3 Importance of water examination for pathogens Water intended for human consumption should not contain any pathogenic organisms.Water is used for many applications either at home for cooking ,washing or drinking or in industries such as food and pharmaceuticals.
4 It is also important for hospitals for example haemodialysis unit Testing of water samples are done regularly to make sure of its safety
5 Supplies of drinking water contaminated with sewage may cause diseases such as: typhoid fever and cholera.All sources of water should be tested regularly.Microorganisms which indicate the fecal pollution in water are usually common intestinal commensal bacteria.
6 Most important indicators of fecal pollution of water Escherichia coli:The essential indicator of fecal pollution of human /animal origin.It is an important member of the coliform bacteria.Coliforms are members of the enterobacteriaceae family and theygrow in the presence of bile salts.produce acid and gas from fermentation of lactose at 37°C.It is the commonly-used bacterial indicator of sanitary quality of food and water.
7 Enterococcus faecalis: less numerous than E.coli in human feces, but more resistant to chlorination.Clostridium perfringens:Less numerous in human fecesIts spores can survive in the environmentResist treatment processes than most of the indicators.
8 Media used in bacteriological examination of water 1. For coliforms:MacConkey’s brothContaining bromocresol purple as the pH indicator.To confirm the presence of E.coli :EMB agar + IMVC
20 Introduction: Human infections may be caused by theingestion of animal milk whichcontains microorganisms derived from:Animal e.g. by contamination with its fecesThe environmentMilk handlers such as dairy workers
21 Importance of milk examination for pathogens It is important to examine milk for pathogens to ensure that it is safe to be consumed by man.Milk is further used for obtaining many milk products like cheese ,cream , butter and ice cream
23 Determination of viable bacterial count: Using the pour plate method after preparation of 10 fold serial dilution from the milk sample with ringer solution.Permissible number of bacterial flora in pasteurized milk is 5 x 104 cfu/mlPermissible number of bacterial flora in long life milk is 10 cfu/ml
24 Methylene Blue Reduction Test To determine quality of the milk Increasing the number of bacterial flora will reducethe color of methylene blue more rapidly due toincreasing consumption of oxygen.i.e.: The speed of reduction of methylene blue color isdirectly proportional to the number of bacteria presentin milk sample.
25 Methylene Blue Reduction Test Results:The shorter the decolorization time, the higherthe number of bacterial flora present in milk,and the poor quality of milkDecolorization timeResult30 min – 2 hrsPoor quality2 – 6 hrsfair quality6 – 8 hrsgood qualityOver 8 hrsexcellent quality
26 Test for coliformsDone by inoculation of MacConkey’s broth with 0.1 ml of milk sample.Examine for the production of acid detected by changing the color of the medium from purple to yellow.-ve result+ve result with gas production
28 Importance of keeping the micro- organisms count low in air Surgical theatersFood preparationsDrug materialsCross infection and out breaks in hospitals
29 Number on bacteria in air depends on Number of personsBody movementDisturbance of clothing
30 Methods of examination of air a. Settle plate:Petri dishes containing an agar medium are left open for a measured period of time.Large bacteria-carrying dust particles settle on the medium.The plates are incubated and a count of the colonies is formed
31 Blood agar is suitable for over all count For detection of a particular microorganism suitable media is used .Disadvantage of this method :Despite its simplicity it measures only therate of deposition of large particles fromthe air
32 b. Slit samplerIt draws in air from the environment at a fixed rate and causes the suspended particles to fall on the surface of the agar plate.
33 c. Air centrifugeCentrifuging particles from the air on to a culture medium.The sampled air passed along a tube lined with nutrient agar which was rotated on its long axis.After sampling the strip is removed from the instrument and incubated then colonies can be counted.
34 Notice:No level of contamination however low can be regarded as certainly safe.Infection can be initiated by deposition of a single infected particle at a favorable site.The probability of S. aureus initiated infection is low in comparison with Mycobacterium tuberculosis
35 Demonstration: Air examination Settle plate Water examination Determination of MPNMilk examinationMethylene blue reduction test