GASTROINTESSTINAL- DETECTION, ORGANISM PATHOGENICITY, SEROTYPING, DIRECT
Serotypes of Salmonella are differentiated by various antigens found within the organism. All of the following antigens are used to serotype Salmonella EXCEPT?
F1 antigen
One of the key biochemical characteristics by which Escherichia coli serogroup O157 can be screened from stool specimens is?
Failure to ferment sorbitoL
A patient presents to the emergency room with hemorrhagic diarrhea. A stool specimen was sent to the microbiology laboratory for culture. The specimen was plated on blood agar, MacConkey (MAC) agar, and Sorbitol MacConkey (SMAC) agar. A Gram-negative, oxidase negative rod (bacilli) grew as a lactose fermenter on the MacConkey agar and as clear colonies on Sorbitol MacConkey agar. Biochemical testing revealed the organism was lysine decarboxylase positive and did not produce hydrogen sulfide (H2S). Which organism is suspected?
Escherichia Coli possibly 0157:H7
Shigella species generally exhibit which of these characteristics?
Non-motile
The likelihood of colonization and/or infection with Clostridium difficile is enhanced by all of the following except:
The patient has been previously treated at an orthopedic sports clinic
Two techs performed E.coli O157:H7 serotyping on a suspected colony. The serotyping uses the O157 somatic antigen as the target for agglutination. One tech performed quality control and patient samples by using a suspension of the colony and latex reagent. The results reported by the tech were positive. The second tech also did the serotyping using quality control and patient samples by using a suspension of colony, latex reagent, and the isolate suspension with the negative control. The second tech's results were negative. Quality control passed in all testing. Why did the techs obtained different results for the serotyping? Category: Analytical Procedures for Bacteriology - Gastrointestinal - Serotyping of E.coli, Salmonella, Shigella
The second tech tested the suspension with negative control
When serotyping Salmonella, Shigella, and Escherichia coli 0157:H7, typing should be performed from a non-sugar-containing medium, such as 5% sheep blood agar. The reason for this is which of the following?
To prevent false positive results
Which of the following organisms are Gram negative?
Vibrio
What tribe is Morganella morganii in?
Proteeae
Which statement about assays for the antigenic detection of both Clostridium difficile toxins A and B is TRUE?
The antigenic assays give rapid results.
Illustrated in this photograph is the surface of a thiosulfate citrate bile sucrose (TCBS) agar plate which are growing colonies of an unknown bacterial species from a diarrheal stool specimen. The most likely identification is:
Vibrio cholerae
Which of the following is only observed in Salmonella infections and not in Shigella infections?
Animals serve as a reservoir of infection.
Which one of the following statements about Campylobacter jejuni is false?
It does not require special incubation conditions to grow in culture.
Which culture medium is specifically formulated to recover Salmonella typhi from stool specimens?
Bismuth sulfite agar
A stool culture showing increased number of fecal leukocytes would correlate with an infection of which of the following species?
Campylobacter jejuni
Which one of the following statements about E.coli O157:H7 is false?
It ferments sorbitol rapidly
All of the following statements concerning Clostridium difficile are true, EXCEPT?
It is an aerobic organism.
The recovery of this bacterial species from diarrhea stool specimens requires the use of selective culture media such as Butzler selective media or Skirrow blood agar incubated at 42° C in an atmosphere of 5% oxygen, 10% CO2, and 85% nitrogen. Growth on Skirrow blood agar as illustrated in the upper image are confluent smooth non-hemolytic colonies growing along the streak line with lateral extensions (arrows). Slender, long branching, S-shaped Gram negative rods are observed on Gram stain, as observed in the lower image. Positive reactions for oxidase, indoxyl, and hippurate provide for a more definitive identification. With these observations, select the name of this isolate.
Campylobacter jejuni
Which of the following is a selective media recommended for the isolation of Clostridium difficile?
Cefoxitin-cycloserine-fructose agar (CCFA)
Which of the culture media listed is selective for the isolation of Yersinia enterocolitica in stool samples?
Cefsulodin-Irgasan-Novobiocin (CIN)
Various methods have been employed for detection of Clostridium difficile disease, which method is the gold standard for detection?
Cell cytotoxicity neutralization assay (CCNA)
A patient presents at the ER with severe diarrhea and dehydration, marked with rice water stool. The patient has travel history to India. A stool culture was obtained and grew comma-shaped, gram negative bacilli. What is the most likely diagnosis for this patient?
Cholera
Rice water stools that are most commonly due to ingestion of contaminated water and have been a major public health concern for centuries, exhibit colonies on TCBS agar consistent with those in the image to the right. These colonies are caused by a condition called:
Cholera
This member of the Enterobacteriaceae was isolated from a stool specimen and gave the following biochemical reactions: TSI: K/A, no gas, no H2S Citrate: Positive Lysine decarboxylase: Negative Ornithine decarboxylase: Positive Indole: Negative This organism agglutinated in Group D Shigella antiserum. All of the above biochemical results are consistent with this identification, EXCEPT?
Citrate
The irregular-sized, gray-white colonies, with irregular margins, as shown in the image to the left in the upper composite photograph, were recovered from a stool specimen in a case of antibiotic associated colitis. The colonies are flat, gray-white and spreading with irregular margins. Some patients with this infection develop pseudomembanous colitis that can be life threatening. Growth is enhanced when Cycloserine-cefoxitin-fructose agar (CCFA) is used, as seen in upper right photograph. The observation of elongated, Gram positive bacilli with distinctive subterminal and central spores in Gram stain mounts provides for a presumptive identification. Additional key identifying reactions is the absence of lipase and lecithinase and a chartreuse pigment under fluorescence light. With these observations, select the presumptive identification of this isolate.
Clostridioides difficile
Which bacterial species listed is a select agent, which is capable of producing an extremely potent, lethal neurotoxin?
Clostridium botulinum
A recto-sigmoidoscopy revealed pseudomembranes in a patient with severe diarrhea following prolonged treatment with ampicillin. Which of the following organisms is MOST likely to be isolated?
Clostridium difficile
Which of the following is the bacterial agent associated with antibiotic-associated pseudomembranous colitis?
Clostridium difficile
Which of the following organisms is responsible for myonecrosis with gas gangrene, food poisoning as well as necrotizing enteritis, a life threatening that causes ischemic necrosis of the jejunum?
Clostridium perfringens
The following is a spore-forming anaerobe that is associated with neutropenic enterocolitis:
Clostridium septicum
The serum medium and methylene blue stain originally described by Loeffler are both helpful in the identification of:
Corynebacterium diphtheriae
Which statement about bacterial culture for Clostridioides (Clostridium) difficile is TRUE?
Culture on appropriate media provides an effective means of recovering the organism
Which of the following is the best media for recovery and presumptive identification of Clostridioides (formerly Clostridium) difficile in suspected cases of pseudomembraneous colitis?
Cycloserine-cefoxitin fructose agar (CCFA)
The following Clostridium difficile virulence factor is significant in the cause of antibiotic-associated pseudomembranous colitis:
Cytotoxin A or B
A stool from a 2-year-old girl grew clear colonies on MacConkey agar, red colonies on XLD (without black centers), and green colonies on HE (without black centers). It is ornithine positive and indole negative. It should agglutinate in antisera of which serogroup of the somatic O antigen?
D
Which of the following statements is correct regarding the glutamate dehydrogenase (GDH) assay for Clostridium difficile?
Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state
Which of the following statements is correct regarding the glutamate dehydrogenase (GDH) assay for Clostridium difficile?
Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state.
Which of the following is the most commonly encountered enterococcal species?
Enterococcus faecalis
Illustrated in the photograph to the right is the growth of bacterial colonies on blood and MacConkey agars. The media on the left with the red pigmentation on MacConkey agar indicates lactose fermentation. Note the sorbitol MacConkey agar plate on the right, which are growing non-pigmented, gray-white colonies. The isolate presented in this exercise is representative of the bacterial species that have been recovered from stool specimens in several outbreaks of patients with diarrhea following ingestion of contaminated ground beef. Which of the following is the identification of this isolate?
Enterohemorhragic E.coli (EHEC)
A stool culture is received and inoculated to sorbitol MacConkey agar, where is exhibits reddish-pink colonies. Based on this colony morphology, which one of the organisms below can you rule out?
Escherichia coli O157:H7
One of the key biochemical characteristics by which Escherichia coli serogroup O157 can be screened from stool specimens is?
Failure to ferment sorbitol
Which of the following conditions is associated with a typical Bacillus cereus infection?
Food borne enteritis
A microbiologist was surprised when he could not recover Helicobacter pylori from gastric biopsies in which organisms were seen in the tissue sections. He was advised to switch from the Campy BAP selective medium to Skirrow's blood agar because the latter is:
Free of cephalothin
A new tech has a presumptive Salmonella species via biochemical identification on a stool culture. To confirm, serological testing is performed. The serological testing is negative and the quality control which was run simultaneously passed. What should the tech do next?
Heat a suspension of the organism and then repeat the serological testing
A new tech has a presumptive Shigella species via biochemical identification on a stool culture. To confirm, serological testing is performed. The serological testing is negative and the quality control which was run simultaneously passed. What should the tech do next?
Heat a suspension of the organism and then repeat the serological testing
When serotyping Salmonella typhi, false negative reactions can occur when testing. For example, a Salmonella typhi isolate tested Vi antiserum positive and O antiserum negative. What should be done next?
Heat specimen and repeat O antiserum test
A microbiologist was performing Shigella serotyping on a probable Shigella isolate and the organism did not serotype. The microbiologist was adamant that the organism was a Shigella species because it was lactose negative on Hekton-Enteric agar and non-motile in motility agar. What should the microbiologist do to ensure that false negative testing did not occur?
Heat specimen for 15 minutes and repeat testing
Which of the following culture media bests supports the growth/identification of Salmonella species?
Hektoen enteric agar
A culture was performed on a stool sample. After growth was obtained on the blood agar plate, the gram stain showed curved gram negative rods. The oxidase, catalase, and urease were positive. What is the most likely bacterial identification?
Helicobacter pylori
Illustrated in this photograph is an H & E-stained section of a gastric biopsy obtained from a patient with suspected peptic ulcer disease. Based on the biopsy findings, the bacterial species that would most likely be recovered is:
Helicobacter pylori
The bacterial species presented here serves as the causative agent of active chronic gastritis of the lower pyloric antrum of the stomach with the complications of peptic ulcer disease and less commonly carcinoma. Small, curved, plump bacilli are seen on stains of tissue sections obtained from infected intestinal mucosa as illustrated in these photomicrographs. This ulcer and carcinoma producing bacterium can be presumptively identified by the use of the urea breath test in which strong urease produced by this bacterial species is detected by capturing radioactive labeled CO2 in the exhaled breath from an infected patient. From these observations, select the causative bacterial species.
Helicobacter pylori
The organism seen in the image is found in the stomach mucosa and presumptive identification is often obtained from a positive urease test. Select the organism below.
Helicobacter pylori
Which of the following species of bacteria is positive for rapid urease production, as demonstrated by a color change in urea agar from yellow to pink within two hours?
Helicobacter pylori
A stool specimen can be suspected of harboring Vibrio cholerae if it possess which of the following characteristics?
If the stool is watery with a high pH and flecks of mucus.
Which one of the following statements about Campylobacter jejuni is false?
It does not require special incubation conditions to grow in culture
A gram-negative rod from a stool culture produces red colonies with black centers on xylose lysine decarboxylase (XLD) agar. When the organism is inoculated to triple sugar iron agar (TSIA) and lysine iron agar (LIA), it should appear as which of the sets of tubes shown in the image?
Left
Which spirochete is a causative agent of human disease and is acquired through contact with the urine of carrier animals?
Leptospira interrogans sensu stricto
Of the organisms listed, which is most likely to be contracted following consumption of unpasteurized milk?
Listeria monocytogenes
Which bacterial species is a common agent of neonatal bacteremia?
Listeria monocytogenes
All of the organisms below are known to cause gastroenteritis, EXCEPT:
Moraxella catarrhalis
In the Escherichia coli 0157:H7 serotype. The 0157 portion of the serotype refers to which of the following?
O somatic antigen
Which one of the following results is typical of Campylobacter jejuni?
Optimal growth at 42 ºC
Which of the following describes the flagella on the bacterium in in image B?
Peritrichous
The cytochrome oxidase-positive bacterial species that is DNAse negative, ornithine decarboxylase positive, and is associated with gastroenteritis in children after the ingestion of contaminated water is most likely:
Plesiomonas shigelloides*
What virulence factor is not inherent to bacterium?
Production of opsonins
Which of the following stool pathogens would demonstrate the following reactions: TSI: A/A with H2S production LIA: R/A
Proteus spp.
The following statements regarding the cell cytotoxicity neutralization assay (CCNA) for Clostridiodes (formerly Clostridium) difficile are correct EXCEPT?
Provides rapid results
Illustrated in this photomicrograph of a gastric biopsy specimen are a few thin, curved and S-shaped bacteria (arrows). This picture is suspicious for Helicobacter pylori. An additional test helpful in confirming this identification is:
Rapid urease
A 62-year-old female undergoing chemotherapy for breast cancer developed fever, abdominal pain, and foul-smelling diarrhea after receiving clindamycin for 5 days. The photomicrograph is an H & E-stained section of colon biopsy revealing focal ulceration and pseudomembranous inflammation. Each of the following laboratory findings will confirm the presumptive diagnosis of Clostridium difficile-associated colitis EXCEPT:
Recovery of C. difficile in the stool
This Xylose Lysine Decarboxylase (XLD) medium shown in this photograph was isolated from a stool specimen of an immunocompetent adult. Your best action would be to:
Report it as no Salmonella or Shigella isolated
On MacConkey (MAC) agar, an isolate from a stool sample produced clear, colorless colonies. On Hektoen enteric (HE) agar, colonies were green with black centers, indicative of H2S production. Additional biochemical tests were positive for methyl red, and negative for indole, VP, citrate, and PAD. From the choices listed, which species best matches the characteristics described?
Salmonella Typhi
Serological detection of the Vi antigen aids in identification of:
Salmonella Typhi
Which Enterobacteriaceae are non-lactose fermenters on MacConkey (MAC) agar, have green colonies with black centers on Hektoen enteric (HE) agar, and on xylose-lysine-deoxycholate (XLD) agar will have red colonies with black centers?
Salmonella spp.
Consumption of undercooked poultry or the handling of reptiles could cause which of the following conditions?
Salmonellosis
A sorbitol fermenting organism from a stool specimen is growing on MacConkey with sorbitol agar. The tech decides to double check for E.coli O157:H7 and a serological testing is performed. The serological testing used to identify the somatic antigen (O157) is positive for agglutination. Quality control also passed. What should the tech do next?
Set up biochemical or other testing to identify the organism
All of following are considered normal flora of the gastrointestinal tract EXCEPT:
Shigella
Shigella serotyping is performed by using a polyvalent somatic (O) antisera. A Shigella species grew from culture and serotyped as Group C. Which of the following Shigella species serotypes as Group C?
Shigella boydii
Shigella serotyping is performed by using a polyvalent somatic (O) antisera. A Shigella species grew from culture and serotyped as Group A. Which of the following Shigella species serotypes as Group A?
Shigella dysenteriae
Shigella serotyping is performed by using a polyvalent somatic (O) antisera. A Shigella species grew from culture and serotyped as Group B. Which of the following Shigella species serotypes as Group B?
Shigella flexneri
Shigella serotyping is performed by using a polyvalent somatic (O) antisera. A Shigella species grew from culture and serotyped as Group D. Which of the following Shigella species serotypes as Group D?
Shigella sonnei
All of the following organisms can exhibit beta hemolysis, EXCEPT
Shigella sp.
A day-care outbreak of diarrhea revealed an oxidase-negative, non-lactose fermenting, nonmotile, gram-negative rod. These characteristics presumptively indicate which organism?
Shigella species
Although some strains may possess K antigen, which member of Enterobacteriaceae is classified serologically by O antigen, because it lacks H antigen?
Shigella species
A tech is using the H (flagellar) antigen to serotype a suspected Salmonella species. The results of the serotyping are agglutination with one well that indicates a group of possible serotypes, not one particular serotype. Quality control passed. Why did this occur?
Some Salmonella H antigens can occur in multiple strains and serotypes
Which of the following gastrointestinal pathogens has an incubation period of 1-8 hours?
Staphylococcus aureus
A tech is testing a sorbitol negative isolate for possible E.coli O157: H7 from the MacConkey with sorbitol agar plate. The biochemical identification proves the organism is E.coli. Serological testing for the O157 somatic antigen is positive. Serological testing for the H7 flagellar antigen is negative. Quality control for all serological testing passed. What should the tech do next?
Subculture the organism to motility medium for repeat H7 serological testing
The fastidious Gram negative bacillus featured here has been recovered from individuals in pandemic outbreaks of diarrhea after ingestion of contaminated stream, lake, or well water. In many cases, life-threatening profuse diarrhea resulting in dehydration and electrolyte loss is experienced. Smooth, entire, convex light gray-yellow colonies are observed on blood agar (left upper image). Note the yellow pigmentation of the colonies growing on TCBS agar (Thiosulfate Citrate Bile Sucrose) on the right of the composite image, indicating strong acid production from sucrose. Cytochrome oxidase is also positive. Small, curved and S-shaped, gram-negative bacilli are seen on the Gram stain. From these observations, select the correct genus/species identification of this isolate.
Vibrio cholerae
What organism has a toxin that, when released, causes profuse, watery diarrhea?
Vibrio cholerae
Infections with this organism typically either present as primary septicemia or wound infections. Septicemia likely occurs after the organism is ingested while consuming shellfish. Wound infections are associated with some type of aquatic exposure. What organism does this describe?
Vibrio vulnificus
Which of the following microorganisms is associated with foodborne illness contracted from oysters and clams?
Vibrio vulnificus
A stool culture from a hospitalized patient produces the following characteristics: Gram-negative bacillusUrease positiveWeakly fermentativeTSI slant is A/A These reactions suggest that the organism is most likely:
Yersinia enterocolitica
Which of the following organisms causes disease by direct invasion of tissues?
Yersinia enterocolitica
This photograph is of an isolate from a stool culture on a 4-year-old child with gastroenteritis. The medium contains cefsulodin, irgasan, novobiocin, bile salts, mannitol, neutral red, and crystal violet. Further identification tests will most likely identify this isolate as:
Yersinia enterocolytica
