Chapter 19: Enterobacterales Flashcards
(42 cards)
What are the general characteristics of Enterobacterales?
Gram-negative, facultatively anaerobic, non-spore-forming bacilli and coccobacilli that live in the gastrointestinal tract
All members ferment glucose and most reduce nitrate to nitrites. All are oxidase negative except Plesiomonas.
What is the motility characteristic of Enterobacterales?
All are motile at body temperature except most Klebsiella, Shigella, and Yersinia
This includes the fact that certain species are non-motile.
What are the biochemical characteristics used for classification of Enterobacterales?
Phenotypical characteristics, biochemical reactions, molecular methods, and DNA relatedness (16S rRNA)
These methods help in the identification and classification of Enterobacterales.
What are the virulence factors associated with Enterobacterales?
Adherence, toxins, invasive enzymes, antibiotic resistance
Extended spectrum β-Lactamases (ESBL) are also noted.
What antigens are associated with Enterobacterales?
- O antigen (somatic antigen)
- H antigen (flagellar antigen)
- K antigen (capsular antigen)
K1 antigen of E. coli and Vi antigen of Salmonella enterica subsp. enterica serotype Typhi are examples.
What is the clinical significance of Enterobacterales?
Human infections, opportunistic pathogens, primary pathogens, antimicrobial resistance
Carbapenem-resistant Enterobacteriaceae (CRE) is an urgent concern.
What infections are commonly caused by Escherichia coli?
- Urinary tract infections
- Diarrheal diseases
- Central nervous system infections
- Meningitis in neonates
E. coli is a frequent isolate in clinical laboratories.
What are the five distinct syndromes of entero-virulent E. coli?
- ETEC: Enterotoxigenic E. coli
- EPEC: Enteropathogenic E. coli
- EIEC: Enteroinvasive E. coli
- STEC: Shiga toxin-producing E. coli
- EAEC: Enteroaggregative E. coli
STEC is known for producing Shiga toxin 1 and/or 2.
What is the most common serotype of Shiga toxin-producing E. coli?
O157:H7
It can cause mild disease to life-threatening conditions such as Hemolytic Uremic Syndrome (HUS).
How is Shiga toxin-producing E. coli detected?
- Stool culture on selective medium
- Detection of Shiga toxin in stool filtrates
- Demonstration of an increase in Shiga toxin–neutralizing antibody titer
Serotyping is also part of the identification process.
What are the clinical characteristics of Klebsiella?
Most grow on Simmons citrate and KCN broth, are methyl red test negative, and Voges-Proskauer positive
None produce H2S and motility is variable.
What infections are associated with Klebsiella species?
- Pneumonia
- Wound infections
- Urinary tract infections
K. pneumoniae is the most common carbapenem-resistant Enterobacteriaceae in the USA.
What are the characteristics of Enterobacter?
Current 22 species, opportunistic infections, widely distributed in soil and water
E. cloacae complex consists of several genetically similar, clinically relevant species.
What infections are commonly caused by Citrobacter?
- Urinary tract infections
- Respiratory tract infections
- Wound infections
- Gastroenteritis
- Meningitis
C. freundii is the most common isolate.
What are the characteristics of the genus Proteus?
Deaminate phenylalanine, do not ferment lactose, found in soil and water
P. mirabilis is the most frequent human isolate and can lead to struvite kidney stones.
What is a notable characteristic of Serratia?
Resistant to a wide array of antibiotics, with S. marcescens being the most significant species
It may produce a red or orange pigment.
What are the main clinical syndromes caused by Salmonella?
- Gastroenteritis
- Bacteremia or septicemia
- Enteric fevers (typhoid fever)
- Carrier state
S. Typhi is responsible for typhoid fever and can lead to a carrier state.
What is Shigella known for?
Most communicable of bacterial diarrheas, causing dysentery
As few as 10-200 organisms can cause infection.
What is the significance of Yersinia pestis?
Agent of plague, known for its zoonotic diseases
It is responsible for historical pandemics and is a potential bioterrorism agent.
What laboratory methods are used for the identification of Enterobacterales?
- Direct microscopic examination
- Culture
- Screening stool cultures
- Serologic Grouping
- Multiplex PCR
Isolation media depends on the specimen source.
What is the significance of MacConkey agar in microbiology?
Selective and differential medium that inhibits gram-positive bacteria and differentiates lactose fermenters
Lactose fermentation produces pink colonies, while non-lactose fermenters produce colorless colonies.
What does the TSI test indicate?
Fermentation of glucose, lactose, and/or sucrose, and hydrogen sulfide production
Results are read based on color change and gas production.
What do IMVC tests stand for?
Indole, Methyl Red, Voges-Proskauer, Citrate
These tests help identify metabolic pathways and characteristics of Enterobacterales.
What is the pH level and reaction with MR indicator for mixed acids?
Acidic pH and positive reaction with MR indicator
Indicates mixed acid fermentation.
