Decline In Bacterial Population Research Articles

High rifampicin peak plasma concentrations accelerate the slow phase of bacterial decline in tuberculosis patients: Evidence for heteroresistance.

Antibiotic treatments are often associated with a late slowdown in bacterial killing. This separates the killing of bacteria into at least two distinct phases: a quick phase followed by a slower phase, the latter of which is linked to treatment success. Current mechanistic explanations for the in vitro slowdown are either antibiotic persistence or heteroresistance. Persistence is defined as the switching back and forth between susceptible and non-susceptible states, while heteroresistance is defined as the coexistence of bacteria with heterogeneous susceptibilities. Both are also thought to cause a slowdown in the decline of bacterial populations in patients and therefore complicate and prolong antibiotic treatments. Reduced bacterial death rates over time are also observed within tuberculosis patients, yet the mechanistic reasons for this are unknown and therefore the strategies to mitigate them are also unknown. We analyse a dose ranging trial for rifampicin in tuberculosis patients and show that there is a slowdown in the decline of bacteria. We show that the late phase of bacterial killing depends more on the peak drug concentrations than the total drug exposure. We compare these to pharmacokinetic-pharmacodynamic models of rifampicin heteroresistance and persistence. We find that the observation on the slow phase's dependence on pharmacokinetic measures, specifically peak concentrations are only compatible with models of heteroresistance and incompatible with models of persistence. The quantitative agreement between heteroresistance models and observations is very good ([Formula: see text]). To corroborate the importance of the slowdown, we validate our results by estimating the time to sputum culture conversion and compare the results to a different dose ranging trial. Our findings indicate that higher doses, specifically higher peak concentrations may be used to optimize rifampicin treatments by accelerating bacterial killing in the slow phase. It adds to the growing body of literature supporting higher rifampicin doses for shortening tuberculosis treatments.

Impact of Electromagnetic Field on Bacterial Population and Physicochemical Properties of Cassava Wastewater

The release of industrial wastewaters into the environment is a major source of toxic contaminants causing global health and environmental challenges. This study aimed to investigate the impact of electromagnetic field (EMF) treatment on bacterial population and physicochemical characteristics of cassava wastewater. Cassava wastewater sample was collected from point source of a small-scale cassava industry in Akure, Nigeria. Sample was thereafter treated with EMF of varying intensities (70- 130nT) and bacterial population and physicochemical properties of raw and treated wastewater sample were determined using standard microbiological, physical and chemical analytical techniques. Results revealed a total bacterial count of 1.34 x 105cfu/ ml. Identity of bacterial genera isolated from wastewater were Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi (Gram negative) while the Gram positive bacteria were Staphylococcus aureus, Bacillus cereus, Bacillus subtilis and Lactobacillus sp. Results also revealed that treatment of wastewater sample with EMF significantly reduced the bacterial load and physicochemical parameters of the sample and dependent on EMF intensity and duration of exposure. Results revealed a decline in bacterial population from 1.34 x 105- 1.0 x 104 at intensities of 70nT-130nT and exposure time of 0- 144hr with the lowest count obtained at 130nT and the highest at 70nT. This study concludes that the use of Electromagnetic Field holds promise as an effective, non-invasive and eco-friendly strategy to improve the physical, chemical and biological quality of wastewater before discharge into the environment.

Bee pollen as a novel substrate in pilot-scale probiotic-mediated lactic fermentation processes

Different process conditions were evaluated to induce lactic acid fermentation of bee pollen at the pilot scale using three different commercial starter cultures. Clean and dry Colombian high Andean bee pollen was used as the sole source of nutrients (substrate). The effect of substrate preparation conditions (water:pollen ratio and initial substrate acidity) on lactic fermentation was evaluated by monitoring pH, titratable acidity, and pollen morphology in 6-kg-fermentation units. A 2:1 water:pollen mixture with an initial pH adjusted to 5.8, pretreated with heat/pressure (10 min; 80 kPa; 115 °C), was determined to be an adequate substrate for pilot-scale lactic fermentation for all lactic starter cultures. At the selected conditions, the kinetics of lactic acid production and the growth of specific lactic bacteria were determined. The fermentation process time was 30 h, after which a significant decline in bacterial populations was observed. Among the starter cultures tested, one constituted exclusively by probiotic Lactobacillus acidophilus NCFM presented the best performance in terms of lactic acid production, with a concentration of 1.65% wt, after 30 h. The results highlight the feasibility of producing fermented bee pollen at a commercial scale as a functional food product with probiotic features.

Holdover Inoculum of Pseudomonas syringae pv. alisalensis from Broccoli Raab Causes Disease in Subsequent Plantings.

Uniform plots of broccoli raab (Brassica rapa subsp. rapa) seedlings were inoculated with a rifampicin-resistant strain of Pseudomonas syringae pv. alisalensis, the causal agent of bacterial blight on crucifers, resulting in 100% disease incidence in mature plants. Diseased plants were incorporated into the soil at maturity and smaller replicated plots were replanted at various times after incorporation. Rifampicin-resistant fluorescent pseudomonads with rep-PCR profiles identical to P. syringae pv. alisalensis were isolated from lesions on plants grown in soil into which the first diseased crop was incorporated. Disease incidence declined in mature plants as the length of time between incorporation of the first planting and seeding of the replanted plots increased. Bacterial population levels in soil decreased over time and bacteria were no longer detectable 3 weeks after incorporation of the diseased crop. In laboratory tests, population levels of P. syringae pv. alisalensis decreased in untreated soil but not in autoclaved soil. Greenhouse studies demonstrated a direct correlation between population levels of P. syringae pv. alisalensis applied to soil and disease incidence in seedlings. However, the decline in bacterial populations in field soils did not wholly account for the decline in disease incidence with subsequent plantings.

Characterisation of cellulase activity in the digestive system of the redclaw crayfish ( Cherax quadricarinatus)

Endogenous cellulase activity was identified in the gastric fluid and digestive gland of the redclaw crayfish. Cellulase showed maximal activity from pH 4 to 5 and was stable for up to 2 h at 40°C. Cellulase activity in the digestive gland was unaffected by antibiotic treatment. Taken together these findings suggest a significant endogenous component for redclaw cellulase activity. Partial purification of cellulase activity was performed using anion exchange and gel filtration chromatography. One major and one minor band of activity were identified subsequently by SDS-PAGE and zymography. The molecular weight of the major band was estimated at 40 kDa while the minor band was estimated at 30 kDa. Redclaw cellulase enzymes demonstrated broad substrate specificity, hydrolysing polysaccharides containing β-1,4 and mixed β-1,4 and β-1,3 glycosidic bonds but showed a preference for soluble substrates. Hydrolysis products of cellodextrins of various lengths also showed that the enzymes liberated free glucose. Exposure of redclaw to antibiotics resulted in a dramatic decline in bacterial populations in the gastric contents (>90%) but only a 40% decline in cellulase activity.

Capacity of recombinant gamma interferon to activate macrophages for Salmonella-killing activity

The ability of recombinant gamma interferon (rIFN-gamma) to activate macrophages for Salmonella-killing activity was kinetically examined in relation to phagosome-lysosome fusion and H2O2 generation. Resident peritoneal macrophages of BALB/c mice incubated with 10(2) to 10(3) U of rIFN-gamma per ml for 12 h exhibited enhanced bactericidal activity against Salmonella typhimurium, although H2O2 generation was unaltered. In contrast, macrophages incubated with equal doses of rIFN-gamma for 48 h showed both an enhanced Salmonella-killing activity and an increased generation of H2O2. To evaluate Salmonella-killing activities of macrophages, intracellular bacteria were assayed at 0, 2, and 8 h after infection. During the initial 2 h of infection, 12-h-activated macrophages, as well as the unstimulated control macrophages, showed a decline in bacterial population at the same rate. Over the next 6 h of infection, however, the number of viable bacteria in activated macrophages remained unchanged, whereas the number of bacteria in control macrophages significantly (P less than 0.05) increased. Similar results were obtained in 48-h-activated macrophages. On the other hand, macrophages incubated with 10 to 10(3) U of rIFN-gamma exhibited enhanced fusion of lysosomes to Salmonella-containing phagosomes in both the 12-h- and 48-h-stimulated stages. Moreover, when 48-h-activated macrophages were incubated concomitantly with superoxide dismutase and catalase, Salmonella-killing activity was not affected. These results indicate that rIFN-gamma per se is able to activate peritoneal macrophages to induce Salmonella-killing activity and suggest that increased phagosome-lysosome fusion followed by an oxygen-independent killing mechanism is primarily responsible for the enhanced Salmonella-killing activity in rIFN-gamma-activated macrophages.

Role of sublethal injury in decline of bacterial populations in lake water.

Following their addition to lake water, the populations of Escherichia coli and of antibiotic-resistant strains of Pseudomonas fluorescens, Agrobacterium tumefaciens, Micrococcus flavus, Rhizobium meliloti, and Klebsiella pneumoniae declined rapidly, as determined by counting on media containing antibacterial compounds. The estimates of population sizes were occasionally higher if procedures were used that permitted possible resuscitation of injured cells. No resuscitation procedure yielded consistently higher estimates of populations of surviving cells than the use of selective media alone. The patterns of survival of the test bacteria in lake water amended with eucaryotic inhibitors were essentially the same whether a resuscitation procedure was used or not, and the patterns of survival in sterile lake water or buffer were the same whether counts were made on selective media or on media without antibacterial agents. On the basis of the methods used to show sublethal injury caused by stress, we suggest that such injury to the test bacteria is not a significant factor involved in their decline in lake water.

Expression of resistance in bean pods to an incompatible isolate of Pseudomonas syringae

Isolates of Pseudomonas syringae from hairy vetch were either virulent (compatible) or avirulent (incompatible) to bean. When bean pods were injected at high inoculum levels (5 × 107 cells/ml), both compatible and incompatible isolates multiplied rapidly and caused water-soaking of injected tissues; populations of both isolates were similar at the end of log phase. Lesions caused by the incompatible isolate turned brown by 3 days after inoculation and did not expand; those caused by the compatible isolate remained water-soaked and expanded into the adjoining, noninoculated tissues. At low inoculum levels (5 × 104 cells/ml), the compatible isolate exhibited the same pattern of multiplication and lesion development as at the high inoculum level. The incompatible isolate, on the other hand, caused necrotic flecking within the injected area by 24 h, and these small lesions remained limited. Appearance of the necrotic flecks was correlated with a progressive decline in bacterial populations; after5 days, the population of incompatible bacteria was about a hundredfold lower than that of compatible ones. Populations of incompatible bacteria within and between the necrotic flecks declined rapidly, indicating the potential accumulation of inhibitors of bacterial growth as a result of an inducible resistance mechanism.The phytoalexin phaseollin reached 280 μg/g fresh weight by 3 days after inoculation of bean pods with incompatible bacteria. However, this compound was not involved in resistance. Neither compatible nor incompatible isolates of the bacterium were significantly inhibited when grown in a medium saturated with phaseollin. When other antibiotic substances in plant extracts were sought, substantial amounts of inhibitory compounds were detected only in the ethanolic extract (fraction soluble in ethyl acetate) of pods previously inoculated with an incompatible isolate of P. syringae. Only low levels of inhibition were obtained from identical extracts of uninfected pods or from pods inoculated with a compatible isolate of P. syringae. Bacterial growth was completely prevented in a bean infusion medium containing 1 g fresh weight equivalent of pod tissue challenged with the incompatible isolate. The active compound(s) was nonfluorescent, had a UV absorption maximum at 286 nm, and gave a positive reaction with reagents for phenolic compounds.

Observations on the influence of deuterium on bacterial growth.

ABS>The influence of different concentrations of deuterium in liquid media on the growth of various microbial species was studied. The concentrations of deuterium studied ranged from 0 to 95 atom per cent. Cultures of M. tuberculosis showed inhibition of growth only when the deuterium concentration surpassed 80 atom per cent. Deuterium concentrations between 25 and 80 atom per cent appeared to stimulate growth slightly but this effect was not apparent until after 21 days incubation. Cultures of unclassified rapid-grower strain of acid- fast bacilli showed only progressive inhibition of growth with increasing concentrations of D/sub 2/0. On adequate media, cultures of Group C hemolytic streptococci demonstrated an inverse relationship between growth and deuterium concentration. On adverse media, the initial decline in bacterial population was inhibited progressively by increasing concentrations of deuterium, but after growth became established deuterium toxicity again became evident. Cultures of Type I pneumococci under poor conditions of growth showed evidence of a protective action of the higher concentrations of deuterium against the initial decline in bacterial population. Once growth became established it reached higher levels and persisted longer as the deuterium concentration was increased. The growth of E. coli was found to be progressively inhibited by increasingmore » deuterium concentrations. Cultures of Candida albicans showed little sensitivity to increasing concentrations of deuterium. (auth)« less