Podcast
Questions and Answers
How does Salmonella appear on MacConkey's medium, and why?
How does Salmonella appear on MacConkey's medium, and why?
- Green colonies, due to their urease production.
- Dark blue colonies, due to sucrose fermentation.
- Pale yellow colonies, due to their inability to ferment lactose. (correct)
- Bright pink colonies, due to rapid lactose fermentation.
Which characteristic is NOT typical of Salmonella?
Which characteristic is NOT typical of Salmonella?
- Gram-negative
- Non-lactose fermenter
- Spore-forming (correct)
- Motile
What is the primary difference between typhoidal and nontyphoidal Salmonella strains in terms of the diseases they cause?
What is the primary difference between typhoidal and nontyphoidal Salmonella strains in terms of the diseases they cause?
- Typhoidal strains cause bacteremia, while nontyphoidal strains cause septicemia.
- Typhoidal strains primarily cause gastroenteritis, while nontyphoidal strains cause enteric fever.
- Typhoidal strains cause enteric fever, while nontyphoidal strains primarily cause gastroenteritis. (correct)
- There is no significant difference in the diseases caused by typhoidal and nontyphoidal Salmonella.
Salmonella choleraesuis is most likely to cause which condition?
Salmonella choleraesuis is most likely to cause which condition?
A patient presents with symptoms of enteric fever. Which Salmonella species is the MOST likely causative agent?
A patient presents with symptoms of enteric fever. Which Salmonella species is the MOST likely causative agent?
Which of the following is a characteristic shared by both Salmonella typhi and Salmonella typhimurium?
Which of the following is a characteristic shared by both Salmonella typhi and Salmonella typhimurium?
Why is the inability of Salmonella to ferment lactose useful in laboratory diagnosis?
Why is the inability of Salmonella to ferment lactose useful in laboratory diagnosis?
A patient is suspected of having a Salmonella infection. The lab results show Gram-negative bacilli that do not ferment lactose. Which further tests would BEST help confirm the presence of Salmonella typhi specifically?
A patient is suspected of having a Salmonella infection. The lab results show Gram-negative bacilli that do not ferment lactose. Which further tests would BEST help confirm the presence of Salmonella typhi specifically?
On XLD agar, how are Shigella colonies differentiated from other bacteria?
On XLD agar, how are Shigella colonies differentiated from other bacteria?
A patient presents with bloody diarrhea, fever, and abdominal cramps. Which Shigella species is most likely suspected if Shiga toxin is detected?
A patient presents with bloody diarrhea, fever, and abdominal cramps. Which Shigella species is most likely suspected if Shiga toxin is detected?
In the Widal test, what is being measured to diagnose typhoid and paratyphoid fever?
In the Widal test, what is being measured to diagnose typhoid and paratyphoid fever?
What is a key characteristic that differentiates Shigella from Salmonella?
What is a key characteristic that differentiates Shigella from Salmonella?
Why is XLD agar considered a selective medium for Shigella?
Why is XLD agar considered a selective medium for Shigella?
During which week of enteric fever is blood culture the MOST effective diagnostic tool?
During which week of enteric fever is blood culture the MOST effective diagnostic tool?
Which biochemical test result can help differentiate between Salmonella typhi and Escherichia coli?
Which biochemical test result can help differentiate between Salmonella typhi and Escherichia coli?
A microbiology lab is attempting to isolate Salmonella from a mixed culture. Which media would be MOST appropriate for this purpose?
A microbiology lab is attempting to isolate Salmonella from a mixed culture. Which media would be MOST appropriate for this purpose?
Why is dilution a crucial step in blood culture for diagnosing bacteremia and typhoid fever?
Why is dilution a crucial step in blood culture for diagnosing bacteremia and typhoid fever?
A Gram-negative, non-capsulated, non-spore forming bacilli is isolated from a patient's stool sample. The bacteria does not ferment lactose. Which of the following organisms is MOST likely?
A Gram-negative, non-capsulated, non-spore forming bacilli is isolated from a patient's stool sample. The bacteria does not ferment lactose. Which of the following organisms is MOST likely?
What is the PRIMARY purpose of using enrichment media like selenite or tetrathionate broth in stool cultures for Salmonella?
What is the PRIMARY purpose of using enrichment media like selenite or tetrathionate broth in stool cultures for Salmonella?
Which of the following techniques is used to concentrate bacteria from urine samples for culture?
Which of the following techniques is used to concentrate bacteria from urine samples for culture?
A lab technician observes pale yellow colonies on MacConkey's agar after subculturing an enriched stool sample. What is the NEXT step in confirming the presence of Salmonella?
A lab technician observes pale yellow colonies on MacConkey's agar after subculturing an enriched stool sample. What is the NEXT step in confirming the presence of Salmonella?
During a Salmonella outbreak investigation, public health officials are trying to identify potential carriers. Which type of individual poses a risk of spreading Salmonella through contaminated food or water?
During a Salmonella outbreak investigation, public health officials are trying to identify potential carriers. Which type of individual poses a risk of spreading Salmonella through contaminated food or water?
A patient is suspected of being a urinary carrier of Salmonella. After centrifuging the urine sample, on which type of media should the sediment be cultured to selectively isolate Salmonella?
A patient is suspected of being a urinary carrier of Salmonella. After centrifuging the urine sample, on which type of media should the sediment be cultured to selectively isolate Salmonella?
A laboratory is using tetrathionate broth as an enrichment medium. What component of this medium allows Salmonella to outgrow competing bacteria?
A laboratory is using tetrathionate broth as an enrichment medium. What component of this medium allows Salmonella to outgrow competing bacteria?
Individuals who harbor Shigella in their feces can unknowingly spread the bacteria through contaminated food or water.
Individuals who harbor Shigella in their feces can unknowingly spread the bacteria through contaminated food or water.
In the first week of enteric fever, detecting antibodies using the Widal test is the primary diagnostic tool.
In the first week of enteric fever, detecting antibodies using the Widal test is the primary diagnostic tool.
In the third week of enteric fever, sputum culture can be used to isolate Salmonella.
In the third week of enteric fever, sputum culture can be used to isolate Salmonella.
Diluting blood samples enhances bacterial growth by diluting inhibitory substances, such as antigens.
Diluting blood samples enhances bacterial growth by diluting inhibitory substances, such as antigens.
Patient stool is added to an enrichment medium like Mannitol Salt Agar, which promotes Salmonella growth.
Patient stool is added to an enrichment medium like Mannitol Salt Agar, which promotes Salmonella growth.
After incubation of the enrichment medium, a portion of the enriched culture is transferred to blood agar for isolation of Salmonella.
After incubation of the enrichment medium, a portion of the enriched culture is transferred to blood agar for isolation of Salmonella.
Salmonella species are able to ferment both lactose and sucrose, which aids in their rapid identification on selective media like MacConkey agar.
Salmonella species are able to ferment both lactose and sucrose, which aids in their rapid identification on selective media like MacConkey agar.
All strains of Salmonella can cause enteric fever, characterized by systemic symptoms and prolonged fever.
All strains of Salmonella can cause enteric fever, characterized by systemic symptoms and prolonged fever.
Urine samples are filtered to concentrate bacteria in the sediment when detecting urinary carriers.
Urine samples are filtered to concentrate bacteria in the sediment when detecting urinary carriers.
Salmonella choleraesuis is associated primarily with gastroenteritis, similar to Salmonella typhimurium and Salmonella enteritidis.
Salmonella choleraesuis is associated primarily with gastroenteritis, similar to Salmonella typhimurium and Salmonella enteritidis.
Selenite Broth inhibits the growth of other bacteria, allowing Salmonella to thrive because it contains tetrathionate.
Selenite Broth inhibits the growth of other bacteria, allowing Salmonella to thrive because it contains tetrathionate.
The presence of capsules and endospores in Salmonella contributes to their increased virulence and survival in harsh environmental conditions.
The presence of capsules and endospores in Salmonella contributes to their increased virulence and survival in harsh environmental conditions.
Salmonella species are oxidase positive, allowing for differentiation from other Gram-negative bacteria through enzymatic testing.
Salmonella species are oxidase positive, allowing for differentiation from other Gram-negative bacteria through enzymatic testing.
Infection with typhoidal Salmonella is usually self-limiting and does not require antibiotic treatment unless complications arise.
Infection with typhoidal Salmonella is usually self-limiting and does not require antibiotic treatment unless complications arise.
Salmonella produces pink colonies on MacConkey agar due to its ability to ferment the lactose present in the medium.
Salmonella produces pink colonies on MacConkey agar due to its ability to ferment the lactose present in the medium.
The identification of Salmonella involves assessing its motility, Gram-stain characteristics, and fermentation capabilities.
The identification of Salmonella involves assessing its motility, Gram-stain characteristics, and fermentation capabilities.
Salmonella-Shigella Agar (SSA) differentiates Salmonella from Shigella based on lactose fermentation and the production of carbon dioxide.
Salmonella-Shigella Agar (SSA) differentiates Salmonella from Shigella based on lactose fermentation and the production of carbon dioxide.
Xylose Lysine Desoxycholate (XLD) Agar inhibits Gram-positive bacteria and differentiates Salmonella and Shigella based on their ability to ferment mannose and lysine.
Xylose Lysine Desoxycholate (XLD) Agar inhibits Gram-positive bacteria and differentiates Salmonella and Shigella based on their ability to ferment mannose and lysine.
Salmonella typhi is Indole-positive, Methyl Red-positive, Voges-Proskauer-negative, Citrate-positive, Urease-negative, and produces $H_2S$.
Salmonella typhi is Indole-positive, Methyl Red-positive, Voges-Proskauer-negative, Citrate-positive, Urease-negative, and produces $H_2S$.
The Widal test measures H and O agglutinins specifically for E. coli and Klebsiella.
The Widal test measures H and O agglutinins specifically for E. coli and Klebsiella.
Shigella are motile, non-lactose fermenting members of the Enterobacteriaceae family.
Shigella are motile, non-lactose fermenting members of the Enterobacteriaceae family.
Shigella is classified into four species or groups: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Salmonella sonnei.
Shigella is classified into four species or groups: Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Salmonella sonnei.
Shigella is the causative agent of bacillary dysentery, characterized by watery diarrhea, fever, and mouth sores.
Shigella is the causative agent of bacillary dysentery, characterized by watery diarrhea, fever, and mouth sores.
Shigella dysenteriae type 1 produces Shiga toxin, a potent heat-stable endotoxin.
Shigella dysenteriae type 1 produces Shiga toxin, a potent heat-stable endotoxin.
Flashcards
Salmonella Key Features
Salmonella Key Features
Gram-negative, motile bacilli that do not form capsules or spores. They don't ferment lactose or sucrose and are urease and oxidase negative.
Salmonella on MacConkey
Salmonella on MacConkey
Pale yellow colonies that occur because Salmonella can't ferment lactose.
Typhoidal Salmonella
Typhoidal Salmonella
Cause enteric fever, including typhoid fever (S. typhi) and paratyphoid fever (S. paratyphi A, B, C).
Nontyphoidal Salmonella
Nontyphoidal Salmonella
Signup and view all the flashcards
Salmonella choleraesuis
Salmonella choleraesuis
Signup and view all the flashcards
Salmonella and Shigella
Salmonella and Shigella
Signup and view all the flashcards
Master Laboratory Diagnosis
Master Laboratory Diagnosis
Signup and view all the flashcards
Understand Disease Causation
Understand Disease Causation
Signup and view all the flashcards
Salmonella Fecal Carriers
Salmonella Fecal Carriers
Signup and view all the flashcards
Salmonella Urinary Carriers
Salmonella Urinary Carriers
Signup and view all the flashcards
Blood Culture (Week 1)
Blood Culture (Week 1)
Signup and view all the flashcards
Widal Test (Week 2)
Widal Test (Week 2)
Signup and view all the flashcards
Stool/Urine Culture (Week 3)
Stool/Urine Culture (Week 3)
Signup and view all the flashcards
Blood Culture Dilution
Blood Culture Dilution
Signup and view all the flashcards
Enrichment Medium (Stool)
Enrichment Medium (Stool)
Signup and view all the flashcards
Enrichment Media
Enrichment Media
Signup and view all the flashcards
Selective Media
Selective Media
Signup and view all the flashcards
Salmonella-Shigella Agar (SSA)
Salmonella-Shigella Agar (SSA)
Signup and view all the flashcards
Xylose Lysine Desoxycholate (XLD) Agar
Xylose Lysine Desoxycholate (XLD) Agar
Signup and view all the flashcards
Widal Test
Widal Test
Signup and view all the flashcards
Shigella Key Features
Shigella Key Features
Signup and view all the flashcards
Shigella Classification
Shigella Classification
Signup and view all the flashcards
Shigella's role
Shigella's role
Signup and view all the flashcards
Shiga Toxin
Shiga Toxin
Signup and view all the flashcards
Salmonella
Salmonella
Signup and view all the flashcards
Shigella
Shigella
Signup and view all the flashcards
Salmonella Characteristics
Salmonella Characteristics
Signup and view all the flashcards
Salmonella & Lactose
Salmonella & Lactose
Signup and view all the flashcards
Typhoidal Salmonella Diseases
Typhoidal Salmonella Diseases
Signup and view all the flashcards
Nontyphoidal Salmonella Disease
Nontyphoidal Salmonella Disease
Signup and view all the flashcards
Bacteremia/Septicemia
Bacteremia/Septicemia
Signup and view all the flashcards
Selenite Broth
Selenite Broth
Signup and view all the flashcards
SSA Use
SSA Use
Signup and view all the flashcards
XLD Agar Function
XLD Agar Function
Signup and view all the flashcards
Widal Test Aim
Widal Test Aim
Signup and view all the flashcards
Widal Test Principle
Widal Test Principle
Signup and view all the flashcards
Shigella motility
Shigella motility
Signup and view all the flashcards
XLD for Shigella
XLD for Shigella
Signup and view all the flashcards
Progression of Dysentery
Progression of Dysentery
Signup and view all the flashcards
Shigella on XLD agar
Shigella on XLD agar
Signup and view all the flashcards
Study Notes
- Salmonella and Shigella are significant bacterial pathogens causing various human diseases.
- Key aspects covered include their characteristics, identification, lab diagnosis, and associated illnesses.
Learning Objectives
- Key traits of Salmonella and Shigella differentiate them from other bacteria.
- Comprehend conditions caused by Salmonella and Shigella, like typhoid fever, dysentery, and gastroenteritis.
- Foster skills for diagnosing these diseases via lab techniques.
Salmonella Key Features
- Salmonella: Gram-negative bacilli.
- Motile but non-capsulated, and non-spore forming.
- Non-lactose/non-sucrose fermenters, indole-negative, urease and oxidase negative.
Salmonella Cultural Characteristics
- On MacConkey's medium, Salmonella forms pale yellow colonies due to lactose fermentation inability.
- This feature assists in Salmonella identification.
Typhoidal Salmonella
- Causes enteric fever, including typhoid fever via Salmonella typhi.
- Paratyphoid fever results from Salmonella paratyphi A, B, and C strains.
Nontyphoidal Salmonella
- Primarily causes gastroenteritis, commonly known as food poisoning.
- Examples: Salmonella typhimurium and Salmonella enteritidis.
Bacteremia and Septicemia
- Salmonella choleraesuis can lead to bloodstream infections: bacteremia and septicemia.
Salmonella Carriers
- Individuals carrying Salmonella in feces/urine can unknowingly spread it via contaminated food/water.
Laboratory Diagnosis of Enteric Fever
- Week 1: Blood culture is the primary diagnostic tool.
- Week 2: Antibody detection using the Widal test becomes relevant.
- Week 3: Stool or urine culture isolates Salmonella.
Blood Culture
- Blood dilution enhances bacterial growth and reduces inhibitory substances.
- Dilution boosts Salmonella isolation, crucial for diagnosing bacteremia and typhoid fever at a 1:10 dilution.
Stool Culture
- Stool samples are added to selenite/tetrathionate broth to boost Salmonella growth.
- Incubate the enrichment medium at 37°C for Salmonella multiplication.
- Post-incubation, transfer a portion to selective media like MacConkey's for isolation.
- Pale yellow colonies on MacConkey's are confirmed via biochemical tests/slide agglutination.
Urine Culture
- Centrifuge urine samples to concentrate bacteria in the sediment.
- Culture the sediment on MacConkey's to isolate Salmonella.
Enrichment Media
- Selenite broth inhibits other bacteria, promoting Salmonella thriving.
- Tetrathionate broth also inhibits competitors, allowing Salmonella to outgrow them.
Selective media
- Salmonella-Shigella Agar differentiates based on lactose fermentation and hydrogen sulfide production.
- XLD agar inhibits Gram-positive bacteria and differentiates Salmonella/Shigella based on xylose/lysine fermentation.
Biochemical Reactions
- Indole, Citrate, and Urease tests yield Negative results.
- Methyl Red and H2S production tests are Positive.
Shigella Key features
- Shigella: non-motile and non-lactose fermenting bacteria in the Enterobacteriaceae family.
- Gram-negative, non-capsulated, and non-spore forming bacilli.
Shigella Classification
- Divided into four species/groups based on biochemical/antigenic structures.
- Includes Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei.
Shigella Symptoms
- The causative agent of bacillary dysentery, marked by bloody diarrhea, fever, and abdominal cramps.
- Progresses from watery diarrhea to dysentery with scant stool containing blood, mucus, and pus.
Selective media for shigella isolation
- XLD agar isolates Shigella from clinical specimens.
- Shigella cannot ferment xylose and forms red colonies; other bacteria produce different colors.
Shiga Toxin
- Shigella dysenteriae type 1 produces Shiga toxin, a potent heat-labile exotoxin worsening dysentery.
- Damages intestinal cells, leading to bloody diarrhea and other symptoms.
Shigella Characteristics and Transmission
- Biochemically inert, meaning limited positive reactions.
- Humans are the only known reservoir.
- Transmitted via the fecal-oral route, through contaminated food/water/contact with infected individuals.
Shigella Biochemical test results
- All tests show negative results except TSI
- Indole, Methyl Red, Voges-Proskauer, Citrate, Urease, and Lysine Iron Agar are all negative.
- H2S production is also negative
- TSI : K/A, no H2S.
Shigella Mannitol Fermentation
- Species categorized by mannitol fermentation abilities.
- Shigella dysenteriae is a non-mannitol fermenter.
- Shigella flexneri, Shigella boydii, and Shigella sonnei all ferment mannitol.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore Salmonella and Shigella, two bacterial pathogens causing human diseases. This lesson covers their characteristics, identification, and lab diagnosis. Learn about typhoid fever, dysentery, and gastroenteritis caused by these bacteria.
