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Microbiology_of_water_air_food_surface.pptx
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- 2. SLO MI 8.8 Describethe methods used and significance of assessing the microbial contamination of food, water and air. 1 List foodborne, waterborne and airborne infections. 2 Enumerate bacterial organisms indicative of faecal contamination of water. 3 Describe collection & transportation of water & food for bacteriological analysis. 4 Mention various methods of bacteriological analysis of water w.r.t community and hospital settings (dialysis water, RO) and interpretation of results. 5 Discuss different microbiological parameters involved in evaluation of quality of air in OT with a brief note on surveillance methods 6 List out different methods for examination of milk and food and their clinical importance
- 3. Importance • Outbreak investigations •Evaluation of infection control practices • Research purpose
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- 5. Wholesome water • Biologicalquality • Chemical quality • Physical quality Bacterial flora in water Naturally occurring water bacteria: Micrococcus, Pseudomonas, Flavobacterium Soil bacteria: Bacillus subtilis, Enterobacter spp Sewage bacteria: E.coli, Enterococcus faecalis, Clostridium perfringens, Proteus spp
- 6. Water borne pathogens BacteriaViruses Protozoa Helminths Diarrheagenic E.coli Enterovirus Entamoeba histolytica Trichuris trichiura Salmonella spp Hepatitis A, E Giardia lamblia Strongyloides stercoralis Shigella spp Norwalk virus Cryptosporidium Ascaris lumbricoides V. cholerae Rotavirus Campylobacter jejuni Common hospital pathogens: E. coli, Klebsiella, Pseudomonas, Acinetobacter, NTM, Legionella pneumophila
- 7. Need for wateranalysis • Detecting fecal contamination of water • Investigation of outbreak • Usage of new water source • Assessing efficacy of chlorination • Checking the potability of water
- 8. Indicator organisms Commensals inintestine Indicates contamination of water with sewage, need for disinfection 2 properties: Presence in large numbers Highly resistant to environmental stress, disinfection • Faecal coliforms (Klebsiella, Citrobacter) – presumptive evidence • Faecal E.coli (thermotolerant) – most sensitive • Faecal Streptococci – remote fecal pollution • Clostridium perfringens – remote contamination • Pseudomonas aeruginosa – least reliable indicator • Bacteriophages
- 9. Collection and Transportof water sample • Screw-capped wide sterile containers • At least 150-200 ml water to be collected • Avoid contaminations • Collected from taps, lakes, well • Hospitals – endoscopy rinse water, dialysis water, etc. • Transported within 6 hours of collection
- 10. Routine tests usedin bacteriological examination of water A. Multiple tube method: Presumptive coliform test B. Eijkman test: Differential coliform test C. Membrane filtration method D. Plate count method E. Presence-Absence method
- 11. MULTIPLE TUBE METHOD– Presumptive coliform count Principle – most probable number of coliforms in 100 ml 1. Water sample added to series of tubes containing indicator broth. 2.Tubes showing color change and gas production is taken positive. 3.The most probable number (MPN) of indicator organisms/100 ml is estimated by reference statistical table.
- 12. • 50 mlwater in 1 bottle of 50 ml double strength medium • 10 ml water each in 5 tubes of 10 ml double strength medium • 1 ml water each in 5 tubes of 5 ml single strength medium • 0.1 ml water each in 5 tubes of 5 ml single strength medium • Compared with McCrady’s probability table • 0 is excellent • 1-3 is satisfactory • 4-9 is intermediate • ≥10 is unsatisfactory Negative Positive
- 13. McCrady’s probability table Doublestrength medium
- 14. EIJKMAN TEST –Differential coliform count Detection of Fecal E.coli Positive tubes of presumptive coliform test sub-cultured on lactose containing medium (brilliant green bile broth) 24 hours incubation at 44 °C Tubes exhibiting gas production are deemed to contain E.coli. Further confirmed by biochemical tests (citrate & indole).
- 15. • Testing dialysiswater • Testing clean water • Measured volume of water • Cellulose membrane pore size 0.2 or 0.45 µm Bacterial growth Result: CFU/100 mL Membrane filter
- 16. Water testing inDialysis Settings • Membrane filtration method-microbial count • Endotoxin detection • Methods: gel clot assay, turbidometric method, chromogenic method • Total microbial count <100 CFU/mL • Endotoxin unit <0.25 EU/mL
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- 18. • Airborne infection:respiratory droplets <5µm • Suspended in air • M.tuberculosis, Varicella-Zoster virus, Influenza viruses • Droplet infection: respiratory droplets >5µm • Close contact • N.meningitidis, C.diphtheriae, B.pertussis, Mumps virus Indications • Outbreak investigation • New constructions / Reconstructions • Post fumigation • Evaluation of infection control practices
- 19. Evaluating air qualityin OT Non-microbiological parameters: • Total Air changes/hr-20 • Air velocity: unidirectional downwards on the OT table (25-35 FPM) • Positive pressure: 2.5pascal • Air filtration: HEPA filters •Temperature & humidity: 210c+20c, 20-60% Microbiological parameters: 2 methods: • Passive Monitoring - settle plate method • Active monitoring - slit sampler method
- 20. Settle plate method •Open plates with culture media are exposed for specific periods • 1, 1, 1 method • Incubation • Colonies counted • Maximum acceptable levels • ≤5 CFU/9 cm diameter plate/h at rest • ≤25 CFU/9cm diameter/h when operational • Relative number and type of microorganisms • Quality of air in Operation theatres and wards
- 21. Slit sampler method •Known volume of air is directed to a plate through a slit • Vacuum pump, perforated lid • Known volume of air • Quantity measured in CFU/m3 of air
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- 23. Milk borne diseases •Classification of milk borne diseases according to Joint FAO/WHO expert committee on Milk Hygiene, 1970: A.Infections of animals that can be transmitted to man by milk. eg: Tuberculosis, Brucellosis, Salmonellosis B. Infections primary to man that can be transmitted through milk. eg: Typhoid
- 24. Methods to sterilizeMilk • Thermized milk: raw milk heated for 15 secs at 57-68°C • Pasteurization: 72°C for 15 secs • Ultra heat treated milk: 135°C for 1 sec • Sterilized milk: 100°C for long period
- 25. Bacteriological examination ofmilk • Colony count tests: 1. viable count test. 2. coliform count test. • Chemical test: 1. Methylene blue reduction test. 2. Phosphatase test. 3. Turbidity test. Detection of specific pathogens
- 26. VIABLE COUNT TEST •Plate dilution method • Serial dilution of milk in yeast extract milk agar Significance Rough and direct estimate of viable bacteria in milk
- 27. METHYLENE BLUE TEST •Reduction of methylene blue by bacteria • 37°C in complete darkness • 1 ml methylene blue in 10 ml milk • No decolourization in 30 mins Satisfactory – if milk fails to reduce dye in 30 minutes
- 28. PHOSPHATASE TEST • Evaluateseffectiveness of pasteurization • Phosphatase is inactivated on pasteurization TURBIDITYTEST • To evaluate sterilization of milk Heat coagulable proteins are precipitated
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- 30. Food-borne pathogens • Staphylococcusaureus (poultry, mayonnaise) • Bacillus cereus (fried rice) • Clostridium perfringens (beef, poultry, legumes) • Salmonella spp (Beef, poultry, eggs, dairy products) • Campylobacter jejuni (poultry, raw milk) • Vibrio parahaemolyticus (mollusks)
- 31. VIABLE PLATE COUNT Foodsampling • 10 g food homogenized in 90 mL of sterile diluent Food processing • Serial dilutions of sample • Cultured on suitable medium
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- 33. SURFACE SURVEILLANCE • Evaluateenvironmental contaminations and detect reservoirs of pathogens • High risk locations – OTs, ICUs • High-touch areas are sampled • Samples collected using moistened sterile swabs • Inoculation into culture media • Growth of pathogens with growth rate provided