Gram-Negative Aerobes and Enterobacterales
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Questions and Answers

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?

  • 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?

  • 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.

    <p>False</p> Signup and view all the answers

    What are some of the common virulence factors associated with Enterobacterales?

    <p>Endotoxin, capsule, antigenic phase variation, type III secretion systems, sequestration of growth factors, resistance to serum killing, and antimicrobial resistance.</p> Signup and view all the answers

    What is the function of lipopolysaccharides in the outer membrane of gram-negative bacteria?

    <p>They are capable of causing lethal shock to cells by activating the complement system, releasing cytokines, and leading to complications like fever, decreased peripheral circulation, and even death.</p> Signup and view all the answers

    What role does the capsule play in protecting encapsulated Enterobacterales?

    <p>The capsule protects them from phagocytosis by hydrophilic capsular antigens, interfering with antibody binding. However, the protective role diminishes if the patient develops specific anticapsular antibodies.</p> Signup and view all the answers

    Which of the following is NOT a common Enterobacterales species?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What are some of the common sites of infection for Enterobacterales?

    <p>Central nervous system, intra-abdominal, urinary tract, respiratory tract, mouth, and skin/soft tissues.</p> Signup and view all the answers

    Which of the following is a selective and differential agar used to identify Enterobacterales?

    <p>MacConkey agar</p> Signup and view all the answers

    Which of the following bacteria is indole-positive?

    <p>Escherichia coli</p> Signup and view all the answers

    What is the function of cytochrome c oxidase?

    <p>It is an enzyme involved in the bacterial electron transport chain.</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Escherichia coli?

    <p>Urinary tract infections, gastroenteritis, meningitis, sepsis, and diarrhea.</p> Signup and view all the answers

    Escherichia coli is the most common and clinically significant Enterobacterales.

    <p>True</p> Signup and view all the answers

    What is the primary cause of neonatal meningitis?

    <p>Escherichia coli</p> Signup and view all the answers

    Escherichia coli is only found in the human gut.

    <p>False</p> Signup and view all the answers

    Escherichia coli has only one serotype.

    <p>False</p> Signup and view all the answers

    What is the most common type of Escherichia coli infection?

    <p>Urinary tract infection</p> Signup and view all the answers

    What are some of the characteristics of Escherichia coli colonies on culture media?

    <p>Circular, smooth, flat, nonviscous colonies with distinct edges, hemolysis on blood agar, and a metallic sheen on different agars.</p> Signup and view all the answers

    What type of fermentation does Escherichia coli exhibit?

    <p>All of the above</p> Signup and view all the answers

    Escherichia coli is indole-negative.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a risk factor for uncomplicated urinary tract infections?

    <p>Indwelling catheters</p> Signup and view all the answers

    Complicated urinary tract infections are more common than uncomplicated urinary tract infections.

    <p>False</p> Signup and view all the answers

    What are some of the common antibiotics used to treat uncomplicated UTIs?

    <p>Fosfomycin and nitrofurantoin.</p> Signup and view all the answers

    What are some of the antibiotics used to treat more complicated or resistant UTIs?

    <p>Trimethoprim/sulfamethoxazole and fluoroquinolones.</p> Signup and view all the answers

    What are the major groups of Escherichia coli strains that cause gastroenteritis?

    <p>Enterotoxigenic (ETEC), Enteropathogenic (EPAC), Enteroaggregative (EAEC), Shiga toxin-producing (STEC), and Enteroinvasive (EIEC).</p> Signup and view all the answers

    What are some of the symptoms of enterotoxigenic Escherichia coli (ETEC) infection?

    <p>Watery nonbloody diarrhea, abdominal cramps, nausea, and vomiting.</p> Signup and view all the answers

    What is the mechanism of pathogenesis for ETEC?

    <p>Plasmid-mediated enterotoxins (heat-stable and heat-liable) that stimulate hypersecretion of fluids and electrolytes in the small intestine, leading to watery diarrhea.</p> Signup and view all the answers

    What is the primary mode of transmission for EPEC?

    <p>Fecal-oral exposure to contaminated food or surfaces.</p> Signup and view all the answers

    What are some of the symptoms of EPEC infection?

    <p>Watery diarrhea and vomiting.</p> Signup and view all the answers

    Explain the pathogenesis of EPEC infection.

    <p>Plasmid-mediated attachment and effacement, where EPEC adheres to epithelial cells in the small intestine and disrupts the microvillus structure, leading to malabsorption and diarrhea. They can also invade epithelial cells lining the colon, leading to destruction of normal mucosal epithelial cells.</p> Signup and view all the answers

    What is the pathogenesis of EAEC infection?

    <p>EAEC bacteria autoagglutinate and adhere to the epithelial cells of the small intestine in a characteristic &quot;stacked bricks&quot; pattern, causing cytokine release, shortening of microvilli, hemorrhage, and decreased fluid absorption.</p> Signup and view all the answers

    STEC infection is commonly associated with consumption of undercooked beef.

    <p>True</p> Signup and view all the answers

    What is the mechanism of pathogenesis for STEC infection?

    <p>The presence of Shiga toxin 1 (Stx1) or 2 (Stx2), which disrupt protein synthesis in host cells.</p> Signup and view all the answers

    What is the most common serotype of STEC associated with severe human disease?

    <p>O157:H7.</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Yersinia pestis?

    <p>Bubonic plague and pneumonic plague.</p> Signup and view all the answers

    Pneumonic plague is more contagious than bubonic plague.

    <p>True</p> Signup and view all the answers

    Yersinia pestis is only transmitted by fleas.

    <p>False</p> Signup and view all the answers

    The Black Death was a pandemic of bubonic plague.

    <p>True</p> Signup and view all the answers

    Which of the following is a clinically important species of Yersinia?

    <p>All of the above</p> Signup and view all the answers

    What are some of the symptoms of Yersinia enterocolitica infection?

    <p>Diarrhea, fever, abdominal pain, and a condition known as &quot;pseudo-appendicitis&quot;.</p> Signup and view all the answers

    Yersinia enterocolitica infection is only found in developing countries.

    <p>False</p> Signup and view all the answers

    What are some of the key characteristics of Klebsiella spp.?

    <p>Non-motile, have large polysaccharide capsules that give them a mucoid appearance, and form wet, heaped, viscous colonies.</p> Signup and view all the answers

    Which of the following Klebsiella spp. is indole-positive?

    <p>K. oxytoca</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Klebsiella spp.?

    <p>Pneumonia, UTIs (cystitis and pyelonephritis), and wound/soft tissue infections.</p> Signup and view all the answers

    What is the name of the gene responsible for carbapenemase production in Klebsiella spp.?

    <p>blaKPC gene.</p> Signup and view all the answers

    The blaKPC gene is only found in Klebsiella pneumoniae.

    <p>False</p> Signup and view all the answers

    Enterobacter spp. are non-motile.

    <p>False</p> Signup and view all the answers

    Which of the following is the most common Enterobacter spp.?

    <p>E. cloacae</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Enterobacter spp.?

    <p>Hospital-acquired infections, pneumonia, UTIs, and wound infections.</p> Signup and view all the answers

    Which of the following is a common clinical species of Citrobacter?

    <p>A and B</p> Signup and view all the answers

    What are some of the key characteristics of Serratia spp.?

    <p>They form small colonies, some of which can be pigmented, and are slow lactose fermenters, often negative for lactose fermentation.</p> Signup and view all the answers

    Which of the following is the most common clinical species of Serratia spp.?

    <p>S. marcescens</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Serratia spp.?

    <p>Pneumonia, bacteremia, and endocarditis.</p> Signup and view all the answers

    What type of beta-lactamase is often associated with resistance to cephalosporins?

    <p>AmpC</p> Signup and view all the answers

    The chromosomal AmpC gene is present in almost all Enterobacter, Citrobacter, and Serratia species.

    <p>True</p> Signup and view all the answers

    Plasmid-mediated AmpC genes are always resistant to antibiotics.

    <p>True</p> Signup and view all the answers

    What are some of the key characteristics of Proteus spp. and Morganella spp.?

    <p>They are motile, slow or non-lactose fermenters, and produce urease.</p> Signup and view all the answers

    Providencia spp. produce urease.

    <p>False</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Proteus spp., Morganella spp., and Providencia spp.?

    <p>UTIs, pneumonia, and bacteremia.</p> Signup and view all the answers

    What are some of the characteristics of Salmonella spp.?

    <p>Motile, ferment glucose and mannose, resistant to bile salts, non-lactose/non-sucrose fermenter, and produce H2S.</p> Signup and view all the answers

    What is the primary mode of transmission for Salmonella spp.?

    <p>Ingestion of contaminated foods and water.</p> Signup and view all the answers

    What are some of the common clinical syndromes associated with Salmonella spp.?

    <p>Gastroenteritis, bacteremia, enteric fever, and asymptomatic colonization.</p> Signup and view all the answers

    What is the most common form of salmonellosis?

    <p>Gastroenteritis.</p> Signup and view all the answers

    Salmonella Typhi is the only species responsible for typhoid fever.

    <p>False</p> Signup and view all the answers

    What is the reservoir for Salmonella Typhi?

    <p>Humans</p> Signup and view all the answers

    What are some of the symptoms of typhoid fever?

    <p>Fever, headache, myalgias, malaise, anorexia, and eventually GI symptoms, bacteremia, colonization of the gallbladder, and re-infection of the intestines.</p> Signup and view all the answers

    What type of agar is commonly used to differentiate between Salmonella spp., Shigella spp., and other gram-negative bacteria?

    <p>Hektoen Enteric Agar</p> Signup and view all the answers

    Shigella spp. are motile.

    <p>False</p> Signup and view all the answers

    Which Shigella species is considered the most serious?

    <p>S. dysenteriae</p> Signup and view all the answers

    What is the primary mechanism of pathogenesis for Shigella spp.?

    <p>Shigella spp. invade M cells in Peyer's patches of the intestine, replicate within the cells, spread through cell-to-cell passage, and ultimately cause cell apoptosis, leading to dysentery.</p> Signup and view all the answers

    What are some of the symptoms of Shigella infection?

    <p>Watery diarrhea, which can progress to mucous/bloody diarrhea, fever, abdominal cramps, and tenesmus.</p> Signup and view all the answers

    Shigella infection requires a high inoculum to cause disease.

    <p>False</p> Signup and view all the answers

    Why is Shigella infection often found in daycares?

    <p>Children in daycares are more likely to be in close contact with each other, increasing the risk of spreading Shigella through fecal-oral transmission.</p> Signup and view all the answers

    Yersinia spp. are primarily associated with human infections.

    <p>False</p> Signup and view all the answers

    What is the most virulent pathogen in the Yersinia genus?

    <p>Yersinia pestis.</p> Signup and view all the answers

    Yersinia entercolitica is a common cause of plague.

    <p>False</p> Signup and view all the answers

    What are some of the symptoms of bubonic plague?

    <p>Inflammation of lymph nodes (buboes), high fever, and bacteremia.</p> Signup and view all the answers

    Pneumonic plague is more common than bubonic plague.

    <p>False</p> Signup and view all the answers

    What is the incubation period for pneumonic plague?

    <p>2-3 days.</p> Signup and view all the answers

    What is the primary mode of transmission for pneumonic plague?

    <p>Respiratory droplets.</p> Signup and view all the answers

    The Black Death pandemic was solely responsible for wiping out 1/3 of Europe's population.

    <p>False</p> Signup and view all the answers

    Yersinia enterocolitica infection can persist for months.

    <p>True</p> Signup and view all the answers

    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 H₂S 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 H₂S.

    Shigella spp.

    • Slender, non-motile bacilli, with convex, circular, transparent colonies.
    • Resistant to bile salts, non-lactose fermenters, and don't produce H₂S.
    • 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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    Gram Negative Aerobes Pt 1 PDF

    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.

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