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109 Cards in this Set
- Front
- Back
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T/F members of the enterobacteriaceae are normally pathogenic
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False. They do not usual cause disease in the intestinal tract. They can cause disease when they are displaced from their natural habitat.
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List some extraintestinal (opportunistic) infections that can be produced by enteric bacteria
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-nosocomial UTI and URT
-bacterima and surgical wounds infections |
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Why is the prescence of E. coli in environmental contaminatino proof of fecal contaminatino
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its only natural habitat is the intestinal tract
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The genera Klebsiella and Enterobacter share biochemical propertiels with E. coli and are collectivley refred to as lactose fermenting organisms. What is the major difference between these two genera and E. coli
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While E. coli is only found naturally in the intestinal tract, Klebsiella and Enterobacter are widely distributed in nature and are isolated from soil, water, and food, in addition to the intestinal tract
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What disease can the heavily encapsulated bacteria Klebsiella pneumoniae cause in debilitated induviduals
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severe respiratory tract infections
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T/F Proteus species ferement lactose
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False. Proteus species do not ferement lactose
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What enzyme do Proteus species produce that is useful in their identification? What does it do?
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Urease
Urease hydrolyzes urea to produce carbon dioxide and ammonia. |
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What leads to the formation of stones in UTI's caused by urease producing bacteria such as Proteus species? Why is this a problem?
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Urease hydrolyzes urea to carbon dioxide and ammonia. Ammonia production causes an increase in pH which leads to alkanization of the urine. Salts such as calcium and magnesium phosphate are less soluble in alkaline solution and therefore precipitate out and form stones. The sontes can trap bacteria and protect them from anitmicrobials.
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What the results of the following tests for Salmonella
gram stain motility lactose fermentation glucose fermentation H2S |
gram negative short rods
motile non lactose fermenting glucose fermentation with gas H2S positive |
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Most Salmonella species ferment glucose with gas production and are H2S positive.What is an important exception
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Salmonella typhi
glucose fermentation acid but NO gas LITTLE H2S |
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What are the two types of salmonella infection? What organisms cause them?
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gastroenteritis-S. enteritidis, S. typhimurium
enteric fever- S. typhi |
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How would one obtain gastroenteritis or enteric fever cause by Salmonella species
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Eating foor or drinking water that is contaminated with a LARGE number of organisms
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T/F Citrobacter freundii causes intestinal disease
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False. Athough its biochemical properties are similar to Salmonella, Citrobacter spp. are rarely associated with intestinal disease. They can cause extraintestinal infections
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What type of infections are cause by Serratia marcescens
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nosocomial opportunistic, can cause ocular infections, invasive and resistant to antimicrobials and disinfectants
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MacConkey's Agar is:
selective differential selective and differential What properties make it this way? |
selective and differential
selectivity (slightly)- bile salts and crystal violet inhibt gram positive bacteria and some non-enterobacteriaceae gram negative bacteria differential-lactose fermentors appear pink because they produce acid when they ferment lactose which changes the pH indicator (neutral red), non lactose fermentors will be transparent and slow fermentors will be colorless or slightly pink |
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EMB agar is
selective differential selective and differential What makes it this way? |
EMB agar is slightly selective and differential
selectivity-gram positives and fastidious gram negatives are inhibited by the aniline dyes eosin and methylene blue differential-lactose fermentors will appear pink to purple and may have a metallic sheen because the dyes precipitate at an acid pH. Nonfermentors appear colorless |
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What is the purpose of TSI (triple sugar iron) broth?
What are the possible reaction results? |
TSI is a differential medium for gram negative enterics. It tests the ability to ferment dextrose (glucose), lactose, and/or sucrose with the formation of acid, gas, and H2S
If the slant and butt are both red, no sugar was fermented If the slant is red but the butt is yellow, only glucose was fermented If both the slant and butt are yellow, glucose, lactose and/or sucrose were fermented H2S production will result in a black precipitate if acid was produced Gas production will result in bubbles or cracks in the medium |
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What is the purpose of Urea Broth (Christensen's Formulaiton) and what does a positive test look like?
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Urea broth tests for the production of urease
In a positive test result the medium turns alkaline because ammonia is produced when urea is hydrolyzed. The pheonl red turns to pink/ red if the media is alkaline. |
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Describe motility medium and what a positive test looks like
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Motility medium test for motility of gram negative enteric bacteria. The semisolid (less than 0.5%) agar contains tetrazlium salts to aid in the visual detection of growth throughout the medium
Result-non motile organisms grow only on the innoculation line while motile ones will grow throughout, the tetrazolium salts are reduce by viable MO forming red (insoluble) formazan which will diffuse throughout the media if the organism is motile |
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Describe tryptophan aka indole broth and a positive reaction
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Use for the detection of indole by enterobacteriaceae to differentiate Escherichia from Klebsiella. Indole is produce through degradation of tryptophan. Kovac's reagent extracts the indole with amyl alchohol and forms a red complex when the indole reacts with the aldehyde group. A bright red color at teh surface of the broth that forms immediately is a positive result
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Describe the citrate slant and a positive result
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The citrate slant tests for the ultilization of citrate as a sole carbon source
A positive reaction is indicated by an increase in the pH from alkaline by products turning the bromthymol blue indicator from green to blue. The slant should not be heavily innoculated |
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Describe purple broth and a positive test result
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Purple broth base if carbohydrate free but can be supplemented with specific carbs to test fermentation reactions for gram - enterics, contaims durham tube to test for gas production
Results: A yellow color (acid changes bromcresol purple to yellow) indicates fermentation with acid production, a bubble in the durham tube indicates gas production |
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Describe Phenylalanine agar and a positive result
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Use to differentiate enteric bacilli on the basis of their ability to produce phenylpyruvic acid by oxidative deamination of phenylalanie
Result: After incubation 4-5 drops of 10% ferric chloride are added and mixed into the growth. An immediate appearance of an intense green color indicates the prescence of phenylpyruvic acid and confirms fermentation |
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Describe the VP/MR tests. What are they used to detect? What are the products? What does a pos/neg test look like?
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VP/MR test determine the type of fermentation that an enterobacteriaceae uses. The VP test detects neutral fermentation products (acetone) with a red color at the surface being at + result. The MR test detects strong acid by products with a red color throughout as a posible test.
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Why is it necessary to have glucose in a decarboxylase broth?
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the decarb enzymes need an acidic pH to become active. Glucose fermentation leads to acid production. Once the glucose is used up the decarb enzymes will become active.
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What does a positive decarb test look like?
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Purple to yellow to purple.
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Why should decarb tubes be overlayed with mineral oil
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to create an anaerobic environment
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What is the purpose of SS agar? Is it selective or differential?
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SS agar is used to select for Salmonella and Shigella. The high concentration of bile salts inhibits other organisms. Lactose is the sole carbohydrate and and lactose fermentors appear dark pink. H2S producing colonies have a black center.
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Whar are the IMViC reactions? How are they used to differentiate E. coli from Klebsiella, Enterobacter, and Serratia?
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The IMViC reactions are indole, methy red, VP and citrate. E. coli is ++-- and the others are --++.
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What are the results of the oxidase test for all enterbacteriacea?
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Negative
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For TSI
K/K K/A A/A |
K/K no sugar was fermented
K/A only glucose was feremented A/A glucose plus lactose and/or sucrose |
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What key reactions differentiate proteus and salmonella
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Urea- proteus is positive
phenylalanine- proteus is positive H2S production- Salmonella has tons! |
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What is the purpose of using PEA plates when cultureing a would sample containing Proteus or E. coli and S. aureus
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PEA is selective for gram + organisms, only the S. aureus would grow
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What feature in the urine might suggest an enterobacteriace based UTI
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nitrities in the urine, all enterobacteriacea reduce nitrate to nitrite
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What is the oxygen relationship of the enterobacteriaceae?
Nutritional requirements? |
facultative, non fastitdious, grown on ordinary media
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Describe the hemolytic reactions of the enterobacteriaceae on BAP
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some E. coli are beta hemolytic, no alpha hemolysis. there may also be discoloration due to indole production
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Do EMB or MacConkey's detect H2S?
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No. Need to use a TSI slant of SS agar
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SS agar contains a higher concentration of selective agents so as to inhibit normal GI flora. Why is this significant?
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Normal gut flora outnumber pathogens 1000:1. To get pure culture of salmonella or shigella, it is necessary to select out the normal gut flora
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What to enzymes are needed to ferment lactose? Which is detected with an ONPG test?
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B galactosidase and B galactoside permease, only B galactosidase is detected in an ONPG test
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What enzyme is being detected in a urea broth? What does a posibiel test look like?
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Urease
Positive test is hot pink due to alkaline environment from ammonia production |
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What are the relative conentrations of the sugars in TSI?
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glucose 1x
lactose and sucrose 10x |
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Is K/K on TSI organism a enterobacteriaceae?
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No. ALl enterics are glucose fermentors
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After 12 hours, an enteric bacteria will turn a TSI slant entirely yellow due to acidic glucose fementation. Why does the top of the slant turn red for some bacteria later on?
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After the glucose is exhaused, the bacteria that are unable to ferment the other sugars will AEROBICALLY use the amino acids or peptides for energy. These are broken down to alkaline byproducts which turn the slant red
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WHich enteric species produce H2S
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Proteus, Salmonella, Citrobacter, Edwardsiella
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Which enterics use lactose on MacConkey's
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E. coli, Klebsiella
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Which enterics are K/A + H2S
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Proteus mirabilis, Salmonella, Citrobacter freundii, Edwardsiella tarda (these are non lactose fermenting)
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Which enterics are A/A no H2S
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Yesinia, E coli, Klebsiella, Enterobacter, Serratia
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How can citrobacter be differentiated from Salmonella
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decarb broths
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How does EHEC (E. coli O157 H7) cause disease? What are the symptoms of infection? What special media can be used to isolate it?
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EHEC causes disease by producing a cytotoxin that causes vascular damage. The toxin leads to bloody diarrhea,a and kidney damage (toxin mediated hemolytic ureic syndrome). MacConkey's with sorbitol can be used to differentiate. EHEC does not ferment sorbitol and appears colorless. Other E. coli's due and appear pink
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Can salmonella ferment lactose?
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no
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HOw can S. typhi be differentiated from other Salmonella species
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S. typhi produces very little H2S whereas the other salmonella spp produce tons
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What are the two types of infection that can result from Salmonella infection? How does infection occur?
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1. gastroenteritis
2. enteric fever- caused by S. typhi Both result from ingetstion of large numbers of the organism |
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What two enterics are non motile
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Klebsiella and Shigella
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T/F Shigella, the cause of bacillary dysentery requires a high infection dose to cause disease
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False. Fewer than 100 organsism can initiate infection in healthy induviduals
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Which lactose negative enteric pathogen grows slowly at 35 and therefore is usually cold enteriched?
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Yersinia enterocolitica
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How would C. jejuni be cultured? What is the infectious dose?
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Culture on BAP at 37 and 42 for 48 hrs in a microaerophilic atmosphere (5% O2, 10% CO2) note darting motility. The infectious dose is very low (~500 cells)
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Name 3 enteric pathogens that have low infectious doses
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Shigella spp., Camphylobacter jejuni, EHEC
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What unique characteristic of H. pylori allows it to grow in the acidic environment of the stomach
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Produces larges amounts of urease to create an alkaline microenvironment
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What does Vibrio cholerae cause? How do infected patients present? How is this organism cultured
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V. cholerae is the etiologic agent of cholera. Patients present with a characteristic rice water stool. Specific selective media is required because the organism is inhibited by EMB and SS agar
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Which two organisms require two motlility tubes? Why?
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Yersinia enterocolitica. Tubes at 25 and 37 cooler temperature may be necessary to organism to be motile
Camphylobacter jejuni incubated at 37 and 42 |
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S. typhi shows only traces of H2S on a TSI slant in contrast to most other Salmonella species. What other test can differentiate this organism?
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S. typhi is ornithine decarboxylase negtaive whereas most other Samonella are positive
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What two techniuqes can be used to definitively identify enteric pathogens like Salmonella, Shigella, and E coli
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detection of antigens, molecular fingerprinting (pulsed field gel electrophoresis PFGE)
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What key reactions differentiate salmonella and shigella
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salmonella is H2S + and is motile. Shigella is H2S- and non motile
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What are the 3 types of antigens detected in definite identification
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O- somatic antigen
H- flagella antigen K- capsular antigen |
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What are the normal flora of the small intestine? What are the innate defenses against pathogens?
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normal flora- Lactobacillus, Streptococcus
defenses- mucouse, bile, Peyer's Patches, IgA, flow, acid, peristalsis |
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What are the 4 "pathways" that should be taken with a stool sample to Dx an enteric infection
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1. Direct exam for blood, mucous, WBCs
2. Entericment broth (selenite or GN) then subculture to highly seletive plates 3. Plating directly onto highly seletive plates 4. Differential and moderately selective plates (MAC or EMB) possiblly SMAC if EHEC is suspected Culture should be set up on 3 stool samples All suspect colonies should be set up on TSI, citrate, Lysine decar, and Urea |
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The gasteroenteritis cause by Salmonella is
A. an infection B. an intoxication |
A. Salmonella requires an infection , symptoms present 8-48 hrs after ingestion of fecal contaminated food. The infectious dose is very large
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What is the cause of enteric/ typhoid fever? Describe the disease
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Salmonella typhi (strict human pathogen) invates the blood stream after leaving the GI tract and lymph nodes. It multiplies within macrophages and must be isolated from the blood.
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Shigellosis is cause by Shigella species which are strict human pathogens.
What are the 4 species of concern? How is it transmitted? What causes the disease? What is the infectious dose? |
species S. dysenteriae (A), S. flexneri (B), S. bodyii (C), S. sonnei (D)
Transmitted person to person fecal oral, and less oftenly in contaminated food and water the disease is the result of the exotoxin "shiga toxin" and it causes watery diarrhea the infectious dose is very low because the organism is resistant to gastric acid |
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What rxn can differentiate S. flexneri from S. sonnei
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a decarboxylase reaction
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What is the infectious dose of EHEC
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low 10-100 organisms
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Describe the antigens detected duriong serological classification
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O- somoatic cell wall Ag (part of LPS), heat stable
H-flagellar protein Ag, heat labile, phase dependent K- capsular, heat labile, K antigen can block or mask O antigen may need to destroy K by boiling |
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Outline the strategy for Serotyping
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1. use biochemical tests to indicate a presumptive ID
2. Use antisera to somatic O antigen to screen isolates 3. if no agglutination, boil the isolate to destroy the K antigen and test for O antigen again |
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What are the 3 illic's of campylobacter
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microaerophillic, capnophilic, thermophiilic
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Chickens and domestic pets can harbor C. jejuni. Humans can become infected with a very low dose leading to gasteroenteritis and blood in stools w/ WBCs. What sequla can result from C. jejuni infection
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Guiilian-Barre syndrome w/ neuropathology
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Describe the enrichment techniques used to isolate C. jejuni
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1. MEdia with amino acids and antimicrobials to inhibit GI normal flora, filtration techniques also used
2. incubation at 37 and 42 to enrich 3. Note that an atmosphere w/ >21 % O2 ihibits 4. direct exam of stool for darting motility |
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Consider Salmonella, Shigella, STEC/EHEC, and C. jejuni
Which of these could be found in the blood? What are the infectious doses? |
Blood Shigella and EHEC for sure, C. jejuni oten, usually not Salmonella
Salmonella is high dose, the others are low |
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What organisms cause gasteroenteritis, diarrhea, and wound infections like the enterobacteriaceae but are oxidase positive
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1. Vibrio species from marine waters
2. Aeromonas from fresh or marine waters |
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While the upper portion of the urethra is maintained sterile, what bacteria normally colonize the lower portion?
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skin bacteria like S. epidermidis, Corynebacteria etc, lactobacillli, nonpathogenic strep, and ocasinally intestinal bacteria
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How are urine cultures normally set up?
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Non selective %5 BAP and Mac or EMB plates. Plate with 10 ul (0.01 ml) quantitative loop streaking down the middle of the plate and then spreading perpendicularly
CFU/ml are done by comparing density or multiplying # of colonies by 100 |
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Why is it considered significant when only a few colonies grow from catheterized urine or suprapubic bladder aspirates?
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These sites should be sterile so any growth is significant. There is no skin flora contamination like for clean catch samples.
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What plate count generally indicates a UTI ? Wet prep?
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10^5 on a plate, two or more organisms per oil imersion field (1000x)
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List some enteric bacteria that are commonly isolated from UTI
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E. coli, Klebsiella, Enterobacter, Proteus, Serratia
remember, PS..EEK!! |
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List some gram positive cocci that are commonly isolated from UTI
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enterococcus faecalis, S. aureus, S. saprophyticus, S. agalatiae,
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Describe the proper urine collection procedure for a female
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1. Wash hands
2. Spread labia with non dominant hand, cleanse vulvar area with towelette fron to back 3. With fingers stationary hodling labia open, void first portion 4. Without stopping flow, pass speciment container into urine stream and obtain sample 5. Remove container before urine flow stops |
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Describe the proper urine collection procedure for a male
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1. Wash hands
2. Cleanse tip of penis with towelette 3. retract foreskin if present, void first portion 4. without stoping flow, pass specimine container into urine stream and obtain sample 5. stop collection before flow stops |
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define incontinence
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involuntary leekage of urine
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define bacteriuria
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bacteria in the urine
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defin pyuria
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pus/ WBCs in the urine
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define dysuria
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painful or difficult urination
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Define hematuria
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blood in the urine
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Define
urethritis cystitis pyelonephritis prostatisitis |
urethritis- inflammation o fthe urethra, could be an STI
cystitis- urniary bladder infection pt. presents with frequent, urgent urination and dysuria pyelonephritis- infection of the kidney, pt presents with fever, flank pain etc. prostatitis- enlarged or inflamed prostate |
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What are the two routes of UTI infection
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ascending- from outside fo the urethra
hamtogenous- from the blood |
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What are some factors that explain the increased incidence of UTIs in women compared to men
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- anatormy of urethra (shorter and closer to GI tract)
- birth control methods -pregnancy |
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What are some other UTI suceptible populations in addition to young, sexually active women
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poorly controlled diabetic, debilitated, elderly, infants, hospitalized pts. with catheters
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What are two products test for on a UA dipstick
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nitries- test for enterobacteriaceae
leukocyte esterase to test for PMNs |
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Why is it necessary to culture for UTIs when things like the UA dipstick exist?
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Detection and ID of pathogen
quantitation differentiation suceptibility testing to determine proper antibiotic |
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In addition to the fact that the patient has a UTI which is a bummer in its own right, why is it particually concening when the infectious agent is a urease producing species like proteus, Klebsiella, or S. saprophyticus?
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Urease creates an alkaline environment which can lead to the preceiptation of calcium. This leads to the formation of stones which are increbily painful to pass and can also trap organissm leading to recurrent infections
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Athough 10^5 CFU/ ml is considered the "magic" number for Dx UTI, lower numbers can be significant. List several cases where this is true?
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with symptoms and pyuria, pregnancy, catheterized and suprapubic samples, recurrent infections, at risk populations
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What is the best time of day to collect a urine sample?
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in the morning when the urine is concentrated
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How does cranberry influence UTIs
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Cranberry extract can decrease the adherence of gram negative bacilli
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How many genera make up the enterobacteriaceae
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6
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which enteric pathgen do you need to isolate from the blood rather than stool
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S. typhi because it is a systemic infection
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Vibrio parahaemolyticus
average duration? implicated foods? Sxs? |
duration- 3 days
foods- shellfish sxs- pain, vomiting, fever, watery diarrhea |
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Vibrio cholerae
average duration? implicated foods? Sxs? |
duration- 3-7 days
foods- seafood, water sxs- rice water stools, severe diarrhea, no fever |
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Salmonella
average duration? implicated foods? Sxs? |
duration- 3 days
foods- eggs, dairy, fowl, beef sxs- Fever, abdominal cramping, diarrhea, mild vomiting, WBC in stool |
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Yersinia enterocolitica
average duration? implicated foods? Sxs? |
duration- 1 day -4 weeks
foods- milk, pork sxs- fever, severe abdominal pain, diarrhea, WBC and RBC in stool, common in winter |
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Shigella
average duration? implicated foods? Sxs? |
duration-3 days
foods- fecal oral contact, water, egg, tuna, lettuce, milk sxs- fever, abdominal cramping, diarrhea, occasional vomiting, WBC, RBC in stool |
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Enterohemorrhagic E. coli (EHEC)
average duration? implicated foods? Sxs? |
duration- 3 days
foods- undercooked ground beef, cider (unpasterized juice), spinach, peppers, water, pools sxs- watery diarrhea progessing to bloody, abdominal cramping, no fever or vomiting |
