1. Indicator Organisms

CONCEPT OF INDICATOR ORGANISM

UNIT OBJECTIVES

By the end of the module the learner should be able to:

1.   Introduction to indicator organism

2.   Identification and enumeration of indicator microorganisms

3.   Discuss indicator of quality and safety

4.   Explain coli forms and fecal forms

 

11.1 Introduction to Indicator Organisms

Indicator organisms can be employed to reflect the microbiological quality of foods relative to product shelf life or their safety from foodborne pathogens.

In general, indicators are most often used to assess food sanitation.

 

11.2 Indicators of Product Quality

Organisms and/or their metabolic products used to indicate the microbiological quality relative to shelf life of food. Where product quality is significantly affected by the presence and quantity of certain metabolic products, they may be used as quality indicators. Indicator organisms should meet the following criteria:

1.   Present and detectable in all given foods to be evaluated.

2.   Their growth and numbers should have a direct negative correlation with product quality.

3.   Should be easily detected and enumerated and be clearly distinguishable from other organisms.

4.   Should be enumerable in a short period of time, ideally within a working day.

5.   Their growth should not be affected adversely by other components of the food microbiota

 

 

11.3 Indicators of Food Safety

Microbial indicators are employed more often to assess food safety and sanitation than quality. Ideally, a food safety indicator should meet certain important criteria. It should

1.   be easily and rapidly detectable

2.   be easily distinguishable from other members of the food biota

3.   Have a history of constant association with the pathogen of concern

4.   Always be present when the pathogen of concern is present.

5.   Be an organism whose numbers ideally should correlate with those of the pathogen of concern

6.   Possess growth requirements and a growth rate equaling those of the pathogen

7.   Have a die-off rate that at least parallels that of the pathogen and ideally persists slightly longer than the pathogen of concern

8.   be absent from foods that are free of the pathogen except perhaps at certain minimum numbers

In the historical use of safety indicators, the pathogens of concern were assumed to be of intestinal origin, resulting from either direct or indirect fecal contamination. Sanitary indicators were used to detect fecal contamination of waters and the possible presence of intestinal pathogens. Following the practice of employing E. coli as an indicator of fecal pollution of waters, other organisms were also suggested for food sanitary indicator

1.   Coliforms

2.   Enterococci

3.   Bifidobacterium

4.   Coliphages/Enteroviruses

 

 

11.4 Coliforms

·         They are indicators of faecal contamination of food

·         They are aerobic and facultative anaerobic gram negative non-spore forming bacilli which ferment lactose with gas formation within 48 hours at a temperature of 350c

·         The coliform group include:- ie bacteria formed

-      E. coli

-      Enterobacter aerogenes

-      Enterobacter cloacae

-      Citrobacter freundii

-      Klebsiella pneumonia

·         All of these coliforms are able to grow in food except those that have a pH of less than or equal to 4 PH ≤4, Aw ≤4, most of them are killed by pasteurization temperature.

·         They are present in faeces of human, warm blooded animals and birds.

·         Some are present in environment and contaminate food e.g. in soil where they can multiply and reach high population levels.

·         Some are found in water, plants etc.

·         They are common inhabitants of intestines in animals.

·         They are found in all of plant materials, milk from cattle with mastitis or contaminated in the milk.

·         They can also be found in eggs by penetrating the freshly laid eggs

·         Can be found in features of live poultry, hides, hooves, hair of animals or of other animals

·         Can be found in shell fish e.t.c

 

 

11.5 Methods of Detecting Coliforms

They are:

a.    Fermentation of lactose of a media

b.   Using MPN methods

c.    An enriched sulphate aniline blue medium give higher coliform and E. Coli yield

d.   The membrane filter technique is used to enumerate.

 

11.6 Faecal Coliforms

·         They are gram negative facultative rods that ferment lactose at 44.50c.

·         Consist of E. coli (but a few Enterobacter and Klebsiella strains) can produce gas in lactose broth 44.50c

·         E. coli is present in the lower intestinal tracts of birds and warm blooded animals.

·         If present in raw food, it is considered as indication of direct or indirect faecal contamination. Direct contamination occurs during processing of raw food of animal origin and because of poor personal hygiene of food handlers.

Indirect contamination occurs through sewage and polluted water.

 

Method of detection

·         Inoculate growth from positive presumptive coliform tubes into tubes of E.C medium and incubate at 44.50c for 24 hrs.

·         Then examine for gas production and number of faecal coliforms estimated with an MPN table.