Microbiology of GU Tract Flashcards
4 bacterial STIs?
chlamydia
gonorrhoea
mycoplasma genitalium
syphylis (treponema pallidum)
3 viral STIs?
HPV (genital warts)
genital herpes (PSV)
hepatitis and HIV
3 parasitic STIs?
trichomonas vaginalis
phthirus pubis (pubic lice)
scabies
what is present in normal vaginal flora?
lactobacillus spp predominate and are protective - L. crispatus - L. jensenii \+/- group B strep \+/- candida \+/- strep viridans
normal vaginal pH in post puberty/pre menopausal female?
acidic - 4-4.5
produces lactic acid +/- hydrogen peroxide
L. acidophilus is not a significant part of flora
what does candida look like?
branches with buds
most common candida in female?
candida albicans
predisposing factors for candida?
recent antibiotics
high oestrogen
poorly controlled diabetes
immunocompromised
how does candida present?
intense itch and white vaginal discharge
diagnosis of candida?
high vaginal swab for culture
treatment of cadida?
topical clotrimazole pessary or cream
oral fluconazole
non-albicans candida more likely to be azole resistant
candida in males?
spotty rash
common presenting feature of ghonoorhoea in males?
tap like pus
how does ghonorrhoea cause infection?
attaches to host epithelial cells and in endocytosed into the cell to replicate within the host cell and are released into the subepithelial space
what is ghonorrhoea?
gram -ve intracellular diplococcus
looks like 2 kidney beans facing each other
easily phagocytosed by polymorphs so often appear intracellularly on gram film
pathogenesis of typical urethral ghonorrhoea infection?
prominent inflammation release of toxic lipo-oliigosaccharide and peptidoglycan fragments as well as the release of chemotactic factors that attract neutrophillic leukocytes
where can ghonorrhoea infect?
urethra
rectum
throat
eyes
gonorrhoea is very fastidious, what does this mean?
does not survive well outside the body, therefore difficult to culture
how is gonorrhoea cultured?
selective agar plate which suppresses other bacteria
done on endocervical, rectal and throat but not high vaginal swabs
what is NAAT?
microbiology test which has increased sensitivity over culture
can be done on urine and self obtained vaginal swabs
gold standard for gonorrhoea testing
only use when high suspicion as can give false positives
main antibiotic choice for gonorrhoea?
IM cephtraixone and azithromycin
most recent guidance = ceftriaxone alone
most common STI in UK?
chlamydia
features of chlamydia bacteria?
obligate intracellular bacteria with biphasic life cycle
“energy parasite”
does not reproduce outside of host cell
does not stain with gram stain (no peptidoglycan in cell wall)
3 serological groups of chlamydia?
serovars A-C = trachoma (eye infection, not STI)
serovars D-K = genital infection
serovars L1-L3 - lymphogranuloma venereum (tropical and homosexual men)
treatment of chlamydia?
azithromycin 1g oral dose then 500mg for 2 days (for uncomplicated)
doxycyline 100mg BD for 7 days = mainstay
chlamydia life cycle?
attachment and entry > migration to perinuclear area and EB > RB transition
> inclusion biogenesis and bacterial replication > RB-EB transition and cell lysis
diagnosis of chlamydia?
combined NAATs or PCR tests for both organisms in one test done on - first pass urine in men - HVS or vulvo-vaginal swab in females - rectal and throat swabs - eye swabs
what is trichomonas vaginalis and what does it cause?
single celled protozoal parasite which is transmitted by sexual contact
causes vaginal discharge and irritation in females (possibly urethritis in males)
diagnosis of trichomonas vaginalis?
high vaginal swab for microscopy
management of trichomonas vaginalis?
oral metronidazole
features of bacterial vaginosis?
homogenous, possibly bubbly discharge
may smell fishy
how is bacterial vaginosis diagnosed?
whiff test
- add 10% potassium hydroxide to the discharge, will cause amine-like, fishy odour
wet mount
- discharge sample put in saline on slide
how does BV alter pH?
makes it more alkaline
associated risks with BV?
increased rate ot upper tract infection (endometritis, salpingitis etc)
premature rupture of membranes and preterm delivery
women with BV may have increased risk of HIV
general description of BV?
not enough good bacteria
too much bad
microflora has changed
how is BV managed?
treatment directed against anaerobic bacteria
- metronidazole for 7 days
(treatment of male partners has no benefit)
features of treponema pallidum (syphilis)?
spiral
(spirochete)
does not stain on gram stain
cannot be grown in artificial media so diagnosis relies on PCR or serological blood tests to detect antibodies
what are the 4 stages of syphilis infection?
- primary lesion (chancre) at site of inoculation and gets into blood (will heal without treatment)
- large numbers of bacteria circulating in blood with multiple sites affected (snail track mouth ulcers, rash, flue etc)
- no symptoms but low level multiplication of spirochete in intima of small blood vessels (latent stage)
- late stage - cardiovascular or neurovascular complications
does everyone with syphilis get to late stage?
no
only 1/3
non-specific serological tests for syphilis?
VDRL
RPR
non-specific tests that indicate tissue inflammation
may cause false positives in SLE, malaria or pregnancy
useful for monitoring response to therapy
usually become negative after successful treatment or over time
how is syphilis diagnosed?
history and examination
caveats (treatment history, reinfection risk, history etc)
primary = dark ground microscopy, PCR, IgM
secondary = serology (specific and non-specific)
tertiary = serology (specific and non-specific)
specific syphilis serology testing?
syphilis combined IgM and IgG screening test
- negative = result goes out as negative
- positive = further tests performed (IgM eliza - specific for acute), VDRL/RPR (activity), TPPA test (specific)
how is syphilis managed?
injectable long-acting preparations of penicillin
penicillin desensitisation may be needed
why are syphilis penicillins different from other penicillins?
syphilis only needs a small concentraiton of penicillin but has to be exposed for a very long time
what causes genital herpes?
HSV1 (also causes cold sores - can cause genital herpes if oral sex)
HSV2
transmitted by close contact with someone shedding the virus
pathogenesis of genital herpes?
asymptomatic primary infection
virus replicates in dermis and epidermis and gets into nerve endings of sensory and autonomic nerves
inflammation at nerve endings causes exquisitely painful multiple small vesicles which are easily de-roofed
virus migrates to sacral root ganglion and hides from immune system
virus can reactivate from there causing recurrent genital herpes attacks
intermittent virus shedding can occur in absence of symptoms
how is genital herpes diagnosed?
swab in virus transport medium of deroofed blister for PCR
(no good test for HSV carriage between recurrences)
serology (IgG, not routine)
how is HSV managed?
aciclovir
pain relief
pathogenesis of pubic lice?
acquired by close genital skin contact lice bite skin and feed on blood causing itching in pubic area female louses lay eggs on hair males live for 22 days females live for 17 days
how is pubic lice managed?
malathion lotion