Gram-Negative Bacilli Flashcards
What specimen is used for laboratory diagnosis of Family Enterobacteriaceae and Related Enterobacteria ?
Urine, blood, pus, spinal fluid, sputum, or other material, as indicated by the localization of the disease process.
What is of unique significance in the gram staining of Klebsiella species ?
presence of large capsules, which can be observed as colorless to light pink halo around the bacilli
What is a useful alternative gram staining for Yersinia species ?
Wayson staining
What are the significant features shown by the Yersinia species under wayson staining ?
bipolar purple staining
central vacuole giving a characteristic “safety pin” appearance
What enrichment medium is best used in isolation of Salmonella ?
Selenite broth
What conditions must be met for Salmonella subcultures to be formed in selenite broth ?
8 - 12 hours
35°C
What is the reason for the specific conditions of Salmonella and selenite broth ?
coliforms or other intestinal flora may overgrow the pathogens within a few hours
What may happen if you overheat selenite broth ?
Overheating may produce a visible precipitate, making it unsatisfactory for use
What makes selenite broth a specific enrichment medium for Salmonella ?
It inhibits the growth of many species of gram-positive and gram-negative bacteria including the coliforms and many strains of Shigella
What is used as an enrichment medium for the recovery of Salmonella and Shigella from clinical and nonclinical specimens ?
GN (Hajna) broth
What conditions must be met for GN (Hajna) broth ?
4 - 6 hours
35°C
What is the reason for the specific conditions of the GN (Hajna) broth ?
Due to the relatively low concentration of desoxycholate, it is less inhibitory to E. coli and other coliforms
In the GN (Hajna) broth higher concentration of mannitol increases the growth of which Enterobacteriaceae species ?
Salmonella and Shigella
In the GN (Hajna) broth what does the sodium citrate and sodium desoxycholate do ?
inhibit gram-positive and some gram-negative bacteria
What broth is used as a selective enrichment for salmonella species ?
Tetrathionate broth with iodine-iodide solution
What makes tetrathionate broth a selective medium ?
The tetrathione which is formed in the medium by the addition of the iodine-iodide solution inhibits the normal intestinal flora of fecal specimens
What conditions must be met for the tetrathione broth ?
18 - 24 hours
35°C
What are things to take note of in preparation of tetrathione broth ?
After heating the broth base to boiling, add the iodine solution
No heating must be done after adding the iodine solution
What hemolytic signs are observed in E. coli on BAM ?
beta-hemolytic, many are shown from isolates of infections
What hemolytic signs are observed for Klebsiella pneumoniae on BAM ?
Non-hemolytic (gamma-hemolytic)
Significant characteristics of growth of Proteus on BAM ?
Swarming growth, distinct zonation
Culture usually gives off a “burnt gun powder” odor
What makes MAC agar a slightly selective medium for Enterobacteriaceae growth ?
The crystal violet dye and bile salts in the medium inhibit G+ bacteria and allow G- bacteria to grow
What change is there on MAC agar when a lactose fermenter is present ? and why ?
Bacteria that ferment lactose, the sole carbohydrate in the medium, produce acids, which, in the presence of neutral red as the pH indicator, results in the formation of pink to red colonies.
What is observed for non-lactose fermenters on MAC agar ?
Colourless colonies