PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Microbial Viability”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed2024

Quorum-sensing agr system of Staphylococcus aureus primes gene expression for protection from lethal oxidative stress.

The agr quorum-sensing system links Staphylococcus aureus metabolism to virulence, in part by increasing bacterial survival during exposure to lethal concentrations of H2O2, a crucial host defense against S. aureus. We now report that protection by agr surprisingly extends beyond post-exponential growth to the exit from stationary phase when the agr system is no longer turned on. Thus, agr can be considered a constitutive protective factor. Deletion of agr resulted in decreased ATP levels and growth, despite increased rates of respiration or fermentation at appropriate oxygen tensions, suggesting that Δagr cells undergo a shift towards a hyperactive metabolic state in response to diminished metabolic efficiency. As expected from increased respiratory gene expression, reactive oxygen species (ROS) accumulated more in the agr mutant than in wild-type cells, thereby explaining elevated susceptibility of Δagr strains to lethal H2O2 doses. Increased survival of wild-type agr cells during H2O2 exposure required sodA, which detoxifies superoxide. Additionally, pretreatment of S. aureus with respiration-reducing menadione protected Δagr cells from killing by H2O2. Thus, genetic deletion and pharmacologic experiments indicate that agr helps control endogenous ROS, thereby providing resilience against exogenous ROS. The long-lived 'memory' of agr-mediated protection, which is uncoupled from agr activation kinetics, increased hematogenous dissemination to certain tissues during sepsis in ROS-producing, wild-type mice but not ROS-deficient (Cybb-/-) mice. These results demonstrate the importance of protection that anticipates impending ROS-mediated immune attack. The ubiquity of quorum sensing suggests that it protects many bacterial species from oxidative damage.

Staphylococcus aureus↗
PubMed1991

[Role of bacterial agglutination in wound infection].

Method of study of bacterial agglutination by means of serum taken from patients with wound infections was suggested. It was found out that agglutination suppresses viability of microbial cells in the center of agglutinate and reduces the risk of bacterial spreading from the wound over the body.

Agglutination↗
PubMed1978

Viability of Leptospira interrogans serotype grippotyphosa in swine urine and blood.

Normal swine urine, devoid of its microbial flora, diminished the viability and virulence of Leptospira interrogans serotype grippotyphosa. Bovine serum albumin diluent effectively offset the urine's deleterious effects. Membrane filtration (0.45 micrometer) rendered urine free of bacteria, but permitted passage of limited numbers of leptospires. Most of the commonly used anticoagulants did not alter viability of grippotyphosa in whole blood. However, EDTA significantly reduced the number of viable cells.

Animals↗
PubMed1979

Bacteria beneath composite restorations--a culturing and histobacteriological study.

The occurrence, viability and identification of the microbial flora under composite fillings using an anaerobic technique were studied. Class V cavities were prepared on clinically healthy buccal surfaces of 7 contralateral pairs of premolars in children 11--15 years of age. After preparation, rubber dam was applied and one cavity in each pair of teeth was washed with water blasted dry with air and filled with Adaptic. The other cavity was washed with a cavity cleaner (Tubulicid) and a cavity liner (Tubulitec) was applicated prior to filling with Adaptic. The teeth were extracted after 4--6 weeks. Under anerobic conditions the tooth crown was split. From one half samples were taken from the pulpal wall under the filling and cultured on blood agar and in broth medium. The other half was examined with histobacteriological technique. No growth occurred in cultures from lined cavities but in 6 of the 7 unlined cavities. Full agreement was observed between the findings from the culturing and histobacteriological examinations concerning presence or absence of microorganisms at the pulpal wall in all 14 teeth. The flora was mixed. Gram-positive bacteria, mainly Streptococcus and Actinomyces, dominated over gram-negative bacteria including Veillonella, Fusobacterium, Campylobacter and Selenomonas. The composition of the flora was more similar to that observed in dental plaque than that found in carious dentin or in saliva in other studies.

Adolescent↗
PubMed1992

On-line biomass monitoring by capacitance measurement.

An in-situ, steam-sterilizable capacitance probe was used to follow the biomass concentration on-line, in bioreactors from 20 to 2000 l total volume. Microbial cultures of Saccharomyces cerevisiae, Pichia pastoris and Streptomyces virginiae were grown in batch and fed-batch culture in both defined and complex media in order to demonstrate the wide dynamic operating range of the instrument. A linear correlation was found between the on-line capacitance measurement and the off-line measurements (optical density, OD620; packed mycelial volume, PMV; biomass concentration X, and colony forming units, CFU ml-1) for biomass concentrations (dry cell weight) up to 30 g l-1 (St. virginiae), 106 g l-1 (S. cerevisiae) and 89 g l-1 (P. pastoris). The on-line capacitance measurement was slightly influenced by variations in agitation speed and strong extraneous radio frequencies. A specific capacitance constant (Cs) was defined for all microbial cells which was dependent on cell viability and cell size. The Cs was easy to calculate using the on-line capacitance measurement and an off-line estimation of biomass concentration. The Biomass Monitor proved suitable for precise on-line monitoring of both homogeneous (uni-cellular) and heterogeneous (mycelial) cultures in bioreactors.

Biotechnology↗
PubMed2026

PGPR inoculation and growth enhancement of crops cultivated in hydroponic systems.

Plant growth-promoting rhizobacteria (PGPR) are ubiquitous rhizosphere microorganisms that promote plant health through various mechanisms. Although the study of PGPR inoculants in soil has been done for ages, their application in hydroponic systems has received relatively limited attention. This review identifies PGPR inoculants that are commonly used in hydroponics, methods of application, and their effects on plant growth and nutrient use efficiency. Literature shows that PGPR inoculants improve plant performance in controlled hydroponic systems through the production of growth-stimulating substances, nitrogen fixation, and improved nutrient acquisition. However, the plant growth responses are highly variable depending on the composition of nutrient solutions, environmental factors, crop and microbe species, and the type of hydroponic system. The review identifies various challenges of PGPR inoculation in hydroponic systems and future research directions to address the current gaps. Generally, the productivity of hydroponic systems can be enhanced through advanced inoculation strategies and the development of suitable carrier materials to improve inoculant survival, viability, and functions. Emphasis should also be placed on designing system-specific microbial consortia and Synthetic communities that are tailored to the unique ecological conditions of hydroponic systems.

Hydroponics↗
PubMed1992

The endodontic microflora revisited.

The microbial flora of 35 dental root canals were examined, taking care to maintain the viability of obligate anaerobes which accounted for 45% of total isolations, while streptococcal species accounted for 24% of the total species isolated. Individual root canals yielded a maximum of eight bacterial species. A total of 40 different species was isolated of which the most prevalent were the facultative anaerobe Streptococcus sanguis and the obligate anaerobe, Peptostreptococcus micros (both in 23% of root canals), followed by Eubacterium aerofaciens and the 'Streptococcus milleri group' (both 17%) then Prevotella melaninogenica (formerly Bacteroides melaninogenicus), Enterococcus faecalis and Prevotella oralis (formerly Bacteroides oralis), which were each isolated from 14% of root canals. Highly significant associations were discovered between four pairs of species, viz P. melaninogenica with P. micros, P. melaninogenica with P. oralis, Prevotella corporis with Streptococcus morbillorum and Actinomyces odontolyticus with E. faecalis.

Dental Pulp Cavity↗
PubMed1975

Effects of human and rabbit serum on viability, permeability, and envelope lipids of Serratia marcescens.

The major action of serum on gram-negative organisms is thought to be on the microbial envelope. We compared the effects of normal human and rabbit serum on the envelope lipids of two strains of Serratia marcescens, one sensitive and one resistant to the bactericidal effects of serum. During killing by either serum, the sensitive strain underwent rapid permeability changes coincident with degradation of microbial phospholipids. The resistant strain exhibited none of these effects. The phospholipid degradation that accompanies killing of the sensitive strain by serum could be caused by phospholipases present in serum or by Serratia's own phospholipid-splitting enzymes. The results indicate that phospholipid breakdown is caused by activation of bacterial of bacterial phospholipases and not by serum phospholipases. This conclusion is based upon the following findings.(i1 Although rabbit serum phospholipase A was at least 10 times more active than human serum phospholipase A, phospholipid degradation in the sensitive Serratia strain was comparable during (equally rapid) killing by human or rabbit serum. (ii) Heat treatment (56 C) of both sera eliminated bactericidal activity as well as microbial lipid degradation but abolished phospholipase activity of human serum only. (iii) Virtually complete removal of phospholipase A activity from human serum by adsorption onto autoclaved Micrococcus lysodeikticus had no effect on the extent of phospholipid hydrolysis or on bactericidal activity. Activation by serum of endogenous phospholipase activity in S. marcescens was accompanied by enhanced incorporation of lipid precursors into bacterial lipids. No evidence was found for increased turnover of protein or ribonucleic acid during killing by serum.

Alkaline Phosphatase↗
PubMed1991

Comparative efficacies of soft contact lens disinfectant solutions against microbial films in lens cases.

Biofilms of Pseudomonas aeruginosa, Serratia marcescens, Staphylococcus epidermidis, Streptococcus pyogenes, and Candida albicans, established in the wells of a polyethylene contact lens case, retained viability to certain soft contact lens disinfectant solutions after exposure for the manufacturer's minimum recommended disinfection times. The relative order of resistance of bacterial biofilms was as follows: S marcescens was greater than P aeruginosa, which was greater than S epidermidis, which was greater than S pyogenes. Air drying of biofilms for 10 hours increased the efficacy of the disinfectant solutions, but drying was not enough to decrease the incidence of recovery to 0% for all solutions. Hydrogen peroxide was more effective against biofilms than disinfectant solutions formulated with chlorhexidine gluconate or polyquaternium-1 or polyaminopropyl biguanide. We recommend that determination of efficacy of contact lens disinfectant solutions should include challenges against biofilms.

Bacteria↗
PubMed1992

Circulatory adaptation to the increased metabolism in the skin at the site of the tuberculin reaction.

The sequence of changes at the site of a positive tuberculin test response were studied in 19 healthy young adults who had been immunised with BCG in childhood. The development of erythema preceded that of induration and both were most intense at 48-72 h. The strongest reactions showed higher laser Doppler (LD) flux at the periphery than at the center (central relative slowing). All showed a substantial reduction in steady-state (ss) tcpO2 from 24 h onwards and the oxygen consumption rate (mlO2.kg-1.min-1), calculated from the rate of fall in tcpO2 during temporary cuff occlusion of arterial input, was raised (greater than two-fold) throughout the period of study (to 96 h). The density of lymphocytes and macrophages in the inflammatory infiltrate in the dermis was related to the fall in tcpO2.ss and to the extent of thickening of the dermis. These experiments showed that the previously healthy dermal microcirculation can adapt to temporary increase in metabolic demands of leucocytes emigrated from the circulation into the tissue: in intense delayed hypersensitivity (DHS) reactions there is considerable hypoxia and respiratory debt, but maintenance of viability in the short-term. It is likely that similar adaptations occur in the period of establishment of microbial infection.

Adaptation, Physiological↗
PubMed1991

Lactose digestion from yogurt: influence of a meal and additional lactose.

Lactose in yogurt is better digested than lactose in other dairy foods by lactase-deficient individuals, in part because of intraintestinal activity of yogurt microbial beta-galactosidase (beta-gal). The survival and activity of yogurt beta-gal depend on gastrointestinal transit, pH, and viability of the yogurt culture. To evaluate the ability of yogurt beta-gal to digest lactose when yogurt is consumed with food or with additional lactose, 22 healthy lactose-maldigesting individuals were fed 10 test meals. Results of breath-hydrogen expiration, incidence of symptoms, and enzyme and lactose content of gastric aspirates indicate that the consumption of a meal with yogurt does not inhibit, and may slightly improve, lactose digestion from yogurt. However, yogurt beta-gal appears unable to assist in the digestion of additional lactose beyond that normally present in yogurt.

Adult↗
PubMed1978

Survival of recombination-deficient mutants of Escherichia coli during incubation with nalidixic acid.

The ability of several Escherichia coli strains deficient in recombination (rec) to survive in the presence of nalidixic acid was determined. Genetic blocks of the RecBC or the RecF pathways resulted in increased sensitivity to nalidixic acid when compared with the wild-type strain. Mutants lacking functional recA, recL, or recB recC recF genes showed the most rapid decrease in colony-forming ability when incubated with nalidixic acid. However, the uvrB gene also plays a role in maintaining cell viability.

DNA Repair↗
PubMed2026

Meta-analysis of growth and inactivation kinetics of Legionella.

Quantitative risk assessments intended to inform evidence-based water management plans and public health targets for Legionella in engineered water systems are constrained by fragmented and heterogeneous growth and inactivation kinetics. We conducted a meta-analysis of 25 growth and 39 thermal- and chemical-inactivation studies, fitting microbial persistence models to harmonize parameters. Nonlinear models outperformed first-order formulations, indicating that lag phases and resistant or protected subpopulations are central to Legionella persistence. Random forest analysis identified environmental and methodological drivers of variability based on 226 growth rates and reduction times for thermal (209) and chemical (135) inactivation. Growth was primarily governed by temperature, nutrient availability, and compatible Legionella-host pairings; thermal inactivation by quantification method, temperature, and turbidity; and chemical inactivation by inoculum size, disinfectant type, concentration, and host-associations. Accordingly, temperature-dependent growth parameters and exposure metrics for heat, free-chlorine, and monochloramine, expressed as TT (Temperature×time) and CT (Concentration×time), were derived as condition-specific inputs for predictive models. Growth optima around 37-40 °C, together with lag-time estimates, indicate that hot-water temperature setbacks and energy-saving practices may favor Legionella proliferation under repeated or prolonged lukewarm exposure. Culture- and viability-based TT differences highlight the need to consider viable‑but-non-culturable persistence in monitoring programs. CT comparisons suggest monochloramine may be advantageous because of its lower apparent sensitivity to host-associated protection. Although limited by restricted experimental conditions, the findings show that predictive models should account for microbial ecology, water matrix effects, and quantification endpoints. Future kinetic studies should prioritize realistic multi-host systems, strain pre-adaptation, complementary viability measurements, and standardized protocols and reporting to ensure reproducibility and enable robust system-level predictive modeling.

Legionella↗
PubMed1975

Soil sterilization effects on in situ indigenous microbial cells in soil.

Soil was sterilized by various procedures, and then the resident microorganisms were physically separated and concentrated from the soil for viewing by transmission electron microscopy as thin sections and frozen-etched preparation. Remaining cell viability in the soil was tested by conventional plating before and after enrichment culture. The soil proved to be sterile after treatment with 60Co radiation, prolonged autoclaving, prolonged dry heat application at 200C, or glutaraldehyde (if followed by subsequent milk heating), and could be considered sterile after OsO4 treatment. Treatment with glutaraldehyde alone, or 160C dry heat for 3 h, did not sterilize the soil. Cellular fine structure was latered or destroyed by the heat treatments, but was not affected to any extent by any of the other treatments including glutaraldehyde followed by milk heating. These findings are considered in relation to the residual biological information observable by electron microscopy in soil samples which have been sterilized to eliminate possible pathogens before handling of the soil. These findings are also considered with the objective of obliterating the fine structure of the indigenous microorganisms during soil sterilization so that electron microscopy studies can be made of microorganisms inoculated into and grown in the presterilized soil. These findings are considered in relation to the residual biological information observable by electron microscopy in soil samples which have been sterilized to eliminate possible pathogens before handling of the soil. These findings are also considered with the objective of obliterating the fine structure of the indigenous microorganisms during soil sterilization so that electron microscopy studies can be made of microorganisms inoculated into and grown in the presterilized soil.

Bacteria↗