Microbiology Flashcards
What is virulence?
the capacity of a microbe to cause damage to the host
What are virulence ffactors?
The factors responsible for the variation in virulence within and between species
What is adhesin?
enables binding of the organism to host tissue
What is invasin
enabled the organism to invade a host cell/tissue
what is impedin?
enables the organims to avoid host defense mechanisms
What is aggressin?
causes damage to the host directly
What is modulin?
induces damage to the host indirectly
Where is S.aureus found on the body?
anterior nares and perineum
What skin diesases can Staph. aureus cause?
rash; folliculitis; carbuncle; impetigo; abscess; scalded skin syndrome
What do adhesins bind to?
extracellular matrix molecules that are present on cell surfaces
Give 2 examples of adhesins?
fibrinogen-binding
collagen-binding
What disease does collagen-binding factor allow Staph. aureus to cause?
osteomyelitis
Do all Staph. aureus have all virulence factors?
No
What is the purpose of hte capsule?
a thick polysaccharide layer that allows bacteria to evade and hide from the immune system
What is a toxinoses?
It is a disease that isn’t caused by the bacteria itself but by the toxin it produces
What is a superantigen?
Doesn’t bind directly to MHC class 2 complex but binds outside conventional binding groove which causes a cytokine storm and inappropriate immune response
Give an example of a superantigen
TSST-1
What disease does TSST-1 cause?
Toxic Shock Syndrome
What are the symptoms of Toxic Shock Syndrome?
fever
diffuse macular rash and desquamation
hypotension
more than three organs involved
What does Panton- Valentine Leukocidin do?
specific toxicity for leukocytes so stop immune system working
What conditions is PVL associated with?
recurrent furunculosis
sepsis/ necrotising fasciitis
necrotising pneumonia
Why do antibiotics fail in the treatment of necrotising penumonia?
The toxin is causing the disease not the bacteria and the antibitocs do not target the toxin
Describe Streptococci
gram positive cocci
chains
coagulase negative
What skin infections does streptococcus pyogenes cause?
impetigo, cellulitis, necrotising fasciitis
If a microbe causes beta haemolysis, what does this mean the bacteria can do?
produce a protein that can destroy RBCs
What proteins are involved in helping Strep. pyogenes in adhesion?
M proteins
What superantigens cause Toxic shock like syndrome?
SpeB and SpeC
What allows both Staph. aureus and Strep. pyogenes to cause Toxic Shock?
Similar exo-proteins, common virulence factors and disease mechanisms
What is variation in disease and virulence the result of?
variation in genes
How do staphylococcus sp. appear on staining
gram positive cocci in clusters
How are staphylococcus differentiated?
coagulase test
Name an important coag negative staph.?
staph. epidermidis
What is the only coagulase positive staph.?
staph. aureus
Name 3 toxins produced by staph. aureus?
enterotoxin; SSSST; PVL
How do streptococcus sp. appear on gram staining?
gram positive cocci in chain
How are strep. sp. classified?
haemolysis
Name 2 bacterium that are alpha haemolytic strep.?
strep. pneumoniae and strep. viridans
What are the bacteria that are beta-haemolytic?
Group A, group B and group C, G
What bacteria is non-haemolytic?
enterococcus
how does partial haemolysis appear on a petri dish?
green
What enzyme do beta-haemolytic streptococci produce?
haemolysin
What is the purpose of having a dry skin surface?
dessication (drying out) of microbes
What is the purpose of sebum?
inhibit bacterial growth
What skin infections does staph. aureus cause?
boils and carbuncles cellulitis infected eczema impetigo wound infection staph. scalded skin syndrom
What skin infections does strep. pyogenes cause?
infected eczema impetigo ceullitis erysipelas (superficial form of cellulitis- raised red patches) nectrotising fasciitis
What antibiotic is given for strep. pyogenes?
penicillin
What is necrotising fasciitis?
bacterial infection spreading along fascial planes below skin surface leading to rapid skin destruction
What are the 2 types of nectrotising fasciitis?
type 1- mixed
type 2-group A strep
Where is tinea capitis found?
scalp
Where is tinea barbae found?
beard
where is tinea corporis found?
body
Where is tinea manuum found?
hand
Where is tinea unguium found?
nails
Where is tinea cruris found?
skin folds- groin; under the arm; under the breast
What other name is tinea pedis known as?
athletes foot
What type of tissue do dermatophytes infect?
keratinised tissues only-skin, hair and nails
what gives a dermatophyte infection its ring appearnace?
lesion grows outward and heals in the centre
What type of skin does fungus enter?
abraded or soggy skin
What is the most common dermatophyte causal organism?
trichophyton rubrum
What type of light can be used to diagnose fungal infections?
Woods light (fluroescence)
What is the name of the anti-fungal cream given?
clotrimazole
What systemic anti-fungal angents can be given?
terbinafine
itraconazole
Where does candida cause skin infections?
in skin folds where area is warm and moist (candida intertrigo)
How are candida skin infections treated?
clotrimazole cream; oral fluconazole
What is scabies caused by?
sarcoptes scabiei
What is the norwegian scabies?
chronic crusted form which is highly infectious
What are the symptoms of scabies?
intensely itchy rash affecting finer webs, wrists and genital area
What is the treatment for scabies?
malathion lotion
benzyl benzoate
What is the treatment for lice (pediculosis)?
malathion
What patients need single room isolation and contact precautions?
Group A strep infections
MRSA infection
Scabies (long sleeved g owns also required for norwegian scabies)
What virus causes chickenpox and shingles?
varicella zoster virus
What happens during chickenpox that allows the virus to reactivate as shingles?
Virus establishes latency in dorsal root ganglia
What is the progression of the rash found in chickenpox?
macules to papules to vesicles to scabs to recovery (centripetal-thickest on torso)
What is associated with chickenpox in addition to the rash?
fever and itch
What are the complications of chickenpox?
secondary bacterial pneumonitis haemorrhagic scarring encephalitis
What factors would predict chickenpox to be severe?
extremes of age; depressed cell mediated immunity
What does neonatal VZV happen secondary to?
chickenpox in mother in late pregnancy
How is neonatal VZV prevented?
varicella zoster immune globulin in susceptible women
What is the rash progression in shingles?
tingling/pain to erythema to vesicles to crusts
What is a compication of shingles?
post-herpetic neuralgia
What increases the chances of getting post-herpetic neuralgia?
eldery
trigeminal distribution
Why is an opthalmogy referral required urgently if zoster affects the trigeminal nerve?
Shingles can cause keratitis- inflammation of the cornea
What is Ramsay-Hunt Syndrome?
When shingles affects CN7 and so causes vesicles and pain in the auditory canal and throat. Also causes facial palsy and if there is irritation of the 8th cranial nerve- deafness; vertigo and tinnitus
What is Ramsay-Hunt syndrome also known as?
geniculate or otic herpes zoster
Why is a vaccination for shingles given?
reduces incidence of shingles as well as post-herpetic neuralgia
What is happens during the first infection of herpes simplex?
gingivostomatitis
What are the symptoms of herpes simplex virus?
recurrent blistering rash at vermillion border
Where can herpes simplex spread to in the body?
fingers- herpetic whitlow
eczema- eczema herpeticum
Which type of herpes simplex mainly causes oral lesions
HSV type 1
How does aciclovir work?
An analogue of guanosine and so is selectively incorporated into viral DNA inhibiting replication
What is the drawback of aciclovir?
Does not eliminate latent virus
What infections can cause erythema multiforme?
herpes simplex virus
mycoplasma pneumoniae bacterium
What is molluscum contagiosum?
fleshy, firm umbilicated pearlescent nodules which are self limiting and common in children
How can molluscum contagiosum be treated?
liquid nitrogen
What virus causes warts?
HPV
How can warts be treated?
topical salicyclic acid
What age are warts most common?
children
What types of HPV are most common in warts/verrucas?
types 1-4
What types of HPV cause genital warts?
types 6 and 11
Which types of HPV cause cervical cancer?
types 16 and 18
What is herpangina?
blistering rash at the back of the mouth
What viruses cause herpangina?
enterovirus- coxsackie virus and echovirus
How can herpangina be treated?
usually self-limiting
What viruses cause hand, foot and mouth disease?
enteroviruses- esp. coxsackie
What age group typically gets hand, foot and mouth disease?
children
What virus causes erythema infectiosum?
human parovirus
What is the common name for erythema infectiosum?
slapped cheek disease
What are the symptoms of erythema infectiosum?
slapped cheek appearance which as it fades becomes a lacy macular rash on the body. headache; fever; arthralgias; sore throat
What is especially seen in adults with erythema infectiosum?
acute arthritis esp. in the wrists as the rash fades
What are the complications of parovirus?
spontaneous abortion
aplastic crises (sudden drop in haemoglobin)
chronic anaemia
How is parovirus diagnosed?
antibody testing - IgM
What is Orf?
virus of sheep “scabby mouth”
How does Orf present?
firm, fleshy nodule on hands of farmers
What is the first phase of a syphilis infection?
chancre- painless ulcers at site of entry
What is the secondary phase of syphilis infection?
red rash over body- which is prominent on soles of feet and palms of hands
mucous membrane- “snail track” ulcers
What is the tertiary phase of syphilis infection?
CNS; CVS; gummatous
What is syphilis caused by
bacterium- treponema pallidum
How is syphilis diagnosed?
blood test or swab of chancre for PCR
How is syphilis treated?
injections of penicillin
What is the vector in Lyme disease?
ticks
What bacterium causese Lyme disease?
Borrelia burgdorferi
What is the early presentation of Lyme disease?
erythema migrans
What is the late presentation of Lyme disease?
heart block; nerve palsies; arthritis
What is the therapy for Lyme disease?
amoxicillin or doxycycline
What is the lab confirmation for Lyme disease?
antibody blood test (mainly for late presentations)
What are the symptoms of Zika virus?
fever; rash (maculopapular); headaches; arthralgia; myalgia; non-purulent conjuctivitis
What is the vector for Zika virus?
mosquito
What are the complications of Zika virus?
microcephaly and guillain barre syndrome