- E. coli
- Salmonella
- Pseudomonas
- Staphylococcus
- Escherichia coli (E. coli) Confirmation
Sample Preparation: Inoculate the sample on MacConkey agar or EMB agar. Colony
Characteristics: E. coli appears as pink colonies on MacConkey agar (lactose fermentation)
and metallic green sheen on EMB agar.
Biochemical Tests
Indole Test: Positive (Inoculate a tryptone broth and add Kovac’s reagent a red ring indicates
indole production)
Methyl Red (MR) Test: Positive
Voges-Proskauer (VP) Test: Negative
Citrate Utilization Test: Negative - Salmonella
Sample Preparation: Inoculate on Xylose Lysine Deoxycholate (XLD) agar or Hektoen Enteric agar.
Colony Characteristics:On XLD agar, Salmonella produces red colonies with black centers (due to hydrogen sulfide production).
Biochemical Tests
TSI (Triple Sugar Iron):Alkaline slant/acid butt with HβS production (blackening).
Urease Test: Negative
Lysine Decarboxylase Test: Positive
Citrate Utilization Test: Positive
Serological Testing: Agglutination with specific Salmonella O and H antisera
Molecular Methods: PCR targeting genes like invA confirms Salmonella. - Pseudomonas aeruginosa
Isolation: Use Cetrimide agar or Pseudomonas isolation agar
Biochemical Tests
Oxidase Test: Positive (distinguishes it from Enterobacteriaceae).
Growth at ππΒ°C: P. aeruginosa can grow at 42Β°C.TSI: K/K (alkaline slant and butt, no sugar fermentation).
Gelatin Liquefaction: Positive
Fluorescence: P. aeruginosa shows fluorescence under UV light (due to pyoverdine production).
Molecular Methods: PCR detecting genes like oprL or toxA confirms Pseudomonas aeruginosa. - Staphylococcus aureus
Sample Preparation: Inoculate on Mannitol Salt Agar (MSA) or Blood Agar.
Colony Characteristics: S. aureus ferments mannitol on MSA, producing yellow colonies. On blood agar, it forms golden-yellow colonies with Ξ²-hemolysis.
Biochemical Tests
Coagulase Test: Positive (S. aureus is coagulase-positive).
Catalase Test: Positive (all Staphylococci are catalase-positive).DNase Test: Positive.
Serological Methods: Latex agglutination tests for protein A and clumping factor.
Molecular Methods: PCR for the mecA gene (for methicillin-resistant Staphylococcus aureus,MRSA) or nuc gene (thermonuclease) confirms S. aureus.
These tests form the basis for confirming these specific pathogens in microbiological samples.
