introduction microbiology exp 6

8/18/2019 Introduction MICROBIOLOGY exp 6

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INTRODUCTION

Fungi consist of yeasts and molds which have been classified to sub-nature based on mycelia

septation and phyla according to its ability to produce spores and types of sexual spores

produced. Both yeasts and molds spoil the food, thus it is important to control the sanitary andsafety of foods although it had been cooked. Some fungi may secrete toxin which is mycotoxin

that hardly damaged even in the extreme condition. Yeasts are unicellular fungi while molds are

larger and easily detected on the food. his is because molds grow as a filament !mycelia"

structure. Saccharomyces cerevisiae is a type of yeast that can be used in the baking process.

#lthough yeasts and molds may ha$ardous to human body, but still there are some advantages

that can be obtained from them. here are several ways to enumerate and detect the yeasts and

molds. Several media are used such as acidified %otato &extrose #gar !%", &ichloran 'ose

Bengal (hloramphenicol #gar !&'B(#" and Yeasts and )olds #gar !Y)#". *ther than

Saccharomyces cerevisiae , other molds which are Aspergillus niger and Aspergillus brasiliensis

also can be enumerate on those agar.

%otato &extrose #gar !%" is a general purpose basal medium for the identification, cultivation

and enumeration of yeast and molds in foods and dairy products. +t may also be used for the

cultivation of yeasts and molds from clinical specimens. Since it stimulates speculation and

pigmentation, it also aids for cultivating and differentiating pathogenic and non-pathogenic

fungi.


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% is also useful for maintaining stock cultures of certain dermatophytes. (ertain antibiotics or

acids like (hloramphenicol, artaric #cids and (hlortetracycline can be added as selective

agents. % with artaric #cids is recommended for the microbial examination of food and

dairy products. #ddition of (hlortetracycline is recommended for the microbial enumeration of

yeasts and mold from cosmetics. % with (hloramphenicol is recommended for the selective

cultivation of fungi from mixed samples.

%otato &extrose #gar !%" contains dextrose as a carbohydrate source which serves as a

growth stimulant and potato infusion that provides a nutrient base for luxuriant growth of most

fungi. #gar is added as the solidifying agent. # specified amount of sterile tartaric acid ! "

may be incorporated to lower the p/ of the medium to 0.1 so that bacterial growth is inhibited.

(are should be taken not to reheat the acidified medium2 heating in the acid state will hydroly$e

the agar which can render the agar unable to solidify.


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OBJECTIVES

he ob3ectives of this experiment are2

. o familiari$e with the enumeration techni4ues employed for yeasts and molds5. o familiari$e with the characteristics of yeasts and molds0. o determine yeasts and molds count on food products.


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RESULTS

)+('**'6#7+S)S8 B#( 9'+#&ilution

factor

7umber of (olonies: ;< ;= ;> 10 − 4 10 − 5 10 − 6

%late 7 ( 7 ( 7 ( 7 ( ?5 @ ?5%late 5 7 ( 7 ( 7 ( 7 ( ?@ A

#verage - - - - ?1 5#mount

of (FCs

per ml

- - - - ?.1x

107

x 107 5. x

109

?.1 x 107

The number of CFUs per ml of sample = the number of olon!es "#$%#$$ plate& ' The

(!lut!on fa tor of the plate ounte( ' )*amount of sample !n the plate

. ml D #mount of sample in the plate

?1 D 7umber of colonies

104

D &ilution factor of plate counted

?.1x 107

D 7umber of (FCs per ml


D 7umber of colonies

105


x10

7



5 D 7umber of colonies


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106


5. x 109


2.1 x 109

4.5 x 107 D ?A.A

/ighest number of cells from the countable plate is more than two times from the lowest

number of cells, take the lowest (FCs per ml as (FC.

introduction microbiology exp 6

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