Inactivation of MarR gene homologs increases susceptibility to antimicrobials in Bacteroides fragilis

ABSTRACT Bacteroides fragilis is the strict anaerobic bacteria most commonly found in human infections, and has a high mortality rate. Among other virulence factors, the remarkable ability to acquire resistance to a variety of antimicrobial agents and to tolerate nanomolar concentrations of oxygen explains in part their success in causing infection and colonizing the mucosa. Much attention has been given to genes related to multiple drug resistance derived from plasmids, integrons or transposon, but such genes are also detected in chromosomal systems, like the mar (multiple antibiotic resistance) locus, that confer resistance to a range of drugs. Regulators like MarR, that control expression of the locus mar, also regulate resistance to organic solvents, disinfectants and oxygen reactive species are important players in these events. Strains derived from the parental strain 638R, with mutations in the genes hereby known as marRI (BF638R_3159) and marRII (BF638R_3706) were constructed by gene disruption using a suicide plasmid. Phenotypic response of the mutant strains to hydrogen peroxide, cell survival assay against exposure to oxygen, biofilm formation, resistance to bile salts and resistance to antibiotics was evaluated. The results showed that the mutant strains exhibit statistically significant differences in their response to oxygen stress, but no changes were observed in survival when exposed to bile salts. Biofilm formation was not affected by either gene disruption. Both mutant strains however, became more sensitive to multiple antimicrobial drugs tested. This indicates that as observed in other bacterial species, MarR are an important resistance mechanism in B. fragilis.

Enterotoxigenic and non-enterotoxigenic Bacteroides fragilis from fecal microbiota of children

Enterotoxigenic Bacteroides fragilis (ETBF) is an important part of the human and animal intestinal microbiota and is commonly associated with diarrhea. ETBF strains produce an enterotoxin encoded by the bft gene located in the B. fragilis pathogenicity island (BfPAI). Non-enterotoxigenic B. fragilis (NTBF) strains lack the BfPAI and usually show two different genetic patterns, II and III, based on the absence or presence of a BfPAI-flanking region, respectively. The incidence of ETBF and NTBF strains in fecal samples isolated from children without acute diarrhea or any other intestinal disorders was determined. All 84 fecal samples evaluated were B. fragilis-positive by PCR, four of them harbored the bft gene, 27 contained the NTBF pattern III DNA sequence, and 52 were considered to be NTBF pattern II samples. One sample was positive for both ETBF and NTBF pattern III DNA sequences. All 19 B. fragilis strains isolated by the culture method were bft-negative, 9 belonged to pattern III and 10 to pattern II. We present an updated overview of the ETBF and NTBF incidence in the fecal microbiota of children from Sao Paulo City, Brazil.

Virulence factors and biofilm production by isolates of Bacteroides fragilis recovered from dog intestinal tracts

Bacteroides fragilis colonizes dog guts both as a commensal and as an opportunistic pathogen. This study aims to evaluate virulence factors of 13 B. fragilis strains isolated from dog intestinal tracts and their ability for biofilm formation. Capsules were detected in all the evaluated strains. A total of 61.5% of all strains were biofilm producers. These attributes most likely play an important role in B. fragilis persistent colonization in the gut.

Primary Aortoenteric Fistula to the Sigmoid Colon in Association with Intra-abdominal Abscess / 대한소화기학회지

Primary aortoenteric fistula (PAEF) is a rare but catastrophic cause of massive gastrointestinal bleeding. Diagnosis of PAEF is difficult to make and is frequently delayed without strong clinical suspicion. Timely surgical intervention is essential for patient's survival. We report on a case of an 86-year-old woman with no history of abdominal surgery, who presented with abdominal pain. Initially, computed tomography scan showed an intra-abdominal abscess, located anterior to the aortic bifurcation. However, she was discharged without treatment because of spontaneous improvement on a follow-up computed tomography scan, which showed a newly developed right common iliac artery aneurysm. One week later, she was readmitted due to recurrent abdominal pain. On the second day of admission, sudden onset of gastrointestinal bleeding occurred for the first time. After several endoscopic examinations, an aortoenteric fistula bleeding site was found in the sigmoid colon, and aortography showed progression of a right common iliac artery aneurysm. We finally concluded that intra-abdominal abscess induced an infected aortic aneurysm and enteric fistula to the sigmoid colon. This case demonstrated an extremely rare type of PAEF to the sigmoid colon caused by an infected abdominal aortic aneurysm, which has rarely been reported.

Prevalence and antibiotic susceptibility of Bacteroides fragilis group isolated from stool samples in North Lebanon

Fifty one strains of the Bacteroides fragilis group were isolated from 45 fecal samples. Classical phenotypic identification showed that 16 isolates were B. thetaiotaomicron, 12 B. uniformis, 9 B. eggerthii,7 B. vulgatus,3 B. caccae,2 Parabacteroides distasonis with 1 identified B. ovatus and 1 B. fragilis. The 51 strains were tested for susceptibility against 16 antimicrobial agents and the MICs for metronidazole were determined. The tests showed that imipenem, meropenem and chloram-phenicol were the most effective antibiotics (98%, 98% and 92.16% of susceptibility, respectively) followed by ticarcillin/clavulanic acid, piperacillin/tazobactam, rifampin (88.24% susceptibility), moxifloxacin 86.27% and tigecycline 84.31%. Ofloxacin and cefotaxime were the least effective antibiotics with 27.45% and 0% of activity respectively. Only six of the 51 isolated strains were resistant to metronidazole with MICs = 64 mg/L (1 strain) and > 256 mg/L (5 strains).

Posible papel de Bacteroides fragilis enterotoxigénico en la etiología de la vaginitis infecciosa / Possible role of enterotoxigenic Bacteroides fragilis in the etiology of infectious vaginitis

La vaginitis es un trastorno ginecológico frecuente producido por distintas causas, algunas de las cuales permanecen desconocidas. Bacteroides fragilis es el anaerobio más importante en bacteriología clínica. Algunas cepas son enterotoxigénicas y se asocian con síndromes intestinales y extraintestinales. Recientemente han sido aisladas de pacientes con vaginitis. En este trabajo se planteó investigar la posible asociación de B. fragilis enterotoxigénico con la vaginitis infecciosa. Fueron procesadas 265 muestras de exudado vaginal. 202 de mujeres sintomáticas y 63 mujeres sanas. La identificación de los microorganismos se realizó por métodos convencionales. En 31,2% de las pacientes sintomáticas se identificaron: Gardnerella vaginalis, Candida albicans, Mobiluncus, Mycoplasma hominis, Ureaplasma urealyticum y Streptococcus agalactiae. En 27 pacientes sintomáticas y en 5 mujeres sanas se identificó B. fragilis. Estas cepas fueron cultivadas en medio líquido e incubadas durante 48 h a 36° C en anaerobiosis. La toxicidad en los sobrenadantes se ensayó en células HT-29. 18 cepas de B. fragilis aisladas de pacientes sintomáticas fueron enterotoxigénicas, ya que indujeron alteraciones en la monocapa celular y en las células. No se identificó en mujeres sanas (P<0,05). 77,7% de las cepas de B. fragilis enterotoxigénicas no se encontraron asociadas con otros patógenos específicos. Este hecho sugiere que pudiera ser un agente causante de vaginitis, ya que el efecto de la enterotoxina sobre la E-cadherina del epitelio vaginal podría facilitar la invasión y su posible papel patógeno en la vagina. Esta es la primera investigación que asocia a Bacteroides fragilis enterotoxigénico como posible causa de vaginitis infecciosa.

Vaginitis is a common gynecologic disorder. It is due to several causes, some even unknown. Bacteroides fragilis is the most important anaerobe in clinical bacteriology, some strains of this group are notable for being enterotoxigenic and they have been associated with intestinal and extraintestinal syndromes. They have recently been isolated from patients with vaginitis. The purpose of this study was to investigate a possible association of enterotoxigenic B. fragilis with infectious vaginitis. 265 samples of vaginal exudate were processed, 202 from symptomatic patients and 63 healthy women. The identification of the microorganisms was carried out by conventional methods. In 31.2% of symptomatic patients were identified: Gardnerella vaginalis, Mobiluncus, Candida albicans, Mycoplasma hominis, Ureaplasma urealyticum and Streptococcus agalactiae. B. fragilis was identified in 27 symptomatic patients and 5 healthy women. These strains were cultivated in liquid medium and incubated during 48 h at 36°C in anaerobe chambers. Supernatant activity was assayed in HT-29 cells. Eighteen B. fragilis strains isolated from symptomatic patients were enterotoxigenic, because induced alterations in target cell morphology. It was not identified in healthy women (P<0.05). 77.7% of enterotoxigenic B. fragilis strains were not associated with other specific pathogens. This fact suggests that enterotoxigenic B. fragilis could be a cause for vaginitis. The effect of enterotoxin on E-cadherin of vaginal epithelium could facilitate invasion and its possible pathogenic role in the vagina. This is the first report that associates enterotoxigenic Bacteroides fragilis as a possible cause of infectious vaginitis.

Bacteroides fragilis endocarditis: a case report and review of literature

Endocarditis due to Bacteroides fragilis is a rare disorder. This article describes a case of Bacteroides fragilis endocarditis associated with portal and superior mesenteric venous thrombosis in a patient without preexisting valvular heart disease and review the cases of endocarditis due to this anaerobic bacterium in medical literature since 1980.

Distribution, detection of enterotoxigenic strains and antimicrobial drug susceptibility patterns of Bacteroides fragilis group in diarrheic and non-diarrheic feces from Brazilian infants

Despite the importance of gastrointestinal diseases and their global distribution, affecting millions of individuals around the world, the role and antimicrobial susceptibility patterns of anaerobic bacteria such as those in the Bacteroides fragilis group (BFG) are still unclear in young children. This study investigated the occurrence and distribution of species in the BFG and enterotoxigenic strains in the fecal microbiota of children and their antimicrobial susceptibility patterns. Diarrheic (n=110) and non-diarrheic (n=65) fecal samples from children aged 0-5 years old were evaluated. BFG strains were isolated and identified by conventional biochemical, physiological and molecular approaches. Alternatively, bacteria and enterotoxigenic strains were detected directly from feces by molecular biology. Antimicrobial drug susceptibility patterns were determined by the agar dilution method according to the guidelines for isolated bacteria. BFG was detected in 64.3 percent of the fecal samples (55 percent diarrheic and 80.4 percent non-diarrheic), and 4.6 percent were enterotoxigenic. Antimicrobial resistance was observed against ampicillin, ampicillin/sulbactam, piperacillin/tazobactam, meropenem, ceftriaxone, clindamycin and chloramphenicol. The data show that these bacteria are prevalent in fecal microbiota at higher levels in healthy children. The molecular methodology was more effective in identifying the B. fragilis group when compared to the biochemical and physiological techniques. The observation of high resistance levels stimulates thoughts about the indiscriminate use of antimicrobial drugs in early infancy. Further quantitative studies are needed to gain a better understanding of the role of these bacteria in acute diarrhea in children.

Complicaciones de apendicitis aguda en el área pediátrica del Hospital Dr. Patrocinio Peñuela Ruíz: período 2001-2006 / Complications of acute appendicitis in the service of pediatrics of the Hospital Dr. Patrocinio Peñuela Ruíz: period 2001-2006

En este trabajo se presenta una revisión de 5 años (2001-2006) de pacientes en área pediátrica con el diagnóstico de apendicitis aguda ingresados en el servicio de cirugía pediátrica del Hospital Dr. Patrocinio Peñuela Ruíz del Estado Táchira para determinar las complicaciones que se presentaron en los casos estudiados. Para tal fin se diseño un estudio retrospectivo el cual reporto un total de 143 pacientes que corresponde al total de pacientes ingresados de los cuales 6,2 por ciento presentaron alguna complicación y las mas frecuente fueron las de tipo infeccioso en herida operatoria.

Rapid detection of enterotoxigenic Bacteroides fragilis in diarrhoeal faecal samples.

BACKGROUND & OBJECTIVES: Enterotoxigenic Bacteroides fragilis (ETBF) is an important aetiological agent of acute diarrhoeal illness in humans. It is a fastidious anaerobe and takes 3-5 days when grown in culture, and test for enterotoxin detection requires additional time conventionally. The present study was aimed to standardize a rapid and sensitive diagnostic assay and to screen the presence of ETBF isolates directly in faecal samples using polymerase chain reaction (PCR) technique. METHODS: A total of 85 faecal samples were processed for both aerobic and anaerobic bacterial isolation by culture technique and also subjected to PCR, for amplification of neuraminidase and enterotoxin genes of B. fragilis using specific primers. RESULTS: PCR was found to be positive for neuraminidase gene in 14/65 (21.5%) and for both neuraminidase and enterotoxin genes in 4/65 (6.1%) faecal samples within 48 h in study group. B. fragilis did not grow in any of the faecal samples when cultured anaerobically. However, the delay in transport and processing of faecal samples for anaerobic culture may be responsible for culture negativity. INTERPRETATION & CONCLUSION: PCR assay can be used as a rapid and sensitive diagnostic tool for the identification of ETBF in culture as well as directly from diarrhoeal faecal samples instead of using conventional technique. The association of ETBF in diarrhoeal diseases is unclear and importance of ETBF as a causal agent will require more studies in Indian population.

Pneumocephalus associated with Bacteroides fragilis meningitis.

Gas within the intracranial cavity (pneumocephalus) commonly results from trauma or after surgery and rarely from infection by gas-forming organisms. The presence of pneumocephalus in the absence of injury or surgery should raise the suspicion of anaerobic infection of the central nervous system. I present a case of pneumocephalus associated with Bacteroides fragilis meningitis where the diagnosis was suspected after CT findings become available. Bacteroides fragilis meningitis is rare and often occurs in premature infants and neonates; only few cases are reported in adults. Pneumocephalus associated with Bacteroides fragilis meningitis is not described in the literature. This case also illustrates the absence of classic findings of meningeal irritation in the elderly. The literature is reviewed.

Microbial profile of neonatal infection in Coimbatore.

In this study, 187 consecutive neonates suspected of having septicaemia were investigated for isolation of micro organisms. Two samples of blood were collected for isolation of aerobes and anaerobes. Cultures were positive in 75 (40%) cases. Aerobic bacteria were the major etiological agent, accounting for 93% of positives including the 8% cases showing polymicrobial etiology. Anaerobic bacteria and Candida species were isolated in 6.6% and 8% of positive cases respectively. Bacteroides fragilis (amongst anaerobic) and Staphylococcus aureus (amongst aerobic) were the predominant organisms isolated. Clinical presentations were not specifically different to distinguish aerobic from anaerobic bacteria. In the present study, 6.6% of bacteremias were due to anaerobes, hence possibility of some of the bactermias being due to anaerobes should be kept in mind while treating cases of neonatal septicaemia. For a complete microbial profile both aerobic and anaerobic cultures should be done.

Association of enterotoxigenic Bacteroides fragilis with childhood diarrhoea.

This study was conducted in a hospital setting to determine whether enterotoxigenic strains of Bacteroides fragilis (ETBF) were associated with childhood diarrhoea. ETBF was isolated from 6 (2.6%) of 226 patients and 3 (1.7%) of 172 controls and was found mostly in children between 1-5 yr of age. The syndrome associated with ETBF was secretory in nature with watery diarrhoea and of mild severity. ETBF may be associated with diarrhoeal illness in children but is not a major problem in this part of the country.

Role of non spore forming anaerobes in diarrheal diseases

The study included 40 diarrheic children under 3 years of age [20 acute and 20 chronic cases] and 20 age matched controls. Fecal specimens were collected from each. Isolation and characterization of non spore forming Gram-negative anaerobic rods was carried out by using non selective media [CDC and blood agar] and selective media [KVA and PVA] media, Gram stain, relationship to oxygen, fluorescence and spot tests. Presumptive identification was done by using several biochemical identification systems [presumpto plates, rapid enzyme systems and API 20 A]. Definitive identification was carried out by using gas liquid chromatography and toxin assays on B. fragilis isolates by using tissue culture cell lines [HELF and VERO] and by inoculation [intraperitoneal and intravenous] in 3-week old mice

Epidemiology and antimicrobial resistance of B. fragilis group organisms isolated from clinical specimen and human intestinal microbiota

Alguns aspectos epidemiologicos e o perfil de sensibilidade a antimicrobianos de amostras do grupo B. fragilis isoladas de especime clinico e microbiota intestinal humana foram delineados neste estudo. As especies do grupo B. fragilis foram isoladas de 46 (37 por cento) de 124 especimes clinicos, como segue: hemocultura (3), infeccao intra-abdominal (27), abscesso cerebral (2), infeccao de tecido mole (17), seios da face (3), aspirado pleural (9), abscesso pulmonar (3), ferida cirurgica (22), doenca inflamatoria pelvica (22), otite media cronica (9) e diversos (7). Mais da metade destes microorganismos foram isolados de infeccao intra-abdominal e infeccao de tecido mole...

Changing anaerobic spectrum in suppurative lung disease: a case report.

A spectrum of three different anaerobes were isolated from a debilitated patient with suppurative lung disease, within a two-year period. Repeated isolation from three consecutive samples and symptomatic relief with metronidazole provide clinical evidence of anaerobic lung infection. This case emphasizes the importance of anaerobic culture in cases of protracted pulmonary suppurative disease.

Bacteriology of acute appendicitis with special reference to anaerobes.

Bacterial flora of 105 patients of acute appendicitis of which 101 showed acute inflammation and 4 a normal appendix, was studied. A total of 121 anaerobes and 149 aerobes were isolated with an average of 1.15 anaerobes and 1.41 aerobes per specimen. Mixed flora was found in 100 (95.2%) specimens. Bacteroides fragilis and Escherichia coli were the most predominant anaerobes and aerobes respectively and their combination was most frequently seen. There were no significant differences in the rate of isolation of B. fragilis between the perforated/non perforated and inflamed/normal appendices. Hundred percent anaerobes were sensitive to clindamycin and 93.38% to metronidazole.

Evaluation of three methods of preservation for Anaerobic bacteriaX

Três métodos de preservaçäo para bactérias foram estudados observando-se a viabilidade e a estabilidade para algumas características morfológicas e bioquímicas de cepas de Bacteroides fragilis, Clostridium perfringens, C difficile, Fusobacterium nucleatum, Peptostreptococcus sp e Prevotella melaninogenicus (B melaninogenicus). Após períodos de estocagem, B fragilis apresentou ótima viabilidade nos métodos de liofilizaçäo e congelamento, enquanto ambas as cepas de Clostridium foram as bactérias mais resistentes, sobrevivendo até um ano após terem sido liofilizadas, congeladas e sub-cultivadas. As cepas de Peptostreptococcus e P melaninogenica perderam a viabilidade já no início da estocagem em todos os métodos estudados. Todas as cepas mostraram, entretanto, estabilidade nos seus padröes coloniais, morfológicos e fisiológicos-bioquímicos durante os seus tempos de estocagem

Sensitivity to mercuric chloride of bacteroides fragilis group isolates in different growth media: medium-dependent varation

Estudou-se a atividade "in-vitro" do bicloreto de mercúrio contra 52 cepas de bactérias do grupo Bacteróides fragilis isoladas de saguis Callithrix penicillata, em diferentes meios de cultura usando-se os métodos de diluiçäo em ágar. Por outro lado, observou-se pobre atividade do bicloreto de mercúrio no meio sólido enriquecido de mercúrio no meio sólido enriquecido com sangue. A maioria das 52 cepas isoladas testadas, assim como as cepas de referência, foram resistentes ao ponto crítico (2 ug/ml) para o metal pesado nos meios sólidos, suplementados com hemina ou com sangue

Rapid identification of clinically important bacteroides by coagglutination method.

A coagglutination technique using indigenous reagents was applied for the rapid identification of Bacteroides fragilis and the black pigmented bacteroides group, using colony suspensions. All the 58 strains of B. fragilis and 42 strains of black pigmented bacteroides tested could be correctly identified by this method. The specificity of the coagglutination reagent was confirmed by the absence of cross reactivity with the related species of bacteroides, viz., B. distasonis, B. ovatus, B. vulgatus and B. thetaiotaomicron as well as other anaerobic and aerobic bacteria. A panel of four antisera against B. fragilis was required for correct identification of the strains tested, indicating the presence of multiple serotypes. On the other hand, all 42 strains of black pigmented bacteroides tested could be identified, using a single reagent as these strains appeared to have no antigenic type variants.