88 terms

3a - Basic bacteriology

3a - Microbiology - Basic bacteriology
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Peptidoglycan
Gives rigid support, protects against osmotic pressure.

Sugar backbone with peptide side chains crosslinked by transpeptidase.
Cell wall/cell membrane (gram positives)
Major surface antigen.

Peptidoglycan for support. Lipoteichoic acid induces TNF and IL-1.
Peptidoglycan
Gives rigid support, protects against osmotic pressure.
Sugar backbone with peptide side chains crosslinked by transpeptidase.
Cell wall/cell membrane (gram positives)
Major surface antigen.
Peptidoglycan for support. Lipoteichoic acid induces TNF and IL-1.
Outer membrane (gram negatives)
Site of endotoxin (lipopolysaccharide [LPS ]); major surface antigen.
Lipid A induces TNF and IL-1; O polysaccharide is the antigen.
Plasma membrane
Site of oxidative and transport enzymes.
Phospholipid bilayer
Ribosome
Protein synthesis.
50S and 30S subunits.
Periplasm
Space between the cytoplasmic membrane and outer membrane in gram-negative bacteria.
Contains many hydrolytic enzymes, including B-lactamases.
Capsule
Protects against phagocytosis.
Polysaccharide (except Bacillus anthracis, which contains D-glutamate) .
Pilus/fimbria
Mediate adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation.
Glycoprotein.
Flagellum
Motility.
Protein.
Spore
Resistant to dehydration, heat, and chemicals.
Keratin-like coat; dipicolinic acid; peptidoglycan.
Plasmid
Contains a variety of genes for antibiotic resistance, enzymes, and toxins.
DNA.
Glycocalyx
Mediates adherence to surfaces, especially foreign surfaces (e.g., indwelling catheters).
Polysaccharide.
Gram-positive Circular (coccus)
Staphylococcus
Streptococcus
Gram-negative Circular (coccus)
Neisseria
Gram-positive Rod (bacillus)
Clostridium
Corynebacterium
Bacillus
Listeria
Mycobacterium (acid fast)
Gardnerella ( Gram variable)
Gram-negative Rod (bacillus) Enterics :
• E. coli
• Shigella
• Salmonella
• Yersinia
• Klebsiella
• Proteus
• Enterobacter
• Serra tia
• Vibrio
• Campylobacter
• Helicobacter
• Pseudomonas
• Bacteroides
Gram-negative Rod (bacillus) Respiratory:
• Haemophilus (pleomorphic)
• Legionella (silver)
• Bordetella
Gram-negative Rod (bacillus) Zoonotic:
• Francisella
• Brucella
• Pasteurella
• Bartonella
Gram-positive Bra nch ing fila m entous
Actinomyces
Nocardia (weakly acid fast)
Gram-negative Pleomorphic
Rickettsiae (Giemsa)
Chlamydiae (Giemsa)
Gram-negative Spiral Spirochetes:
• Leptospira
• Borrelia (Giemsa)
• Treponema
No cell wall
Mycoplasma (does not Gram stain)
Contain sterols and have no cell wall.
Mycoplasma
Contain mycolic acid . High lipid content.
Mycobacteria
These bugs do not Gram stain well:
Treponema (too thin to be visualized) .
Rickettsia (intracellular parasite).
Mycobacteria (high lipid content in cell wall detected by carbolfuchsin in acid-fast stain).
Mycoplasma (no cell wall) .
Legionella pneumophila (primarily intracellular).
Chlamydia (intracellular parasite; lacks muramic acid in cell wall) .

These Rascals May Microscopically Lack Color.
Treponemes - dark-field microscopy and fluorescent antibody staining.
Legionella -silver sta in.
Giemsa
Chlamydia, Borrelia, Rickettsiae, Trypanosomes, Plasmodium.

Certain Bugs Really Try my Patience.
PAS (periodic acid-Schiff)
Stains glycogen, mucopolysaccharicles; used to diagnose Whipple's disease (Tropheryma whipplei).
PASs the sugar.
Ziehi- Neelsen (carbol fuchsin)
Acid-fast organisms (Nocardia, Mycobacterium) .
India ink
Cryptococcus neoformans (mucicarmine can also be used to stain thick polysaccharide capsule red).
Silver stain
Fungi (e.g., Pneumocystis) , Legionella, Helicobacter pylori.
H. influenzae
Chocolate agar with factors V (NAD+) and X (hematin)
N. gonorrhoeae, N. meningitidis
Thayer-Martin (or VPN) media-Vancomycin (inhibits gram-positive organisms) , Polymyxin (inhibits gram-negative organisms except Neisseria), and Nystatin (inhibits fungi); "to connect to Neisseria, please use your VPN client"
B. pertussis
Bordet-Gengou (potato) agar (Bordet for Bordetella)
C. diphtheriae
Tellurite plate, Loffler's media
M. tuberculosis
Lowenstein-Jensen agar
M. pneumoniae
Eaton's agar
Lactose-fermenti ng enterics
Pink colonies on MacConkey's agar (fermentation produces acid, turning colony pink); E. coli is also grown on eosin-methylene blue (EMB) agar as colonies with green metallic sheen
Legionella
Charcoal yeast extract agar buffered with cysteine and iron
Fungi
Sabouraud's agar. "Sab's a fun guy!"
Obligate aerobes
Use an O2-dependent system to generate ATP.
Examples include Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacillus.
Reactivation of M. tuberculosis (e.g., after immune compromise or TNF-a inhibitor use) has a predilection for the apices of the lung, which have the highest Po2 .

Nagging Pests Must Breathe .
P. aeruginosa is anaerobe seen in burn wounds, complications of diabetes, nosocomial pneumonia, and pneumonias in cystic fibrosis
patients.

Pseudomonas aeruginosa may use some nitrogen-containing compounds (e.g., nitrates) as terminal electron acceptors for anaerobic metabolism in environments with low or absent oxygen.
Obligate anaerobes
Examples include Clostridium, Bacteroides. They lack catalase and/or superoxide dismutase and are thus susceptible to oxidative damage. Generally foul smelling (short-chain fatty acids), are difficult to culture, and produce gas in tissue (CO2 and H2).

Anaerobes Can't Breathe Air.
Anaerobes are normal flora in GI tract, pathogenic elsewhere. AminO2glycosides are ineffective against anaerobes because these antibiotics require O2 to enter into bacterial cell.

Actinomyces israelii is better classified as a facultative anaerobe, not an obligate one.
Obligate intracellular
Rickettsia, Chlamydia. Can't make own ATP.
Stay inside (cells) when it is Really Cold.
Facultative intracellular
Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis.
Some Nasty Bugs May Live FacultativeLY
Encapsulated baderia
Positive quellung reaction
Examples are Streptococcus pneumoniae, Haemophilus infiuenzae type B , Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, and group B Strep. Their capsules serve as an antiphagocytic virulence factor. Capsule + protein conjugate serve as an antigen in vaccines.

SHiNE SKiS .
Are opsonized, and then cleared by spleen. Asplenics have decreased opsonizing ability and are at risk for severe infections. Give S. pneumoniae, H. infiuenzae, N. meningitidis vaccines.
Positive quellung reaction
if encapsulated bug is present, capsule swells when specific anticapsular antisera are added.
Quellung = capsular "swellung."
Catalase-positive organisms
Catalase degrades H2O2 before it can be converted to microbicidal products by the enzyme myeloperoxidase. People with chronic granulomatous disease (NADPH oxidase deficiency) have recurrent infections with these microbes because they degrade the limited H2O2.

Examples : Pseudomonas, Listeria, Aspergillus, Candida, E. coli, S. aureus, Serratia.

You need PLAC E S S for your cats .
Vaccines
For vaccines containing polysaccharide capsule antigens, a protein is conjugated to the polysaccharide antigen to promote T-cell activation and subsequent class switching. A polysaccharide antigen alone cannot be presented to T cell s ; therefore, only IgM antibodies would be produced.

Pneumovax (polysaccharide vaccine with no conjugated protein) and Prevnar (conjugated vaccine)
H. influenzae type B (conjugated vaccine)
Meningococcal vaccines (conjugated vaccines)
Urease-positive bugs
Cryptococcus, H. pylori, Proteus, Ureaplasma, Nocardia, Klebsiella, S. epidermidis, S. saprophyticus.
CHuck Norris hates PUNKSS.
Actinomyces israelii
yellow "sulfur" granules, which are composed of filaments of bacteria.
Israel has yellow sand.
S. aureus
yellow pigment.
aureus (Latin) = gold.
Pseudomonas aeruginosa
blue-green pigment.
Aerugula is green.
Serratia marcescens
red pigment.
Serratia marcescens-think red maraschino cherries.
Bacterial virulence factors
These promote evasion of host immune response.
Protein A
Binds Fc region of Ig. Prevents opsonization and phagocytosis. Expressed by S. aureus.
lgA protease
Enzyme that cleaves IgA. Secreted by S. pneumoniae, H. influenzae type B, and Neisseria (SHiN) in order to colonize respiratory mucosa.
M protein
Helps prevent phagocytosis. Expressed by group A streptococci.
Exotoxin
SOURCE
Certain species of some gram-positive and gram-negative bacteria
SECRETED FROM CELL
Yes
CHEMISTRY
Polypeptide
LOCATION OF GENES
Plasmid or bacteriophage
TOXICITY
High (fatal dose on the order of 1 ug)
ANTIGENICITY
Induces high-titer antibodies called antitoxins
VACCINES
Toxoids used as vaccines
HEAT STABILITY
Destroyed rapidly at 60°C (except staphylococcal enterotoxin)
TYPICAl DISEASES
Tetanus, botulism, diphtheria
Endotoxin
SOURCE
Outer cell membrane of most gram-negative bacteria
SECRETED FROM CELL
No
CHEMISTRY
Lipopolysaccharide (structural part of bacteria; released when lysed)
LOCATION OF GENES
Bacterial chromosome
TOXICITY
Low (fatal dose on the order of hundreds of micrograms)
ClINICAL EFFECTS
Fever, shock
MODE OF ACTION
Induces TNF and IL-1
ANTIGENICITY
Poorly antigenic
VACCINES
No toxoids formed and no vaccine available
HEAT STABILITY
Stable at 100°C for 1 hour
TYPICAL DISEASES
Meningococcemia; sepsis by gram-negative rods
Corynebacterium diphtheriae
Inhibit protein synthesis
Diphtheria toxin
Inactivate elongation factor (EF-2)
Pharyngitis with pseudomembranes in throat and severe lymphadenopathy (bull neck)
Pseudomonas aeruginosa
Inhibit protein synthesis

Exotoxin A
Inactivate elongation factor (EF-2)
Host cell death
Shigella spp.
Inhibit protein synthesis

Shiga toxin (ST)
Inactivate 60S ribosome by removing adenine from rRNA
GI mucosal damage -> dysentery; ST also enhances cytokine release, causing HUS
Enterohemorrhagic E. coli (EHEC), including O157:H7 strain
Inhibit protein synthesis

Shiga-like toxin (SLT)
Inactivate 60S ribosome by removing adenine from rRNA
SLT enhances cytokine release, causing HUS; unlike Shigella, EHEC does not invade host cells
Enterotoxigenic E. coli ( ETEC)
Increase fluid secretion

Heat-labile toxin (LT)
Overactivates adenylate cyclase (increased cAMP) -> increased Cl- secretion in gut and H2O efflux
Heat-stable toxin (ST)
Overactivate guanylate cyclase (increased cGMP) -> decreased resorption of NaCl and H2O in gut

Watery diarrhea: labile in the Air (Adenylate cyclase), stable on the Ground (Guanylate cyclase).
Bacillus anthracis
Increase fluid secretion

Edema factor
Mimics the adenylate cyclase enzyme (increased cAMP)
Likely responsible for characteristic edematous borders of black eschar in cutaneous anthrax
Vibrio cholerae
Increase fluid secretion

Cholera toxin
Overactivates adenylate cyclase (increased cAMP) by permanently activating Gs -> increased Cl- secretion in gut and H2O efflux
Voluminous "rice-water" diarrhea
Bordetella pertussis
Pertussis toxin
Overactivates adenylate cyclase (increased cAM P) by disabling Gi, impairing phagocytosis to permit survival of microbe

Inhibit phagocytic ability

Whooping cough
Whooping cough
child coughs on expiration and "whoops" on inspiration (toxin may not actually be a cause of cough; can cause "100-day cough" in adults)
Clostridium tetani
Tetanospasmin
Cleave SNARE protein required for neurotransmitter release
Muscle rigidity and "lock jaw"; toxin prevents release of inhibitory ( GABA and glycine) neurotransmitters in spinal cord

Inhibit release of neurotransmitter
Clostridium botulinum
Botulinum toxin
Cleave SNARE protein required for neurotransmitter release
Flaccid paralysis, floppy baby; toxin prevents release of stimulatory (ACh) signals at neuromuscular junctions -> flaccid paralysis

Inhibit release of neurotransmitter
ADP ribosylating A-B toxin
Toxin is an ADP ribosylating A-B toxin: B (binding) component binds to host cell surface receptor, enabling endocytosis; A (active) component attaches ADP-ribosyl to disrupt host cell proteins.

Bordetella pertussis
Vibrio cholerae
Enterotoxigenic E. coli ( ETEC)
Pseudomonas aeruginosa
Corynebacterium diphtheriae
Clostridium perfringens
Alpha toxin
Phospholipase that degrades tissue and cell membranes
Degradation of phospholipid C -> myonecrosis ("gas gangrene") and hemolysis ("double zone" of hemolysis on blood agar)

Lyse cell membranes
Streptococcus pyogenes
Streptolysin O
Protein that degrades cell membrane
Lyses RBCs; contributes to B-hemolysis; host antibodies against toxin (ASO) used to diagnose rheumatic fever (do not confuse with immune complexes of poststreptococcal glomerulonephritis)

Lyse cell membranes
Staphylococcus aureus
Toxic shock syndrome toxin (TSST-l)

Bring MHC II and TCR in proximity to outside of antigen binding site to cause overwhelming release of IFN-gamma and IL-2 -> shock

Toxic shock syndrome: fever, rash , shock; other toxin s cause scalded skin syndrome (exfoliative toxin) and food poisoning (enterotoxin)

Superantigens causing s hock
Streptococcus pyogenes
Exotoxin A

Bring MHCII and TCR in proximity to outside of antigen binding site to cause overwhelming release of IFN-gamma and IL-2->shock

Toxic shock syndrome : fever, rash , shock

Superantigens causing s hock
Endotoxin
A lipopolysaccharide found in outer membrane of gram-negative bacteria.

ENDOTOXIN :
Edema
Nitric oxide
DIC/Death
Outer membrane
TNF-a
O-antigen
eXtremely heat stable
IL-1
Neutrophil chemotaxis
Lag phase
Metabolic activity without division.
Exponential/log phase
Rapid cell division. Penicillins and cephalosporins act here as peptidoglycan is being made.
Stationary phase
Nutrient depletion slows growth . Spore formation in some bacteria.
Death
Prolonged nutrient depletion and buildup of waste products lead to death .
Transformation
Ability to take up naked DNA (i.e., from cell lysis) from environment (also known as "competence") . A feature of many bacteria, especially S. pneumoniae, H. influenzae type B, and Neisseria (SHiN). Any DNA can be used. Adding deoxyribonuclease to environment will degrade naked DNA in medium -> no transformation seen.
Conjugation F+ X F
F+ plasmid contains genes required for sex pilus and conjugation. Bacteria without this plasmid are termed F-. Plasmid (dsDNA) is replicated and transferred through pilus from P cell. No transfer of chromosomal genes.
Conjugation Hfr x F-
F+ plasmid can become incorporated into bacterial chromosomal DNA, termed high-frequency recombination (Hfr) cell . Replication of incorporated plasmid DNA may include some flanking chromosomal DNA. Transfer of plasmid and chromosomal genes.
Transposition
Segment of DNA that can "jump" (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa. When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into a plasmid and transferred to another bacterium.
Generalized Transduction
A "packaging" event. Lytic phage infects bacterium, leading to cleavage of bacterial DNA. Parts of bacterial chromosomal DNA may become packaged in viral capsid. Phage infects another bacterium, transferring these genes.
Specialized Transduction
An "excision" event. Lysogenic phage infects bacterium; viral DNA incorporates into bacterial chromosome. When phage DNA is excised, flanking bacterial genes may be excised with it. DNA is packaged into phage viral capsid and can infect another bacterium.
Genes for the following 5 bacterial toxins encoded in a lysogenic phage :
• ShigA-l ike toxin
• Botulinum toxin (certain strains)
• Cholera toxin
• Diphtheria toxin
• Erythrogenic toxin of Streptococcus pyogenes

ABCDE