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Alternative indicator systems for water quality analysis
Published in Cara Gleeson, Nick Gray, The Coliform Index and Waterborne Disease, 1996
Both the membrane filtration and most probable number techniques may be used for the isolation of faecal streptococci. As Ent. faecalis and closely related species are able to reduce 2,4,5-triphenyltetrazolium chloride (TTC) to formazan, a red dye, isolation methods use agar containing TTC with faecal streptococci colonies appearing red, maroon or pink due to formazan formation. Membrane filtration: the method used is similar to that used for coliforms except that the medium used is Membrane-Enterococcus Agar (MEA) with incubation at 37°C for 48 hours for treated potable waters and for untreated water 37°C for 4 hours followed by 44°C for 44 hours. The more temperature-sensitive faecal streptococci can be inhibited if incubated at 45°C even though this is more selective. In fact inhibition of temperature sensitive species may occur with a temperature rise of less than 0.5°C. All red, maroon and pink colonies which are smooth and convex in shape are counted as presumptive faecal streptococci. Colourless colonies may be produced by some faecal streptococci. Confirmation of faecal streptococci is by subculture onto Bile Aesulin Agar and incubation for 18 hours at 44°C. Faecal streptococci form discrete colonies surrounded by a brown or black halo due to aesculin hydrolysis (APHA, 1992; Department of the Environment, 1994a). This method is specified for use in the EU Drinking Water Directive (EU, 1995).The most probable number technique: the technique employed is similar to that previously described for coliforms (MPN) except that Azide Dextrose Broth (APHA, 1992) or Glucose Azide Broth (GAB) is used (Mara, 1974; Department of the Environment, 1994a). Tubes containing Azide Dextrose Broth are incubated at 35°C and examined for turbidity after 24 and 48 hours. All turbid tubes are then subjected to the confirmation test, while tubes containing GAB are incubated at 37°C and examined after 24 and 48 hours. Growth and acid production is a positive result indicating the presence of presumptive faecal streptococci, although subculture into Bile Aesculin Agar is required for confirmation.Other techniques: Clark’s PA technique may also be used for detection of faecal streptococci. This technique is, however, very time con-suming and awkward for faecal streptococci enumeration (Clark, 1968). Enumeration techniques for faecal streptococci have been revised by a number of workers (Audicana, Perales and Borrego, 1995; Dionisio and Borrego, 1995). Dionisio and Borrego (1995) found membrane filtration using MEA to give the best performance characteristics of the enumeration media they evaluated in terms of recovery efficiency, precision, accuracy and specificity.
Association between Streptococcus gallolyticus and colorectal cancer in Mansoura University hospitals
Published in Egyptian Journal of Basic and Applied Sciences, 2021
Heba E. Eldegla, Mohamed Abdel-Wahhab, Dalia Moemen
The isolation of S. gallolyticus was done according to the following protocol for preparation of colorectal tissue sample [18]. For detection of surface bacteria, colorectal samples were rinsed thoroughly by shaking for 3 minutes in 1 ml of PBS for the recovery of mucosal attached bacteria then PBS was centrifuged at 3000 x g for 5 minutes at 15°C [19]. The pellet was suspended in 0.5 ml of brain heart infusion broth and an antibiotic disc impregnated with ertapenem was added in order to delay growth of Gram-negative rods. Samples were incubated aerobically for 18 h at 37°C, then 5 µl of the samples were seeded on bile esculin agar which was incubated for 18 h at 37°C in 5% CO2 atmosphere [20]. For detection of bacteria infiltrating colorectal tissues, the rinsed colorectal samples were washed three times with PBS to get rid of any remaining surface bacteria and was then homogenized manually by glass rod in 0.5 ml of brain heart infusion broth and antibiotic disk impregnated with ertapenem was added in order to delay growth of Gram negative rods [19]. Samples were incubated for 18 h at 37°C, then 5 µl of the samples were seeded on bile esculin agar and were incubated for a period of 18 h at 37°C in 5% CO2 atmosphere [20].