Block 9 Bacteria Exotoxin & Capsule MCQ's
Questions and Answers
- 1.
A patient who had received an artificial hip 5 months previously presented with persistent pain in the new joint that he had noticed for the last week or so. A CT scan showed inflammation around the prosthetic, and a series of CT-guided aspirations of penprosthetic tissue grew isolates which, when plated, produced entire, smooth, greyish, gamma- hemolytic colonies, The isolate was resistant to multiple antibiotics, and treatment with vancomycin was begun. After 10 days of treatment, inflammation had decreased but sonication (ultrasonic shaking) of an explanted fragment of the joint itself released large numbers of viable organisms. Eventually, after several months of unsuccessful antimicrobial therapy, the prosthetic was removed. What characteristics are associated with the most likely causative agent?
- A.
Gram-negative, oxidase-positive, bacillus producing exotoxin A and exoenzyme S
- B.
Gram-positive, catalase-positive, coagulase-negative coccus producing delta-toxins
- C.
Gram-negative, oxiclase-negative, lactose-fermenting bacillus producing intimin
- D.
Gram-negative, branching bacillus growing anaerobically
- E.
Gram-positive, catalase-positive, coagulase-positive coccus producing alpha-toxins
Correct Answer
B. Gram-positive, catalase-positive, coagulase-negative coccus producing delta-toxinsExplanation
The ability to form biofilms on plastic devices is a major virulence factor for S. epidermidis. One probable cause is surface proteins that bind blood and extracellular matrix proteins. The organism's capsule, known as polysaccharide intercellular adhesion (PIA), is made up of sulfated polysaccharide. It allows other bacteria to bind to the already existing biofilm, creating a multilayer biofilm. Such biofilms decrease the metabolic activity of bacteria within them. This decreased metabolism, in combination with impaired diffusion of antibiotics, makes it difficult for antibiotics to effectively clear this type of infection. S. epidermidis strains are often resistant to antibiotics, including penicillin, amoxicillin, and methicillin.
As mentioned above, S. epidermidis causes biofilms to grow on plastic devices placed within the body. This occurs most commonly on intravenous catheters and on medical prostheses.Infection can also occur in dialysis patients or anyone with an implanted plastic device that may have been contaminated. Another disease it causes is endocarditis. This occurs most often in patients with defective heart valves. In some other cases, sepsis can occur in hospital patients.
Antibiotics are largely ineffective in clearing biofilms. The most common treatment for these infections is to remove or replace the infected implant, though in all cases, prevention is ideal.
The drug of choice is often vancomycin, to which rifampin or aminoglycoside can be added.Hand washing has been shown to reduce the spread of infection.
Identification
The normal practice of detecting S. epidermidis is by using the Baird-Parker agar with egg yolk supplement. Colonies appear small and black. They can be confirmed using the coagulase test. Increasingly, techniques such as real-time PCR and quantitative PCR are being employed for the rapid detection and identification of Staphylococcus strains.[Rate this question:
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- 2.
Tracheal cytotoxin, involved in the pathogenesis of whooping cough by Bordetella pertussis, is released from the bacterial cell via which mechanism?
- A.
A Type III secretion system
- B.
A cell wall-degrading enzyme
- C.
A Type V secretion system
- D.
A capsule-dependent system
- E.
A signal peptidase enzyme
Correct Answer
B. A cell wall-degrading enzymeExplanation
Tracheal cytotoxin, involved in the pathogenesis of whooping cough by Bordetella pertussis, is released from the bacterial cell via a cell wall-degrading enzyme. This enzyme is responsible for breaking down the cell wall of the bacteria, allowing the release of the cytotoxin into the surrounding environment. This mechanism enables the cytotoxin to interact with the host cells and contribute to the development of the disease.Rate this question:
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- 3.
A 33-year-old man sustained compound fractures of his right tibia and fibula during a car accident. Within hours, surgical debridement of the wound and a leg immobilization was completed. The patient improved until four days following the surgery, at which time he became febrile (38°C), tachycardic (120bprn) and complained that his leg was painful. After opening the cast, the lower leg was noted to be swollen, reddish-purple, and exuding a foul- smelling exudate. Crepitations were palpable over the entire gastrocnemius. A Gram-stain of the exudate revealed both Gram-negative and Gram-positive rods. What is the function of the toxin produced by Gram-positive rod most likely growing in this man's leg?
- A.
Degrades lipids in host cell membranes
- B.
Inhibits host cell protein synthesis
- C.
Forms pores in host cell membranes
- D.
Causes activation of large numbers of T cells
- E.
Triggers massive cytokine secretion and activation of complement and coagulation cascades
Correct Answer
A. Degrades lipids in host cell membranesExplanation
The toxin produced by the Gram-positive rod in this man's leg most likely degrades lipids in host cell membranes. This can lead to the destruction of the cell membrane, causing cell death and contributing to the symptoms observed, such as swelling, discoloration, and exudate.Rate this question:
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- 4.
Antitoxin is an important component in the treatment of
- A.
Pseudomembranous colitis
- B.
Gas gangrene
- C.
Bactericides and prevotella infections
- D.
Food-borne botulism
- E.
C. perfringens food poisoning
Correct Answer
D. Food-borne botulismExplanation
Antitoxin is an important component in the treatment of food-borne botulism. Food-borne botulism is caused by the ingestion of food contaminated with the toxin produced by Clostridium botulinum bacteria. Antitoxin works by neutralizing the toxin and preventing it from causing further harm to the body. Therefore, the use of antitoxin is crucial in the treatment of food-borne botulism to counteract the effects of the toxin and aid in the recovery of the patient.Rate this question:
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- 5.
Production of diphtheria toxin is regulated by a repressor that is usually active, but in certain circumstances (such as in a patient) this repressor becomes inactive. What is the factor which causes the inhibition of the diphtheria toxin repressor?
- A.
CD11b/CD8
- B.
EF-2
- C.
Iron
- D.
ADP
Correct Answer
C. IronExplanation
Iron is the factor that causes the inhibition of the diphtheria toxin repressor. In certain circumstances, such as in a patient, the repressor becomes inactive. Iron is known to play a crucial role in the regulation of diphtheria toxin production. When iron levels are low, the repressor is active and prevents the production of the toxin. However, when iron levels are high, the repressor becomes inactive, allowing the production of the toxin to occur. Therefore, iron acts as a factor that inhibits the diphtheria toxin repressor.Rate this question:
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- 6.
Scarlet fever (scarietna) is known to be caused by bacterial production of which toxin?
- A.
Streptokinase
- B.
Erythrogenic toxin
- C.
Pneurnolysin
- D.
Panton-Valentine leukocidin (PVL)
Correct Answer
B. Erythrogenic toxinExplanation
Erythrogenic toxin is the correct answer because it is a known bacterial toxin that is produced by Streptococcus pyogenes, the bacteria responsible for causing scarlet fever. This toxin is responsible for the characteristic rash seen in scarlet fever, as it causes the dilation and leakage of blood vessels in the skin. Streptokinase is not associated with scarlet fever, as it is an enzyme produced by bacteria that helps dissolve blood clots. Pneumolysin is a toxin produced by Streptococcus pneumoniae, a different bacteria that is not associated with scarlet fever. Panton-Valentine leukocidin (PVL) is a toxin produced by certain strains of Staphylococcus aureus, which is also not associated with scarlet fever.Rate this question:
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- 7.
In May 2011, an outbreak of foodborne illness, presenting with bloody diarrhea and complicated in many cases by hemolytic uremic syndrome, was seen in Germany. In thousands of patients, the causative agent was identified as a lactose-fermenting, Gram- negative, oxidase-negative rod of the novel 0104:H4 serotype. Interestingly, while the pathogen causes a disease similar to that caused by the 0157:H7 strain, it does not have the attaching/effacing genes found in this latter organism. What virulence factor is most likely responsible for the similarities in clinical presentation between the new strain and the 0157:H7 strain?
- A.
Intimin
- B.
Endotoxin
- C.
Exotoxin A
- D.
Shiga toxin
- E.
Alpha hemolysin
Correct Answer
D. Shiga toxinExplanation
Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of -lambdoid prophages.- The most common sources for Shiga toxin are the bacteria Shigella dysenteriae and the Shigatoxigenic group of Escherichia coli (STEC), which includes serotypes O157:H7, O104:H4, and other enterohemorrhagic E. coli (EHEC).Rate this question:
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- 8.
The possession of a capsule is often considered to be an important feature of pathogenic bacteria. Which of the following organisms does not possess a capsule?
- A.
Streptococcus pneumonia
- B.
Haemophilus influenzae type b
- C.
Neisseria menigitidis
- D.
Corynebacterium diphtheria
Correct Answer
D. Corynebacterium dipHtheriaExplanation
Corynebacterium diphtheria does not possess a capsule. Capsules are an important feature of pathogenic bacteria as they help protect the bacteria from the host's immune system. Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis are known to possess capsules, which contribute to their pathogenicity. However, Corynebacterium diphtheria does not possess a capsule, making it an exception among the given organisms.Rate this question:
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- 9.
The capsule surrounding Streptococcus pneumoniae makes bacteria pathogenic by what mechanism?
- A.
It inhibits phagocytoss by preventing activation of complement and preventing binding of C3b to bacteria
- B.
It releases toxins and enzymes into lung tissue to cause destruction of alveolar septae
- C.
It acts as a barrier that prevents antibodies from binding to bacterial cell wall
- D.
It is responsible for penicillin resistance by blocking access of antibiotic to bacterial cell wall
Correct Answer
A. It inhibits pHagocytoss by preventing activation of complement and preventing binding of C3b to bacteriaExplanation
The capsule surrounding Streptococcus pneumoniae inhibits phagocytosis by preventing the activation of complement and the binding of C3b to bacteria. This means that the bacteria are able to evade the immune system's response, making them more pathogenic. The complement system is an important part of the immune response, as it helps to tag bacteria for destruction by phagocytes. By preventing the activation of complement and the binding of C3b, the capsule allows the bacteria to avoid being recognized and destroyed by the immune system.Rate this question:
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- 10.
An 18-year-old college student presents with fever, headaches, photophobia, nuchal rigidity, and petechiae. Gram-staining of both blood cultures and cerebrospinal fluid reveals red pairs of kidney bean-shaped bacterial cells. One of the ways this organism is able to survive in the bloodstream is by evading phagocytosis. What is the general structure of the virulence factor most responsible for this ability?
- A.
Trirneric protein embedded in the outer membrane
- B.
Short surface protein filaments
- C.
Surface-anchored polysaccharide
- D.
Crystalline layer of self-assembling surface proteins
- E.
Polymer of sugars cross-linked via peptides
Correct Answer
C. Surface-anchored polysaccharideExplanation
1) Capsules are a type of exopolysaccharide, which means that they are composed of long strands of sugar and are found on the outer surface of the microbe.
• They are often anchored into either the plasma or outer membrane.
• Capsules may be composed of a wide variety of sugars. Many bacterial capsules, including those of most pathogens, include anionic sugars, which imparts an overall negative charge to the surface of the cell. The sugars are organized in repeating units, which may be a single sugar or short oligosaccharides. These are polymerized to make the long polysaccharide chain. Some may contain amino acids, but the capsules of Bacillus anthracis and Yersinia pestis are exceptional in that they are made solely of amino acids (poly-D-glutamate and F1 protein, respectively).Rate this question:
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Mar 21, 2023Quiz Edited by
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May 05, 2012Quiz Created by
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