Commensal flora FGT Flashcards
Distinguish between upper and lower FGT
The upper FGT refers to everything above the cervix.
The lower FGT refers to everything below the cervix.
List and describe the factors affecting flora composition
Local Defenses
- Cervical mucociliary escalator:
- Helps to prevent endogenous and exogenous microbes of the lower genital tract reaching the uterus and upper reproductive tract sterile
- Cervical mucus
- contains antimicrobial proteins e.g. lysozyme, lactoferrin and IgA
- protects cell receptors from microbial adhesins
- serves as a source of microbial nutrients
Temperature
### pH
- pH variations influenced by age and hormones
- neutral pre-menarche
- varies monthly post-menarche pH 4-7; lower at end of follicular and halfway through luteal phase
Availability of Oxygen (or lack of oxygen)
- “Microaerophilic” environment: oxygen availability is typically ~2% of that found in air
- Factors affecting oxygen content
- hormones: most ‘anaerobic’ in mid cycle
- tampons
- contraceptives
Energy and Nutrient Sources for the microorganisms
This includes host secretions and dead cells, as well as metabolites produced by other members of the commensal microflora.
- Mucus: mucins, proteins, organic and inorganic compounds
- Vaginal fluid: rich source of protein and amino acids, carbohydrate, lipids and inorganic ions
- Menstrual fluid: various nutrients e.g. Fe
- Glycogen: present only during reproductive years
- obtained by microbes from desquamated epithelial cells
- very important energy source for dominant bacteria of commensal microflora (lactobacilli) - Sexual fluids
List some importative facultative and olbligate anaerobes of the FGT
The most important of these is the facultative anaerove Lactobacillis spp.
Other potential endogenous pathofens include Staphylococcus spp., Corynebacterium spp., Streptococcus spp., and Enterococcus spp., along with some yeasts.
The vagina is a favorable environment for bacterial and fungal colonization.
Describe lactobacilli
Lactobacilli
- Key characteristics of the genus:
- Gram positive bacilii
- Anaerobic - obligate anaerobe to aerotolerant
- Aciduric or acidophilic: grow over pH range 3-7
- Mesophilic: grow over 15-45 C
- Fermentation of simple carbohydrates to lactic acid (homofermentative), formic acid, acetic acid, carbon dioxide and alcohol (heterofermentative)
- Part of commensal flora of vagina, oral cavity, and gastrointestinal tract
- Rarely associated with invasive infection and disease
- Decreases in numbers of lactobacilli in vagina are associated with development of:
- vaginal candidiasis
- bacterial vaginosis
Describe vaginal candidiasis
- Most commonly caused by Candida albicans
- Part of commensal microflora of skin, mouth, GI tract and urogenital tract of healthy individuals
- Potential for systemic mycoses in immunocompromised individuals, as well as part of healthcare associated bloodstream infections
- Also commonly causes superficial, cutaneous and mucocutaneous infections including vulvovaginitis and vaginitis
- Two forms: budding yeast which undergoes asexual reproduction and pseudo hyphae which is the growth form
- Vulvovaginal candidiasis results when Candida sp. increases in numbers or overgrows. Contributing factors include:
- recent antibiotic therapy
- pregnancy
- hormones e.g. oral contraceptives or HRT
- diabetes (uncontrolled – sugars)
Describe the symptoms, diagnosis and treatment of vaginal candidiasis
- Symptoms: inflammation, burning, itching and ‘cheesy’ discharge
- Diagnosis: based on symptoms/signs and/or microscopy and culture
- Treatment: change reversible factors, topical (cream, powder, pessary) or oral antifungal agents
- Can be recalcitrant in some people, therefore need to address underlying cause
Describe bacterial vaginosis
Overview
- Non-inflammatory nature
- Poorly understood pathophysiology
- Results with in Gram-variable anaerobes, e.g., Gardnerella vaginalis numbers aka overgrowth. Contributing factors include:
- decrease or change in Lactobacillus populations
- onset of menses
- use of vaginal medications or medications
- use of spermicides
- increased number or frequency of sexual partners, or new sexual partner (but it is not an STI)
Describe the symptoms, diagnosis and treatment for bacterial vaginosis
Symptoms and Diagnosis
- Excessive, grey, watery, malodorous discharge resulting from metabolic activities of anaerobes, may be implicated in irritation
- Pre laboratory test: vaginal swab
- pH > 4.5
- Whiff test: fishy odour when 10% KOH added
- Microscopy shows:
- loss of lactobacilli
- increase in gram variable coccobacilli
- clue cells: squamous cells coated with bacteria
Treatment
- metronidazole:
- nitroimidazole drug
- used against anaerobic bacteria and protozoal infections
- alters or breaks down DNA (NA inhibitor)
- clindamycin
- macrolide
- inhibits protein synthesis by binding to 5os rRNA subunit
Describe routes of infection in the neonate
Routes of Infection
- Infections of the fetus or neonate can occur via:
- Haematogenous dissemination: from the ability of a pathogen to overcome the maternal: fetal placental barriers
- Direct infection by endogenous or exogenous pathogens
- Ascending (intrauterine) infection: infection of the aminotic membranes and fluid, which is inhaled by the foetus
- Exposure during passage through the birth canal
List and briefly describe some common neonatal infections during delivery
- Neonatal candidiasis (mainly mucocutaneous)
- Herpes simplex virus (severe disseminated infection)
- Chlamydia trachomatis & Neisseria gonorrhoeae (pneumonia/conjunctivitis)
- Group B Streptococcus (GBS) – Streptococcus agalactiae (bacteraemia, pneumonia, meningitis)
- Screening for GBS in pregnant women at about 36 weeks
- Prophylactic antibiotics (penicillin) administration immediately prior to delivery if culture is positive OR regardless, if risk factors are present
- Usually does not cause symptoms in the woman, but may be implicated in vaginitis or pp-endometritis or puerperal sepsis
Describe and explain the imapct of GBS in the neonate
- Commensal microflora of the gastrointestinal tract and vagina.
- Found in 20-30% of healthy women
- Common cause of neonatal septicaemia and meningitis (50-70% of neonates born to women with GBS will become colonised)
- Early and late onset infections within 7 days (median 6-8 hours) and 7 months of birth respectively
- Associated with opportunistic adult infections: skin, soft tissue, urinary tract and bacteraemia
- GBS colonization in the maternal vagina/bowel by binding to various materials and foetal/neonatal cells (Respiratory, blood-brain endothelium)
- Ascending infection leading to various outcomes (invasive = traverses placental membranes):
- miscarriage
- foetal death in utero
- preterm birth (due to rupture)
- Infection during vaginal delivery causing :
- Bacteraemia
- Pneumonia (because of access to foetal lungs via aspiration or infected amniotic fluid or neonatal lungs due to aspiration of vaginal fluid during delivery)
- Meningitis
List some other endogenous infections that cause disease
- Pelvic Inflammatory Disease (considering STIs)
- Endometritis
- Chorioamnionitis – E. coli and GBS commonly implicated
- Preterm birth
List the diagnostic tests for some common diseases
- Vulvovaginitis (skin rather than mucous membranes): Candida sp, S. Aureus, GAS/GBS
- Vulvovaginal swab MCS
- Vaginal discharge/vaginitis: Candida sp, bacterial vaginosis, GBS
- Vaginal swab MCS
- PID: mixed flora - coliform, anaerobes, Streptococci
- Cervical swab MCS - hard to access site where infection is occurring
- Asymptomatic pregnancy screen: GBS
- Vaginal swab MCS
Describe how to investigate an infection
- light microscopy: T. vaginalis
- Gram stain:
- inflammation: polymorphs on Gram stain
- normal vs abnormal vaginal bacteria on Gram stain
- yeast
Sperm is also commonly seen on microscopy and Gram stain.
It is not normally reported, but potentially an issue if specimen is obtained from a child.
Describe vaginal swabbing
Vaginal Swab Culture
- Depends on clinical history
- “Standard”
- Chocolate and gonococcus specific plate
- Note that cervical swab is specimen of choice for gonococcus
- “Candidiasis”
- Add a Sabouraud plate (selective yeast agar)
- “Pregnancy Group B Streptococcus screening”
- Specialised broth and agar
- “Post partum/gynaecological surgery/PID”
- Add an anaerobic plate
A standard swab:
- normal vaginal flora will mainly contain lactobacilli but also small amounts of other micro-organisms e.g. coliforms, GAS and S. aureus
- The lab is mainly looking for a change in the normal flora and a predominance of an organism which may be pathogenic
- this is a split plate
- chocolate agar is on the left, specialised gonococcus agar ison the right
- the gonococcus agar has inhibitors to stop growth of other organisms, as well as nutrients to support N. gonorrhoeae
- IF gonorrhoeae is suspected, a cervical swab is the specimen of choice
