Normal flora: diversity and functions

Meta-analysis of probiotics for the prevention of traveler's diarrhea

BACKGROUND

Traveler's diarrhea (TD) is a common health complaint among travelers. Rates of TD can range from 5% to 50%, depending on the destination. The use of probiotics for this disease remains controversial. The objective of this study was to compare the efficacy of probiotics for the prevention of TD based on published randomized, controlled clinical trials.

METHODS

PubMed, Google Scholar, metaRegister, NIH registry of clinical trials and Cochrane Central Register of Controlled Trials were searched from 1977 to 2005, unrestricted by language. Secondary searches of reference lists, authors, reviews, commentaries, associated diseases, books and meeting abstracts. Inclusion criteria included: randomization, controlled, blinded, efficacy trials, in humans, peer-reviewed journals. Exclusion criteria were: pre-clinical, safety, phase 1 studies in volunteers, reviews, duplicate reports, trials of unspecified probiotics, trials of prebiotics, and inconsistent outcome measures.

RESULTS

Twelve of 940 screened studies met the inclusion and exclusion criteria. The pooled relative risk indicates that probiotics significantly prevent TD (RR=0.85, 95% CI 0.79,0.91, p<0.001).

CONCLUSION

Several probiotics (Saccharomyces boulardii and a mixture of Lactobacillus acidophilus and Bifidobacterium bifidum) had significant efficacy. No serious adverse reactions were reported in the 12 trials. Probiotics may offer a safe and effective method to prevent TD.

Review article: tolevamer, a novel toxin-binding polymer: overview of preclinical pharmacology and physicochemical properties

BACKGROUND

Tolevamer is a novel toxin-binding polymer that is currently being investigated in clinical trials for the treatment of patients who have Clostridium difficile-associated diarrhoea.

AIMS

To summarize the results of in vitro and in vivo preclinical studies of tolevamer. In contrast to antibiotics, tolevamer binds C. difficile toxins to interrupt toxin-mediated intestinal inflammation and tissue damage, and does not demonstrate direct antimicrobial activity.

METHODS

Pharmacokinetics/pharmacodynamics were studied in rats and dogs; efficacy was studied in a hamster model.

RESULTS

Studies in rats and dogs indicate that tolevamer is essentially non-absorbed from the gastrointestinal tract and show that drug interactions with commonly used therapies are unlikely. Pharmacologic studies indicate that tolevamer reduces disease severity and recurrence rates in the hamster model of C. difficile-associated diarrhoea and blocks the enterotoxic effects of toxin A in rat ileum. The binding parameters calculated for the interaction of tolevamer with toxins A and B provide a reasonable physicochemical model that supports the potential clinical utility of tolevamer.

CONCLUSIONS

These preclinical results are consistent with the effectiveness and safety profile of tolevamer observed in clinical studies in patients with C. difficile-associated diarrhoea.

Antagonistic activity against pathogenic bacteria by human vaginal lactobacilli

This study attempted to isolate lactobacilli strains from healthy vaginal ecosystem to search for a new effective antibacterial probiotic strain. The strains were identified and characterized for their probiotic properties including bile salt and acid tolerance, growth at acidic pH, their ability to utilize protein, starch, and lipid, the production of hydrogen peroxide and bacteriocin as well as their antibiotic resistance patterns. The antibacterial activity of the culture supernatant of these strains were tested against a wide range of Gram-positive and Gram-negative pathogenic bacteria including Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae. Salmonella typhi, and Salmonella typhimurium. None of the strains inhibited the growth of Gram-negative bacteria. Contrastly, the culture supernatant of strain L 22, identified as Lactobacillus reuteri, significantly inhibited all of the clinical isolates of methicillin-resistant S. aureus (MRSA). The antibacterial effect of the selected strain L 22 was further investigated. In the presence of L 22, the bacterial growth was assessed in vitro by viable bacterial counting. The numbers of viable cells were significantly lower in L 22-containing broth than those in the control by 6h. This finding clearly demonstrates that strain L 22 can produce an anti-MRSA effect. The antibacterial ability of the strain L 22 was fundamentally attributed to their bacteriocin production which can cause both cell inhibition and cell death.

Meta-analysis of probiotics for the prevention of antibiotic associated diarrhea and the treatment of Clostridium difficile disease

CONTEXT

Antibiotic-associated diarrhea (AAD) is a common complication of most antibiotics and Clostridium difficile disease (CDD), which also is incited by antibiotics, is a leading cause of nosocomial outbreaks of diarrhea and colitis. The use of probiotics for these two related diseases remains controversial.

OBJECTIVE

To compare the efficacy of probiotics for the prevention of AAD and the treatment of CDD based on the published randomized, controlled clinical trials.

DATA SOURCES

PubMed, Medline, Google Scholar, NIH registry of clinical trials, metaRegister, and Cochrane Central Register of Controlled Trials were searched from 1977 to 2005, unrestricted by language. Secondary searches of reference lists, authors, reviews, commentaries, associated diseases, books, and meeting abstracts.

STUDY SELECTION

Trials were included in which specific probiotics given to either prevent or treat the diseases of interest. Trials were required to be randomized, controlled, blinded efficacy trials in humans published in peer-reviewed journals. Trials that were excluded were pre-clinical, safety, Phase 1 studies in volunteers, reviews, duplicate reports, trials of unspecified probiotics, trials of prebiotics, not the disease being studied, or inconsistent outcome measures. Thirty-one of 180 screened studies (totally 3,164 subjects) met the inclusion and exclusion criteria.

DATA EXTRACTION

One reviewer identified studies and abstracted data on sample size, population characteristics, treatments, and outcomes.

DATA SYNTHESIS

From 25 randomized controlled trials (RCTs), probiotics significantly reduced the relative risk of AAD (RR = 0.43, 95% CI 0.31, 0.58, p < 0.001). From six randomized trials, probiotics had significant efficacy for CDD (RR = 0.59, 95% CI 0.41, 0.85, p = 0.005).

CONCLUSION

A variety of different types of probiotics show promise as effective therapies for these two diseases. Using meta-analyses, three types of probiotics (Saccharomyces boulardii, Lactobacillus rhamnosus GG, and probiotic mixtures) significantly reduced the development of antibiotic-associated diarrhea. Only S. boulardii was effective for CDD.

Comparison of antagonistic ability against enteropathogens by G+ and G− anaerobic dominant components of human fecal microbiota

To confirm if anaerobic G+-components are those responsible for the function of colonization resistance, obligate anaerobic G+- and G- -bacteria from normal dominant microbiota of human feces were isolated from three successive collections and then used in in vitro assays for antagonism against two enteropathogenic bacteria. The production of inhibitory diffusible compounds was determined on supplemented BHI agar and MRS agar media for G- - and G+-bacteria, respectively. Salmonella enterica subsp. enterica serovar Typhimurium and Shigella sonnei were used as indicators. G+-bacteria presented a higher overall antagonistic frequency against both pathogenic bacteria (57 and 64 % for S. enterica serovar Typhimurium and S. sonnei, respectively) when compared to G+-microorganisms but with a quite elevated variation between volunteers (0-100 %) and collection samples (40-72 and 40-80 % for S. enterica sv. Typhimurium and S. sonnei, respectively). On the other hand, only three among 143 G- -isolates tested showed antagonistic activity. The results showed that, at least in vitro, obligate anaerobic G+-components of the dominant human fecal microbiota present a higher potential for antagonism against the enteropathogenic models tested than do G- -bacteria.

Aerobic bacterial flora of the nasal cavity in Gulf of California sea lion (Zalophus californianus) pups

Nasal swab samples from clinically healthy California sea lions pups (Zalophus californianus) from six different reproductive rookeries in the Gulf of California were collected to determine the type and frequency of the representative aerobic bacterial microflora of their nasal mucosa. A total of 114 samples were examined and 100 bacterial isolates were identified and typified by microbiological and biochemical standard tests. Fifty four isolates corresponded to Gram positive bacteria (54%) and 46 isolates to Gram negative bacteria (46%). Fifteen bacterial genera were identified, including Micrococcus, Arcanobacterium, Corynebacterium, Moraxella, Neisseria, Escherichia, Kurthia, Acinetobacter, Staphylococcus, Brevibacillus, Bacillus, Klebsiella, Stenotrophomonas, Pseudomonas and Aeromonas. The most frequently isolated genera were Moraxella (24%), Micrococcus (18%), and Corynebacterium (15%). These results show the presence in the nasal cavity of sea lions of several microorganisms. Although considered part of the normal microflora, they may also be opportunistic pathogens for their hosts and may act as a potential natural sentinel of environmental changes.

Oral lactobacilli in chronic periodontitis and periodontal health: species composition and antimicrobial activity

BACKGROUND/AIMS

Lactobacilli are known to play an important role in the maintenance of health by stimulating natural immunity and contributing to the balance of microflora. However, their role in chronic periodontitis is unclear. We aimed to identify oral lactobacilli in chronic periodontitis and periodontally healthy subjects, and to determine their antimicrobial activity against putative oral pathogens.

METHODS

A total of 238 Lactobacillus isolates from the saliva and subgingival sites of 20 chronic periodontitis and 15 healthy subjects were collected. In all, 115 strains were identified using rapid amplified ribosomal DNA restriction analysis. Antimicrobial activity against Streptococcus mutans, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia was assessed.

RESULTS

Lactobacilli belonging to 10 species were identified. The most prevalent strains in healthy persons were Lactobacillus gasseri and Lactobacillus fermentum and in chronic periodontitis patients, Lactobacillus plantarum. Obligately homofermentatives, particularly L. gasseri, were less prevalent in chronic periodontitis patients compared with healthy subjects (8% vs. 64% for L. gasseri, P < 0.01). Sixty-nine percent of tested lactobacilli inhibited S. mutans, 88% A. actinomycetemcomitans, 82% P. gingivalis and 65% P. intermedia. The strongest antimicrobial activity was associated with Lactobacillus paracasei, L. plantarum, Lactobacillus rhamnosus, and Lactobacillus salivarius. The strains from periodontally healthy patients showed a lower antimicrobial activity against S. mutans than the strains from chronic periodontitis patients.

CONCLUSION

The composition of oral lactoflora in chronic periodontitis and healthy subjects differs, with a higher prevalence of homofermentative lactobacilli, particularly L. gasseri, in the latter group. Both homo- and heterofermentative oral lactobacilli suppress the growth of periodontal pathogens, but the antimicrobial properties are strain, species and origin specific.

Giardia immunity--an update

Giardia lamblia is a flagellated protozoan that causes watery diarrhea worldwide but the mechanisms of pathogenicity and the major host defenses against Giardia infection are not well characterized. The recent sequencing of the G. lamblia genome and the development of methods for genome-wide analyses of gene expression have made it possible to characterize the host-parasite interaction more fully. It is becoming clear that the host defense against a Giardia infection involves several different immunological and non-immunological mucosal processes.

Trypanosoma cruzi: Influence of predominant bacteria from indigenous digestive microbiota on experimental infection in mice

To verify the influence of some predominant components from indigenous microbiota on systemic immunological responses during experimental Chagas disease, germ-free NIH Swiss mice were mono-associated with Escherichia coli, Enterococcus faecalis, Bacteroides vulgatus or Peptostreptococcus sp. and then infected with the Y strain of Trypanosoma cruzi. All the mono-associations predominantly induced a Th1 type of specific immune response to the infection by T. cruzi. A direct correlation was observed between a higher survival rate and increased IFN-gamma and TNF-alpha production (P<0.05) in E. faecalis-, B. vulgatus-, and Peptostreptococcus-associated mice. Moreover, higher levels of anti-T. cruzi IgG1 and anti-T. cruzi IgG2a were also found in mono-associated animals after infection. On the other hand, with the exception of E. faecalis-associated mice, mono-association induced a lower IL-10 production after infection (P<0.05) when compared with germ-free animals. Interestingly, spleen cell cultures from non-infected germ-free and mono-associated mice spontaneously produced higher levels (P<0.05) of IL-10 than cultures from infected mono-associated mice, except again for E. faecalis-associated animals. In conclusion, the presence of the components of the indigenous microbiota skews the immune response towards production of inflammatory cytokines during experimental infection with T. cruzi in gnotobiotic mice. However, the degree of increase in production of cytokines depends on each bacterial component.

Evolutionary nursing: the case of infectious diseases

AIM

The aim of this paper is to examine the effect of evolution on infectious diseases nursing, and propose a model that may help to increase understanding of how hosts and microorganisms co-exist and how humans can alter the delicate balance between them.

BACKGROUND AND RATIONALE

Infectious diseases occur as the result of interactions between hosts and microorganisms. There is an increasing acceptance that the evolution of host and parasite is important in the development of infectious diseases. However, such views have made little impact in nursing, and the use of evolutionary interventions remains controversial.

METHOD

The Medline database was searched from 1966 to present using the terms pathogen$, virulen$, evolution, bacteria, and all combinations of these. Additionally reference lists of text books and papers were hand searched for relevant papers. Papers were selected from a variety of disciplines, including infectious diseases, microbiology, evolutionary biology, and ecology. Recurrent themes from these papers were identified and a model of evolutionary nursing constructed.

RESULTS

Microorganisms are plentiful, ubiquitous, and rapidly evolving by comparison with humans and other animals. As a result of this, attempts to 'outwit' them have been, and are, doomed to failure. However, through careful management of public and personal health, a balance encouraging co-existence may be possible. A number of specific interventions is proposed.

CONCLUSIONS

There are a number of key interventions that may reduce the virulence of microorganisms. With an increasing world population, antibiotic resistance and international travel, such an approach may be one way of reducing the morbidity associated with infectious diseases.

Alternative treatments for Clostridium difficile disease: what really works?

Vancomycin and metronidazole have been used for treating Clostridium difficile-associated disease (CDAD) for the past 25 years, but approximately 20 % of patients develop recurrent disease. The increasing incidence of nosocomial outbreaks, cases of recurrent CDAD and other complications (toxic megacolon, ileus, sepsis) has fuelled the search for different types of treatments. As the understanding of the pathogenesis of this disease has matured, newer treatment strategies that take advantage of these mechanisms have been developed. This review will describe such treatments and examine the evidence for each strategy.

Developmental changes in the adhesive disk during Giardia differentiation

Giardia lamblia is a protozoan parasite infecting the upper mammalian small intestine. Infection relies upon the ability of the parasite to attach to the intestine via a unique cytoskeletal organelle, the ventral disk. We determined the composition and structure of the disk throughout the life cycle of the parasite and identified a new disk protein, SALP-1. SALP-1 is an immunodominant protein related to striated fiber-assemblin (SFA). The disk is disassembled during encystation and stored as four fragments in the immobile cyst. Serial Analysis of Gene Expression (SAGE) showed that the mRNA levels of the disk proteins decreased in encystation but two-dimensional protein gels showed that the protein levels were more constant. The parasite emerges without a functional disk but the four disk fragments are quickly reassembled into two new disks on the dividing, early excysting form. Thus, disk proteins are stored within the cyst, ready to be used in the rapid steps of excystation.

Dental plaque as a microbial biofilm

New technologies have provided novel insights into how dental plaque functions as a biofilm. Confocal microscopy has confirmed that plaque has an open architecture similar to other biofilms, with channels and voids. Gradients develop in areas of dense biomass over short distances in key parameters that influence microbial growth and distribution. Bacteria exhibit an altered pattern of gene expression either as a direct result of being on a surface or indirectly as a response to the local environmental heterogeneity within the biofilm. Bacteria communicate via small diffusible signalling molecules (e.g. competence-stimulating peptide, CSP; autoinducer 2); CSP induces both genetic competence and acid tolerance in recipient sessile cells. Thus, rates of gene transfer increase in biofilm communities, and this is one of several mechanisms (others include: diffusion-reaction, neutralization/inactivation, slow growth rates, novel phenotype) that contribute to the increased antimicrobial resistance exhibited by bacteria in biofilms. Oral bacteria in plaque do not exist as independent entities but function as a co-ordinated, spatially organized and fully metabolically integrated microbial community, the properties of which are greater than the sum of the component species. A greater understanding of the significance of dental plaque as a mixed culture biofilm will lead to novel control strategies.

Are dental diseases examples of ecological catastrophes?

Dental diseases are among the most prevalent and costly diseases affecting industrialized societies, and yet are highly preventable. The microflora of dental plaque biofilms from diseased sites is distinct from that found in health, although the putative pathogens can often be detected in low numbers at normal sites. In dental caries, there is a shift towards community dominance by acidogenic and acid-tolerant Gram-positive bacteria (e.g. mutans streptococci and lactobacilli) at the expense of the acid-sensitive species associated with sound enamel. In contrast, the numbers and proportions of obligately anaerobic bacteria, including Gram-negative proteolytic species, increase in periodontal diseases. Modelling studies using defined consortia of oral bacteria grown in planktonic and biofilm systems have been undertaken to identify environmental factors responsible for driving these deleterious shifts in the plaque microflora. Repeated conditions of low pH (rather than sugar availability per se) selected for mutans streptococci and lactobacilli, while the introduction of novel host proteins and glycoproteins (as occurs during the inflammatory response to plaque), and the concomitant rise in local pH, enriched for Gram-negative anaerobic and asaccharolytic species. These studies emphasized (a). significant properties of dental plaque as both a biofilm and a microbial community, and (b). the dynamic relationship existing between the environment and the composition of the oral microflora. This research resulted in a novel hypothesis (the 'ecological plaque hypothesis') to better describe the relationship between plaque bacteria and the host in health and disease. Implicit in this hypothesis is the concept that disease can be prevented not only by directly inhibiting the putative pathogens, but also by interfering with the environmental factors driving the selection and enrichment of these bacteria. Thus, a more holistic approach can be taken in disease control and management strategies.

Breaking the cycle: treatment strategies for 163 cases of recurrent Clostridium difficile disease

OBJECTIVE

There is currently uncertainty as to the best treatment for patients with recurrent episodes of Clostridium difficile disease (RCDD). Our objective was to evaluate the success of treatment strategies in a cohort of 163 RCDD patients.

METHODS

Data were used from patients who had participated in the placebo arm in two national referral clinical trials evaluating a new combination treatment. Patients with active RCCD were enrolled, prescribed either vancomycin or metronidazole, and randomized to either the investigational biological or a placebo. All patients were observed for at least 2 months for a subsequent episode of RCCD.

RESULTS

Of the 163 cases, 44.8% recurred. A tapering course of vancomycin resulted in significantly fewer recurrences (31%, p = 0.01), as did pulsed dosing of vancomycin (14.3%, p = 0.02). A trend (p = 0.09) for a lower recurrence frequency was observed for high-dose (> or =2 g/day) vancomycin and low-dose (< or =1 g/day) metronidazole. Vancomycin was significantly more effective in clearing C. difficile culture and/or toxin by the end of therapy than metronidazole (89% vs 59%, respectively; p < 0.001).

CONCLUSIONS

These data show that tapered or pulsed dosing regimens of vancomycin may result in a significantly better cure of RCDD. The persistence of C. difficile spores suggests that additional strategies to restore the normal colonic microflora may also be beneficial.

Use of Lactobacillus to prevent infection by pathogenic bacteria

This review focuses on the use and potential of Lactobacillus to prevent infections of the urogenital and intestinal tracts. The presence and dominance of Lactobacillus in the vagina is associated with a reduced risk of bacterial vaginosis and urinary tract infections. The mechanisms appear to involve anti-adhesion factors, by-products such as hydrogen peroxide and bacteriocins lethal to pathogens, and perhaps immune modulation or signaling effects. The instillation of Lactobacillus GR-1 and B-54 or RC-14 strains into the vagina has been shown to reduce the risk of urinary tract infections, and improve the maintenance of a normal flora. Ingestion of these strains into the gut has also been shown to modify the vaginal flora to a more healthy state. In addition, these strains inhibit the growth of intestinal, as well as urogenital pathogens, colonize the gut and protect against infections as shown in mice. Other probiotic strains, such as Lactobacillus GG, have been shown to prevent and treat gastroenteritis caused by rotavirus and bacteria. Given that lactobacilli are not the dominant commensals in a gut which comprises around 10(10) organisms, much work is still needed to define the mechanisms whereby GR-1, RC-14, GG and other strains contribute to health restoration and maintenance. Such critically important studies will require the medical science community to show a willingness to turn away from pharmaceutical remedies as the only solution to health and disease.