A New Selective and Differentiative Medium for the Isolation of<i>Bacteroides fragilis</i>

Papastathopoulou, Eugenia Angeliki

doi:10.1080/089106098435359

Cited by 2 publications

(4 citation statements)

References 22 publications

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“…Several antibiotics (gentamicin, kanamycin, and novobiocin) were chosen based on their stability in prepared medium and antibacterial activities for common aerobes and facultative anaerobes that may hydrolyze esculin (19,24). Concentrations of the antibiotics were chosen empirically after reviewing those that were previously used in various selective media (18,19,24). The final formulation of the new medium consisted of (per liter) 15 g of bacteriological agar (Oxoid agar no.…”

Section: Methodsmentioning

confidence: 99%

“…The hemin-vitamin K mixture and the antibiotics were then added aseptically. It was assumed that the ability of B. fragilis to ferment glucose would lower the pH of the medium and change the color of the indicator to yellow, thereby producing yellow colonies, while hydrolysis of esculin and subsequent reaction with iron in the medium would produce a diffusible black complex that would cause blackening of the medium surrounding the colonies (16,18,20). Antibiotics, including gentamicin, kanamycin, and novobiocin, were added to inhibit the growth of common bacteria (Enterobacteriaceae, enterococci, and lactobacilli) that are esculin positive, thereby facilitating the recognition of B. fragilis in mixed growth.…”

Section: Methodsmentioning

confidence: 99%

“…While Bacteroides bile-esculin (BBE) agar supplemented with gentamicin has been developed for such a purpose, the selectivity of the medium is limited by increasing gentamicin resistance among enterococci and by the medium's inability to inhibit some lactobacilli (14)(15)(16)(17). Furthermore, BBE agar may not produce large colonies for some B. fragilis strains, and culture media based on brain heart infusion have been found to be superior to BBE agar for recovery of B. fragilis (18,19). Previous studies further reported that B. fragilis produced yellow colonies in the presence of glucose or glucuronic acid as a fermentable carbon source, and this may be a useful marker for enhancing recognition of the organism in mixed growth (18,20).…”

mentioning

confidence: 99%

“…Furthermore, BBE agar may not produce large colonies for some B. fragilis strains, and culture media based on brain heart infusion have been found to be superior to BBE agar for recovery of B. fragilis (18,19). Previous studies further reported that B. fragilis produced yellow colonies in the presence of glucose or glucuronic acid as a fermentable carbon source, and this may be a useful marker for enhancing recognition of the organism in mixed growth (18,20). In an attempt to improve the detection of B. fragilis, the aforementioned principles were used to design a new medium.…”

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confidence: 99%

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Novel selective medium for isolation of bacteroides fragilis from clinical specimens

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A novel Bacteroides fragilis selective (BFS) medium, consisting of a brain heart infusion agar base supplemented with yeast extract, cysteine hydrochloride, bile salts, vitamin K, hemin, glucose, esculin, ferric ammonium citrate, bromothymol blue, gentamicin, kanamycin, and novobiocin, was evaluated. When BFS agar was tested with a collection of 303 bacteria of different genera, it allowed the growth of B. fragilis as large yellow colonies, with blackening of the medium after 48 h of anaerobic incubation, while the growth of most other anaerobes, facultative anaerobes, and aerobes was inhibited. In a prospective comparison of BFS agar with a routinely used medium (neomycin blood agar) in 1,209 clinical specimens, 60 B. fragilis bacteria were detected on BFS agar while 46 were detected on the routine agar (McNemar's test, P ϭ 0.008). In conclusion, this novel medium may be added to improve the recovery of B. fragilis in clinical specimens and to facilitate surveillance of antimicrobial-resistant strains. KEYWORDS selective medium, Bacteroides, media B acteroides species colonize the human gut as commensals, but they can also cause infections if translocated into the bloodstream or other tissues following disease, an operation, or trauma (1, 2). In the genus Bacteroides, Bacteroides fragilis is regarded as the most virulent species and has been implicated in various infections such as intra-abdominal sepsis, deep-seated abscesses, and necrotizing skin and soft tissue infections (2). In B. fragilis, emerging resistance to antibiotics is a big concern (3, 4). Among isolates from large hospitals in the United States and Europe, resistance rates for clindamycin and moxifloxacin are now Ͼ20% to 30% (3, 4). Currently, carbapenem and metronidazole resistance rates among B. fragilis isolates from the United States and Europe remain low (Ͻ1% to 2%) in general (3, 4). However, higher carbapenem resistance rates have been reported by investigators from Taiwan (7% to 12%) (5), Germany (4.9% to 5.3%) (1), and Canada (2.3% to 12.7%) (6), suggesting that this resistance phenotype may be emerging in certain hotspots in those countries. Most seriously, rare strains of multidrug-resistant B. fragilis with simultaneous resistance to carbapenems and metronidazole have also been identified (7, 8). In B. fragilis, two divisions (I and II) have been identified by using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) (9). Metronidazole is administered as an inactive prodrug, and reduction of the nitro group is required for activation to the active compounds. In B. fragilis, metronidazole resistance is usually attributed to acquisition of the nitroimidazole resistance gene (nim), encoding a nitroimidazole reductase which is presumed to modify metronidazole to an inactive compound (10). The acquisition of carbapenem resistance usually correlates with the activation of the carbapenemase gene, cfiA, in division II strains by an upstream insertion sequence (11). Most of the genetically characterized ...

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