Enrichment of Bacteroides fragilis and enterotoxigenic Bacteroides fragilis in CpG island methylator phenotype-high colorectal carcinoma

OBJECTIVES

Data support that enterotoxigenic Bacteroides fragilis (ETBF) harbouring the Bacteroides fragilis toxin (bft) gene may promote colorectal tumourigenesis through the serrated neoplasia pathway. We hypothesized that ETBF may be enriched in colorectal carcinoma subtypes with high-level CpG island methylator phenotype (CIMP-high), BRAF mutation, and high-level microsatellite instability (MSI-high).

METHODS

Quantitative PCR assays were designed to quantify DNA amounts of Bacteroides fragilis, ETBF, and each bft gene isotype (bft-1, bft-2, or bft-3) in colorectal carcinomas in the Health Professionals Follow-up Study and Nurses' Health Study. We used multivariable-adjusted logistic regression models with the inverse probability weighting method.

RESULTS

We documented 4476 colorectal cancer cases, including 1232 cases with available bacterial data. High DNA amounts of Bacteroides fragilis and ETBF were positively associated with BRAF mutation (p ≤ 0.0003), CIMP-high (p ≤ 0.0002), and MSI-high (p < 0.0001 and p = 0.01, respectively). Multivariable-adjusted odds ratios (with 95% confidence interval) for high Bacteroides fragilis were 1.40 (1.06-1.85) for CIMP-high and 2.14 (1.65-2.77) for MSI-high, but 1.02 (0.78-1.35) for BRAF mutation. Multivariable-adjusted odds ratios for high ETBF were 2.00 (1.16-3.45) for CIMP-high and 2.86 (1.64-5.00) for BRAF mutation, but 1.09 (0.67-1.76) for MSI-high. Neither Bacteroides fragilis nor ETBF was associated with colorectal cancer-specific or overall survival.

DISCUSSION

The tissue abundance of Bacteroides fragilis is associated with CIMP-high and MSI-high, whereas ETBF abundance is associated with CIMP-high and BRAF mutation in colorectal carcinoma. Our findings support the aetiological relevance of Bacteroides fragilis and ETBF in the serrated neoplasia pathway.

Novel and rare β-lactamase genes of Bacteroides fragilis group species: Detection of the genes and characterization of their genetic backgrounds

OBJECTIVES

This study screened the prevalence of rare β-lactamase genes in Bacteroides fragilis group strains from clinical specimens and normal microbiota and examined the genetic properties of the strains carrying these genes.

METHODS

blaHGD1, blaOXA347, cblA, crxA, and pbbA were detected by real-time polymerase chain reaction in collections of Bacteroides strains from clinical (n = 406) and fecal (n = 184) samples. To examine the genetic backgrounds of the samples, end-point PCR, FT-IR, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were used.

RESULTS

All B. uniformis isolates were positive for cblA in both collections. Although crxA was B. xylanisolvens-specific and associated with carbapenem resistance, it was only found in six fecal and three clinical B. xylanisolvens strains. Moreover, the crxA-positive strains were not clonal among B. xylanisolvens (contrary to cfiA in B. fragilis), implicating a rate of mobility or emergence by independent evolutionary events. The Phocaeicola (B.) vulgatus/P. dorei-specific gene blaHGD1 was detected among all P. vulgatus/P. dorei isolates from fecal (n = 36) and clinical (n = 26) samples. No blaOXA347-carrying isolate was found from European collections, but all US samples (n = 6) were positive. For three clinical isolates belonging to B. thetaiotaomicron (n = 2) and B. ovatus (n = 1), pbbA was detected on mobile genetic elements, and pbbA-positive strains displayed non-susceptibility to piperacillin or piperacillin/tazobactam phenotypically.

CONCLUSIONS

Based on these observations, β-lactamases produced by rare β-lactamase genes in B. fragilis group strains should not be overlooked because they could encode important resistance phenotypes.

First Report of Antibiotic Resistance Markers cfiA and nim Among Bacteroides fragilis Group Strains in Ecuadorian Patients

In recent years, increasing resistance of Bacteroides fragilis to several antibiotics has been reported in different countries. The aim of this study was to evaluate the antibiotic resistance profiles of Bacteroides spp. isolated from clinical samples by phenotypic and molecular methods. A total of 40 nonrepetitive isolates of the B. fragilis group were studied from 2018 to 2019. The species was identified by API 20A system. The minimum inhibitory concentrations (MICs) were determined by Sensititre anaerobe MIC plate. The presence of the nim and cfiA genes was checked by conventional PCR. The association between genes and insertion sequence (IS) was performed by whole genome sequencing. Eleven isolates were categorized as metronidazole-resistant and only 2 isolates harbored the nim gene. Five isolates were imipenem-resistant, but cfiA gene was detected in two isolates. cfiA gene was closely related to the cfiA-4 allele and associated with IS614B. The nim gene was not related to any nim gene type and was considered a new variant named nimL. IS612 was found upstream of nimL gene. In view of the scarcity of data on B. fragilis, there is a need to surveil antibiotic resistance levels and molecular mechanisms to implement better antimicrobial therapies against this important group of bacteria.

Comparison of microbiological profile of enterotoxigenic Bacteroides fragilis (ETBF) isolates from subjects with colorectal cancer (CRC) or intestinal pre-cancerous lesions versus healthy individuals and evaluation of environmental factors involved in intestinal dysbiosis

OBJECTIVE

The aim of this study was to analyze enterotoxigenic Bacteroides fragilis (ETBF) isolates from colorectal biopsies of subjects with a histological analysis positive for colorectal cancer (CRC), pre-cancerous lesions (pre-CRC) or with a healthy intestinal tissue and to evaluate the environmental factors that may not only concur to CRC development but may also affect gut microbiota composition.

METHODS

ETBF isolates were typed using the ERIC-PCR method, while PCR assays were performed to investigate the bft alleles, the B. fragilis pathogenicity island (BFPAI) region and the cepA, cfiA and cfxA genes. Susceptibility to antibiotics was tested using the agar dilution method. Environmental factors that could play a role in promoting intestinal dysbiosis were evaluated throughout a questionnaire administered to the subjects enrolled.

RESULTS

Six different ERIC-PCR types were identified. The type denominated C in this study was the most prevalent, in particular among the biopsies of subjects with pre-CRC, while an isolate belonging to a different type, denominated F, was detected in a biopsy from a subject with CRC. All the ETBF isolates from pre-CRC or CRC subjects had a B. fragilis pathogenicity island (BFPAI) region pattern I, while those from healthy individuals showed also different patterns. Furthermore, 71% of isolates from subjects with pre-CRC or CRC were resistant to two or more classes of antibiotics vs 43% of isolates from healthy individuals. The B. fragilis toxin BFT1 was the most frequently detected in this study, confirming the constant circulation of this isoform strains in Italy. Interestingly, BFT1 was found in 86% of the ETBF isolates from patients with CRC or pre-CRC, while the BFT2 was prevalent among the ETBF isolates from healthy subjects. No substantial differences based on sex, age, tobacco and alcohol consumption were observed between healthy and non-healthy individuals included in this study, while most of the subjects with CRC or pre-CRC lesions were subjected to pharmacological therapy (71%) and showed a body mass index (BMI) that falls within the overweight range (86%).

CONCLUSIONS

Our data suggest that some types of ETBF seem to better adapt and colonize the human gut and that the selective pressure exerted by factors related to lifestyle, such as pharmacological therapy and weight, could facilitate their persistence in the gut and their possible involvement in CRC development.

Haemin deprivation renders Bacteroides fragilis hypersusceptible to metronidazole and cancels high-level metronidazole resistance

BACKGROUND

Infections with Bacteroides fragilis are routinely treated with metronidazole, a 5-nitroimidazole antibiotic that is active against most anaerobic microorganisms. Metronidazole has remained a reliable treatment option, but resistance does occur, including in B. fragilis.

OBJECTIVES

In this study we tested whether haemin, a growth supplement for B. fragilis in vivo and in vitro, had an influence on the susceptibility of resistant B. fragilis strains to metronidazole. We further tested whether haemin-deprived B. fragilis would be more susceptible to oxygen and oxidative stress. Metronidazole has been described to cause oxidative stress, which we argued would be exacerbated in haemin-deprived B. fragilis because the bacteria harness haemin, and the iron released from it, in antioxidant enzymes such as catalase and superoxide dismutase.

METHODS

Haemin was omitted from growth media and the effect on metronidazole susceptibility was monitored in susceptible and resistant B. fragilis strains. Further, haemin-deprived B. fragilis were tested for resistance to aeration and hydrogen peroxide and the capacity for the removal of oxygen.

RESULTS

Omission of haemin from the growth medium rendered metronidazole-resistant B. fragilis strains, including an MDR isolate from the UK, highly susceptible to metronidazole. Haemin deprivation further rendered B. fragilis highly susceptible to oxygen, which was further exacerbated in resistant strains. B. fragilis was incapable of scavenging oxygen when haemin was omitted.

CONCLUSIONS

We propose that haemin deprivation overrules resistance mechanisms by rendering B. fragilis hypersusceptible to metronidazole due to a compromised antioxidant defence. Monitoring of haemin concentrations is imperative when conducting metronidazole susceptibility testing in B. fragilis.

What we actually know about the pathogenicity of Bacteroides pyogenes

The aim of the study was to evaluate the pathogenic potential of Bacteroides pyogenes, rarely identified in clinical laboratories anaerobic bacteria. To increase the knowledge about this poorly understood anaerobic microorganism, the study also includes cases of infections described so far in the literature. Only the use of 16S rRNA sequencing and mass spectrometry technique allowed the identification of B. pyogenes from clinical specimens. We reported 13 severe human infections caused by B. pyogenes. Bacteria were cultured from the wound after biting by animals, chronic infections within the oral cavity, from patients with histologically or radiological proven osteomyelitis, surgical site infection, and from urine sample collected after a urological procedure. Most (9/13) of the patients required hospitalization. Almost 70% of them needed urgent admission via the emergency room. Two inpatients due to a life-threatening condition were admitted to the intensive care unit. Almost 50% of isolates were resistant to penicillin. All resistant to penicillin strains were isolated from skin and mucous membrane infections.

Bloodstream Infection Caused by Bacteroides caccae in a Diabetic Patient: a Case Report and Review of the Literature

BACKGROUND

Bacteroides caccae is a ubiquitous, anaerobic bacteria, but it is not a common cause of pathologic bloodstream infection. Diabetic patients are at increased risk of developing anaerobic bacteria infection. Here, we report a repeated fever case caused by Bacteroides caccae in a diabetic patient. The aim of this study was to describe the clinical characteristics and manifestations of Bacteroides caccae.

METHODS

The pathogenic bacteria isolated from patient blood was identified as Bacteroides caccae. Identification of the Bacteroides caccae was done by 16s rDNA sequencing and matrix-assisted laser desorption/ionization-time of light spectrometry. The infection was cured by one-week combined therapy of intravenous Piperacillin tazobactam and oral Ornidazole tablet.

RESULTS

After treatment had been completed, no episodes of fever occurred during the follow-up to date.

CONCLUSIONS

Bacteroides caccae is regarded as an intestinal, opportunistic pathogenic bacteria. It can invade the mucosa of the intestine and cause various abdominal suppurative infections. Sequencing and matrix-assisted laser desorption/ionization-time of flight spectrometry could have a role for Bacteroides caccae diagnosis. The curative effect of using first generation cephalosporines therapy was unsatisfactory. Using intravenous Piperacillin tazobactam and ornidazole tablet might obtain certain curative effect. Early diagnosis and appropriate anti-infection therapy were necessary to improve the outcome of patients with Bacteroides caccae bloodstream infection.

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.

Evaluation of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card for identification of Bacteroides fragilis group isolates and antimicrobial susceptibilities of these isolates in a Chinese university hospital

BACKGROUND AND PURPOSE

Bacteroides fragilis group isolates are most frequently isolated anaerobic pathogens. This study aimed to evaluate the accuracy of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card on the identification of clinical B. fragilis group isolates, as well as to determine their antimicrobial susceptibilities.

METHODS

A total of 138 isolates of B. fragilis group isolates were identified with the three MALDI-TOF MS systems and VITEK 2 ANC cards. 16S rRNA gene sequencing was used as the reference identification method for comparison. Antimicrobial susceptibilities were determined by agar dilution method to 19 antimicrobial agents recommended by Clinical and Laboratory Standards Institute (CLSI).

RESULTS

Hundred thirty three isolates of Bacteroides spp. and 5 isolates of Parabacteroides spp. were identified by 16S rRNA sequencing. The rates of accurate identification at species level of VITEK MS, Clin-ToF-II MS, Autof MS 1000 and VITEK 2 ANC card were 94.2%, 94.2%, 98.6% and 94.9%, respectively, while that at genus level were 99.3%, 100%, 100% and 97.8%, respectively. Metronidazole and chloramphenicol were the most susceptible agents (99.3% and 92.8%, respectively), followed by meropenem, ertapenem, imipenem and piperacillin/tazobactam to which the susceptible rates ranged from 76.8% to 79.0%. The susceptible rates to carbapenems decreased 12.4-15.3% from 2010-2013 to 2014-2017.

CONCLUSION

All the four systems provided high accurate rate on the identification of B. fragilis group isolates. Metronidazole showed highest activity against these isolates. Attention should be paid to the higher resistant rates to carbapenems, clindamycin, moxifloxacin and tigecycline than the other countries.

Transposon Mutagenesis of Bacteroides fragilis

Bacteroides fragilis is Gram-negative obligatory anaerobe which usually resides in the gut of humans and animals. As an important member of the human gut microbiota it plays a vital role in digestion and absorption of nutrients as well as shaping of host immune system. B. fragilis is also infamous for causing serious infections. Treatment of B. fragilis infections caused emergence of multidrug-resistant strains. Molecular biology tools such as transposon mutagenesis help to decipher and understand commensal and pathogenic faces of B. fragilis. Using two mariner transposon vectors we describe the detailed methodology for the transposon mutagenesis of B. fragilis. We also describe two methods for the identification of transposon integration site (TIS) in transposon mutants. Transposon mutagenesis methods described in this chapter serve as a great tool for studying B. fragilis.

Orthopedic infections caused by obligatory anaerobic Gram-negative rods: report of two cases

Anaerobic bone and joint infections are uncommon, although the number of anaerobic infections is presumably underestimated because of difficulties with isolation and identification of obligate anaerobes. This study describes two cases of complicated Bacteroides fragilis peri-implant infection of the lumbar spine, infection of the hip and osteomyelitis. Bacteria were identified with the use of a mass spectrometer, VITEK MS system. Drug susceptibility was performed with the use of E-test. The EUCAST breakpoints were used for interpretation with B. fragilis ATCC 25285 as a control. In the two described cases clinical samples were collected for microbiological examination intraoperatively and simultaneously empirical treatment was applied. B. fragilis was isolated in monoculture or in a combination with other bacteria. The treatment was continued according to the susceptibility tests. In a case one clindamycin failure was observed and clindamycin resistance of the isolate was likely due to inadequate time of therapy. Difficulties in collecting an adequate samples and culturing anaerobic bacteria cause that not all infections are properly recognized. In a successful therapy, identification and determination of the susceptibility of the pathogen are essential as well as an appropriate surgical debridement.

TLR2-stimulating contaminants in glycoconjugate fractions prepared from Bacteroides fragilis

Bacteroides fragilis is a member of the normal intestinal flora and is involved in host immunostimulation via TLR2. On the bacterial cell surface, glycoconjugates, such as LPS and capsular polysaccharide A (PSA), have been reported to participate in host immunostimulation via TLR2. Previously, we identified a TLR2-stimulating lipoprotein in B. fragilis cells. In this study, we demonstrated that TLR2-stimulating principal molecules in glycoconjugate fractions prepared from B. fragilis are contaminating proteinous molecules, which may also be lipoproteins. The glycoconjugate fractions were prepared by phenol-hot water extraction of B. fragilis wild type and PSA-deficient strains, followed by hydrophobic interaction chromatography. TLR2-stimilating activities of the fractions were not affected by PSA deficiency. By in-gel TLR2-stimulation assay, molecules in high-molecular-mass area, where capsular polysaccharides were migrated, were found not to stimulate TLR2, but those in the range of 15-40 kDa were active. Further, proteinase K could digest the latter molecules and the TLR2-stimulating activities were migrated to the area of below 15 kDa. These results support that proteinous molecules, which are estimated to be lipoproteins, are responsible for almost all TLR2-stimulating activity in the glycoconjugate fractions prepared from B. fragilis.

Monoclonal antibodies specific for Bacteroides fragilis enterotoxins BFT1 and BFT2 and their use in immunoassays

We have developed 22 mouse IgG₁ monoclonal antibodies (mAbs) against Bacteroides fragilis zinc metalloprotease toxins 1 and 2 (BFT1 and BFT2). Mice were immunized with recombinant BFT1 or BFT2 proteins with metalloprotease activity. Eight of the mAbs bind specifically to BFT1. One mAb, 2H6, binds specifically to BFT2. The remaining 13 mAbs bind to both BFT1 and BFT2. The eight BFT1-specific mAbs recognize at least five different epitopes on the toxin. Four of the BFT1-specific mAbs neutralized rBFT1 metalloprotease activity. Only one of these four mAbs, 1D9, neutralizes the cytotoxic effect of BFT1. Here, we describe the development of enzyme-linked immunosorbent assays (ELISAs) to detect BFT1 or BFT2 toxin in an isotype-specific manner. The sandwich ELISAs have a detection limit of 20 to 40 ng/ml when purified recombinant BFT protein is diluted into PBS. The sandwich ELISA can be used to distinguish and quantify levels of rBFT1 and rBFT2 in stool. This ELISA can be an important tool to investigate the association between BFT expression by enterotoxigenic B. fragilis and diseases such as diarrhea, inflammatory bowel disease and colorectal cancer.

A case of Bacteroides pyogenes bacteremia secondary to liver abscess

Bacteroides pyogenes, a non-spore-forming, anaerobic, gram-negative rod, is a component of the oral flora of animals and has, on occasion, been reported to cause human infection through dog or cat bites. We report the first case of B. pyogenes bacteremia secondary to liver abscess with no history of an animal bite. The microorganism was identified by 16S rRNA sequencing.

The Dysregulation of Polyamine Metabolism in Colorectal Cancer Is Associated with Overexpression of c-Myc and C/EBPβ rather than Enterotoxigenic Bacteroides fragilis Infection

Colorectal cancer is one of the most common cancers in the world. It is well known that the chronic inflammation can promote the progression of colorectal cancer (CRC). Recently, a number of studies revealed a potential association between colorectal inflammation, cancer progression, and infection caused by enterotoxigenic Bacteroides fragilis (ETBF). Bacterial enterotoxin activates spermine oxidase (SMO), which produces spermidine and H2O2 as byproducts of polyamine catabolism, which, in turn, enhances inflammation and tissue injury. Using qPCR analysis, we estimated the expression of SMOX gene and ETBF colonization in CRC patients. We found no statistically significant associations between them. Then we selected genes involved in polyamine metabolism, metabolic reprogramming, and inflammation regulation and estimated their expression in CRC. We observed overexpression of SMOX, ODC1, SRM, SMS, MTAP, c-Myc, C/EBPβ (CREBP), and other genes. We found that two mediators of metabolic reprogramming, inflammation, and cell proliferation c-Myc and C/EBPβ may serve as regulators of polyamine metabolism genes (SMOX, AZIN1, MTAP, SRM, ODC1, AMD1, and AGMAT) as they are overexpressed in tumors, have binding site according to ENCODE ChIP-Seq data, and demonstrate strong coexpression with their targets. Thus, increased polyamine metabolism in CRC could be driven by c-Myc and C/EBPβ rather than ETBF infection.

Bacteriology of middle meatal aspirate of adult patients with chronic rhinosinusitis in Lagos. University Teaching Hospital, Lagos

BACKGROUND

Chronic rhinosinusitis (CRS) significantly lowers the quality of life of patients. The common use of broad spectrum antibiotics for its treatment may alter the pathogens that promote the persistence of this condition. However, the data concerning the distribution of bacteria species. in patients with CRS are not consistent.

OBJECTIVE

To isolate the common aerobic and anaerobic bacteria from the middle meatal aspirates of adult patients with CRS and determine their antibiotic sensitivity patterns Methods: This was a case-control study of adults with diagnosis of CRS. Middle meatal aspirate and swab were obtained from cases and control respectively for bacteriological studies. Data analysis was done using Statistical package for social sciences (SPSS) version 17 Result: Forty one aerobic bacteria were cultured. Sixty one percent of the aerobic bacteria isolated were gram positive (staphlylococcus.aureus was the most frequently found) organisms while the remaining 39% was gram negative. Fifteen peicent of the cultured isolates yielded mixed growth of both aerobes (Gram positive and gram negative).3(6%) isolates of Bacteroides species were cultured Conclusion: The present study found that Staphylococcus aureus, streptococcus pneumoniae, Proteus mirabilis, Klebsiella spp, Escherichia coli and Bacteroides spp) were the common bacterial flora in the paranasal sinuses of patients with CRS.

Pyogenic arthritis of native joints due to Bacteroides fragilis: Case report and review of the literature

Pyogenic arthritis of native joints due to Bacteroides fragilis seems to be an infrequent disease. We analyzed the cases diagnosed in a tertiary hospital during a 22-year period and reviewed the literature to summarize the experience with this infectious entity.In our institution, of 308 patients with pyogenic arthritis of native joints, B fragilis was the causative organism in 2 (0.6%) cases. A MEDLINE search (1981-2015) identified 19 additional cases.Of the 21 patients available for review (13 men and 8 women, with a mean age, of 54.4 ± 17 years), 19 (90%) presented a systemic predisposing factor for infection; the most common associated illness was rheumatoid arthritis (8 patients). Bacteremia was documented in 65% (13/20) of cases. In 5 patients (24%), 1 or more concomitant infectious process was found. Metronidazole was the most frequently used antibiotic. Surgical drainage was performed in 11 cases (52%). The overall mortality rate was 5%.Pyogenic arthritis of native joints due to B fragilis is an infrequent disease that mainly affects elderly patients with underlying medical illnesses and in whom bacteremia and the presence of a concomitant infectious process are frequent conditions.

Post-Thoracic Endovascular Aortic Repair Complicated with Mycotic Aneurysm Rupture, Repaired by Redo Thoracic Endovascular Aortic Repair

Mycotic aneurysms although rare can be devastating. We encountered a dialysis patient with rapidly expanding distal aortic arch aneurysm who underwent axilloaxillary bypass and thoracic endovascular aortic repair (TEVAR). Three months later, he suffered mycotic aneurysm rupture for which redo TEVAR was performed. Antibiotic therapy was discontinued 16 weeks after the second operation, and renal transplantation was performed 6 months later. Dialysis was discontinued in the patient without infection recurrence.

[DYNAMICS OF INDICES OF A LOCAL IMMUNITY IN AN ACUTE APPENDICITIS]

Abstract The results of investigation on dynamics of a local immunity indices in an acute appendicitis, depending on the pathological process stage as well as on bacteriological investigation of parietal microflora of processus vermicularis, were adduced. The sIgA and lisocymal dynamics have witnessed that while a destructive process progressing their concentration was enhanced, and in a gangrenous acute appendicitis they practically disappeared. Due to affection of a barrier function of the processus vermicularis wall a favorable conditions were created for the microorganisms intramural translocation as well as to abdominal cavity.

Mycotic Aneurysm Caused by Bacteroides fragilis in an Elderly Immunosuppressed Patient

An 82-year-old Japanese man, who presented with a fever and abdominal pain, was admitted to our hospital. According to enhanced computed tomography images, the probable diagnosis was abdominal aortic mycotic aneurysm. Eight sets of blood cultures obtained from the patient were negative. Despite administering treatment with vancomycin and ceftriaxone, the aneurysm progressively enlarged. He underwent open debridement surgery and in situ replacement because of an aneurysmal rupture. Bacteroides fragilis was isolated from the tissue culture of the aortic wall. Metronidazole was administered and discontinued without any infection relapse. When faced with similar cases, rare pathogens should thus be considered as possible causes of mycotic aneurysms.

Characterization of a multidrug-resistant, novel Bacteroides genomospecies

Metronidazole- and carbapenem-resistant Bacteroides fragilis are rare in the United States. We isolated a multidrug-resistant anaerobe from the bloodstream and intraabdominal abscesses of a patient who had traveled to India. Whole-genome sequencing identified the organism as a novel Bacteroides genomospecies. Physicians should be aware of the possibility for concomitant carbapenem- and metronidazole-resistant Bacteroides infections.

Fecal detection of enterotoxigenic Bacteroides fragilis

Bacteroides fragilis is a common colonic symbiote of which one subtype, enterotoxigenic Bacteroides fragilis (ETBF), causes inflammatory diarrhea. However, asymptomatic ETBF colonization is common. Through its primary virulence factor, B. fragilis toxin (BFT), ETBF causes asymptomatic, chronic colitis in C57BL/6 mice and increased colon tumorigenesis in multiple intestinal neoplasia mice. Human studies suggest an association between ETBF infection, inflammatory bowel disease, and colon cancer. Additional studies on ETBF epidemiology are, therefore, crucial. The goal of this study is to develop a reliable fecal diagnostic for ETBF. To develop a sensitive assay for ETBF, we tested multiple protocols on mouse stools spiked with serially diluted ETBF. Each assay was based on either touchdown or quantitative polymerase chain reaction (qPCR) and used primers targeted to bft to detect ETBF. Using touchdown PCR or qPCR, the mean ETBF detection limit was 1.55 × 10(6) colony-forming units (CFU)/g stool and 1.33 × 10(4) CFU/g stool, respectively. Augmentation of Bacteroides spp. growth in fecal samples using PYGB (Peptone Yeast Glucose with Bile) broth enhanced ETBF detection to 2.93 × 10(2) CFU/g stool using the touchdown PCR method and 2.63 × 10(2) CFU/g stool using the qPCR method. Fecal testing using combined culture-based amplification and bft touchdown PCR is a sensitive assay for the detection of ETBF colonization and should be useful in studying the role of ETBF colonization in intestinal diseases, such as inflammatory bowel disease and colon cancer. We conclude that touchdown PCR with culture-based amplification may be the optimal ETBF detection strategy, as it performs as well as qPCR with culture-based amplification, but is a less expensive technique.

[VERTEBRAL OSTEOMYELITIS CAUSED BY RARE PATHOGENS--THE NEED FOR HIGH INDEX OF SUSPICION]

Vertebral OsteomyeLitis (V.O.) is a rare event that usually presents insidiously and follows an indolent clinical course, making early diagnosis difficult. The most important infecting organism in V.O. is Staphylococcus aureus, followed by gram-negative bacilli. We describe herein two cases of V.O. hospitalized in our department during the same week, caused by rare pathogens--Streptococcus sanguis (viridans) and Bacteroides fragilis. V.O. must be recognized rapidly because delay in diagnosis and treatment can result in neurologic compromise and high mortality. Its prompt and accurate diagnosis depends on detailed knowledge of the disease along with a high index of suspicion, even in face of rare pathogens on bacteriology results.

Giant Septic Lymphadenitis with Marked Gas Formation Caused by Bacteroides fragilis in a Patient with Adult T-cell Leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATL) sometimes causes opportunistic infections. A 53-year-old woman with systemic lymphadenopathies was diagnosed with ATL by inguinal lymph node biopsies and underwent oral chemotherapy. Two months later, high grade fever, lower abdominal pain and lymphadenopathy recurred. Computed tomography revealed the presence of lymphadenopathy with marked gas formation in the pelvic lesion. Blood cultures were suggestive of septic lymphadenitis by Bacteroides fragilis (BF). This represents the first demonstration of giant lymphadenitis with gas formation caused by BF in a patient with ATL. Notably, septic lymphadenitis is pivotal in the differential diagnosis of systemic lymphadenopathy in ATL.

Development of EUCAST disk diffusion method for susceptibility testing of the Bacteroides fragilis group isolates

With the emergence of antibiotic resistance among Bacteroides fragilis group isolates the need of susceptibility testing in routine laboratories is increasing. The aims of the present study were to evaluate the disk diffusion method for susceptibility testing in case of different clinical isolates of Bacteroides spp by comparing zone diameter results with MICs obtained earlier during an Europe-wide antibiotic susceptibility surveillance, and to propose zone diameter breakpoints, which correlate for the EUCAST MIC breakpoints. We tested 381 clinical isolates of the B. fragilis group to amoxicillin/clavulanic acid, cefoxitin, clindamycin, imipenem, metronidazole, moxifloxacin, piperacillin/tazobactam, tigecycline by agar dilution method previously. The inhibition zones of the same antibiotics including meropenem disc were determined by the disc diffusion on Brucella blood agar supplemented with haemin and vitamin K1. Plates were incubated at 37 °C in an anaerobic atmosphere for 24 h. The zone diameters were read at 100% inhibition. In case of discrepant results MICs were determined by gradient test and compared with the inhibition zones on the same plate. We found a good agreement between the inhibition zone diameters and the MICs for imipenem, metronidazole, moxifloxacin and tigecyclin. The inhibition zone diameters of meropenem also separated clearly the isolates, which can be considered wild-type isolates. In case of amoxicillin/clavulanic acid and piperacillin/tazobactam intermediate and susceptible isolates according to the MIC determination, overlap during the zone diameter determination. Isolates with an inhibition zone <23 mm for amoxicillin/clavulanic acid and <25 mm for piperacillin/tazobactam should be retested by a MIC determination method. The 10 μg clindamycin disc clearly separated the resistant and the susceptible population of B. fragilis group strains. In the case of cefoxitin only resistant population could be separated with an inhibition zone <17 mm, intermediate and susceptible isolates overlap. In conclusion, we suggest that disk diffusion can be an option for susceptibility testing of B. fragilis group isolates for most relevant antibiotics in routine laboratories.

Bacteroides fragilis subverts mucosal biology: from symbiont to colon carcinogenesis

The human body comprises fewer host cells than bacterial cells, most of which are obligate anaerobes residing in the gut. The symbiont Bacteroides fragilis constitutes a relatively small proportion (up to 1%-2%) of cultured fecal bacteria, but colonizes most humans. There are 2 classes of B. fragilis distinguished by their ability to secrete a zinc-dependent metalloprotease toxin, B. fragilis toxin (BFT). Strains that do not secrete BFT are nontoxigenic B. fragilis (NTBF), and those that do are called enterotoxigenic B. fragilis (ETBF). ETBF can induce clinical pathology, including inflammatory diarrhea, although asymptomatic colonization may be common. Intestinal inflammation is mediated by BFT, as yet the only known virulence factor of ETBF. Recent experimental evidence demonstrating that ETBF-driven colitis promotes colon tumorigenesis has generated interest in the potential contribution of ETBF to human colon carcinogenesis. Critical questions about the epidemiology of chronic, subclinical human colonization with ETBF and its impact on the biology of the colon need to be addressed.

Individually addressable arrays of replica microbial cultures enabled by splitting SlipChips

Isolating microbes carrying genes of interest from environmental samples is important for applications in biology and medicine. However, this involves the use of genetic assays that often require lysis of microbial cells, which is not compatible with the goal of obtaining live cells for isolation and culture. This paper describes the design, fabrication, biological validation, and underlying physics of a microfluidic SlipChip device that addresses this challenge. The device is composed of two conjoined plates containing 1000 microcompartments, each comprising two juxtaposed wells, one on each opposing plate. Single microbial cells are stochastically confined and subsequently cultured within the microcompartments. Then, we split each microcompartment into two replica droplets, both containing microbial culture, and then controllably separate the two plates while retaining each droplet within each well. We experimentally describe the droplet retention as a function of capillary pressure, viscous pressure, and viscosity of the aqueous phase. Within each pair of replicas, one can be used for genetic analysis, and the other preserves live cells for growth. This microfluidic approach provides a facile way to cultivate anaerobes from complex communities. We validate this method by targeting, isolating, and culturing Bacteroides vulgatus, a core gut anaerobe, from a clinical sample. To date, this methodology has enabled isolation of a novel microbial taxon, representing a new genus. This approach could also be extended to the study of other microorganisms and even mammalian systems, and may enable targeted retrieval of solutions in applications including digital PCR, sequencing, single cell analysis, and protein crystallization.

Stat3 activation in murine colitis induced by enterotoxigenic Bacteroides fragilis

BACKGROUND

Enterotoxigenic Bacteroides fragilis (ETBF), a molecular subclass of the common human commensal, B. fragilis, has been associated with inflammatory bowel disease. ETBF colitis is characterized by the activation of Stat3 and a Th17 immune response in the colonic mucosa. This study was designed to investigate the time course and cellular distribution of Stat3 activation in ETBF-colonized mice.

METHODS

C57BL/6 wild-type, C57BL/6, or Rag-1 mice were inoculated with saline, nontoxigenic B. fragilis or ETBF. Histologic diagnosis and mucosal Stat activation (immunohistochemistry, Western blot, and/or electrophorectic mobility shift assay) were evaluated over time (6-24 h, 1-7 d, and 1-18 mo after inoculation). Mucosal permeability was evaluated at 16 hours, 1 day, and 3 days. Mucosal immune responses were evaluated at 1 week, and 12 and 18 months.

RESULTS

ETBF induced rapid-onset colitis that persisted for up to 1 year. Stat3 activation (pStat3) was noted in the mucosal immune cells within 16 hours, with colonic epithelial cell activation evident at 24 hours after inoculation. ETBF-induced increased mucosal permeability was first observed at 24 hours after inoculation, after which the initial immune cell pStat3 activation was noted. Immune cell pStat3 was present in the absence of epithelial pStat3 (C57BL/6). Epithelial pStat3 was present in the absence of T and B cells (Rag-1 mice). pStat3 persisted in the epithelial and immune cells for 1 year, characterized by isolated pStat3-positive cell clusters, with varying intensity distributed through the proximal and distal colon. Similarly, mucosal Th17 immune responses persisted for up to 1 year. Loss of fecal ETBF colonization was associated with the loss of mucosal pStat3 and Th17 immune responses.

CONCLUSIONS

ETBF rapidly induces immune cell pStat3, which is independent of epithelial pStat3. This occurs before ETBF-induced mucosal permeability, suggesting that ETBF, likely through B. fragilis toxin and its action on the colonic epithelial cell, triggers mucosal immune cell Stat3 activation. Peak mucosal Stat3 activation (immune and epithelial cells) occurs subsequently when other colonic bacteria may contribute to the ETBF-initiated immune response due to barrier dysfunction. ETBF induces long-lived, focal colonic Stat3 activation and Th17 immune responses dependent on the ongoing ETBF colonization. Further study is needed to evaluate the early mucosal signaling events, resulting in epithelial Stat3 activation and the sequelae of long-term colonic Stat3 activation.

Resistance of Bacteroides isolates recovered among clinical samples from a major Costa Rican hospital between 2000 and 2008 to ß-lactams, clindamycin, metronidazole, and chloramphenicol

OBJECTIVE

To assess the susceptibility of 100 isolates of Bacteroides spp. recovered in a major Costa Rican hospital between 2000 and 2008 to several ß-lactams, chloramphenicol, clindamycin and metronidazole.

METHODS

Susceptibility to amoxicillin, amoxicillin with clavulanic acid, piperacillin, piperacillin with tazobactam, ticarcillin, ticarcillin with clavulanic acid, cefoxitin, cefotetan, imipenem, chloramphenicol, clindamycin, and metronidazole was determined with the ATB ANA® system. In addition, minimum inhibitory concentrations (MIC) of clindamycin and metronidazole were determined with the broth microdilution method because these drugs are the treatment of choice for anaerobic infections in Costa Rica. Reference strains ATCC® 25285 and ATCC® 29741 were employed as indicated.

RESULTS

According to the ATB ANA® system, 93 isolates were resistant to at least one antibiotic. Resistance to ß-lactams was common. By contrast, resistance to ß-lactams supplemented with ß-lactamase inhibitors was rare. All of the strains were inhibited by imipenem and chloramphenicol. By a broth microdilución test, resistance to clindamycin was 20%, with MIC ranging from 64 mg/L to 256 mg/L; all of the strains were susceptible to metronidazole.

CONCLUSIONS

The high MIC for clindamycin obtained for the majority of the resistant strains is highly suggestive of the presence of mechanisms of acquired resistance among the isolates, therefore surveillance studies are required to determine its efficacy. The low resistance to metronidazole observed underlines its value as a first-line drug. On the other hand, imipenem could be used to treat infections that do not respond well to metronidazole or clindamycin.

Spondylodiscitis complicated by an epidural abscess and meningitis caused by Bacteroides fragilis

Bacteroides fragilis is a rare causative agent of spondylodiscitis. The pathophysiology of B. fragilis in spondylodiscitis remains largely unclear because of its rare occurrence. We herein report a case of spondylodiscitis complicated by an epidural abscess and meningitis; B. fragilis was detected in the blood of the patient. Moreover, the patient had a splenic abscess that was confirmed on magnetic resonance imaging. The patient completely recovered with antimicrobial therapy alone.

[Metabolic correction of structural changes in adrenal glands during experimental widespread purulent peritonitis]

Experiments on 55 male chinchilla rabbits with model widespread purulent peritonitis have been performed for determinig structural changes in adrenal glands with the aid of optical microscopy. The introduction of aerobic-anaerobic culture of E. Coli and B. Fragilis into the abdominal cavity causes expressed structural changes in parenchyma of adrenal glands within 6 hours. It is established for the first time that the administration of metabolic drugs citoflavin (containing succinic acid) and neoton (containing creatine phosphate) prevents the development of pathological structural changes in adrenal glands under conditions of experimental widespread purulent peritonitis.

Bacteroides mobilizable and conjugative genetic elements: antibiotic resistance among clinical isolates

The conjugation is one of the most important mechanisms of horizontal gene transfer in prokaryotes, leading to genetic variation within a species and the acquisition of new traits, such as antibiotic resistance. Bacteroides is an obligate anaerobe of the colon and a significant opportunistic pathogen. Antibiotic resistance among Bacteroides spp. is rapidly increasing, largely due to the dissemination of DNA transfer factors (plasmids and transposons) harbored by members of this genus. Transfer factors can be divided into two classes, conjugative and mobilizable. Species of the intestinal Bacteroides have yielded different resistance plasmids, all of which have been intensely studied, the plasmids encode high-level MLS resistance conferred by a conserved erm gene. It has been reported an interesting observation associated with the transfer of several of these types of elements, all of which conferred Tcr and displayed greatly increased transfer efficiency following exposure to tetracycline. Many of the conjugative transposons (CTns) in Bacteroides are related to various genetic elements (such as CTnDOT, CTnERL, NBU and others). CTnDOT carries a tetracycline resistance gene, tetQ, and an erythromycin resistance gene, ermF. Resistance to drugs used to treat Bacteroides infections, such as clindamycin, has also been increasing. These conjugal elements have been found in Bacteroides clinical isolates. Thus, horizontal gene transfer could conceivably have played a role in the rising incidence of resistance in this bacterial group.

Investigation of the prevalence of tetQ, tetX and tetX1 genes in Bacteroides strains with elevated tigecycline minimum inhibitory concentrations

In this study, the antibiotic susceptibilities to tigecycline and tetracycline of 35 selected Bacteroides fragilis group strains were determined by Etest, and the presence of tetQ, tetX, tetX1 and ermF genes was investigated by polymerase chain reaction (PCR). tetQ was detected in all 12 B. fragilis group isolates (100%) exhibiting elevated tigecycline minimum inhibitory concentrations (MICs) (≥ 8 μg/mL) as well as the 8 strains (100%) with a tigecycline MIC of 4 μg/mL, whilst tetX and tetX1 were present in 15% and 75% of these strains, respectively. All of these strains were fully resistant to tetracycline (MIC ≥ 16 μg/mL). On the other hand, amongst the group of strains with tigecycline MICs< 4 μg/mL (15 isolates), tetQ, tetX and tetX1 were found less frequently (73.3%, 13.3% and 46.7%, respectively). All but two strains harbouring the tetQ gene in this group were non-susceptible to tetracycline, with a MIC> 4 μg/mL. These data suggest that in most cases tigecycline overcomes the tetracycline resistance mechanisms frequently observed in Bacteroides strains. However, the presence of tetX and tetX1 genes in some of the strains exhibiting elevated MICs for tigecycline draws attention to the possible development and spread of resistance to this antibiotic agent amongst Bacteroides strains. The common occurrence of ermF, tetX, tetX1 and tetQ genes together predicted the presence of the CTnDOT-like Bacteroides conjugative transposon in this collection of Bacteroides strains.

[Can meropenem E-test be used to estimate the presence of carbapenem resistance gene cfiA among Bacteroides fragilis strains?]

Bacteroides fragilis, which is found in normal colon flora, is the most commonly encountered pathogen in anaerobic infections and more resistant to antimicrobial agents than the other anaerobes. Limited number of antibiotics; such as carbapenems, beta-lactam/beta-lactamase inhibitors and nitroimidazoles are the most effective antibiotics against Bacteroides, however resistant isolates to these antimicrobials have been reported recently. Resistance against carbapenems occurs due to a metallo-beta-lactamase enzyme expressed by cfiA gene. While agar dilution method is used to test the antimicrobial susceptibility of anaerobic organisms, E-test is recommended for susceptibility testing of anaerobes associated with life-threatening infections with high mortality and morbidity. In this study, meropenem E-test was used to determine the carbapenem resistance of B.fragilis strains and to estimate the presence of cfiA gene. A total of 63 B.fragilis strains that were previously isolated from clinical samples (of which 16 were from stool samples) in our laboratory, were enrolled in the study. Minimum inhibitory concentration (MIC) values were determined by meropenem E test (AB Biodisk, Sweden) and presence of cfiA genes were investigated by in-house polymerase chain reaction. The MIC ranges of meropenem were < 0.002 - > 32 µg/ml and the resistance rate was 9.5% (6/63). Thirty-three percent (21/63) of strains harboured cfiA gene. A statistically significant relation (p< 0.0001) was determined between presence of cfiA gene and high MIC value (MIC 0.5 µg/ml). The proportion of cfiA-positive isolates detected in this study was substantially higher than that reported in other countries. This might be attributed to the frequent use of carbapenems in our hospital. The results of this study indicated that meropenem E-test method could be useful to estimate the presence of cfiA gene in B.fragilis strains and thus to detect the resistant strains.

Determinants of periodontopathogens in microbiological monitoring of diabetic patients with periodontitis

OBJECTIVE

To determine and analyze the frequency of periodontopathogens in microbiological monitoring of diabetic patients with periodontitis.

METHODS

This cross-sectional study included 352 diabetic patients with periodontitis who were registered at Riyadh Armed Forces Hospital, King Faisal Specialist Hospital and Research Centre, King Abdul Aziz Medical City, Naval Base Hospital, and Sultan Bin Adulaziz Humanitarian City, Riyadh, Kingdom of Saudi Arabia from July 2004 to August 2008. Microbiological analysis comprised the detection of Bacteroides forsythus (Bf), Aggregatibacter actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg), and Prevotella intermedia (Pi) by polymerase chain reaction method.

RESULTS

The mean age of patients was 54.4 +/- 0.67 (range: 21-80 years). There were 214 (61%) males and 138 (39%) females. Among the study population, 36 (10%) had type 1, and 316 (90%) patients had type 2 diabetes. The results showed that 55.6% of patients had Bf, 51.7% had Aa, 63.7% had Pg, and 6.1% had Pi. The frequencies of periodontopathogens were higher in males than females in all age groups. The risk of periodontopathogens Bf were found higher level in 41-50 age group, Aa in 51-60, Pg in 51-60, and Pi in 31-40 age groups.

CONCLUSION

This study found that the frequencies of periodontal pathogens Bf, Aa, and Pg were higher than Pi in diabetic patients with periodontitis.

Tannerella forsythia detected in infected root canals using nested PCR

PURPOSE

This study assessed the occurrence of Tannerella forsythia in patients with acute and chronic primary endodontic infections.

METHODS

Clinical samples were collected from 40 patients with acute and chronic periradicular disease. Nested polymerase chain reaction (PCR) assay technique was used to detect the presence of T. forsythia in primary endodontic infections. The first round of PCR amplification used universal primers to detect the 16S rDNA sequence. Product from the first round was then used to amplify T. forsythia specific fragment with species-specific pairs of primers.

RESULTS

T. forsythia was found in 12 of 27 chronic and 5 of 13 acute infected patients for an overall occurrence frequency of 42.5%. No significant correlation was found between patients with the T. forsythia positive genotype and the occurrence of clinical symptoms in the primary endodontic infections (P < 0.05) (P = 0.496). Also, no significant relationship was found between the occurrence of T. forsythia and the patient's age (P = 0.61) or gender (P = 0.239).

Clinical significance of and outcomes for Bacteroides fragilis bacteremia

BACKGROUND AND PURPOSE

Bacteroides fragilis is a virulent anaerobic pathogen, resulting in considerable mortality. This study was conducted to investigate the clinical characteristics, significance of polymicrobial bacteremia, and treatment outcomes of B. fragilis bacteremia.

METHODS

This retrospective analysis enrolled 199 adult patients with B. fragilis bacteremia, who were admitted to hospital between January 2004 and May 2007. Chi-squared and Fisher's exact tests were used for comparison. A p value of <0.05 was considered statistically significant.

RESULTS

142 patients with B. fragilis bacteremia (71.4%) had at least 1 underlying disease. Malignancy was the commonest comorbidity (n = 62; 31.2%). Intra-abdominal infection accounted for 49.3% of the infection sources. Seventy seven patients (38.7%) had polymicrobial bacteremia and Escherichia coli was the most common concurrent isolate (n = 24). There was no significant difference in septic shock incidence and clinical outcome between the monomicrobial and polymicrobial groups. The overall 30-day crude mortality rate was 30.7%. Inappropriate early antimicrobial therapy did not affect outcome, but a higher mortality rate was noted for patients who never received appropriate antimicrobial therapy (55.2% vs 26.5%; p = 0.002). Independent risk factors for mortality were age 65 years and older (p = 0.010), malignancy (p = 0.001), shock (p < 0.001), thrombocytopenia (p = 0.026), and lack of surgical intervention (p = 0.035).

CONCLUSIONS

B. fragilis bacteremia causes a high mortality rate, especially for elderly people and patients with cancer. Clinicians should be alert to the infectious focus, and appropriate surgical intervention may be necessary to improve outcomes.

Bacteroides fragilis: a case study of bacteremia and septic arthritis

A 67-year-old African-American male presented with nausea, vomiting, diarrhea, fever, and knee pain. Four sets of blood cultures were collected and resulted in the growth of Bacteroides fragilis in all anaerobic bottles. Later, a fluid and tissue sample from the patient's knee grew the same species of bacteria. The patient was placed on intravenous antibiotics to fight the infection.

Bacteroides fragilis bacteremia associated with vertebral osteomyelitis in a sickle cell patient

Osteomyelitis and septic arthritis are serious complications of sickle cell disease which occur at rates of 18% and 7%, respectively. In two small studies of osteomyelitis in sickle cell patients, the most common causative organisms were Salmonella spp. and Staphylococcus spp. Anaerobic infection is uncommon. Here, we report an 18-year-old girl with sickle cell disease and suspected spontaneous vertebral osteomyelitis due to Bacteroides fragilis. The diagnosis was based on multiple positive blood cultures. Despite extensive investigation, the port of entry could not be determined. The patient responded well to a four-week therapy with metronidazole, without the need for surgical debridement.

Bacteroides (Parabacteroides) distasonis splenic abscess in a sickle cell patient

Splenic abscess is not an uncommon complication of patients with sickle-cell disease. Here we describe an 18 year-old boy with sickle cell disease and left upper quadrant abdominal pain. Computerized axial tomography revealed left sided free flowing pleural effusion and splenomegaly with liquefaction and possible gas formation. The splenic fluid grew an unusual organism known as Bacteroides distasonis. The patient received antimicrobial therapy and underwent a splenectomy with full recovery. The spleen was cystically infarcted and measured 22 x 16 x 5 cm. The capsule was thickened and covered by fibrinous exudate. Histopathologic examination of the spleen showed complete necrosis with reparative fibrosis. This case presents an unusual cause of splenic abscess due to Bacteroides distasonis with a subacute to chronic course. The presence of fever and left sided pleuritic chest pain in patients with sickle cell disease should raise the suspicion of splenic abscess.

Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis

Results of this study showed that the anaerobic, opportunistic pathogen Bacteroides fragilis lacks the glutathione/glutaredoxin redox system and possesses an extensive number of putative thioredoxin (Trx) orthologs. Analysis of the genome sequence revealed six Trx orthologs and an absence of genes required for synthesis of glutathione and glutaredoxins. In addition, it was shown that the thioredoxin reductase (TrxB)/Trx system is the major or sole redox system for thiol/disulfide cellular homeostasis in this anaerobic bacterium. Expression of the B. fragilis trxB gene was induced following treatment with diamide or H(2)O(2) or exposure to oxygen. This inducible trxB expression was OxyR independent. Northern blot hybridization analysis showed that the trxB mRNA was cotranscribed with lolA as a bicistronic transcript or was present as a monocistronic transcript that was also highly induced under the same conditions. The role of LolA, a prokaryotic periplasmic lipoprotein-specific molecular chaperone in the thiol/disulfide redox system, is unknown. A trxB deletion mutant was more sensitive to the effects of diamide and oxygen than the parent strain. In addition, the trxB mutant was unable to grow in culture media without addition of a reductant. Furthermore, the trxB mutant was not able to induce intraabdominal abscess formation in a mouse model, whereas the parent strain was. Taken together, these data strongly suggest that TrxB/Trx is the major, if not the sole, thiol/disulfide redox system in this anaerobe required for survival and abscess formation in a peritoneal cavity infection model.

Bacteroides coprophilus sp. nov., isolated from human faeces

Three Gram-negative, anaerobic, rod-shaped bacteria (strains CB40, CB41 and CB42(T)) were isolated from human faeces. Based on phylogenetic analysis and specific phenotypic characteristics, these strains were included in the genus Bacteroides, and 16S rRNA gene sequence analysis indicated that these strains represented a novel species. The strains were most closely related to the type strains of Bacteroides barnesiae and Bacteroides salanitronis, with sequence similarities of 93.4 and 89.8 %, respectively. The G+C content of strain CB42(T) is 44.7 mol%. Major fatty acids were anteiso-C(15 : 0), C(16 : 0), iso-C(17 : 0) 3-OH and C(18 : 1)omega9c. On the basis of the data presented, a novel Bacteroides species, Bacteroides coprophilus sp. nov., is proposed, with CB42(T) (=JCM 13818(T)=DSM 18228(T)) as the type strain.

Impact of anatomic site on growth, efflux-pump expression, cell structure, and stress responsiveness of Bacteroides fragilis

This study investigated whether B. fragilis from various human sites acquired stable traits enabling it to express certain efflux pumps (EPs), adopt a particular cell structure, and tolerate certain stressors. Isolates from blood, abscess, and stool (n = 11 each) were investigated. Bacteria from various sites portrayed different ultrastructres and EP expression. Blood isolates were tolerant to nutrient limitation and stool isolates to NaCl and bile salt stress. Stressors significantly increased EP expression. These data demonstrate that (1) B. fragilis acquires stable traits from various in vivo microenvironments; (2) that EPs are involved in stress responsiveness; and (3) that EP expression is tightly controlled and site dependent.

Effect of dosing and dosing frequency on the efficacy of ceftizoxime and the emergence of ceftizoxime resistance during the early development of murine abscesses caused by Bacteroides fragilis and Enterobacter cloacae mixed infection

The efficacy of beta-lactams is thought to be dependent on the time that the unbound concentrations exceed the MIC (fT>MIC). However, the pharmacokinetic/pharmacodynamic index (PDI) that correlates best to the selection of resistance is not yet clear. The selection of ceftizoxime (CZX)-resistant Enterobacter cloacae mutant strains during the development of murine mixed-infection abscesses was studied to determine the PDI that is important for the emergence of resistance and the PDI value needed for the prevention of resistance. Studies were carried out 24 h after inoculation with Bacteroides fragilis ATCC 23745 and E. cloacae 22491. Six to 1,536 mg of CZX/kg of body weight/day given every 2 h (q2h), q4h, q6h, or q8h was started 30 min before inoculation and continued for 24 h. Resistant mutants were isolated to determine mutant frequencies (MF). The fT>MIC varied from 9 to 98% for E. cloacae, the peak concentration (unbound fraction) was 0.6 to 578 mg/liter, and the area under the concentration-time curve (unbound fraction) (fAUC) was 1.9 to 553 mg.h/liter. The fAUC-to-MIC ratio best explained the in vivo efficacy. CZX-resistant B. fragilis and E. cloacae mutants were isolated from untreated controls at an MF of 10(-5) to 10(-7). The MF of resistant B. fragilis did not increase during therapy. The selection of resistant E. cloacae strains at an MF of 10(-1) to 10(-2) was related to the fT>MIC and the ratio of fAUC to MIC following an inverse U shape. However, the ratio of fAUC to MIC was the stronger driver of resistance. The highest MFs were 0.7 to 0.9 at an fAUC-to-MIC ratio of approximately 250. We conclude that the ratio of fAUC to MIC is the PDI that correlated best to the in vivo efficacy of CZX and probably also to the emergence of resistant E. cloacae mutants. An fAUC-to-MIC ratio of 1,000 was needed to prevent the emergence of this resistance.