28 Questions
What is the phase of the microbial growth curve where the metabolic activities of individual surviving cells slow down and the number of new cells formed is balanced by the number of cells that die?
Stationary phase
Which of the following best describes the meaning of 'death' in the context of microbial cells?
Failure to give rise to a colony
What is the key challenge in measuring the death of bacterial cells?
All of the above
What is the phase of the microbial growth curve where cells begin to divide and enter a period of growth or logarithmic increase, and are most active metabolically?
Log phase
What is the phase of the microbial growth curve where there is a period of little or no cell division, which can last for 1 hour or several days?
Lag phase
Which enzyme is produced by Clostridium perfringens to degrade collagen?
Collagenase
Which type of secretion system in Gram-negative bacteria is responsible for exporting an autotransporter to the periplasm?
Type 5 secretion system
Which of the following bacterial enzymes can dissolve red blood cells (hemolysins)?
Cytolysins
Which type of secretion system in Gram-negative bacteria forms a tunnel structure?
Type 4 secretion system
Which bacterial pathogens are commonly found in biofilms on central venous catheters?
Staphylococcus epidermidis and Staphylococcus aureus
Which of the following is a correct statement about sterilization?
It destroys or eliminates all forms of microbial life from an object or environment.
Which of the following statements about disinfection is correct?
It eliminates many or all pathogenic microorganisms, except bacterial spores, from an object or an environment.
What is the mechanism of action of alcohols as biocides?
They act as liquid desiccants, causing dehydration of microbial cells.
Which of the following statements about pasteurization is correct?
It is the application of heat for the purpose of killing or retarding the development of pathogenic bacteria.
Which of the following terms refers to the presence of pathogenic microbes in living tissues?
Septic
Which of the following is a correct statement about bacteriostatic agents?
They inhibit bacterial multiplication, but upon removal of the agent, multiplication resumes.
What is the primary measurement of microbial concentration?
Cell concentration
What is the relationship between turbidity and viable cell count?
Turbidity is measured using a standard curve to relate it to viable cell count
What is the formula for the growth rate constant (k)?
$k = \frac{B}{t}$
Which of the following is NOT one of the five groups based on optimum growth temperature?
Cryophiles
What is the key difference between cell multiplication and increase in the number of single bacteria?
Cell multiplication refers to an individual cell dividing, while increase in the number of single bacteria refers to the overall population growth
Which of the following is NOT a way to measure microbial concentration?
Exponential growth
What is the primary mechanism by which bacterial DNA can be transferred via phages?
Phages mistakenly package bacterial DNA instead of their own DNA.
What is the key requirement for conjugation to occur between bacterial cells?
The donor cell must carry a conjugative plasmid, and the recipient cell must not carry that plasmid.
Which of the following is NOT a key characteristic of plasmids described in the text?
Plasmids often carry genes essential for bacterial survival.
What is the primary purpose of bacterial toxoids, as described in the text?
Toxoids are modified bacterial exotoxins that are no longer toxic.
Which of the following terms best describes a 'carrier' as defined in the text?
An organism that harbors a pathogenic microorganism but does not show any symptoms of disease.
Which of the following terms best describes the ability of a microorganism to cause disease, as discussed in the text?
Virulence
Study Notes
Bacterial Growth and Death
- LAG (latency period): 1 hour to several days, little or no cell division
- LOG (logarithmic growth phase): cells divide and enter a period of growth
- STATIONARY (equilibrium phase): metabolic activities slow, microbial death balances new cell growth
- DEATH: irreversible loss, no cell division, depends on the medium
Measurement of Bacterial Death
- Death is measured as a statistical problem, not individual cell death
- Constant per unit time, not customarily measured
Bacterial Control of Microbial Growth
- Phages can transfer bacterial DNA, not phage DNA
- Plasmids are self-replicating circular DNA molecules, often carrying non-essential genes
- Conjugation: plasmid-dependent DNA transfer, requires cell-to-cell contact, "bacterial sex"
Pathogenesis of Bacterial Infection
- Adherence: bacteria sticking to surfaces
- Carrier: organism with asymptomatic infection
- Infection: multiplication of infectious agents
- Invasion: organism entering a host cell and spreading
- Microbiota: microbial flora in a healthy individual
- Opportunistic pathogen: capable of causing disease
- Pathogen: capable of causing disease
- Pathogenicity: ability of an agent to cause disease
- Superantigens: protein toxins activating the immune system
- Toxigenicity: ability to produce toxins
- Virulence: quantitative ability of an agent to cause disease
Toxins and Enzymes
- Endotoxins: present in Gram-negative rods' outer membrane
- Exotoxins: classified by mechanism of action and impact on host cells
- Toxoids: made from exotoxins, modified to be non-toxic
- Tetanospasmin: toxin produced by C. tetani
- Cholera: V. cholerae
- Tissue-degrading enzymes: C. perfringens (collagenase), S. aureus (coagulase), Staphylococci, Streptococci, and Anaerobes (hyaluronidases)
- Cytolysins: dissolve red blood cells (hemolysins) or kill tissue cells/leukocytes (leukocidins)
Bacterial Secretion System
- Sec-dependent (type 2 and 5) and Sec-independent (type 1, 3, 4, 6) secretion systems
- Type 2: pore-forming protein complex, cholera toxin
- Type 5: gen.sec.to export an autotransporter to periplasm
- Type 1 and 3: do not interact with protein
- Type 4 and 6: 4 forms tunnel, 6 virulence protein
Biofilm
- Aggregates of interactive bacteria attached to a solid surface
- Found on human body surfaces and in nature
- S. epidermis and S. aureus: central venous catheter
- P. aeruginosa: cystic fibrosis
- Immune system and nutrient limitation, physical methods: sterilization, disinfection, pasteurization, aseptic technique
Microbial Control
- Antimicrobial agents: alcohols, aldehydes, Biguanides, Bisphenols, Halogen-releasing agents, heavy metal derivatives, organic acids, peroxygens, phenols, and cresol, quaternary ammonium compounds, vapor phase
- Sterilization: destroys all microbial life
- Disinfection: eliminates pathogenic microorganisms, except bacterial spores
- Pasteurization: application of heat to kill or retard pathogenic bacteria
- Sanitization: reduces pathogenic organisms to safe levels on inanimate objects
- Cleaning: removal of organic or inorganic material from objects and surfaces
- Biocide: chemical or physical agent that inactivates microorganisms
- Bactericidal: kills bacteria, causes lysis or dissolution of cells
- Bacteriostatic: inhibits bacterial multiplication, upon removal of the agent, multiplication resumes
Explore the concept of growth in microorganisms, including cell multiplication and increase in population. Learn how microbial concentration is measured using cell concentration and biomass concentration. Test your knowledge on viable cell count and other related topics.
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