Water and Milk Bacteriology

Question 1

Index of fecal contamination in drinking water

Answer 1

E. coli

Question 2

Indicator organisms of contamination in water

Answer 2

Coliforms

Question 3

10 Mandatory water parameters to be tested (DOH)

Answer 3

E. coli/coliform, Arsenic, Cadmium, Lead, Nitrate, Color, Turbidity, pH, total dissolved solids, disinfectant residue

Question 4

Bacteriologic analysis of water

Answer 4

Total plate count; Presence/absence of coliform; MPN count

Question 5

Methods of Microbiologic Water analysis

Answer 5

Multiple tube fermentation (MPN count), Membrane filtration, Defined substrate, Presence/absence of coliform, Pour plate method, Chromogenic substance

Question 6

Chlorine residual presence in water

Answer 6

Indicates sufficient chlorine to inactivate bacteria/viruses and protect from recontamination during storage

Question 7

Residual chlorine should be

Answer 7

2 mg/L 30 mins after addition of NaOCl; 0.2 mg/L 24 hours after addition of NaOCl in water

Question 8

Neutralizes free chlorine in swimming pool water

Answer 8

Sodium thiosulfate

Question 9

Incubation of broth/cultures

Answer 9

24-48 hours at 35°C (up to 44.5°C for thermotolerant E. coli)

Question 10

Positive results in broths/cultures

Answer 10

ACID and Gas production in broths; characteristic coliform colonies in plated media

Question 11

Indicators commonly used for acid production

Answer 11

Phenol red (yellow for acid production)

Question 12

Indicators commonly used for gas detection

Answer 12

Durham tube (bubble for gas detection)

Question 13

Multiple Tube Fermentation test (MTFT) Quantitative test reported in

Answer 13

Most Probable Number (MPN); determines coliform count and potability of water

Question 14

Gold standard for MTFT

Answer 14

5 sets of test tubes; MPN calculated from a standard chart based on number of tubes with positive results

Question 15

Positive result in MTFT

Answer 15

> 1.1 MPN/100 mL

Question 16

Negative result in MTFT

Answer 16

<1.1 MPN/100 mL (indicates potable water)

Question 17

Stage 1: Presumptive test for water bacteriology

Answer 17

Lauryl Tryptose broth / Lactose broth + water sample (Incubate at 35°C for 24-48hrs); Acid and Gas production (+)

Question 18

Stage 2: Confirmatory test for Total Coliform

Answer 18

BGLBB medium or EC broth + inoculum from stage 1; gas production (+)

Question 19

Stage 2: Confirmatory test for Fecal Coliform

Answer 19

BGLBB medium or EC broth + inoculum from stage 1; gas production (+)

Question 20

Stage 2: Confirmatory test using EMB/Endo agar

Answer 20

EMB / Endo agar + inoculum from stage 1 (Incubate at 35°C for 24-48hrs); look for green metallic sheen

Question 21

Stage 3: Completed test

Answer 21

Lauryl Tryptose broth + inoculum → Gas production (+); LES Endo agar or MacConkey agar → Gram negative bacilli; IMViC for differentiation of coliforms

Question 22

Stage 3: Completed test using Lactose broth

Answer 22

Lactose broth + inoculum (from stage 2) Incubate at 35°C for 24-48hrs → look for acid and gas production

Question 23

Heterotrophic Plate Count

Answer 23

Negative: <500 CFU/mL; Dialysis water <200 CFU/mL; Estimates live heterotrophic bacteria in water

Question 24

Methods for Heterotrophic Plate Count

Answer 24

Pour plate method, Spread plate method, Membrane filter method

Question 25

Culture media for Heterotrophic Plate Count

Answer 25

R2A, NWRI agar, PCA

Question 26

Millipore water sampler

Answer 26

Detects coliforms in environment, food, and beverage (Incubate at 35°C for 24 hours); characteristic color forms in presence of coliforms

Question 27

Pathogenic bacteria in milk

Answer 27

Coxiella burnetti, Campylobacter, Brucella, Bacillus anthracis, Streptobacillus, Salmonella, Y. enterocolitica, Listeria, Vibrio, Mycobacterium bovis, E. coli (EHEC)

Question 28

Test that should be NEGATIVE; positive result indicates improper pasteurization

Answer 28

Phosphatase (ALP) test

Question 29

Analysis of Milk quality

Answer 29

Milk is serially diluted and plated in culture media for colony counting

Question 30

Milk quality Satisfactory result should be

Answer 30

comparable to Grade A milk

Question 31

Methods for Milk Quality Analysis

Answer 31

Somatic cell count (WBC count for infection), Agar plate count, Lab pasteurized count, Coliform count (fecal coliform)

Question 32

Dark background, Manual (Wolffheugel grids) or Automatic counter

Answer 32

Quebec Darkfield colony counter

Question 33

Light or Dark background, Pressure-sensitive counting, connected to computer/printer

Answer 33

SC6 Colony counter

Question 34

Manual counting of colonies in a plate, Traditional method like in Hemocytometer in Hematology

Answer 34

Tally counter

Question 35

Dye is reduced (decolorized) by oxygen-consuming bacteria; speed of reduction is directly proportional to the number of bacteria present

Answer 35

Methylene blue reduction test