Microbiology of STI's Flashcards
Give 3 examples of bacterial causes of STI’s.
- Chlamydia trachomatis (chlamydia)
- Neisseria gonorrhoeae (gonorrhoea)
- Treponema pallidum (syphilis)
Give 3 examples of viral causes of STI’s.
- Human papilloma virus (genital warts)
- Herpes simplex (genital herpes)
- Hepatitis and HIV
Give 3 examples of parasitic causes of STI’s.
- Trichomonas vaginalis
- Phthirus pubis (pubic lice or “crabs”)
- Scabies
Describe the response generally produced by gonococci that infects the male urethra.
An intense neutrophil response that leads to a purulent discharge and pain on urination
Describe the response generally produced by chlamydia that infects the male urethra.
More likely to produce a mild, watery discharge, or no sx at all
What is transmission of STI’s solely?
Human-human
What organism, is the exception to human-human transmission and has some inanimate sources?
T. vaginalis
What does the efficacy of transmission depend on?
- Concentration of phenotype of that organism in the genital tract
- Susceptibility of the sexual partner
- Resistance of the host (hereditary, acquired or innate)
Immunity is ____
RARE
Re-infection is ______
COMMON
What % of females are colonised with small amounts of flora and have no symptoms?
30%
Give the 4 predisposing factors to candida infection.
- Recent antibiotics
- High oestrogen levels
- Poorly controlled diabetes
- Immunocompromised patients
What 3 things would predispose someone to high oestrogen levels?
- Pill
* Pregnancy
How does a candida infection present?
As an intensely itchy white vaginal discharge
How is candida infection diagnosed?
This is a CLINICAL DIAGNOSIS.
Do a high vaginal swab for culture!
What are the majority of cases of candida infection caused by?
C. albicans.
How is candida infection treated?
Topical clotrimazole pessary or cream (available OTC).
Oral fluconazole.
What are the important features of a gram film of someone with candida?
Budding + Hyphae
In men, what does candida infection present as?
A ‘spotty’ rash of Candida balanitis
What are the 3 classes of prostatitis?
- Acute bacteria
- Chronic bacterial
- Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS)
Acute bacterial and chronic bacterial prostatitis account for
<5%
What signs + symptoms does acute bacterial prostatitis present with?
UTI symptoms \+ * Lower abdomen pain * Back pain * Perineal pain * Penile pain * Tender prostate on examination
What are the signs + symptoms of a UTI?
- Dysuria
- Frequency of urination + nocturnal
- Haematuria
What symptoms are associated with an upper UTI?
- Fever
- Loin pain
- Rigors
In men, what is prostatitis a rare complication of?
UTI
What organisms can cause prostatitis?
Same organisms as UTI – E coli and other coliforms, Enterococcus sp.
BUT . . .
Check for STI in patients <35years (gonorrhoea, chlamydia).
How is prostatitis diagnosed?
Clinical signs \+ MSSU (mid-stream specimen of urine) for culture and sensitivity \+ First pass urine for STI's
From what part of the stream, is urine taken for an STI check in males?
First pass
From what part of the stream, is urine taken for an UTI check in males?
Mid-stream
How is prostatism treated?
Ciprofloxacin for 28days – altered depending on culture result.
Trimethoprim for 28days – if high C diff risk. (in Tayside, we much prefer trimethoprim)
How would gonorrhoea appear on a gram film?
As gram negative intracellular diplococci
Why are confections common?
STI pathogens move together
What do genital ulcers highly increase the probability of?
HIV acquisition
What can STI’s cause?
Urethritis
What bacteria predominates in the ‘healthy’ vagina?
Lactobacillus spp
What does lactobacillus produce? What is the effect of this?
Lactic acid +/- hydrogen peroxide
- These suppress growth of other bacteria
Give examples of organisms that may also be part of the normal vaginal flora.
- Strep ‘viridans’ – there are many different species within this group.
- Group B beta-haemolytic Streptococcus.
- Candida spp. (small numbers)
What does normal vaginal flora contain?
Hydrogen peroxide-producing lactobacilli, such as Lactobacillus crispatus and Lactobacillus jensenii
What is the purpose of normal vaginal flora?
Help ‘defend’ the vagina against a number of pathogens (an e.g. of innate immunity).
What Lactobacillus is rarely found in the normal vagina? What does this explain
Lactobacillus acidophilus.
Explains the failure of yogurt to serve as a remedy for or as a preventive for BV.
What is the normal pH of the vagina? When does it increase?
4-4.5
Increases in bacterial vaginosis
In bacterial vaginosis, what is the normal vaginal flora replaced by?
Gardnerella vaginalis and many species of anaerobic bacteria
What, essentially, is bacterial vaginosis?
An imbalance of vaginal flora
Describe the discharge in bacterial vaginosis.
Homogenous (like a film), and may contain bubbles
Describe how to carry out a ‘whiff test’ for bacterial vaginosis. Describe a positive result.
Add 10% potassium hydroxide to the discharge on a slide.
This elicits an amine-like, fishy odour due to the amines from the anaerobic flora.
What are the results from a wet mount in a sample from a patient with bacterial vaginosis
- Absence of bacilli, and their replacement with clumps of coccobacilli.
- Some vaginal epithelial cells are coated with coccobacilli, which may obscure their edges (clue cells), or the normally clear appearance of the cytoplasm.
- Relatively few polymorphonuclear leukocytes are observed.
What does large numbers of leukocytes in the wet mounts of a patient with bacterial vaginosis.
A coincident infection, possibly trichomoniasis or bacterial cervicitis
Describe the gram stain of someone with bacterial vaginosis. (BUZZWORD !!!)
Epithelial ‘clue cells’ covered with gram variable bacilli
What (in terms of infection) is this associated with increased risk of in someone with bacterial vaginosis?
Upper tract infection – endometritis, salpingitis
In relation to pregnancy, what is BV associated with an increased risk of?
Premature rupture of the membranes and preterm delivery
What may women with BV have an increased risk of?
HIV
What is the treatment of BV directed against?
Anaerobic flora
How is BV treated?
Metronidazole for 7 days
What is the BV relapse rate?
30%
Who does the treatment of BV not help?
Male partners
What is the commonest STI in the UK?
Chlamydia
Where in the body does chlamydia infect?
- Urethra
- Rectum
- Throat
- Eyes
- Endocervix
What type of bacteria is chlaymdia?
Obligate intracellular bacteria with biphasic life cycle – “energy parasite”
Does NOT reproduce outside a host cell
What does chlamydia behave like?
A parasite
Does chlamydia gram stain?
No – because there is no peptidoglycan in the cell wall
Outline the different serological groupings of chlamydia.
Serovars A-C = Trachoma (eye infection) (NOT an STI)
Serovars D-K = Genital infection
Serovars L1-L3 = Lymphogranuloma venereum
Serovars D-K is what type of infection?
STI - thick DicK
Serrovasrs A-C is what type of infection?
Eye (trachoma) - think ‘A canny c’ - c-see
Serovars L1-L3 is what type of infection? Describe this.
Lymphogranuloma venereum
- Seen in MSM
How is serovars L1-L3 tested for?
Look for chlamydia trachomatis serovars L1-L3
How is serovars L1-L3 treated?
With doxycycline for 3 weeks
How can serovars present?
Can present with a proctitis which histologically mimics Crohn’s, rectal bleeding, pain and tenesmus.
How is chlamydia treated?
Doxycycline 100mg bd x 7 days
What test, tests for both chlamydia and gonorrhoea at the same time?
Combined nucleic acid amplification tests (NAATs)
OR
Polymerase chain reaction test (PCR).
NAATs and PCR are highly ________ and _________ tests
- Specific
* Sensitive
Outline what samples are taken in a STI test for chlamydia and gonorrhoea.
- Male pts – FIRST PASS urine sample
- Female pts – HVS or vulvo-vaginal swab (VVS), which can be self-taken by pt or clinician taken endocervical swab (if pt is having speculum examination).
- Rectal and throat swabs (can be self-taken).
- Eye swabs (babies and adults).
Why is first pass urine taken in an STI test and not MSSU?
Not MSSU as want urine to come from urethra).
Outline the pathogenesis of gonorrhoea.
Attaches to host epithelial cells and is endocytosed into the cell to replicate within the host cell and are released into the subepithelial space.
What do urethral infections usually result in?
Prominent inflammation.
Release of toxic lipo-oligosaccharide and peptidoglycan fragments, as well as the release of chemotactic factors that attract neutrophilic leukocytes
What do some gonococcal strains selectively cause?
Asymptomatic genital infection
The discharge in gonorrhoea is ________
Purulent
What is the appearance on gram film of neisseria gonorrhoea?
Gram negative diplococcus.
- look like ‘2 kidney beans facing each other.’
- easily phagocytosed by polymorphs, so often appear intracellularly on a Gram film.
Neisseria gonorrhoea is described as a fastidious organism’, what does this mean?
Does not survive well in less than ideal growth conditions ie. outside the body
Name 2 tests that can be done to look for neisseria gonorrhoea.
- Microscopy of urethral/endocervical swabs.
* Culture on selective agar plates
What does selective agar do?
Suppress growth of normal flora
What does pharyngeal gonococcal infection result from?
Orogenital exposure
Pharyngeal gonococcal infection is more efficiently acquired by fellatio (oral sex act on male) than by cunnilingus (oral sex act on female)
TRUE
What % of MSM with genital tract gonorrhoea have the infection in the pharynx too?
10-30%
Gonorrhoea infection is usually symptomatic
FALSE - usually asymptomatic
What is the treatment for N. gonorrohoea in the UK?
Intramuscular ceftriaxone + oral azithromycin
After treatment for gonorrhoea, what is recommended for all patients?
Test of cure
How is rectal gonorrhoea diagnosed?
The identification of N. gonorrhoeae, usually by NAAT
Who, is screening for rectal gonorrhoea routine in?
MSM
Greater than 50% of MSM with gonorrhoea will have?
ONLY extragenital infections
What is syphilis caused by?
The spirochaete organism, Treponema pallidum
What does treponema palladium NOT do?
Stain with a gram stain
What does diagnosis of syphilis rely on?
PCR test (reference labs)
OR
Serological (blood) tests to detect antibodies.
*As the organism cannot be grown in artificial culture media.
How many stages are there do the illness of syphilis?
4
Outline the 4 different stages of syphilis.
- Primary lesion (chancre) - organism multiplies at inoculation site and gets into bloodstream. Chancre (painless ulcer at site of contact) will heal without treatment
- Secondary stage – large nos. bacteria circulating in blood with multiple manifestations at different sites (“snail-track” mouth ulcers, generalised rash, flu-like symptoms etc.)
- Latent stage – no symptoms, but low-level multiplication of spirochaete in intima of small blood vessels. Can be divided into early latent and late latent periods
** Some patients will self-cure or be treated co-incidentally **
- Late stage syphilis – cardiovascular or neurovascular complications many years later
Where, commonly, is the rash of secondary syphilis found?
Palms and soles
What kind of microscopy is done for syphilis?
Dark background microscopy
Describe the swab for PCR in syphilis.
Swab primary or secondary lesions sent to reference lab for PCR
What does serology of syphilis look for?
Tests for non-specific and specific antibodies to T. pallidum in blood
What do non- specific test for syphilis indicate? What are they useful in?
How active the disease is and are useful to monitor the response to treatment
What do specific test for syphilis do?
Confirm the diagnosis.
BUT antibody levels decrease very slowly even after successful treatment, and often remain positive for life.
Name 2 of these non-specific serological tests.
VDRL – venereal diseases research laboratory.
RPR – rapid plasma reagin.
What do non-specific tests indicate?
Tissue inflammation
When may non-specific tests for syphilis be falsely positive?
SLE, malaria, pregnancy.
What is RPR, the non-specific test for syphilis used for?
Monitoring response to therapy
When does non-specific tests become negative?
After successful treatment
Give 2 examples of specific serological tests.
- TPPA (T. pallidum particle agglutination assay)
* TPHA (T. pallidum haemagglutination assay)
TPHA remains positive for ____ but is not ________ for syphilis
LIFE
Specific
What is used as the “screening” test for syphilis?
Combined IgG & IgM ELISA.
There are lots of false positives when testing for syphilis
TRUE
What is always used to follow response to treatment for syphilis?
RPR
What is syphilis very sensitive to?
PENICILLIN !!!!
What penicillin preparation is used to treat syphilis?
Injectable long-acting preparations of penicillin (unless pt is penicillin hypersensitive).
Why can labs not grow the organism and check sensitivities for syphilis?
The organism cannot be grown in artificial culture medium
What is genital herpes caused by?
Herpes simplex virus type 1 (also causes ‘cold sores’) and type 2.
Describe the herpes simplex virus.
Enveloped virus, containing double-stranded DNA
What is herpes transmitted by?
Close contact with someone shedding the virus
How is herpes spread?
By either genital/genital or oropharyngeal/genital contact.
What may the primary infection in syphilis be like?
Asymptomatic (or very florid).
Where does the herpes virus replicate?
In the dermis and epidermis.
What does the HERPES virus get into? What does this result in?
Gets into nerve endings of sensory and autonomic nerves.
Results in inflammation at nerve endings exquisitely painful multiple small vesicles, which are easily deroofed
Where does the herpes virus migrate to?
The sacral root ganglion.
- ‘hides’ from the immune system (probs remains for life).
- virus can reactivate from there causing recurrent genital herpes attacks (trigger factors for this not understood)
In the absence of symptoms in herpes, what can occur?
Intermittent virus shedding.
How is genital herpes diagnosed?
Swab in virus transport medium of deroofed blister for PCR test - highly sensitive and specific
How is herpes treated?
- ACICLOVIR may be helpful if taken early enough.
* Pain relief.
What is Trichomonas vaginalis?
A single-celled protozoal parasite
How does Trichomonas vaginalis divide?
By binary fission – no cyst form is known
What type of host does TV live in?
Human only
How is TV transmitted?
Sexual contact
What symptoms does TV cause?
Vaginal discharge and irritation in females
Urethritis in males
How is TV diagnosed?
High vaginal swab for microscopy (PCR test also available, but not used in Tayside, so no good test for males)
How is TV treated?
With oral metronidazole
How is pubic lice acquired?
By close genital skin contact
How do pubic lice act?
Lice bite skin and feed on blood, causing itching in the pubic area
On average, how long do i) male ii) female lice live for?
i) 22 days.
ii) 17 days.
What is used to treat pubic lice?
Malathion lotion.
