Bacteria Flashcards
What is the correct definition of infectivity?
The ability of an organism to infect a host
Which of the following fluids should be microbe-free in a healthy individual?
Blood
What is the primary function of bacterial fimbriae and pili?
Adhesion to host cells
Which of the following is NOT a component of the innate immune response?
T cells
Which bacterial structure helps in immune system evasion by preventing phagocytosis?
Capsule
Which of the following is an example of an opportunistic pathogen?
Pseudomonas aeruginosa
Which bacterial species produces a neurotoxin that blocks acetylcholine release, causing flaccid paralysis?
Clostridium botulinum
Which of the following is a strategy bacteria use to evade the immune system?
Antigenic variation
Which bacterial pathogen is capable of living intracellularly and escaping from vacuoles to survive in the host cell’s cytoplasm?
Listeria monocytogenes
What type of bacterial toxin is heat stable and weakly toxic, but causes general symptoms such as fever and diarrhea?
Endotoxin
What is the correct definition of a commensal bacterium?
A bacterium that benefits from the host without harming it
How can commensal bacteria prevent pathogen colonization?
By occupying available niches and competing for resources
What can cause an imbalance in the human microbiome, leading to overgrowth of certain commensal bacteria?
Antibiotic use and immune deficiency
what does pathogenicity refer to?
Pathogenicity refers to a pathogen’s ability to cause disease
The human microbiome consists of:
Microorganisms and their genomes that inhabit the human body
What is dysbiosis?
A microbial imbalance or maladaptation in the body
What best describes a prebiotic?
A non-digestible food ingredient that promotes beneficial bacterial growth
What is the role of probiotics in the human microbiome?
They help stimulate immune system development and prevent pathogen colonization
Which of the following best describes probiosis?
An association between organisms that enhances life processes for both
How does the human microbiome influence bacterial pathogenesis?
It can contain bacteria that are commensal or mutualistic, but some may become pathogenic
What is one potential risk of disrupting the balance of the microbiome?
Development of dysbiosis, leading to infections
Which of the following is a potential benefit of the human microbiome?
Producing beneficial nutrients and destroying toxins
How do antibiotics contribute to microbial imbalance?
By killing both harmful and beneficial bacteria, disrupting microbiome balance
What happens when commensal bacteria spread into previously sterile areas of the body?
They may cause infections
Which of the following is an example of a prebiotic?
Fiber-rich foods that promote beneficial bacterial growth
Why is the microbiome sometimes referred to as a “second genome”?
It contains DNA that contributes to the overall genetic makeup of humans
What is the main function of gut microbiota in digestion?
Breaking down and fermenting complex carbohydrates
How does the microbiome contribute to immune system development?
It trains immune cells to recognize beneficial and harmful microbes
How many bacterial species can be found as normal oral flora?
Up to 500 species.
How many bacterial cells can be found in 1 mL of saliva?
40 million
Which bacterial genus and species is commonly known as a “lab rat” and is non-pathogenic?
Escherichia coli K12.
Which strain of E. coli is known for causing food poisoning and hemolytic uremia?
Escherichia coli O157:H7.
What is the difference between Bacillus subtilis and Bacillus anthracis?
B. subtilis is a soil bacterium and non-pathogenic, whereas B. anthracis causes anthrax.
What disease is caused by Neisseria meningitidis?
Bacterial meningitis.
What disease is caused by Neisseria gonorrhoeae?
Gonorrhea.
What is the primary function of flagella in bacteria?
Motility.
Which bacterium is responsible for peptic ulcers and requires motility for virulence?
Helicobacter pylori.
Does Listeria monocytogenes require flagella for virulence?
No, flagella-mediated motility is not essential for virulence.
What are the main methods used to classify bacteria?
Gram staining, morphology, nutritional/enzymatic properties, protein/lipid profiling.
What is the key difference between Gram-positive and Gram-negative bacteria?
Gram-positive bacteria have a thick peptidoglycan layer, whereas Gram-negative bacteria have an outer membrane and a thin peptidoglycan layer.
Which component in Gram-negative bacteria contributes to their outer protective layer?
Lipopolysaccharide (LPS).
Which type of bacteria contain teichoic acid in their cell wall?
Gram-positive bacteria.
Which bacterial species lack a conventional cell wall?
Chlamydia species.
Which staining method is used for Mycobacterium tuberculosis?
Acid-fast staining.
What is a bacterial capsule composed of?
Strain-specific complex carbohydrates.
Which bacterial species produces a slimy, mucoid colony due to its capsule?
Klebsiella pneumoniae.
Which bacterial shape is typically arranged in chains?
Cocci (e.g., Streptococcus species).
Which Gram-positive bacteria can form spores?
Bacillus and Clostridium species.
What are spores resistant to?
Heat (100°C), desiccation, and chemicals.
What are the basic elements required for bacterial growth?
Carbon, nitrogen, phosphate, sulfate, minerals, and trace elements like iron
What is MacConkey agar used for?
It is selective for Gram-negative bacteria and differentiates lactose fermenters.
Why do lactose fermenters appear different on MacConkey agar?
Fermentation lowers pH, causing a color change.
What is the oxygen requirement of Escherichia coli?
Facultative anaerobe.
What is MALDI-TOF MS used for?
Protein and lipid profiling for bacterial identification.
What is a limitation of MALDI-TOF MS in bacterial identification?
It is not suitable for very closely related strains or rare pathogens.
What is serotyping used for?
To detect specific surface structures (capsule, O-antigen, flagella).
What do the letters “K,” “O,” and “H” stand for in Escherichia coli serotyping?
K = Capsule, O = O-antigen, H = Flagella.
What are the two main genetic components of bacteria?
Chromosome (usually circular) and plasmids.
What are plasmids, and why are they important?
Plasmids are small, circular DNA molecules that can carry antibiotic resistance genes.
What is the purpose of PCR in bacterial identification?
To detect the presence of specific DNA sequences in a sample.
What is the advantage of whole genome sequencing in microbiology?
It helps track outbreaks, predict antibiotic resistance, and study pathogen evolution.
What are the three main mechanisms of horizontal gene transfer in bacteria?
Transformation, transduction, and conjugation.
Which form of gene transfer involves a bacterial virus (phage)?
Transduction.
Which form of gene transfer involves bacteria transferring DNA through direct contact?
Conjugation.
What is a transposon?
A “jumping gene” that can move within the genome.
How do bacteria reproduce?
Binary fission.
What is the formula for bacterial growth after n generations?
N = 2ⁿ.
What is the approximate doubling time of Escherichia coli under ideal conditions?
20 minutes.
After 8 hours, how many bacteria can a single E. coli cell produce?
About 16.7 million
What are the four phases of bacterial growth?
Lag, exponential (log), stationary, and death.
Which phase of bacterial growth is characterized by rapid division?
Exponential (log) phase.
What happens during the lag phase of bacterial growth?
Bacteria adapt to new conditions before starting to divide.
What is an antimicrobial?
A natural or synthetic chemical that kills or inhibits the growth of microorganisms.
What is the difference between an antibacterial agent and an antibiotic?
An antibacterial agent is any antimicrobial targeting bacteria, whereas an antibiotic traditionally refers to antibacterial compounds produced by microorganisms.
What is the difference between narrow-spectrum and broad-spectrum antimicrobials?
Narrow-spectrum antimicrobials target a limited number of bacterial genera, while broad-spectrum antimicrobials are effective against many bacterial genera.
What are the four main targets of antibacterial drugs?
1) Cell wall synthesis, 2) Protein synthesis, 3) Nucleic acid synthesis, 4) Metabolic pathways & cytoplasmic membrane.
How do beta-lactam antibiotics work?
They inhibit penicillin-binding proteins (PBPs), preventing transpeptidation in peptidoglycan cross-linking.
Why are glycopeptides only effective against Gram-positive bacteria?
Their large size prevents them from crossing the outer membrane of Gram-negative bacteria.
What is the mechanism of action of fosfomycin?
It inhibits MurA (enolpyruvate transferase), blocking the synthesis of N-acetylmuramic acid, a key bacterial cell wall component.
Which ribosomal subunit do aminoglycosides and tetracyclines target?
The 30S subunit.
Which ribosomal subunit do macrolides, chloramphenicol, and oxazolidinones target?
The 50S subunit.
Why are tetracyclines avoided in pregnant women and children?
affect bone and teeth development due to poor selectivity between bacterial and eukaryotic ribosomes.
What is the mechanism of action of quinolones?
inhibit DNA replication by targeting DNA gyrase and topoisomerases.
What is the mechanism of action of rifamycins?
block mRNA synthesis by inhibiting RNA polymerase.
How do sulfonamides work?
They prevent folic acid synthesis by competitively inhibiting the enzyme that binds PABA.
Why are sulfonamides selectively toxic to bacteria?
Humans acquire folic acid from their diet, while bacteria must synthesize it.
How do polymyxins work?
They act like detergents, disrupting bacterial membranes.
What are the steps in antimicrobial drug development?
Identifying targets, designing drugs, testing efficacy in vitro, testing in model organisms, clinical trials, and market approval.
What is peptidoglycan, and why is it important?
A unique component of bacterial cell walls that provides structural integrity.
How do beta-lactam antibiotics work?
They inhibit penicillin-binding proteins (PBPs), preventing transpeptidation in peptidoglycan synthesis.
What was the first beta-lactam antibiotic discovered?
Penicillin, discovered by Alexander Fleming in 1929.
What is the difference between bacterial and eukaryotic ribosomes?
Bacterial ribosomes are 70S (30S + 50S), while eukaryotic ribosomes are 80S (40S + 60S).
How do sulfonamides work?
They competitively inhibit an enzyme required for folic acid synthesis.
Why do sulfonamides have selective toxicity?
Humans acquire folic acid from their diet, whereas bacteria must synthesize it.
What is the mechanism of action of trimethoprim?
It inhibits dihydrofolate reductase (DHR), preventing tetrahydrofolic acid (THFA) synthesis.
What is the Minimum Inhibitory Concentration (MIC)?
The lowest concentration of an antibiotic that inhibits bacterial growth in vitro.
How is MIC used in clinical labs?
It helps determine if a bacterial isolate is sensitive, intermediate, or resistant to an antibiotic.
What are the two main mechanisms of beta-lactam resistance?
1) Producing beta-lactamases to degrade the antibiotic
2) Modifying PBPs to prevent binding.
What are the two ways bacteria acquire resistance?
1) Horizontal gene transfer
2) Mutations in target genes.
What is multidrug resistance (MDR)?
When bacteria develop resistance to multiple antibiotic classes.
What factors influence the pharmacokinetics of antibiotics?
Stability, dosage, tissue distribution, toxicity, and drug interactions.
Why is broad-spectrum antibiotic use a concern?
It increases resistance and disrupts normal microbiota.
What is antibiotic stewardship?
A strategy to optimize antibiotic use, reduce misuse, and prevent resistance.
How can hospitals reduce antibiotic resistance?
Proper hygiene, reducing device use, environmental cleaning, and antibiotic stewardship programs.
What is dual therapy, and why is it useful?
Using two antibiotics together to enhance effectiveness and reduce resistance development.
How can resistance enzymes be targeted to restore antibiotic activity?
By using inhibitors that block the resistance enzyme, allowing the antibiotic to work.
What is an example of combining old and new antibiotics to combat resistance?
Ceftazidime/avibactam – a cephalosporin combined with a novel beta-lactamase inhibitor.
How can hospitals reduce infection reservoirs?
Proper cleaning, minimizing catheter use, and maintaining aseptic techniques.
What public health measures help slow antibiotic resistance?
Education campaigns, antibiotic stewardship, and global surveillance (e.g., GLASS).
Why is antibiotic discovery challenging?
Clinical trials are expensive, failure rates are high, and patents last only ~15 years.
