005 ◽  
Vol 187 (11) ◽  
pp. 3708-3712 ◽  
Author(s):  
Lisa Nonaka ◽  
Sean R. Connell ◽  
Diane E. Taylor

ABSTRACT Tetracycline resistance in clinical isolates of Helicobacter pylori has been associated with nucleotide substitutions at positions 965 to 967 in the 16S rRNA. We constructed mutants which had different sequences at 965 to 967 in the 16S rRNA gene present on a multicopy plasmid in Escherichia coli strain TA527, in which all seven rrn genes were deleted. The MICs for tetracycline of all mutants having single, double, or triple substitutions at the 965 to 967 region that were previously found in highly resistant H. pylori isolates were higher than that of the mutant exhibiting the wild-type sequence of tetracycline-susceptible H. pylori. The MIC of the mutant with the 965TTC967 triple substitution was 32 times higher than that of the E. coli mutant with the 965AGA967 substitution present in wild-type H. pylori. The ribosomes extracted from the tetracycline-resistant E. coli 965TTC967 variant bound less tetracycline than E. coli with the wild-type H. pylori sequence at this region. The concentration of tetracycline bound to the ribosome was 40% that of the wild type. The results of this study suggest that tetracycline binding to the primary binding site (Tet-1) of the ribosome at positions 965 to 967 is influenced by its sequence patterns, which form the primary binding site for tetracycline.


2004 ◽  
Vol 186 (22) ◽  
pp. 7704-7713 ◽  
Author(s):  
Josephine Kang ◽  
Don Tavakoli ◽  
Ariane Tschumi ◽  
Rahul A. Aras ◽  
Martin J. Blaser

ABSTRACT Recombination is a fundamental mechanism for the generation of genetic variation. Helicobacter pylori strains have different frequencies of intragenomic recombination, arising from deletions and duplications between DNA repeat sequences, as well as intergenomic recombination, facilitated by their natural competence. We identified a gene, hp1523, that influences recombination frequencies in this highly diverse bacterium and demonstrate its importance in maintaining genomic integrity by limiting recombination events. HP1523 shows homology to RecG, an ATP-dependent helicase that in Escherichia coli allows repair of damaged replication forks to proceed without recourse to potentially mutagenic recombination. Cross-species studies done show that hp1523 can complement E. coli recG mutants in trans to the same extent as E. coli recG can, indicating that hp1523 has recG function. The E. coli recG gene only partially complements the hp1523 mutation in H. pylori. Unlike other recG homologs, hp1523 is not involved in DNA repair in H. pylori, although it has the ability to repair DNA when expressed in E. coli. Therefore, host context appears critical in defining the function of recG. The fact that in E. coli recG phenotypes are not constant in other species indicates the diverse roles for conserved recombination genes in prokaryotic evolution.


2005 ◽  
Vol 389 (2) ◽  
pp. 541-548 ◽  
Author(s):  
Rajesh K. Soni ◽  
Parul Mehra ◽  
Gauranga Mukhopadhyay ◽  
Suman Kumar Dhar

In Escherichia coli, DnaC is essential for loading DnaB helicase at oriC (the origin of chromosomal DNA replication). The question arises as to whether this model can be generalized to other species, since many eubacterial species fail to possess dnaC in their genomes. Previously, we have reported the characterization of HpDnaB (Helicobacter pylori DnaB) both in vitro and in vivo. Interestingly, H. pylori does not have a DnaC homologue. Using two different E. coli dnaC (EcdnaC) temperature-sensitive mutant strains, we report here the complementation of EcDnaC function by HpDnaB in vivo. These observations strongly suggest that HpDnaB can bypass EcDnaC activity in vivo.


Gene ◽  
1999 ◽  
Vol 239 (2) ◽  
pp. 351-359 ◽  
Author(s):  
Mutsunori Shirai ◽  
Ryutaro Fujinaga ◽  
Junko K Akada ◽  
Teruko Nakazawa

2002 ◽  
Vol 68 (2) ◽  
pp. 981-984 ◽  
Author(s):  
Katherine H. Baker ◽  
John P. Hegarty ◽  
Brady Redmond ◽  
Nathan A. Reed ◽  
Diane S. Herson

ABSTRACT The susceptibility of Helicobacter pylori to disinfectants was compared to that of Escherichia coli. H. pylori is more resistant than E. coli to chlorine and ozone but not monochloramine. H. pylori may be able to tolerate disinfectants in distribution systems and, therefore, may be transmitted by a waterborne route.


2001 ◽  
Vol 69 (9) ◽  
pp. 5914-5920 ◽  
Author(s):  
Catherine S. Beckwith ◽  
David J. McGee ◽  
Harry L. T. Mobley ◽  
Lela K. Riley

ABSTRACT Helicobacter hepaticus causes disease in the liver and lower intestinal tract of mice. It is strongly urease positive, although it does not live in an acidic environment. The H. hepaticus urease gene cluster was expressed in Escherichia coli with and without coexpression of the Helicobacter pylori nickel transporter NixA. As for H. pylori, it was difficult to obtain enzymatic activity from recombinant H. hepaticus urease; special conditions including NiCl2supplementation were required. The H. hepaticus urease cluster contains a homolog of each gene in the H. pyloriurease cluster, including the urea transporter gene ureI. Downstream genes were homologs of the nik nickel transport operon of E. coli. Nongastric H. hepaticusproduces urease similar to that of H. pylori.


2005 ◽  
Vol 187 (5) ◽  
pp. 1710-1715 ◽  
Author(s):  
John Klena ◽  
Pei Zhang ◽  
Olivier Schwartz ◽  
Sheila Hull ◽  
Tie Chen

ABSTRACT The dendritic-cell-specific intercellular adhesion molecule nonintegrin (DC-SIGN) CD209 is a receptor for Escherichia coli K-12 that promotes bacterial adherence and phagocytosis. However, the ligand of E. coli for DC-SIGN has not yet been identified. In this study, we found that DC-SIGN did not mediate the phagocytosis of several pathogenic strains of E. coli, including enteropathogenic E. coli, enterohemorrhagic E. coli, enterotoxigenic E. coli, and uropathogenic E. coli, in dendritic cells or HeLa cells expressing human DC-SIGN antigen. However, we showed that an outer core lipopolysaccharide (LPS) (rough) mutant, unlike an inner core LPS (deep rough) mutant or O-antigen-expressing recombinant of E. coli K-12 was phagocytosed. These results demonstrate that the host cells expressing DC-SIGN can phagocytose E. coli in part by interacting with the complete core region of the LPS molecule. These results provide a mechanism for how O antigen acts as an antiphagocytic factor.


Genetics ◽  
1990 ◽  
Vol 125 (4) ◽  
pp. 691-702 ◽  
Author(s):  
B L Berg ◽  
V Stewart

Abstract Formate oxidation coupled to nitrate reduction constitutes a major anaerobic respiratory pathway in Escherichia coli. This respiratory chain consists of formate dehydrogenase-N, quinone, and nitrate reductase. We have isolated a recombinant DNA clone that likely contains the structural genes, fdnGHI, for the three subunits of formate dehydrogenase-N. The fdnGHI clone produced proteins of 110, 32 and 20 kDa which correspond to the subunit sizes of purified formate dehydrogenase-N. Our analysis indicates that fdnGHI is organized as an operon. We mapped the fdn operon to 32 min on the E. coli genetic map, close to the genes for cryptic nitrate reductase (encoded by the narZ operon). Expression of phi(fdnG-lacZ) operon fusions was induced by anaerobiosis and nitrate. This induction required fnr+ and narL+, two regulatory genes whose products are also required for the anaerobic, nitrate-inducible activation of the nitrate reductase structural gene operon, narGHJI. We conclude that regulation of fdnGHI and narGHJI expression is mediated through common pathways.


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