Bacterial, Viral, Fungal Infections I Flashcards
initiation of infection: those that enter through bites/scratches
Streptococci., Mixed aerobic/anaerobic
bacteria, Pasteurella, many more species
initiation of infection: those that enter through trauma
Cellulitis, fasciitis, myonecrosis, bone inf.
causes of pasteurella multocida
deep skin infection, bacteriemia, endocarditis, osteomyelitis, septic arthritis
what is pasteurella multocida
primarily zoonotic and part of normal flora of upper RT
how does one get pasteurella multocida
via a cat or dog by bite or scratches, licking of broken skin,
infections in keratinized epithelium and epidermis
keratinized epithelium: dermatophytic fungi
epidermis: warts (HPV), impetigo (staph `aureus and group A strep), cold sores (HHV-1)
infections in dermis and hair follicles
dermis: cellulitis and erysipelas
hair follicles: folliculitis and abscesses
infection in sebaceous glands
acne (propionibacterium acne)
bacteria seen in hot tub folliculitis
pseudomonas
where is streptococci normal seens
as part of normal flora in oral cavity, GI, and genital tract
features of strep
gram positive cocci in chains, classified based on hemolysis on blood agar
features of strep pyogenes
gram positive, beta hemolytic, strep that form pus and can occasionally cause purulent infections, infections can be in upper skin layer or it can go deep
toxin of strep pyogenes
pyrogenic exotoxin (SPE) once called erythrogenic toxin minority of strain carry this toxin which is carried on a phage
what does the pyrogenic exotoxin do
stimulates cytokine release causing multiple effects like: red rash on skin –> scarlet fever
how is pharyngitis spread
direct contact or aerosol
carrier rate of untreated pharyngitis and where it is located
1-4 weeks or more after infection as organisms in in throat and sometimes anus
type of infection is scarlet fever
group A beta strep infection
symptoms of scarlet fever
strep throat with a characteristic rash deep red color cheeks, temples, buccal mucosa strawberry tongue punctuate hemorrhages on palate sandpaper rash on trunks, arms, and legs
the exotoxin released from strep pyogenes can be attributed to what symptom in scarlet fever
sandpaper rash on trunks, arms, and legs
what is staph aureus
gram positive cocci found in clusters and in thick cell walls
often found intracellularly in granulocytes
cultural characteristics of staph aureus
grows on blood agar with aerobic conditions
white colony but can become yellow with age
usually beta hemolytic
positive for staph aureus in about 30% of population
anterior nares
virulence factors of staph aureus
coagulase, exotoxin, hemolysins, leukocidins
diseases caused by staph infections
scalded skin syndrome, S. aureus exfoliatins, toxic shock syndrome,
how does one get scalded skin syndrome
toxin is absorbed into the blood stream with erythema and intraepidermal desquamation occurring at remote sites
can staph aureus be isolated from desquamation sites of scalded skin syndrome
no
what is occurring staph aureus exfoliatins
exfoliatins are leading to intercellular splitting of the epidermis – between the stratum spinosum and stratum granulosum by disruption of the intercellular junctions
in s. aureus exfolatins, if toxin is produced at the site of infection what happens
epithelial desquamation at the remote sites of the body –> staph scalded skin syndrome
what is toxic shock syndrome characterized by
high fever, vomiting, diarrhea, sore throat, muscle pain, shock within 48 hours with renal and hepatic damage
also skin rash, strawberry tongue
describe what happens after skin rash in toxic shock syndrome
desquamation at a deeper level than scalded skin syndrome
what is the toxin in toxic shock syndrome
pyrogenic toxin called toxic shock syndrome toxin-1 (TSST-1)
what does TSST-1 do
stimulates release of cytokines and direct toxic effects on endothelial cells
Stimulates enhanced T-lymphocyte responses by direct interaction with surface receptors on T cell.
situation where TSS is usually seen
when woman is menstruating and wears tampon for long periods of time – provides environment for products of toxin which is absorbed from the local site (1 in 5 women have staph aureus as part of normal flora of vagina)
non menstrual TSS does occur
cause of impetigo and causative agent
insect bite or minor abrasion
staph aureus or group A strep
what is impetigo characterized by
–Small vesicles with erythema
–Become pustular and later crusted
complication of impetigo
post strep glomerulonephritis 2-4 weeks after skin infection but only if caused by strep pygogenes aka group A strep
what can occur after beta strep infections
acute rheumatic fever
what are characteristics of acute rheumatic fever
– Inflammatory disease
• Fever, carditis, subcutaneous nodules, migratory polyarthritis
– Heart valve damage
• Murmurs, cardiac enlargement.
• Repeat infections lead to progressive damage
CCSEA and P-FACE
chorea, carditis, subcutaneous nodules, erythematous marginatum, arthritis, pr elongation, fever, arthralgia, increased CRP and ESR
pathogenesis of acute glomerulonephritis
antigen-antibody complexes in the kidney (type III hypersensitivity)
what population acute glomerulonephritis after strep infection usually seen in
children
other than straph aureus what other organism can cause TSS
strep pyogenes
can staph aureus be found together strep pyogenes in impetigo
yeah in about 30% of cases
coagulase and catalase positive
staph aureus
is coagulase a toxin
no but it plays a role in its pathogenesis
coagulase – what does staph coated with fibrin prevent
phagocytosis (helps localize the lesion)
other biological substances that staph aureus produces
Hemolysins, hyaluronidase, nuclease, lipase, protease
major cytotoxin of staph aureus
staph aureus alpha toxin
characteristic of alpha toxin
– chromosomally encoded, low molecular weight protein
– Causes necrosis or death in experimental animals
– Causes certain mammalian cell membranes to leak through pores formed by toxin
– Causes RBC’s to lyse.
what is panton valentine leukocidin (PVL)
it is a cytotoxin that lyses neutrophils and releases enzymes that damages host cells
what is PVL associated with
- severe pneumonia
- severe skin infections
- common in community acquired methicillin resistant strains
