132 Questions
What is the role of pili size in conjugation?
It may influence the efficiency of DNA transfer
Which of the following is true about transposons?
They are segments of DNA that can move within a genome
What happens when both conjugation occurs in a cell?
Both the donor and recipient cells have a complete copy of the plasmid
What is the main function of a conjugative plasmid in conjugation?
To be replicated in the donor and transferred through the pilus
What is the significance of transposons jumping onto a conjugative plasmid?
Results in the acquisition of resistance or virulence genes by transposition
What are some factors that influence recipient cell uptake of exogenous DNA?
The presence of various promoters and terminators
Which process involves the release of DNA in genetic transformation through the active secretion by live cells?
Active secretion
In genetic transformation, what role do plasmids play in the process of donor cell releasing DNA?
Plasmids release small fragments during passive leakage
What is the primary concern associated with the transfer of antibiotic resistance genes between bacterial strains?
Risk of spreading resistant genes to the environment
How does intraspecies transfer primarily occur within a species?
Via sexual reproduction and parasexual processes
What is the main difference between generalized and specialized transduction?
Generalized transduction can transfer any part of the bacterial genome, while specialized transduction transfers specific parts near the prophage integration site.
Which type of transduction involves the transfer of botulinum toxin or cholera toxin genes?
Specialized transduction
What happens when a prophage is excised from the bacterial chromosome in specialized transduction?
The recipient cell receives a specific set of genes from the donor.
In specialized transduction, why are only close genes to the prophage integration site affected?
To ensure the recipient receives a specific set of genes.
Which statement accurately describes how generalized transduction introduces new genes into the recipient?
By transferring any part of the bacterial genome through recombination with the recipient's chromosome.
What distinguishes generalized and specialized transducing phages based on their virulence factor encoding abilities?
Generalized phages do not encode virulence factors, specialized phages do.
What is the primary reason for slipped-strand mispairing leading to insertions or deletions in DNA?
Errors in DNA replication
Which of the following mechanisms can introduce genetic material from closely related species into bacterial genomes?
Natural transformation
What is the consequence of hyper slipped-strand mispairing where a nucleotide is added or subtracted?
Premature stop codon or nonfunctioning protein
Which process involves the exchange of genetic material within the same genome?
Intra-genomic recombination
During chronic infection with 'non-issue causing' colonizing microbes, approximately how much of the genome can be replaced in 40 years?
50%
What is the main result of variable motility due to slip strand mispairing in multiple phase variable genes?
Change in gene regulation
Which process involves bacteria taking up free DNA fragments from the environment?
Natural transformation
What role does active secretion of DNA play in antigenic variation?
Enables bacteria to share genetic material and surface antigen genes
How does natural competency contribute to antigenic variation in bacteria?
Enables bacteria to uptake and incorporate foreign DNA, potentially changing their antigenic profiles
What is the main outcome of the interaction between active DNA secretion and natural competency in bacteria?
Facilitation of rapid antigenic evolution
How does reversible DNA sequence change differ from antigenic variation?
Antigenic variation involves change via DNA recombination
In the context of bacterial evolution, what is the significance of phase variation?
Enables bacteria to switch between only two variants of a surface antigen
What is the specific role of phage receptors in the infection process?
Attaching to the bacterial cell to initiate the infection process
During which stage of phage replication does the genetic material take control of the host cell's machinery?
Biosynthesis
What occurs during the lysis and release phase of phage replication?
Release of phage particles from the host cell
What is the primary function of the phage capsid during the infection process?
Facilitating attachment to the bacterial cell
Why is it essential for phages to redirect the host cell's machinery during replication?
To produce new genetic material for the phage
What is a key requirement of Koch's postulate for confirming that a microbe causes a specific disease?
The microbe must cause the disease symptoms in a lab setting without infecting a host
Who among the 'Founding Fathers of Microbiology' is credited with the pasteurization of milk?
Louis Pasteur
Which of the Founding Fathers of Microbiology is known for being the 'father of microbiology' due to his invention of the first microscope?
Antonie Van Leeuwenhoek
What distinguishes Joseph Lister's contribution among the Founding Fathers of Microbiology?
Discovery of sterilization methods for surgery equipment
Who developed the first vaccine for polio among the Founding Fathers of Microbiology?
Jonas Salk
Why is it important to target unique bacterial components when developing antimicrobial agents?
To ensure that antimicrobials selectively attack bacteria without harming the host's cells
What is the significance of targeting essential functions for bacterial growth with antimicrobial agents?
It effectively kills or inhibits the growth of bacteria
How does targeting virulence factors impact bacteria's ability to cause infections?
It disarms the bacteria, making them less able to establish infections or evade the immune system
Which process do antimicrobials target by focusing on DNA replication, protein synthesis, and cell division?
Critical processes for bacterial survival and proliferation
In developing antimicrobials, why is it crucial to consider the host's cells?
To reduce toxicity and side effects in humans
What is the primary advantage of targeting unique bacterial components over broadly attacking all cellular functions?
It minimizes damage to host cells
How does targeting essential functions for bacterial growth with antimicrobials relate to bacterial survival?
It effectively kills or inhibits the growth of bacteria
What is the primary intention behind targeting virulence factors with antimicrobial agents?
To weaken bacteria's ability to infect host organisms and cause diseases
Which characteristic makes targeting unique components in bacteria more advantageous than generalized antimicrobial approaches?
Reduces the risk of side effects in humans
How does focusing on essential functions for bacterial growth aid in combating bacterial infections?
Eliminates bacteria effectively without harming host cells
What is the primary role of Bacitracin in inhibiting bacterial cell wall synthesis?
Disrupts the synthesis of cell walls
Which biochemical process does Fluoroquinolone impact to exert its effect?
Inhibits DNA gyrase/topoisomerase
What is the main target of Beta-lactams in bacterial cells?
Transpeptidation process
How does Cycloserine exert its inhibitory action on bacteria?
Promotes DNA gyrase activity
Which of the following is a direct impact of microbes requiring folic acid for DNA biosynthesis?
Requirement for folic acid in diet
How do Beta-Lactam antibiotics work?
Block the transpeptidation step in cell wall synthesis
What is the role of D-ala in peptidoglycan synthesis of Gram-negative bacteria?
It is used to link one brick to another during transpeptidation
What sets Gram-positive bacteria apart from Gram-negative bacteria in terms of their cell wall synthesis?
Formation of an interpeptide bridge
What happens when Beta-Lactam antibiotics block the transpeptidation step?
Causes the formation of a weak cell wall
Why are Gram-positive bacteria harder for antibiotics to penetrate compared to Gram-negative bacteria?
They possess an interpeptide bridge in their cell wall
What makes Beta-Lactam antibiotics effective against bacterial infections?
They disrupt the formation of strong chemical bonds between peptidoglycan units
In peptidoglycan synthesis, what is the consequence of inhibiting transpeptidation?
Formation of a thinner cell wall
Which step in cell wall synthesis do Beta-Lactam antibiotics specifically target?
'Cementing' by transpeptidation
What effect does the formation of an interpeptide bridge have on Gram-positive bacteria?
It increases resistance to antibiotics
What is the main consequence of targeting transpeptidation in bacterial cell wall synthesis with Beta-Lactam antibiotics?
Weakening of peptidoglycan structure
What is the mechanism by which bacteria have developed resistance to beta-lactams?
By acquiring beta-lactamases to cleave the beta-lactam ring
What action do bacteria take to counteract the use of beta-lactam antibiotics combined with beta-lactamase inhibitors?
Acquiring alternate transpeptidases like PBPs
How do bacteria make beta-lactam antibiotics ineffective?
By evolving to replace D-ala with other amino acids in cross-linking peptides
What role do penicillin-binding proteins (PBPs) play in bacterial resistance to antibiotics?
They are acquired by bacteria as a defense mechanism
How does vancomycin-resistant Enterococcus (VRE) evade the inhibitory action of vancomycin?
By replacing D-ala-Dala with D-ala-Delactate in cross-linking peptides
What strategy are scientists exploring to combat bacterial resistance to beta-lactams?
Developing analogs that mimic the structure of D-ala
How does cycloserine inhibit bacterial growth?
By preventing L-ala conversion to D-ala by racemase
Why are beta-lactam antibiotics rendered ineffective against bacteria that have acquired beta-lactamases?
The beta-lactam ring is cleaved before transpeptidase can recognize it
How do bacteria make Beta-Lactams ineffective?
They replace D-alanine with other amino acids in cross-linking peptides
What is a common strategy used by bacteria to resist Beta-Lactams?
Utilizing Beta-Lactamases to cleave the Beta-Lactam ring
Why is Mycoplasma resistant to Beta-lactam antibiotics?
It does not have a cell wall
What is a common mechanism of resistance found in Acinetobacter baumannii?
Efflux systems
Which bacterial species is intrinsically resistant to vancomycin due to the termination of its pentapeptides in D-ala-D-lactate?
Leuconostoc
What is the approximate spontaneous mutation rate frequency for antibiotic resistance?
One mutation per 10^8 cells
Which bacterial alteration causes methicillin resistance in Staphylococcus?
Mutation of penicillin-binding proteins
What type of bacterial mutation can cause resistance to quinolones in E. coli?
Mutation of DNA gyrase
What role do altered ribosomes play in bacterial resistance to antibiotics?
Altered structure preventing correct antibiotic binding
How do porin mutations contribute to bacterial antibiotic resistance?
By reducing antibiotic uptake through the cell membrane
What is a specific advantage of phage therapy compared to antibiotics?
Can evolve host range mutants
What is a characteristic of lytic phages used therapeutically in phage therapy?
They replicate rapidly
Why did phage therapies drop after the introduction of antibiotics?
Antibiotics were considered miracle drugs
What is a drawback associated with early phage therapy experiments?
Limited controls in experiments
Why are lytic phages preferred over temperate phages in phage therapy?
They are less pathogenic
What makes phages unique compared to antibiotics in terms of administration?
They can be taken orally
What issue arises due to the large number of unidentified ORFs found in phages?
Difficulty in determining their activity
In what context can bacteriophages be used as biomarkers?
Microbiota drivers investigation
What is the historical significance of phage typing in microbiology?
A method of identifying bacteria based on their susceptibility to specific bacteriophages
What term did Felix d’Herelle coin to describe viruses that infect bacteria?
Bacteriophages
What is the outcome of the destruction of bacterial DNA during the bacteriophage lifecycle?
Lysis of the bacterial cell
What is the primary function of phage display in microbiology?
Creating a library of peptides or proteins displayed on the surface of phages
What is the relationship between bacteriophages and cloning vectors?
Cloning vectors are derived from bacteriophages
What happens when a bacterial cell is lysed during the lytic/virulent phage lifecycle?
The bacterial cell is killed by the phage particles released.
What contributes to the virulence of the bacterium in cases where lysogen-carrying bacteria are present?
Phage genes carried by the bacteria.
How do eukaryotic viruses differ from bacterial viruses in terms of their effect on host cells?
Eukaryotic viruses can cause chronic infections like HIV in host cells.
Which scenario can result from an Eukaryotic virus mutating to change host preferences?
Eukaryotic virus becoming resistant to immune attacks.
In what way do temperate phages differ from lytic/virulent phages in their impact on infected cells?
Lytic/virulent phages can contribute to increased virulence of infected cells.
What allows C. Difficile to survive passage through the stomach when ingested?
Formation of spores
Which factor is directly linked to the risk of C. Difficile colonization in healthcare settings?
Length of hospital stays
What is the primary role of Toxin B in causing pseudomembranous colitis symptoms?
Causing inflammation in the colon
In the mechanism of action of Toxin A and Toxin B, what type of proteins do they inactivate by glucosylation?
G proteins
Which characteristic of C. Difficile contributes to its persistence in the environment for many months?
Formation of spores
How can members of a hospital transmit C. Difficile spores to other patients?
Through the air as aerosols
Which condition is ideal for C. Difficile to overgrow in the colon?
Use of probiotics
Which characteristic of C. Difficile makes it a challenge to eradicate from healthcare settings?
Formation of biofilms on surfaces
What is the primary role of IgG response to ToxA when faced with toxigenic c.diff?
Induces symptomatic CDI
How does the use of antibiotics contribute to the proliferation of C.diff?
Removal of beneficial bacteria
What consequence arises when an individual acquires Toxigenic c.diff WITHOUT IgG response to ToxA?
Symptomatic CDI
What happens when Non-toxigenic c.diff is acquired?
Asymptomatic colonization
Why is CDI more prevalent in hospitals compared to outside settings?
Opportunistic after antibiotic use
What is the impact of antibiotics on the bacteria that aid in defense during an infection?
Removing them from the gut microbiota
What determines whether an individual with Toxigenic c.diff will be symptomatic or asymptomatic?
Composition of microbiota
What is the significance of the release of toxins causing organ failure?
Inducing systematic inflammation
How does the acquisition of Non-toxigenic c.diff differ from acquiring Toxigenic c.diff WITH IgG response to ToxA?
Asymptomatic colonization vs. symptomatic CDI
Why are vancomycin and metronidazole preferred for treating Clostridium difficile infections?
They are ineffective against normal gut flora
Why is it important to stop treating Clostridium difficile infections with the antibiotics that led to the disease?
The antibiotics can kill off normal gut flora
Why is vancomycin not effective against Bacteroides species?
Vancomycin cannot penetrate the outer membrane of Bacteroides species
Why is metronidazole not effective on some gut bacteria?
Some gut bacteria deactivate metronidazole with enzymes
What makes Clostridia a polyphyletic group?
Their uncertain relationships between species within the group
What characteristic protects Clostridia from environmental stressors?
Endospore formation
What happens if Pseudomembranous Colitis is left untreated?
'Patch coalescing' into septic shock
What is the purpose of Fecal Transplant in dealing with Clostridium difficile (C.Diff) infections?
Introduce healthy flora to the patient
Which Clostridium species is known for causing gas gangrene in open wounds?
Clostridium perfringens
What is the function of Butyrate produced by certain groups of Clostridium bacteria in the colon?
Suppress pathogen proliferation
Which toxin, when released by Clostridium tetani, results in violent muscle spasms?
Tetanus toxin
What is the main benefit of using Clostridium acetobutylicum engineered into E. coli?
Production of short chain alcohols
What is the primary effect of Butyrate on the colon's barrier integrity?
Increase in epithelial cell proliferation
Which Clostridium bacteria was used by Chaim Weizmann to produce short chain alcohols?
Clostridium acetobutylicum
What is the role of Botulinum toxin released by Clostridium botulinum?
Inhibits release of acetylcholine from axons
What is a characteristic of Clostridium bacteria that produce Butyrate?
Ferment non-digestible carbs to form Butyrate
Study Notes
Conjugation Plasmids
- In conjugation, the pili size might influence the efficiency of DNA transfer
- Donor carrying plasmid creates a pilus that is attached to the recipient
- Conjugative plasmid is replicated in the donor and then single-stranded transferred through the pilus to the recipient
- Recipient can now express plasmid genes
- Results in the acquisition of resistance or virulence genes by transposition
Genetic Transformation
- Genetic transformation is a technique used to introduce foreign genetic material into the genome of living organisms
- Process involves two main components: vector (plasmid carrying a selectable marker gene) and target bacteria or other organism(s)
- Steps to achieve successful transformation: donor cell releases free circular DNA, recipient cell engulfs the plasmid, and plasmid replicates and integrates into the host genome or remains episomal
- Antibiotic resistance genes can be transferred between bacteria, and non-antibiotic resistance genes can also be transferred, indicating a broader potential impact on environmental communities
Recipient Cell Uptake
- Recipient cell uptake of exogenous DNA plays a crucial role in genetic transformation
- Factors influencing uptake efficiency: size, shape, and chemical modification of DNA molecule, presence of promoters and terminators, and biological properties of recipient cell type
Intraspecies Transfer
- Intraspecies transfer occurs primarily through sexual reproduction and parasexual processes like illegitimate recombination
- Interspecies transfer happens through horizontal gene transfer mechanisms like transformation, conjugation, and transduction
Donor Cell Releasing DNA
- Process of genetic transformation relies on the ability of recipient cells to take up and incorporate foreign DNA
- Donor cells release DNA through passive leakage, active secretion, or programmed cell death
Transduction
- Transduction is a mechanism of horizontal gene transfer that occurs through bacteriophages
- Generalized transduction: phage infects bacterium and begins lytic cycle, can transfer any part of bacterial genome
- Specialized transduction: occurs with lysogenic phages, transfers specific parts of bacterial genome, and DNA transferred is usually located near the prophage's integration site
Mechanisms of Genetic Diversity
- Reassortment, diversification, natural transformation, point mutation, intra-genomic recombination, and slipped-strand mispairing are mechanisms that create genetic diversity
Genetic Modification
- Mutation: DNA sequence changes that are usually non-reversible
- Reversible DNA sequences: change via DNA recombination or mutations with repeated sequences
- Antigenic variation: alternate expression of multiple variants of surface antigen
- Phase variation: on-off expression or switching between only two variants of a surface antigen
Phage Infection and Replication
- Attachment: phage attaches to a bacterial cell by binding to specific receptor sites
- Penetration: phage injects its genetic material into the host cell
- Biosynthesis: phage's genetic material takes over the host cell's machinery
- Assembly: newly synthesized phage genomes and capsids are assembled into complete phage particles
- Lysis and Release: phage concludes its replication cycle by lysing the host cell, releasing new phage particles
Microbiology
- Koch's postulate: microbe must be associated with symptoms of the disease, isolated from the lesion, and reproduce the disease in a susceptible host
- Features of a good target for antimicrobial agents: targeting unique bacterial components, essential functions for bacterial growth, and virulence factors
- Antibiotic resistance: targeting cell wall synthesis, ribosome, and DNA gyrase/topoisomerase
Cell Wall Synthesis
- Synthesis of peptidoglycan: gram-negative bacteria, gram-positive bacteria, and transpeptidation
- Beta-lactam antibiotics: inhibit transpeptidation, and bacteria develop resistance by acquiring beta-lactamases, alternate transpeptidases, and modifying the terminal amino acid
ESKAPEE Pathogens
- Enterococcus faecium (VRE)
- Staphylococcus aureus (MRSA)
- Klebsiella pneumonia (ESBL-producing)
- Acinetobacter baumannii
- Enterobacter species
- Escherichia coli
Mechanisms of Resistance to Antimicrobials
-
Natural resistance: lack of permeability, lack of target, and chromosomal-encoded efflux pumps
-
Mutation: spontaneous mutation rate frequency, reduced uptake, altered target, and mutation of penicillin-binding proteins
-
Horizontal gene transfer: sharing of genetic material between bacteria### Phage Therapy
-
Phage therapy has several advantages, including:
- Specificity: can target specific pathogens without disrupting normal bacteria flora
- Nontoxic: phages are regularly consumed in foods and have been shown to be unintended contaminants in various medications and vaccines
- Cheap: phages are the only medicine that multiplies, making them cost-effective
- Rapid activity: phages have a high rate of success in treating bacterial infections
- Resistance: while phage-resistant bacterial mutants can occur, most cases are less pathogenic
- Evolve host range mutants: phages can evolve to target specific hosts, making them a unique medicine
-
However, phage therapy also has some drawbacks, including:
- Narrow specificity: phages can be limited in their target range
- Problems in certain industries (e.g. dairy industry)
- Large number of unidentified ORFs (open reading frames)
- Potential to carry virulence genes (although this is less likely with lytic phages)
- Problems with early phage therapy, including exaggerated or unsubstantiated claims, poorly conceived experiments, and limited controls
Discovery of Bacteriophages
- Bacteriophages were first discovered by E.H. Hankin in 1896, who reported that something in the waters of the Ganges River could pass through a fine porcelain filter and had marked antibacterial action
- Frederick Tworth and Felix d'Herelle later recognized viruses that infect bacteria, which d'Herelle called "bacteriophages" (eaters of bacteria)
Phage Lifecycle
- The phage lifecycle includes:
- Infection: phages attach to and penetrate host cells
- Destruction of bacterial DNA: phages break down the host cell's DNA
- Replication of viral genome: phages replicate their own genetic material
- Production of viral parts: phages assemble new viral particles
- Packaging: phages package their genetic material into new viral particles
- Lysis: phages lyse the host cell to release new viral particles
Variants of Phage Lifecycle
- There are two types of phage lifecycles:
- Lytic/virulent: phages always lyse infected cells
- Temperate: phages lyse cells 50% of the time, and can be induced by certain chemicals, UV light, and antibiotics
Phage Behaving Badly
- Phages can sometimes behave badly, including:
- Lysogen-carrying bacteria: many bacteria carry phage genes, which can contribute to the virulence of the bacterium
- Lethal for starter cultures: phages can infect and kill bacteria in starter cultures, such as those used in cheese and yogurt production
C.Difficile Infections
- C.Difficile infections are a major problem, especially in hospitals, where:
- Antibiotic use: inhibits the growth of beneficial bacteria, allowing C.Diff to overgrow
- Hospital stays: increase the risk of colonization and transmission
- C.Diff spores: can persist in the environment for many months and survive passage through the stomach
- Early symptoms: include diarrhea, which can lead to aerosol and fecal contamination
Pathogenic Mechanism of C.Difficile
- C.Difficile produces two main toxins: Toxin A and Toxin B, which:
- Glucosylate (inactivate) a threonine residue on certain G proteins
- Interfere with normal cellular function, leading to symptoms of pseudomembranous colitis
Treatment Strategies for C.Difficile
- Current treatment strategies include:
- Stopping antibiotics and administering vancomycin or metronidazole
- Fecal transplants: reintroducing healthy flora to the gut
- Phage therapy: targeting C.Difficile with specific phages
Prevention Strategies for C.Difficile
- Prevention strategies include:
- Reducing antibiotic use
- Improving hospital hygiene and infection control
- Using probiotics to promote healthy gut flora
- Developing vaccines against C.Difficile
Test your knowledge on the transfer of plasmids between bacterial cells through conjugation. Explore how pili size can impact the efficiency of DNA transfer and how plasmids can acquire new resistances or virulence factors. Understand the process of replication and single-stranded transfer of conjugative plasmids.
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