Effect of hyperbaric oxygen on the growth and susceptibility of facultatively anaerobic bacteria and bacteria with oxidative metabolism to selected antibiotics.

Wild strains of Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis were tested in an experimental hyperbaric chamber to determine the possible effect of hyperbaric oxygen on the susceptibility of these strains to the antibiotics ampicillin, ampicillin + sulbactam, cefazolin, cefuroxime, cefoxitin, gentamicin, sulfamethoxazole + trimethoprim, colistin, oxolinic acid, ofloxacin, tetracycline, and aztreonam during their cultivation at 23 °C and 36.5 °C. Ninety-six-well inoculated microplates with tested antibiotics in Mueller-Hinton broth were cultured under standard incubator conditions (normobaric normoxia) for 24 h or in an experimental hyperbaric chamber (HAUX, Germany) for 24 h at 2.8 ATA of 100% oxygen (hyperbaric hyperoxia). The hyperbaric chamber was pressurised with pure oxygen (100%). Both cultures (normoxic and hyperoxic) were carried out at 23 °C and 36.5 °C to study the possible effect of the cultivation temperature. No significant differences were observed between 23 and 36.5 °C cultivation with or without the 2-h lag phase in Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Cultivation in a hyperbaric chamber at 23 °C and 36.5 °C with or without a 2-h lag phase did not produce significant changes in the minimum inhibitory concentration (MIC) of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. For the tested strains of Pseudomonas aeruginosa, the possible effect of hyperbaric oxygen on their antibiotic sensitivity could not be detected because the growth of these bacteria was completely inhibited by 100% hyperbaric oxygen at 2.8 ATA under all hyperbaric conditions tested at 23 °C and 36.5 °C. Subsequent tests with wild strains of pseudomonads, burkholderias, and stenotrophomonads not only confirmed the fact that these bacteria stop growing under hyperbaric conditions at a pressure of 2.8 ATA of 100% oxygen but also indicated that inhibition of growth of these bacteria under hyperbaric conditions is reversible.

Stable microbial community in compacted bentonite after 5 years of exposure to natural granitic groundwater.

The Materials Corrosion Test (MaCoTe) at the Underground Research Laboratory in Grimsel, Switzerland, assesses the microbiology and corrosion behavior of engineered barrier components of a deep geological repository (DGR) for long-term disposal of high-level nuclear waste. Diversity and temporal changes of bentonite-associated microbial community profiles were assessed under DGR-like conditions for compacted Wyoming MX-80 bentonite (1.25 g/cm3 and 1.50 g/cm3 targeted dry densities) exposed to natural groundwater. Using culture-dependent and molecular techniques, samples taken from the outside layer of 5-year borehole modules revealed up to 66% and 23% of 16S rRNA gene sequences affiliated with Desulfosporosinus and Desulfovibrio, respectively. Putatively involved in sulfate reduction, these taxa were almost undetectable within the bentonite core. Instead, microbial profiles of the inner bentonite core were similar to uncompacted bentonite used to pack modules years earlier, and were consistent with a previously published 1-year time point, revealing no detectable microbial growth. Abundances of culturable aerobic and anaerobic heterotrophic bacteria in the uncompacted bentonite were relatively low, with less than 1,000 and 100 colony-forming units (CFUs) per gram dry weight, respectively. Nearly 5 years after emplacement, culturable heterotrophic bacterial CFUs and sulfate-reducing bacteria did not change significantly inside the bentonite core. Phospholipid fatty acid data indicated similar lipid abundance, and corresponding cell abundance estimates, for inner 5-year MaCoTe bentonite samples compared to those previously obtained for 1-year incubations. Collectively, our results provide complementary evidence for microbial stability inside highly compacted bentonite exposed to conditions that mimic engineered barrier components of a deep geological repository. IMPORTANCE The long-term safety of a deep geological repository for used nuclear fuel is dependent on the performance of the engineered and natural barriers. Microbial activity can produce chemical species that can influence the corrosion of the disposal containers for used nuclear fuel. Although previous studies have evaluated the microbiology of compacted bentonite clay within subsurface environments, these have been limited to relatively short incubations (i.e., 1 year). The current study provides a unique 5-year perspective that reinforces previous findings of growth inhibition for bentonite clay exposed to in situ subsurface conditions.

Emergence of putative energy parasites within Clostridia revealed by genome analysis of a novel endosymbiotic clade.

The Clostridia is a dominant bacterial class in the guts of various animals and are considered to nutritionally contribute to the animal host. Here, we discovered clostridial endosymbionts of cellulolytic protists in termite guts, which have never been reported with evidence. We obtained (near-)complete genome sequences of three endosymbiotic Clostridia, each associated with a different parabasalid protist species with various infection rates: Trichonympha agilis, Pseudotrichonympha grassii, and Devescovina sp. All these protists are previously known to harbor permanently-associated, mutualistic Endomicrobia or Bacteroidales that supplement nitrogenous compounds. The genomes of the endosymbiotic Clostridia were small in size (1.0-1.3 Mbp) and exhibited signatures of an obligately-intracellular parasite, such as an extremely limited capability to synthesize amino acids, cofactors, and nucleotides and a disrupted glycolytic pathway with no known net ATP-generating system. Instead, the genomes encoded ATP/ADP translocase and, interestingly, regulatory proteins that are unique to eukaryotes in general and are possibly used to interfere with host cellular processes. These three genomes formed a clade with metagenome-assembled genomes (MAGs) derived from the guts of other animals, including human and ruminants, and the MAGs shared the characteristics of parasites. Gene flux analysis suggested that the acquisition of the ATP/ADP translocase gene in a common ancestor was probably key to the emergence of this parasitic clade. Taken together, we provide novel insights into the multilayered symbiotic system in the termite gut by adding the presence of parasitism and present an example of the emergence of putative energy parasites from a dominant gut bacterial clade.

Anaerobic selenite-reducing bacteria and their metabolic potentials in Se-rich sediment revealed by the combination of DNA-stable isotope probing, metagenomic binning, and metatranscriptomics.

Microorganisms play a critical role in the biogeochemical cycling of selenium (Se) in aquatic environments, particularly in reducing the toxicity and bioavailability of selenite (Se(IV)). This study aimed to identify putative Se(IV)-reducing bacteria (SeIVRB) and investigate the genetic mechanisms underlying Se(IV) reduction in anoxic Se-rich sediment. Initial microcosm incubation confirmed that Se(IV) reduction was driven by heterotrophic microorganisms. DNA stable-isotope probing (DNA-SIP) analysis identified Pseudomonas, Geobacter, Comamonas, and Anaeromyxobacter as putative SeIVRB. High-quality metagenome-assembled genomes (MAGs) affiliated with these four putative SeIVRB were retrieved. Annotation of functional gene indicated that these MAGs contained putative Se(IV)-reducing genes such as DMSO reductase family, fumarate and sulfite reductases. Metatranscriptomic analysis of active Se(IV)-reducing cultures revealed significantly higher transcriptional levels of genes associated with DMSO reductase (serA/PHGDH), fumarate reductase (sdhCD/frdCD), and sulfite reductase (cysDIH) compared to those in cultures not amended with Se(IV), suggesting that these genes played important roles in Se(IV) reduction. The current study expands our knowledge of the genetic mechanisms involved in less-understood anaerobic Se(IV) bio-reduction. Additinally, the complementary abilities of DNA-SIP, metagenomics, and metatranscriptomics analyses are demonstrated in elucidating the microbial mechanisms of biogeochemical processes in anoxic sediment.

Dark fermentative hydrogen production: Potential of food waste as future energy needs.

Globally, food waste (FW) is found to be one of the major constituents creating several hurdles in waste management. On the other hand, the energy crisis is increasing and the limited fossil fuel resources available are not sufficient for energy needed for emerging population. In this context, biohydrogen production approach through valorization of FW is emerging as one of the sustainable and eco-friendly options. The present review explores FW sources, characteristics, and dark fermentative production of hydrogen along with its efficiency. FW are highly biodegradable and rich in carbohydrates which can be efficiently utilized by anaerobic bacteria. Based on the composition of FW, several pretreatment methods can be adapted to improve the bioavailability of the organics. By-products of dark fermentation are organic acids that can be integrated with several secondary bioprocesses. The versatility of secondary products is ranging from energy generation to biochemicals production. Integrated approaches facilitate in enhanced energy harvesting along with extended wastewater treatment. The review also discusses various parameters like pH, temperature, hydraulic retention time and nutrient supplementation to enhance the process efficiency of biohydrogen production. The application of solid-state fermentation (SSF) in dark fermentation improves the process efficiency. Dark fermentation as the key process for valorization and additional energy generating process can make FW the most suitable substrate for circular economy and waste based biorefinery.

Actividad antimicrobiana in vitro del extracto de hojas de Bixa orellana L. contra bacterias anaerobias asociadas a la vaginosis bacteriana y Lactobacillus spp / In vitro antimicrobial activity of Bixa orellana L. leaves extract against anaerobic bacteria associated to bacterial vaginosis and Lactobacillus spp.

Objetivos . Describir la actividad antimicrobiana in vitro del extracto metanólico de las hojas de Bixa orellana L. contra las bacterias anaerobias asociadas a la vaginosis bacteriana y Lactobacillus spp. Materiales y métodos . Se incluyeron en el estudio ocho cepas de referencia ATCC; Gardnerella vaginalis, Prevotella bivia, Peptococcus niger, Peptostreptococcus anaerobius, Mobiluncus curtisii, Atopobium vaginae, Veillonella parvula y Lactobacillus crispatus, y 22 aislamientos clínicos; once aislados de Gardnerella vaginalis y once aislados de Lactobacillus. La susceptibilidad antimicrobiana se determinó mediante el método de difusión en agar. La concentración mínima inhibitoria (CMI) y la concentración bactericida mínima (CBM) fueron determinadas utilizando el método de dilución en agar y un método de dilución modificado, respectivamente. Resultados . Todas las cepas de referencia ATCC tuvieron un alto nivel de susceptibilidad al extracto, con excepción de P. vibia, V. parvula y L. crispatus. Interesantemente, los aislamientos clínicos de G. vaginalis y la cepa ATCC de G. vaginalis fueron los más susceptibles al extracto dados los bajos valores de CMI (1,0 - 2,0 mg/mL) y CBM (1,0 - 4,0 mg/mL), mientras que, los aislamientos clínicos de Lactobacillus spp. y la cepa ATCC de L. crispatus fueron los menos susceptibles debido a los altos valores de CMI (32,0 mg/mL) y CBM (≥ 32,0 mg/mL). Conclusiones . Los experimentos in vitro sugieren que el extracto posee propiedades antibacterianas selectivas dada su alta actividad contra bacterias anaerobias asociadas a vaginosis bacteriana y baja actividad contra especies de Lactobacillus.

Objective. To describe the in vitro antimicrobial activity of the methanolic extract of Bixa orellana L. leaves against anaerobic bacteria associated to bacterial vaginosis and Lactobacillus spp. Materials and methods. Eight ATCC reference strains; Gardnerella vaginalis, Prevotella bivia, Peptococcus niger, Peptostreptococcus anaerobius, Mobiluncus curtisii, Atopobium vaginae, Veillonella parvula, and Lactobacillus crispatus, and twenty-two clinical isolates; eleven Gardnerella vaginalis and eleven Lactobacillus strains, were included in the study. The antimicrobial susceptibility was determined by the agar diffusion method. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by using agar dilution and a modified dilution plating method, respectively. Results. All ATCC reference strains showed high levels of susceptibility to the extract, except P. vibia, V. parvula and L. crispatus. Interestingly, all G. vaginalis clinical isolates and the G. vaginalis ATTC strain were the most susceptible to the extract, given their low MIC (1.0 - 2.0 mg/mL) and MBC (1.0 - 4.0 mg/mL) values, whereas, the Lactobacillus spp. clinical isolates and the L. crispatus ATCC strain were the least susceptible bacteria given their high MIC (32.0 mg/mL) and MBC (≥ 32.0 mg/mL) values. Conclusions. In vitro experiments suggest that the extract possesses selective antimicrobial properties given its high activity against bacterial vaginosis-associated anaerobic bacteria and low activity against Lactobacillus species.

The influence of anaerobic dechlorination on the aerobic degradation of PCBs in e-waste-contaminated soils in an anaerobic-aerobic two-stage treatment.

The combination of microbial reductive dechlorination and aerobic oxidation (RD-AO) process was proposed to be a promising strategy for extensive bioremediation of highly chlorinated polychlorinated biphenyls (PCBs). Nonetheless, experimental evidence on the impact of the RD on subsequent AO in anaerobic-aerobic two-stage treatment remains scarce. The present study applied stable-isotope probing (SIP) to explore the RD-AO mediated degradation of PCBs in an e-waste-contaminated soil. The RD-AO treatment resulted in 37.1 % and 48.2 % degradation of PCB180 and PCB9, respectively, while the PCB9 degradation efficiency decreased compared to the sole AO (81.2 %). The inhibition of PCB aerobic degradation might be caused by the alteration of aerobic bacterial community, which was proved by a higher abundance of anaerobic bacteria and a lower abundance of aerobic bacteria being observed in the aerobic stage of RD-AO. Further evidence was obtained using DNA-SIP that the anaerobic stage altered the PCB degraders' community structures and changed three of the five degraders. There were four lineages (Arenimonas, Steroidobacter, Sulfurifustis, and Thermoanaerobacterales) identified as PCB degraders for the first time. Interestingly, three of them were found in RD-AO microcosm, suggesting that anaerobic-aerobic two-stage treatment can recruit novel bacteria involved in PCBs aerobic degradation. The present study provided novel insight into the synergistic integration of anaerobic and aerobic processes for extensive degradation of highly chlorinated PCBs.

Time for Some Group Therapy: Update on Identification, Antimicrobial Resistance, Taxonomy, and Clinical Significance of the Bacteroides fragilis Group.

Bacteroides fragilis group (BFG) species are common members of the human microbiota that provide several benefits to healthy hosts, yet BFG are also the most common anaerobes isolated from human infections, including intra-abdominal infections, abscesses, and bloodstream infection. Compared to many other anaerobes associated with disease, members of the BFG are more likely to be resistant to commonly used antimicrobials, including penicillin (>90% resistant), carbapenems (2 to 20% resistant), and metronidazole (0.2 to 4% resistant). As a result, infection with BFG bacteria can be associated with poor clinical outcomes. Here, we discuss the role of BFG in human health and disease, proposed taxonomic reclassifications within the BFG, and updates in methods for species-level identification. The increasing availability of whole-genome sequencing (WGS) supports recent proposals that the BFG now span two families (Bacteroidaceae and "Tannerellaceae") and multiple genera (Bacteroides, Parabacteroides, and Phocaeicola) within the phylum Bacteroidota. While members of the BFG are often reported to "group" rather than "species" level in many clinical settings, new reports of species-specific trends in antimicrobial resistance profiles and improved resolution of identification tools support routine species-level reporting in clinical practice. Empirical therapy may not be adequate for treatment of serious infections with BFG, warranting susceptibility testing for serious infections. We summarize methods for antimicrobial susceptibility testing and resistance prediction for BFG, including broth microdilution, agar dilution, WGS, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). We examine global trends in BFG antimicrobial resistance and review genomics of BFG, revealing insights into rapid activation and dissemination of numerous antimicrobial resistance mechanisms.

Clostridium weizhouense sp. nov., an anaerobic bacterium isolated from activated sludge of petroleum wastewater.

A Gram-stain-positive, anaerobic, spore-forming, rod-shaped (0.4-0.6 µm×2.5-3.2 µm), flagellated bacterium, designated strain YB-6T, was isolated from activated sludge of an anaerobic tank at Weizhou marine oil mining wastewater treatment plant in Beihai, Guangxi, PR China. The culture conditions were 25-45 °C (optimum, 37 °C), pH 4-12 (pH 7.0) and NaCl concentration of 0-7 % w/v (0%). Strain YB-6T grew slowly in petroleum wastewater and removed 68.2 % of the total organic carbon in petroleum wastewater within 10 days. Concentrations of naphthalene, anthracene and phenanthrene at an initial concentration of 50 mg l-1 were reduced by 32.8, 40.4 and 14.6 %, respectively, after 7 days. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain YB-6T belongs to Clostridium cluster I and is most closely related to Clostridium uliginosum CK55T (98.5 % similarity). The genome size of strain YB-6T was 3.96 Mb, and the G+C content was 26.5 mol%. The average nucleotide identity value between strain YB-6T and C. uliginosum CK55T was 81.9 %. The major fatty acids in strain YB-6T were C14 : 0 FAME, C16 : 0 FAME and summed feature 4 (unknown 14.762 and/or C15 : 2 FAME). The main polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified aminophospholipids, one unidentified glycolipid and one unidentified aminolipid. Diaminopimelic acid was not detected in the strain YB-6T cell walls. Whole-cell sugars mainly consisted of ribose and galactose. Based on the results of phenotypic and genotypic analyses, strain YB-6T represents a novel species of the genus Clostridium, for which the name Clostridium weizhouense sp. nov. is proposed. The type strain is YB-6T (=GDMCC 1.2529T=JCM 34754T).

Enhanced anaerobic degradation of thiobencarb using a horizontal-flow anaerobic immobilized biomass bioreactor.

Thiobencarb is a herbicide globally used in the agricultural sector, and its extensive application leads to severe environmental pollution. In this study, the thiobencarb supplementation caused a significant shift in the bacterial community in the sediment slurry. An analysis of the degradation metabolites of microorganisms from the sediment indicated that deschlorothiobencarb, S-4-chlorobenzyl ethylthiocarbamate, 4-chlorobenzyl mercaptan, 4-chlorobenzyl alcohol, 4-chlorobenzoic acid and chlorobenzene were the main intermediates. The degradation rates were significantly enhanced using a horizontal-flow anaerobic reactor with immobilized cells in polyurethane foam. The degradation rates at 2.6, 12.9 and 25.6 mg L-1 concentrations by suspended microorganisms from the sediment in the mineral medium supplemented with glucose were 0.085 ± 0.000, 0.383 ± 0.010 and 0.500 ± 0.045 mg day-1, respectively. The corresponding data for degradation in the reactor were 2.54 ± 0.03, 11.69 ± 0.72 and 18.58 ± 1.83 mg day-1 at the sixth operation period. Moreover, COD removal efficiencies were >90% achieved in the reactor. The proposed method facilitates degradation using a horizontal-flow anaerobic immobilized biomass bioreactor. Moreover, this study reveals the degradation of metabolites of thiobencarb under anaerobic conditions.

In Vitro Evaluation of the Activity of Aztreonam-Avibactam against 341 Recent Clinical Isolates of Anaerobes.

Aztreonam-avibactam is under clinical development for multidrug-resistant Gram-negative infections. We evaluated in vitro activity against 341 recent clinical isolates. The addition of avibactam to aztreonam had no effect on the anaerobic activity of aztreonam. IMPORTANCE This work shows that aztreonam-avibactam lacks activity against anaerobic organisms.

Indigofera tinctoria leaf powder as a promising additive to improve indigo fermentation prepared with sukumo (composted Polygonum tinctorium leaves).

Being insoluble in the oxidize form, indigo dye must be solubilized by reduction for it to penetrate textile. One of the procedures is the reduction by natural bacterial fermentation. Sukumo, composted leaves of Polygonum tinctorium, is a natural source of indigo in Japan. Although sukumo has an intrinsic bacterial seed, the onset of indigo reduction with this material may vary greatly. Certain additives improve indigo fermentation. Here, we studied the effects of Indigofera tinctoria leaf powder (LP) on the initiation of indigo reduction, bacterial community, redox potential (ORP), and dyeing intensity in the initial stages and in aged fermentation fluids prepared with sukumo. I. tinctoria LP markedly decreased ORP at day 1 and stabilised it during early fermentation. These effects could be explained by the phytochemicals present in I. tinctoria LP that act as oxygen scavengers and electron mediators. Using next generation sequencing results, we observed differences in the bacterial community in sukumo fermentation treated with I. tinctoria LP, which was not influenced by the bacterial community in I. tinctoria LP per se. The concomitant decrease in Bacillaceae and increase in Proteinivoraceae at the onset of fermentation, increase in the ratio of facultative to obligate anaerobes (F/O ratio), or the total abundance of facultative anaerobes (F) or obligate anaerobes (O) (designated F + O) are vital for the initiation and maintenance of indigo reduction. Hence, I. tinctoria LP improved early indigo reduction by decreasing the ORP and hasten the appropriate transitions in the bacterial community in sukumo fermentation.

Selenium respiration in anaerobic bacteria: Does energy generation pay off?

Selenium (Se) respiration in bacteria was revealed for the first time at the end of 1980s. Although thermodynamically-favorable, energy-dense and documented in phylogenetically-diverse bacteria, this metabolic process appears to be accompanied by a number of challenges and numerous unanswered questions. Selenium oxyanions, SeO42- and SeO32-, are reduced to elemental Se (Se0) through anaerobic respiration, the end product being solid and displaying a considerable size (up to 500 nm) at the bacterial scale. Compared to other electron acceptors used in anaerobic respiration (e.g. N, S, Fe, Mn, and As), Se is one of the few elements whose end product is solid. Furthermore, unlike other known bacterial intracellular accumulations such as volutin (inorganic polyphosphate), S0, glycogen or magnetite, Se0 has not been shown to play a nutritional or ecological role for its host. In the context of anaerobic respiration of Se oxyanions, biogenic Se0 appears to be a by-product, a waste that needs proper handling, and this raises the question of the evolutionary implications of this process. Why would bacteria use a respiratory substrate that is useful, in the first place, and then highly detrimental? Interestingly, in certain artificial ecosystems (e.g. upflow bioreactors) Se0 might help bacterial cells to increase their density and buoyancy and thus avoid biomass wash-out, ensuring survival. This review article provides an in-depth analysis of selenium respiration (model selenium respiring bacteria, thermodynamics, respiratory enzymes, and genetic determinants), complemented by an extensive discussion about the evolutionary implications and the properties of biogenic Se0 using published and original/unpublished results.

Pairing denitrifying phosphorus accumulating organisms with anaerobic ammonium oxidizing bacteria for simultaneous N and P removal.

Coupling of denitrifying polyphosphate accumulating organisms (DPAO) with anaerobic ammonium oxidizing (Anammox) bacteria in a single treatment scheme has so far been unsuccessful but could offer substantial energy savings, minimize sludge production, while achieving simultaneous carbon, nitrogen and phosphate removal. However, both organisms compete for nitrite and have vastly different growth rates and therefore the goal of this study was to uncouple their solid retention time (SRT) by growing them in different sludge fractions and to determine their biomass specific kinetic properties. Anammox bacteria were grown in a biofilm for longer SRTs and DPAO in flocs to allow shorter SRTs. Exposure of DPAO to anaerobic conditions was accomplished by recycling the flocs to a separate reactor by which simultaneous P, N, and C removal was accomplished. The diffusion limited biofilm lowered the biomass specific nitrite affinity for Anammox (KsAMX = 0.091 mM), which gave DPAO a competitive edge to consume nitrite (KsDPAO = 0.022 mM) in the suspended floc fraction. However, DPAO are more sensitive to nitrite (KiDPAO = 0.377 mM) than Anammox bacteria and (KiAMX > 1.786 mM), and therefore the DPAO would be better suited to grow in the protective biofilm, showing that both biomass growth types (flocs and granules) have advantages (and disadvantages) depending on the setting. This work is an important steppingstone to understanding resource competition amongst Anammox and DPAO and SRT management strategies to allow their pairing in combined reactor configurations.

Antimicrobial susceptibility testing of Eggerthella lenta blood culture isolates at a university hospital in Belgium from 2004 to 2018.

OBJECTIVES: Eggerthella lenta is a Gram-positive anaerobic bacillus that is an important cause of bloodstream infections. This study aims to test the susceptibility of Eggerthella lenta blood culture isolates to commonly used antibiotics for the empirical treatment of anaerobic infections. METHODS: In total, 49 positive blood cultures for Eggerthella lenta were retrospectively included from patients hospitalised at the Universitair Ziekenhuis Brussel, Belgium, between 2004 and 2018. Identification was done by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) system. Antimicrobial susceptibility testing was performed using the reference agar dilution method according to Clinical and Laboratory Standards Institute (CLSI) guidelines with Brucella agar supplemented with 5 µg/mL hemin, 1 µg/mL vitamin K1 and 5% laked sheep blood. The minimal inhibitory concentrations were interpreted using the EUCAST breakpoints. Clinical characteristics were collected by reviewing the patient's medical records. RESULTS: All isolates were susceptible to amoxicillin-clavulanate, metronidazole and meropenem. Eighty-eight % of them were susceptible to clindamycin and 94% (20% S, 74% I) were susceptible to piperacillin-tazobactam. The mean age of the patients was 64 (±20) and they showed a 30-day mortality of 27%. The source of infection was in 65.3% of the cases abdominal, 20.4% were sacral pressure ulcers and 14.3% were unknown causes. While all isolates were fully susceptible at standard dosing regimen to amoxicillin-clavulanate, most were only susceptible at increased exposure or resistant to piperacillin-tazobactam. CONCLUSIONS: Our results suggest to be careful with the use of piperacillin-tazobactam and clindamycin in the empirical treatment of Eggerthella lenta infections.

[Progress in the treatment of intra-abdominal anaerobic infection].

Most abdominal infections are mixed infections caused by aerobic and anaerobic bacteria. Anaerobic infections are characterized by rancid secretions or abscess formation. Early implementation of source control is the key in the treatment of abdominal anaerobic infections. Damage control should be followed as one of the principles of surgical treatment. As the in vitro isolation and culture of anaerobic bacteria as well as its drug sensitivity test are time-consuming and sometimes inaccurate, the treatment of anaerobic bacteria infection is mostly empirical. Anti-infective therapy should be employed once anaerobic bacteria infection is confirmed. Ertapenem, Mosifloxacin, and Cefoperazone-sulbactam can be used for first-line monotherapy, while combination therapy can use second- or third-generation Cephalosporin, Quinolones plus Nitroimidazoles. Nutritional support and anti-shock treatment should not be neglected when implementing surgical control of infection source and antimicrobial therapy. Considering the increasing drug resistance of anaerobic bacteria, and the higher drug resistance rate in China as compared to western countries, the choice of antibiotics should be made rationally and based on epidemiological characteristics of anaerobic bacteria in different regions.

Dose-response analysis of toxic effect from palm oil mill effluent (POME) by-products on biohydrogen producing bacteria - A preliminary study on microbial density and determination of EC50.

The stimulant and toxicity effects of reported organic (acetic acid, propionic acid, butyric acid, formic acid, oil & grease) and inorganic (copper) by-products presented in palm oil mill effluent on anaerobic bacterial population were examined in this paper. The toxicity test had shown that acetic, propionic and butyric acids tend to stimulate the bacterial density level (survival rate more than 50%), while formic acid, copper, oil and grease were shown to have suppressed the density level (survival rate less than 50%). The highest biomass recorded was 1.66 mg/L for the concentration of acetic acid at 216 mg/L and lowest biomass concentration, 0.90 mg/L for copper at 1.40 mg/L. Biohydrogen-producing bacteria have a favourable growth rate around pH 5.5. The comparison of half maximal effective concentration (EC50) values between two test duration on the effects of organic and inorganic by-products postulate that bacteria had a higher tolerance towards volatile fatty acids. While acetic, butyric and propionic acids had exhibited higher tolerance EC50 values for bacteria, but the opposite trend was observed for formic acid, copper and oil & grease.

Bacteria producing antimicrobials against Clostridium difficile isolated from human stool.

Clostridium difficile infection (CDI) is a common cause of morbidity and mortality in hospitalized patients worldwide. The major problem facing current treatment is multiple recurrences, prompting the need for alternative therapies. In this study we isolated bacterial species, from Egyptian individuals' stool, with antimicrobial activity against clinical isolates of C. difficile and tried to examine the nature of the produced antimicrobials. In vitro antibacterial activity against C. difficile was initially screened in 123 fecal samples cultures using an agar overlay method. The isolates with antimicrobial activity against C. difficile in addition to Clostridium isolates were identified using partial 16S rDNA gene sequencing analysis. The isolates acting against C. difficile belonged to Lactobacillus, Enterococcus and Clostridium genera. The concentrated cell-free supernatants (CFSs) from these bacterial isolates were examined for antimicrobial activity against C. difficile growth by broth dilution method. 10 x concentrated CFSs of five isolates showed inhibition for C. difficile growth which was significantly different (p < 0.001) from control. Lactobacillus agilis T99A and Clostridium butyricum T58A isolates were selected for further evaluation of the produced antimicrobials. The antimicrobial activity of 10x CFSs of the two isolates was stable after enzymatic treatment with proteinase K or heating treatments up to 90 °C or neutralizing pH. The spectrum of activity of the two isolates was evaluated using different gram-positive and gram-negative bacterial species and did not show antimicrobial activity against these species. Our results showed two unconventional bacterial isolates: L. agilis T99A and C. butyricum T58A producing extracellular thermo stable antimicrobial agents against C. difficile clinical isolates.

A phase conversion headspace technique for the determination of anti-anaerobic activity of drug candidate based on the metabolic acidity change in culture medium.

Screening for anti-anaerobic drug candidates is still challenging although the anaerobic bacteria are important sources for human infections, because the method for anti-anaerobic activity testing is not readily available with low-cost and -expertise. We report a novel method for the determination of the anti-anaerobic activity of drug candidates by automated headspace-gas chromatography (HS-GC). Anaerobic bacteria were inoculated in an anaerobic atmosphere or rapidly using sterile syringe in an air-tight manner, and incubated with and without drugs for 48 h. The metabolic acidities of the cultured media were used as an indicator of cell activities and measured as end-products in place by HS-GC after being completely converted to CO2 with sodium bicarbonate. The present method is precise (relative standard deviation is below 5%) and validated by excellent agreements with a reference method on the determinations of the inhibition rates (root-mean-square error = 10%, n = 48) and half maximal inhibitory concentrations (R2 = 0.996, n = 8) of both pure drug compounds and plant extracts. Advantageously, the present method is sensitive in response to cell activity, safe with regard to cross contamination, and suitable for routine screening of diversified drug candidates for anti-anaerobic activity.

Fortified hyperbranched PEGylated chitosan-based nano-in-micro composites for treatment of multiple bacterial infections.

Bacterial resistance is a real threat to human health. One of the most common strategies used to overcome this problem is the combination therapy. This study proposes a new chitosan-based nano-in-microparticles (NIMs) antibacterial platform that can deliver multiple antibacterial therapeutics at the same time. Chitosan (CS) was PEGylated to overcome its limited water solubility. Then, the antibacterial activity of the resulting PEG-CS was fortified via conjugation with dendritic polyamidoamine hyperbranches (HB) as well as in-situ immobilization of silver nanoparticles (AgNPs) to be efficient against multiple bacterial strains. Montmorillonite nanoclay (MMT) was prepared and used to encapsulate ibuprofen (IBU) as anti-inflammatory drug to reduce any concomitant inflammatory response during bacterial infection. The successful synthesis of PEG-HBCS-AgNPs as well as IBU-MMT nanocomplex was confirmed using FTIR, 1H NMR, DSC, TGA and EDX. SEM micrographs showed a complete formation of NIM spherical particles with a size around 13 µm. Besides, the newly developed drugs-loaded CS-based NIM formulation showed a better widespread activity on the tested aerobic and anaerobic bacterial species, and it may represent, after further optimization, a promising approach for overcoming multiple-bacterial infection.