isolation and identification of pseudomonas and salmonella

Isolation and Identification of

Pseudomonas and Salmonella

Course: Medical Bacteriology

Lab. No 9

4th Grade – Fall Semester 2021-2022

Dr. Salah Tofik Balaky

Ph. D. Medical Microbiology

Salah.balaky@tiu.edu.iq

21/ 12/ 2021

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Pseudomonas (P. aeruginosa)

General characteristics

▪ G-ve rods, motile by polar flagella.

• Obligately aerobic, grow well at 42⁰C and Non-lactose

fermenting.

• Produce fruity odor (grape-like) on culture media.

• Oxidase test positive .

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Pseudomonas (P. aeruginosa)

Pigment production

They can produce pigments, such as:

• Pyocyanine (blue-green)

• Pyoverdin (fluorescent yellow- greenish pigment)

• Pyorubrin (red)

• Pyomelanin (brown)

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Laboratory diagnosis

▪ Specimen

▪ blood.

▪ Wound discharge

▪ sputum

▪ Urine

▪ CSF

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Microscopy

Gram stain

G-ve rod similar to members of enterobacteriaceae.

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On Nutrient Agar

• Colonies are smooth, large, translucent

• Greenish blue diffusible pigment

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On Blood Agar

• Grayish colonies

• Many are hemolytic

B-hemolytic colonies of P. aeruginosaColonies of Pseudomonas aeruginosa

cultivated aerobically on horse blood

agar at 37°C. colonies are gray in color.

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On MacConkey agar

Non-lactose fermenting (colourless colonies)

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On EMB

Colorless colonies due to non lactose fermenting

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Biochemical Test

• Oxidase test - positive

• Catalase test – positive

• Citrate test – positive

• Gelatin hydrolysis - positive

• Indole test – negative

• Urease test – negative

• H2S production – negative

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Salmonella

General characteristics

▪ They are rod-shaped bacteria, G-ve, motile by

peritrichous flagella.

▪ They are non-lactose fermenter, facultative anaerobes

and H2S producer

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Laboratory diagnosis

Specimen

1. For enteric fever

• Blood, Bone marrow, Stool, urine and Serum

2. For gastroenteritis

• Stool

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Gram stain

Gram-negative rod-shaped bacterium

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On MacConkey agar

The bacteria do not ferment lactose, the colonies growth

appear colorless and the agar surrounding the bacteria

remains relatively transparent.

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On EMB

Because Salmonella species do not ferment lactose or

produce acid, their colonies appear grey on EMB agar.

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On Salmonella Shigella Agar

The SS agar is used for the isolation of Salmonella spp. and

Shigella spp. The media inhibit G+ve bacteria, most coliform

bacteria, and inhibit swarming Proteus spp., while allowing

Salmonella spp. to grow.

Salmonella do not ferment lactose, but produce hydrogen sulfide

gas. The resulting bacterial colonies will appear colorless with

black centers.

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On Xylose lysine deoxycholate agar (XLD)

Salmonella metabolise thiosulfate to produce hydrogen sulfide,

which leads to the formation of colonies with black centers and

allows them to be differentiated from the similarly coloured

Shigella colonies.

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Biochemical test

Oxidase test Negative

Catalase test Positive

Indole Negative

Citrate Positive

H2S production Positive

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Next Lab

Acinetobacter and Vibrios

Any questions or comments