Microbial Classification and Bacterial Morphology
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Questions and Answers

Which mechanism of action describes a drug that disrupts the bacterial cell wall?

  • Modification of Ribosomal Structure
  • Inhibition of Bacterial Cell Wall Synthesis (correct)
  • Disruption of Cytoplasmic Membrane Functions
  • Inhibition of Bacterial Protein Synthesis

Which of the following examples illustrates broad-spectrum antibiotics?

  • Gentamicin
  • Ampicillin (correct)
  • Vancomycin
  • Penicillin

What defines a narrow-spectrum antibiotic?

  • Works by disrupting bacterial membrane functions
  • Active against many types of bacteria, including both gram positive and gram negative
  • Primarily effective against specific types of bacteria (correct)
  • Causes cell death by inhibiting nucleic acid synthesis

Which of the following is NOT a characteristic of an ideal antimicrobial agent?

<p>Broad-spectrum activity against all microorganisms (A)</p> Signup and view all the answers

How do aminoglycosides primarily exert their antimicrobial action?

<p>By inhibiting protein synthesis at the 30S ribosomal subunit (B)</p> Signup and view all the answers

Which of the following drugs acts by disrupting cytoplasmic membrane functions?

<p>Polymyxins (A)</p> Signup and view all the answers

Bacteriostatic drugs primarily function by:

<p>Inhibiting bacterial multiplication (B)</p> Signup and view all the answers

Which of the following antibiotics is primarily effective against gram-positive bacteria?

<p>Vancomycin (B)</p> Signup and view all the answers

Which mechanism do common pili primarily utilize for bacterial adherence to host tissues?

<p>Surface adhesion (C)</p> Signup and view all the answers

What is the primary role of bacterial flagella in host invasion?

<p>Motility towards nutrients (C)</p> Signup and view all the answers

Which type of bacterial toxin is specifically associated with Gram-positive bacteria and has the ability to trigger fever?

<p>Endotoxins (D)</p> Signup and view all the answers

Which class of antimicrobial drugs functions by targeting the bacterial ribosome to inhibit protein synthesis?

<p>Macrolides (B)</p> Signup and view all the answers

What is the process by which bacterial endospores can convert back to vegetative cells when conditions are favorable?

<p>Germination (A)</p> Signup and view all the answers

Which factor is most directly associated with the metabolic activity and growth rate of oral microbes?

<p>Temperature fluctuations (B)</p> Signup and view all the answers

What is the primary role of the antimicrobial factors found in saliva?

<p>Controlling microbial growth and invasion (C)</p> Signup and view all the answers

How do dietary sugars influence microbial growth in the oral cavity?

<p>They provide essential nutrients for energy. (D)</p> Signup and view all the answers

Which type of immune response is primarily associated with the components found in GCF?

<p>Primarily innate immune response (D)</p> Signup and view all the answers

What impact does the genetic makeup of an individual have on their oral microbiome?

<p>It influences microbial colonization and growth patterns. (C)</p> Signup and view all the answers

Which of the following best describes how regular exposure to antimicrobial agents affects oral microbes?

<p>It can inhibit certain microbes or shift microbial balance. (B)</p> Signup and view all the answers

Which type of pH is typically maintained in the oral cavity, fostering microbial growth?

<p>Slightly acidic to neutral (6.5–7.5) (D)</p> Signup and view all the answers

What role does the complement system play in the immune response within the oral cavity?

<p>Promoting inflammation and enhancing phagocytosis (A)</p> Signup and view all the answers

What is a potential consequence of lactic acid production by oral bacteria?

<p>Alteration of the oral pH, increasing the risk of dental caries. (D)</p> Signup and view all the answers

Which of the following factors does NOT directly affect microbial growth in the oral cavity?

<p>Age of the individual (A)</p> Signup and view all the answers

What is the primary mechanism of drug synergism involving sulfonamides and trimethoprim?

<p>Both drugs block two steps in the folic acid synthesis pathway. (D)</p> Signup and view all the answers

Which type of symbiotic interaction occurs when both organisms benefit from their relationship?

<p>Mutualism (A)</p> Signup and view all the answers

Which of the following is NOT a harmful effect of normal flora?

<p>Stimulate immune system development (D)</p> Signup and view all the answers

What effect does clavulanic acid have when combined with amoxicillin?

<p>Inhibits bacterial enzymes that destroy amoxicillin. (C)</p> Signup and view all the answers

In which scenario is the risk of drug resistance most effectively reduced?

<p>Employing combination therapy with synergistic antibiotics. (C)</p> Signup and view all the answers

What is the primary role of normal microbiota in preventing colonization by pathogens?

<p>They compete for attachment and nutrients. (B)</p> Signup and view all the answers

Which of the following describes the process of one organism benefiting at the other's expense?

<p>Parasitism (A)</p> Signup and view all the answers

In the context of chronic infections, what is one of the primary concerns with prolonged antimicrobial treatment?

<p>Increased risk of drug reactions and superinfection. (D)</p> Signup and view all the answers

Which mechanism allows certain bacteria to resist the action of penicillin?

<p>Producing β-lactamase enzymes. (B)</p> Signup and view all the answers

Which of the following best describes the role of bacteria in synthesizing vitamins for the host?

<p>They secrete vitamins that are essential for host metabolism. (B)</p> Signup and view all the answers

Which mechanism allows bacteria to bypass reactions inhibited by certain drugs?

<p>Development of altered metabolic pathways (A)</p> Signup and view all the answers

What action do quinolones have in bacterial treatment?

<p>Inhibit the synthesis of bacterial DNA by blocking DNA gyrase (A)</p> Signup and view all the answers

What is the primary role of sulphonamides in bacterial inhibition?

<p>Compete with PABA for the same enzyme (D)</p> Signup and view all the answers

Which of the following is NOT a mechanism of resistance developed by bacteria against antimicrobial agents?

<p>Increased atmospheric oxygen levels (B)</p> Signup and view all the answers

In surgical prophylaxis, which patients are most likely to receive antimicrobial agents?

<p>Patients at high risk for infective endocarditis (A)</p> Signup and view all the answers

Which type of antibiotic primarily acts by damaging bacterial DNA?

<p>Nitrofurantoin (B)</p> Signup and view all the answers

What enzyme do sulphonamides inhibit to affect folic acid synthesis?

<p>Dihydropholic acid reductase (C)</p> Signup and view all the answers

Which of the following statements about competitive inhibition is true?

<p>It competes with an essential metabolite for the same enzyme. (B)</p> Signup and view all the answers

What is the role of rifampicin in bacterial treatment?

<p>Inhibit RNA synthesis (B)</p> Signup and view all the answers

Which type of drug resistance involves the production of enzymes that degrade the antibiotic?

<p>Inactivation through enzyme production (D)</p> Signup and view all the answers

Flashcards

Bacteriostatic drugs

Drugs that inhibit bacterial growth but do not kill them directly.

Broad-spectrum antibiotics

Antibiotics that are effective against multiple types of bacteria.

Narrow-spectrum antibiotics

Antibiotics that are effective against only a small group of bacteria.

Selective toxicity

The ability of a drug to harm a microorganism without harming the host cells.

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Bacterial cell wall synthesis inhibition

Antibiotics that stop bacteria from building their cell walls.

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Bacterial cytoplasmic membrane disruption

Antibiotics that damage the bacterial cell membrane, causing leakage of the cell contents.

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Bacterial protein synthesis inhibition

Antibiotics that prevent bacteria from making proteins.

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Bacterial ribosome differences

The distinct 70S (bacteria) and 80S (humans) ribosomes is why some drugs can target bacteria without harmful effects to the host.

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Drug Synergism

When two drugs work together to achieve a greater effect than either drug could alone.

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Sequential Block

Two drugs target different steps in a microbial metabolic pathway, effectively shutting down the process.

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Enhanced Drug Uptake

One drug alters the bacterial cell membrane, allowing the other drug to enter more easily.

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Enzyme Inhibition

One drug prevents bacterial enzymes from breaking down the other drug, extending its effectiveness.

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Normal Flora

Microorganisms (bacteria, fungi, protozoa) that live on/in animal and plant bodies without harming the host.

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Symbiosis

A close interaction between two different species.

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Commensalism

One organism benefits, the other remains unaffected.

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Mutualism

Both organisms benefit from the interaction.

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Parasitism

One organism benefits at the expense of the other, causing harm.

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Benefits of Normal Flora

Normal flora provides essential functions like vitamin production, defense against pathogens, and immune system stimulation.

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Quinolones' target

Quinolones target DNA gyrase, an enzyme essential for bacterial DNA replication. By blocking its activity, they prevent DNA from unwinding and replicating.

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Nitrofurantoin's mechanism

Nitrofurantoin works by damaging bacterial DNA directly, causing breaks and preventing its proper replication.

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Rifampicin's target

Rifampicin blocks bacterial RNA synthesis by binding to RNA polymerase, an enzyme responsible for transcribing DNA into RNA.

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Trimethoprim and Sulfonamides' mechanism

Trimethoprim and sulfonamides work by inhibiting the synthesis of folic acid, a critical component for bacterial nucleic acid production.

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Competitive inhibition explained

In competitive inhibition, a drug resembles a normal substrate and competes for the same active site on an enzyme, blocking its activity.

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PABA's role

Para-aminobenzoic acid (PABA) is a crucial metabolite for many bacteria, used as a precursor in folic acid synthesis, essential for nucleic acid production.

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Sulfonamides' competition with PABA

Sulfonamides are structurally similar to PABA and competitively inhibit its use in folic acid synthesis, blocking bacterial nucleic acid production.

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Trimethoprim's target

Trimethoprim inhibits dihydrofolic acid reductase, an enzyme crucial for converting dihydrofolic acid to tetrahydrofolic acid, a vital coenzyme in purine synthesis.

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Antimicrobial prophylaxis

Antimicrobial prophylaxis involves using antibiotics to prevent infections in individuals at risk, such as those with weakened immune systems or undergoing procedures.

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Mechanisms of bacterial resistance

Bacteria can develop resistance to antibiotics through various mechanisms, including inactivating enzymes, altering drug permeability, modifying drug targets, changing metabolic pathways, or altering enzyme activity.

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Lateral Mesosomes Function

Lateral mesosomes are invaginations of the plasma membrane in bacteria that increase the surface area for respiration, essentially providing extra space for energy production.

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Bacterial Nucleoid

The nucleoid is the region in a bacterial cell where the DNA is concentrated. Unlike eukaryotic cells, it lacks a membrane.

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Plasmid Function

Plasmids are small, circular DNA molecules found in bacteria. They can carry genes for antibiotic resistance, toxin production, and other traits which can be transferred to other bacteria.

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Bacterial Capsule Function

The capsule is a protective layer surrounding some bacteria. It helps bacteria evade the immune system, adhere to surfaces, and can be used in vaccines.

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Flagella Arrangement Types

Flagella are hair-like structures responsible for bacterial movement. There are four main arrangements: monotrichate (one at one pole), amphitrichate (one at each pole), lophotrichate (a group at one or both poles), and peritrichate (all around).

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GCF's Role

Gingival crevicular fluid (GCF) acts as a defense mechanism by containing immune components like IgG, neutrophils, complement proteins, and enzymes that combat microbial invasion, especially during increased bacterial activity.

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GCF Volume & Infection

During infection or inflammation, GCF volume increases, strengthening the immune response to protect periodontal tissues.

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Oral Cavity Temperature

The mouth provides a stable, warm environment (37°C) ideal for microbial growth. However, temperature fluctuations from hot or cold food/drinks can affect microbial activity.

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Oral Cavity pH

The mouth usually has a slightly acidic to neutral pH (6.5-7.5), favorable for most microbes. Saliva buffers pH, but acidic foods and microbial metabolism can change it, influencing microbial survival and dental caries.

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Nutrients for Microbes

Dietary sugars, proteins, and saliva glycoproteins provide nutrients for microbial growth in the mouth.

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Host Defenses in Saliva

Saliva contains antimicrobial factors like lysozyme, lactoferrin, and secretory IgA, which target and neutralize microbes.

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Host Defenses in GCF

GCF has leukocytes and antibodies that help fight pathogenic invasion, limiting microbial overgrowth and infection.

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Genetics & Oral Microbiome

Individual genetic variations influence the composition and resilience of the oral microbiome. Genetics impact immune responses, saliva composition, and oral surface features, shaping microbial colonization.

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Antimicrobial Agents & Microbes

Mouthwashes and toothpastes contain antimicrobial agents that can inhibit microbial growth or shift the microbial balance.

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Factors Affecting Microbial Growth

Factors like temperature, pH, nutrients, host defenses, genetics, and antimicrobial agents all influence microbial growth in the oral cavity.

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Study Notes

Microbial Classification

  • Microorganisms are divided into eukaryotes (contain a membrane-bound nucleus) and prokaryotes (lack a nuclear membrane).
  • Eukaryotic cells have a true nucleus, a nucleolus, a nuclear membrane, more than one chromosome, 80S ribosomes, and a respiratory system localized in mitochondria. They multiply by mitosis (e.g., fungi).
  • Prokaryotic cells have a premature nucleus, no nuclear membrane, one chromosome, 70S ribosomes, mesosomes, and a respiratory system localized in the cytoplasmic membrane. They multiply by binary fission (e.g., bacteria & rickettsia).

Bacterial Morphology and Staining

  • Bacteria are small, unicellular, prokaryotic organisms with a rigid cell wall, multiplying by binary fission.
  • Gram staining divides bacteria into Gram-positive and Gram-negative groups based on their reaction to the stain.
    • Gram-positive bacteria resist decolorization, appearing violet.
    • Gram-negative bacteria decolorize, appearing red.
  • Cell wall structure differs between Gram-positive and Gram-negative bacteria.
    • Gram-positive cell walls are thick (50-60%), composed of peptidoglycan and teichoic acid.
    • Gram-negative cell walls are thin (5-10%), composed of peptidoglycan, lipoprotein, outer membrane, lipopolysaccharide (endotoxin).

Function of the Bacterial Cell Wall

  • Preserves cell shape (rigidity).
  • Provides osmotic stability.
  • Differentiates Gram-positive and Gram-negative bacteria in staining.
  • Acts as an antigen.
  • Target for antibiotics (e.g., penicillin).

Cytoplasmic Membrane

  • Semi-permeable double-layered structure composed of phospholipids and proteins.
  • Involved in selective permeability and active transport.
  • Site of respiratory enzymes.
  • Excretion of toxins/proteins.

Bacterial Endospores

  • Highly resistant dormant forms of certain bacteria.
  • Formed during unfavorable environmental conditions.
  • Resistant to heat, chemicals and dehydration.
  • Have a thick cortex, low water content, and low metabolic activity.

Bacterial Growth Requirements and Physiology

  • Nutrients: Autotrophs use inorganic carbon sources like CO2 and nitrogen; heterotrophs rely on organic sources like sugars and proteins.
  • Oxygen: Strict aerobes require oxygen, obligate anaerobes cannot tolerate oxygen, facultative anaerobes can grow with or without oxygen, and microaerophiles require low oxygen levels.

Bacterial Products

  • Endopigments are localized inside the bacteria and color bacterial colonies (e.g., golden, yellow).
  • Exopigments diffuse outside the bacteria coloring the surrounding medium (e.g., greenish-blue ).

Bacterial Toxins

  • Exotoxins: Protein toxins that are diffusible, highly toxic, have strong specificity, are destroyed by heat, and can be detoxicated by formalin.
  • Endotoxins: Lipopolysaccharide toxins that are bound to the bacterial body, less toxic, have weak specificity, are stable, and not detoxicated by toxins.

Bacterial Growth and Reproduction

  • Bacterial growth is an increase in number via binary fission.
  • Lag phase: An initial period of adaptation to the new environment.
  • Log (exponential) phase: Rapid and continuous growth.
  • Stationary phase: Growth rate equals death rate resulting in no net change in population.
  • Decline (death) phase: Population decreases as resources are depleted.

Pathogenesis of Bacterial Infection

  • Pathogenicity: Ability to cause disease.
  • Virulence: Degree of pathogenicity (e.g., invasive factors like exotoxins and endotoxins)
  • Saprophytic bacteria: Grow on dead tissue.
  • Parasitic bacteria: Live within/on host tissues.
  • Commensal: Live in balance with the host, non pathogenic.
  • Opportunistic pathogen: Normally harmless but cause disease with impaired immunity or change in habitat.
  • Factors affecting host-parasite relationships: host factors, virulence/pathogenicity, mechanisms for colonization, and toxin production.

Antimicrobial Chemotherapy

  • Bactericidal: kill bacteria (e.g., penicillins).
  • Bacteriostatic: inhibit bacterial growth (e.g., tetracyclines).
  • Mechanisms of action: Target cell wall synthesis, cytoplasmic membrane functions, protein synthesis, and nucleic acid synthesis.
  • Resistance mechanisms: Inactivation enzymes, altered permeability, altered target receptors, and altered metabolic pathways.

Resistance to Antimicrobial Agents

  • Mechanisms: enzyme production, alteration of permeability, alteration of target, and alteration of metabolic pathways.
  • Avoiding antibiotics leads to the evolution of resistant pathogens.

Microbial Ecology of the Oral Cavity

  • Normal flora: Microorganisms living in balance with the host.
  • Types of symbiotic interactions: commensalism, mutualism, and parasitism.
  • Benefits of normal flora: synthesize vitamins, prevent pathogen colonization, and stimulate immune system.
  • Harmful effects: opportunistic pathogenicity, biofilm formation, and displacement.
  • Factors affecting growth: temperature, pH, nutrients, host, antimicrobial agents and genetics.

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Microbial Classification PDF

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Explore the fascinating world of microorganisms in this quiz. Learn about the differences between eukaryotic and prokaryotic cells, how bacteria are classified, and the significance of Gram staining in bacterial morphology. Test your knowledge on these fundamental concepts of microbiology.

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