Infectious Disease Flashcards
Prokaryotes
no membrane bound organelle; no nucleus so nuclear material is free inside of cell; bacteria are prokaryotes
Eukaryotes
membrane bound organelle that contain a nucleus; these include plant and animal cells, protozoa and fungi
Bacteria
single cell organism where the cell wall is a key component - helps differentiate gram (+) and gram (-) bacteria
Gram (+) bacteria characteristics
thicker cells wall organisms (up to 40 sheets of peptidoglycan - 50% of cell wall); the thicker layer retains the gram stain and makes them purple; contains lipoteichoic acids (LTA) that drive lots of immune infections
Gram (-) bacteria characteristics
thinner cell wall (very few sheets of peptidoglycan - 5-10% of cell wall) with an ADDED outer membrane that contains lipopolysaccharides (LPS) makes people VERY VERY sick (sicker than gram (+)); Periplasm (space between cell membrane and outer-membrane) contains B-lactamase (inactivates antibiotics)
Peptides are always attached to what molecule in the peptidoglycan structure?
N-acetylmuramic acid (NAM); not NAG; some antibiotics act on peptidoglycan - penicillin and cephalosporins
Unique cell wall bacteria
- Mycoplasma (can cause interstitial pneumonia) - no cell wall, does NOT gram stain; the membrane has sterols for extra stability
- Mycobacteria (TB or leprosy) - cell wall has mycolic acid so does NOT stain well, needs a special Ziehl-Neelsen stain
- Chlamydia (STD and other infections) - lacks muramic acid
Cell membrane of bacteria
present in gram (+) and gram (-) bacteria; there is where electron transport (in humans takes place in mitochondria) and oxidative phosphorylation occurs
Lipopolysaccharide (LPS)
an ENDOTOXIN - only on gram (-) bacteria on their outer membrane; contains 3 components:
- polysaccharide
- Lipid A - HIGHLY toxic; triggers cytokine release (TNF and IL-1) - sepsis/septic shock
- O antigen - target for antibodies
Capsule
sticky gelatinous layer that both gram (+) and gram (-) bacteria can have that helps attach to host cells and also protects against phagocytosis; they are mostly made up of water and polysaccharides w/ ONE exception:
Bacillus anthraces (anthrax) - peptide capsule (d-glutamate); major virulence factor that allows for unimpeded growth; pts get REALLY sick!
Capsules and Immunology
B-cells secrete IgG and these bind/tag the capsule for phagocytosis; antibodies can also activate complement - formation of MAC (cell death) and formation of C3b (opsonin)
pt population who are at risk of recurrent encapsulated bacterial infections
pt who have loss of antibodies or complement or have had their spleen removed or sickle cell anemia pts (asplenia) loss of splenic phagocytes
Capsular vaccines for encapsulated bacteria
Neisseria meningitides
Streptococcus pneumonia
Haemophilus influenza type b
Glycocalyx
similar to a capsule, but is a “sugar coat” made of polysaccharides; irregular, slimy fuzzy layer that is used to adhere to surfaces (mainly catheters); pts with a IV line or a folly placement watch for Strep epidermidis - skin flora! (creates biofilms)
Spores and why are they so resistant?
Coat:
outermost layer “keratin-like” protein that is impermeable to many chemicals and antibacterial agents
Core:
Innermost layer compress of peptidoglycan
Dipicolinic acid:
large amounts inside spore that helps with heat resistance
5 major examples of spore forming bacteria
- Bacillus anthracis - potential weapon of bioterroism
- Bacillus cereus - food poisoning
- Clostridium perfringens - food poisoning
- Clostridium tetani - food poisoning
- Clostridium botulism - food poisoning
Key bacteria with Pili and Fimbria
structurally similar to flagella; made of protein and is more like an appendage or arm of the bacteria; allow for adherence or attaches to another bacteria and allow for conjugation - antigenic variation
E. coli - UTIs/Pyelonephritis (adherence)
Neisseria Gonorrhea (antigenic variation)
bacterium that is a common cause of pneumonia and respiratory failure in CF pts
Pseudomonas aeruginosa; oxidase (+) gram (-) rod; bacteria frequently colonize and form biofilms that allow for the bacterium to evade the immune system via their glycocalyx
Most cocci are gram (+) bugs, what are the gram (-) exceptions?
Neisseria (meningitis/gonorrhea) and Moraxella catarrhalis
most rods are gram (-) bugs, what are the few gram (+) exceptions?
Corynebacterium (diphtheria)
Clostridium
Listeria
Bacillus (anthrax, cereus)
Branching/Filamentous bacteria
resembles fungi
Actinomyces
Nocardia
Spirochetes
treponema (syphilis)
borrelia (Lyme disease)
leptospira (leptospirosis)
the one gram (+) vibrio (curved/coma shaped) bacterium?
Vibrio cholerae (cholera)
The two pleomorphic bacteria
can take any shape; also both are intracellular pathogens
Rickettsia
Chlamydia
gram stain steps
bacterium that do not stain well
- Treponema (syphilis) to thin to see
- Mycobacteria (TB) - mycelia acid in cell wall
- Mycoplasma (interstitial pneumonia) - no cell wall (Eaton’s agar)
- Intracellular bacteria (need to be a cell to grow)
-Rickettsia
-Chlamydia
-Legionella
Giemsa Stain
useful stain to get inside of cells
Protozoa: Plasmodium and Trypanosomes
Intracellular: Chlamydia, Rickettsia and Borrelia (sometimes intracellular)
Ziehl-Neelsen Stain
“acid-fast” stain - contains carbolfuchsin
Used to detach mycobacterium (TB) and can be used for Nocardia
Silver Stain is a special stain for which 3 organisms?
- Pneumocystis pneumonia (HIV/AIDs pt) - causes fungal infection and diffuse interstitial pneumonia
- Legionella - contaminated water (nursing homes) and causes pneumonia
- H. pylori (gastric ulcers)
India Ink
it is a negative stain that stains the background and NOT the bug, so unstained organisms stand out. Used primarily for cryptococcus neoformans which is a fungi that exists as a yeast
Bug that produces as golden/yellow pigment?
Staph aureus
Bug that produces as blue-green pigment?
Pseudomonas aeruginosa (pyocyanin)
Bug that produces a red pigment?
Serratia
Bug that produces colonies that have a yellow-orange appearance?
Actinomyces - filamentous bacteria that “comets” together - known as “sulfur granules”
Thayer-Martin is a selective media that only grow which bug?
Neisseria
Only which type of bacteria grow on a Eosin Methylene Blue agar?
selective because only gram (-) bacteria; also a differential agar because lactose fermenters grow
Fastidious bacteria
organisms that require special nutrients to grow:
H. influenza - chocolate agar
Legionella - buffered charcoal yeast extract
Chocolate Agar
a variant of blood agar used for H. influenza - contains red blood cells that are lysed; contain NAD (factor V) and hemming (factor X)
Note: H. influenza will grow on a blood agar if Staph aureus is present (because is beta hemolytic and completely lysis the blood)
Bordet-Gengou Agar
potato agar (high starch) special for Bordetella pertussis - whooping cough (extremely rare due to vaccinations)
Loeffler’s Media/Tellurite Plate
selective for Corynebacterium diphtheriae; produces gray-black colored colonies
Eaton’s Agar
culture for mycoplasma pneumonia; no cell wall so poorly visualized w/ gram stain; requires cholesterol to grow; takes week to grow so rarely used in the modern era
MacConkey is a selective media for what type of bugs?
selective gram - rods
differential for lactose fermenters
sOrbital MacConkey Agar
detection for E. coli 0157:H7 strains (shiga-like toxin)
sOribital = 0157
Buffered charcoal yeast extract is used to only identify which bug?
Legionella - very important to culture this bacteria b/c can cause outbreaks (contaminate water supplies - nursing homes)
Sabouraud’s Agar
selective media for fungi
Obligate anaerobes
do NOT need O2 to generate ATP; lack catalase or superoxide dismutase (no need); normal in GI (about 99%/100x more than aerobes); don’t typically cause diseases; disease when mucosal surfaces break down; often present in abscesses; use fermentation and produces CO2 and H2 (gases and foul smelling)
AminOglycosides are ineffective (require O2 to work)
Obligate aerobes
NEED O2 to generate ATP; under high O2 contents - need superoxide dismutase/catalase to protect against damage of free radicals that form
Pseudomonas aeruginosa
Mycobacterium (TB) - loves lungs b/c loves oxygen
Nocardia (opportunistic infection)
Abdominal abscesses/perforations
contain many gram (-) anaerobic bacterium; most common bug is Bacteroides fragilis
tx - Metronidazole (anaerobic med for below the diaphragm) and a gram (-) agent
Diverticulitis/Appendicitis
Aspiration pneumonia
when mouth anaerobes enter the lungs; commonly Peptostreptococcus, Fusobacterium and Prevotella
tx - Clindamycin (anaerobic medication for above the diaphragm)
anaerobic medication for below the diaphragm
Metronidazole and a gram (-) agent
Diverticulitis/Appendicitis
anaerobic medication for above the diaphragm
Clindamycin
Facultative Anaerobes
can live w/o O2 but will use it if available; perform respiration and fermentation
many bacteria fall into this category
Obligate Intracellular bacteria
cannot synthesize their own ATP (chlamydia) or depend on host ATP (rickettsia)
Rickettsia - Rocky Mountain spotted fever - diagnoses clinically or w/ serology test
Chlamydia - diagnosis w/ DNA testing
Virulence Factor Protein A
key virulence factor for staph aureus; part of the peptidoglycan cell wall; inhibits phagocytosis and complement activation
Virulence Factor Protein A
key virulence factor for staph aureus; part of the peptidoglycan cell wall; inhibits phagocytosis and complement activation
IgA Protease is a virulence for which 3 bugs?
enzyme that cleaves IgA and allows for colonization of mucosal surfaces
Strep pneumonia
H. influenza
Neisseria (gonorrheae/meningitidis)
M protein is an important virulence for which organism?
surface molecule for group A strep (pyogenes) - causes strep throat and rheumatic fever
prevents phagocytosis by binding factor H
Endotoxin receptor on macrophages
CD14
endotoxin/LPS on gram (-) activates the CD14 receptor on macrophages and releases IL-1 causing fever
Staphylococcus aureus
gram (+) cocci, catalase (+), coagulase (+) B-hemolytic cocci; mannitol salt agar - ferments mannitol (yellow)
Protein A virulence factor - prevents phagocytosis
Diseases:
-pneumonia - patchy infiltrates (usually secondary infection after a viral infection)
-septic arthritis (most common cause)
-acute bacterial endocarditis (IV drug user - RA tricuspid)
-osteomyelitis (most common cause)
-Scalded Skin Syndrome (toxin that causes a bad sunscreen)
-Toxic Shock Syndrome (superag TSST)
- Fast (1-8 hrs) onset food poison (preformed toxin - vomiting - meats and mayonnaise left out too long)
-MRSA (altered penicillin-binding proteins PBP) tx w/ vancomycin
Tx w/ Nafcillin (Naph for Staph)
Disease caused by Staphylococcus aureus
-pneumonia - patchy infiltrates (usually secondary infection after a viral infection)
-septic arthritis (most common cause)
-acute bacterial endocarditis (IV drug user; RA tricuspid)
-osteomyelitis (most common cause)
-Scalded Skin Syndrome (toxin that causes something like a bad sunscreen)
-Toxic Shock Syndrome (superag TSST; tampons left in too long)
- Fast (1-8 hrs) onset food poison (preformed toxin - vomiting - meats and mayonnaise left out too long)
-MRSA (altered penicillin-binding proteins PBP) tx w/ vancomycin
Tx w/ Nafcillin (Naph for Staph)
Staphylococcus epidermidis
gram (+), catalase (+), coagulase (-)
normal skin flora - can easily contaminate when blood is drawn;
enemy of orthopedic surgeons - causes a lot of prosthetic joint infection; catheter-assocaited infections; endocarditis of artificial heart valves; creates biofilms via glycolyx
tx w/ vancomycin
Novobiocin sensitive on agars
Staphylococcus saprophyticus
gram (+), catalase (+), coagulase (-)
Diseases:
-honeymoon cystitis; UTI occurs in associated with sexual activity (not a STD)
-acute bacterial prostatitis
Novobiocin resistant on agars
Streptococcus pyogenes
Group A Strep (Bacitracin sensitive)
encapsulated - hyaluronic acid; B- hemolytic
Infections:
-impetigo - pyogenic honey crusted skin infection (also caused by staph aureus)
-strep throat (pharyngitis)
-cellulitis and erysipelas
Strep pyogenes Exotoxins (SPEs):
-Scarlet fever (3 main symptoms):
1. Red and swollen tongue (strawberry tongue)
2. Pharyngitis (strept throat)
3. Wide spread rash that spares the face
-Toxic Shock Like Syndrome (TLS) - superag syndrome similar to staph auereus
-Necrotizing fasciitis “flesh eating bacteria”
Serious complications:
1. Rheumatic Fever
2. Post-Strep Glomerulonephritis
Strep pyogenes Exotoxins (SPEs) infections
-Scarlet fever (3 main symptoms:
1. Red and swollen tongue (strawberry tongue)
2. Pharyngitis (strept throat)
3. Wide spread rash that spares the face
-Toxic Shock Like Syndrome (TLS) - superag syndrome similar to staph auereus
-Necrotizing fasciitis “flesh eating bacteria”
Rheumatic Fever
Serious complication of Strep pyogenes infections; pharyngitis precipitates RF; type II hypersensitivity reaction
M protein virulence factor (anti-phagocytic and strong humoral response); molecular mimicry in mitral valve causing mitral stenosis
JONES criteria - joints, heart probs, nodules (elbows and knees), erythema marginatum (rash w/ nice borders), Sydenham’s chorea (rapid involvement movements
commonly tested concepts:
-ONLY occurs after pharyngitis (unlike PSG)
-early tx can prevent Rh (unlike PSG)
tx w/ penicillin
Post-Strep Glomerulonephritis
Serious complication of Strep pyogenes infections (about 2 weeks post infection); pharyngitis precipitates kidney injury; type III hypersensitivity reaction
2 weeks after dark brown “cola cola” urine and facial puffiness from edema
virulence factor of streptolysin O
commonly tested concepts:
-can occur after pharyngitis OR impetigo (unlike Rh)
-cannot be prevented w/ early tx
tx w/ penicillin
Scarlet fever (3 main symptoms)
caused by Strep pyogenes Exotoxins (SPEs); symptoms:
1. Red and swollen tongue (strawberry tongue)
2. Pharyngitis (strept throat)
3. Wide spread rash that spares the face
Streptococcus Agalactiae
Group B Strep (Bacitracin resistant)
Hippurate (+), CAMP test (+), B hemolytic
Poly A capsule
causes meningitis in neonates (#1 cause)
sepsis in neonates
pneumonia
transmitted via vaginal canal during delivery - all moms need to be swapped at 35 weeks; if (+) tx mom w/ intrapartum penicillin
Streptococcus pneumoniae
1 cause of community acquired pneumonia (rust color sputum; lobar pneumonia)
encapsulated gram (+) lancet-shaped diplococci; alpha hemolytic (partial); optochin sensitive; bile soluble
sickle cell and asplenic pt are at risk
Meningitis
Otitis media
Pneumonia
Sinusitis
Virulence factors:
IgA protease - cleaves IgA
tx w/ macrolides or ceftriaxone (3rd gen)
vaccines: 23 valent adult vaccine (IgM response) and a 7 valent children vaccine (IgG response)
Streptococcus viridans
gram (+) diplococci; alpha hemolytic (partial); optochin resistant; bile resistant
commonly associated with dental caries - subacute endocarditis that affects damaged heart valves (mitral)
adheres to platelets (dextrans - glue that helps them stick to platelets)
Enterococcus
Enterococcus faecium (more dangerous) & faecalis (more common); intestinal tract bacterium; can grow in 6.5% NaCl; bile resistant; 3 infections (Do U Heart Trees?)
UTIs
Endocarditis
Biliary tree infections
VRE (vancomycin resistant enterococcus)
tx w/ Linezolid or Tigecycline
Streptococcus gallolyticus
Group D Strep (aka Strep Bovis)
encapsulated gram (+) cocci (chains or pairs); gamma hemolytic (no hemolysis); bile-soluble; creates a biofilm - heart valves; normal GL tract flora
Clinical relevance:
Endocarditis
STRONG association with colorectal cancer (obtain a colonoscopy)
tx w/ 3rd gen cephalosporins or vancomycin or penicillin
Bacillus anthracis
gram (+) bacillus obligate aerobe that has the unique feature is looking like rods and chains; **encapsulated (protein - Poly D glutamate) - black eschar - black cutaneous lesions; **spore-forming
Toxins:
1. Edema Factor (EF) - AC analog that increases cAMP
2. Lethal Factor (LF) - endotoxin that acts as a protease that cleaves MAP kinase (controls cell growth) - leading to impeded growth
Pulmonary anthrax - spores in sheep’s wool
tx: 1st choice - fluoroquinolone 2nd choice - doxycycline
Bacillus cereus
gram (+) bacillus; associated with food poisoning of **reheating fried rice
tx: 1st choice - fluoroquinolone 2nd choice - doxycycline
Pulmonary anthrax
inhalation of Bacillus anthracis spores; watch for people who handle sheep/wool; presents w/ non specific pulmonary symptoms (dry cough) but can rapidly progress to pulmonary hemorrhage; CXR widened mediastinum - 100% fatal
tx; 1st choice - fluoroquinolone 2nd choice - doxycycline
Clostridium tetani
gram (+) bacillus; spore-forming obligate anaerobe - the cause of tetanus
often found in soil - puncture wounds causes by **rusty nails or barged wire (construction worker or child playing near a construction zone) neuromuscular symptoms:
-spastic paralysis
-risus saronicus “an evil grin” or lock jaw symptoms
-opisthotonus “exaggerated arching of back”
Mechanism:
spores are in flesh - releases Tetanus toxin - travels retrograde (periphery to spinal cord) - cleaves SNARE proteins and prevents exocytosis at the NMJ synapse inhibiting GABA and Glycine (from Renshaw cells) - uncontrolled firing with no inhibition leading to spastic paralysis
Vaccine - toxoid vaccine
Mechanism of Clostridium tetani
puncture wounds causes by **rusty nails or barged wire (construction worker or child playing near a construction zone) - spores are in flesh - releases Tetanus toxin - travels retrograde (periphery to spinal cord) - cleaves SNARE proteins and prevents exocytosis at the NMJ synapse inhibiting GABA and Glycine (from Renshaw cells) - uncontrolled firing with no inhibition leading to spastic paralysis
Clostridium botulinum
gram (+) bacillus - the cause of botulism
improper of canning of food (spores) - cook canned food thoroughly; won’t say canned food - more like a family and everyone is the home is experiencing very similar neural symptoms:
- descending flaccid paralysis
-diplopia and ptosis
Mechanism:
ingestion of preformed toxin - travels to the peripheral nervous system through the gut - cleaves the SNARE proteins of motor neurons that release Ach
Babies:
“floppy baby syndrome” - HONEY!! (ingestion of spores)
Mechanism of Clostridium botulinum
gram (+) bacillus - the cause of botulism
ingestion of preformed toxin - travels to the peripheral nervous system through the gut - cleaves the SNARE proteins of motor neurons that release Ach
Babies:
“floppy baby syndrome” - HONEY!! (ingestion of spores)
Clostridium perfringens
gram (+) bacillus causing infections associated w/ motorcycle vehicle accidents and military combat wounds - large amount of flesh is exposed to dirt - spore transmission
“double zone of hemolysis on blood agar”
Infections:
1. gas gangrene (produces gas under tissues) - alpha toxin or lecithinase
2. late/slow onset food poisoning - watery diarrhea (transient)
tx; IV penicillin G
Clostridioides difficile (C. diff)
gram (+) bacillus obligate anaerobe spore forming - fecal/oral route (ingestion of spores) - typically hospital acquired - can be caused by antibiotic use (wipes out normal flora):
- Clindamycin, Fluoroquinolone, Penicillin, Cephalosporins and PPI
Toxins MOA: disruption of tight jxns in colon - increased paracellular permeability - water goes into lumen and leads to foul smoking HIGH volume watery diarrhea - can see “pseudomembranous colitis” - fear complication of toxic megacolon
Diagnose w/ EIA for toxins or PCR for toxins
tx: oral vancomycin (poor systemic absorption) or oral fidaxomicin severe C. diff tx with IV metronidazole in addition; if these fail do a fecal microbiota transplant (restores normal gut microbiome)
Corynebacterium diphtheria
the cause of diphtheria - transmitted by respiratory droplets
gram (+) non spore forming bacillus; “club shape in a “Y” or “V” formation w/ metachromatic granules; exotoxin - 2 subunits A (active) and B (binding subunit) - inhibits elongation factor 2 (EF-2) to inhibit protein synthesis (ribosylation) - leading to cell death “pseudomembrane formation”; presents with “bullneck” thickening of the neck due to lymphadenopathy; systemic effects on heart - arrhythmias and heart blocks; local paralysis (posterior oral pharynx)
Diagnosis: Tellurite agar or Loeffler’s medium for culturing the bacteria; Elek’s test let you know that is toxin strain
Toxoid vaccine given in the US - look for kids who emigrated who were not vaccinated
Listeria monocytogenes
gram (+) bacillus most commonly infects pregnant woman; narrow zone of hemolysis when plated (Beta- hemolytic) motile and “tumbling motility”; ‘actin rockets’ use for movement inside the cell; able to survive and multiple in freezing temperatures - can contaminate food even if refrigerated (dairy products); pregnant women are discouraged from eating soft cheese; can cause meningitis in newborns and in adults over 60 yrs
Tx: ampillicin
Actinomyces israelii
gram (+) filamentous rod; obligate anaerobe (contrast w/ nocardia obligate aerobe); normal flora of oral cavity - common w/ recent dental work - invades surrounding structures (jaw trauma)
Slow onset - starts off non-tender lump on jaw - leading to abscess -drainage sinus tracks - yellow pus w/ “yellow sulfur granules”
Tx: Penicillin G
Nocardia asteroides
gram (+) filamentous rod; obligate aerobe (contrast w/ actinomycete obligate anaerobe); catalase (+) and urease (+); found primary in the soil (but does NOT form spores); weakly stains acid-fast (mycolic acids); mainly affects immunocomprised pts
Symptoms are pulmonary, CNS and cutaneous
-pneumonia w/ lung abscess formation (cavitation lesions)
-brain abscess formation
-cutaneous indurated lesions
tx: Sulfonamides
The two gram (-) cocci?
Neisseria (meningitidis/gonorrhoeae)
Moraxella catarrhalis
Neisseria overview
Meningoencephalitis caused by Cryptococcus neoformans
occurs in immunocompromised pt; appears as budding yeasts w thick polysaccharide capsules which can be demonstrated using miciarmine or India ink staining
Condylomata acuminata
anogenital warts present as pink- or skin-colored plaques and verrucous lesions on the genitalia, perineum or perianal skin; primarily caused by HPV 6,11; lesions are associated w increased risk for HIV infection; HIV testing is recommended
walking pneumonia w organism that form COLD agglutinins
mycoplasma pneumoniae can result in the formation of cold agglutinins, which are IgM antibodies that bind RBCs and cause clumping at low body temperatures
HIV-2
most cases of AIDS worldwide are caused by HIV-1, however, AIDS can also be caused by infection of HIV-2 which is endemic to West Africa; HIV-2 infection is associated w lower viral loads, less risk of transmission and slower progression to AIDS; the dx is often suspected when HIV tests are incongruent; confirmation can be made using HIV-1/HIV-2 assay
acute diarrhea
EHEC is primarily contracted after eating undercooked ground beef; EHEC produces Shiga toxin, which causes hemorrhagic colitis and can lead to hemolytic-uremic syndrome (HUS); HUS is characterized by acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia; children under 10 yrs are at greater risk
Mumps
Vibrio vulnificus
a curved, gram (-), free-living bacterium that grows in marine environments; transmission primarily occurs due the consumption of raw seafood (oysters) or wound contamination; manifestations are often mild, but individuals w liver disease or iron overload are at very high risk of severe, fulminant infections (sepsis, necrotizing fasciitis)
Angiostrongylus infection
Eosinophilic meningitis is often due to helminth infection (Angiostrongylus); peripheral eosinophilia is largely mediated by the release of IL-5 response to helminths, allergens, drugs or rheumatic disease
cat scratch disease
caused by Bartonella henselae, a gram (-) coccobaciluus transmitted by cat scratch or bite; pts commonly present w tender lymphadenopathy proximal to the inoculation site; lymph node histopathology often shows necrotizing granulomas and stellate-shaped micro abscesses
