General microbiology-2 Flashcards
What is the basic structure of peptidoglycan?
Repeating disaccharide units:
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
Peptide cross-links provide rigidity
Which enzyme cross-links peptidoglycan, and which drug inhibits it?
Enzyme: Transpeptidase (Penicillin-Binding Protein, PBP)
Inhibitor: Beta-lactam antibiotics (e.g., Penicillins, Cephalosporins, Carbapenems)
What is the function of lysozyme, and which bacteria are resistant to it?
Function: Cleaves β-1,4 glycosidic bonds between NAG & NAM
Resistant Bacteria: Gram-negative bacteria (due to outer membrane protection)
Which bacterial structures are present in the Gram-negative outer membrane?
Lipopolysaccharide (LPS) → Endotoxin (Lipid A)
Porins → Allow passage of small molecules
Braun’s lipoprotein → Anchors outer membrane to peptidoglycan
What is the clinical significance of LPS in Gram-negative infections?
Lipid A triggers septic shock → Fever, hypotension, DIC
Causes activation of macrophages, complement, and cytokines (TNF-α, IL-1, IL-6)
What are L-form bacteria, and why are they important?
Bacteria that lack a cell wall but can still survive
Can be induced by penicillin or lysozyme
Significance: Persistent infections & antibiotic resistance
Which bacteria contain D-amino acids in their cell wall, and why is this important?
Most bacteria have D-alanine & D-glutamate in peptidoglycan
Prevents degradation by proteases that usually target L-amino acids
Why is Chlamydia resistant to β-lactam antibiotics?
Lacks muramic acid, a key component of peptidoglycan
β-lactams target peptidoglycan synthesis, making them ineffective
What is protoplast vs. spheroplast?
Protoplast: Gram-positive bacteria without a cell wall (completely removed)
Spheroplast: Gram-negative bacteria partially stripped of the cell wall
Which antibiotics target cell wall synthesis?
Beta-lactams (Penicillins, Cephalosporins, Carbapenems, Monobactams) → Inhibit PBP (Transpeptidase)
Glycopeptides (Vancomycin) → Binds D-Ala-D-Ala, blocking polymerization
Bacitracin → Inhibits bactoprenol recycling
Fosfomycin → Inhibits MurA (UDP-NAM synthesis)
Dip in cell membranes are called
Mesosomes/ Chondroids- respiratory unit of bacteria seen in both Gram + and Gram -ve but more in positive
Bacterial ribosomes
70 S- 50S + 30S
What is the composition of bacterial flagella?
Flagellin (protein subunit)
Three main parts:
Filament – Long, helical structure
Hook – Connects filament to basal body
Basal body – Anchors flagellum to the bacterial membrane and powers rotation
What are the different types of flagellar arrangements?
Monotrichous – Single flagellum (e.g., Vibrio, Pseudomonas)
Lophotrichous – Multiple flagella at one pole (e.g., Pseudomonas spp.)
Amphitrichous – Single flagellum at both ends
Peritrichous – Flagella all over the surface (e.g., Proteus mirabilis, Escherichia coli, Listeria)
Which bacteria show swarming motility due to peritrichous flagella?
Proteus mirabilis
Clostridium tetani
How does the basal body differ in Gram-positive vs. Gram-negative bacteria?
Gram-Positive
2 rings (M & S rings) in Plasma membrane
Gram-Negative
4 rings (L, P, M, S rings)
Outer membrane + Peptidoglycan + Plasma membrane
Which test detects bacterial motility due to flagella?
Hanging drop method – Direct microscopic observation
Motility agar test – Semi-solid agar showing diffused growth
What is the significance of the H antigen?
Flagellar antigen present in motile bacteria
Used in serotyping (e.g., Salmonella species)
What are spirochetes, and how do they move?
Spirochetes (e.g., Treponema pallidum, Borrelia burgdorferi)
Move by axial filaments (endoflagella), which run along the periplasmic space
Which antibiotic affects flagella-driven motility?
Metronidazole (affects flagellated anaerobes like Trichomonas and Giardia)
Which bacteria shows swarming growth pattern?
Proteus
C. tetani
B. cereus
V. parahemolyticus
V. alginolyticus
Serratia
What are pili (fimbriae), and what is their function?
Hair-like appendages on bacterial surfaces
Functions: Adhesion, biofilm formation, twitching motility, and conjugation
Fimbriae vs Pili
Fimbriae- shorter, numerous, for adhesion and biofilm formation
Pili- longer, few, for conjugation and motility
What are type I pili, and what is their role?
Mediate adhesion to host cells
Recognize mannose receptors on epithelial cells
Example: Escherichia coli (UTI-causing strains)
What are type IV pili, and what is their function?
Twitching motility → Extend, attach, and retract
Found in Neisseria gonorrhoeae, Pseudomonas aeruginosa, and Vibrio cholerae
What is the function of sex pili?
Involved in bacterial conjugation (gene transfer)
Encoded by F (fertility) plasmid
What are P pili, and what is their significance?
Found in uropathogenic Escherichia coli (UPEC)
Bind to P blood group antigens on uroepithelial cells → Cause pyelonephritis
Which lab test detects mannose-sensitive pili?
Hemagglutination inhibition test
What are curli fibers, and how do they differ from pili?
Curli fibers: Amyloid-like structures for biofilm formation
Found in Enterobacteriaceae (E. coli, Salmonella, etc.)
How do pili affect antibiotic resistance?
Facilitate horizontal gene transfer via conjugation
Spread antibiotic resistance genes (e.g., beta-lactamase genes)
Obligate aerobes
‘Must Let Nagging Pets Breathe’
MTB
Legionella
Nocardia
Pseudomonas
Bacillus, Brucella, Bordatella
Obligate anerobes
‘Choked By Air’
Clostridium
Bacteroides
Actinomyces
Facultative anerobes
Prefer O2 but can grow anerobically
Staph
Strept
Enterobacteriaceae
Hemophilus
Vibrio
Microaerophillic
5% of Oxygen needed
Helicobacter, Campylobacter
Capnophilic bacterua
Require CO2
Ex: Campylobacter, N. gonorrheae
Types of bacteria acc to temp it grows in-
Psychrophilic- <20 C
Mesophilic- 20-50 C
Thermophilic- 55-80 C
What enzymes protect bacteria from reactive oxygen species (ROS)?
Superoxide dismutase (SOD) – Converts superoxide (O₂⁻) → H₂O₂
Catalase – Converts H₂O₂ → H₂O + O₂
Peroxidase – Detoxifies H₂O₂ without releasing O₂
Example: Obligate anaerobes lack these enzymes → Susceptible to oxygen damage
What is the optimal pH range for bacterial growth?
Most bacteria: pH 6.5–7.5
Acidophiles: pH <6 (Helicobacter pylori, Lactobacillus)
Alkaliphiles: pH >8 (Vibrio cholerae)
What are obligate intracellular bacteria, and give examples?
Require a host cell for growth
Examples:
Chlamydia trachomatis
Rickettsia rickettsii
What is the bacterial growth curve, and what are its phases?
Lag phase – No increase in number, increase in size, enzymes and metabolites +
Max size seen at end of lag phase
Log (Exponential) phase – Rapid growth, most susceptible to antibiotics, max metabolic activity
Stationary phase – Nutrient depletion, growth rate = death rate
‘STAB’- Sporulation, exoToxin production, Antibiotic production, Bacteriocin production
Death phase – Exponential decline
What are quorum sensing bacteria, and why are they important?
Bacteria communicate using signaling molecules to coordinate group behavior
Important for biofilm formation & virulence
Example: Pseudomonas aeruginosa
How do anaerobic bacteria generate energy?
Use fermentation or anaerobic respiration
Final electron acceptors: Nitrate (NO₃⁻), Sulfate (SO₄²⁻), CO₂
What is the generation time, and which bacterium has the fastest one?
Time required for bacterial population to double
Fastest: Escherichia coli (~20 minutes)
Slowest: Mycobacterium tuberculosis (~18-24 hours)
On bacterial growth curve, X axis and Y axis represents?
X axis- time
Y axis- number of bacteria
What are the three main mechanisms of genetic exchange in bacteria?
Transformation, Transduction, and Conjugation
What is transformation in bacterial genetics?
It is the uptake of naked DNA from the environment by a competent bacterial cell and incorporation into its genome.
Done through cell wall or during log phase. Requires competence factor
Eg. S. pneumoniae
What are the two types of transduction?
Generalized Transduction (random DNA transfer via lytic phage) and Specialized
Transduction (specific gene transfer via lysogenic phage).
MC mode of drug resistance in S. aureus is via
Transduction
Generalized Transduction
(Random DNA Transfer)
Happens during the lytic cycle of a phage.
The bacteriophage mistakenly packages random bacterial DNA instead of its own viral DNA.
When this phage infects another bacterium, it injects this random bacterial DNA, which may integrate into the recipient’s genome.
🔹 Example: Imagine a thief robbing a house and accidentally grabbing a stranger’s wallet instead of valuables—then giving that wallet to someone else later.
Specialized Transduction
(Specific DNA Transfer)
Happens during the lysogenic cycle of a temperate phage.
The phage integrates into a specific site in the bacterial genome as a prophage.
When the phage exits the bacterial genome, it accidentally takes nearby bacterial genes along with it.
These specific genes get transferred to a new bacterium when the phage infects it.
🔹 Example: Think of a book being returned to the library, but a page from the borrower’s diary is stuck inside. The next person who reads it gets that extra information.
Example- Toxin genes like A and C toxin of S. pyogenes, Botulinum toxin, Cholera, Diphtheria, EHEC
What are the two main types of bacteriophages?
Lytic (virulent) phages and Lysogenic (temperate) phages.
What is the lytic cycle?
A process where a phage infects, replicates rapidly, and lyses the bacterial cell, releasing new phages.
What is the lysogenic cycle?
A process where the phage integrates its DNA into the bacterial genome as a prophage without killing the host immediately.
What is a prophage?
The integrated viral DNA inside the bacterial chromosome during lysogeny.
What is lysogenic conversion?
When a bacterium gains new properties (e.g., toxin production) due to prophage genes.
🔹 Example: Diphtheria toxin from Corynebacterium diphtheriae.
What is bacterial conjugation?
A process of direct gene transfer between bacteria through cell-to-cell contact, usually via a sex pilus.
What distinguishes conjugation from other horizontal gene transfer mechanisms?
Physical contact between bacteria is required, facilitated by the F pilus (sex pilus).
What happens when an F+ donor conjugates with an F- recipient?
The F plasmid is transferred, converting the F- bacterium into an F+ bacterium.
What is the F plasmid?
A fertility plasmid that carries genes required for conjugation, including pilus formation genes.
What is an Hfr bacterium?
High frequency recombination
A bacterium where the F plasmid is integrated into its chromosome, allowing transfer of chromosomal genes during conjugation.
What happens when an Hfr bacterium conjugates with an F- recipient?
Part of the chromosomal DNA is transferred, but the recipient remains F- unless the entire F plasmid is transferred.
What is an F’ plasmid?
An F plasmid carrying some bacterial chromosomal genes, formed due to improper excision from an Hfr strain.
How does conjugation contribute to antibiotic resistance?
R (resistance) plasmids carrying antibiotic resistance genes can be spread via conjugation.
How does conjugation differ between Gram-positive and Gram-negative bacteria?
Gram-negative bacteria use a sex pilus (e.g., E. coli).
Gram-positive bacteria use surface adhesins for direct contact (e.g., Enterococcus).
MC mode of MDR is ___
Except?
Conjugation
Except, S. aureus- Transduction»_space;» conjugation
S. pneumoniae- Transformation
F plasmid
Fertility factor
F+- male, present
F-= female, absent
F’ x F- =
F’ F’
R plasmid
Resistance Transfer factor (RTF) + Resistance determinants
Can carry many r at the same time
More dangerous, difficult to treat
Mutational drug resistance
D/t single mutation, easier to treat
Eg. Rifampicin resistance in TB d/t RPOB gene
CRISPR-Cas9
Cas9- ‘scissors’- cuts previously encountered viral DNA to protect bacteria from phage infections
C-Clustered
R- Regularly
I- Interspersed
S-Short
P-Palindromic
R- Repeats
It is the Bacterial defense system
Which test was developed based on CRISPR-Cas9?
FELUDA test for COVID
