Enterbacteriaecea Flashcards
What type of bacteria are all members of Enterobacterales?
Gram negative bacilli
Are Enterobacterales anaerobic or aerobic?
Facultatively anaerobic
What are the common characteristics shared by all species in Enterobacterales?
- All ferment glucose
- All reduce nitrates to nitrites
- Oxidase negative
- All except Klebsiella, Shigella, and Yersinia are motile
What types of media are used for the presumptive identification of Enterobacterales?
- MacConkey agar
- Hektoen enteric (HE) agar
- XLD (xylose-lysine deoxycholate agar)
What antigenic factors are useful for identifying different serogroups of Enterobacterales?
- O antigen
- H antigen
- K antigen
Where are Enterobacterales commonly found in nature?
In the gastrointestinal tract of humans and animals as normal flora
How are Enterobacterales classified in terms of pathogenicity?
- Opportunistic pathogens
- Primary intestinal pathogens
Which organisms are considered true intestinal pathogens in the Enterobacterales family?
- Salmonella spp.
- Shigella spp.
- Yersinia enterocolitica
Which Klebsiella species is known for causing urinary tract infections and respiratory infections in hospitals?
Klebsiella oxytoca
What key characteristic differentiates Klebsiella species from other Enterobacteriaceae?
Absence of motility
What is the significance of the polysaccharide capsule in Klebsiella pneumoniae?
Contributes to the virulence of the organism
What genera are included in the Enterobacterales opportunistic members of the family?
- Klebsiella
- Enterobacter
- Serratia
What unique feature do Serratia species possess compared to other Enterobacteriaceae?
Produce extracellular DNase
What infections are associated with Serratia marcescens?
- Hospital-acquired UTIs
- Respiratory infections
What distinguishes Proteus species in Enterobacterales?
Ability to deaminate phenylalanine
What is a common characteristic feature of Proteus mirabilis and Proteus vulgaris on media?
Distinctive swarming colonies
What is the clinical significance of Morganella morganii?
Causes nosocomial infections and UTIs
Which species of Providencia is known for causing UTIs and outbreaks in burn units?
Providencia stuartii
What is a key differentiating feature of Citrobacter species?
Most hydrolyze urea slowly and ferment lactose
What are the distinguishing tests for Salmonella and Citrobacter?
Lysine decarboxylase test
Fill in the blank: Klebsiella pneumoniae is a common cause of ______ in hospitalized patients.
lower respiratory tract infections
True or False: All Enterobacterales are lactose fermenters.
False
What is the typical odor produced by Proteus mirabilis and Proteus vulgaris?
Burned chocolate
What are the common sources of Salmonella infection?
Contaminated animal products, undercooked poultry, milk, eggs, dairy products
Ingestion is the primary route of infection.
What are the biochemical features of Salmonella?
- Do not ferment lactose
- Negative for indole
- Negative for Vogues-Proskauer test
- Negative for phenylalanine
- Negative for urease
- Most produce H2S on TSI
- Positive for methyl red and citrate
These characteristics help in identification.
What are the main antigens used for the serologic diagnosis of Salmonella?
Somatic O antigen and flagellar H antigen
Serologic grouping of the Vi antigen is used to identify S. typhi.
What are the two forms of plague caused by Yersinia pestis?
- Bubonic plague
- Pneumonic plague
Bubonic plague is the primary illness; pneumonic is a secondary disease.
What is the main characteristic of Shigella species?
Causes bacillary dysentery
All species are not part of the normal bowel flora.
What are the four species of Shigella?
- Shigella dysenteriae (group A)
- Shigella flexneri (group B)
- Shigella boydii (group C)
- Shigella sonnei (group D)
Different O antigens are used for serologic identification.
What is a key characteristic of Escherichia coli?
Commonly isolated from the normal bowel flora
Recognized as an important human pathogen.
What infections can E. coli cause?
- Meningitis (particularly in newborns)
- Gastrointestinal infections
Some strains have virulence factors that can cause diarrhea.
What is a significant biochemical test result for E. coli?
Positive indole and methyl red tests
E. coli does not produce H2S, DNase, urease, or phenylalanine deaminase.
Fill in the blank: The causative agent of the bubonic plague is ______.
[Yersinia pestis]
True or False: Salmonella species can ferment lactose.
False
Salmonella species do not ferment lactose.
What types of infections can Escherichia coli cause?
- Meningitis
- Gastrointestinal illness
- Urinary tract infections (UTI)
- Wound infections
- Bacteremia
Particularly notable in newborns for meningitis and in adults for UTIs.
What are the different types of diarrheagenic E. coli?
- Enteropathogenic (EPEC)
- Enterotoxigenic (ETEC)
- Enteroinvasive (EIEC)
- Enterohemorrhagic (EHEC)
- Enteroaggregative (EaggEC)
Each type is associated with different clinical presentations and mechanisms of infection.
Where is Enterotoxigenic E. coli (ETEC) commonly acquired?
Via ingestion of contaminated food or water
ETEC is particularly prevalent in tropical and subtropical climates.
What characterizes the diarrhea caused by Enteroinvasive E. coli (EIEC)?
It is similar to dysentery caused by Shigella
Symptoms include fever, severe abdominal cramps, and diarrhea that may contain pus, mucus, and blood.
What is the primary strain of Enterohemorrhagic E. coli (EHEC) responsible for serious infections?
E. coli O157:H7
This strain can cause hemorrhagic colitis and hemolytic uremic syndrome.
How can E. coli O157:H7 be identified in the laboratory?
- Stool culture on MacConkey agar containing sorbitol
- Latex agglutination test
- MUG assay
E. coli O157:H7 does not ferment sorbitol, resulting in colorless colonies on specific agar.
What is the most common cause of urinary tract infections (UTI)?
Escherichia coli
These strains are often resident or transient members of the normal colon flora.
What is the significance of fecal leukocytes in diagnosing bacterial infections?
As few as 3 neutrophils per high-power field may indicate an invasive bacterial infection
This can differentiate from intoxication or parasitic infections.
What is the procedure for serogrouping Salmonella?
- Emulsify a pure culture in saline
- Add antisera and bacterial emulsion
- Heat and test for agglutination
This process helps confirm the biochemical test identification.
