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61 Cards in this Set
- Front
- Back
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List the 4 major groups of GNRs and the percentage of each that are isolated in labs
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Enteric GNR- 70-80%
NFB- 10-15% Fastidious GNR- 10-15% Misc. and infrequently encountered GNR- 1% |
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List and explain the common characteristics of Enterobacteriaceae
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1) Facultative anaerobes- can cause infection at any site
2) Non-fastidious- will grow on SBA and CHOC 3) Most are normal fecal flora known as enterics or coliforms 4) Ubiquitous in nature- except for intestinal pathogens 5) All reduce nitrate to nitrite 6) Oxidase Neg 7) All ferment glucose 8) Stain as G neg pleiomorphic rods. Can appear as diplos due to bipolar staining 9) Choc & SBA- Large grey mucoid, hemolysis is variable 10) Divided into lac pos and lac neg |
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List the 3 broad MAC result categories
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Lac Pos, Delayed Lactose, and Lac Neg
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Manual testing for Entereobacteriaceae
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-Gram stain
-Differential media such as MAC & HEA. we know it's a GNR if it's growing on a MAC - Biochemical tests such as TSI, MIO, Citrate, or PAD tubes -Pofile of 3-4 key test to look for "BEST FIT" |
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Automated testing for Entereobacteriaceae
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Two instruments that involve 20-30 biochemical tests
- Microscan walkaway - Vitec Kits include: -Crystal ID system - API strips |
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Major antigenic properties of Entereobacteriaceae
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K= capsular antigen. e.g. K1 antigen of E. coli or Vi antigen of Salmonella
O= somatic antigen located in cell wall H= flagellar antigen |
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Overall plan for identifying GNR's
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Look at growth characteristics on plates, do spot test, biochemical tests, and find a presumptive or definitive ID
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Explain TSI
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Contains 0.1% glucose, 1.0% lactose, 1.0% sucrose, 2.0% peptones, phenol red pH indicator, and sodium thiosulfate and iron salts
Organisms that cannot ferment sugars will give K/K or no RXN Organisms break down sodium thiosulfate into H2S and the Fe salts combine to form Ferrous Sulfide a black precipitate |
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H2S producers
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Proteus
Citrobacter Freundii Salmonella Edwardsiella |
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Lac pos organisms
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Escherichia
Enterobacter Citrobacter Klebsiella Serratia |
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Lac neg organisms
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Edwardsiella
Proteus Morganella Providencia Salmonella Shigella Yersinia |
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TSI reads for organisms that can utilize glucose, and lactose or sucrose
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A/A
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TSI reads for organisms that can utilize glucose only
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K/A
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What are two alternatives to the TSI tubes
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KLA= Kliger iron agar, contains glucose and lactose
LIA= Lysine iron agar, contains lysine and glucose |
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4 groups of GNRs determined by TSI
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1) organisms that ferment glucose A/A or K/A
2) organisms that cannot ferment glucose, lactose, or sucrose K/K or N/N 3)H2S production 4) Sucrose neg, Lac Neg K/A, allows us to identify Salmonella and Shigella |
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Explain MR-VP
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Methyl Red- Voges Proskauer test
Methyl red test for mixed acid fermentation pathway of Escherichia Voges Proskauer test for butanediol pathway in Klebsiella and Enterobacter |
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Reagents and products of Methyl red test
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mixed acid fermentation reacts with methyl red and gives a red color
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Reagents and products of Voges Proskauer
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If organism uses the butanediol pathway (butylene glycol pathway) acetoin will be produced.
KOH breaks down acetoin into diacetyl Alpha natpthol catalyzes a reaction between diacetyl an dpeptones resulting in a red color |
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Tests used to identify lactose fermenting Enterics
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TSI (H2S)
Indole Citrate Ornithine Motility DNase MR-VP |
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Role of E. coli and how it is transmitted
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- Aids in digestion and competes with other bacteria by producing BACTERIOCINS which inhibits the growth of other bacteria
Modes of Transmission - Endogenous (opportunistic pathogen) - fecal oral route - Person to person |
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Five groups of E. coli that can cause gastrointestinal infections
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- Enterotoxigenic (ETEC)
- Enteroaggregative (EAEC) - Enteropathogenic (EPEC) causes infantile diarrhea - Enteroinvasive (EIEC) causes dysentery - Enterohemorrhagic (EHEC) |
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Enteroaggregative pathogenic mechanisms
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Must have fimbreae
Secrete enterotoxins which cause GI cells to undergo hypersecretion |
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Enterohemorrhagic pathogenic mechanisms
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Most sever of the 5 categories
- causes hemorrhagic colitis and HUS - Predominately caused by O157:H7 - causes watery diarrhea progressing to bloody diarrhea due to inflammation and bleeding of intestinal mucosa - only takes about 100 bacteria to cause infection - produces Shiga-like toxin |
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Shiga-like toxin
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Inhibits host cell by inhibiting protein synthesis
- Attaches to neutrophils and is spread throughout the body causing widespread death of host cells and tissues - |
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4 media and tests for O157:H7
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SMAC plate- O157:H7 is sorbitol neg, but this is not definitive
MUG assay- detects beta glucouronidase- O157:H7 is MUG neg Latex Agglutination test- O157:H7 is Pos Chromagar- for isolation and direct differentiatin of O157:H7. Definitive for O157:H7 |
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Key profile lab tests for E. coli
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Indole- pos
Citrate- Neg Motility- Pos Fruity smell |
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Key profile lab tests for Enterobacter
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MAC- moderate mucoid
Indole Neg Ornithine pos Citrate pos Motility pos |
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Key profile lab tests for Citrobacter
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MAC- 50% are delayed lactose
Citrate Pos C. freundii is indole Neg, H2S pos, Ornithine neg C. Koseri is Indole pos, H2S neg, ornithine Pos |
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Key profile lab tests for Klebsiella
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MAC- very mucoid
Indole- K. pneumonia is Neg K. oxytoca is Pos Citrate Pos Ornithine Neg Motility Neg |
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Key profile lab tests for Serratia
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MAC- delayed lac pos
DNase- Pos Citrate Pos Ornithine Pos Indole Neg 20% of S. marcescens produces a red pigment |
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Old designation of C. freundii
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C. rodentium
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Tests to differentiate C. freundii and C. koseri
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C. Freundii= indole neg, H2S pos, Ornithine Neg
C. koseri= Indole pos, H2S neg, Ornithine pos |
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Tests to differentiate K. pneumoniae and K. oxytoca
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K. pneumoniae= indole neg
K. oxytoca= indole pos |
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List primary plates used for stool and GI sources and why they are used
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MAC and HEA
MAC specific for GNR HEA gives special RXN for salmonella and shigella |
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Key tests used to identify Proteus
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H2S pos
PAD pos Urease pos |
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Key tests used to identify Morganella
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H2S neg
PAD pos Urease pos Ornithine pos Citrate neg |
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Key tests used to identify Providencia
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H2S neg
PAD pos Ornithine neg Citrate Pos |
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Which genera are in the tribe proteeae
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Proteus
Providencia Morganella |
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Two test to differentiate between P. Vulgaris and P. Mirabilis
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Vulgaris is indole pos ornithine neg
Mirabilis is indole neg and ornithine pos |
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Confluent growth
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Entire plate is covered
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Swarming growth
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Proteus hasn't covered the entire plate yet just a shload of it
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Define peritrichous flagella
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Multiple flagella surrounding entire rod
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Which genera are in the tribe proteeae
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Proteus
Providencia Morganella |
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Two test to differentiate between P. Vulgaris and P. Mirabilis
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Vulgaris is indole pos ornithine neg
Mirabilis is indole neg and ornithine pos |
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Confluent growth
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Entire plate is covered
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Swarming growth
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Proteus hasn't covered the entire plate yet just a shload of it
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Define peritrichous flagella
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Multiple flagella surrounding entire rod
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Intestinal pathogens
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Salmonella, shigella, and yersinia enterocolitica
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Coliforms
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Bacteria that are lactose fermenters such as serratia, escherichia, enterobacter, klebsiella, and citrobacter
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Define bacillary dysentery and the organism that causes it
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Mild to moderate diarrhea and fever
- blood, mucus, and pus in stool - pus is result of many leukocytes due to invasion of tissues of colon, causing inflammatory response - caused by Shigella - AKA shigellosis |
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Two types of infection caused by slalmonella and species involved
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S. Enterica- causes gastroenteritis
Salmonella serotype Typhi causes typhoid fever |
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Why is S. enterica the one clinically significant species
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All of the old species were found to be serotypes of this species. 2,400 in all
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Salmonella on HEA and SS
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HEA-
salmonella is lac neg and sucrose neg, and H2S pos giving it a black dark green colony SS- lac neg and H2S pos |
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Shigella on HEA and SS
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Shigella is lac beg, suc neg, and no H2S
Appears as a green colony SS- lac. Neg, no H2S |
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Ingredients os HEA
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Bile salts- inhibit G pos and many intestinal GNRs
Ferric ammonium citrate and sodium thiosulfate- detects prescence of H2S Acid fuchsin and bromthymol blue- pH indicators Lactose, sucrose, salicin- CHO source |
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Nonpathogens on HEA that may. Be interpreted as salmonella
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Certain strains of Citrobacter and Proteus produce H2S and may have black colonies
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Explain SS
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Sodium selentine- Used for the recovery of low numbers of sallmonella and shigella
- most effective at neutral pH - medium contains lactose and phosphate buffers - may include cystine - broth should be subcultured at 12-18 hrs |
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Yersinia enterolictica
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Causes acute gastroenteritis, and mesenteric lymphadenitis which mimics appendicitis
-selective media is CIN (cefsulodin-Irgason-novobiocin) these are 3 antimicrobials |
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Yersinia pestis
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Causes bubonic plague and pneumonic plague
- has a "safety pin" appearance in gram stain due to bipolar staining with methylene blue - organism can be isolated on routine culture media - prefers temps of 25-30 C |
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Role of type 3 secretion system in E. coli O157:H7
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Allows bacteria to inject 2 types of proteins into intestinal cells
1- One type interferes with the cells metabolism 2- The second type gets lodged in the cells cytoplasmic membrane and acts as a receptor for other O157:H7 to attach enabling this strain to displace other harmless E. Coli strains |
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Explain shiga-like toxin
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Produced by E. coli O157:H7
- inhibits Protein synthesis in host cells - attaches to surface of neutrophils and is Spread by them throughout the body causing widespread cell and tissue death - antimicrobials increase the production of shiga-like toxin exacerbating the disease |
