Gut bacteria promote proliferation in benign S/RG/C2 colorectal tumour cells, and promote proliferation, migration and invasion in malignant HCT116 cells

Colorectal cancer (CRC) is a significant global health burden with a rising incidence worldwide. Distinct bacterial populations are associated with CRC development and progression, and it is thought that the relationship between CRC and associated gut bacteria changes during the progression from normal epithelium to benign adenoma and eventually malignant carcinoma and metastasis. This study compared the interaction of CRC-associated species Enterotoxigenic Bacteroides fragilis, Enterococcus faecalis and Fusobacterium nucleatum and one probiotic species, Escherichia coli Nissle 1917 with a colorectal adenoma (S/RG/C2) and a colorectal adenocarcinoma (HCT116) derived cell line. Gentamicin protection assays showed that all species displayed higher attachment to benign tumour monolayers when compared to malignant monolayers. However, invasion of 3/4 species was higher in the HCT116 cells than in the adenoma cells. All species were found to persist within tumour cell monolayers for a minimum of 48 h under standard aerobic cell culture conditions, with persistence significantly higher in HCT116 cells. Downstream assays were performed to analyse the behaviour of S/RG/C2 and HCT116 cells post-infection and revealed that all species increased the tumour cell yield of both cell lines. The migratory and invasive potential of HCT116 cells was increased after infection with F. nucleatum; however, no species significantly altered these characteristics in S/RG/C2 cells. These results add to the growing evidence for the involvement of microorganisms in CRC progression and suggest that these interactions may be dependent on tumour cell-specific characteristics.

A case study: The deployment of a novel in situ fluorimeter for monitoring biological contamination within the urban surface waters of Kolkata, India

The quality and health of many of our vital freshwater systems are poor. To tackle this with ever increasing pressures from anthropogenic and climatic changes, we must improve water quality monitoring and devise and implement more appropriate water quality parameters. Recent research has highlighted the potential for Peak T fluorescence (tryptophan-like fluorescence, TLF) to monitor microbial activity in aquatic systems. The VLux TPro (Chelsea Technologies Ltd., UK), an in situ real-time fluorimeter, was deployed in different urban freshwater bodies within Kolkata (West Bengal, India) during March 2019. This study is the first to apply this technology in surface waters within a densely populated urban area. Spot-sampling was also undertaken at 13 sampling locations enabling physicochemical analysis, bacterial enumeration and determination of nutrient (nitrate and phosphate) concentrations. This case study has demonstrated the ability of an in situ fluorimeter, VLux TPro, to successfully identify both biological contamination events and potential elevated microbial activity, related to nutrient loading, in complex surface freshwaters, without the need for expensive and time-consuming laboratory analysis.

The in situ Production of Aquatic Fluorescent Organic Matter in a Simulated Freshwater Laboratory Model

Dissolved organic matter (DOM) is ubiquitous throughout aquatic systems. Fluorescence techniques can be used to characterize the fluorescing proportion of DOM, aquatic fluorescent organic matter (AFOM). AFOM is conventionally named in association with specific fluorescence “peaks,” which fluoresce in similar optical regions as microbially-derived proteinaceous material (Peak T), and terrestrially-derived humic-like compounds (Peaks C/C+), with Peak T previously being investigated as a tool for bacterial enumeration within freshwaters. The impact of anthropogenic nutrient loading on the processing of DOM by microbial communities is largely unknown. Previous laboratory studies utilizing environmental freshwater have employed growth media with complex background fluorescence, or very high nutrient concentrations, preventing the investigation of AFOM production under a range of more representative nutrient concentrations within a matrix exhibiting very low background fluorescence. We describe a laboratory-based model with Pseudomonas aeruginosa that incorporates a low fluorescence growth matrix consisting of a simulated freshwater (SFW), representative of low-hardness freshwater systems allowing controlled nutrient conditions to be studied. The effects of microbial processing of DOM as a function of available nitrogen, phosphorous, and dissolved organic carbon (DOC) in the form of glucose were investigated over 48 h at highly resolved time increments. The model system demonstrates the production of a range of complex AFOM peaks in the presence and absence of DOC, revealing no linear relationship between cell numbers and any of the peaks for the bacterial species studied, with AFOM peaks increasing with microbial cell number, ranging from 55.2 quinine sulfate units (QSU) per 10⁶ cells to 155 QSU per 10⁶ cells (p < 0.05) for Peak T during the exponential growth phase of P. aeruginosa under high nutrient conditions with 5 mg L⁻¹ DOC. Nutrient and DOC concentration was found to cause differential production of autochthonous- or allochthonous-like AFOM, with lower DOC concentrations resulting in higher Peak T production relative to Peaks C/C+ upon the addition of nutrients, and high DOC concentrations resulting in higher Peak C/C+ production relative to Peak T. Our results show the production of allochthonous-like AFOM from a simple and non-fluorescent carbon source, and provide uncertainty in the use of Peak T as a reliable surrogate for specific bacterial enumeration, particularly in dynamic or nutrient-impacted environments, pointing toward the use of fluorescence as an indicator for microbial metabolism.

A systematic approach to understand hydrogeochemical dynamics in large river systems: Development and application to the River Ganges (Ganga) in India

Large river systems, such as the River Ganges (Ganga), provide crucial water resources for the environment and society, yet often face significant challenges associated with cumulative impacts arising from upstream environmental and anthropogenic influences. Understanding the complex dynamics of such systems remains a major challenge, especially given accelerating environmental stressors including climate change and urbanization, and due to limitations in data and process understanding across scales. An integrated approach is required which robustly enables the hydrogeochemical dynamics and underpinning processes impacting water quality in large river systems to be explored. Here we develop a systematic approach for improving the understanding of hydrogeochemical dynamics and processes in large river systems, and apply this to a longitudinal survey (> 2500 km) of the River Ganges (Ganga) and key tributaries in the Indo-Gangetic basin. This framework enables us to succinctly interpret downstream water quality trends in response to the underpinning processes controlling major element hydrogeochemistry across the basin, based on conceptual water source signatures and dynamics. Informed by a 2019 post-monsoonal survey of 81 river bank-side sampling locations, the spatial distribution of a suite of selected physico-chemical and inorganic parameters, combined with segmented linear regression, reveals minor and major downstream hydrogeochemical transitions. We use this information to identify five major hydrogeochemical zones, characterized, in part, by the inputs of key tributaries, urban and agricultural areas, and estuarine inputs near the Bay of Bengal. Dominant trends are further explored by investigating geochemical relationships (e.g. Na:Cl, Ca:Na, Mg:Na, Sr:Ca and NO₃:Cl), and how water source signatures and dynamics are modified by key processes, to assess the relative importance of controls such as dilution, evaporation, water-rock interactions (including carbonate and silicate weathering) and anthropogenic inputs. Mixing/dilution between sources and water-rock interactions explain most regional trends in major ion chemistry, although localized controls plausibly linked to anthropogenic activities are also evident in some locations. Temporal and spatial representativeness of river bank-side sampling are considered by supplementary sampling across the river at selected locations and via comparison to historical records. Limitations of such large-scale longitudinal sampling programs are discussed, as well as approaches to address some of these inherent challenges. This approach brings new, systematic insight into the basin-wide controls on the dominant geochemistry of the River Ganga, and provides a framework for characterising dominant hydrogeochemical zones, processes and controls, with utility to be transferable to other large river systems.

Real-time detection of volatile metabolites enabling species-level discrimination of bacterial biofilms associated with wound infection

Aims

The main aim of this study was to investigate the real‐time detection of volatile metabolites for the species‐level discrimination of pathogens associated with clinically relevant wound infection, when grown in a collagen wound biofilm model.

Methods and Results

This work shows that Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pyogenes produce a multitude of volatile compounds when grown as biofilms in a collagen‐based biofilm model. The real‐time detection of these complex volatile profiles using selected ion flow tube mass spectrometry and the use of multivariate statistical analysis on the resulting data can be used to successfully differentiate between the pathogens studied.

Conclusions

The range of bacterial volatile compounds detected between the species studied vary and are distinct. Discrimination between bacterial species using real‐time detection of volatile metabolites and multivariate statistical analysis was successfully demonstrated.

Significance and Impact of the Study

Development of rapid point‐of‐care diagnostics for wound infection would improve diagnosis and patient care. Such technological approaches would also facilitate the appropriate use of antimicrobials, minimizing the emergence of antimicrobial resistance. This study further develops the use of volatile metabolite detection as a new diagnostic approach for wound infection.

An in vitro collagen perfusion wound biofilm model; with applications for antimicrobial studies and microbial metabolomics

Background

The majority of in vitro studies of medically relevant biofilms involve the development of biofilm on an inanimate solid surface. However, infection in vivo consists of biofilm growth on, or suspended within, the semi-solid matrix of the tissue, whereby current models do not effectively simulate the nature of the in vivo environment. This paper describes development of an in vitro method for culturing wound associated microorganisms in a system that combines a semi-solid collagen gel matrix with continuous flow of simulated wound fluid. This enables culture of wound associated reproducible steady state biofilms under conditions that more closely simulate the dynamic wound environment. To demonstrate the use of this model the antimicrobial kinetics of ceftazidime, against both mature and developing Pseudomonas aeruginosa biofilms, was assessed. In addition, we have shown the potential application of this model system for investigating microbial metabolomics by employing selected ion flow tube mass spectrometry (SIFT-MS) to monitor ammonia and hydrogen cyanide production by Pseudomonas aeruginosa biofilms in real-time.

Results

The collagen wound biofilm model facilitates growth of steady-state reproducible Pseudomonas aeruginosa biofilms under wound like conditions. A maximum biofilm density of 10¹⁰ cfu slide^− 1 was achieved by 30 h of continuous culture and maintained throughout the remainder of the experiment. Treatment with ceftazidime at a clinically relevant dose resulted in a 1.2–1.6 log reduction in biofilm density at 72 h compared to untreated controls. Treatment resulted in loss of complex biofilm architecture and morphological changes to bacterial cells, visualised using confocal microscopy. When monitoring the biofilms using SIFT-MS, ammonia and hydrogen cyanide levels peaked at 12 h at 2273 ppb (±826.4) and 138 ppb (±49.1) respectively and were detectable throughout experimentation.

Conclusions

The collagen wound biofilm model has been developed to facilitate growth of reproducible biofilms under wound-like conditions. We have successfully used this method to: (1) evaluate antimicrobial efficacy and kinetics, clearly demonstrating the development of antimicrobial tolerance in biofilm cultures; (2) characterise volatile metabolite production by P. aeruginosa biofilms, demonstrating the potential use of this method in metabolomics studies.

The in situ bacterial production of fluorescent organic matter; an investigation at a species level

Aquatic dissolved organic matter (DOM) plays an essential role in biogeochemical cycling and transport of organic matter throughout the hydrological continuum. To characterise microbially-derived organic matter (OM) from common environmental microorganisms (Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa), excitation-emission matrix (EEM) fluorescence spectroscopy was employed. This work shows that bacterial organisms can produce fluorescent organic matter (FOM) in situ and, furthermore, that the production of FOM differs at a bacterial species level. This production can be attributed to structural biological compounds, specific functional proteins (e.g. pyoverdine production by P. aeruginosa), and/or metabolic by-products. Bacterial growth curve data demonstrates that the production of FOM is fundamentally related to microbial metabolism. For example, the majority of Peak T fluorescence (> 75%) is shown to be intracellular in origin, as a result of the building of proteins for growth and metabolism. This underpins the use of Peak T as a measure of microbial activity, as opposed to bacterial enumeration as has been previously suggested. This study shows that different bacterial species produce a range of FOM that has historically been attributed to high molecular weight allochthonous material or the degradation of terrestrial FOM. We provide definitive evidence that, in fact, it can be produced by microbes within a model system (autochthonous), providing new insights into the possible origin of allochthonous and autochthonous organic material present in aquatic systems.

Assessing the antimicrobial potential of aerosolised electrochemically activated solutions (ECAS) for reducing the microbial bio-burden on fresh food produce held under cooled or cold storage conditions

The main aim of this study was to assess the antimicrobial efficacy of electrochemically activated fog (ECAF) for reducing the microbial bio-burden on artificially inoculated fresh produce held under cooled (cucumber and vine tomatoes) or cold (rocket and broccoli) storage conditions. The ECAF treatment (1100 ± 5 mV ORP; 50 ± 5 mg L^-1 free chlorine; 2.7 ± 0.1 pH) resulted in a significant log reduction in the potential pathogen E. coli recovered from rocket (2.644 Log₁₀ CFU g^-1), broccoli (4.204 Log₁₀ CFU g^-1), cucumber (3.951 Log₁₀ CFU g^-1) and tomatoes (2.535 Log10 CFU g-1) after 5 days. ECAF treatment also resulted in a significant log reduction in potential spoilage organisms, whereby a 3.533 Log₁₀ CFU g^-1, 2.174 Log₁₀ CFU g^-1 and 1.430 Log₁₀ CFU g^-1 reduction in presumptive Pseudomonads was observed for rocket, broccoli and cucumber respectively, and a 3.527 Log₁₀ CFU g^-1 reduction in presumptive Penicillium spp. was observed for tomatoes (after 5 days). No adverse visual effects on produce were recorded. The results of this study will inform industrial scale-up trials within commercial facilities (assessing shelf-life, microbial quality and organoleptic assessment) to assess the developed ECAF technology platform within a real food processing environment.

In vitro discrimination of wound-associated bacteria by volatile compound profiling using selected ion flow tube-mass spectrometry

AIMS

To determine if bacterial species responsible for clinically relevant wound infection produce specific volatile profiles that would allow their speciation.

METHODS AND RESULTS

Selected ion flow tube-mass spectrometry (SIFT-MS) in full mass scan mode was used to analyse headspace gases produced by wound-associated bacteria grown in vitro, so as to enable identification of bacterial volatile product ion profiles in the resulting mass spectra. Applying multivariate statistical analysis (hierarchical clustering and principal component analysis) to the resultant mass spectra enabled clear speciation. Moreover, bacterial volatile product ions could be detected from artificially contaminated wound dressing material, although the pattern of product ions detected was influenced by culture conditions.

CONCLUSIONS

Using selected product ions from the SIFT-MS mass spectra it is possible to discriminate wound-associated bacterial species grown under specific in vitro culture conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study have shown that wound-associated bacteria can be discriminated using volatile analysis in vitro and that bacterial volatiles can be detected from wound dressing material. This indicates that volatile analysis of wounds or dressing material to identify infecting microbes has potential and warrants further study.

Use of a bioluminescent Pseudomonas aeruginosa strain within an in vitro microbiological system, as a model of wound infection, to assess the antimicrobial efficacy of wound dressings by monitoring light production

A bioluminescent Pseudomonas aeruginosa was incorporated into an in vitro static diffusion method to determine whether light output could be used as a measure of wound dressing efficacy. A significant linear correlation was observed between viable counts and bioluminescence during exponential growth in planktonic culture (r(2) = 0.969). Exponential-phase cells were used to inoculate cellulose discs for integration into an in vitro wound model that incorporated a reservoir of serum. A significant linear correlation was found between bioluminescence (photon counts monitored by a low-light camera) and viable counts in this growth environment (r(2) = 0.982). Three antimicrobial wound dressings were applied to the surface of freshly prepared sample discs within the wound model, and the kill kinetics were codetermined by photon and viable counts. Quantifiable kill rates gave the same order of efficacy for the three wound dressings using both types of measurement, and a significant linear correlation was shown between photon and viable counts (r(2) = 0.873) within this killing environment. Under all defined conditions, a significant linear correlation between bioluminescence and viable counts was shown but the actual slope of the correlation was different, depending on the physicochemical environment of the cells. Hence, significantly more light per cell (P < 0.0001) was produced when cells in discs were exposed to a killing environment compared to a growing environment. As long as defined conditions are employed, the resulting linear correlation enables the state of the system to be continually monitored without disturbance, allowing more immediate and accurate calculations of kill rates without the need for viable counting.

In vitro diffusion bed, 3-day repeat challenge 'capacity' test for antimicrobial wound dressings

The aim of this study was to develop an in vitro wound infection model that allows the comparison of the bacterial kill rate of antimicrobial wound dressings over the course of 3 days, with renewed microbial challenges each day, under realistic wound-like conditions. A test bed model of a moderately exuding wound was constructed from a hydrogel containing releasable foetal calf serum (FCS), and cellulose discs dosed with test microbes (Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa) suspended in 50% FCS applied at the interface between the test dressing and the hydrogel test bed. Freshly prepared discs were used to challenge the same dressing over a 23-hour period for a course of 3 days. Different test dressings produced differing kill rates, allowing quantitative comparison of both their immediate activity and their capacity to continue working over 3 days, within a fluid-donating system similar to the situation in vivo. The reported method has significant advantages over established test procedures since it enables the researcher to assess the antimicrobial capacity of wound dressings to continue working under conditions that match those encountered in wounds. These key conditions are those that would be expected to impede the action of the dressing and protect the infecting organisms.

An in vitro study of antimicrobial activity and efficacy of iodine-generating hydrogel dressings

OBJECTIVE

To determine the antimicrobial activity and efficacy of different formulations of novel bioxygenating hydrogel dressings (which deliver both iodine and oxygen into the wound) against various target organisms by means of an in vitro test system that more effectively mimics the conditions encountered when dressings are in contact with wounds.

METHOD

Three bioxygenating hydrogels were tested: Oxyzyme, which releases low levels of iodine into the wound, and Iodozyme 402 and Iodozyme 401, which release higher levels of iodine, with Iodozyme 402 releasing twice the amount of 401. Cellulose filter disks (n = 32) were inoculated with indicator species and placed equidistant from each other as a matrix onto agar test beds. Cut squares of control or test dressings were placed on top of each disk. Kill curves were constructed from determinations of the numbers of survivors (log cfu per disk) over time by removing disk samples at various time points.

RESULTS

Significant differences (p < 0.05) were observed between the controls and test samples. The order of sensitivity for Oxyzyme was Fusobacterium nucleatum, Bacteroides fragilis, Propionibacterium acnes, Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus (MRSA), Candida albicans and Pseudomonas aeruginosa. The order of efficacy of the three hydrogel dressings (Iodozyme 402, followed by Iodozyme 401 and then Oxyzyme) was the same regardless of the target species.

CONCLUSION

The novel hydrogel skin surface wound dressings are broad-spectrum in activity, encompassing antibiotic-resistant organisms, anaerobes and yeasts; their antimicrobial function appears to be rapidly effective.

In vitro method to assess the antimicrobial activity and potential efficacy of novel types of wound dressings

AIMS

To develop a simple, reproducible in vitro static diffusion method using cellulose disks and defined species to test antimicrobial efficacy of wound dressings.

METHODS AND RESULTS

Cellulose disks were inoculated by immersion in cell suspensions of target species Staphylococcus epidermidis, Candida albicans and Fusobacterium nucleatum. Test and control wound dressings were cut into equal sized squares (25 x 25 mm) and applied to the surface of 10-mm thick tryptone yeast extract agar on test beds. Following a 2-h equilibration period, inoculated cellulose disks were inserted (one per dressing) at the interface between dressing and agar surface and a small weight applied over each square. At various sampling times, disks were removed and surviving cells enumerated by viable counts. Disk to disk variation for microbial loading was assessed using S. epidermidis for both initial (n = 16) and standard treatment (n = 16) conditions. The coefficient of variation was low (<5%) indicating good reproducibility for cell loading and treatment position on the test bed. Replicate assays (n = 6) using S. epidermidis and oxyzyme gels produced similar kill rates with low scatter (R2 > 0.9) indicating good reproducibility between assays. Significant differences (P < 0.05) in kill rates were observed for different target species, types of dressing and test bed conditions (+/-blood and nutrients).

CONCLUSIONS

The method is reproducible and useful in tracking the death kinetics of test species, enabling the comparison of different types of dressing.

SIGNIFICANCE AND IMPACT OF THE STUDY

The reported method has significant advantages over established test procedures; it can be applied equally across a wide range of target species (including anaerobes and yeasts), a wide range of conditions, and different types of surface dressings, including those relying upon oxygen diffusion.