Food Microbiologee

Listeria sp. Identification Test

2012-08-30T04:01:00.003-07:00

Listeria sp.

Morphology: Rods

Gram: Positive

Catalase: Positive

Respiratory system: Facultative anaerobe

Motility: Peritrichous

Tests to identify the genus

Hemolysis test - Sheep blood agar
CAMP factor - Sheep blood agar
Mixed acid or butane-diol fermentation - Clark and Lubs medium
Sugar fermentation: xylose, mannitol, rhamnose
Nitrate reductase

Culture

PALCAM agar

Listeria sp. on PALCAM agar

On BD PALCAM Listeria Agar, colonies of Listeria appear gray-green with a black halo. Confirmation of the presence of Listeria is made following subculture onto appropriate media and biochemical/serological identification. Colonies of mannitol-fermenting organisms such as staphylococci, which may grow on this medium, appear yellow with a yellow halo.

Refererence: BD™ [Link]

ALOA™ agar

Listeria monocytogenes on ALOA™

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Bacillus sp. Identification Test

2012-08-30T03:41:00.000-07:00

Bacillus sp.

Morphologie: Rods

Gram: Positive

Catalase: Positive

Respiratory system: Facultative aerobe (B. subtilis: Obligate aerobe)

Motility: Peritrichous
Characteristic: Produces endospores

Tests to identify spieces

CO₂ production - Gibson Abdel Malek (GAM) medium
Acetyl-methyl-carbinol (AMC) production - AMC medium
Indole production - Peptone water indole-free
Urease test - Christensen medium
Citrate utilization - Simmons medium
Growth at 65° C
7 % NaCl resistance
Proteolysis test
Gelatinase test
Amylase test
Hemolysis - Sheep blood agar
Sugar fermentations: glucose, arabinose, mannitol and xylose

Please, feel free to comment if there is any mistake.

Clostridium sp. Identification Test

2012-08-30T02:25:00.002-07:00

Clostridium sp.

Morphology: Rods

Gram: Positive

Catalase: Negative
Oxidase: Negative

Respiratory system: Obligate anaerobe

Motility: Motile

Characteristic: Produces endospores

Tests to identify the genus

API 20A
Rosenow medium
Nitrate reductase test
Proteolysis and acidification
Sulfites reduction
Lecithinase test

Test to identify butyric Clostridium

Lactate utilization: butyric acid and CO₂ production - Bryant and Burkey medium

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Lactic Acid Bacteria (rods) Identification Test

2012-08-30T02:14:00.002-07:00

Lactic acid bacteria (rods)

Lactobacillus casei, L. plantarum, L. fermentum, L. acidophilus, L. bulgaricus and L. helveticus

Morphology: Rods

Gram: Positive

Catalase: Negative
Motility: Non-motile
Respiratory system: Facultative aerobe

Tests to identify the genus Lactobacillus

CO₂ production from glucose
Culture at 15° C and 45° C - MRS medium
Arginine dihydrolase - Moeller medium
Sugar fermentation : ribose, lacotse, maltose, sorbitol or sucrose

Test to identify the species

Esculin hydrolysis - Esculin agar
Acidification and reduction

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Lactic Acid Bacteria (cocci) Identification Test

2012-08-30T01:52:00.001-07:00

Lactic acid bacteria

Lactococcus lactis, Lactococcus lactis subsp. lactis biovar diacetylactis, Lactococcus lactis subsp. cremoris, Streptococcus thermophilus, Pedicoccus acidilactici and Leuconostoc sp.

Morphology: Cocci

Gram: Positive

Catalase: Negative
Respiratory system: Facultative anaerobe

Tests to identify the genus

Growth at 10° C and 45° C - Elliker/M17 broth
NaCl resistance: 2, 4, 6 % NaCl
CO2 production - MRS medium with bell

Tests to identify the species

Acidification and reduction test
Citratase test
Arginine dihydrolase test - Moeller medium
Sugar fermentations: glucose, sucrose, ribose, xylose, maltose, lactose

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Fecal contamination indicators

2012-08-30T01:33:00.006-07:00

Fecal contamination indicators

Enterococcus fæcalis (Streptococcus fæcalis), Enterococcus fæcium (Streptococcus fæcium), Enterococcus durans (Streptococcus durans) and Streptococcus equinus (Streptococcus bovis)

Morphology: Cocci

Gram: Positive

Catalase: Negative

Respiratory system: Facultative anaerobe
Characteristic: bile-resistant

Characteristics

Growth at 10° C and 45° C
Temperature resistance - 60° C for 30 minutes
Methylene blue reduction - Sherman's milk
NaCl-resistant: 6,5 %

Identification tests

Tellurite resistance - Potassium tellurite agar
Tetrazolium chloride (TTC) reduction - Barnes medium
Hemolysis - Sheep blood agar (5 %)
Gelatinase - gelatine broth
Sugar fermentation (lactose, sucrose, mannitol, arabinose, sorbitol)

Culture

Slanetz & Bartley medium

Selective enumeration of Enterococci in water

Sodium azide inhibits the growth of Gram-negative bacteria. TTC is an indicator of bacterial growth. It is reduced to an insoluble formazan inside the cells. This reaction is seen by the formation of red to maroon colonies.

Retain only membranes containing fewer than 100 colonies. Red, maroon or pink colonies are

considered as characteristic. Carry out confirmation of typical colonies using Bile Esculin Azide Agar.

Reference: Biokar Diagnostics [Link]

Bile Esculin Agar

Organisms positive for esculin hydrolysis hydrolyze the esculin to esculetin and dextrose. The esculetin reacts with the ferric citrate to form a dark brown or black complex. Oxbile is used to inhibit Gram-positive bacteria other than enterococci. Beef Extract and Enzymatic Digest of Gelatin are the carbon and nitrogen sources used for general growth requirements in Bile Esculin Agar. Agar is the solidifying agent.

Reference: Neogen [Link]

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Microccus & Staphylococcus Identification Test

2012-08-30T00:59:00.001-07:00

Microccus & Staphylococcus

Morphology: Cocci
Gram: Positive
Catalase: Positive

Differences between Micrococcus and Staphylococcus

Characteristics	Micrococcus spp.	Staphylococcus spp.
Respiratory system	Obligate aerobe	Facultative anaerobe
Oxidase	Positive	Negative
Resistance to vibriostatic agent O/129	S	R
Resistance to lysostaphin	R	S (±R)
Resistance to bacitracin	S	R
Growth in presence of furazolidone	+	-
% GC	66-75 %	30-39 %

Tests to identify pathogenic Staphylococci

Free coagulase test - Coagulase broth
Clumping factor - Slidex staph kit
Deoxyribonuclease (DNAse) test
Thermostable DNAse test - Lachica medium
Hemolysis test - Sheep blood agar (5 %)

Cultures

Baird-Parker Agar

Principles:

Enzymatic Digest of Casein and Beef Extract are the carbon and nitrogen sources in Baird Parker Agar. Yeast Extract supplies B-complex vitamins that stimulate bacterial growth. Glycine and Sodium Pyruvate stimulate growth of staphylococci. The selectivity of the medium is due to Lithium Chloride and a 1% Potassium Tellurite Solution, suppressing growth of organisms other than staphylococci. The differentiation of coagulase-positive staphylococci is based on Potassium Tellurite and Egg Yolk Emulsion. Staphylococci that contain lecithinase break down the Egg Yolk and cause clear zones around the colonies. An opaque zone of precipitation may form due to lipase activity. Reduction of Potassium Tellurite is a characteristic of coagulasepositive staphylococci, and causes blackening of colonies. Agar is the solidifying agent.

Results:

Staphylococcus aureus on Baird-Parker agar

Coagulase-positive staphylococci produce black, shiny, convex colonies with entire margins and clear zones. Sometimes, an opaque zone of precipitation may form due to lipase activity around that clear zone. Coagulase-negative staphylococci produce poor or no growth. If growth occurs, colonies are black; clear or opaque zones are rare. The majority of other organisms are inhibited or grow poorly. If growth appears, colonies are light to brown-black, with no clear or opaque zones.

Reference: Neogen [Link]

Baird-Parker RPF (Rabbit Plasma Fibrinogen)

Champan agar

Staphylococcus aureus on Chapman agar

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Eterobacteriaceae Identification Test

2012-08-30T00:38:00.001-07:00

Enterobacteriaceae

Morphology: Rod-shape
Gram: Negative
Oxidase: Negative
Motility: Peritrichous (except Klebsiella sp. & Shigella sp.)
Respiratory system: Facultative anaerobe

Tests to identify genus & species

Carbon metabolism

Methyl red & Voges Proskauer - Clark & Lubs medium
Glucose and lactose fermentation, gas and H₂S production - Kligler medium
β-galactosidase - ONPG
Citrate utilization - Simmons medium
Malonate utilization - Leifson medium

Nitrogen metabolism

Gelatinase test
Amino-acids deamination
Lysine decarboxylase - Taylor or Moeller media with and without Lysine
Indole production - Peptone water indole-free
Urease - Christensen medium

IMViC - Indole Methyl red Voges Proskauer Citrate

Micro-organism	Indole	MR	VP	Citrate
E. coli	+	+	-	-
Edwardsiella	+	+	-	-
Proteus sp.	+	+	-	-
Klebsiella pneumoniae	-	+	-	+
Klebsiella oxytoca	+	-	+	+
Enterobacter sp.	-	-	+	+
Serratia sp.	-	-	+	+
Citrobacter freundii	-	+	-	+
Citrobacter koseri	+	+	-	+

Please, feel free to comment if there is any mistake.