Micro (1) Flashcards
What is the role of peptidoglycan?
Gives rigid support and protects against osmotic pressure. Composed of a sugar backbone with peptide side chains cross linked by transpeptidase
What is the role of the outer membrane in gram negatives?
this is the stie of endotoxin (LPS)
What are the ribosomal subunits for bacteria?
50S and 30S
What bacteria has a capsule (protects against phagocytosis) made of D-glutamate?
Bacillus anthracis
What is the chemical composition of plii/flagella?
glycoproteins
What are the major gram + cocci?
streptococci and staphylococci
What are the major gram - cocci?
Neisseria
Moraxella catarrhalis
What are the major gram + bacilli?
Bacillus
clostridium
Corynebacterium
Gardnerella (gram variable)
Listeria
Mycobacterium (acid fast)
Lactobacillus
What are the major enteric gram - bacilli?
Bacteriodes, Campylobacter. E. Coli
Helicobacter, Proteus, Pseudomonas
Salmonella, Vibrio
Yersinia
Serratia
What are the major respiratory gram - bacilli?
Bordetella
Haemophilus (pleomorphic)
Legionella (silver stain)
hat are the major Zoonotic gram - bacilli?
Bartonella
Brucella
Francisella
Pasteurella
What are the branching filamentous bacteria?
Actinomyces
Nocardia (weakly acid fast)
What are the spirochetes?
Borrelia
Leptospira
Treponema
What bugs do not gram stain well?
Treponema (cell wall too thin to visualize)
Myobacteria (high lipid content, myolic acids in cel wall detected by carbolfuchsin in acid-fast stain)
Mycoplasma (no cell wall)
Legionella pneumophilia (primarily intracellular)
Rickettsia (intracellular parasite)
Chlamydia (lacks classic peptidoglycan because of low muramic acid)
What bugs can be visualized with a Giemsa stain?
Chlaymdia,
Borrelia
Rickettsia
Trypanosomes
Plasmodium
Certain Bugs Really Try my Patience
What bugs can be visualized with a PAS (periodic acid-Schiff) stain?
Stains glycogen, mucopolysaccharides; used to diagnosed Whipple Disease (tropheryma whipplei)
What bugs can be visualized with a Ziehl-Neelsen (carbol fuchsin) stain?
Acid fast bacteria such as Nocardia, Mycobacteria and protozoa such as Cyrptosporidium occysts
Alternative stain for screening Auramine-Rhodamine (cheaper)
What bugs can be visualized with India Ink?
Cyrptococcus neoformans (nucicarmine can also be used to stain thick polysaccharide capsule red)
What bugs can be visualized with a Silver stain?
Fungi (e.g. Pneumocystis), Legionella, Helicobacter pylori
What special media is needed to culture H. influenza?
Chocolate agar with factors V (NAD+) and X (hematin)
What special media is needed to culture N. gonorrhoeae and N. meningitidis?
Thayey-Martin agar with Vanco (inhibits gram + organisms), Trimethoprim, Colistin (inhibits gram- negative organisms except Neisseria), and Nystatin (inhibits Fungi)
What special media is needed to culture B. pertussis?
Bordet-Gengou agar (with potato) or
Regan-Lowe medium (with charcoal, blood, and ABX)
What special media is needed to culture C. diptheriae?
Tellurite agar, Loffler medium
What special media is needed to culture M. tuberculosis?
Lowenstein-Jensen agar
What special media is needed to culture M. pneumoniae?
Eaton Agar (requires cholesterol)
What special media is needed to culture lactose-fermenting enterics?
MacConkey agar (colonies will turn pink)
What special media is needed to culture E. Coli?
EMB agar (colonies with green metallic sheen)
What special media is needed to culture Legionella?
Charcoal yeast extract agar buffered with cysteine and iron
What special media is needed to culture fungi?
Sabourand agar “Sab’s a fun guy!”
Aerobes
These use an O2-dependent system to generate ATP
-Examples include Nocardia, Pseudomonas aeruginosa, and MyoBacterium tuberculosis
Where does reactivated M. Tb like to infect?
the apices of the lung, which have the highest PO2 (make sure to do a PPD before starting on a TNFa inhibitor)
What are some examples of anaerobes?
Fusobacterium
Clostridium
Bacteriodes
Actinomyces
(Anaerobes Frankly Cant Breathe Air)
Notes about anaerobes
They lack catalase and/or superoxide dismutase and thus are susceptible to oxidative damage.
These are generally foul-smelling (short-chain FAs),, are difficult to culture, and produce gas in tissue
These are normal flora in the GI tract, and typically pahogenic everywhere else.
What ABX is ineffective against anaerobes? Why?
Aminoglycosides because they require O2 to enter into bacterial cells
What are some exs of obligate intracellular bugs?
Rickettsia
CHlamydia
Coxiella
What are some exs of facultative intracellular bugs?
Salmonella
Neisseria
Brucella
Mycobacterium
Listeria
Francisella
Legionella
Yersinia pestis
Some Nasty Bugs May Live FacultativeLY
What are some exs of encapsulated bacteria?
Strep pneumo
Haemophilus infulenza type B
Neisseria meningitidis
E. Coli
Salmonella
Klebsiella pneumoniae
GBS
SHiNE SKiS
Notes about encapsulated bacteria
Their capsules serve as na antiphagocytic virulence factor
These bugs must be opsonized and cleared by the spleen (thus, asplenic pts are at risk)
Describe the basis of encapsulated bacteria vaccines
Some vaccines containing polysaccharide capsule antigens are conjugated to a carrier protein, enhancing immunogenicity by promoting T-cell activation and subsequent class switching.
A polysaccharide antigen alone cannot be presented to T cells
Examples of encapsulated bacteria vaccines
Pneumoccal vaccine: PCV (peumococcal conjugate vaccine, i.e. Prevnar)
PPSV (penumococcal polysaccharide vaccine with no conjugated protein, i.e. Pneumovax)
H. influnzae type B (conjugate vaccine)
N. meningitidis (conjugate vaccine)
What are the urease positive organisms?
Cyrptococcus
H. pylori
Proteus
Ureaplasma
Nocardia
Klebsiella
S. epidermidis
S. saprophyticus
CHuck norris hates PUNKSS
What does catalase do?
catalase degrades hydrogen peroxide into water and bubbles of O2 before it can be converted to micobicidal products by the enzyme myeloperoxidase.
People with what disease have recurrent infections with certain catalse + organisms?
Chronic Granulomatous disease (NADPH oxidase deficiency)
What are the catalase + organisms?
Nocardia
Pseudomonas
Listeria
Aspergillus
Candida
E. Coli
Staphylococci
Serratia
Cats Need PLACESS to hide
What pigment does Actinomyces isrealii produce?
yellow ‘sulfur’ granules which are composed of filaments of bacteria
What pigment does S. aureus produce?
yellow pigment
What pigment does Pseudomonas aeruginosa produce?
blue-green pigment
What pigment does Serratia marcecens produce?
red pigment
What does Protein A do?
Binds to the Fc region of IgG to prevent opsonization and phagocytosis.
Expressed by Staph Aureus
What is IgA protease and who makes it?
Enzyme that cleaves IgA
Expressed by: S. pneumo, H. influenza (type B) and Neisseria (SHiN) in order to colonize the respiratory
Describe the M protein
Surface protein expressed by GAS and is the source of molecular mimicry seen in rheumatic fever
What is a Type III secretion system and who makes it?
AKA injectisome- a needle like protein appendage faciltating direct delivery of toxins from certain gram negative bacteria such as Pseudomonas, Salmonella, Shigella, E. Coli
Describe exotoxins
Source: certain speceisa of gram+ and gram- bacteria
Secreted from cell: Yes
Chemistry: Polypeptide
Location of Genes: Plasmid or bacteriophage
More on exotoxins
Toxicity: High (Fatal dose on the order of 1ug)
Heat Stability: Destroyed rapidly at 60C (except stapylcoccal enterotoxin)
Typical diseases: Tetanus, botulism, diptheria
Describe endotoxins
Source; outer cell membrane of most gram- bacteria
Secreted from cell: No
Chemistry: Lipopolysaccarhide (released when lysed)
Location of genes: Bacterial chromosome
More on endotoxins
Clinical features: Fever, shock (hypotension), DIC
Mode of Action: Induces TNF, IL-1, and IL6
Antigenicity: poor
Heat Stability: Stable at 100C for 1 hr
What two bacteria have toxins that inhibits EF-2?
Corynebacterium diphtheriae (Diphtheriae toxin) and Pseudomonas (Exotoxin A)
What is this?
Pseudomembrane formation in Corynebacterium dip. infection (also seen with Bull’s neck LAD)
What two bacteria have toxins that inhibit 60S ribosomes by removing adenine from rRNA?
Shigella (Shiga Toxin) and EHEC (Shiga-like toxin)
What are the main toxins of ETEC?
Heat-Stabile toxin (ST)
Heat Labile toxin (LT)
What does Heat-Stabile toxin (ST) do?
overactivates guanylate cyclase (increases cGMP) leading to decreased resorption of NaCl and H2O in the gut
What does Heat-Labile toxin (LT) do?
Overactivates adenylate cyclase to increase cAMP resulting in icnreased Cl secretion into the gut
What is the main toxin of Bacillus anthracis?
Edema toxin, which momics adenylate cyclase to increase cAMP causing the classic edematous borders of the black eschars in cutaneous anthrax)
The main toxin of Vibrio cholerae is the cholera toxin. How does it work?
It overactivates adenylate cyclase to increase cAMP by permanently activating Gs resulting in increased Cl- secretion into the gut leading to the classic rice water diarrhea
What is the main toxin of Bordetella pertussis and how does it work?
Pertussis toxin, which overactivates adenylate cyclase to increase cAMP by disabling Gi, impairing phagocytosis to permit microbe survival
What is the clinical presentation of Bordetella pertussis?
Whopping cough (aka 100 day cough) in which children cough on expiration and whoop on inspiration
Tetanospasmin is a main toxin in what bacteria?
Clostridium tetani
How does Tetanospasmin work?
It, and botulinum toxin from Clostridium bptulinum, are proteases that cleaves SNARES
How does tetanus present?
Spasticity, risus sardonicus, and lackjaw due to the toxin preventing release of inhibitory GABA and glycine NTMs from Renshaw cells in the spinal cord
How does botulism present?
Flaccid paralysis, floppy baby due to toxin preventing release of stimulatory (ACh) signals are neuromuscular junctions
Note about Diphtheria toxin, Exotoxin A (Pseudomonas), Shiga toxin, and Shiga-like toxin (EHEC)
These are ADP ribosylating AB toxins in which the B subunit binds to host cell surface receptors, enabling endocytosis and the A subunit attached ADP-ribosyl to disrupt host cell proteins
What is the main toxin of Clostridium perfrigens?
Alpha toxin, which is a phospholipase that degrades tissue and cell membranes leading to myonecrosis (gas gangrene) amd hemolysis (“double zone” on blood agar)
What bacteria uses Streptolysin O and how does it work?
Strep pyogenes and this is a protein which degrades cell membranes
What bacteria hvae superantigens causing shock?
Staph aureus (TSST-1) and Strep pyogenes (Exotoxin A)- both bind to MHC class II and TCR receptors outside of the antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-y, and TNFa leading to shock
Describe the pathogenesis of Endotoxin (LPS found in the outer membranes of both gram+ and gram- bacteria)(especially Lipid A)
It:
1) Activates macrophages causing release of IL1 (fever), TNFa (Fever and hypotension), and NO (hypotension)
2) Activates complement causing release of C3a (hypotension and edema) and C5a (neutrophil chemotaxis)
3) Activates tissue factor which can lead to DIC
What is transformation?
the ability of some abcteria to take up naked DNA (i.e. from cell lyssi) from the environment (also known as competence). This is a feature of many bacteria, especially S. pneumo, H. influenza type B, and Neisseria (SHiN)
NOTE: Addin deoxyribonuclease to the environment will degrade naked DNA in the medium and block transformation
What is F+ x F- conjugation?
F+ plasmids contain gene required for sex pilus and conjugation. Bacteria without this plasmid are termed F-.
The sex pilus on F+ bacterium contact F- bacterium and a single strand of plasma DNA is transferred across the conjugal bridge (no transfer of chromosomal DNA)
What is Hfr x F- conjugation?
A F+ plasmid can become incorporated into bacterial chromosomal DNA, termed a high freuqency recombination cell
What is transposition?
When a segment of DNA (eg. transposon) can jump from one location to another- can transfer genes from plasmids to chromosomes and vice versa.
When excision occurs, some flanking chromosomal DNA may be included, which can be incorporated into a plasmid and then be tranferred to another bacterium (i.e. vanA gene from vanco-resistant Enterococccus to S. aureus)
What is generalized transduction?
A packaging event in which a lytic phage infects a bacterium, leading to cleavage of bacterial DNA and some parts of the bacterial DNA may become packaged in a viral capsid and tranferred to another bacterium when the virus leaves
What is specialized transduction?
An excision event in which a lysogenic phage infects a bacterium, viral DNA incorporates into the bacterial chromosome, and when the phage DNA is excised, flanking bacterial DNA genes may be excised with it. These segments may then be packaged to a viral capsid and transferred to another bacterium
The genes for what bacterial toxins are encoded in a lysogenic phage?
ABCDE
ShigA-like toxin
Botulinum toxin
Chlorea toxin
Diphtheria toxin
Erythrogenic toxin of Strep pyogenes
What are the major E. Coli virulence determinants?
1) Fimbriae= cystitis and pyelonephritis
2) K capsule= pneumonia, neonatal meningitis
3) LPS Endotoxin= septic shock
Describe EIEC
Microbe invades intestinal mucosa and causes necrosis and inflammation.
Presents as invasive and dysentery similar to Shigella
Describe ETEC
Produces heat labile and heat stable intertoxins. No inflammation or invasion
Traveler’s diarrhea
Describe EPEC
No toxins produces. Adheres to the apical surface, flattens villi, and prevents absroption
Presents with diarrhea, usually in children (Pediatrics)
Describe EHEC
AKA STEC (Shiga toxin producing E. Coli) (O157:H7 is the most common serotype in the US)
causes dysenteric diarrhea
does not ferment sobitol (distinguishes from other E. Coli)
Shiga like toxin can cause HUS
How does HUS present?
With a classic triad of anemia, thrombocytopenia, and acute renal failure due to microthrombi forming on damaged endothelium leading to mechanicla hemolysis (with schistocytes on blood smear), platelet consumption, and decreased renal blood flow
Describe Mycoplasma pneumoniae
Classic cause of atypical “walking” pneumonia (insidious onset, HA, nonproductive cough, patchy or diffuse interstitial infiltrate). X-ray looks worse than pt.
Typically has a high titer of cold agglutinins (IgM), which can agglutinate or lyse RBCs.
Grows on Eaton Agar
