Chapter 19: Enterobacteriaceae. All Answers

MULTIPLE CHOICE 1. Which of the following agars is not selective for Enterobacteriaceae? a. Buffered charcoal yeast extract b. MacConkey c. Hektoen enteric d. Xylose-lysine deoxycholate A A wide variety of ...

MULTIPLE CHOICE 1. Which of the following agars is not selective for Enterobacteriaceae? a. Buffered charcoal yeast extract b. MacConkey c. Hektoen enteric d. Xylose-lysine deoxycholate A A wide variety of differential and selective media, such as MacConkey agar, and highly selective media, such as HE and XLD agar, are available for the presumptive identification of enteric pathogens. REF: 421 OBJ: Level 1: Recall 2. The primary pathogens of the Enterobacteriaceae include all the following except: a. Salmonella enterica. b. Proteus mirabilis. c. Shigella spp. d. Yersinia spp. B The primary pathogens, which include S. enterica, Shigella spp., and Yersinia spp., are considered true pathogens—that is, they are not present as commensal flora in the GI tract of humans. These organisms produce infections resulting from ingestion of contaminated food or water, or from other sources. REF: 423 OBJ: Level 1: Recall 3. What organism presents as a pink colony with a halo on MacConkey media and a green metallic sheen on eosin methylene blue (EMB)? a. Salmonella enterica b. Proteus mirabilis c. Escherichia coli d. Klebsiella pneumonia C On certain selective and differential media, such as MacConkey or EMB agars, E. coli has distinctive morphology. It usually presents as a lactose-positive (pink) colony with a surrounding area of precipitated bile salts on MacConkey agar. On EMB agar, it presents with a green metallic sheen. REF: 424 OBJ: Level 2: Interpretation 4. Escherichia coli strains have all the following properties except: a. indole production. b. fermentation of glucose and lactose. c. methyl red (MR) positive, Voges-Proskauer (VP) negative. d. can use citrate as a sole carbon source. D Characteristically, E. coli strains are associated with the following properties: fermentation of glucose, lactose, trehalose, and xylose; indole production; glucose fermentation by the mixed acid pathway—MR positive and VP negative; does not produce H2S, DNase, urease, or phenylalanine deaminase; and cannot use citrate as a sole carbon source. REF: 424 OBJ: Level 1: Recall 5. Which organism is the most common cause of urinary tract infections (UTIs) in humans? a. Escherichia coli b. Klebsiella oxytoca c. Proteus mirabilis d. Enterobacter cloacae A E. coli is widely recognized as the most common cause of urinary tract infections in humans. The E. coli strains that cause UTIs usually originate in the large intestine as resident or transient flora and may exist either as the predominant E. coli population or as a small part of the E. coli strains in the large intestine. REF: 424 OBJ: Level 1: Recall 6. All of the following are categories of diarrhea-causing Escherichia coli except: a. ETEC. b. EMEC. c. EIEC. d. EPEC. B Based on definitive virulence factors, clinical manifestation, epidemiology, and different O and H serotypes, there are five major categories of diarrheogenic E. coli: enterotoxigenic (ETEC), enteroinvasive (EIEC), enteropathogenic (EPEC), and enterohemorrhagic (EHEC), which includes the diffusely adherent (DAEC) and the enteroaggregative (EaggEC) strains. REF: 425 OBJ: Level 1: Recall 7. The Escherichia coli serotype O157:H7 is associated with all the following except: a. hemorrhagic diarrhea. b. colitis. c. liver damage. d. hemolytic-uremic syndrome. C The EHEC strain serotype O157:H7 has since been associated with hemorrhagic diarrhea, colitis, and hemolytic-uremic syndrome (HUS). HUS is characterized by low platelet count, hemolytic anemia, and kidney failure. REF: 426 OBJ: Level 1: Recall 8. A microbiologist is reading a stool culture and notices a very moist and mucoid pink colony on MacConkey agar. What is the most likely organism? a. Klebsiella pneumoniae b. Escherichia coli c. Proteus vulgaris d. Acinetobacter A K. pneumoniae is the most commonly isolated species and has the distinct feature of possessing a polysaccharide capsule. The capsule offers the organism protection against phagocytosis and antimicrobial absorption, thus contributing to its virulence. This capsule is also responsible for the moist, mucoid colonies characteristic of K. pneumoniae. REF: 428 OBJ: Level 2: Interpretation 9. All of the following are clinically significant isolates of the genus Enterobacter except: a. Enterobacter cloacae. b. E. aerogenes. c. E. gergoviae. d. E. hartmanni. D The genus Enterobacter is composed of at least 12 species. Clinically significant Enterobacter spp. isolated from clinical samples include E. cloacae, E. aerogenes, E. gergoviae, and E. hormaechei. REF: 429 OBJ: Level 1: Recall 10. What genus of bacteria is considered an opportunistic pathogen often associated with nosocomial outbreaks? a. Enterobacter b. Serratia c. Proteus d. Escherichia B The genus Serratia is composed of S. marcescens, S. liquefaciens, S. rubidaea, S. odorifera, S. plymuthica, S. ficaria, S. entomophila, and S. fonticola. Serratia spp. are opportunistic pathogens associated with outbreaks in health care settings. REF: 431 OBJ: Level 2: Interpretation 11. What two bacteria produce swarming colonies on nonselective media, such as sheep blood agar (SBA)? a. Enterobacter aerogenes and Serratia marcescens b. Proteus pannier and Klebsiella pneumoniae c. P. vulgaris and P. mirabilis d. P. mirabilis and Escherichia coli C P. mirabilis and P. vulgaris are easily identified in the clinical laboratory because of their characteristic colony morphology. Both species produce swarming colonies on nonselective media, such as SBA. This characteristic swarming is a result of a tightly regulated cycle of differentiation from standard vegetative cells (swimmers) to hyperflagellated, elongated, polyploid cells (swarmers) capable of coordinated surface movement. REF: 431 OBJ: Level 1: Recall 12. This genus currently has only one species associated with it that has been implicated in urinary tract infections. What is the name of this organism? a. Klebsiella pneumoniae b. Escherichia coli c. Hafnium alvei d. Morganella morganii D The genus Morganella currently has only one species, M. morganii, with two subspecies: M. morganii subsp. morganii and M. morganii subsp. sibonii. Neither subspecies have been implicated in diarrheal illness, but the role they play as an etiologic agent of diarrheal disease has not been fully examined. M. morganii is, however, a documented cause of urinary tract infections and has been isolated from other human body sites. REF: 432 OBJ: Level 2: Interpretation 13. What organism in the genus Providencia is incriminated in nosocomial outbreaks in burn units and has been isolated from urine cultures? a. Providencia stuartii b. P. heimbachae c. P. rustigianii d. P. alcalifaciens A Similarly, P. stuartii has been incriminated in nosocomial outbreaks in burn units and has been isolated from urine cultures. P. alcalifaciens is usually found in the feces of children with diarrhea; however, its role as a cause of diarrhea has not been proved. P. rustigianii is rarely isolated, and its pathogenicity also remains unproven, whereas P. heimbachae has yet to be isolated from any clinical specimens. REF: 432 OBJ: Level 2: Interpretation 14. What genus has the following characteristics: negative for urea, positive for lysine decarboxylase, positive for hydrogen sulfide, positive for indole, and does not grow on Simmon’s citrate? a. Providencia b. Edwardsiella c. Escherichia d. Morganella B The genus Edwardsiella is composed of three species: E. tarda, E. hoshinae, and E. ictaluri. E. tarda is the only recognized human pathogen. Members of this genus are negative for urea and positive for lysine decarboxylase, hydrogen sulfide, and indole, and do not grow on Simmon’s citrate. REF: 432 OBJ: Level 2: Interpretation 15. All of the following are members of the Citrobacter genus except: a. Citrobacter freundii. b. C. koseri. c. C. asteroides. d. C. braakii. C The genus Citrobacter currently consists of 11 species that have all been isolated from clinical specimens: C. freundii, C. koseri (diversus), C. amalonaticus, C. farmeri, C. braakii, C. gillenii, C. murliniae, C. rodentium, C. sedlakii, C. werkmanii, and C. youngae. REF: 433 OBJ: Level 1: Recall 16. What is the name of the organism that has been a documented cause of nursery outbreaks of neonatal meningitis and brain abscesses? a. Citrobacter freundii b. C. asteroides c. C. braakii d. C. koseri D C. koseri is a pathogen documented as the cause of nursery outbreaks of neonatal meningitis and brain abscesses. REF: 433 OBJ: Level 2: Interpretation 17. All the following are biochemical features of Salmonella except: a. lactose positive. b. indole negative. c. hydrogen sulfide positive. d. Voges-Proskauer (VP) negative. A The biochemical features for the genus include the following: (1) in almost every case, they do not ferment lactose; (2) they are negative for indole, the VP test, phenylalanine, and urease; (3) most produce hydrogen sulfide; (4) they do not grow in medium containing potassium cyanide. REF: 433 OBJ: Level 1: Recall 18. Which animals are a common source of Salmonella serotypes? a. Dogs b. Cold-blooded animals (fish) c. Cats d. Horses B Most Salmonella serotypes are found in cold-blooded animals, as well as in rodents and birds, which serve as their natural hosts. REF: 433 OBJ: Level 1: Recall 19. What substance, when produced by the Salmonella spp., which cause gastroenteritis, has been implicated as a significant virulence factor? a. Hyaluronidase b. Protease c. Enterotoxin d. Endotoxin C Enterotoxin produced by certain salmonella strains that cause gastroenteritis has been implicated as a significant virulence factor. REF: 434 OBJ: Level 2: Interpretation 20. What are the primary antigens used in serologic grouping of salmonellae? a. Somatic A antigen and flagellar O antigens b. Capsular A antigen and somatic O antigen c. Flagellar H antigen and capsular A antigen d. Flagellar H antigen and somatic O antigen D Salmonellae possess antigens similar to those of other enterobacteria. The somatic O antigens and flagellar H antigens are the primary antigenic structures used in serologic grouping of salmonellae. REF: 434 OBJ: Level 1: Recall 21. What organism possesses the Vi antigen? a. Salmonella typhi b. S. sonnei c. Shigella sonnei d. Citrobacter freundii A A few strains may possess capsular K surface antigens, designated as the Vi antigen. The serologic identification of the Vi antigen is important in identifying Salmonella serotype typhi. REF: 434 OBJ: Level 1: Recall 22. What disease produced by a Salmonella spp. is a severe form of enteric fever? a. Pontiac fever b. Typhoid fever c. Undulant fever d. Malignant fever B Typhoid fever, the most severe form of enteric fever, is caused by Salmonella enterica serotype typhi. Humans acquire the infection by ingesting food contaminated with the organisms originating from infected individuals or carriers. REF: 434 OBJ: Level 1: Recall 23. All of the following are symptoms of salmonellosis that may appear 8 to 36 hours after ingestion of contaminated food except: a. nausea. b. vomiting. c. headache. d. watery diarrhea. C The symptoms of intestinal salmonellosis, which may appear 8 to 36 hours after ingestion of contaminated food, include nausea, vomiting, fever, and chills, accompanied by watery diarrhea and abdominal pain. REF: 435 OBJ: Level 1: Recall 24. Why is it that most cases of salmonella food poisoning are not treated with antibiotics? a. The organisms are very resistant to antibiotics. b. Antibiotics cannot reach the organisms, because they are deeply embedded in the intestinal walls. c. Antibiotics would only kill the bacteria, then release the endotoxins into the blood, making things worse. d. The disease is self-limiting and will subside on its own. D Most cases of Salmonella gastroenteritis are self-limiting. Symptoms disappear usually within a few days, with little or no complications. REF: 435 OBJ: Level 2: Interpretation 25. In the carrier state, where are pathogenic salmonella carried? a. Gallbladder b. Liver c. Intestines d. Stomach A Individuals who recover from infection may harbor the organism in the gallbladder, which becomes the site of chronic carriage. REF: 436 OBJ: Level 1: Recall 26. All of the following are characteristics of Shigella spp. except: a. nonmotile. b. urea positive. c. hydrogen sulfide negative. d. lysine decarboxylase negative. B Characteristics of Shigella spp. are the following: they are nonmotile; they do not produce gas from glucose (except Shigella flexneri); they are urea negative, hydrogen sulfide negative, and lysine decarboxylase negative. REF: 436 OBJ: Level 1: Recall 27. Bacillary dysentery caused by this organism is marked by penetration of intestinal epithelial cells following attachment of the organisms to mucosal surfaces, local inflammation, shedding of the intestinal lining, and formation of ulcers that follow the epithelial penetration. What is this organism? a. Enterobacter b. Citrobacter c. Shigella d. Salmonella C Bacillary dysentery caused by Shigella spp. is marked by penetration of intestinal epithelial cells following attachment of the organisms to mucosal surfaces, local inflammation, shedding of the intestinal lining, and formation of ulcers that follow the epithelial penetration. The clinical manifestation of shigellosis varies from asymptomatic to severe forms of the disease. REF: 437 OBJ: Level 3: Synthesis 28. What bacterium is the causative agent of the plague? a. Salmonella enteritidis b. Citrobacter freundii c. Shigella sonnei d. Yersinia pestis D Yersinia pestis is the causative agent of the plague, a disease of rodents transmitted to humans by fleas. REF: 438 OBJ: Level 1: Recall 29. What enteric organism may produce a blue-violet pigment on non–blood-containing media? a. Kluyvera b. Shigella c. Ewingella d. Cedecea A The genus Kluyvera is made up of three closely related species: K. ascorbata, K. cryocrescens, and K. georgiana. They have been found in respiratory, urine, and blood cultures and may produce a blue-violet pigment, usually but not exclusively, on non–blood-containing media. REF: 440 OBJ: Level 2: Interpretation 30. Why can direct microscopy not be used to provide a presumptive identification of the enteric bacteria? a. Some members of the genus Gram stain weakly. b. The microscopic characteristics are indistinguishable from other gram-negative bacteria. c. Some members of the genus do not decolorize well and appear gram-positive. d. Some members have very thick capsules, and these do not allow the penetration of the Gram stain. B Unlike the case with gram-positive bacteria, in which microscopic morphology may essentially provide a presumptive identification, the microscopic characteristics of enterics are indistinguishable from other gram-negative bacteria. REF: 441 OBJ: Level 2: Interpretation