Searching the point of no return in Helicobacter pylori life: necrosis and/or programmed death?

Comparative transcriptome analysis to investigate the mechanism of anti-Helicobacter pylori activity of zinc

As a potential anti-Helicobacter pylori agent, zinc causes impairment of Helicobacter pylori growth, and this property of zinc is of broad interest to biological investigators. However, little is known about the molecular mechanisms by which zinc inhibits the growth of Helicobacter pylori. Here, an in vitro experiment revealed that zinc at specific concentrations inhibits Helicobacter pylori growth. Furthermore, an RNA sequencing-based investigation of the global regulatory response to zinc revealed that exposure to zinc altered the Helicobacter pylori transcriptional profile in numerous ways. A high concentration of zinc induced the upregulation of genes related to ribosomal subunit, ribosome biosynthesis, chaperone and adhesins. However, flagellar assembly genes and some type IV secretion system genes were repressed. In addition, the expression levels of some genes that encode transporters of metal ions and that play key roles in Helicobacter pylori pathogenicity were altered under conditions of zinc-induced stress. In summary, high concentrations of zinc initiated antimicrobial activity to Helicobacter pylori under the combined effect of multiple repressed or altered pathogenetic genes and metabolic pathways associated with bacteria growth. This result has significant implications for understanding not only the antimicrobial activity mechanism of zinc but also the role of zinc-mediated homeostasis in Helicobacter pylori.

Optimization of pre- treatments with Propidium Monoazide and PEMAX™ before real-time quantitative PCR for detection and quantification of viable Helicobacter pylori cells

Accurate detection of H. pylori in different environmental and clinical samples is essential for public health strtdudies. Now, a big effort is being made to design PCR methodologies that allow for the detection of viable and viable but non-culturable (VBNC) H. pylori cells, by achieving complete exclusion of dead cells amplification signals. The use of DNA intercalating dyes has been proposed. However, its efficacy is still not well determined. In this study, we aimed to test the suitability of PMA and PEMAX™ dyes used prior to qPCR for only detecting viable cells of H. pylori. Their efficiency was evaluated with cells submitted to different disinfection treatments and confirmed by the absence of growth on culture media and by LIVE/DEAD counts. Our results indicated that an incubation period of 5 min for both, PMA and PEMAX™, did not affect viable cells. Our study also demonstrated that results obtained by using intercalating dyes may vary depending on the cell stress conditions. In all dead cell's samples, both PMA and PEMAX™ pre-qPCR treatments decreased the amplification signal (>10³ Genomic Units (GU)), although none of them allowed for its disappearance confirming that intercalating dyes, although useful for screening purposes, cannot be considered as universal viability markers. To investigate the applicability of the method specifically to detect H. pylori cells in environmental samples, PMA-qPCR was performed on samples containing the different morphological and viability states that H. pylori can acquire in environment. The optimized PMA-qPCR methodology showed to be useful to detect mostly (but not only) viable forms, regardless the morphological state of the cell.

Daphnetin: A Novel Anti-Helicobacter pylori Agent

Background: Antibiotic-resistant H. pylori was increasingly found in infected individuals, which resulted in treatment failure and required alternative therapeutic strategies. Daphnetin, a coumarin-derivative compound, has multiple pharmacological activities. Methods: The mechanism of daphnetin on H. pylori was investigated focusing on its effect on cell morphologies, transcription of genes related to virulence, adhesion, and cytotoxicity to human gastric epithelial (GES-1) cell line. Results: Daphnetin showed good activities against multidrug resistant (MDR) H. pylori clinical isolates, with minimal inhibitory concentration (MIC) values ranging from 25 to 100 μg/mL. In addition, daphnetin exposure resulted in H. pylori morphological changes. Moreover, daphnetin caused increased translocation of phosphatidylserine (PS), DNA damage, and recA expression, and RecA protein production vs. control group. Of great importance, daphnetin significantly decreased H. pylori adhesion to GES-1 cell line vs. control group, which may be related to the reduced expression of colonization related genes (e.g., babA and ureI). Conclusions: These results suggested that daphnetin has good activity against MDR H. pylori. The mechanism(s) of daphnetin against H. pylori were related to change of membrane structure, increase of DNA damage and PS translocation, and decrease of H. pylori attachment to GES-1 cells.

Methods for Detecting the Environmental Coccoid Form of Helicobacter pylori

Helicobacter pylori is recognized as the most common pathogen to cause gastritis, peptic and duodenal ulcers, and gastric cancer. The organisms are found in two forms: (1) spiral-shaped bacillus and (2) coccoid. H. pylori coccoid form, generally found in the environment, is the transformed form of the normal spiral-shaped bacillus after exposed to water or adverse environmental conditions such as exposure to sub-inhibitory concentrations of antimicrobial agents. The putative infectious capability and the viability of H. pylori under environmental conditions are controversial. This disagreement is partially due to the fact of lack in detecting the coccoid form of H. pylori in the environment. Accurate and effective detection methods of H. pylori will lead to rapid treatment and disinfection, and less human health damages and reduction in health care costs. In this review, we provide a brief introduction to H. pylori environmental coccoid forms, their transmission, and detection methods. We further discuss the use of these detection methods including their accuracy and efficiency.

STRATEGY OF PROGRAMMED CELL DEATH IN PROKARYOTES

Programmed cell death (PCD) was first studied in eukaryotic organisms. This system also operates in the development life cycle of prokaryotes. The system PCD in microorganisms is activated a wide range of signals in response to the stresses associated with adverse environmental conditions or exposure to antibacterial agents. The results of numerous studies in the past decade allow considering the system PCD in prokaryotes as an evolutionary conservation of the species. These results significantly expanded understanding of the role of PCD in microorganisms and opened a number of important areas of research of the morphological and molecular genetic approaches to the study of death strategies for the survival in bacterial populations. The purpose of the review is to summarize the morphological and molecular genetic characteristics of PCD in prokaryotes which are real manifestations of the mechanisms of this phenomenon. 

Die for the community: an overview of programmed cell death in bacteria

Programmed cell death is a process known to have a crucial role in many aspects of eukaryotes physiology and is clearly essential to their life. As a consequence, the underlying molecular mechanisms have been extensively studied in eukaryotes and we now know that different signalling pathways leading to functionally and morphologically different forms of death exist in these organisms. Similarly, mono-cellular organism can activate signalling pathways leading to death of a number of cells within a colony. The reason why a single-cell organism would activate a program leading to its death is apparently counterintuitive and probably for this reason cell death in prokaryotes has received a lot less attention in the past years. However, as summarized in this review there are many reasons leading to prokaryotic cell death, for the benefit of the colony. Indeed, single-celled organism can greatly benefit from multicellular organization. Within this forms of organization, regulation of death becomes an important issue, contributing to important processes such as: stress response, development, genetic transformation, and biofilm formation.

Proliferative and apoptotic effects of gastric epithelial cells induced by coccoid Helicobacter pylori

Helicobacter pylori exhibit morphology convertion in a spiral or coccoid form. This study aims to reveal the impact of coccoid H. pylori on the proliferation and apoptosis of gastric epithelial cells. The cagA and vacA genes of H. pylori were detected by semi-quantitative RT-PCR. Proliferation and apoptosis were analyzed by the CCK-8 colorimetric method and TUNEL assay, respectively. Egr-1 mRNA and PCNA expression affected by the ERK1/2-specific inhibitor were detected by RT-PCR and immunochemistry. At low density of infection (MOI < 125:1), coccoid H. pylori exerted a stronger effect on proliferation and a weaker effect on apoptosis than did spiral form. The ERK1/2-specific inhibitor significantly blocked the increased expression in Egr-1 and PCNA induced by coccoid H. pylori. Expression of vacA and cagA in coccoid H. pylori decreased compared with the spiral form, whereas vacA decreased more than cagA. The difference of proliferation and apoptosis may be related to the unequal decreased expression of vacA and cagA in coccoid H. pylori. Activation of the ERK1/2-Egr-1-PCNA signal transduction pathway may play an important role in coccoid H. pylori-induced cell proliferation. Long latency of the coccoid form of H. pylori in gastric tissue may be associated with gastric cancer caused by H. pylori.

Putative mechanisms and biological role of coccoid form formation in Campylobacter jejuni

In certain conditions Campylobacter jejuni cells are capable of changing their cell shape from a typically spiral to a coccoid form (CF). By similarity to other bacteria, the latter was initially considered to be a viable but non-culturable form capable of survival in unfavourable conditions. However, subsequent studies with C. jejuni and closely related bacteria Helicobacter pylori suggested that CF represents a non-viable, degenerative form. Until now, the issue on whether the CF of C. jejuni is viable and infective is highly controversial. Despite some preliminary experiments on characterization of CF cells, neither biochemical mechanisms nor genetic determinants involved in C. jejuni cell shape changes have been characterized. In this review, we highlight known molecular mechanisms and genes involved in CF formation in other bacteria. Since orthologous genes are also present in C. jejuni, we suggest that CF formation in these bacteria is also a regulated and genetically determined process. A possible significance of CF in the lifestyle of this important bacterial pathogen is discussed.

Helicobacter pylori-coccoid forms and biofilm formation

Electron microscopic studies have shown that Helicobacter pylori occurs in three stages: spiral forms, coccoid forms and degenerative forms. The spiral forms are viable, culturable, virulent and can colonize experimental animals and induce inflammation. The coccoid forms may also be viable but are nonculturable, less virulent and are less likely to colonize and induce inflammation in experimental animals than the spiral forms. The degenerative forms are pyknotic, nonculturable, coccoid forms of dead H. pylori. These forms cannot be cultured and the cell membrane has disintegrated but gene material can be detected by PCR in water supplies. There is no substantial evidence for viable H. pylori persisting in water supplies. Epidemiological studies suggest that environmental water is a risk factor for H. pylori infection when compared with tap water, and formation of H. pylori biofilm cannot be excluded. Helicobacter pylori does not seem to take part in biofilm formation in the oral cavity even though the bacterium may be detected.

Morphological changes of Aeromonas hydrophila in response to osmotic stress

The adaptive response of bacteria to stressful environmental situations may lead to a modification of physiological and phenotypical characteristics, including morphology. The aim of this study was the analysis of the ultrastructural changes in Aeromonas hydrophila exposed to different NaCl concentrations (1.7%, 3.4%, 6%) at 4 and 24 degrees C for 188 days. Bacterial cultures were processed for scanning and transmission electron microscopy, and specimens were analysed at different times during osmotic stress. SEM reveals the presence of three predominant morphotypes: rod, filamentous and spherical forms, depending on the time and culture conditions. Normal rod cells prevail in 1.7% NaCl growth conditions, maintaining high rates until the end of the trial at 4 degrees C. The most favourable conditions for the elongated morphotype are 3.4% NaCl at 4 degrees C. Spherical forms appear later, increase with time and are the prevalent population at the end of the trial at 24 degrees C, in all culture conditions. TEM reveals the presence of normal, necrotic-like and apoptotic-like forms; these latter forms increase with time according to salt concentration and temperature. Initially, a detachment of the external membrane appears, with cytoplasmic clumping into small, dense masses; as the process continues, both these features become more evident with increasing salt concentrations. This behaviour has been compared to that of eukaryotic cells undergoing growth factor deprivation-induced apoptosis. Occasionally, surface blebs are observed. In conclusion, the study suggests that the exposure of A. hydrophila to stressful conditions (osmolarity, temperature and nutrients) leads to the generation of varying morphotypes, which promote cell survival in adverse conditions and a rapid repopulation in post-stress environments.

Helicobacter pylori produces unique filaments upon host contact in vitro

Helicobacter pylori exists in 2 distinct morphological states, helicoid and coccoid. Both have been observed in in vitro culture and in gastric biopsies. We visualized H. pylori during AGS cell infections using immunofluorescence microscopy. Anti-H. pylori mouse serum as well as human serum from H. pylori-positive patients recognized long, thin bacterial filaments, which formed on helicoids and more frequently on coccoids. These filaments reached lengths of 59 microm and often connected bacteria. Periodate oxidation abolished antibody recognition, suggesting that carbohydrates compose a major antigenic component of the filaments. Similar to results obtained using immunofluorescence microscopy, scanning electron microscopy imaging revealed thin filamentous structures, which were absent on uninfected cells. Both coccoid conversion and filament development increased over the time course of infection with peak filament formation at 4 h. The number of visible filaments then decreased as bacteria clustered on the apical surface of AGS cells. Since the observed filaments were clearly distinct from previously described surface structures, including flagella and the cag type IV secretion system, our results demonstrate that these filaments represent a unique, previously unrecognized, organelle.

Helicobacter pylori in the palatine tonsils of patients with IgA nephropathy compared with those of patients with recurrent pharyngotonsillitis

Helicobacter pylori infection is acquired by oral ingestion. However, the morphology and microscopic localization of H pylori in the human oral cavity and pharynx are unknown. In the present study, we performed immunohistochemistry, immunoelectron microscopy, in situ hybridization, and polymerase chain reaction to identify H pylori in the palatine tonsils of 32 patients with immunoglobulin A nephropathy (IgAN) and 141 patients with recurrent pharyngotonsillitis (RPT). H pylori in coccoid form was present in bacterial colonies and horny layers of the stratified squamous epithelium in tonsillar crypts. We described for the first time the morphology of H pylori in palatine tonsils. Most bacterial colonies were sulfur granules with Actinomyces israelii (A israelii), and A israelii showed significant coexistence with H pylori (P=.011). The prevalence of H pylori in palatine tonsils of the RPT group increased steeply with age, but one fourth of the patients were found not to have tonsillar H pylori in adulthood. All patients with IgAN had H pylori in palatine tonsils. The prevalence of H pylori was greater in the IgAN group than in the RPT group, and the difference was statistically significant (P<.001). In contrast, A israelii was unrelated to age and clinical diagnosis (P=.722). In conclusion, our results demonstrate that H pylori in coccoid form is present in palatine tonsils and may indicate that H pylori in palatine tonsils is among the antigens causative of IgAN.

Effects of subinhibitory concentrations of clindamycin on the morphological, biochemical and genetic characteristics ofBacteroides fragilis

The effects of subinhibitory concentrations of clindamycin on the morphological, biochemical and genetic characteristics of species of the Bacteroides fragilis group isolated from children with diarrhea were determined. The minimal inhibitory and subinhibitory concentrations for clindamycin were determined. Minimal inhibitory concentration values ranging from 0.25 to 512 microg mL(-1) were observed. Cultures grown with clindamycin were used to determine the macroscopic morphological characteristics, cellular viability, ultrastructural characteristics and DNA integrity. Clindamycin did not alter colonial morphology, but after 6 h elongated cells were observed. Also, extracellular vesicles and electron-lucent areas inside the cytoplasm were observed. Bacteria treated with clindamycin also showed fragmentation of DNA as determined by electrophoresis. The alterations produced by clindamycin might be indicative of a possible modification of the structures involved in bacterial pathogenesis.

Influence of the growth phase and culture medium on the survival of Mannheimia haemolytica during storage at different temperatures

AIMS

To quantify the influence of the growth phase, storage temperature and nutritional quality of the plate count medium on the apparent viability of Mannheimia haemolytica during storage at different temperatures.

METHODS AND RESULTS

Mannheimia haemolytica was grown in shake flasks and in aerobic continuous culture to investigate factors affecting cell viability during storage, which was determined using plate counts on different media and epifluorescence microscopy. The high specific death rates of cells harvested after cessation of exponential growth and stored at 22, 4, -18 and -75 degrees C could be related to the rapid onset of exponential death in batch cultures. Yeast extract supplementation of the culture medium increased the viability of cells at most of the above-mentioned storage temperatures. Of the total cell count in continuous culture, only 48% could be recovered on brain-heart infusion agar, whereas supplementation of the agar medium with foetal calf serum increased the plate count to 71% of the total count.

CONCLUSIONS

Mannheimia haemolytica cells harvested from the exponential growth phase had the highest survival rate during storage at low temperatures. Plate count values also depended on the nutritional quality of the agar medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results presented here impact on the procedures for culture preservation and plate count enumeration of this fastidious animal pathogen.

Death's toolbox: examining the molecular components of bacterial programmed cell death

Programmed cell death (PCD) is a genetically determined process of cellular suicide that is activated in response to cellular stress or damage, as well as in response to the developmental signals in multicellular organisms. Although historically studied in eukaryotes, it has been proposed that PCD also functions in prokaryotes, either during the developmental life cycle of certain bacteria or to remove damaged cells from a population in response to a wide variety of stresses. This review will examine several putative examples of bacterial PCD and summarize what is known about the molecular components of these systems.