Microbiology of Genital Tract Infection Flashcards
What are some common bacterial causes of STIs?
Chlamydia trachomatis, neisseria gonororhoeae, mycoplasma genitalium, treponema pallidum
What are some common viral causes of STIs?
HPV (genital warts), herpes simplex, hepatitis, HIV
What are some parasites that cause STIs?
Trichomonas vaginalis, phthirus pubis (pubic lice), scabies
What do gonococci that infect the male urethra cause?
Generally produce intense neutrophil response causing purulent discharge and dysuria
What bacterial STIs cause urethritis?
Gonorrhoea and chlamydia
What do genital ulcers increase the probability of?
HIV infection
What bacterial predominate in the normal vaginal flora?
Lactobacillus spp = mostly L. crispatus and L. jensenu, produce lactic acid and hydrogen peroxide
What is the normal pH of the vagina?
Acidic = pH of 4-4.5
What are some other organisms that can be present in the normal vaginal flora?
Group B strep and strep viridans
30% colonised symptomatically with small numbers of candida
What causes most candida infections?
Candida albicans = intensely itchy white vaginal discharge
What are the risk factors for candida infection?
Recent antibiotic therapy, high oestrogen levels, pregnancy, poorly controlled diabetes, immunocompromised
How is candida infection diagnosed?
Often clinical
Can do high vaginal swab for culture
What is the treatment for candida infection?
Topical clotrimazole pessary/cream
Oral fluconazole
Non-albicans species more likely to be resistant
What are some features of candida balanitis infection?
Causes characteristic spotty rash
Less common and not sexually transmitted
What does gonorrhoea bacteria do once it has attached to epithelial host cells?
Endocytosed into cell to replicate within the host cell = released into subepithelial space
What do typical urethral gonorrhoea infections cause?
Prominent inflammation, release of toxic lipo-oligosaccharides and peptidoglycan fragments as well as release of chemotactic factors that attract neutrophilic leukocytes
Is gonorrhoea always symptomatic?
No = some strains selectively cause asymptomatic genital infection
What is neisseria gonorrhoea?
Gram negative diplococcus = look like two kidneys facing each other. often appear intracellularly on gram film, doesn’t survive well outside body
What are some features of neisseria gonorrhoea infection?
Much less common than chlamydia
Infects urethra, rectum, throat, eyes and endocervix
How is neisseria gonorrhoea diagnosed?
Microscopy of urethral/endocervical swabs = done in SRH, 90+% specificity in males but less in females
Culture on selective agar plates = not suitable for high vaginal swabs, only done in SRH in Tayside
What are the benefits for NAATs?
More sensitive than culture and able to test urine specimens and self obtained vaginal swabs
What are the limits of NAATs?
Can’t perform antimicrobial susceptibility testing and have poor positive predictive value when used to test low prevalence populations
Why do you have to wait 5 weeks before using NAAT to test for a cure?
It can detect dead organisms
What is the most common bacterial STI in the UK?
Chlamydia = infects urethra, rectum, endocervix, throat and eyes
What are some features chlamydia trachomatis?
Obligate intracellular bacteria with biphasic life cycle = doesn’t reproduce outside host cell
Doesn’t stain with gram stain
What are the three serological groupings of chlamydia trachomatis?
Serovars A-C = trachoma (eye infection, not STI)
Serovars D-K = genital infection
Serovars L1-L3 = lymphogranuloma venereum (tropical, male/male sex)
How is chlamydia treated?
Doxycycline 100mg twice daily for 7 days
What are combined NAATS or PCR used to diagnose?
Chlamydia and gonorrhoea = tests for both in 1 procedure
What is the mainstay for diagnosing gonorrhoea?
Culture
What patients receive combined NAATs testing?
Male patients = first pass urine sample
Female patients = high vaginal or vulvovaginal swab or clinician taken endocervical swab if getting speculum
Rectal and throat swabs, and eye swabs in babies and adults
What is trichomonas vaginalis?
Single celled protozoal parasite = divides by binary fission (only in human host), transmitted by sexual contact
What does trichomonas vaginalis infection cause in females?
Vaginal discharge and irritation
How is trichomonas vaginalis infection diagnosed and treated?
Diagnosis = high vaginal swab for microscopy Treatment = oral metronidazole
What is the discharge that occurs in bacterial vaginosis like?
Homogenous and may contain bubbles
What is the whiff test performed for bacterial vaginosis?
10% potassium hydroxide added to discharge = positive result produced amine-like fishy odour
What does a wet mount of a patient with bacterial vaginosis show?
Absence of bacilli and their replacement with clumps of coccobacilli
What can happen to vaginal epithelial cells in bacterial vaginosis?
Some become coated with coccobacilli which obscures their edges (clue cells) or the clear appearance of their cytoplasm
What does a large number of leukocytes in a patient with bacterial vaginosis mean?
Suggests coincident infection = patients normally have relatively few polymorphonuclear leukocytes
What are some complications of bacterial vaginosis?
Increased rate of upper tract infection = endometritis, salpingitis
Premature rupture of membranes and preterm delivery
Increased risk of HIV infection
What is the treatment for bacterial vaginosis?
Metronidazole for 7 days
30% relapse rate
No benefit treating male sexual partners
What causes syphilis?
Spirochaete called treponema pallidum = doesn’t stain with gram stain
Can syphilis be grown on a culture?
No = relies on PCR or serological diagnosis
What are the 4 stages of syphilis infection?
Primary (chancre), secondary, latent and late stage
What occurs in the primary stage of syphilis?
Organism multiplies at inoculation site and gets into bloodstream, heals without treatment
What occurs in the secondary stage of syphilis?
Large number of bacteria circulating in blood with multiple manifestations at different sites
What occurs in the latent stage of syphilis?
No symptoms = low level multiplication of bacteria in intima of small blood vessels, divided into early and late periods
What occurs in the late stage of syphilis infection?
CV or neurological complications many years later
How is syphilis diagnosed?
Primary = dark ground microscopy, PCR, IgM
Secondary and tertiary = specific and non-specific serology
What is the diagnostic pathway for syphilis?
Positive ELISA (IgG and IgM) - IgM ELISA or VDRL test/RPR or TPPA test
What is the treatment for syphilis?
Long acting injectable penicillin = may need penicillin desensitisation
What are some examples of non-specific serological tests?
VDRL = venereal diseases research laboratory RPR = rapid plasma reagin
What are some features of non-serological tests?
Indicate tissue inflammation = may be falsely positive
Useful for monitoring therapy response
Become negative after successful treatment or over time
What causes genital herpes?
HSV type 1 and 2 = enveloped virus containing double-stranded DNA
How is genital herpes transmitted?
By close contact with someone shedding HSV = spread by genital/genital contact or oropharyngeal/genital contact
Can genital herpes be asymptomatic?
Yes = primary infection may be asymptomatic
Intermittent viral shedding can occur while asymptomatic
Where does HSV replicate?
In dermis and epidermis = gets into nerve endings causing inflammation and very painful multiple small vesicles which are easily deroofed
Where can HSV hide to become latent?
Hides in sacral root ganglion and can reactivate
How is genital herpes diagnosed and treated?
Diagnosed by PCR = swab of deroofed blister in viral transport medium
Treatment = aciclovir helpful if taken early enough, pain relief
What causes pubic lice?
Phthirus pubis = acquired by close genital skin contact
What causes itching in pubic lice infection?
Lice bite skin and feed on blood
How long do pubic lice live for?
Females live for 17 days and lay eggs in hair
Males live for 22 days
How are pubic lice treated?
Malathion lotion
