Applied Environmental Microbiology. Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

Transcription

1 43 Applied Environmental Microbiology Copyright McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

2 Water Purification and Sanitary Analysis Microbial containment candidates potential pathogens that can survive in water and represent severe health risks Water purification critical link in controlling waterborne disease

3 Problem Microbes Not consistently removed by coagulation, rapid sand filtration, and disinfection processes Giardia intestinalis slow sand filters effectively remove Giardia cysts Cryptosporidium small protozoan that escape usual purification schemes Cyclosporan protozoan that causes diarrhea viruses up to 99.9% removed by usual purification; may not be sufficient protection

4

5 Water Purification Water held with high levels of suspended material sedimentation basin where large particles settle out Partially clarified water mixed with chemicals such as alum and lime and settling basin more material precipitates out in coagulation or flocculation process removes microbes, organic matter, toxic contaminants and suspended fine particles Water rapid sand filters physically trap fine particles and flocs Water treated with disinfectant chlorine concern about disinfection by-products (DBPs) such as trihalomethanes (THMs) which may be carcinogens ozone

6

7 Water Purification EPA has developed regulations called the Long Term 2 Enhanced Surface Water Treatment Rule (LT2 rule) sets maximum containment level goal (MCLG) for specific pathogens health goals set at a level at which no known or anticipated adverse effects on health of persons occur and which allows an adequate margin on safety

8 Water Purification Precise treatment depends on level of contamination but generally involves filtration techniques slow sand filters water passed over bed of sand with microbial layer (biofilm) cover the surface of each sand grain waterborne microbes are removed by adhesion to biofilm aeration and disinfection also used

9 Sanitary Analysis of Waters Based on detecting indicator organisms indicate fecal contamination of water supplies indicate possible contamination by human pathogens

10 Ideal Indicator Organism Suitable for analysis of all types of water Present whenever enteric pathogens are present Survives longer than hardiest enteric pathogen Does not reproduce in contaminated water Its level in water reflects degree of fecal pollution Detected by highly specific test test easy to do and sensitive Harmless to humans

11 Two Commonly Used Indicators Coliforms Fecal streptococci (enterococci) increasingly used to test brackish and marine water Other: Fecal coliforms Coliphage

12 Coliforms Facultative anaerobic, Gram-negative, nonendospore forming, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 35 C Traditional method of detection is multipletube fermentation test (MPN) Presumptive, Confirmed and Completed tests Fecal coliforms same definition but are incubated at 44.5 C

13

14 Other Tests for Indicator Organisms Membrane filtration technique Presence-absence (P-A) test Defined substrate tests Molecular analysis

15 Membrane Filtration Technique 1. water passed through filter 2. filter placed on surface of growth medium (usually ENDO agar selective and differential for GNRs like EMB) 3. incubate 4. count colonies (green sheen or pink mucoid with dark centers) Used to detect total coliforms, fecal streptococci, and fecal coliforms (from intestines of warm-blooded animals)

16 Presence-Absence Test Modification of MPN Uses larger water sample (100 ml) Sample added to lactose containing medium contains ph indicator to detect acid production Based on assumption that no indicator organisms should be present in 100 ml of water Detects total coliforms and fecal coliforms

17 Defined Substrate Tests Tests for both total coliforms and E. coli; e.g., Colilert 100 ml sample added to medium containing ONPG and MUG Produces a fluorescent product Other indicator microorganisms are fecal enterococci used for brackish and fresh water