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Questions and Answers
What distinguishes prokaryotic cells from eukaryotic cells?
What distinguishes prokaryotic cells from eukaryotic cells?
Which of the following statements is true about bacterial cell walls?
Which of the following statements is true about bacterial cell walls?
What is a major difference in ribosomal structure between eukaryotes and prokaryotes?
What is a major difference in ribosomal structure between eukaryotes and prokaryotes?
Which process is characteristic of prokaryotic reproduction?
Which process is characteristic of prokaryotic reproduction?
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What type of bacteria will appear red under a microscope after Gram staining?
What type of bacteria will appear red under a microscope after Gram staining?
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Which component is not found in the cell wall of Gram negative bacteria?
Which component is not found in the cell wall of Gram negative bacteria?
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What type of microorganism is characterized by having a rigid cell wall and reproducing through binary fission?
What type of microorganism is characterized by having a rigid cell wall and reproducing through binary fission?
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Which antimicrobial agent directly inhibits RNA synthesis?
Which antimicrobial agent directly inhibits RNA synthesis?
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What is the mechanism of action for sulphonamides?
What is the mechanism of action for sulphonamides?
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Which of the following mechanisms does NOT contribute to microbial resistance to antibiotics?
Which of the following mechanisms does NOT contribute to microbial resistance to antibiotics?
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In what situation is antimicrobial prophylaxis most commonly recommended?
In what situation is antimicrobial prophylaxis most commonly recommended?
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Which of the following is an example of an alteration of an enzyme as a resistance mechanism?
Which of the following is an example of an alteration of an enzyme as a resistance mechanism?
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What is the function of flagella in bacterial cells?
What is the function of flagella in bacterial cells?
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Which structure plays a critical role in bacterial virulence through adherence?
Which structure plays a critical role in bacterial virulence through adherence?
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What is the primary role of plasmids in bacterial cells?
What is the primary role of plasmids in bacterial cells?
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Which of the following correctly identifies a characteristic of bacterial endospores?
Which of the following correctly identifies a characteristic of bacterial endospores?
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What is the composition of the capsule in bacterial cells generally made of?
What is the composition of the capsule in bacterial cells generally made of?
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What type of pili is primarily involved in bacterial conjugation?
What type of pili is primarily involved in bacterial conjugation?
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Which subunits make up bacterial ribosomes?
Which subunits make up bacterial ribosomes?
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During sporulation, which structure is crucial for the formation of the resistant endospore?
During sporulation, which structure is crucial for the formation of the resistant endospore?
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Which type of flagella arrangement features a tuft of flagella at one or both poles?
Which type of flagella arrangement features a tuft of flagella at one or both poles?
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Which characteristic is true of exotoxins compared to endotoxins?
Which characteristic is true of exotoxins compared to endotoxins?
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What is the lag phase in bacterial growth characterized by?
What is the lag phase in bacterial growth characterized by?
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In which of the following scenarios is a shorter lag phase likely to occur?
In which of the following scenarios is a shorter lag phase likely to occur?
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Which statement about endotoxins is correct?
Which statement about endotoxins is correct?
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During which phase of the bacterial growth curve did the bacteria undergo rapid multiplication?
During which phase of the bacterial growth curve did the bacteria undergo rapid multiplication?
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What is the primary factor that affects the duration of the lag phase?
What is the primary factor that affects the duration of the lag phase?
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Which type of bacteria primarily produces exotoxins?
Which type of bacteria primarily produces exotoxins?
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What is the main reason spores are resistant to heat?
What is the main reason spores are resistant to heat?
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Which type of bacteria can survive in the absence of oxygen?
Which type of bacteria can survive in the absence of oxygen?
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How are exotoxins affected by heat?
How are exotoxins affected by heat?
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What change occurs to exotoxins when they are treated with formalin?
What change occurs to exotoxins when they are treated with formalin?
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What type of nutrient do heterotrophic bacteria require for growth?
What type of nutrient do heterotrophic bacteria require for growth?
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What aspect of endotoxins contributes to their weaker toxicity?
What aspect of endotoxins contributes to their weaker toxicity?
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What is the optimal temperature range for most pathogenic bacteria?
What is the optimal temperature range for most pathogenic bacteria?
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What type of growth conditions do facultative anaerobic bacteria prefer?
What type of growth conditions do facultative anaerobic bacteria prefer?
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Which of the following is true regarding bacterial pigments?
Which of the following is true regarding bacterial pigments?
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What is a common characteristic of strict aerobic bacteria?
What is a common characteristic of strict aerobic bacteria?
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What is required for the metabolic activity of bacteria in terms of temperature?
What is required for the metabolic activity of bacteria in terms of temperature?
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Which of the following is essential for all types of bacteria to grow?
Which of the following is essential for all types of bacteria to grow?
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Which statement accurately describes the quality of anaerobic bacteria?
Which statement accurately describes the quality of anaerobic bacteria?
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What is a consequence of the depletion of normal bowel flora following antibiotic therapy?
What is a consequence of the depletion of normal bowel flora following antibiotic therapy?
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What is the primary function of the peptidoglycan layer in bacterial cell walls?
What is the primary function of the peptidoglycan layer in bacterial cell walls?
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Which mechanism allows normal flora to cause opportunistic infections in immunocompromised individuals?
Which mechanism allows normal flora to cause opportunistic infections in immunocompromised individuals?
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Which component is specifically associated with Gram negative bacteria?
Which component is specifically associated with Gram negative bacteria?
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Which of the following statements regarding the characteristics of the oral cavity's microbial environment is true?
Which of the following statements regarding the characteristics of the oral cavity's microbial environment is true?
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Which statement accurately reflects the difference in cell wall composition between Gram positive and Gram negative bacteria?
Which statement accurately reflects the difference in cell wall composition between Gram positive and Gram negative bacteria?
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How do certain bacteria in the colon contribute to carcinogenesis?
How do certain bacteria in the colon contribute to carcinogenesis?
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What role does the lipopolysaccharide (LPS) layer play in Gram negative bacteria?
What role does the lipopolysaccharide (LPS) layer play in Gram negative bacteria?
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What is the role of biofilms in the oral cavity?
What is the role of biofilms in the oral cavity?
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Which condition can lead to the formation of protoplasts and spheroplasts?
Which condition can lead to the formation of protoplasts and spheroplasts?
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In what way does the cytoplasmic membrane contribute to bacterial cell function?
In what way does the cytoplasmic membrane contribute to bacterial cell function?
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Which of the following accurately describes the function of mesosomes in bacteria?
Which of the following accurately describes the function of mesosomes in bacteria?
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What is the primary reason spores are resistant to chemical disinfectants?
What is the primary reason spores are resistant to chemical disinfectants?
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Which type of bacteria relies on organic sources of carbon and nitrogen for growth?
Which type of bacteria relies on organic sources of carbon and nitrogen for growth?
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Which of the following is a characteristic of obligate anaerobic bacteria?
Which of the following is a characteristic of obligate anaerobic bacteria?
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What defines the optimal temperature for the majority of pathogenic bacteria?
What defines the optimal temperature for the majority of pathogenic bacteria?
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What is a condition that facultative anaerobic bacteria can thrive in?
What is a condition that facultative anaerobic bacteria can thrive in?
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Which factor is associated with the resistance of spores to drying?
Which factor is associated with the resistance of spores to drying?
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What typically distinguishes strict aerobic bacteria from other types?
What typically distinguishes strict aerobic bacteria from other types?
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Which of the following pigments might diffuse outside the bacterial cells affecting the surrounding medium?
Which of the following pigments might diffuse outside the bacterial cells affecting the surrounding medium?
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What is necessary for sufficient growth of bacteria concerning carbon dioxide concentration?
What is necessary for sufficient growth of bacteria concerning carbon dioxide concentration?
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Which mechanism explains how one drug may increase the uptake of another drug?
Which mechanism explains how one drug may increase the uptake of another drug?
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What is a primary disadvantage of using a combination of antibiotics?
What is a primary disadvantage of using a combination of antibiotics?
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In mutualistic symbiosis, how does the relationship benefit both organisms?
In mutualistic symbiosis, how does the relationship benefit both organisms?
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What is a common effect of normal flora on the host?
What is a common effect of normal flora on the host?
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What can result from a harmonious relationship between microflora and the host being disrupted?
What can result from a harmonious relationship between microflora and the host being disrupted?
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Which type of drug synergy involves blocking multiple steps in a metabolic pathway?
Which type of drug synergy involves blocking multiple steps in a metabolic pathway?
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What can occur as a disadvantage of combined antibiotic therapy?
What can occur as a disadvantage of combined antibiotic therapy?
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What role do enteric bacteria play for humans in regards to vitamins?
What role do enteric bacteria play for humans in regards to vitamins?
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Which statement is false regarding drug combinations?
Which statement is false regarding drug combinations?
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What type of symbiotic interaction causes harm to one organism while benefiting the other?
What type of symbiotic interaction causes harm to one organism while benefiting the other?
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What is the primary action of rifampicin in bacterial nucleic acid synthesis?
What is the primary action of rifampicin in bacterial nucleic acid synthesis?
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How do sulfonamides function as competitive inhibitors in bacterial metabolism?
How do sulfonamides function as competitive inhibitors in bacterial metabolism?
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Which of the following is NOT a mechanism by which bacteria may develop resistance to antimicrobial agents?
Which of the following is NOT a mechanism by which bacteria may develop resistance to antimicrobial agents?
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In surgical prophylaxis, which scenario does not typically require antibiotic administration?
In surgical prophylaxis, which scenario does not typically require antibiotic administration?
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What is the role of trimethoprim in the inhibition of bacterial nucleotide synthesis?
What is the role of trimethoprim in the inhibition of bacterial nucleotide synthesis?
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Which mechanism describes how bacteria can alter their metabolic pathways to resist antibiotics?
Which mechanism describes how bacteria can alter their metabolic pathways to resist antibiotics?
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Which statement accurately explains the purpose of antimicrobial combinations?
Which statement accurately explains the purpose of antimicrobial combinations?
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What does the alteration of permeability in bacterial resistance to antibiotics entail?
What does the alteration of permeability in bacterial resistance to antibiotics entail?
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In which condition is prophylactic antibiotic administration most necessary?
In which condition is prophylactic antibiotic administration most necessary?
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Which of the following statements about quinolones is true?
Which of the following statements about quinolones is true?
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Study Notes
Microbial Classification
- Microorganisms are divided into eukaryotes (with a membrane-bound nucleus) and prokaryotes (without a nuclear membrane).
- Eukaryotes have a true nucleus and nucleolus, a nuclear membrane, chromosomes greater than one, and sterols in their cytoplasmic membranes.
- Eukaryotes multiply through mitosis. Fungi are an example of eukaryotes.
- Prokaryotes have a premature nucleus without a nuclear membrane, single chromosomes, and no sterols in their cytoplasmic membranes, except for mycoplasma.
- Prokaryotes multiply by binary fission. Bacteria and rickettsia are examples of prokaryotes.
- Prokaryotes have 70S ribosomes, whereas eukaryotes have 80S ribosomes.
- Prokaryotic cells contain mesosomes, while eukaryotic cells do not have mesosomes.
Bacterial Morphology
- Bacteria are small, unicellular, prokaryotic organisms with a rigid cell wall that multiply by binary fission.
- Bacteria are categorized into Gram-positive and Gram-negative based on their staining properties.
- Gram-positive bacteria resist decolorization by alcohol, appearing violet under a microscope.
- Gram-negative bacteria decolorize with alcohol, taking up a counterstain (red) under a microscope.
- Bacterial cell walls have a distinct structure: Peptidoglycan layer varies greatly in thickness in positive versus negative. Teichoic acid is present in Gram-positive cells and absent in Gram-negative cells. Lipoproteins and outer membranes are present only in Gram-negative cells. Lipopolysaccharides (endotoxins) are also found only in Gram-negative cells
Bacterial Cell Wall Function
- The bacterial cell wall provides structural support and prevents osmotic lysis.
- It plays a role in differentiating Gram-positive and Gram-negative bacteria.
- The cell wall is antigenic.
- Teichoic acids in Gram-positive cells and lipopolysaccharides in Gram-negative cells are major antigens.
- The cell wall can serve as a target for antibiotics like penicillin and cephalosporins.
- Certain bacteria, such as mycoplasma, lack a cell wall.
Cytoplasmic Membrane
- The cytoplasmic membrane (plasma membrane) is a semi-permeable double-layered structure composed of phospholipids and proteins.
- It is involved in selective permeability, active transport, energy production (respiration), and excretion of toxins.
- It is site of respiratory enzymes.
Bacterial Endospores
- Endospores are highly resistant, dormant structures formed by certain Gram-positive bacteria (Bacillus and Clostridium) under adverse environmental conditions.
- These structures are resistant to heat, chemicals, and radiation, and can remain dormant for extended periods.
- Spores have a thick coat, low water content, and low metabolic activity.
- The process of spore formation is called sporulation, and its conversion back into a vegetative cell is named germination.
Bacterial Growth and Reproduction
- Bacterial growth is an increase in bacterial number.
- Bacteria multiply by simple binary fission.
- Bacterial growth is measured and described using a growth curve. Four phases include: lag phase, log phase, stationary phase, and death phase.
- Lag phase: A period of adaptation, where bacterial cells increase enzymes necessary for growth, but no increase in cell count is observed.
- Log (exponential) phase: The period of rapid bacterial growth, a constant increase in cell copy number.
- Stationary phase: Growth rate equals death rate, leading to a stable population size.
- Death phase: A period where cell death exceeds cell division, a decrease in cell copy number.
Bacterial Products
- Bacteria produce various products, some of which can have physiological and clinical relevance.
- Endopigments: Localized pigments within the bacteria. Examples include golden & yellow colors in staphylococcus.
- Exopigments: Pigments secreted outside the bacteria, coloring the media around bacterial colonies. Examples include greenish-blue pigments in species like pseudomonas.
Bacterial Toxins
- Bacteria produce several types of toxins.
- Endotoxins are lipopolysaccharides (LPS) bound to the bacterial cell wall that are released only when the cell disintegrates. They are less toxic and not destroyed by heat.
- Exotoxins are proteins released by living bacteria. Exotoxins are highly toxic, destroyed by heat, and usually specific to particular structures or tissues within the host.
Pathogenesis of bacterial infection
- Pathogenicity refers to the ability to cause disease in a host; its degree is measured by virulence.
- Bacteria are categorized into saprophytes (growing on dead tissue), commensals (causing no harm), or parasites (causing harm).
- Pathogenic bacteria may cause disease through colonization, infection, and various mechanisms.
- Factors affecting the host-parasite relationship include the host's natural and acquired immunity, as well as virulence and pathogenic factors in the bacteria.
Antimicrobial Chemotherapy
- Antimicrobial chemotherapy uses drugs to treat bacterial infections.
- Bactericidal drugs kill bacteria, whereas bacteriostatic drugs inhibit bacterial growth, which may require the host immune system to intervene.
- Mechanisms of action include targeting bacterial cell wall synthesis, cytoplasmic membrane function, protein synthesis, and nucleic acid synthesis.
- Drug resistance in bacteria arises from inactivation of drugs, alteration in permeability, alteration of targets, alteration in metabolic pathways, or enzyme alterations.
Microbial Ecology of the Oral Cavity
- The oral cavity contains a complex microbial community known as normal flora (bacteria, fungi, protozoa) which exists in harmony with the host, without causing harm or disease.
- This association can take on different forms—commensal, mutualist, or parasitic (when causing disease).
- Types of symbiotic interactions include: commensal, mutualist, and parasitic.
- Normal flora can, however, become pathogenic if factors like overgrowth, alteration in host tissues, or immune impairment occur, leading to opportunistic infection.
Four Distinct Features of the Oral Cavity
- Specialized mucosal surfaces (lips, cheeks etc) allow for microbial colonization;
- Teeth, also, are non-shedding surfaces that allow biofilms (bacterial colonies) to form in fissures, crevices, etc.
- Saliva contains antimicrobial factors including lysozyme and antimicrobial peptides which inhibit microbial growth.
- Saliva neutrally buffers the pH of the oral cavity, and provides nutrients to some bacteria.
- Gingival crevicular fluid (GCF) contains antibodies and other immune components that combat microbial invasion.
Factors Affecting Microbial Growth in the Oral Cavity
- Factors such as temperature, pH, nutrients, host defenses, genetics, and antimicrobial agents can influence microbial growth in the oral cavity.
- Temperature is a critical factor because oral microbial growth primarily occurs at approximately 37°C;
- pH influence microbial survival since most resident microbes thrive best within a narrow, slightly acidic to neutral pH range;
- Nutrients such as dietary sugars, proteins, and glycoproteins are essential for microbial growth.
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Description
Explore the fascinating world of microorganisms through this quiz on microbial classification and bacterial morphology. Learn about the differences between eukaryotes and prokaryotes, their unique characteristics, and how they reproduce. Test your knowledge on bacterial structures and classifications to deepen your understanding of microbiology.
