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 H₂S 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 𝟒𝟐°𝐂: P. aeruginosa can grow at 42°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 β-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.
