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MCB 4203 Exam 3 2024/2025 COMPLETE Pathogenic Microbiology
EXAM WITH ANSWERS GRADED A+ FSCJ
Why are bacterial toxins well-known among virulence factors? they can be easily purified from bacterial supernatant What is the role of horizontal gene transfer (HGT) in the evolution and spread of toxin- producing bacteria? it allows rapid spread of toxin genes among bacteria Which bacterial toxin is primarily associated with Shigella bacteria but can also be produced by certain strains of E. coli? shiga toxin What is the primary component of LPS endotoxin found in Gram-negative bacteria? Lipid A Which class of toxins possesses both cytotoxic and immunosuppressive properties? mycolactone toxins Which bacterium is responsible for causing Buruli ulcer? Mycobacterium ulcerans Type I toxins primarily act on the: host cell surface Type III toxins have an A-B structure with two functional components, where the B component: binds to the host cell surface
Superantigens exert their effects by binding to: T-cell receptors (TCRs) Which type of hemolysis causes the lysis of surrounding red blood cells, leaving a yellowish zone? beta-hemolysis Pore-forming toxins cause cell lysis by: forming channels in the membrane Clostridium perfringens produces an alpha-toxin that causes: gangrene A-B toxins, also known as Type III toxins, typically have two functional domains or subunits. The A domain is responsible for: conferring toxic activity, usually enzymatic The B domain of A-B toxins: facilitates the translocation of the A domain across the membrane Proteolytic cleavage separates the A and B domains in A-B toxins, which remain connected by a: disulfide bond The host cell specificity of A-B toxins is determined by: the B domain AB-type toxins consist of: A and B portions
the nontoxic components of the progenitor toxin provide protection What is the specific effect of the botulinum neurotoxin on peripheral neurons? inhibition of neurotransmitter release What role do SNARE proteins play in normal neurotransmission? they help mediate vesicle docking and fusion What is the role of an antitoxin in the treatment of botulism? neutralizing the botulinum neurotoxin Which term refers to the trafficking of proteins from the cytosol through the cell membrane? translocation What are the Sec and Tat pathways? protein secretion systems in both Gram-positive and Gram-negative bacteria Which protein secretion systems are Sec-dependent in Gram-negative bacteria? type 2 and 5 What is the role of the Sec system? translocating proteins from the cytosol to the periplasm What is the unique characteristic of the Tat system? it transports fully folded proteins What is the role of the N-terminal signal sequence in the Sec system? guides the protein to its destination
Which bacteria fold the transported protein in the periplasmic space? Gram-negative bacteria Which system is the most common mechanism in bacteria for protein translocation? post-translational system What happens to the signal sequence after protein secretion or export? it is cleaved by peptidases Which protein complex acts as an unfolded polypeptide-conducting channel in the Sec system? SecYEG translocon What is the role of SecA in the post-translational mechanism of the Sec system? binds to the signal peptide of the secretion substrate protein How many distinct secretion systems do Gram-negative bacteria have? six Which secretion system shuttles proteins from the cytoplasm to the extracellular space? type I Which type of secretion system injects products into the cytoplasm of other cells? type III Which type of secretion system is commonly used to secrete AB toxins? type II
The type six secretion system (T6SS) is evolutionarily related to: bacteriophage T4 tail and baseplate The T6SS has a unique capability to deliver effector molecules: into the adjacent cell when in close proximity to the T6SS spike In Gram-positive bacteria, protein secretion can occur through both Sec-dependent and Sec- independent mechanisms. Which of the following is an example of a Sec-dependent mechanism? sortase system The SecA2 accessory system in Gram-positive bacteria is responsible for exporting: serine-rich glycosylated virulence factor proteins The cytolysin-mediated translocation (CMT) system in Streptococcus pyogenes is functionally similar to which secretion systems found in Gram-negative bacteria? type III and type IV secretion systems Quorum sensing in bacteria relies on the production and detection of small diffusible signaling molecules called: autoinducers Autoinducer concentrations increase as cell density: increases What are autoinducers in quorum sensing? small, diffusible signaling molecules used by bacteria to coordinate their activities Which statement is true regarding autoinducers?
autoinducers contribute to inter-species interactions and communication between different species of bacteria Which molecules are primarily used as autoinducers in Gram-negative bacteria? N-acyl homoserine lactones (AHLs) Which molecules are primarily used as autoinducers in Gram-positive bacteria? autoinducing peptides (AIPs) How do autoinducing peptides (AIPs) facilitate intraspecies communication in Gram-positive bacteria? they remain in the extracellular environment and interact with membrane receptor proteins What is the advantage of autoinducer-2 (AI-2) in interspecies cell-cell communication? AI-2 indicates the presence of other bacteria regardless of their type What is the role of Vibrio fischeri in the Bobtail squid? it serves as a symbiont within the squid's light organ What happens under conditions of high cell densities in Vibrio fischeri? phosphatase activity is activated, reducing biofilm formation What is the role of cholera toxin in Vibrio cholerae infection? it disrupts ion flow control, leading to water loss and watery diarrhea What are the two autoinducer molecules involved in quorum sensing in Vibrio cholerae? CAI-1 and AI- 2 Which of the following is NOT a characteristic of Staphylococcus aureus?
Which of the following is an adhesin used by Yersinia to facilitate attachment to host cells? invasin How does Yersinia regulate its motility and attachment to host cells based on temperature? decreased motility and increased attachment at higher temperatures What modification does Yersinia make to its lipopolysaccharide (LPS) structure at higher temperatures? it becomes tetra-acylated What is the function of cytosolic chaperones in Yersinia infection? to ensure proper folding and secretion of Yop effectors How do YopP/YopJ and YopH contribute to the evasion of the host immune response? by inhibitng NF-kappaB and MAP-kinase signaling pathways What type of cell death is induced by Yersinia infection?
- apoptosis
- necrosis
- pyroptosis What is the main difference between bacteriostatic and bactericidal compounds in antimicrobial therapy? bactericidal compounds kill bacteria, while bacteriostatic compounds inhibit bacterial growth Bacteriostatic substances are most suitable for patients with: intact immune systems What does the MIC test determine?
the lowest concentration of an antibiotic required to prevent bacterial growth What does the large size of the clearance zone in the Kirby-Bauer Assay indicate? the high effectiveness of the antibiotic in inhibiting bacterial growth What is the primary difference between disinfectants and antiseptics? disinfectants are used on surfaces, while antiseptics are used on the skin Which phase of antibiotic discovery is considered the most challenging and time-consuming? lead optimization Why have pharmaceutical companies lost interest in antibiotic discovery? challenges and costs involved in the process Why do antibiotics primarily focus on a limited set of targets? these targets have been successful in the past What is the final step in peptidoglycan biosynthesis? cross-linking of peptidoglycan What is the target of the antibiotic fosfomycin? conversion of UDP-NAG to UDP-NAM Which step of peptidoglycan biosynthesis is targeted by bacitracin? phosphorylation and recycling of undecaprenyl pyrophosphate Which antibiotics act on the transpeptidation step of peptidoglycan biosynthesis? beta-lactams
Tetrahydrofolate biosynthesis inhibitors affect bacterial cells by: targeting enzymes involved in folic acid synthesis Clavulanic acid is often combined with other β-lactam antibiotics to: prevent degradation of beta-lactam antibiotics What strategy have pharmaceutical companies adopted to combat resistance? enhancing existing antibiotics What are nosocomial infections also known as? healthcare-associated infections (HAIs) Which group of bacteria is referred to as ESKAPE pathogens?
- Enterococcus faecium
- Staphylococcus aureus
- Klebsiella pneumoniae
- Acinetobacter baumannii
- Pseudomonas aeruginosa
- Enterobacter species How are bacteria classified as multidrug-resistant (MDR)? if they are resistant to more than two categories of antibiotics Under what conditions do certain bacteria become more resistant to aminoglycosides? anaerobic conditions What is the main function of efflux pumps in bacteria? to maintain cellular balance and remove toxins Which family of efflux pumps is particularly important in Gram-negative bacteria?
resistance-nodulation-division (RND) family How do β-lactamases render β-lactam antibiotics inactive? by attacking the beta-lactam ring with an active-site serine residue What are extended-spectrum β-lactamases (ESBLs) resistant to? narrow-spectrum beta-lactams, beta-lactamase inhibitors, and later-generation extended- spectrum beta-lactams Which bacteria within the Enterobacteriaceae family can produce ESBLs?
- E. coli
- Klebsiella pneumoniae
- Enterobacter spp.
- Proteus mirabilis Aminoglycoside resistance primarily occurs through: ribosome modification Chloramphenicol acetyltransferase (CAT) adds an acetyl group to chloramphenicol, preventing its: binding to the ribosome What is the role of the antitoxin in a TA system? inhibiting toxin activity Opportunistic infections occur when normally harmless microbes become pathogenic in individuals with compromised:
- innate barriers
- adaptive immunity
- genetic defects
S. pneumoniae evades immune cells by utilizing its: exopolysaccharide capsule The widely used vaccine for preventing pneumococcal pneumonia consists of antigens from: the 23 most common capsular types Influenza vaccinations for healthcare workers have been employed to indirectly protect the elderly from S. pneumoniae infections because: influenza and S. pneumonia often co-infect individuals Which vaccine significantly reduced invasive pneumococcal diseases among infants? PCV- 7 Which proteins are being explored as potential vaccine candidates for Streptococcus pneumoniae? pneumolysin and Streptococcus pneumoniae surface proteins Pneumolysin, a virulence factor of Streptococcus pneumoniae, activates pro-inflammatory responses by binding to: toll-like receptor 4 (TLR4) Which enzyme present in Staphylococcus aureus causes blood clotting? coagulase Methicillin-resistant Staphylococcus aureus (MRSA) strains often exhibit resistance to which class of antibiotics? beta-lactams What is the role of surface proteins in Staphylococcus aureus?
binding to extracellular matrix proteins Which toxin released by Staphylococcus aureus causes lysis of polymorphonuclear leukocytes (PMNs)? alpha-toxin What happens to the risk of Clostridium difficile infection (CDI) when antibiotic treatment begins? the risk increases due to the presence of antibiotic-resistant strains How is Clostridium difficile primarily transmitted from person to person? through direct contact with feces How do toxins A and B (TcdA and TcdB) disrupt host cells? they disrupt cytoskeletal function What is one strategy to treat recurrent pseudomembranous colitis? using enema with diluted feces from family members Which of the following is NOT an example of a Gram-negative opportunistic pathogen? Staphlyococcus aureus The distinguishing characteristic of EPEC is its ability to cause enterocyte attachment and effacement (EAE), which results in the alteration of the ultrastructure of: mucosal epithelial cells Enteroinvasive E. coli (EIEC) strains are genetically similar to which bacterial species? Shigella
- it is easily eradicated by common disinfectants and does not form biofilms
- it is a Gram-positive bacterium that is motile and aerobic
- it gained attention during the Iraq war and is associated with wound, bloodstream, and respiratory infections
- it is primarily found in the air and can cause respiratory infections it gained attention during the Iraq war and is associated with wound, bloodstream, and respiratory infections What are dual-use agents in the context of bioweapons? agents that can be also used for non-malicious purposes like therapeutics or education Which of the following bioterror agents requires fleas as a vehicle for transmission? Yersinia pestis What is the main mode of action of the Botulinum neurotoxin? blocking the release of acetylcholine at neuromuscular junctions Why is acquiring Botulinum neurotoxin relatively easy compared to other bioweapons? it can be introduced into water or food supplies What is the recommended treatment for Botulinum neurotoxin poisoning? administration of antitoxin and supportive care What is the primary reason behind the ease of acquiring Botulinum neurotoxin compared to other bioweapons? it occurs naturally int eh environment and can be extracted Which of the following accurately describes the mortality rate of smallpox in unvaccinated populations? up to 30%
What triggers the formation of a pre-pore in anthrax toxin? cleavage of PA What happens to the pre-pore of anthrax toxin inside the endosome? it undergoes conformational change Which group is primarily recommended for the anthrax vaccine? military personnel and researchers What is one of the recommendations by the National Science Advisory Board for Biosecurity in the United States? preventing bioterrorism through policies on research publications
