Intro to Microbiology and Bacterial Morphology MCQ

*The answer is B.* Lipid A is the toxic moiety of LPS.

A 81-year-old woman who is receiving chemotherapy for leukemia develops a fever to 40°C and has two episodes of teeth-chattering chills, and her blood pressure drops to 80/20 mmHg. Of the following factors, which one is MOST likely to be the cause of her fever, chills, and hypotension? A. Coagulase B. Lipid A C. Polysaccharide capsule D. Mycolic acid

*The answer is D.* A selective growth medium that contains a high salt concentration would permit bacterial growth.

Bacteria capable of growth in a high salt concentration are best isolated in which of the following media? (A) Minimal growth media (B) Complex growth media (C) Differential growth media (D) Selective growth media

*The answer is C.* Antibiotics exert their microbial effect by inhibiting biosynthesis of the peptidoglycan polymer, resulting in the inhibition of cell-wall formation.This results in the inability of the bacterium to survive because of the absence of a protective covering.

Cell-wall biosynthesis is inhibited by antibiotics by inhibiting the biosynthesis of which of the following ? a) lipopolysaccharide b) cellulose c) peptidoglycan d) proteins

*The answer is B.* Peptidoglycan is thicker in gram-positive than in gram negative cells.

Each of the following statements concerning peptidoglycan is correct EXCEPT: A. It can be degraded by lysozyme B. It is thinner in gram-positive than in gram negative cells C. Cross-links between the tetrapeptide involve D-alanine D. It has a backbone composed of alternating units of muramic acid and acetylglucosamine

*The answer is B.* Lysogenic phage conversion refers to a change in bacterial phenotype resulting from the presence of a lysogenic prophage of a temperate phage.

Lysogenic phage conversion involves (A) The transformation of a virulent phage to a lysogenic phage (B) A change in bacterial phenotype due to the presence of a prophage (C) The conversion of a prophage to a temperate phage (D) The incorporation of a prophage into the bacterial chromosome

*The answer is A.* Phages that destroy host cell DNA, direct synthesis of phage particles, and cause lysis of the host cell are called virulent phages.

Phages that destroy host cell DNA, direct synthesis of phage particles, and cause lysis of the host cell are called: A. Virulent phages B. Prophages C. Temperate phages D. Lysogenic phages E. Transductions

*The answer is E.* DNA or genetic recombination is the general term used to describe the exchange of allelic forms of genes in bacteria or eukaryotic cells.

The exchange of allelic forms of genes is involved in which of the following processes? (A) Transformation (B) Conjugation (C) Transduction (D) Transcription (E) Recombination

*The answer is D.* The plasma membrane contains the enzymes involved in oxidative phosphorylation.

The plasma membrane (A) Contains matrix porins (B) Includes endotoxin (C) Contains glycocalyx (D) Contains the enzymes involved in bacterial oxidative phosphorylation

*The answer is B.* Human and fungal cells have similar ribosomes, whereas bacterial ribosomes are different.

Which one of the following statements is the MOST accurate comparison of human, bacterial, and fungal cells? A. Human cell undergo mitosis, whereas neither bacteria nor fungi do B. Human and fungal cells have similar ribosomes, whereas bacterial ribosomes are different C. Human and bacterial cells have plasmids, whereas fungal cells do not D. Human and fungal cells have a similar cell wall, in contrast to bacteria, whose cell wall contain peptidoglycan

*The answer is C.* Bacteriophages containing portions of host-cell DNA can introduce this genetic material into new host cells via the process of transduction.

Bacteriophage containing host-cell DNA is involved in which of the following processes? (A) Transformation (B) Conjugation (C) Transduction (D) Transcription (E) Recombination

*The answer is B.* N-acetylglucosamine and N-acetylmuramic acid are polymerized to form the peptidoglycan backbone of the cell wall.

Polymers of N-acetylglucosamine and N-acetylmuramic acid are found in which of the following structures? (A) Teichoic acid (B) Cell wall (C) Glycocalyx (D) Lipopolysaccharide

*The answer is D.* The statement fits the definition of competency required for transformation.

The ability of a cell to bind DNA to its surface and import it is required for which genetic process? A. Homologous recombination B. Generalized transduction C. Conjugation D. Transformation E. Specialized transduction

*The answer is C.* The association of endotoxin in Gram-negative bacteria is a result of the presence of lipopolysaccharide.

The association of endotoxin in Gram-negative bacteria is a result of the presence of: A. Steroids B. Polypeptide C. Lipopolysaccharide D. Peptidoglycan

*The answer is C.* The form of genetic exchange in which donor DNA is introduced to the recipient by a bacterial virus is transduction.

The form of genetic exchange in which donor DNA is introduced to the recipient by a bacterial virus is A. Horizontal transfer B. Transformation C. Transduction D. Transfection E. Conjugation

*The answer is B.* The formation of a mating pair during the process of conjugation in Escherichia coli requires sex pilus.

The formation of a mating pair during the process of conjugation in Escherichia coli requires A. Restriction endonuclease B. sex pilus C. Lysis of the donor D. Transfer of both strands of DNA E. Intergration of Transposon

*The answer is A.* Generalized transduction occurs when bacteriophage package a portion of the donor bacterium's DNA. The phage particle carrying the bacterial DNA infects another cell, transferring the bacterial DNA to the new cell.

The process by which bacterial or plasmid DNA may be mistakenly incorporated (during assembly) into one phage being produced by the lytic life cycle and then that DNA-transferred to another bacterial cell which may acquire some new genetic traits is called A. Generalized transduction B. Homologous recombination C. Transformation D. Conjugation E. Specialized transduction

*The answer is A.* Conjugation involves sex pilus.

Which one of the following processes involves a sex pilus? A. Conjugation resulting in transfer of an R (resistance) factor B. Transposition of a mobile genetic element C. Integration of a temperate bacteriophage D. Transduction of a chromosomal gene

*The answer is C.* Plasmids are small, circular, supercoiled DNA molecules found in some bacteria. They usually do not carry essential genes, but some plasmids, such as R (resistance) plasmids, carry genes coding for antibiotic resistance. All plasmids have their own origin of replication, so that they are replicated along with the host chromosome and passed along to progeny cells. Only some plasmids possess genes that allow for transmittal to other bacteria by the process of conjugation.

Which one of the following statements concerning plasmids is true? A. All plasmids can be transfered between bacteria by conjugation. B. Much of the information coded in the plasmid is essential to the survival of the bacteria cell. C. Resistance plasmids carry genes for antibiotic resistance. D. Resistance plasmids cannot be transferred to other bacterial cells. E. Plasmids lack an origin of replication.

*The answer is A.* Transformation is susceptible to the activity of deoxyribonuclease.

Which type of genetic exchange in bacteria is susceptible to the activity of deoxyribonuclease? A. Transformation B. Conjugation C. Transduction D. Transfection

*The answer is D.* The causal agent is Streptococcus pyogenes. The clues: sore throat, beta hemolytic, gram-positive cocci. To answer this question, you have to know that the agent is gram-positive and that gram-positive organisms have a thick peptidoglycan layer that protects them from osmotic damage. Lipopolysaccharide is only found on gram-negative organisms and is associated with shock. Phospholipids are found in the membranes of gram-positive and gram-negative organisms. Polysaccharide can be found on gram-positive and gram-negative organisms. Teichoic acid is only found on gram-positives and is used for attachment.

A 12-year-old boy presents to his pediatrician with fever, malaise, and a sore throat. Physical examination reveals a fever of 103°F, cervical lymphadenopathy, and pharyngeal erythema. A swab is taken from some of the tonsillar exudate and cultured on blood agar. Culture reveals beta hemolytic, gram-positive cocci, and a rapid antigen test is positive. What is the major component that protects the causal agent from osmotic damage? A. Lipopolysaccharide B. Phospholipids C. Teichoic acid D. Peptidoglycan E. Polysaccharide

*The answer is A.* The patient's clinical picture is consistent with S. aureus meningitis. S. aureus looks purple after a gram stain ("gram-positive"), because the cell wall retains the violet dye. The vast majority of bacteria can be divided into gram-3positive bacteria and gram-negative bacteria. These terms refer to the color of the bacteria after performing a gram stain, which involves first processing a sample slide with crystal violet dye, and then with a counterstain (often fuchsin). This stain differentiates between bacteria that have a single, membrane bilayer encased with a thick layer of peptidoglycan ("gram-positive"), from bacteria that have two membrane bilayers with a thin layer of peptidoglycan in between ("gram-negative"). This difference is perhaps most clinically relevant when considering antibiotic coverage of different types of organisms. Some antibiotics are not able to penetrate the membrane bilayer of gram-negative bacteria, while other antibiotics are not able to penetrate the thick peptidoglycan layer of gram-positive bacteria.

A 43-year-old patient with a history of esophageal cancer presents with sudden onset slurred speech. On CT scan, she is found to have an acute intraparenchymal hemorrhage, likely from a metastasis, with interventricular extension. Due to concern for hydrocephalus, an external ventricular drain is placed in order to control the intracerebral pressure. Two weeks later, she undergoes a lumbar puncture due to altered mental status, and the gram stain of the fluid is depicted in Figure A. Which part of the bacteria is responsible for the blue color on the stain? Review Topic A. Cell wall B. Mitochondria C. Golgi D. Nucleus E. Endoplasmic reticulum

*The answer is C.* Common pili, adhesins, and the glycocalyx are three bacterial structures that are involved in adherence.

A bacterial structure involved in adherence is (A) Capsule (B) Lipopolysaccharide (C) Common pili (D) O-specific side chain (E) Teichoic acid

*The answer is A.* A lysogenic bacterium can generate phage because it carries phage genes in a latent state (prophage). Lysogeny does not impart any special lytic properties to the bacterium nor, in general, does it affect conjugal transfer or the ability to support the replication of other unrelated phage. The presence of a prophage can convert certain bacteria to human pathogens, but such cases are rare.

A lysogenic bacterium A. carries a prophage. B. causes lysis of other bacteria on contact. C. cannot support the replication of a virulent phage. D. is often a human pathogen. E. is usually not capable of conjugal genetic transfer.

*The answer is E.* Nucleotide substitution and some missense mutations can be silent and not affect gene product function.

A mutation which rarely disrupts gene product function is a (A) Deletion (B) Frameshift (C) Insertion (D) Nonsense (E) Nucleotide substitution

*The answer is B.* Endotoxin is another name for lipopolysaccharide (LPS). This molecule is found projecting from the outer membrane of Gram-negative bacteria. It is composed of a glycolipid called lipid A which is anchored in the outer membrane. Attached to the lipid A is a group of sugars that make up the core polysaccharide and O side chain regions of the molecule. The toxic activity of LPS is attributed to lipid A, which is able to activate immune cells through the stimulation of Toll-like receptor 4 (TLR-4). Activation of cells through TLR-4 leads to NF-κ B-dependent transcription of proinflammatory cytokines such as tumor necrosis factor and interleukin-1. When endotoxin is present in large amounts in the blood, the massive release of these vasoactive cytokines increases vascular permeability leading to hypotension, or endotoxic shock. N-acetylmuramic acid is a component of peptidoglycan which makes up the bacterial cell wall. Teichoic acid is a polymer of ribose and glycerol and is found in the cell wall of Gram-positive bacteria.

A surgery patient at risk for Gram-negative sepsis is part of a research project to prevent endotoxic shock using monoclonal antibodies to inhibit the endotoxin molecule. What is the active component of the endotoxin molecule against which the monoclonal antibody would most likely be directed? (A) Core polysaccharide (B) Lipid A (C) N-acetylmuramic acid (D) O side chain (E) Teichoic acid

*The answer is C.* Transduction is the process by which genetic material is transferred from donor to recipient within a bacteriophage. This process does not require cell-to-cell contact and is resistant to DNase. Conjugation requires cell-to-cell contact between the donor and receipient cells. Transformation involves the exchange of naked DNA between donor and recipient in the absence of cell-to cell contact. However, DNA transformation is sensitive to DNase treatment. Transposition is the process in which a transposon excises from one location and integrates in another location within the same bacterial cell. Thus this process would not explain the transfer of a genetic marker between different bacterial cells. Transversion is not a means of geneticexchange.

A virulence factor can be transferred from one strain of bacteria to another in a genetic process that is independent of cell-to-cell contact between the donor and the recipient. Addition of DNase does not interfere with the transfer of the virulence factor either. From these characteristics, which of the following processes is involved in this genetic transfer? A. Conjugation B. Transformation C. Transduction D. Transposition E. Transversion

*The answer is B.* Resistance genes can be transferred by conjugation.

Each of the following statements concerning the mechanisms of resistance to antimicrobial drugs is correct EXCEPT: A. Resistance to some drugs is due to a chromosomal mutation that alters the receptor for the drug. B. Resistance genes are rarely transferred by conjugation. C. R factors are plasmids that carry the genes for enzymes that modify one or more drugs. D. Resistance to some drugs is due to transposon genes that code for enzymes that inactivate the drugs.

*The answer is C.* Isoniazid inhibits the mycolic acid synthesis in mycobacteria.

Each of the following statements regarding the selective action of antibiotics on bacteria is correct EXCEPT: A. Sulfonamides affect folic acid synthesis in bacteria, a pathway that does not occur in human cells. B. Penicillins affect bacteria rather than human cells because bacteria have a cell wall, whereas human cells do not. C. Isoniazid affects the DNA polymerase of bacteria but not that of human cells. D. Chloramphenicol affects the large subunit of the bacterial ribosome, which is different from the large subunit of the human ribosome.

*The answer is C.* Capsules, cell wall, and cytoplasmic membranes are found in both gram-positive and gram-negative bacteria. Endospores occur with certain gram-positive bacteria, e.g., Bacillus and Clostridium. Only gram-negatives have an outer membrane (Lipopolysaccharide layer).

What is the structure that is found in gram-negative but not in gram-positive bacteria? A. Cytoplasmic membrane B. Capsule C. Outer membrane D. Cell wall E. Endospore

*The answer is E.* There are two types of bacteriophages: lytic and temperate. The distinction is made according to the life cycle of the bacteriophage. On entering a bacterium, lytic phages produce phage nucleic acids and proteins, assemble many new phage particles, lyse the cell, and release the progeny phage. Temperate phages, however, can penetrate the bacterium and enter a dormant state called lysogeny, in which most viral genes are repressed. Bacterial functions remain active and the bacterium is not harmed. Some dormant phages replicate as plasmids; others, such as phage λ (lambda), become integrated into the host genome as prophages. The prophage DNA is replicated along with the host DNA as the bacterium grows and divides.

What occurs when a temperate bacteriophage enters a state called "lysogeny"? A. Most viral genes are expressed. B. The bacterial cell is lysed. C. Many new viruses are produced. D. Most normal bacterial functions are turned off. E. The virus may become integrated into the host genome.

*The answer is E.* Gram-positive bacteria have thick, multilayered, peptidoglycan cell walls that are exterior to the membrane. The peptidoglycan in most gram-positive species is covalently linked to teichoic acid, which is essentially a polymer of substituted glycerol units linked by phosphodiester bonds. All gram-positive species also have lipoteichoic acid in their membranes, where it is covalently linked to glycolipid. Teichoic acids are major cell surface antigens. Gram-negative bacteria have two membranes—an outer membrane and an inner (cytoplasmic) membrane. Their peptidoglycan layer is located between the two membranes in the periplasmic space. The periplasmic space also contains enzymes and various other substances. The outer membrane is distinguished by the presence of various lipopolysaccharides.

Which of the following components are found in the cell walls of gram-positive bacteria but not gram-negative bacteria? A. Cytoplasmic membrane B. Lipopolysaccharide C. Outer membrane D. Peptidoglycan E. Teichoic acid

*The answer is C.* This is an example of bacterial transformation.

Which of the following events is most likely due to bacterial transformation? A. A strain of Neisseria gonorrhoeae starts producing a plasmid-encoded beta-lactamase similar to that another Gram-negative strain. B. A formerly non-toxigenic strain of Corynebacterium diphtheriae becomes toxigenic. C. A non-encapsulated strain of Streptococcus pneumoniae acquires a gene for capsule formation from the extract of an encapsulated strain. D. A gene for gentamicin resistance from an Escherichia coli chromosome

*The answer is E.* Multiple drug resistance is almost always plasmid-mediated, which rules out 3 other options. Transposition is moving a piece of DNA to another molecule of DNA within the cell.

Which of the following mechanisms is most likely to be involved in multiple drug resistance transfer from one cell to another? A. Conjugation with a cell with chromosomal drug resistance appears in the genome of a bacteriophage that has infected it. B. Transposition C. Specialized transduction of a chromosomal gene for drug resistance D. Transformation of chromosomal genes E. Conjugation with a cell with a free plasmid carrying drug resistance

*The answer is E.* High-frequency recombination donors, which result from the integration of a fertility (F) factor into chromosomal DNA, are created by recombination.

Which of the following processes creates high-frequency recombination donors? (A) Transformation (B) Conjugation (C) Transduction (D) Transcription (E) Recombination (F) Translation