Shared Flashcard Set

Details

Foundations in Microbiology
DRx Microbiology
63
Microbiology
Graduate
08/14/2013

Additional Microbiology Flashcards

 


 

Cards

Term
Phenotypic Bacterial Classification
Definition

- Hemolysis: Gamma (none), alpha (partial), and beta (full)

- Gram staining: G+ (purple) and G- (pink/red)

- Cell shape: Coccus (sphere), bacillus (rods), coccobacillus, spirochete (spiral), and vibrio (kidney bean)

- Arrangement: Chains, clusters, and pairs (diplococci)

Term
Bacterial Species not seen through Gram Staining
Definition

- Mycobacteria: Too much lipid in cell wall --> Acid-fast stain

- Treponema pallidum: Too thin to see --> Dark-field microscopy or immunofluorescence

- Mycoplasm pneumoniae: No cell wall/very small --> No stain

- Legionella pneumoniae: Intracellular --> Silver stain/immunofluorescence

- Chlamydiae: Intracellular --> Giemsa stain or inclusions

- Rickettsiae: Intracellular --> Giemsa or immunofluoresence

Term
Oxidative-Fermentation Test
Definition

- Determines if the strain is a obligate aerobe, facultative anaerobe, aerotolerant anaerobe, and obligate anaerobe

- Yellow discoloration in tubes means culture growth

Term
Coagulase Test
Definition

- Coagulase: Stimulates coagulation

- S. aureus: +

- S. epidermidis: -

- Easy way to test for the difference between the two

Term
Antibiotic Resistance and Susceptibility Testing
Definition

- Kirby-Bauer and E-strip Tests

- Particularly important now because so many organisms are antibiotic resistant

Term
Common Causes of Meningitis
Definition

- Depends on age group

- S. pneumoniae, N. meningitidis, enterovirus, and herpes simplex virus for 6-60 year olds

- N. meningitidis --> G- diplococci

- S. pneumoniae --> G+ diplococci

Term
Eukaryotes vs. Prokaryotes
Definition

- Eukaryotes: Nuclear membrane, 23 pairs of chromosomes, divides via mitosis, 80S ribosomes, presence of organelles, no cell wall, and cell membrane with sterols

- Prokaryotes: No nucleus, 1 chromosome, divides via binary fission, no organelles, 70S ribosomes, cell wall and cell membrane but no sterols

Term
Cell Wall of Gram-negative vs. Gram-positive Bacteria
Definition

- Gram-positive: Thick peptidoglycan layer, teichoic acid, no LPS, no periplasmic space, and no outer membrane

- Gram-negative: Thinner peptidoglycan layer within periplasm, no teichoic acid, and LPS and lipid A in outer membrane

Term
Peptidoglycan Structure
Definition

- Repeating units of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) units

- Cross-linked by tetrapeptide

- Cross-linking is the site for B-lactams such as penicillin G

- Lysozyme cleaves NAM and NAG bonds --> Weakens cell wall so cell might burst when put in hypotonic medium

- Found both in gram-negative and gram-positive

Term
Lipopolysaccharide (LPS) Structure
Definition

- Outer portion: repeating O-antigen subunits

- Middle portion: Core polysaccharide --> Hydrophilic

- Inner portion: Lipid A --> Embeds structure into the outer membrane

- Potent endotoxin due to lipid A --> Important in sepsis responses

- Found only in gram-negative bacteria

Term
Teichoic Acid Structure
Definition

- Found only in some gram-positive bacteria

- Polymers of ribitol or glycerol connected by phosphates

- Found in peptidoglycan layer

- Endotoxin but less potent than LPS

- Can mediate cell attachments and may contain antigenic determinants for vaccines, identification, and antibody formation

Term
Gram-Negative Bacterial Cell Wall
Definition

- Inner membrane

- Periplasm containing thin peptidoglycan layer

- LPS, mebrane proteins, and porins within outer layer

- Porins determine what moves in and out of the cell wall and membranes

- No sterols in either the inner or outer membranes

Term
Bacterial Cytoplasmic Membrane
Definition

- Does not contain sterols

- Site of active transport of molecules, electron transport chain, synthesis of cell wall precursors, and signal transduction

Term
Bacterial Cytoplasm
Definition

- Contains nucleoid, 70S ribosomes, granules, plasmids, and transposons

Term
Bacterial Capsule
Definition

- Polysaccharide layer surrounding outer membrane

- Found in some gram-postive and gram-negative strains

- Increases virulence

- Makes surface sticky --> Non-specific binding to surrounding

- Seen on staining through the Quellung reaction

- Inhibits phagocytosis

- Surface of capsule can be used to create vaccines that will opsonize the bacteria

Term
Biofilms
Definition

- Collections of bacteria

- Bacteria stick together via capsules

- Develop on the surface of teeth, contact lenses, mechanical valves, and artificial joints

- Produce polysaccharides which form mushroom-like shapes that help surround and protect bacterial colonies from phagocytosis and opsonization

- Overwhelm immune response simply by being too large for one macrophage or phagocytic cell to engulf on it's own

Term
Flagellum Structure
Definition

- Found on some gram-positive and gram-negative bacteria

- Good target for antibodies

- Allows bacterium to move

- Structure is anchored into the inner plasma membrane and functions as a protein motor

- Movement can increase virulence

- E. coli have flagella --> Cause UTIs by traveling up the urethra

Term
Pilus Structure
Definition

- Pili/fimbriae

- Shorter than flagella

- Allow specific adhesion and binding of bacterium to surfaces or specific host cells

- Can be used as targets for vaccines, etc

Term
Sex Pillus
Definition

- Long pillus extended from one bacterium to another

- Pulls two cells close enough to eachother to transfer genetic material

- Conjugation: Process for genetic exchange

Term
Secretion Systems
Definition

- Primarily present in G- bacteria

- Proteinaceous syringes that extend from the bacterium to the host cell

- Injects substances into host cell --> Genetic material, proteins, etc

- Makes the host cell do what the bacterium wants it to

Term
Spores
Definition

- Only present in Clostridium and Bacillus (G+ rods)

- Mechanism for survival in response to adverse environmental stimuli

- Have a keratin-like coat --> Extremely resistant to heat and disinfectants

- Metabolically inactive so can survive for many years

- Can germinate when conditions are right --> One bacterial cell

- Dipicolinic acid in the coat is also a Ca++ chelator

- Interior contains basically just the nucleoid and no other cytoplasm

Term
Bacterial Replication
Definition

- Occurs through binary fission

- Can be alot faster than in eukaryotes

- Only need to replicate one chromosome

- Replication time will determine how fast species can be cultured --> S. pneumoniae needs 2 weeks

- Transcription and translation are coupled so DNA replication and protein synthesis can be very fast

Term
Bacterial Growth
Definition

- Can occur on solid media, broth culture, blood agar, or on biofilms

- Lag phase: Bacteria are acclamating to their new environment --> No growth

- Exponential phase: Exponential growth

- Stationary phase: Growth stops

- Decline: Cells begin to die

- Four phases represented on a standard growth curve

- Phases and cell number can be seen by performing a direct cell count

- Turbidity of broth culture is also proportional to cell mass

Term
Bacterial Cell Division
Definition

1. Cell wall extends to size of about 2 cells

2. Chromosome replicates

3. Septum forms and DNA binds at the mesosome

4. Cell splits into two separate daughter cells

Term
Bacterial Metabolism
Definition

- Primarily through catabolism to form ATP

- Cellular components are then synthesized through anabolism

- Minimal growth requirements: Carbon, nitrogen, and iron

Term
Differences in Catabolism
Definition

- Anaerobes: Glucose --> Pyruvate via glycolysis --> Fermentation to get ATP + NADH (2 ATP)

- Aerobes: Glucose --> Pyruvate --> Kreb's --> Electron Transport Cahin (38 ATP)

Term
Metabolism and Classification
Definition

- Specific can be classified by:

1. Carbon source

2. Obligate vs. facultative intracellular grwoth

3. Aerobes vs. anaerobes

4. Ability to ferment certain sugars

Term
Anaerobes vs. Aerobes
Definition

- Obligate aerobe --> +SOD/+catalase

- Facultative anaerobe --> +SOD/+catalase

- Aerotolerant anaerobe --> +SOD/-catalase

- Strict anaerobe --> -SOD/-catalase

- Microaerophile --> +SOD/(-/+catalase)

- SOD and catalase used to degrade free radicals such as superoxide and hydrogen peroxide that are normally produced through ETC

Term
Catalase Test
Definition

- Identification test

- Determines Staphylococcus from Streptococcus bacteria

- Staphylococcus + --> Facultative anaerobe

- Streptococcus - --> Strict anaerobe

Term
MacConkey Agar
Definition

- Determines the ability to ferment lactate

- If bacteria grows then bacteria is able to ferment, if not then no

Term
Antibiotic Targets
Definition

- Many antibiotics target the assembly of cell wall proteins/structures

- Peptidoglycan units must be transported into periplasm to be assembled

- Bacitracin: Inhibits recycling of bactoprenol (NAM transporter)

- B-lactams: Inhibit tetrapeptide cross-linking

- Fosfomycin: Inhibits NAG-NAM binding

Term
Virulence Gene/Factor
Definition

- Encodes a protein that is required for virulence

- Might allow for adhesion and allow the bacteria to establish infection

- Examples: Pili/adhesin or biofilm protein

Term
Virulence Gene Cues
Definition

1. Low free iron availability: Stimulates diptheria toxin production

2. 37C vs. 20C: Stimulates pilin protein production by E. coli that allows bacteria to adhere to bladder wall

3. Eukaryotic cell binding: Initiates type III secretion system formation --> Inserts genes that inhibit macrophage phagocytosis, cytokine secretion, and initiate apoptosis (Yersinia)

4. High cell density/Quorum sensing: Used by P. aeuruginosa in CF patientsĀ 

Term
Negative Regulatory Protein
Definition

- Binds gene promoter and inhibits transcription

- Ex. Diptheria toxin promoter region bound when Fe concentrations are high

Term
Positive Regulatory Proteins
Definition

- Activator proteins bind DNA at promoter to activate transcription

- Also directly interact with RNA polymerase

- Two component system: Signal sensor in membrane and transducer that actually binds DNA + RNA polymerase

- Ex. Salmonella: Type III secretion system injects proteins to induce gut epithelial cells to engulf bacteria --> Sensor in bacterial membrane now realize that it's in phagosome --> Stimulates proteins that allow bacteria to live in that environment

Term
Methods for Evading Host Immune System
Definition

- Anti-phagocytic capsule (H. influenzae, N. meningiditis, and S. pneumoniae)

- Intracellular growth

- Antigenic variation (N. gonorrhoeae): DNA rearrangement occurs within pilin protein genes

Term
Mechanism of Antigenic Variation
Definition

- N. gonorrhoeae: Has 18 pilin genes --> Only PilE gene can be transcribed because it has promoter, others are PilS genes

- Variation due to recombination of PilS genes into the PilE gene to create a new pilin gene formation

Term
Transformation
Definition

- Bacteria pickes up naked DNA from the environment

- DNA then inserts itself into the chromosome via homologous recombination

- Common in N. gonorrhoeae and S. pneumoniae

- Transformation can occur to change pilin protein and account for antigenic variation as well

Term
Mutagenesis
Definition

- Process of mutations causing a gene to now encode a protein with different function --> Generally presents as a difference in phenotype

- Genotype: Linear DNA sequence

- Phenotype: Growth/appearance of bacterial cell

- Can result from a missense, nonsense or frame-shift mutation

- Most mutations are silent or very detrimental

- Slow and inefficent process but it does happen

Term
Development of Antibiotic Resistance
Definition

- Due to the prevalence of prophylactic treatment with antibiotics

- Antibiotics are put into cattle feed --> Environmental tolerance

- Resistance found in chromosomal DNA that has entered via recombination

- Changes the structure of antibiotic targets such as ribosomes, membrane transporters, and RNA polymerase

- Renders the antibiotic ineffective at active site

- DNA can also now encode sequences for efflux pumps for antibiotics

- Ex. DNA might now encode for a methylase which methylates active site

Term
Plasmids
Definition

- Small circular replicons --> Contain origin of replication (ori) site

- Carry non-essential genes for cell growth/replication

- Some carry transfer (Tra) genes --> Allows for transfer or conjugation between cells

- Other plasmids not containing Tra genes can be transferred but they must be recombined into a plasmid containing the Tra gene first (mobilization)

- Can transfer between bacteria and even yeast

Term
Fertility Plasmid Conjugation
Definition

1. One bacterial cell with a plasmid containing the F+ gene will extend sex pilus to another cell

2. Sex pilus then contracts to pull cells close together

3. Plasmid undergoes special type of DNA replication --> One parent strand goes to one cell while the other remains --> Complementary strands replicated during transfer

4. Plasmids can then recombine with other plasmids or incorporate into chromosome

Term
Mobile Genetic Elements
Definition

1. Transposons: Carry genes needed for transposition (transposase) and generally carry the antibiotic resistance genes --> Must be taken up from environment by bacterial cellsĀ 

2. Conjugative Transposons: Also have tra genes --> Able to move between two bacterial cells

- Transposons can then insert themselves into plasmids within the cytoplasm

Term
Bacteriophage
Definition

- Viruses that infect bacterial cells

- Consist of DNA/RNA molecule and surrounding proteins

- Most have a capsid and phage tail --> Attachment

- Need to infect a cell to replicate

Term
Lytic Phase of Bacteriophage
Definition

- Converts the infected bacteria into a phage-producing factory

- Virulent phage: Phage that only grows lytically

- Can produce 100-10,000 new phage

- Proteins and DNA synthesized --> Phage particles assembled

- Bacterial cell wall degraded by enzymes --> Phages released

Term
Lysogenic Phase for Bacteriophage
Definition

- Phage DNA becomes incorporated into bacterial chromosome at attachment (att) site

- Some phage have tRNA-like genes that simply integrate via homologous recombination with tRNA genes

- Repressor protein is transcribed --> Represses the lytic gene

- Prophage: Phage integrated into host DNA

- Lysogenic/Temperate Phage: Capable of both the lytic and lysogenic phases

- Enters into lytic phase once repressor protein is no longer produced and lytic gene is turned on --> Random event

Term
Generalized Transduction by Bacteriophage
Definition

- Phage carried bacterial chromosomal DNA within its capsule

- This DNA was acquired during lytic phase when bacterial DNA was packaged into phage instead of phage DNA

- These phage cannot duplicate because they do not contain phage DNA

- This DNA must be integrated into the host in order to replicate again

Term
Specialized Transducing by Bacteriophage
Definition

- Phage DNA contains extra genes that appeared due to imprecise excision from host DNA, integration of a transposon or another random recombination event

- These phages are always lysogenic

- DNA is then incorporated into new host DNA

- Lysogenic conversion occurs in the host

- Ex. Diptheria and cholera toxins

Term
Therapeutic Uses of Bacteriophage
Definition

- Since bacteriophages infect bacteria, could potentially be used to treat infections

- Highly specific to bacterial species

- Non-toxic to animals and plants

- Side effects and allergic reactions have rarely been seen

Term
Pathogenicity Islands
Definition

- Contiguous blocks of virulence genes found in bacterial DNA --> Usually on plasmids

- Found in diverse bacterial species

- Genes generally code for proteins with the same functions and amino acid sequences

- Implies that these genes came from one common ancestor

- Acquired by genetic transfer between species --> Different GC content from rest of DNA

- Bacterial strains without island of DNA show little or no virulence --> Specific DNA sequences confer virulence

Term
Virulence
Definition

- Ratio determined by the LD50/ID50

- Can change depending on particular host --> Age, disease state, medications, etc

- Decreased LD50 --> Increased virulence

- Shigella: Extremely virulent (ID50~10-100)

- Salmonella: ID50= 10^6 normally, but much lower in patients on antacids

- Factors: Pili, capsules, LPS, peptidoglycan, and teichoic acid structure, flagella, outer membranes, and surface proteins

Term
Susceptibility in Immunodeficiencies
Definition

- B-cells: Bacterial infections (antibodies crucial)

- T-cells: Viral and fungal infections (Killer T-cells crucial)

- B+T-cells: Bacterial, viral, fungal, and protozoal infections

- Phagocytic deficiencies

- Complement deficiences: Recurrent Neisseria infections

- Factors for immunodeficiencies: AIDS, immunosuppressive drugs, diabetes, genetic disorders, old age, stress, poor nutrition, pregnancy, splenectomy, tobacco, drugs, alcohol, and medications

Term
Acute vs. Chronic Infections
Definition

- Most infections are acute and assymptomic

- Symptoms short lived if present at all

- Chronic infections --> May begin as asymptomatic (carrier) but can transmit to others

- MRSA, gonorrhea, and chlamydia are common chronic infection bacteria

Term
Stages of Disease
Definition

1. Incubation period: Time from acquisition to first specific symptom (days to months)

2. Prodrome: Period with general illness symptoms (fever, malaise, muscle cramps, etc)

3. Clinical Illness: Time from the first specific symptom to the resolution

4. Recovery: Time till you're back to normal

Term
Transmission and Entry of Pathogen
Definition

- Relates back to the structure of the bacteria itself

- G- are tough --> Can live in water/environment

- G+ are more delicate --> Transmitted by close contact (Neisseria)

- Points of entry: Nose, mouth, eyes, respiratory tract, genitourinary tract, and skin (cuts and sores)

Term
Evasion of Host Defenses
Definition

- Must overcome normal flora for space, food, etc

- Normal flora also produce natural antibiotics

- IgA protease --> Break down mucosal IgA antibodies

- Factor A: Binds Fc region on IgG to inhibit complement activation

- Leukocidins: Destroy leukocytes and macrophages

- Coagulase: Helps surround pathogen with fibrin clot

- Capsules inhibit phagocytosis

- Biofilm formation also inhibits phagocytosis and opsonization

- Ability to escape phagosome after phagocytosis

- Ability to inhibit lysosome binding with phagosome after phagocytosis

Term
Adherence to Host Cells
Definition

- Pili, capsules, and teichoic acid structure

Term
Colonization and Spread
Definition

- Localized --> S. aureus abcess

- Minimal spread --> Erysipelas due to Strep.

- Disemination systemically --> N. gonorrhoeae

- Intracellular growth: Invade using special surface proteins or type III secretion systems

- Can also grow in biofilmsĀ 

Term
Invasion, Inflammation and Intracellular Survival
Definition

- One way to cause disease

- Produce enzymes to help spread and break down barriers --> hyaluronidase, collagenase, phospholipase, and streptokinase

- Anti-phagocytic factors --> Factor A and capsule

- Pyogenic inflammation --> Pus-producing --> Neutrophils (acute)

- Granulomatous inflammation --> Chronic with macrophages and T-cells

Term
Exotoxins
Definition

- Secreted by pathogens

- Encoded by genes on phages or plasmids

- Very toxic in small doses

- Good antigens --> Can produce toxoids

- Some have A-B subunit --> A is active (toxic) and B is the binding portion for cell receptors

- Superantigens: Simultaneously bind T-cell receptor and MHC class II molecule on APC --> Cytokine storm!!!

Term
Endotoxins
Definition

- Integral part of cell wall of G- rods and cocci --> Primarily LPS

- Also possible with peptidoglycan, teichoic acid on G+ bacteria (S. aureus) --> Not as potent

- Encoded by genes in bacterial chromosome

- Less toxic than exotoxins

- Not good antigens --> No toxoids

- Released upon lysis or blebbing of bacteria

- Most common cause of sepsis and disseminated intravascular coagulation (DIC)

- Induce high concentrations of IL-1, TNF, NO, and complement

Term
Other Causes of Bacterial Pathogenesis
Definition

- By-products: Acids and gas production leading to tissue damage

- Immunopathogenesis: Molecular mimicry --> Cross-reactivity between pathogen and host tissue

- Ex. Rheumatic heart disease

- Neoplasia: Can be caused by persistent infections

Term
Gram Staining Procedure
Definition

1. Stain with crystal violet

2. Stain with Grams iodine

3. Wash with alcohol

4. Stain with safranin

Supporting users have an ad free experience!