Microbiology Flashcards
Functions of bacterial cell wall
- Resist osmotic stress
- primer for own synthesis
- shape
- Protection
Encapsulated bacteria
Strep pneumoniae Klebsiella pneumoniae H. influenzae N. meningitidis Salmonella Group B strep
Bacterial capsules
Composed of glycocalyx (except b. anthracis)
Gram positive bacteria
Thick cell wall with lots of PG. Assoc with techoic and lipoteichoic acids
Gram negative bacteria
Thin PG layer and outer membrane. LPS.
Phases of bacterial growth
Lag, Log, Stationary, Decline
Obligate aerobes
Require O2. Nocardia, pseudomonas, mycobacterium tuberculosis, bacillus. (“Nagging pests must breathe”)
Obligate anaerobes
Cannot grow in presence of O2. Clostridium, bacteroides, actinomyces. (“Can’t breathe air”)
Microaerophilic
Requires very little levels of O2 for growth
Conjugation
One-way transfer of DNA from a donor cell to a recipient cell through sex (F) pilus. Donor bacterium must carry F plasmid (F+, male) and other must not (F-, female)
Spores
Dehydrated, multicelled structure that allows bacteria to survive when nutrients are limited. Only autoclaving will kill. Only certain gram positive rods can form spores.
Transformation
Bacteria take up fragments of naked DNA and incorporate them into their genomes if recipient is sufficiently homologous for recomb to occur
Transduction
Genetic transfer mediated by bacteriophages
Pigment producing bacteria
S aureus (yellow) P aeruginosa (blue-green) Serratia marcescens (red)
Bacteria that carry IgA proteases
S pneumoniae
N meningitidis
N gonorrhoeae
H influenzae
alpha hemolysis
Green darkening of blood agar. S pneumoniae, viridans strep
beta-hemolysis
Complete clearing of blood agar. S pyogenes, agalactiae, aureus. Listeria.
Gamma-hemolysis
no hemolysis. Enterococcus
Endotoxin
LPS. Outer cell membrane of gram neg bacteria. Can cause fever and shock
Exotoxin
Polypep secreted by bacteria that harm host by altering cellular structure or fn. Very potent and potentially lethal.
Enterotoxins
Act on gut.
Bacteria not amenable to Gram staining
Mycobacteria. mycoplasma, rickettsia, chlamydia, treponema, legionella
MacConkey agar
Inhibits Gram+. Lactose fermenters: red. Non-lactose fermenters: white.
Chocolate agar
Good for H influenzae. Contains X, V factors.
Bordet-Gengou medium
Good for B pertussis
Bile esculin agar
Good for Group D streptococci
Silver stain
Good for Legionella pneumophilia
Hemolysis on blood agar
Differentiates streptococci
Streptococcus pyogenes
Pyogenic. B hemolysis. Causes wide variety diseases
Streptococci
Catalase negative, grm positive
Rheumatic fever
Caused by cross rxn of Abs raised against streptococcus bacteria with antigens in heart, causing pancarditis initially and potentially later-onset valvular disease.
Streptococcal pharyngitis
Odynophagia, high fever, regional lymphadenopathy, and most notably, erythema and frank white exudate on palatine tonsils. Scarlet fever is a complication from lysogenized pyrogenic exotoxin.
Impetigo
Common childhood colonization of upper epidermis. Perioral vesicular/blistered lesions that eventually develop honey-colored crust. Can be caused by streptococcus or S aureus.
Necrotizing fasciitis
Rapidly progressive infection of deep subcutaneous tissue. Purple-blue bullae on overlying skin following cellulitis-like picture, overt gangrene, systemic sxs, MOF.
Erysipelas
Acute skin infection-erythema, edema, warmth, systemic sxs. Streptococcus or other orgs like s aureus if immunocompromised
Cellulitis
Acute skin infection-erythema, edema, warmth, systemic sxs. Streptococcus or other orgs like s aureus if immunocompromised
Strep agalactiae
Common cause UTIs in pregnant women, comm cause neonatal infection. Indistinguishable from strep pyogenes on microscopy. B hemolysis. High rate of asymptomatic carriage in pregnant women.
Yellow fever
Flavivirus
Poliovirus
RNA enterovirus. Acute flaccid paralysis in <1%
Cat scratch disease
Bartonella henselae
Lyme disease
Borrelia burgdorferi, by Ixodes tick
EBV
Assoc with Burkitt lymphoma
S saprophyticus
5-20% cystitis
K pneumoniae
Community acquired pneumonia or secondary infections in COPD patients
Currant-jelly sputum
Alcoholics and aspirators at risk
WBC casts
Only if in kidney
Pyelonephritis
Costovertebral angle tenderness, fever, chills, with or without sxs UTI. In kids, may ascend to kidneys through incompetent ureterovesical sphincters
Histoplasma
Can live intracellularly
Blastomyces
Big, Broad Based, Budding
Mississippi River Basin
Histoplasmosis, blastomycosis
Central and S America-fungi
Paracoccidioidomycosis
Paracoccidioidomycosis
Captains wheel/Mickey Mouse appearance
Atypical pneumonia
Mycoplasma pneumoniae, legionelle pneumoniae, chlamydia pneumoniae
IgM cold agglutinin production
Only seens with mycoplasma infection
Legionella pneumoniae
Cultured on charcoal yeast extract medium
OR SILVER STAIN
Gram -
Severe community acq pneumonia, mostly affecting elderly with pre-existing lung disease
Reticulate bodies
Intracellular form of chlamydia species
Progressive multifocal leukoencephalopathy
Immunodef. pts. Caused by JC virus
CMV encephalitis
Uncommon except in HIV, homeless
Toxoplasmosis
Most comm cause cerebral mass lesions in HIV infected pts. Ring enhancing lesions on head CT.
TORCH infection.
Cat feces.
Rubeola
Measles. Koplik spots (red oral lesions with blue-white centers).
Diptheria
membraous pharyngitis
Rubella
German measles
Roseola
HHV6. V young kids, Rash, high fever
Rocky Mtn Spotted Fever
Petechial rash beginning around ankles and wrists
Eczema herpeticum
Vesicular rash. Pruritic. HSV-1 with disrupted skin barrier.
Impetigo
Honey colored crusting. Itchy btu not painful. S aureus or sometimes S pyogenes
P. malariae
72 hr cycle
P ovale
24 hr cycle
P vivax
24 hr cycle
P knowlensi
Macaques
Viral meningitis
Normal or raised ICP, high lymphos, normal protein, sugar
HPV
Inactivates p53, Rb
Influenza
Hemagglutinin and neuraminidase on surface allow absorption and penetration of host cells
Antigenic shift
New virus, can cause pandemics
Guillan Barre
Assoc with campylobacter jejuni
Symmetrical ascending paralysis
Neurocysticercosis
Pork tapeworm. Most comm parasitic infxn CNS worldwide. Brain, muscles, skin, heart.
B. Pertussis-stages
Incubation: 7-10 days
Catarrhal stage: URTI sxs. Max infectivity
Paroxysmal-single deep breath then whooping
Convalescent stage: decrease in intensity
Macrolides only work in incubation, catarrhal stages.
H influenzae
Chocolate agar + factor V, X
Does not cause influenza! (But can be post-influenza pneumonia)
Hib vaccine covers serotype B
Epiglottitis, meningitis, otitis media, pneumonia, eye infections, sinusitis
Corynebacterium diptheriae
Loeffler medium
N gonorrhoeae
Thayer-Martin medium
C botulinum
fresh honey (babies). Babies-unable to swallow, general weakness. Heat labile toxins that inhibit ACh release into NMJ. Home-canned or preserved food in adults.
Exotoxin A
TSS, Scarlet fever