E.Coli, Enterobacteriacae, Shigella and Salmonella – Flashcards
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| What are the characteristics of Enterobacteriaceae? |
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| Gram (-), facultative anaerobic rod Ferments glucose Oxidase negative Reduce nitrates to nitrites Motile by pertrichous flagella |
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| What characteristics of enterobacteriaceae are used to distinguish from Pseudomonas? |
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| Ferments glucose Oxidase negative |
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| What characteristic of Enterobacteriaceae can be used as a diagnostic in a urine dip stick test? |
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| Reduce Nitrates to Nitrites |
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| What Enterobacteriaceae are non-motile? |
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| Klebsiella and Shigella |
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| What type of media is used to isolate Enterobacteriaceae? Why? |
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| MacConkey agar contains: bile salts and crystal violet that inhibit gram + pH indicator and lactose - E. coli ferment lactose, Shigella and Salmonella do not |
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| What color does E.Coli change the MacConkey agar? |
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yellow -> Red Because E.Coli ferments lactose to acid decreasing pH (lactose negative bacteria like Shigella and Salmonella grow white colonies) |
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| What antigens are used in classification/typing of Enterobacteriaceae? |
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| K antigens (capsular polysaccharide) H antigens (flagellar proteins) O antigens (somatic - on LPS) |
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| What color do Lac- organisms appear on MacConkey agar? |
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| White |
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| What are the characteristics of Non-inflammatory diarrhea? |
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(ETEC, Vibrio cholera) Watery, high volume usually due to enterotoxin Low Grade Fever or No Fever Non-invasive No Fecal Leukocytes |
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| What are the Characteristics of Inflammatory Diarrhea? |
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( Less Volume Invasion of epithelium, Cytotoxins Fecal Leukocytes - methylene blue positive Fever Dysentery Blood and mucus in feces Tenesmus Lower quadrant cramping |
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| If diarrhea persist for >2 wks what should be considered? |
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| Parasites Cryptosporidium and Giardia |
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| What should be considered in a patient with Chronic Diarrhea? |
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| HIV-AIDS |
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| What should be done for patients with non-inflammatory diarreah suffering from dehydration? |
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| Oral Replacement Therapy of water/glucose/salts Anti-motility drugs Antibiotics in some cases |
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| What should be done for patients suffering from inflammatory diarrhea? |
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| Rehydration Antibiotics Anti-motility drugs CONTRAINDICATED |
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| What organism are antibiotics contraindicated for? |
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| EHEC enterohemorrhagic E. coli |
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| What is Clostridium difficile enterocolitis treated with? |
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| Metronidazole |
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| What are 4 complications seen in inflammatory bacterial diarrheas? |
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| Hemolytic Uremic Syndrome - EHEC Disseminated infection - Susceptible populations Guillain-Barre syndrome - campylobacter Postinfectious arthritis - Shigella, Camphlobacter, Yersinia, Salmonella |
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| E. Coli Culture characteristics |
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| Lac + Ferments glucose with gas (H2) Does not produce H2S Motile KIA Slant - All Yellow, raised in tube |
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| Salmonella cultural characteristics |
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| H2S+ Gas + (except S. typhi) KIA Slant - Yellow Butt, Raised in tube |
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| Shigella cultrue characteristics |
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| H2S (-) No Gas KIA Slant - Yellow Butt, not raised(no gas) |
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| What is EHEC caused by? |
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| O157:H7 |
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| What are the symptoms of EHEC? |
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| Mild watery diarrhea -> hemorrhagic colitis Severe cramping Bloody diarrhea Low or No Fever No fecal Leukocytes |
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| What complications can occur in children <5 or elderly with EHEC? |
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| Hemolytic uremic Syndrome |
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| Symptoms of Hemolytic uremic syndrome? |
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| Anemia Low Platelet count acute kidney failure Can develop seizures or strokes |
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| What is the major reservoir of EHEC? |
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| Cattle |
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| What is the infectious dose of EHEC for humans? |
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| ~100 organisms |
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| What type of cytotoxins does EHEC produce? |
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| Shiga-like toxins, inhibits protein synthesis dissemination to kidney causes HUS |
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| What is responsible for the diarrhea caused by EHEC? |
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| LEE - Locus of enterocyte effacement |
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| How does LEE allow adhesion of the bacterium to the host cell? |
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| secreted protein that incorpartes into enterocyte membrane to for a pedestal where bacterium can bind |
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| Why is EHEC not treated with antibiotics? |
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| Does not alter the severity of colitis and encourages development or HUS |
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| How is EHEC cultured? |
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| Sorbitol MacConkey agar O157:H7 is sorbitol negative so will show up white on agar |
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| WHat is the most common cause of Traveler's Diarrhea? |
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| ETEC - Enterotoxigenic E. Coli |
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| What kind of virulence factors does ETEC produce? |
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| Heat-labile toxin Heat-Stable toxin Fimbriae adhesion species specific |
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| What E. coli has a toxin that's mechanism of action is identical to cholera toxin? |
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| ETEC Heat Labile toxin |
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| What is the mechanism of action of ETECs heat labile toxin? |
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| Activates adenylate cyclase-> increase cAMP-> activates Protein Kinase A-> Phosphorylates CFTR-> Cl flows out, NA and water follow |
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| What is the mechanism of the Heat Stable toxin of ETEC? |
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| Activates guanylyl cyclase-> increases cGMP-> activates protein kinase A-> phosphorylates CFTR |
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| What E. coli closely resembles Shigella? |
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| EIEC - Enteroinvasive E. Coli |
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| How is EIEC unlike other E. coli? |
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| non-motile Do not decarboxylate lysine Do not fement lactose |
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| What E. coli is responsible for 90% of UTIs? |
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| Uropathogenic E. Coli (UPEC) |
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| What are the symptoms of a UTI? |
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| frequency dysuria pyuria suprapubic pain cloudy urine Cramping Low Grade Fever or Afebrile |
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| What are the virulence factors of UPEC? |
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| P fimbriae (PAP pili) hemolysin sideropore capsule (K-antigen) |
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| What is the major determinant of virulence amoung strains of E. coli that cuase neonatal meningitis? |
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| K-1 antigen |
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| What is the agent of typhoid fever? |
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| Salmonella Typhi |
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| What are the characteristics of Salmonella? |
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| Lac- ferment glucose with gas (except typhi) Produce H2S |
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| What is of major importance in identificaiton of Salmonella? |
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| H serotyping |
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| What salmonellae is incapsulated? |
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| S. Typhi |
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| What species of Salmonella is medically important? |
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| S. enterica |
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| What are the 2 most frequent serotypes of Salmonella that cause disease in the US? |
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| S. enteritidis S. Typhimurium |
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| What are the sources of Salmonella? |
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| contaminated meat, dairy products, poultry, eggs, pet reptiles, turtles |
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| What are the symptoms of Salmonella gastroenteritis? |
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| Appears 20-72 hrs after infection Inflammatory Diarrhea Nausea, vomiting, followed by or concomitant with abdominal cramps and diarrhea. Fever in 1/2 May be blood in stools |
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| How does salmonella infect the gut? |
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| enters through M cells in distal small intestine, proximal large bowel. establishment a localized infection within the lamina propria |
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| Who is bacteremia and disseminated infection of Salmonella a problem for? |
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| Anyone with T cell deficiencies: AIDS, Hodgkins, skeletal prosthesis, atherosclerotic plaque, elderly and the very young, sickle cell children |
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| What does S. Typhi infect? |
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| exclusively a parasite of humans |
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| What are the symptoms of Typhoid Fever? |
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| High Fever, Slow Pulse, headache, mental confusion Maybe a skin rash May be constipated Disseminated to RES organs |
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| what are the virulence mechanisms of S. Typhi? |
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| Type III secretion systmes: -injects proteins into M cells to induce entry -injects proteins in macrophages, allowing survival and disseminated disease. |
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| How is Typohid fever diagnosed? |
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| Culture of blood and feces Serotyping for Vi capsule antigen (feces may not be positive until late in infection) |
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| What species of Shigella produces ~1000x more shiga toxin than other shigellae? |
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| S. dysenteriae |
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| Where are S. dysenteriae epidemics found? |
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| South and Central America |
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| What species of Shigella is associated with disease in the Indian Subcontinient? |
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| S. boydii |
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| What is the cause of 70% of all shigellosis in the US? |
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| S. sonnei |
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| What is the Second most common Shigella found in the US, most common in gay men? |
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| S. flexneri |
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| What is the sole source of Shigella infection and what is the route of infection? |
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| Humans are sole source fecal-oral route |
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| Who and where is Shigella most common? |
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| Children Day care centers mental instiutions and jails |
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| What is the pathogenesis of Shigella? |
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| 1. Entry into microfold cells in gut 2. Escape from phagocytic vesicle 3. Extension to neighboring enterocytes |
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| What are the symptoms of Shigellosis? |
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| Watery diarrhea with abdominal pain-> 1-2 days colon is involved-> Scant, bloody diarrhea with pus/mucus-> severe cramps, tenesmus, high fever (Like EIEC) |
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| What is prominent in the feces from Shigellosis? |
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| Fecal leukocytes, often in sheets |
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| What can Shigella dysenteriae cause? |
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| HUS (like EHEC) |
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| What are the characteristics of Shigellae? |
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| Lac(-) No gas from glucose Nonmotile H2S(-) |
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| What Shigellae produces high amounts of cytotoxins? |
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| S. dysenteriae (and EHEC) |
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| What is the reservoir of Yersinia enterocolitica? |
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| Animals Pigs, Pets |
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| What are large outbreaks of Yersinia enterocolitica associated with? |
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| contaminated milk |
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| What is the main source of Yersinia enterocolitica in the US? |
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| Pigs |
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| What are the symptoms of Yersinia enterocolitica, what can it mimic? |
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| fever, diarrhea, abdominal pain Mimic appendicitis |
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| What is a complication of Yersinia enterocolitica? |
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| Reiter's Syndrome |
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| What Enterobacteriaceae is associated with "Current jelly" pneumonia, Alcoholics, and Nosocomial infections? |
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| Klebsiella pneumoniae |
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| What oppertunistic organism contaminates wounds and cause bacteremia and UTI in hospital patients? |
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| Enterobacter |
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| What Enterobacteriaceae have Brick-rd colonies? |
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| Serratia marcescens |
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| How does Urease produced by Proteus and Morganella promote UTIs? |
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| raising pH of urine and potentiating formation of stones within which the organism may remain viable after apparently effective antibiotic therapy |
