Environmental microbiology.docx

Vibrio cholerae Gram-negative Highly motile - possess a polar flagellum. Has a pili. Non-spore forming Oxidase positive= produces cytochrome c oxidase. It colonises the epithelium of the small intestine. Releases enterotoxin which disrupts ion transport= loss of water and electrolytes causing diarrh...

Vibrio cholerae Gram-negative Highly motile - possess a polar flagellum. Has a pili. Non-spore forming Oxidase positive= produces cytochrome c oxidase. It colonises the epithelium of the small intestine. Releases enterotoxin which disrupts ion transport= loss of water and electrolytes causing diarrhoea. Laboratory diagnosis Enriched dipstick test Negative sample= no colour change Positive sample=colour change to pink Thiosulphate citrate bile-salt sucrose agar (TCBS) Bromothymol blue and thymol blue in the agar is ph indicators and are used to highlight the Vibrio cholerae as bright yellow on the agar plate. Indicator organisms Easily detectable Present when pathogen present and likewise for when pathogen is absent. Its concentration must corellate with the pathogen’s concentration. Survives easier and longer than pathogen. Detection of indicator organism is easy safe and inexpensive. Should be effective for all water types. Coliforms Rod shaped. Gram-negative Non-spore forming Motile and non-motile Lactose fermenters Produces gas and acid at 37C. Most probable number (MPN) analysis. Add reagent to sample and it turns pink. Pour in Quanti-tray and seal. Incubate at 35C for 24 hours. Read under UV light- count blue, fluorescent wells. Other tests include: Membrane filtration Catalase test Oxidase test Gram staining 3 steps to treat water Coagulation Add positive salts to neutralise suspended particles. Larger particles settle. Doesn’t remove virus or bacteria. Filtration Forces water through porous material varying in the sizes of pores. Slow sand filtration= removes bacteria and viruses Rapid sand filtration= removes suspended particles. Chlorination Chemical disinfections Inactivates bacteria by damaging cell membrane and DNA. Compact dry plates are used to detect microorganism in a food production area. RIDA CHECK is also used: Independent of ATP Reacts with indictor molecule. Colour change from yellow to green.