Objectives To become familiar with the selective and
Objectives To become familiar with: ü the selective and differential media used to identify the GIT infections associated bacteria ü the biochemical tests used to isolate these bacteria
Types of specimen ü Stool (direct culture) ü Stool in fecal transport system (in delay longer than 1 hour) ü Rectal swab • Pass swab beyond anal sphincter, carefully rotate, and withdraw Criteria of specimen rejection ü Specimen contaminated with urine, residual soap, or disinfectants. ü Specimens received in grossly leaking transport containers ü Dry specimens ü Specimens submitted in fixative or additives
Processing of stool samples
Identification of Enterobacteriaceae 1 - Using selective and differential media Enterobacteriaceae divided into two main groups according to lactose fermentation Enterobacteriaceae Lactose fermenters (Lf) E. coli, Klebsiella, Enterobacter Non Lactose fermenters (n. Lf) Salmonella, Shigella, Proteus There are several selective and differential media used to isolate and distinguish between Lf & n. Lf including ü Mac. Conkey agar ü Salmonella Shigella agar (SS agar)
Mac. Conkey agar is a selective and differential media for Enterobacteriaceae
Mac. Conkey agar Lactose fermenter Non Lactose fermenter
Suspected EHEC (O 157: H 7)
Diagnosis of Salmonella Shigella 1 - Salmonella Shigella agar (SS agar) Results ü Lactose fermenters: pink to red colonies (few can grow) ü Non lactose fermenters: translucent, colorless colonies with or without black centers Salmonella: colorless colonies with black centers Shigella: colorless colonies without black centers Lactose fermenter flora: pink to red
Diagnosis of Salmonella Shigella 2 - Hektoen enteric agar (cat eye apperance)
Identification of Enterobacteriaceae 2 - Using special biochemical reactions The differentiation of the principle groups of Enterobacteriaceae Can be accomplished on the basis of their biochemical prosperities and enzymatic reactions in the presence of the specific substrate One important group of biochemical reactions is: Indoile, Methyle red, Vogus proskaur, Citrate utilization tests (IMVi. C)
Bacterial Barcodes E. Coli Salmonella
Cholera identification Identification ü Thiosulfate citrate bile salt sucrose agar or TCBS agar ü The medium is alkaline (p. H 8. 6) which enhances the growth of Vibrio species Important components ü Sucrose: sugar source ü Bromothymol blue: p. H indicator - p. H<6. 0 - yellow - p. H>7. 6 –blue
Cholera identification Results ü Vibrio cholera: Ferment sucrose smooth yellow colonies ü Vibrio parahemolyticus: non-sucrose fermenter, green colonies TCBS media V. cholera V. parahemolyticus
Cholera identification
S. aureus associated food poisoning Ø 25% of healthy people are carriers Ø Mainly S. aureus food poisoning is diagnosed in case of outbreaks Ø Diagnosis based on ü gram positive cocci ü catalase & coagulase positive ü oxidase positive ü ß-hemolysis on blood agar ü Grow on MSA with mannitol fermentation Blood agar MSA
Diagnosis of C. difficile infection
Diagnosis of C. difficile infection Culture • Clostridium difficile bacteria. Colonies of C. difficile bacteria after 48 hours growth on blood agar. • Results: Clostridium difficile will appear as flat to low umbonate, yellow colonies with a ground glass-like appearance and a slightly filamentous edge.
Diagnosis of C. difficile infection Culture • C. difficile Selective Agar (CDSA) is recommended as a selective and differential medium for the primary isolation of C. difficile from fecal specimens. • Results : ØAfter 48 – 72 h incubation, Clostridium difficile will appear as flat to low umbonate, yellow colonies with a ground glasslike appearance and a slightly filamentous edge. ØC. difficile colonies may be surrounded by a yellow zone of about 2 – 3 mm, depending on colony size and incubation time. Growth may be examined with a long-wave UV light for yellow fluorescence within 1 h of removal from the anaerobic atmosphere.
Clostridia Ø Rod-shaped Ø Gram positive anaerobic Ø spore-forming Ø Diagnosis - Clinical picture - Gram stain - Toxin detection by serological techniques
Adult an larve of Schistosomulum
Schistosoma egg • JK Sch. mansoni egg Sch. Haematobium egg Sch. japonicum egg
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Mansoni egg 23
Heamatobium egg 24
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