Microbial Biosurfactants: Antimicrobial Activity and Potential Biomedical and Therapeutic Exploits

The rapid emergence of multidrug-resistant pathogens worldwide has raised concerns regarding the effectiveness of conventional antibiotics. This can be observed in ESKAPE pathogens, among others, whose multiple resistance mechanisms have led to a reduction in effective treatment options. Innovative strategies aimed at mitigating the incidence of antibiotic-resistant pathogens encompass the potential use of biosurfactants. These surface-active agents comprise a group of unique amphiphilic molecules of microbial origin that are capable of interacting with the lipidic components of microorganisms. Biosurfactant interactions with different surfaces can affect their hydrophobic properties and as a result, their ability to alter microorganisms' adhesion abilities and consequent biofilm formation. Unlike synthetic surfactants, biosurfactants present low toxicity and high biodegradability and remain stable under temperature and pH extremes, making them potentially suitable for targeted use in medical and pharmaceutical applications. This review discusses the development of biosurfactants in biomedical and therapeutic uses as antimicrobial and antibiofilm agents, in addition to considering the potential synergistic effect of biosurfactants in combination with antibiotics. Furthermore, the anti-cancer and anti-viral potential of biosurfactants in relation to COVID-19 is also discussed.

Association Between Household Location (Urban versus Rural) and Fundamental Care Provided to Domestic Dogs (Canis Familiaris) in Northern Ireland

This study aimed to generate information regarding living conditions (e.g. indoors and outdoors, living space available), fundamental care (e.g. feeding and exercise) and owners' perceptions of dog's preferences (e.g. living conditions) in the urban and rural areas of Northern Ireland via a cross-sectional survey questionnaire. The responses were collected from May to August 2022, at 24 locations across Northern Ireland, including 15 agricultural shows and livestock markets and nine large supermarkets (single supermarket chain) located in an area of the show or market grounds. In all, 548 questionnaires were collected and after exclusion of questionnaires with missing or incomprehensible responses, 507 questionnaires were included in the final database. Out of 507 questionnaires, 264 respondents resided in a city while 243 respondents resided on farms. The majority of respondents from the city locations perceived their dogs as pets, while those living on farms regarded their dogs as working animals. The populations of dogs in the city locations and on the farms in this study were similar regarding the age range and numbers of the animals, but more female dogs were spayed in the city locations than on the farms. Most respondents in this study, regardless of their household location, declared that they did not monitor their animal's body weight or body condition. When feeding their dogs, the respondents from the city locations were predominantly following veterinary advice or instructions on food labels. On the other hand, the respondents from farm locations mostly reported that they fed their dogs based on 'a visual inspection of dog condition'; this type of feeding was associated with a certain type of household occupancy (more frequent in single and adults only households) and respondents' employment status (more frequent by retired and those managing the home). The living conditions of dogs in city and farm locations in this study were different, namely dogs in the city were kept predominantly indoors with access to outdoors while dogs from farm locations were kept predominantly outdoors. The dogs were reported to be walked daily for a shorter time (up to 1 h/day) in the city locations and longer on the farm locations (1-2 h/day). Regardless of household location (city versus farm) respondents believed that exercise needs depend on animal age, body condition and medical condition, that dogs need to be kept active by owners to keep them fit, that dogs cannot self-regulate the amount of food they eat daily, and finally that walking with a dog a few times a day is difficult due to other commitments. On the other hand, the respondents from farm locations more often believe that dogs can get all the exercise they need by themselves if kept outdoors and they are happier with living outdoors, while the respondents from city locations believed that dogs are happier with living indoors. In conclusion, the results of this study have shown a number of differences in basic care and perception of dogs kept in city locations and on farm locations. Further studies are required to understand the provision of health care and fulfilments of all welfare needs of the dogs kept on farms.

Glycolipid Biosurfactants in Skincare Applications: Challenges and Recommendations for Future Exploitation

The 21st century has seen a substantial increase in the industrial applications of glycolipid biosurfactant technology. The market value of the glycolipid class of molecules, sophorolipids, was estimated to be USD 409.84 million in 2021, with that of rhamnolipid molecules projected to reach USD 2.7 billion by 2026. In the skincare industry, sophorolipid and rhamnolipid biosurfactants have demonstrated the potential to offer a natural, sustainable, and skin-compatible alternative to synthetically derived surfactant compounds. However, there are still many barriers to the wide-scale market adoption of glycolipid technology. These barriers include low product yield (particularly for rhamnolipids) and potential pathogenicity of some native glycolipid-producing microorganisms. Additionally, the use of impure preparations and/or poorly characterised congeners as well as low-throughput methodologies in the safety and bioactivity assessment of sophorolipids and rhamnolipids challenges their increased utilisation in both academic research and skincare applications. This review considers the current trend towards the utilisation of sophorolipid and rhamnolipid biosurfactants as substitutes to synthetically derived surfactant molecules in skincare applications, the challenges associated with their application, and relevant solutions proposed by the biotechnology industry. In addition, we recommend experimental techniques/methodologies, which, if employed, could contribute significantly to increasing the acceptance of glycolipid biosurfactants for use in skincare applications while maintaining consistency in biosurfactant research outputs.

Association between Socio-Demographic Factors and Owners' Beliefs and Attitudes to Pet Cats Fundamental Dietary and Physical Exercise Needs, in City of Belfast

A cross-sectional survey questionnaire was developed in-house to investigate pet cat owners’ beliefs and attitudes related to the fundamental care of their pet cats. The questionnaire consisted of questions which were grouped into the following sections: (i) owners’ socio-demographics; (ii) cat(s) body weight and body condition monitoring; (iii) owners’ attitudes to cats’ dietary preferences, needs and satisfaction, (iv) owners’ perceptions of their cats’ physical exercise needs and satisfaction. The sample size of 376 was estimated to be required to represent the population of the given geographical location (Belfast, NI, UK). Hard copies of the questionnaires were distributed in January and February 2019 and in total 402 completed questionnaires were collected; questionnaires which included >20% of missing or incomprehensible responses were excluded from the database, resulting in 398 questionnaires being included in the final database. The study identified a number of socio-demographic factors associated with owners’ beliefs and attitudes that directly affect care provided to pet cats, e.g., the owner’s occupation has been identified as a factor associated with owner perception of certain cats’ behaviours, e.g., a cat brushing against the owner as food requests by their animal (Chi-Square 7.711 (df1), exact p = 0.006). Furthermore, most female respondents, aged 26−67 years and in an occupation not related to animals, reported selecting cat food based on their animal preferences (Chi-Square 10.332 (df1), exact p = 0.003). In contrast, female owners in animal and veterinary occupations were significantly more likely as compared to other respondents (Chi-Square 15.228 (df1), exact p < 0.001), to select cat food based on its perceived health benefit to the cat. Analysis of the respondents’ opinions of cats’ abilities to self-regulate physical activity showed that owners age was the main differentiating determinant, i.e., cat owners over 25 years old were significantly more likely than younger adults to believe that pet cats can regulate their own physical activity to keep healthy (Chi-Square 6.313 (df1), exact p = 0.025). Furthermore, respondents’ opinions of their cat’s ability to self-regulate feed intake were mainly associated with owner’s education level (Chi-Square 6.367 (df1), exact p = 0.036). The study results indicated that the attitude and beliefs behind the fundamental care practices provided to pet cats depends on particular demographic factors, especially owners’ education and occupation.

Enterococcal biofilm - a nidus for antibiotic resistance transfer?

Enterococci, important agents of hospital acquired infection, are listed on the WHO list of multi-drug resistant pathogens commonly encountered in hospital acquired infections are now of increasing importance, due to the development of strains resistant to multiple antibiotics. Enterococci are also important microorganisms in the environment and their presence is frequently used as an indicator of faecal pollution. Their success is related to their ability to survive within a broad range of habitats and the ease by which they acquire mobile genetic elements, including plasmids, from other bacteria. The enterococci are frequently present within a bacterial biofilm which provides stability and protection to the bacterial population along with an opportunity for a variety of bacterial interactions. Enterococci can accept extrachromosomal DNA both from within its own species and from other bacterial species and this is enhanced by the proximity of the donor and recipient strains. It is this exchange of genetic material that makes the role of biofilm such an important aspect of the success of enterococci. There remain many questions regarding the most suitable model systems to study enterococci in biofilm and regarding the transfer of genetic material including antibiotic resistance in these biofilms. This review focuses on some important aspects of biofilm in the context of horizontal gene transfer (HGT) in enterococci.

The Fate of Foodborne Pathogens in Manure Treated Soil

The aim of this review was to provide an update on the complex relationship between manure application, altered pathogen levels and antibiotic resistance. This is necessary to protect health and improve the sustainability of this major farming practice in agricultural systems based on high levels of manure production. It is important to consider soil health in relation to environment and land management practices in the context of the soil microflora and the introduction of pathogens on the health of the soil microbiome. Viable pathogens in manure spread on agricultural land may be distributed by leaching, surface run-off, water source contamination and contaminated crop removal. Thus it is important to understand how multiple pathogens can persist in manures and on soil at farm-scale and how crops produced under these conditions could be a potential transfer route for zoonotic pathogens. The management of pathogen load within livestock manure is a potential mechanism for the reduction and prevention of outbreaks infection with Escherichia coli, Listeria Salmonella, and Campylobacter. The ability of Campylobacter, E. coli, Listeria and Salmonella to combat environmental stress coupled with their survival on food crops and vegetables post-harvest emphasizes the need for further study of these pathogens along with the emerging pathogen Providencia given its link to disease in the immunocompromised and its’ high levels of antibiotic resistance. The management of pathogen load within livestock manure has been widely recognized as a potential mechanism for the reduction and prevention of outbreaks infection but any studies undertaken should be considered as region specific due to the variable nature of the factors influencing pathogen content and survival in manures and soil. Mediocre soils that require nutrients could be one template for research on manure inputs and their influence on soil health and on pathogen survival on grassland and in food crops.

Caring practices of pet cat and dog owners in Northern Ireland vs potential implications for animals' health and welfare

This prospective, descriptive study assessed caring practices of pet cat and dog owners in Northern Ireland with a survey questionnaire, focusing primarily on feeding and exercising. Owners of both pet cats and dogs reported that they fed their pets either twice or three times a day (53 and 78% for cats and dogs, respectively). However, in the case of nearly 40% of pet cat owners it transpired that they fed their cat(s) as often as the animal demanded (18.8%) or that food was available all the time (20.7%). Cat owners reported that their pets had access to outdoors (84%) and were not provided with any play time (53.1%). The highest number of pet dogs (46.1%) were reported as being walked daily for less than 1 h, and the highest number (38.4%) were played with daily for less than 1 h. Both cat (60%) and dog (61%) owners perceived the body condition of their animal as it should be for animal age/sex. However, both pet cat (76%) and dog (63%) owners reported that neither their pets bodyweight nor its body condition was monitored. Our results suggest not all pet cat and dog owners are aware of the fundamentals of their animals feeding requirements as regards health and many provide insufficient physical activity required for their animals health and welfare. The major strengths of the study include the size and geographic distribution of the study population allowing the generalisation of the results to other locations.

Microscopic Investigation of the Combined Use of Antibiotics and Biosurfactants on Methicillin Resistant Staphylococcus aureus

One current strategy to deal with the serious issue of antibiotic resistance is to use biosurfactants, weak antimicrobials in their own right, with antibiotics in order to extend the efficacy of antibiotics. Although an adjuvant effect has been observed, the underlying mechanisms are poorly understood. To investigate the nature of the antibiotic and biosurfactant interaction, we undertook a scanning electron microscopy (SEM) and atomic force microscopy (AFM) microscopic study of the effects of the tetracycline antibiotic, combined with sophorolipid and rhamnolipid biosurfactants, on Methicillin-resistant Staphylococcus aureus using tetracycline concentrations below and above the minimum inhibitory concentration (MIC). Control and treated bacterial samples were prepared with an immersion technique by adsorbing the bacteria onto glass substrates grafted with the poly-cationic polymer polyethyleneimine. Bacterial surface morphology, hydrophobic and hydrophilic surface characters as well as the local bacterial cell stiffness were measured following combined antibiotic and biosurfactant treatment. The sophorolipid biosurfactant stands alone insofar as, when used with the antibiotic at sub-MIC concentration, it resulted in bacterial morphological changes, larger diameters (from 758 ± 75 to 1276 ± 220 nm, p-value = 10^-4) as well as increased bacterial core stiffness (from 205 ± 46 to 396 ± 66 mN/m, p-value = 5 × 10^-5). This investigation demonstrates that such combination of microscopic analysis can give useful information which could complement biological assays to understand the mechanisms of synergy between antibiotics and bioactive molecules such as biosurfactants.

Effects of freshwater sponge Ephydatia fluviatilis on conjugative transfer of antimicrobial resistance in Enterococcus faecalis strains in aquatic environments

Filter feeding is a biotic process that brings waterborne bacteria in close contact with each other and may thus support the horizontal transfer of their antimicrobial resistance genes. This laboratory study investigated whether the freshwater sponge Ephydatia fluviatilis supported the transfer of vancomycin resistance between two Enterococcus faecalis strains that we previously demonstrated to exhibit pheromone responsive plasmid conjugation. Microcosm experiments exposed live and dead colonies of laboratory-grown sponges to a vancomycin-resistant donor strain and a rifampicin-resistant recipient strain of Ent. faecalis. Enterococci with both resistance phenotypes were detected on double selection plates. In comparison to controls, abundance of these presumed transconjugants increased significantly in water from sponge microcosms. Homogenized suspensions of sponge cells also yielded presumed transconjugants; however, there was no significant difference between samples from live or dead sponges. Fluorescent in situ hybridization analysis of the sponge cell matrix using species-specific probes revealed the presence of enterococci clusters with cells adjacent to each other. The results demonstrated that sponge colonies can support the horizontal transfer of antimicrobial resistance although the mechanism underlying this process, such as binding of the bacteria to the sponge collagen matrix, has yet to be fully elucidated.

Competent but complex communication: The phenomena of pheromone-responsive plasmids

Enterococci are robust gram-positive bacteria that are found in a variety of surroundings and that cause a significant number of healthcare-associated infections. The genus possesses a high-efficiency pheromone-responsive plasmid (PRP) transfer system for genetic exchange that allows antimicrobial-resistance determinants to spread within bacterial populations. The pCF10 plasmid system is the best characterised, and although other PRP systems are structurally similar, they lack exact functional homologues of pCF10-encoded genes. In this review, we provide an overview of the enterococcal PRP systems, incorporating functional details for the less-well-defined systems. We catalogue the virulence-associated elements of the PRPs that have been identified to date, and we argue that this reinforces the requirement for elucidation of the less studied systems.

Microbial biosurfactants: current trends and applications in agricultural and biomedical industries

Synthetic surfactants are becoming increasingly unpopular in many applications due to previously disregarded effects on biological systems and this has led to a new focus on replacing such products with biosurfactants that are biodegradable and produced from renewal resources. Microbially derived biosurfactants have been investigated in numerous studies in areas including: increasing feed digestibility in an agricultural context, improving seed protection and fertility, plant pathogen control, antimicrobial activity, antibiofilm activity, wound healing and dermatological care, improved oral cavity care, drug delivery systems and anticancer treatments. The development of the potential of biosurfactants has been hindered somewhat by the myriad of approaches taken in their investigations, the focus on pathogens as source species and the costs associated with large-scale production. Here, we focus on various microbial sources of biosurfactants and the current trends in terms of agricultural and biomedical applications.

Interspecies transfer of vancomycin, erythromycin and tetracycline resistance among Enterococcus species recovered from agrarian sources

Background

Enterococci are now well recognised for their ability to transfer antibiotic resistance and for their association with nosocomial infections, but less is known regarding their relevance in the wider environment. Enterococcus faecalis and Enterococcus faecium were isolated from a range of agrarian associated sources (low-flow water, septic tank, poultry litter, high flow water, slurry/soil) and were assessed for latent ability to transfer antimicrobial resistance.

Results

The isolates were tested for phenotypic clumping in the presence of cell-free supernatant from other isolates. Some isolates were identified which demonstrated clumping, indicating that they possessed peptide sex pheromone conjugal machinery. All isolates were also tested for antibiotic resistance phenotypes using both disc diffusion and minimum inhibitory concentration (MIC) assays. These tests revealed that the enterococci demonstrated both phenotypic clumping and antibiotic resistance phenotypes. Based on these selection criteria, the isolates were identified as having the potential for horizontal gene transfer and were used to investigate the transfer of multiple antibiotic resistance phenotypes. Conjugal transfer of antibiotic resistance phenotypes was determined using a solid agar mating method followed by a standard antibiotic selection test resulting in different transfer patterns. An interspecies conjugal transfer of vancomycin resistance from E. faecalis to E. faecium was identified while the remaining reactions were within the same species. Transfer efficiencies ranging from 2 × 10⁻¹ to 2.3 × 10⁻⁵ were determined based on the reactions of three donor isolates (MF06036, MF0410 and MF06035) and two recipient isolates (MW01105^Rif and ST01109^Rif), with the transfer of vancomycin, erythromycin and tetracycline resistance genes.

Conclusions

The conjugation reactions and selection conditions used in this study resulted in a variety of co-transferred resistance phenotypes suggesting the presence of different mobile elements in the set of natural isolates. This study highlights the potential for extensive horizontal gene transfer in a previously neglected reservoir for enterococci.

Duodenal application of Li+ in a submaximal therapeutic dose inhibits exocrine pancreatic secretion and modulates gastro-duodenal myoelectrical activity in a conscious pig model

This study tested whether duodenal application of lithium inhibits gastroduodenal motility, and whether it suppresses secretion from the exocrine pancreas. Five suckling pigs, 16–18 days old, were surgically fitted with 3 serosal electrodes on the wall of the gastric antrum and the duodenum for electromyography of smooth muscles, and with a pancreatic duct catheter and a duodenal T-cannula for collection and re-entrant flow of pancreatic juice. After the recovery period, on alternative days, each animal was tested once with an intraduodenal infusion of Li+ (100 mmol·L–1C3H5LiO3,10 mL·kg−1·h−1) for 1 h, and once with an intraduodenal infusion of NaCl (154 mM, 10 ml·kg−1·h−1), also for 1 h, with the first treatment, i.e., Li+ or NaCl, randomly assigned. Individual pigs served as their own controls, with data recorded prior to a treatment being used as the baseline. Li+ increased the duration of quiescence (P < 0.05) and activity phase (P < 0.05) in the antrum, thus increasing (P < 0.05) the duration of antral myoelectrical cycles. Li+ shortened (P < 0.05) phase I, but it did not affect phase II or phase III or the MMC in the duodenum. Li+ inhibited pancreatic juice outflow as well as pancreatic enzyme and bicarbonate output (P < 0.05 for all pancreatic parameters).

Similitude Conditions Modeling Geosynthetic-Reinforced Piled Embankments Using FEM and FDM Techniques

The numerical modelling of geosynthetic-reinforced piled embankments using both the finite element method (FEM) and finite difference method (FDM) are compared. Plaxis 2D (FEM) was utilized to replicate FLAC (FDM) analysis originally presented by Han and Gabr on a unit cell axisymmetric model within a geosynthetic reinforced piled embankment (GRPE). The FEM and FED techniques were found to be in reasonable agreement, in both characteristic trend and absolute value. FEM consistently replicated the FDM outputs for deformational, loading, and load transfer mechanism (soil arching) response within the reinforced piled embankment structure with a reasonable degree of accuracy. However the FDM approach was found to give a slightly higher reinforcement tension and stress concentration but lower reinforcement strain at the pile cap than FEM, which was attributed to the greater discretize of the model geometry in the FDM than in FEM.

Changes in calcium status in aged rats fed Lactobacillus GG and Bifidobacterium lactis and oligofructose-enriched inulin

In this study we hypothesized that an increase in numbers of beneficial bacteria in the large intestine can affect calcium (Ca) status in the elderly. Adult and aged rats were fed a diet with or without synbiotics for 21 days. Synbiotics increased the numbers of lactobacilli and bifidobacteria in large intestine in both adult and aged rats. The plasma Ca concentration was significantly increased while osteocalcin concentration was significantly decreased only in aged rats fed synbiotics.

Effect on components of the intestinal microflora and plasma neuropeptide levels of feeding Lactobacillus delbrueckii, Bifidobacterium lactis, and inulin to adult and elderly rats

The aim of this study was to compare the effects of the mixture of Lactobacillus delbrueckii subsp. rhamnosus strain GG, Bifidobacterium lactis Bb12, and inulin on intestinal populations of lactobacilli, bifidobacteria, and enterobacteria in adult and elderly rats fed the same (in quality and quantity) diet. The portal plasma levels of two neuropeptides, neuropeptide Y (NPY) and peptide YY (PYY), were also evaluated to assess the physiological consequences of the synbiotic treatment for the gastrointestinal (GI) tracts of rats of different ages. Adult (n = 24) and elderly (n = 24) male rats were fed the AIN-93 M maintenance diet. After 2 weeks of adaptation, the diet of 12 rats of each age group was supplemented with 8% inulin and with strains GG and Bb12 to provide 2.2 x 10(9) CFU of each strain g(-1) of the diet. Blood and different regions of the GI tract were sampled from all rats after 21 days of the treatment. Treatment with the mixture of strain GG, strain BB12, and inulin induced significantly different changes in the numbers of lactobacilli, bifidobacteria, and enterobacteria of the stomach, small intestine, cecum, and colon microflora. Moreover, the GG, BB12, and inulin mixture increased the concentrations of NPY and PYY for adult rats. For the elderly animals, the PYY concentration was not changed, while the NPY concentration was decreased by treatment with the GG, BB12, and inulin mixture. The results of the present study indicate that the physiological status of the GI tract, and not just diet, has a major role in the regulation of important groups of the GI bacteria community, since even the outcome of the dietary modification with synbiotics depends on the ages of the animals.

Relationship between dietary-induced changes in intestinal commensal microflora and duodenojejunal myoelectric activity monitored by radiotelemetry in the rat in vivo

Interdigestive intestinal motility, and especially phase III of the migrating myoelectric/motor complex (MMC), is responsible for intestinal clearance and plays an important role in prevention of bacterial overgrowth and translocation in the gut. Yet previous results from gnotobiotic rats have shown that intestinal microflora can themselves affect the characteristics of the myoelectric activity of the gut during the interdigestive state. Given that the composition of the intestinal microflora can be altered by dietary manipulations, we investigated the effect of supplementation of the diet with synbiotics on intestinal microflora structure and the duodenojejunal myoelectric activity in the rat. To reduce animal distress caused by restraint and handling, which can itself affect GI motility, we applied radiotelemetry for duodenojejunal EMG recordings in conscious, freely moving rats. Thirty 16-month-old Spraque-Dawley rats were used. The diet for 15 rats (E group) was supplemented with chicory inulin, Lactobacillus rhamnosus and Bifidobacterium lactis. The remaining 15 rats were fed control diet without supplements (C group). Three rats from each group were implanted with three bipolar electrodes positioned at 2, 14 and 28 cm distal to the pylorus. After recovery, two 6 h recordings of duodenojejunal EMG were carried out on each operated rat. Subsequently, group C rats received feed supplements and group E rats received only control diet for 1 week, and an additional two 6 h recordings were carried out on each of these rats. Non-operated C and E rats were killed and samples of GI tract were collected for microbiological analyses. Supplementation of the diet with the pro- and prebiotics mixture increased the number of bifidobacteria, whereas it decreased the number of enterobacteria in jejunum, ileum, caecum and colon. In both caecum and colon, the dietary supplementation increased the number of total anaerobes and lactobacilli. Treatment with synbiotics increased occurrence of phase III of the MMC at all three levels of the small intestine. The propagation velocity of phase III in the whole recording segment was also increased from 3.7 +/- 0.2 to 4.4 +/- 0.2 cm min(-1) by dietary treatment. Treatment with synbiotics increased the frequency of response potentials of the propagated phase III of the MMC at both levels of the jejunum, but not in the duodenum. In both parts of the jejunum, the supplementation of the diet significantly decreased the duration of phase II of the MMC, while it did not change the duration of phase I and phase III. Using the telemetry technique it was demonstrated that changes in the gastrointestinal microflora exhibited an intestinal motility response and, more importantly, that such changes can be initiated by the addition of synbiotics to the diet.

Effect of feed particle size and feed processing on morphological characteristics in the small and large intestine of pigs and on adhesion of Salmonella enterica serovar Typhimurium DT12 in the ileum in vitro1

A 2 x 2 factorial experiment with pigs was undertaken to investigate the effect of particle size (fine and coarse) and feed processing (pelleted and nonpelleted) on morphological characteristics in the small intestine, cecum, and colon of pigs and on the adhesion of Salmonella enterica serovar Typhimurium DT12 to the ileum in vitro. Ninety-six pigs (average BW = 33 +/- 7 kg) were fed the experimental diets. After 4 wk, 24 pigs were selected (six pigs per diet) and euthanized, and tissue samples were taken from the mid and distal small intestine, cecum, and distal colon. The effects of particle size and feed processing on villus height and crypt depth in the small intestine were minor. Feeding coarse diets increased (P = 0.05) the crypt depth in the colon. The crypt depth was 420 +/- 12 and 449 +/- 12 microm in pigs fed finely and coarsely ground feed, respectively. Pigs fed pelleted diets had a larger (P = 0.01) staining area for neutral mucins, as well as for acidic and sulfomucins on the villi of the distal small intestine than pigs fed nonpelleted diets. The area was 41, 46, and 33% larger for neutral, acidic, and sulfomucins, respectively. The mucin-staining areas of the crypts in the cecum and the colon were not affected by the experimental diets. Examination of lectin binding characteristics of the distal small intestine and the cecum did not reveal any differences between the experimental diets. Using a pig intestine organ culture model, Salmonella adhered less (P < 0.05) to the ileal tissue of pigs fed the nonpelleted diets than to those fed pelleted diets; the adherence was 60% less in these pigs. Results of this study suggest that pigs fed pelleted diets secrete mucins that are capable of binding Salmonella enterica serovar Typhimurium DT12 and thereby allowing for colonization. Therefore, pigs fed a nonpelleted diet are better protected against Salmonella infections than pigs fed a pelleted diet.

Effects of physical properties of feed on microbial ecology and survival of Salmonella enterica serovar Typhimurium in the pig gastrointestinal tract

A two-by-two factorial experiment with pigs was conducted to study the effect of feed grinding (fine and coarse) and feed processing (pelleted and nonpelleted) on physicochemical properties, microbial populations, and survival of Salmonella enterica serovar Typhimurium DT12 in the gastrointestinal tracts of pigs. Results demonstrated a strong effect of diet on parameters measured in the stomachs of the pigs, whereas the effect was less in the other parts of the gastrointestinal tract. Pigs fed the coarse nonpelleted (C-NP) diet showed more solid gastric content with higher dry matter content than pigs fed the fine nonpelleted (F-NP), coarse pelleted (C-P), or fine pelleted (F-P) diet. Pigs fed the C-NP diet also showed significantly increased number of anaerobic bacteria (P < 0.05), increased concentrations of organic acids, and reduced pH in the stomach. In addition, pigs fed the C-NP diet showed increased in vitro death rate of S. enterica serovar Typhimurium DT12 in content from the stomach (P < 0.001). Pigs fed the C-NP diet had a significantly higher concentration of undissociated lactic acid in gastric content than pigs fed the other diets (P < 0.001). A strong correlation between the concentration of undissociated lactic acid and the death rate of S. enterica serovar Typhimurium DT12 was found. In the distal small intestine, cecum, and midcolon, significantly lower numbers of coliform bacteria were observed in pigs fed the coarse diets than in pigs fed the fine diets (P < 0.01). Pigs fed the C-NP diet showed the lowest number of coliform bacteria in these segments of the gastrointestinal tract. Pigs fed the coarse diets showed increased concentration of butyric acid in the cecum (P < 0.05) and colon (P < 0.10) compared with pigs fed the fine diets. It was concluded that feeding a coarsely ground meal feed to pigs changes the physicochemical and microbial properties of content in the stomach, which decreases the survival of Salmonella during passage through the stomach. In this way the stomach acts as a barrier preventing harmful bacteria from entering and proliferating in the lower part of the gastrointestinal tract.

Survival and distribution of cell-free SEF 21 of Salmonella enterica serovar Enteritidis in the stomach and various compartments of the rat gastrointestinal tract in vivo

Rats were dosed for 6 days with purified SEF 21 fimbriae of Salmonella enterica serovar Enteritidis 10360. The levels of fimbriae in gut contents associated with tissues and in the faeces were quantified by direct non-competitive ELISA. SEF 21 was distributed throughout the gut. The majority was found in the large intestine where it was primarily in the luminal contents. In contrast, a high proportion of SEF 21 detected in the ileum, the main site of salmonella colonisation and invasion, was tissue-bound. Thus, purified SEF 21 survived intestinal passage and associated with the stomach and gastrointestinal tract in a pattern similar to that found with whole Salmonella cells.

A bioreactor system to study survival of Salmonella Typhimurium in pig gut content

The batch culture system included six bioreactors. Three bioreactors containing stomach slurry were maintained at pH 4.5 and 6 respectively. Bioreactors containing small intestine slurry were maintained at pH 5.6 and 7 respectively. The bioreactors were inoculated with 10 ml of viable Salmonella. The bioreactors were maintained for 6 hours. Samples of 10 ml were taken at 0 time and at 1, 2, 4 and 6 hours. The samples were analysed for the presence of Salmonella and SCFA. In the stomach samples Salmonella numbers increased at pH 6 but fell at pH 4. In the small intestine sample Salmonella numbers increased at pH 6 and 7. In terms of SCFA production, in the stomach, with samples at pH 6 there was little change in the amounts of lactate, succinate and formate to that detected at 0 time, however levels of acetate did increase slightly. In the small intestine samples levels of succinate and formate increased slightly up to 4 hours, levels of acetate increased significantly from 0 to 6 hours. In terms of the specific growth rates of the individual strains, both strains grew at pH 6 in the stomach content and to a greater extent in the small intestinal content. A bactericidal effect was observed at pH 4 in the stomach content while neither killing nor growth occurred at pH 5 either in the stomach or the small intestine content. Both strains grew well in the small intestine content at pH 7, showing generation times of up to 24 min.

Effects of nondigestible oligosaccharides on Salmonella enterica serovar Typhimurium and nonpathogenic Escherichia coli in the pig small intestine in vitro

An in vitro intestinal tissue model was developed for the investigation of bacterial association in the pig small intestine under different dietary regimes. In preliminary experiments, jejunal and ileal tissue was taken from Danish Landrace pigs fed standard diet and inoculated with either Salmonella or nonpathogenic Escherichia coli strains. Higher numbers of salmonellae associated with the ileal tissues, but the numbers did not reach significance. Hence, jejunal sections were inoculated with nonpathogenic E. coli and ileal sections were inoculated with salmonellae in the presence of mannose or commercial nondigestible oligosaccharides (NDO) at 2.5%. There was a significant decrease in E. coli associated with the jejunum in the presence of mannose (P < 0.05). Furthermore, in pigs fed a diet supplemented with commercial NDO at 4% there was a significant reduction in the numbers of E. coli in jejunal organ cultures of pigs fed the FOS diet (P < 0.05). There was a reduction, though not a significant one, in the association of Salmonella sp. to the ileal sections of pigs fed the commercial FOS diet. The feeding of commercial GOS or its addition to organ cultures did not affect E. coli or Salmonella numbers.

Expression of type 1 fimbriae (SEF 21) of Salmonella enterica serotype enteritidis in the early colonisation of the rat intestine

The involvement of type 1 fimbriae in colonisation of the rat gastrointestinal tract in vivo was investigated with Salmonella enterica serotype Enteritidis LA5 and a mutant of LA5 denoted EAV3 unable to elaborate type 1 fimbriae (SEF 21). Rats were given a single dose of LA5 or EAV3 or a 1:1 mixture of both. LA5 was found in higher numbers in the stomach and small intestine than EAV3 at 6 h after infection with a single strain, but not after 6 days. LA5 did not out-compete EAV3 when the strains were administered together. Indeed, after 6 and 21 days, EAV3 was found in the distal small intestine and large intestine in far higher numbers than LA5. These findings suggest that SEF 21 have an important role(s) in the early stages of infection in vivo. However, SEF 21 expression may disadvantage the pathogen in the longer term as indicated by EAV3 out-competing LA5 in the gut at 21 days.

Modulation of Salmonella infection by the lectins of Canavalia ensiformis (Con A) and Galanthus nivalis (GNA) in a rat model in vivo

The plant lectins, Concanavalin A (Con A) and Galanthus nivalis agglutinin (GNA) have been prefed to rats for 3 d pre- and 6 d postinfection with Salmonella typhimurium S986 or Salm. enteritidis 857. Con A significantly increased numbers of Salm. typhimurium S986 in the large intestine and in faeces, and severely impaired growth of the rats, more severely than is the case of infection with Salmonella typhimurium alone. Con A had much less effect on rats infected with Salm. enteritidis 857 only showing a significant increase in numbers in the colon, accompanied by intermittent increases of Salmonella in the faeces during the study. GNA significantly reduced pathogen numbers in the lower part of the small bowel and the large intestine of rats infected with Salm. typhimurium S986 and significantly improved rat growth. GNA had little effect on infection by Salm. enteritidis 857 with slight decreases in Salmonella numbers in the small intestine and large intestine and transient increases in the faeces.

Salmonella enterica var Typhimurium and Salmonella enterica var Enteritidis express type 1 fimbriae in the rat in vivo

In a series of experiments rats were dosed with purified type 1 fimbriae from Salmonella enterica var Enteritidis or with fimbriated cultures of either S. enterica var Typhimurium or S. enterica var Enteritidis. Paraffin-wax embedded histological sections of jejunal and ileal tissue were taken and stained by the streptavidin biotin complex (sABC) staining technique for the detection of salmonella and type 1 fimbriae. On oral infection with Enteritidis and Typhimurium both bacteria were shown to be closely associated with the rat ileal epithelium and expressed type 1 fimbriae, thus clearly demonstrating that type 1 fimbriae are expressed by salmonellae in vivo. Moreover, association with the ileum was also shown to occur when purified type 1 fimbriae were orally administered to rats. Our results suggest that type 1 fimbriae alone or in combination with other fimbriae may play an important role in the early stages of infection with these pathogenic bacteria.

A rat model of infection by Salmonella typhimurium or Salm. enteritidis

Salmonellosis in the rat has many similarities with the disease in humans, with the ileum thought to be the main site of colonization/invasion in both species. Thus, the rat may be a useful way to study the mechanism of infection by these pathogenic bacteria. A series of infection trials carried out with Hooded Lister rats showed that a salmonella infection persisted for an extended period of time and that salmonellae bind to the small intestinal epithelium as early as 4 h after intragastric intubation. Reinfection from the large intestine may not therefore initially play a significant role in the salmonella infection process. The rat model may therefore provide a means to test in vivo interventionist strategies, designed to block binding of the pathogens in the gastrointestinal tract.

Salmonella typhimurium and Salmonella enteritidis induce gut growth and increase the polyamine content of the rat small intestine in vivo

The effects of infection by Salmonella enteritidis and S. typhimurium on the small and large intestines, liver, spleen and mesenteric nodules of rats were studied in vivo. Both Salmonella serotypes persisted and proliferated in the gastrointestinal tract and invaded sub-epithelial tissues, mainly the ileum, leading to the systemic distribution of these pathogens. Coincidental with infection, the rate of crypt cell proliferation increased resulting in substantial growth of the small intestine. The extent of this and the accompanying accumulation of polyamines was particularly dramatic in the ileum where there was also some disruption of the villus epithelium. It is possible that these effects of the infection on the metabolism and morphology of the small bowel, which strongly resembled the changes induced by some plant lectins, may facilitate the colonisation and invasion of the gut by Salmonellae.