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Questions and Answers
What is the primary action of the heat labile toxin (LT) in the small intestine?
What is the primary action of the heat labile toxin (LT) in the small intestine?
Which of the following infections is commonly associated with fimbriae?
Which of the following infections is commonly associated with fimbriae?
What type of diarrhea is caused by the heat stable toxin (ST)?
What type of diarrhea is caused by the heat stable toxin (ST)?
Which clinical condition can lead to fatal outcomes after surgery?
Which clinical condition can lead to fatal outcomes after surgery?
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What is the role of guanylate cyclase activated by Heat Stable toxin (ST)?
What is the role of guanylate cyclase activated by Heat Stable toxin (ST)?
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Which of the following is a characteristic of pyogenic infections?
Which of the following is a characteristic of pyogenic infections?
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What mechanism results in increased secretion of chloride into the bowel lumen during the action of LT?
What mechanism results in increased secretion of chloride into the bowel lumen during the action of LT?
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Which type of diarrhea is associated with infantile and bloody conditions?
Which type of diarrhea is associated with infantile and bloody conditions?
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What characteristic is common to most members of the Bacteriaceae family?
What characteristic is common to most members of the Bacteriaceae family?
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Which of the following is associated with significant human diseases caused by members of the Bacteriaceae family?
Which of the following is associated with significant human diseases caused by members of the Bacteriaceae family?
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Which of the following bacteria is categorized as a non-lactose fermenter within the Bacteriaceae family?
Which of the following bacteria is categorized as a non-lactose fermenter within the Bacteriaceae family?
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What temperature range is optimal for the growth of E.coli?
What temperature range is optimal for the growth of E.coli?
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What term best describes Escherichia coli in its motility characterization?
What term best describes Escherichia coli in its motility characterization?
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What biochemical test results indicate that E.coli is positive for Indole?
What biochemical test results indicate that E.coli is positive for Indole?
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What type of infections can E. coli represent as an endogenous source?
What type of infections can E. coli represent as an endogenous source?
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What is the significance of clinical samples from patients infected with members of the Bacteriaceae family?
What is the significance of clinical samples from patients infected with members of the Bacteriaceae family?
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Which antigen type is associated with the flagellar structure of E.coli?
Which antigen type is associated with the flagellar structure of E.coli?
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Which of the following represents a common feature of the Bacteriaceae family in clinical isolation?
Which of the following represents a common feature of the Bacteriaceae family in clinical isolation?
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How many different serotypes of E.coli have been identified based on O-Ag?
How many different serotypes of E.coli have been identified based on O-Ag?
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Which toxin is specifically associated with the pathogenesis of diarrhea caused by E.coli?
Which toxin is specifically associated with the pathogenesis of diarrhea caused by E.coli?
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What role do pili (fimbriae) serve in the E. coli bacterium?
What role do pili (fimbriae) serve in the E. coli bacterium?
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What is the primary method used for serotyping E.coli based on O and H antigens?
What is the primary method used for serotyping E.coli based on O and H antigens?
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What is a key requirement for the diagnosis of infections caused by members of the Bacteriaceae family?
What is a key requirement for the diagnosis of infections caused by members of the Bacteriaceae family?
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Which bacteria is commonly recognized as an opportunistic pathogen within the Bacteriaceae family?
Which bacteria is commonly recognized as an opportunistic pathogen within the Bacteriaceae family?
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Which type of E.coli virulence factor is the LPS surface O antigen associated with?
Which type of E.coli virulence factor is the LPS surface O antigen associated with?
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What is the biochemical result for Citrate in E.coli?
What is the biochemical result for Citrate in E.coli?
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What characteristics do colonies of E.coli exhibit when grown on MacConkey agar?
What characteristics do colonies of E.coli exhibit when grown on MacConkey agar?
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Which of the following is NOT a method used for E.coli typing?
Which of the following is NOT a method used for E.coli typing?
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Study Notes
Introduction to Enterobacteriaceae
- This family of bacteria is a large group
- Most are non-pathogenic, normal flora
- Some are opportunistic pathogens associated with human diseases
- Members are commonly found in soil and water, as well as in the intestinal tracts of animals and humans.
- They are Gram-negative bacilli
- They have similar gram stain characteristics
- They are associated with various human diseases, like GIT infection, UTI, wound infections, and respiratory tract infections.
Family Members
- Escherichia coli (E.coli) is the most commonly isolated member.
- Other members include Klebsiella, Enterobacter, Citrobacter, Serratia, Pantoea, Salmonella, Shigella, Proteus, Morganella morganii, Providencia, and Yersinia.
- Some are lactose fermenting, others are non-lactose fermenting
E.coli Species
- E.coli is a motile, non-spore-forming, non-capsulated bacterium
- E.coli is commonly found in the gastrointestinal tracts of humans and animals.
- Different E.coli serotypes can cause various infections, each requiring different diagnostic methods.
- E. coli species are distinguished by their specific antigens
Identification-Culture and Colony Characters
- E.coli is aerobic and facultative anaerobic
- Optimum temperature range is 10-40°C (1-37°C)
- Can grow on nutrient agar
- Nutrient agar colonies are typically large, 2-3mm, circular, opaque, gray, or white.
- Blood agar and MacConkey's agar are used for identifying E.coli's traits
- Gram's stain, Beta-haemolytic traits identified on Blood agar, MacConkey's Pink flat-due to L.F
- Biochemical tests are used for more specific identification.
Identification-Biochemical Reactions
- Various biochemical tests are used, including IMViC, Voges-Proskauer, Methyl Red, Citrate, Triple Sugar Iron, and Urease tests
- E.coli's tests give: Indole (I)-Positive, Methyl red (MR)-Positive, Voges-Proskauer (VP)-Negative, and Citrate (C)-Negative.
Antigenic Diversity
- E.coli has various antigens, including H antigens (flagellar), O antigens (somatic), and K antigens (capsular).
- Different antigens and their variations are used to differentiate the serotypes of the bacteria
- O Antigen, commonly used in conjunction with K antigen serotyping, aid in epidemiological studies.
- K-Ag and F-Ag are associated with Urinary Tract Infections (UTIs)
Serotype and Typing Method
- Over 700 serotypes of E.coli have been identified
- Serotyping is based on O and H antigens
- Various typing methods are used to identify E.coli serotypes
Factors of Pathogenicity and Virulence
- Surface antigens (including LPS, envelope/K-Ag, fimbriae) play a role in infection
- Toxins (enterotoxins, e.g., LT, ST, VT and verocytotoxins/shiga-like toxins, and hemolysins) affect pathogenicity
- Specific characteristics of the various E.coli toxins lead to symptoms like watery diarrhea, intestinal infections, and urinary tract infections
Heat Labile Toxin (LT)
- LT is heat-labile
- Binds to specific GM1 gangliosides receptors on small intestine epithelial cells
- Stimulates cAMP production, leading to Cl secretion
- Resulting in secretory diarrhea
Heat Stable Toxin (ST)
- ST is heat-stable
- Activates guanylate cyclase, leading to cGMP production
- cGMP inhibits sodium chloride co-transport.
- Resulting in diarrhea
Pathogenicity/Clinical Infections
- E.coli is associated with various infections, including diarrhea, urinary tract infections (UTIs), wound infections, and septicemia
Urinary Tract Infections (UTIs)
- E.coli is a leading cause of UTIs.
- Predisposing Factors include female gender, pregnancy, sexual activity, urinary tract abnormalities, and catheters.
- Symptoms include frequent urination, pain, and cloudy/bloody urine.
- Pathogenesis involves colonization, multiplication, and immune response in the urinary tract.
Symptoms of UTI
- Pain, burning sensation, or frequent urination, cloudy urine, strong smelling urine, pelvic pain
- Additional symptoms relating to kidney involvement (high fever, nausea, vomiting, shaking, chills).
Pathogenesis of UTIs
- E.coli infections often arise from contamination of the periurethral areas (e.g., fecal matter or poor hygiene).
- The bacteria then adhere to and penetrate the bladder wall, increasing in numbers and leading to the symptoms associated with UTIs
Diarrheal and Dysentery Pathotypes
- Some E.coli infections come from different classifications like EPEC, ETEC, EIEC, EHEC, and EAEC
- The specific variations of each lead to different symptoms like diarrhea
EPEC-Enteropathogenic E.coli
- Usually associated with diarrhea in infants and children
- Attaches to small intestinal mucosa, damaging the brush border of microvilli
ETEC-Enterotoxigenic E.coli
- Endemic in tropical regions of developing countries
- Causes mild diarrhea to cholera, traveller's diarrhea
- Produces enterotoxins (LT and ST) which cause diarrhea
EIEC-Enteroinvasive E.coli
- Invasive diseases are similar to Shigellosis (Dysentery)
- Causes diseases like Shigellosis-dysentery (non-motile and non-lactose fermenters).
EHEC-Enterohemorrhagic E.coli
- Symptoms range from mild diarrhea to severe hemolytic uremic syndrome (HUS).
- Produces verocytotoxins (VT) which can cause serious health complications
EAEC-Enteroaggregative E.coli
- Associated with persistent diarrhea in developing countries
- Forms aggregates on HEp2 cells, causing the stacked-brick form.
Pyogenic infection and Septicemia
- E.coli causes various infections like wound infections, peritonitis, biliary tract infections, and meningitis (newborns).
- Sepsis caused by E.coli can lead to serious conditions like septic shock and systemic inflammatory response syndrome (SIRS).
Summary
- E. coli is a significant pathogen, causing a wide range of infections.
- UTIs, Diarrhea, and septicemia are commonly linked to E.coli.
- Specific strains show various virulence factors leading to different symptoms.
- Prevention of cross contamination is crucial.
Klebsiella
- Klebsiella species are gram-negative, non-motile, non-spore-forming rods.
- They are encapsulated, often causing mucoid colonies.
- They are opportunistic pathogens.
Clinical Significant Species of Klebsiella
- K.pneumoniae (important species), K.oxytoca, K.planticola, K.ornithinolytica, K.ozaenae, K.pneumoniae, K.rhinoscleromatis, K.aerogens
Morphological Features of Klebsiella
- Gram-negative, non-motile, non-sporing bacilli
- Often capsulated, producing mucoid colonies
- Size range from 1 to 2um in length and 0.5 to 0.8um in width
- Visible Capsule staining (Quelling Reaction)
Cultural and Biochemical Characteristics of Klebsiella
- Optimum temperature 37°C, pH 7–2 - 7–.4
Infections Caused by Klebsiella
- Respiratory infections may occur
- Urinary tract infections (UTIs), wounds commonly associated infections
- Atrophic Rhinitis, ozaena, Rhinoscleroma
- Meningitis and pyogenic infections.
Other Enterobacteriaceae genera
- Various other genera often associated with E.coli infections or opportunistic pathogenic infections include Enterobacter, Serratia, Edwardsiella tarda, Citrobacter, Hafnia, and Erwinia
Proteus
- Proteus is a gram-negative species
- Pleomorphic and actively motile
- Possesses Peritrichous flagella
- Nonsporing and non-capsulated
Proteus Morphological Features
- Gram-Negative coccobacilli
- Pleomorphic
- Size- 1-3μ X 0.6μ
- Long filaments up to 80µ
- Active motile-peritrichous flagella
Proteus Cultural characteristics
- Growth can occur in aerobic or facultative anaerobic environments
- Often has a seminal or fishy odour
- Colonies sometimes appear as a swarm on agar
- Swarming is a result of chemotaxis (migration of bacteria towards a chemoattractant).
Proteus Biochemical Reactions
- L-Negative, G-Positive, M-Negative, S-Negative, I-Variable
- Motility positive, VP-Negative, Citrate-Variable, Urease-Positive, TSI-alkaline with H2S
Proteus Pathogenesis
- Causes UTIs, more serious infections compared to E.coli.
- Causes wound infections and other pyogenic infections.
- Causes bacterial ammonia production and precipitation of phosphates leading to calcium formation in the urinary tract, resulting in calculus formation.
Shigella
- Shigella is a genus of bacteria causing bacterial dysentery
- These are gram-negative bacilli, non-motile, non-spore forming; nonspecific shape.
- Four species of Shigella: dysenteriae, flexneri, boydii, sonnei
- Shigellae are relatively small and are only 2-4um × 0.6um in size
Shigella Morphological Features
- Gram-negative
- Small, rod-shaped bacteria
- Nonmotile and non-spore-forming
- Non-capsulated
- Specific stains showing fimbriae (pili)
Shigella Cultural Characteristics
- Aerobic and facultative anaerobic bacteria that grow well at their optimal pH and temperature.
Shigella Biochemical Reactions
- Oxidase-Negative
- Indole-Variable for Shigella dysenteriae types 1 -
- Methyl Red-Positive
- VP-negative
- Urease-negative
- Mannitol-fermented by all, except Sh.dysenteriae
Shigella Serotypes
- Sh.dysenteriae (Serogroup A, 1-12), Sh.flexneri (Serogroup B, 1-6 with 15 subtypes), Sh.boydii (Serogroup C, 1-18) and Sh.sonnei (Serogroup D,1)
Shigella Pathogenesis and Virulent Factors
- Infection occurs through ingestion
- Bacteria invade colon mucosa cells
- Infections result in inflammation and dysentery with abdominal cramps, fever, bloody diarrhea (dysentery with bloody diarrhea), and in extreme cases, hemolytic uremic syndrome (HUS).
Shigella Mode of Transmission
- Transmission primarily through the fecal-oral route (e.g., contaminated food/water or person-to-person contact)
- Vectors like flies can contribute to transmission.
Shigella Prevention and Control
- Shigella prevention centers around hygiene practices: proper hand washing, waste disposal, and access to safe drinking water.
- Vaccines may become available, but careful monitoring and control of susceptible populations is crucial
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Description
Explore the fascinating family of Enterobacteriaceae, a large group of bacteria primarily found in soil, water, and the intestines of animals and humans. While many members are part of the normal flora and non-pathogenic, some are opportunistic pathogens linked to various human diseases. This quiz covers key species like E.coli and their characteristics.
