Antibiotics and anaerobes of gut origin

Anaerobe-Targeted Antibiotic Therapy in the Neonatal Intensive Care Unit

Anaerobe-targeted antibiotic (ATA) therapy may adversely impact the developing neonatal microbiome. We describe utilization patterns, potential indications, and related outcomes of ATA therapy in neonatal intensive care units across the United States over 13 years. While overall antibiotic use decreased, ATA use was unchanged. Potentially associated indications were inconsistent.

Comprehensive insight into the alterations in the gut microbiome and the intestinal barrier as a consequence of iron deficiency anaemia

BACKGROUND

Iron deficiency is the top leading cause of anaemia, whose treatment has been shown to deteriorate gut health. However, a comprehensive analysis of the intestinal barrier and the gut microbiome during iron deficiency anemia (IDA) has not been performed to date. This study aims to delve further into the analysis of these two aspects, which will mean a step forward minimising the negative impact of iron supplements on intestinal health.

METHODS

IDA was experimentally induced in an animal model. Shotgun sequencing was used to analyse the gut microbiome in the colonic region, while the intestinal barrier was studied through histological analyses, mRNA sequencing (RNA-Seq), qPCR and immunofluorescence assays. Determinations of lipopolysaccharide (LPS) and bacteria-specific immunoglobulins were performed to assess microbial translocation.

RESULTS

Microbial metabolism in the colon shifted towards an increased production of certain amino acids, short chain fatty acids and nucleotides, with Clostridium species being enriched during IDA. Structural alterations of the colonic epithelium were shown by histological analysis. RNA-Seq revealed a downregulation of extracellular matrix-associated genes and proteins and an overall underdeveloped epithelium. Increased levels of serum LPS and an increased immune response against dysbiotic bacteria support an impairment in the integrity of the gut barrier during IDA.

CONCLUSIONS

IDA negatively impacts the gut microbiome and the intestinal barrier, triggering an increased microbial translocation. This study emphasizes the deterioration of gut health during IDA and the fact that it should be addressed when treating the disease.

Unveiling the Intricate Link Between Anaerobe Niche and Alzheimer Disease Pathogenesis

Dysbiosis within microbiomes has been increasingly implicated in many systemic illnesses, such as cardiovascular disease, metabolic syndrome, respiratory infections, and Alzheimer disease (Ad). The correlation between Ad and microbial dysbiosis has been repeatedly shown, yet the etiologic cause of microbial dysbiosis remains elusive. From a neuropathology perspective, abnormal (often age-related) changes in the brain, associated structures, and bodily lumens tend toward an accumulation of oxygen-depleted pathologic structures, which are anaerobically selective niches. These anaerobic environments may promote progressive change in the microbial community proximal to the brain and thus deserve further investigation. In this review, we identify and explore what is known about the anaerobic niche near or associated with the brain and the anaerobes that it is harbors. We identify the anaerobe stakeholders within microbiome communities and the impacts on the neurodegenerative processes associated with Ad. Chronic oral dysbiosis in anaerobic dental pockets and the composition of the gut microbiota from fecal stool are the 2 largest anaerobic niche sources of bacterial transference to the brain. At the blood-brain barrier, cerebral atherosclerotic plaques are predominated by anaerobic species intimately associated with the brain vasculature. Focal cerebritis/brain abscess and corpora amylacea may also establish chronic anaerobic niches in direct proximity to brain parenchyma. In exploring the anaerobic niche proximal to the brain, we identify research opportunities to explore potential sources of microbial dysbiosis associated with Ad.

The mystery of rich human gut antibiotic resistome in the Yellow River with hyper-concentrated sediment-laden flow

Human gut antibiotic resistome widely occur in anoxic environments characterized by high density of bacterial cells and frequent transmission of antibiotic resistance genes (ARGs). Such resistome is greatly diluted, degraded, and restrained in the aerobic habitats within most natural rivers (regarded as "terrestrial guts") connecting continents and the oceans. Here we implemented a large-scale monitoring campaign extending 5,200 km along the Yellow River, and provide the first integral biogeographic pattern for both ARGs and their hosts. We identified plentiful ARGs (24 types and 809 subtypes) and their hosts (24 phyla and 757 MAGs) in three media (water, suspended particulate matter (SPM), and sediment). Unexpectedly, we found diverse human gut bacteria (HGB) acting as supercarriers of ARGs in this oxygen-rich river. We further discovered that numerous microhabitats were created within stratified biofilms that surround SPMs, particularly regarding the aggregation of anaerobic HGB. These microhabitats provide numerous ideal sinks for anaerobic bacteria and facilitate horizontal transfer of ARGs within the stratified biofilms, Furthermore, the stratification of biofilms surrounding SPMs has facilitated synergy between human gut flora and denitrifiers for propagation of ARGs in the anoxic atmospheres, leading to high occurrence of human gut antibiotic resistome. SPMs play active roles in the dynamic interactions of river water and sediment, thus accelerating the evolution of riverine resistome and transmission of human gut antibiotic resistome. This study revealed the special contribution of SPMs to the propagation of ARGs, and highlighted the necessity of making alternative strategies for sustainable management of large rivers with hyper-concentrated sediment-laden flows.

Understanding risk factors and microbial trends implicated in the development of Whipple-related surgical-site infections

Objective

The purpose of this study is to understand the role of risk factors and postoperative complications seen in patients undergoing Whipple procedures in the development of surgical site infections. Our secondary goal was to evaluate whether microbial patterns differed between preoperative antibiotic classes, offering insight into the effectiveness of current practices while promoting antibiotic stewardship.

Design

We performed a retrospective cohort study comparing patients with and without SSIs.

Setting

This study was conducted at a tertiary-care center in the southeastern United States.

Participants

Patients who underwent a Whipple procedure between 2012 and 2021 were acquired from the National Surgical Quality Improvement Program (NSQIP) database.

Results

Patients with a bleeding disorder reported higher SSI rates (P = .04), whereas patients with a biliary stent reported lower surgical site infection (SSI) rates (P = .02) Those with postoperative complications had higher SSI rates, including delayed gastric emptying (P < .001) and pancreatic fistula (P < .001). Patients with longer operative times were 1.002 times more likely to develop SSIs (adjusted odds ratio [aOR], 1.002; 95% confidence interval [CI], 1.001-1.004; P = .006) whereas surgical indications for malignancy correlated with decreased SSIs risk (aOR, 0.578; 95% CI, 0.386-866) when adjusting for body mass index, surgical indication, and duration of surgical procedure.

Conclusions

Optimizing preoperative management of modifiable risk factors for patients undergoing pancreatoduodenectomies and decreasing operative times may reduce SSI rates and patient and hospital burden. Further research is needed to understand whether stent placement reduces SSI risk in pancreatoduodenectomy.

Routine antibiotics may not be needed to treat uncomplicated right diverticulitis: A retrospective cohort study

We aimed to investigate whether antibiotic administration is necessary for patients with uncomplicated right colonic diverticulitis. Data from patients diagnosed with uncomplicated right colonic diverticulitis, who received inpatient treatment at a single center between January 2019 and January 2021, were retrospectively examined. The patients were divided into two groups according to whether antibiotics were administered. The patients were matched between groups using propensity score matching in a 1:1 ratio using logistic regression with the nearest-neighbor method. The primary study outcome was the length of hospital stay, and the secondary outcomes were time to the introduction of sips of water and a soft diet. The study included 138 patients who received antibiotics and 59 who did not. After propensity score matching, 55 patients were assigned to each treatment group. There was no significant difference between the two groups in terms of age (p = 0.772), sex (p>0.999), body mass index (p = 0.121), prehospital symptom duration (p = 0.727), initial body temperature (p = 0.661), white blood cell count (p = 0.688), or C-reactive protein level (p = 0.337). There was also no statistically significant difference in the length of hospital stay between the no antibiotic and antibiotic groups (3.1±0.7 days vs. 3.0±1.0 days, p = 0.584). Additionally, no significant difference was observed between the no antibiotic and antibiotic groups with respect to time to sips of water (2.1±0.7 days vs. 1.8±0.9 days, p = 0.100) and time to the introduction of a soft diet (2.4±0.8 days vs. 2.1±0.9 days, p = 0.125). The findings suggest that routine antibiotics may be not required for treating patients with uncomplicated right colonic diverticulitis.

What can microfluidics do for human microbiome research?

Dysregulation of the human microbiome has been linked to various disease states, which has galvanized the efforts to modulate human health through microbiomes. Currently, human microbiome research is going through several phases to identify the constituent components of the microbiome, associate microbiome changes with physiological and pathological states, understand causative relationships, and finally translate this knowledge into therapeutics and diagnostics. The convergence of microfluidic technologies with molecular and cell profiling, microbiology, and tissue engineering can potentially be applied to these different phases of microbiome research to overcome the existing challenges faced by conventional approaches. The goal of this paper is to discuss and highlight the opportunities of applying different microfluidic technologies to specific areas of microbiome research as well as unique challenges that microfluidics must overcome when working with microbiome-relevant biological materials, e.g., micro-organisms, host tissues, and fluids. We will discuss the applicability of integrated microfluidic systems for processing biological samples for genomic sequencing analyses. For functional analysis of the microbiota, we will cover state-of-the-art microfluidic devices for microbiota cultivation and functional measurements. Finally, we highlight the use of organs-on-chips to model various microbiome-host tissue interactions. We envision that microfluidic technologies may hold great promise in advancing the knowledge on the interplay between microbiome and human health, as well as its eventual translation into microbiome-based diagnostics and therapeutics.

Prevention of enteric bacterial infections and modulation of gut microbiota with conjugated linoleic acids producing Lactobacillus in mice

Probiotics are recognized for outcompeting pathogenic bacteria by competitive receptor-mediated colonization and secretion of functional metabolites which are antimicrobial against certain microbes as well as improving host's gut health and immunity. Recently, we have constructed a bioactive Lactobacillus casei (LC) strain, LC^+mcra , by inserting mcra (myosin cross-reactive antigen) gene, which stimulates the conversion of conjugated linoleic acids. In this study, we evaluated the modulation of gut microbiome and protective roles of LC^+mcra against pathogenic Salmonella enterica serovar Typhimurium (ST) and enterohemorrhagic E. coli (EHEC) infections in BALB/cJ mice. We observed that LC^+mcra colonized efficiently in mice gut intestine and competitively reduced the infection with ST and EHEC in various locations of small and large intestine, specifically cecum, jejunum, and ileum (p < 0.05). Positive modulation of the cecal microbiota, for example, higher relative abundances of Firmicutes, lower relative abundances of Proteobacteria, and increased bacterial species diversity/richness, was detected in ST-challenged mice pretreated with LC^+mcra based on 16S metagenomic sequencing. Cytokine gene expression analysis indicated that mice pretreated with LC^+mcra associated with attenuated bacterial pathogen-induced gut inflammation. Furthermore, mice fed daily with LC^+mcra for one week could protect themselves from the impairments caused by enteric infections with ST or EHEC. These impairments include weight loss, negative hematological changes, intestinal histological alterations, and potential death. This in vivo study suggests that daily consumption of novel conjugated linoleic acids over-producing probiotic effectively improves intestinal microbiota composition and prevents/combats foodborne enteric bacterial infections with pathogenic Salmonella and diarrheagenic E. coli.

Prospective randomized clinical trial of uncomplicated right-sided colonic diverticulitis: antibiotics versus no antibiotics

PURPOSE

Antibiotics are widely used in the treatment of uncomplicated left-sided colonic diverticulitis. In Asian countries, however, right-sided colonic diverticulitis is more common than left-sided colonic diverticulitis. The aim of the present study was to evaluate the need for antibiotics in the treatment of uncomplicated right-sided colonic diverticulitis in an Asian population.

METHODS

Patients were randomized to two management strategies: antibiotics and no antibiotics. At 4-6 weeks after discharge, the patients in both groups underwent computed tomography or were contacted by phone to confirm the effectiveness of the treatment. The primary end point was the treatment failure rate of the initial treatment, and secondary end points were the length of hospital stay and total admission costs.

RESULTS

Patients were randomized to treatment with (61 patients) or without (64 patients) antibiotics. The rates of treatment failure in the antibiotics and no antibiotics groups were 1.7% and 4.6%, respectively, with no significant difference (P = 0.619). There was also no significant difference in the length of hospital stay between the groups (P = 0.983). Total admission costs were lower in the no antibiotics group than in the antibiotics group (US$1004.70 vs US$1112.40, respectively, P = 0.037).

CONCLUSION

Conservative management of uncomplicated right-sided colonic diverticulitis without antibiotics shows similar treatment failure rates and length of hospital stay, and is associated with lower hospital costs, compared with standard antibiotic treatment. Therefore, conservative management can be considered as a safe treatment option.

TRIAL REGISTRATION

ClinicalTrial.gov No. NCT02314013.

Novel large-scale chromosomal transfer in Bacteroides fragilis contributes to its pan-genome and rapid environmental adaptation

Bacteroides fragilis, an important component of the human gastrointestinal microbiota, can cause lethal extra-intestinal infection upon escape from the gastrointestinal tract. We demonstrated transfer and recombination of large chromosomal segments from B. fragilis HMW615, a multidrug resistant clinical isolate, to B. fragilis 638R. In one example, the transfer of a segment of ~435 Kb/356 genes replaced ~413 Kb/326 genes of the B. fragilis 638R chromosome. In addition to transfer of antibiotic resistance genes, these transfers (1) replaced complete divergent polysaccharide biosynthesis loci; (2) replaced DNA inversion-controlled intergenic shufflons (that control expression of genes encoding starch utilization system outer membrane proteins) with more complex, divergent shufflons; and (3) introduced additional intergenic shufflons encoding divergent Type 1 restriction/modification systems. Conjugative transposon-like genes within a transferred segment and within a putative integrative conjugative element (ICE5) ~45 kb downstream from the transferred segment both encode proteins that may be involved in the observed transfer. These data indicate that chromosomal transfer is a driver of antigenic diversity and nutrient adaptation in Bacteroides that (1) contributes to the dissemination of the extensive B. fragilis pan-genome, (2) allows rapid adaptation to a changing environment and (3) can confer pathogenic characteristics to host symbionts.

Beneficial Microbes: The pharmacy in the gut

The scientific evidence supporting the gut microbiome in relation to health maintenance and links with various disease states afflicting humans, from metabolic to mental health, has grown dramatically in the last few years. Strategies addressing the positive modulation of microbiome functionality associated with these disorders offer huge potential to the food and pharmaceutical industries to innovate and provide therapeutic solutions to many of the health issues affecting modern society. Such strategies may involve the use of probiotics and prebiotics as nutritional adjunct therapies. Probiotics are generally recognized to be a good form of therapy to keep harmful, intestinal microorganisms in check, aid digestion and nutrient absorption, and contribute to immune function. Probiotics are reported to improve microbial balance in the intestinal tract and promote the return to a baseline microbial community following a perturbing event (dysbiosis) such as antibiotic therapy. Prebiotics are selectively fermented ingredients that allow specific changes, both in the composition and/or activity in the gastrointestinal microflora, which confers benefits upon host well-being and health.

Activation of HIF-1α and LL-37 by commensal bacteria inhibits Candida albicans colonization

Candida albicans colonization is required for invasive disease^1-3. Unlike humans, adult mice with mature intact gut microbiota are resistant to C. albicans gastrointestinal (GI) colonization^2,4. But the factors that promote C. albicans colonization resistance are unknown. Here we demonstrate that commensal anaerobic bacteria – specifically Clostridial Firmicutes (Clusters IV and XIVa) and Bacteroidetes – are critical for maintaining C. albicans colonization resistance in mice. Using Bacteroides thetaiotamicron as a model organism, we find that HIF-1α, a transcription factor important for activating innate immune effectors, and the antimicrobial peptide LL37-CRAMP are key determinants of C. albicans colonization resistance. While antibiotic treatment enables C. albicans colonization, pharmacologic activation of colonic Hif1a induces CRAMP expression and results in a significant reduction of C. albicans GI colonization and a 50% decrease in mortality from invasive disease. In the setting of antibiotics, Hif1a and Cramp are required for B. thetaiotamicron-induced protection against CA colonization of the gut. Thus, C. albicans GI colonization modulation by activation of gut mucosal immune effectors may represent a novel therapeutic approach for preventing invasive fungal disease in humans.

Relating the metatranscriptome and metagenome of the human gut

Although the composition of the human microbiome is now well-studied, the microbiota's >8 million genes and their regulation remain largely uncharacterized. This knowledge gap is in part because of the difficulty of acquiring large numbers of samples amenable to functional studies of the microbiota. We conducted what is, to our knowledge, one of the first human microbiome studies in a well-phenotyped prospective cohort incorporating taxonomic, metagenomic, and metatranscriptomic profiling at multiple body sites using self-collected samples. Stool and saliva were provided by eight healthy subjects, with the former preserved by three different methods (freezing, ethanol, and RNAlater) to validate self-collection. Within-subject microbial species, gene, and transcript abundances were highly concordant across sampling methods, with only a small fraction of transcripts (<5%) displaying between-method variation. Next, we investigated relationships between the oral and gut microbial communities, identifying a subset of abundant oral microbes that routinely survive transit to the gut, but with minimal transcriptional activity there. Finally, systematic comparison of the gut metagenome and metatranscriptome revealed that a substantial fraction (41%) of microbial transcripts were not differentially regulated relative to their genomic abundances. Of the remainder, consistently underexpressed pathways included sporulation and amino acid biosynthesis, whereas up-regulated pathways included ribosome biogenesis and methanogenesis. Across subjects, metatranscriptional profiles were significantly more individualized than DNA-level functional profiles, but less variable than microbial composition, indicative of subject-specific whole-community regulation. The results thus detail relationships between community genomic potential and gene expression in the gut, and establish the feasibility of metatranscriptomic investigations in subject-collected and shipped samples.

The approach to sample acquisition and its impact on the derived human fecal microbiome and VOC metabolome

Recent studies have illustrated the importance of the microbiota in maintaining a healthy state, as well as promoting disease states. The intestinal microbiota exerts its effects primarily through its metabolites, and metabolomics investigations have begun to evaluate the diagnostic and health implications of volatile organic compounds (VOCs) isolated from human feces, enabled by specialized sampling methods such as headspace solid-phase microextraction (hSPME). The approach to stool sample collection is an important consideration that could potentially introduce bias and affect the outcome of a fecal metagenomic and metabolomic investigation. To address this concern, a comparison of endoscopically collected (in vivo) and home collected (ex vivo) fecal samples was performed, revealing slight variability in the derived microbiomes. In contrast, the VOC metabolomes differ widely between the home collected and endoscopy collected samples. Additionally, as the VOC extraction profile is hyperbolic, with short extraction durations more vulnerable to variation than extractions continued to equilibrium, a second goal of our investigation was to ascertain if hSPME-based fecal metabolomics studies might be biased by the extraction duration employed. As anticipated, prolonged extraction (18 hours) results in the identification of considerably more metabolites than short (20 minute) extractions. A comparison of the metabolomes reveals several analytes deemed unique to a cohort with the 20 minute extraction, but found common to both cohorts when the VOC extraction was performed for 18 hours. Moreover, numerous analytes perceived to have significant fold change with a 20 minute extraction were found insignificant in fold change with the prolonged extraction, underscoring the potential for bias associated with a 20 minute hSPME.

Normal to cancer microbiome transformation and its implication in cancer diagnosis

Microbial communities coexisting with humans are collectively known as microbiome. It influences almost every aspect of an individual's body function. Microbiome is idiosyncratic for body condition and its alteration is indicative for several abnormalities. This article discusses about recent ideas for developing microbiology based cancer indicators using alterations in microbiome. It is noteworthy that large exploratory studies are required to identify cancer indicator microorganisms from complex and diverse microbiome constituents. This complexity also warrants that these markers should be used in conjunction with other routine cancer indicators. The present article concludes that such studies can spur development of novel microbiome based cancer diagnostics.

Effect of Caenorhabditis elegans age and genotype on horizontal gene transfer in intestinal bacteria

Horizontal gene transfer (HGT) between bacteria occurs in the intestinal tract of their animal hosts and facilitates both virulence and antibiotic resistance. A model in which both the pathogen and the host are genetically tractable facilitates developing insight into mechanistic processes enabling or restricting the transfer of antibiotic resistance genes. Here we develop an in vivo experimental system to study HGT in bacteria using Caenorhabditis elegans as a model host. Using a thermosensitive conjugative system, we provide evidence that conjugation between two Escherichia coli strains can take place in the intestinal lumen of N2 wild-type worms at a rate of 10(-3) and 10(-2) per donor. We also show that C. elegans age and genotype are important determinants of the frequency of conjugation. Whereas ∼1 transconjugant for every 100 donor cells could be recovered from the intestine of N2 C. elegans, for the age-1 and tol-1 mutants, the detected rate of transconjugation (10(-3) and 10(-4) per donor cell, respectively) was significantly lower. This work demonstrates that increased recombination among lumenal microbial populations is a phenotype associated with host aging, and the model provides a framework to study the dynamics of bacterial horizontal gene transfer within the intestinal environment.

Effect of solar particle event radiation on gastrointestinal tract bacterial translocation and immune activation

Space flight conditions within the protection of Earth's gravitational field have been shown to alter immune responses, which could lead to potentially detrimental pathology. An additional risk of extended space travel outside the Earth's gravitational field is the effect of solar particle event (SPE) radiation exposure on the immune system. Organisms that could lead to infection include endogenous, latent viruses, colonizing pathogenics, and commensals, as well as exogenous microbes present in the spacecraft or other astronauts. In this report, the effect of SPE-like radiation on containment of commensal bacteria and the innate immune response induced by its breakdown was investigated at the radiation energies, doses and dose rates expected during an extravehicular excursion outside the Earth's gravitational field. A transient increase in serum lipopolysaccharide was observed 1 day after irradiation and was accompanied by an increase in acute-phase reactants and circulating proinflammatory cytokines, indicating immune activation. Baseline levels were reestablished by 5 days postirradiation. These findings suggest that astronauts exposed to SPE radiation could have impaired containment of colonizing bacteria and associated immune activation.

Antimicrobial resistance in Clostridium difficile

Clostridium difficile is the leading cause of hospital-acquired diarrhoea and the number of outbreaks has risen markedly since 2003. The emergence and spread of resistance in C. difficile is complicating treatment and prevention. Most isolates are still susceptible to vancomycin and metronidazole (MTZ), however transient and heteroresistance to MTZ have been reported. The prevalence of resistance to other antimicrobial agents is highly variable in different populations and in different countries, ranging from 0% to 100%. Isolates of common polymerase chain reaction (PCR) ribotypes are more resistant than uncommon ribotypes. Most of the resistance mechanisms that have been identified in C. difficile are similar to those in other Gram-positive bacteria, including mutation, selection and acquisition of the genetic information that encodes resistance. Better antibiotic stewardship and infection control are needed to prevent further spread of resistance in C. difficile.

Antibiotic resistance: a guide for effective prescribing in women's health

Current national and international trends in antibiotic resistance are becoming a public health crisis. Multi-drug resistant organisms are more prevalent in hospital settings and, alarmingly, are now being identified in the community. Over-reliance on broad-spectrum antibiotics, as well as inappropriate prescribing practices, play a significant role in encouraging the emergence of resistant organisms. This article reviews the mechanisms of bacterial resistance, current trends in national and international antibiotic resistance, and examines approaches to combat pathogens while sparing benign microbes.

Gene transfer events and their occurrence in selected environments

Genes encoding virulence determinants are transferred between species in many different environments. In this review we describe gene transfer events to and from different species of bacteria, from bacteria to plants, and from plants to bacteria. Examples of the setting for these transfer events include: the GI tract, the rumen, the oral cavity, and in food matrixes. As a case study, the flux of virulence factors from E.coli O157:H7 is described as an example of gene flow in the environment.

Antimicrobial phenotypes and molecular basis in clinical strains of Clostridium difficile

Clostridium difficile remains the leading cause of nosocomial-acquired diarrhea. This study investigated antimicrobial susceptibility patterns of C. difficile over a 3-year period. Three hundred seventeen C. difficile isolates recovered between 2002 and 2004 were analyzed for their susceptibility to erythromycin (ERY), clindamycin (CLI), moxifloxacin (MXF), doxycycline (DOX), vancomycin (VAN), and metronidazole (MTR) by Etest. The molecular basis for resistance was investigated using polymerase chain reaction (PCR) and DNA sequencing. PCR ribotyping was used to differentiate strains. All strains were susceptible to VAN and MTR. Resistance rates to ERY/CLI, MXF, and DOX increased during the study period. Eighty-four (26.5%) strains exhibited resistance against ERY/CLI, MXF, and DOX. Prevalence of resistance genes was as follows: ermB, 83; ermQ, 0; ermFS, 1; tetM, 84; tetP, 0; tetO, 2; and gyrA mutation, 76. These results indicate an increasing trend in the prevalence of combined resistance against macrolide-lincosamide-streptogramin B antibiotics, fluoroquinolones, and tetracycline in C. difficile. The lack of understanding of antibiotic resistance mechanisms in C. difficile and the increased resistant strains warrants further investigations.

Two membrane proteins from Bifidobacterium breve UCC2003 constitute an ABC-type multidrug transporter

Intrinsic resistance to drugs is one of the main determining factors in bacterial survival in the intestinal ecosystem. This is mediated by, among others, multidrug resistance (MDR) transporters, membrane proteins which extrude noxious compounds with very different chemical structures and cellular targets. Two genes from Bifidobacterium breve encoding hypothetical membrane proteins with a high homology with members of the ATP-binding cassette (ABC) family of multidrug efflux transporters, were expressed separately and jointly in Lactococcus lactis. Cells co-expressing both proteins exhibited enhanced resistance levels to the antimicrobials nisin and polymyxin B. Furthermore, the drug extrusion activity in membrane vesicles was increased when both proteins were co-expressed, compared to membranes in which the proteins were produced independently. Both proteins were co-purified from the membrane as a stable complex in a 1:1 ratio. This is believed to be the first study of a functional ABC-type multidrug transporter in Bifidobacterium and contributes to our understanding of the molecular mechanisms underlying the capacity of intestinal bacteria to tolerate cytotoxic compounds.

Conservative treatment of acute colonic diverticulitis: are antibiotics always mandatory?

OBJECTIVE

Most patients admitted for acute colonic diverticulitis (AD) are managed conservatively and receive antibiotics, although it is uncertain whether all patients with AD benefit from this treatment. The aim of this study was to evaluate the influence of antibiotic treatment on outcome in the conservative management of patients with mild AD.

MATERIAL AND METHODS

A retrospective audit of 311 patients (64% F, mean age 60 years) hospitalized for AD was carried out. All patients were initially treated conservatively with observation and restriction of oral intake. Patients receiving antibiotics (n=118) were compared with patients treated with observation and restriction of oral intake only (n=193). Mean follow-up time (FU) was 30 months.

RESULTS

Inflammation in patients treated with antibiotics was more pronounced (laboratory parameters (C-reactive protein, white blood cell count) were higher (p<0.01), fever was more common (p<0.01) and CT grading of inflammation was classified as severe in a higher proportion (p<0.01)) compared with patients treated without antibiotics. When initially treated with antibiotics, 3 patients (3%) failed to respond to treatment and had to undergo surgery. There were 7 (4%) failures in patients initially treated without antibiotics, and antibiotics were then added. During FU, 29% of patients treated with antibiotics had further events (recurrent AD and/or subsequent surgery) compared with 28% (NS) among those treated without antibiotics. In a multivariate analysis, the risk of a further event was not influenced by antibiotic treatment (OR 1.03, CI 95% 0.61-1.74).

CONCLUSIONS

Our results indicate that antibiotics are not mandatory in mild AD. Treatment without antibiotics appears to be safe and seems not to change the rate of further events. These results warrant further randomized prospective studies.

Rifaximin, a poorly absorbed antibiotic: pharmacology and clinical potential

Rifaximin (4-deoxy-4'-methylpyrido[1',2'-1,2]imidazo- [5,4-c]-rifamycin SV) is a synthetic antibiotic designed to modify the parent compound, rifamycin, in order to achieve low gastrointestinal (GI) absorption while retaining good antibacterial activity. Both experimental and clinical pharmacology clearly show that this compound is a nonsystemic antibiotic with a broad spectrum of antibacterial action covering Gram-positive and Gram-negative organisms, both aerobes and anaerobes. Being virtually nonabsorbed, its bioavailability within the GI tract is rather high with intraluminal and fecal drug concentrations that largely exceed the minimal inhibitory concentration values observed in vitro against a wide range of pathogenic organisms. The GI tract represents, therefore, the primary therapeutic target and GI infections the main indication. The appreciation of the pathogenic role of gut bacteria in several organic and functional GI diseases has increasingly broadened its clinical use, which is now extended to hepatic encephalopathy, small intestine bacterial overgrowth, inflammatory bowel disease and colonic diverticular disease. Potential indications include the irritable bowel syndrome and chronic constipation, Clostridium difficile infection and bowel preparation before colorectal surgery. Because of its antibacterial activity against the microorganism and the lack of strains with primary resistance, some preliminary studies have explored the rifaximin potential for Helicobacter pylori eradication. Oral administration of this drug, by getting rid of enteric bacteria, could also be employed to achieve selective bowel decontamination in acute pancreatitis, liver cirrhosis (thus preventing spontaneous bacterial peritonitis) and nonsteroidal anti-inflammatory drug (NSAID) use (lessening in that way NSAID enteropathy). This antibiotic has, therefore, little value outside the enteric area and this will minimize both antimicrobial resistance and systemic adverse events. Indeed, the drug proved to be safe in all patient populations, including young children. Although rifaximin has stood the test of time, it still attracts the attention of both basic scientists and clinicians. As a matter of fact, with the advancement of the knowledge on microbial-gut interactions in health and disease novel indications and new drug regimens are being explored. Besides widening the clinical use, the research on rifaximin is also focused on the synthesis of new derivatives and on the development of original formulations designed to expand the spectrum of its clinical use.