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Questions and Answers
What type of bacteria are classified under the order Enterobacterales?
What type of bacteria are classified under the order Enterobacterales?
Gram-negative bacteria
What are the key features of gram-negative aerobic bacteria that are compared?
What are the key features of gram-negative aerobic bacteria that are compared?
- Habitat, diet, and reproduction
- Size, shape, and color
- Morphology, growth characteristics, and classification (correct)
- Virulence, resistance, and susceptibility
What are the characteristics of bacteria in the Enterobacterales order?
What are the characteristics of bacteria in the Enterobacterales order?
- They are spiral-shaped and obligate anaerobes.
- They are spherical and obligate aerobes.
- They are rod-shaped and facultative anaerobes. (correct)
- They are filamentous and facultative aerobes.
Gram-negative bacteria have a thick peptidoglycan layer in their cell wall.
Gram-negative bacteria have a thick peptidoglycan layer in their cell wall.
What are some of the common virulence factors associated with Enterobacterales?
What are some of the common virulence factors associated with Enterobacterales?
What is the function of lipopolysaccharides in the outer membrane of gram-negative bacteria?
What is the function of lipopolysaccharides in the outer membrane of gram-negative bacteria?
What role does the capsule play in protecting encapsulated Enterobacterales?
What role does the capsule play in protecting encapsulated Enterobacterales?
Which of the following is NOT a common Enterobacterales species?
Which of the following is NOT a common Enterobacterales species?
What are some of the common sites of infection for Enterobacterales?
What are some of the common sites of infection for Enterobacterales?
Which of the following is a selective and differential agar used to identify Enterobacterales?
Which of the following is a selective and differential agar used to identify Enterobacterales?
Which of the following bacteria is indole-positive?
Which of the following bacteria is indole-positive?
What is the function of cytochrome c oxidase?
What is the function of cytochrome c oxidase?
What are some of the common clinical syndromes associated with Escherichia coli?
What are some of the common clinical syndromes associated with Escherichia coli?
Escherichia coli is the most common and clinically significant Enterobacterales.
Escherichia coli is the most common and clinically significant Enterobacterales.
What is the primary cause of neonatal meningitis?
What is the primary cause of neonatal meningitis?
Escherichia coli is only found in the human gut.
Escherichia coli is only found in the human gut.
Escherichia coli has only one serotype.
Escherichia coli has only one serotype.
What is the most common type of Escherichia coli infection?
What is the most common type of Escherichia coli infection?
What are some of the characteristics of Escherichia coli colonies on culture media?
What are some of the characteristics of Escherichia coli colonies on culture media?
What type of fermentation does Escherichia coli exhibit?
What type of fermentation does Escherichia coli exhibit?
Escherichia coli is indole-negative.
Escherichia coli is indole-negative.
Which of the following is NOT a risk factor for uncomplicated urinary tract infections?
Which of the following is NOT a risk factor for uncomplicated urinary tract infections?
Complicated urinary tract infections are more common than uncomplicated urinary tract infections.
Complicated urinary tract infections are more common than uncomplicated urinary tract infections.
What are some of the common antibiotics used to treat uncomplicated UTIs?
What are some of the common antibiotics used to treat uncomplicated UTIs?
What are some of the antibiotics used to treat more complicated or resistant UTIs?
What are some of the antibiotics used to treat more complicated or resistant UTIs?
What are the major groups of Escherichia coli strains that cause gastroenteritis?
What are the major groups of Escherichia coli strains that cause gastroenteritis?
What are some of the symptoms of enterotoxigenic Escherichia coli (ETEC) infection?
What are some of the symptoms of enterotoxigenic Escherichia coli (ETEC) infection?
What is the mechanism of pathogenesis for ETEC?
What is the mechanism of pathogenesis for ETEC?
What is the primary mode of transmission for EPEC?
What is the primary mode of transmission for EPEC?
What are some of the symptoms of EPEC infection?
What are some of the symptoms of EPEC infection?
Explain the pathogenesis of EPEC infection.
Explain the pathogenesis of EPEC infection.
What is the pathogenesis of EAEC infection?
What is the pathogenesis of EAEC infection?
STEC infection is commonly associated with consumption of undercooked beef.
STEC infection is commonly associated with consumption of undercooked beef.
What is the mechanism of pathogenesis for STEC infection?
What is the mechanism of pathogenesis for STEC infection?
What is the most common serotype of STEC associated with severe human disease?
What is the most common serotype of STEC associated with severe human disease?
What are some of the common clinical syndromes associated with Yersinia pestis?
What are some of the common clinical syndromes associated with Yersinia pestis?
Pneumonic plague is more contagious than bubonic plague.
Pneumonic plague is more contagious than bubonic plague.
Yersinia pestis is only transmitted by fleas.
Yersinia pestis is only transmitted by fleas.
The Black Death was a pandemic of bubonic plague.
The Black Death was a pandemic of bubonic plague.
Which of the following is a clinically important species of Yersinia?
Which of the following is a clinically important species of Yersinia?
What are some of the symptoms of Yersinia enterocolitica infection?
What are some of the symptoms of Yersinia enterocolitica infection?
Yersinia enterocolitica infection is only found in developing countries.
Yersinia enterocolitica infection is only found in developing countries.
What are some of the key characteristics of Klebsiella spp.?
What are some of the key characteristics of Klebsiella spp.?
Which of the following Klebsiella spp. is indole-positive?
Which of the following Klebsiella spp. is indole-positive?
What are some of the common clinical syndromes associated with Klebsiella spp.?
What are some of the common clinical syndromes associated with Klebsiella spp.?
What is the name of the gene responsible for carbapenemase production in Klebsiella spp.?
What is the name of the gene responsible for carbapenemase production in Klebsiella spp.?
The blaKPC gene is only found in Klebsiella pneumoniae.
The blaKPC gene is only found in Klebsiella pneumoniae.
Enterobacter spp. are non-motile.
Enterobacter spp. are non-motile.
Which of the following is the most common Enterobacter spp.?
Which of the following is the most common Enterobacter spp.?
What are some of the common clinical syndromes associated with Enterobacter spp.?
What are some of the common clinical syndromes associated with Enterobacter spp.?
Which of the following is a common clinical species of Citrobacter?
Which of the following is a common clinical species of Citrobacter?
What are some of the key characteristics of Serratia spp.?
What are some of the key characteristics of Serratia spp.?
Which of the following is the most common clinical species of Serratia spp.?
Which of the following is the most common clinical species of Serratia spp.?
What are some of the common clinical syndromes associated with Serratia spp.?
What are some of the common clinical syndromes associated with Serratia spp.?
What type of beta-lactamase is often associated with resistance to cephalosporins?
What type of beta-lactamase is often associated with resistance to cephalosporins?
The chromosomal AmpC gene is present in almost all Enterobacter, Citrobacter, and Serratia species.
The chromosomal AmpC gene is present in almost all Enterobacter, Citrobacter, and Serratia species.
Plasmid-mediated AmpC genes are always resistant to antibiotics.
Plasmid-mediated AmpC genes are always resistant to antibiotics.
What are some of the key characteristics of Proteus spp. and Morganella spp.?
What are some of the key characteristics of Proteus spp. and Morganella spp.?
Providencia spp. produce urease.
Providencia spp. produce urease.
What are some of the common clinical syndromes associated with Proteus spp., Morganella spp., and Providencia spp.?
What are some of the common clinical syndromes associated with Proteus spp., Morganella spp., and Providencia spp.?
What are some of the characteristics of Salmonella spp.?
What are some of the characteristics of Salmonella spp.?
What is the primary mode of transmission for Salmonella spp.?
What is the primary mode of transmission for Salmonella spp.?
What are some of the common clinical syndromes associated with Salmonella spp.?
What are some of the common clinical syndromes associated with Salmonella spp.?
What is the most common form of salmonellosis?
What is the most common form of salmonellosis?
Salmonella Typhi is the only species responsible for typhoid fever.
Salmonella Typhi is the only species responsible for typhoid fever.
What is the reservoir for Salmonella Typhi?
What is the reservoir for Salmonella Typhi?
What are some of the symptoms of typhoid fever?
What are some of the symptoms of typhoid fever?
What type of agar is commonly used to differentiate between Salmonella spp., Shigella spp., and other gram-negative bacteria?
What type of agar is commonly used to differentiate between Salmonella spp., Shigella spp., and other gram-negative bacteria?
Shigella spp. are motile.
Shigella spp. are motile.
Which Shigella species is considered the most serious?
Which Shigella species is considered the most serious?
What is the primary mechanism of pathogenesis for Shigella spp.?
What is the primary mechanism of pathogenesis for Shigella spp.?
What are some of the symptoms of Shigella infection?
What are some of the symptoms of Shigella infection?
Shigella infection requires a high inoculum to cause disease.
Shigella infection requires a high inoculum to cause disease.
Why is Shigella infection often found in daycares?
Why is Shigella infection often found in daycares?
Yersinia spp. are primarily associated with human infections.
Yersinia spp. are primarily associated with human infections.
What is the most virulent pathogen in the Yersinia genus?
What is the most virulent pathogen in the Yersinia genus?
Yersinia entercolitica is a common cause of plague.
Yersinia entercolitica is a common cause of plague.
What are some of the symptoms of bubonic plague?
What are some of the symptoms of bubonic plague?
Pneumonic plague is more common than bubonic plague.
Pneumonic plague is more common than bubonic plague.
What is the incubation period for pneumonic plague?
What is the incubation period for pneumonic plague?
What is the primary mode of transmission for pneumonic plague?
What is the primary mode of transmission for pneumonic plague?
The Black Death pandemic was solely responsible for wiping out 1/3 of Europe's population.
The Black Death pandemic was solely responsible for wiping out 1/3 of Europe's population.
Yersinia enterocolitica infection can persist for months.
Yersinia enterocolitica infection can persist for months.
Flashcards
Enterobacterales
Enterobacterales
A group of gram-negative bacteria sharing a common antigen, previously classified under the family Enterobacteriaceae.
Gram Staining
Gram Staining
A laboratory technique used to differentiate bacteria based on their cell wall structure.
Gram-Positive Bacteria
Gram-Positive Bacteria
A thick layer of peptidoglycan in the cell wall gives these bacteria a purple color in Gram staining.
Gram-Negative Bacteria
Gram-Negative Bacteria
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Endotoxin
Endotoxin
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Capsule
Capsule
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Antigenic Phase Variation
Antigenic Phase Variation
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Type III Secretion Systems
Type III Secretion Systems
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Sequestration of Growth Factors
Sequestration of Growth Factors
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Resistance to Serum Killing
Resistance to Serum Killing
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Antimicrobial Resistance
Antimicrobial Resistance
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MacConkey Agar
MacConkey Agar
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Spot Indole Test
Spot Indole Test
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Oxidase Test
Oxidase Test
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Escherichia coli (E. coli)
Escherichia coli (E. coli)
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Uropathogenic E. coli (UPEC)
Uropathogenic E. coli (UPEC)
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Escherichia coli Diarrhea
Escherichia coli Diarrhea
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Enterotoxigenic E. coli (ETEC)
Enterotoxigenic E. coli (ETEC)
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Enteropathogenic Escherichia coli (EPEC)
Enteropathogenic Escherichia coli (EPEC)
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Enteroaggregative Escherichia coli (EAEC)
Enteroaggregative Escherichia coli (EAEC)
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Shiga Toxin-Producing Escherichia coli (STEC)
Shiga Toxin-Producing Escherichia coli (STEC)
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Proteus spp., Morganella spp., Providencia spp.
Proteus spp., Morganella spp., Providencia spp.
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Salmonella spp.
Salmonella spp.
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Hektoen Enteric Agar
Hektoen Enteric Agar
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Salmonella: Gastroenteritis
Salmonella: Gastroenteritis
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Salmonella: Bacteremia
Salmonella: Bacteremia
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Salmonella: Enteric Fever (Typhoid Fever)
Salmonella: Enteric Fever (Typhoid Fever)
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Salmonella: Asymptomatic Colonization
Salmonella: Asymptomatic Colonization
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Shigella spp.
Shigella spp.
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Yersinia spp.
Yersinia spp.
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Yersinia pestis: Plague
Yersinia pestis: Plague
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Bubonic Plague
Bubonic Plague
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Pneumonic Plague
Pneumonic Plague
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Yersinia entercolitica
Yersinia entercolitica
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Study Notes
Gram-Negative Aerobes
- Gram-negative aerobes are a group of bacteria with key characteristics in morphology, growth, and classification.
- Biochemical tests are used to identify gram-negative aerobic bacteria.
- Clinically relevant species of gram-negative aerobic bacteria include Enterobacterales.
Enterobacterales
- An order of gram-negative bacteria.
- Share an enterobacterial common antigen.
- Historically classified under Enterobacteriaceae.
- Moderate-sized, short bacilli (rod-shaped).
- Facultative anaerobes.
- Ferment glucose (some also ferment lactose).
- Reduce nitrate to nitrite.
- Catalase (+).
- Oxidase (-).
- Some are resistant to bile salts.
Gram Stain Review
- Gram-negative bacteria have an outer membrane, lipoproteins, peptidoglycan, periplasmic space, and a cytoplasmic membrane.
- Gram-positive bacteria have a thick peptidoglycan layer in their cell wall and no outer membrane.
- Gram-positive bacteria produce exotoxins, while gram-negative bacteria produce endotoxins.
- Gram-negative bacteria stain red/pink, while gram-positive bacteria stain purple.
Pathogenesis and Immunity
- Common virulence factors associated with Enterobacterales include Endotoxin and Capsule.
- Additional examples are Antigenic phase variation, Type III secretion systems, Sequestration of growth factors, Resistance to serum killing, and Antimicrobial resistance.
- Lipopolysaccharides in the outer membrane of gram-negative bacteria can cause lethal shock.
- The activation of the complement system results in the release of cytokines, leukocytosis, thrombocytopenia, fever, and decreased peripheral circulation, potentially leading to shock.
Common Enterobacterales
- Listed are several bacteria in this group, like Citrobacter freundii, Citrobacter koseri, Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Morganella morganii, Salmonella serotype Typhi, Salmonella nontyphoidal serotypes, Serratia marcescens, Shigella sonnei, Shigella flexneri, Yersinia pestis, Yersinia enterolitica, and Yersinia pseudotuberculosis.
Sites of Infection
- Gram-negative bacteria can cause infections in various body sites, including the central nervous system (meningitis), intra-abdominal, and urinary tract.
- Other common sites of infection include the mouth and respiratory tract, skin, and soft tissue.
How Can We Identify Organisms?
- Gram staining, growth media (selective and non-selective), biochemical tests (automated and benchtop), rapid diagnostic tests (multiplex PCR, MALDI-TOF MS) are used to identify organisms. Specific examples like MacConkey agar are mentioned.
Spot Indole Test
- The spot indole test identifies bacteria's ability to metabolize tryptophan to produce indole.
- Positive results show a color change with indole reagent.
Oxidase Test
- Used to identify bacteria that produce cytochrome c oxidase.
- A color change indicates a positive result.
Escherichia coli
- Part of the normal GI tract flora.
- Associated with UTIs, gastroenteritis, meningitis, and sepsis.
- Different serotypes of E. coli have varying virulence factors.
Morphology
- E. coli colony morphology is circular, smooth, flat, non-viscous with distinct edges.
- E. coli shows hemolysis on blood agar.
- E. coli exhibits metallic sheen on different agars.
- E. coli is a lactose fermenter and is indole positive.
Clinical Syndromes- UTI
- Various bacteria are major causes of uncomplicated and complicated UTIs.
Clinical Syndromes- Escherichia coli Diarrhea
- E. coli strains causing gastroenteritis are grouped as Enterotoxigenic (ETEC), Enteropathogenic (EPEC), Enteroaggregative (EAEC), Shiga toxin-producing (STEC), and Enteroinvasive (EIEC).
Enterotoxigenic Escherichia coli (ETEC)
- Causes traveler's diarrhea and infant diarrhea in developing countries.
- Transmission involves the consumption of contaminated food or water.
- Symptoms include watery diarrhea, abdominal cramps, nausea, and vomiting.
Enteropathogenic Escherichia coli (EPEC)
- Infant diarrhea in developing countries, and rare in the US.
- Transmitted by exposure to contaminated food/surfaces.
- Symptoms involve watery diarrhea and vomiting.
Enteroaggregative Escherichia coli (EAEC)
- Infant diarrhea can be chronic in developing countries.
- Transmission is fecal-oral and symptoms are watery diarrhea, vomiting, and low-grade fever.
- Pathogenesis is autoagglutination with the adherence of rods over the small intestine epithelium resulting in cytokine release, microvilli shortening, hemorrhage, and decreased fluid absorption.
Shiga Toxin-Producing Escherichia coli (STEC)
- Caused by the consumption of undercooked ground meat, water, and unpasteurized milk/fruit juices.
- Symptoms are bloody diarrhea (hemorrhagic colitis), abdominal cramps, and the potential progression to hemolytic uremic syndrome (HUS).
- Transmission is primarily person-to-person.
Enteroinvasive Escherichia coli (EIEC)
- Rare in developed, however, common in developing countries.
- Similar to Shigella.
- Symptoms include watery diarrhea, progressing to dysentery in some cases with abdominal cramps and blood in the stool.
Clinical Syndromes- Bacteremia/sepsis
- Escherichia coli can cause blood stream infections.
- The infection typically originates from the urinary or gastrointestinal tract.
Resistance Mechanisms
- Escherichia coli can develop resistance against antibiotics via activation of drug efflux pumps, drug-inactivating enzymes, and mutations in drug targets.
Escherichia coli: Resistance
- E. coli exhibits resistance to antibiotics through beta-lactamases, mutations in DNA topoisomerases, acetyltransferases, tet genes encoding efflux pumps, and mutations in dihydrofolate reductase.
Beta-Lactamase Resistance
- Beta-lactamases are bacterial enzymes that provide resistance to beta-lactam antibiotics like penicillins, cephalosporins, and carbapenems.
- Extended-spectrum beta-lactamases (ESBLs), and other enzymes pose a problem in terms of resistance among gram-negative bacteria.
Klebsiella spp.
- Klebsiella is a genus associated with mucoid colonies, often lactose-fermenting.
- Klebsiella can be associated with pneumonia, UTIs and wound infections.
- Klebsiella has resistance mechanisms similar to E. coli.
Enterobacter spp.
- Enterobacter species are motile and somewhat mucoid.
- Common species, like E. cloacae, are associated with hospital-acquired infections, pneumonia, UTIs, and wound infections
Citrobacter spp.
- Citrobacter species are motile and citrate-positive.
- Common species like C. freundii or C. koseri are associated with hospital-acquired infections, UTIs, wound infections, and infections in immunocompromised patients/neonates.
Serratia spp.
- Serratia species form small colonies which may be pigmented.
- The most common species in this genus is S. marcescens, a lactose fermenter and oxidase-negative bacteria, that is common in patients with pneumonia, bacteremia, and endocarditis.
Proteus spp., Morganella spp., Providencia spp.
- Proteus, Morganella, and Providencia are motile, slow-fermenters that are urease-positive(Proteus, Morganella) or urease-negative(Providencia).
- Can cause UTIs, pneumonia, and bacteremia.
Salmonella & Shigella
- Both Salmonella and Shigella are gram-negative bacteria of concern for foodborne illnesses.
Salmonella spp.
- Motile, ferment glucose and mannose, and resistant to bile salts.
- Are non-lactose/non-sucrose fermenter, produce Hâ‚‚S and are not part of the human microbiome.
- Associated with gastroenteritis, bacteremia, enteric fever, and asymptomatic colonization.
- Different species have different serotypes.
Hektoen Enteric Agar
- A selective and differential medium used to distinguish between Salmonella and Shigella from other gram-negative bacteria.
- Utilizes ingredients that limit non-targeted growth such as Bile salts.
- Salmonella and Shigella are isolated based on color changes and fermentation products, like Hâ‚‚S.
Shigella spp.
- Slender, non-motile bacilli, with convex, circular, transparent colonies.
- Resistant to bile salts, non-lactose fermenters, and don't produce Hâ‚‚S.
- Important species include S. dysenteriae, S. sonnei, and S. flexneri.
- Symptoms include watery diarrhea that can progress to dysentery, which is characterized by bloody diarrhea, fever, abdominal cramps, and tenesmus.
Yersinia
- Zoonotic infections
- Yersinia pestis is exceptionally virulent and causes the plague.
- Yersinia enterocolitica and Yersinia pseudotuberculosis are primarily enteric pathogens and less common.
- Yersinia pestis*: Plague
- Bubonic is transmitted by flea bites, incubates for 7 days, affects lymphatic systems, and without treatment, has a 75% mortality rate.
- Pneumonic plague is transmitted via respiratory droplets, has a shorter incubation period (2-3 Days), is potentially more lethal than bubonic, and has a ~95% mortality rate if untreated.
Yersinia enterocolitica
- Yersinia enterocolitica is characterized by enterocolitis, an infection that results from contaminated food/water.
- Incubation period lasts from 1–10 days, with an average of 4–6 days.
- Main Symptoms are diarrhea, fever, and abdominal pain, sometimes mimicking appendicitis (pseudo-appendicitis).
- Chronic infection can persist for several months.
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Description
This quiz covers the characteristics, classification, and identification of gram-negative aerobic bacteria, specifically focusing on the Enterobacterales order. Learn about their morphology, biochemical tests, and the distinction between gram-positive and gram-negative bacteria. Test your knowledge on these clinically significant microorganisms.