Microbiology Flashcards
Beta haemolytic strep on agar and examples
Beta-hemolysis (β-hemolysis) is associated with complete lysis of red cells surrounding the colony.
It exhibits a wide zone (2-4 mm wide). Beta hemolysis is more marked when the plate has been incubated anaerobically. They are generally commensals of throat and causes opportunistic infections.
Examples: Streptococcus pyogenes, or Group A beta-hemolytic Strep (GAS).
Alpha haemolytic strep on agar and examples
Alpha-hemolysis (α-hemolysis) is a partial or “green” hemolysis associated with reduction of red cell hemoglobin. Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin.
It exhibit incomplete haemolysis with 1-2 mm wide. Persistence of some unhaemolysed RBC’s can be seen microscopically.
Examples: Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci)
Prevalence of HIV in UK Obstetric population
2 per 1000 live births
Infant antiretroviral therapy
V Low risk (Mother been on cART for >10 weeks and 2x documented maternal HIV viral loads <50 HIV RNA copies/ ml during pregnancy at least 4 weeks apart AND maternal HIV viral load <50 at 36 weeks) –> 2 weeks zidovudine monotherapy
Low risk (maternal viral load <50 at 36 weeks or at time of delivery if premature) –> 4 weeks zidovudine mono therapy
High risk (doesn’t meet low risk criteria) –> Combination PEP
HIV viral load at 36 weeks and recommendation for delivery
<50 HIV RNA copies/ml: vaginal delivery
50-399: PCLS considered (factor in actual viral load, trajectory of viral load, length of time on treatment, adherence issues, obstetric factors & woman’s views)
> 400: PLCS
Infant HIV testing
Formula fed infants:
- During the first 48 hours and prior to hospital discharge
- If HIGH RISK, at 2 weeks of age
- 6 weeks (at least 2 weeks post cessation of infant prophylaxis)
- 12 weeks (at least 8 weeks post cessation of infant prophylaxis)
- On other occasions if additional risk
- HIV antibody testing for seroreversion should be checked at age 18-24 months
Breastfed infants as above plus the following additional tests:
- At 2 weeks of age
- Monthly for the duration of breastfeeding
- At 4 and 8 weeks after cessation of breastfeeding
Breastfeeding is advised to be avoided regardless of viral load
What family of viruses does rubella belong to?
Togavirus (single stranded RNA genome)
Structure of rotavirus
Double stranded RNA virus
Examples of double stranded DNA viruses
Hep B
CMV
VZV
HSV1 & 2
HPV
EBV
Structure of parvovirus B19
Single stranded DNA virus
Single stranded RNA viruses
Hep A/C/D/E
Rubella
HIV
Zika
Ebola
What is pelvic actinomyces associated with?
IUCDs- usually prolonged use (>2 years), symptoms of fever, vaginal discharge, pelvic or abdominal pain & weight loss.
On microscopy, may see sulphur granules
What are HPV 6 and 11 associated with?
Genital warts and low grade squamous intraepithelial lesions of the cervix (can correspond cytologically to CIN1)
Gardasilu vaccine
Quadrivalent vaccine against HPV 6, 11, 16, 18
Which genotypes of HPV are the most important?
16 and 18
They are responsible for 70% of cases of HPV related cancers
How does HPV induce cancer?
Via Onco-proteins.
The primary Onco-proteins are E6 and E7 which inactivate two tumour suppressor proteins, p53 (inactivated by E6) and pRb (inactivated by E7)
How quickly are HPV infections typically cleared?
70% within 1 year and 90% within 2 years
Intrapartum antibiotics for GBS
3g Benzylpenicillin should be administered as soon as possible after the onset of labour and 1.5g 4 hourly until delivery.
If penicillin allergic the alternative depends on severity of reaction.
Provided a woman has not had severe allergy to penicillin, a cephalosporin should be used.
If there is any evidence of severe allergy to penicillin, vancomycin should be used.
Suggested regimens are: Cefuroxime 1.5 g loading dose followed by 750 mg every 8 hours or if allergy to beta-lactams is severe then IV vancomycin 1 g every 12 hours.
Most common causative organism for cellulitis and other possible microorganisms
Streptococcus pyogenes (group A strep- also causes tonsillitis, scarlet fever and rheumatic fever)
Staph. aureus is the second most common
Staph. epidermis can form biofilms on catheters/implants
Clostridia Perfringens causes gas gangrene
Strep. Mutans causes tooth decay and dental cavities
Types of alpha haemolytic streptococci
Strep pneumoniae
Strep viridans
Types of beta haemolytic strep and the diseases they cause
A: strep pyogenes:
- Scarlet fever
- Rheumatic fever
- Tonsilitis/ pharyngitis
- Glomerulonephritis
- Toxic shock
- Nec Fasc
B: Strep agalactia
- GBS disease of newborn
- Chorioamnionitis
- Endometritis
C: Strep dysgalactiae
- Pharyngitis
- Endocarditis
- Toxic shock
- Nec fasc
D: reclassified as enterococcus
- Colitis
- Endocarditis
F: Strep anginosus
- Liver abscess
G: group G strep
- Toxic shock
- Nec fasc
- Vaginitis
Incubation period of chickenpox, rubella, influenza, parvovirus, strep pyogenes (scarlet fever), CMV
Chickenpox: 14 (10-21)
Rubella: 14 (12-23)
Influenza: 1-3
Parvovirus (Fifth disease): 4-20
Strep pyogenes (Scarlet fever): 1-7
CMV: 3-12 weeks
Features of congenital CMV infection
Diagnosis
Sensorineural Hearing Loss
Visual Impairment
Microcephaly
Low Birth weight
Seizures
Cerebral Palsy
Neurodevelopment delay
Hepatosplenomagaly with jaundice
Thrombocytopenia with petechial rash
10-15% of infected infants will be symptomatic at birth
A further 10-15% who are asymptomatic at birth will develop symptoms later in life
Diagnosis of fetal CMV infection is via amniocentesis
Amniocentesis should not be performed for at least 6 weeks after maternal infection and not until the 21st week of gestation
Risk of congenital CMV infection with primary/ recurrent infection during pregnancy
Risk of congenital infection is 30-40% with primary infection during pregnancy (vertical transmission)
Risk of congenital infection is 1-2% with recurrent CMV infection in pregnancy
Congenital rubella syndrome features
Risk of transmission in 1st/2nd trimester
Sensorneural Deafness
Ophthalmic Defects: Retinopathy, Glaucoma, Cataracts, Micropthalmia
Cardiovascular Defects:
PDA, VSD, Pulmonary stenosis
CNS:
Neurodevelopmental delay, Microcephaly, Meningoencephalitis
Others:
Thrombocytopenia (rash described as blueberry muffin), Hepatosplenomegaly
Late onset: diabetes, GH deficiency, thyroiditis
Risk of transmission:
1st: 80-90%
2nd: 25%
Congenital toxoplasmosis infection clinical features
Risk of placental transmission/ adverse fetal outcome
Hydrocephalus
Microcephaly
Intracranial calcifications
Ophthalmic Defects (chorioretinitis, strabismus, blindness)
Epilepsy
Neurodevelopmental delay
Thrombocytopenia
Anaemia
Risk of placental transmission increases with gestation (1st TM 14%, 3rd TM >50%)
Adverse fetal outcome risk dereases with gestation
Congenital HSV infection clinical features
Neonatal Herpes can lead to severe neurological impairment and death
Genital HSV infection occurring in early pregnancy is associated:
Increased risk of spontaneous abortion, IUGR, preterm labour and congenital herpes (rare 2 per 100,000 live births)
What type of organism is toxoplasma gondii?
Source?
Intracellular protozoan parasite
Source: uncooked meat, cat faeces
When are fetal consequences highest for toxoplasmosis infection?
Diagnosis?
Treatment?
First 10 weeks gestation, however maternal-fetal transmission risk increases as the pregnancy proceeds but the consequences become less severe
Diagnosis can be via PCR or Immunoglobulins (IgM,IgG and IgA). MRI/CT may show ring enhancing lesions in CNS tissues
Treatment not usually required in the immunocompetent.
In pregnancy treatment is indicated if recent infection suspected
Treatment varies depending on local protocols (Spiromycin or combination of pyrimethamine, sulfadiazine, and folinic acid)
Interpretation of immunoglobulins for rubella infection
IgM- acute infection
IgG- produced in response to infection, but produced later than IgM. Also produced in response to vaccination.
If both negative = susceptible to infection
Risk of congenital fetal varicella syndrome (FVS) in pregnant women who develop chickenpox
The risk of FVS to babies born to mothers who have chickenpox during the first 20 weeks gestation is 0.4% (1-12 weeks) - 2.0% (13-20 weeks).
If a mother has chickenpox in late pregnancy (5 days prior to delivery) then there is risk of neonatal varicella infection (25%) which may be severe.
Features of FVS
Hypoplasia of one limb
Cicatricial lesions with a dermatomal distribution
CNS abnormalities
Eye abnormalities
What is the causative organism of gas gangrene?
Clostridium perfringens
What is the most common causative organism in necrotizing fasciitis?
Group A streptococcus (strep pyogenes)
HPV vaccine Gardasil is what type of vaccine?
Recombinant vaccine of virus-like particles (VPLs)
Most common cause of endometritis (bacteria)
Polymicrobial
Incidence of listeriosis in pregnancy
1 in 10,000 or 12 per 100,000
Listeriosis:
- Source/ type of bacteria
- Features
- Impact on pregnancy
- Fetal morality rate
- Treatment
- Source/ type of bacteria: gram positive bacillus, intracellular pathogen, diagnosed by blood cultures. Source is soil, water and contaminated food (raw meats, dairy)
- Features: typically mild illness in adults unless immunocompromised
- Impact on pregnancy: causes chorioamnionitis, placental necrosis and granuloma formation. Miscarriage, stillbirth and meningitis
- Fetal mortality rate: 20-30% (some sources quote up to 50%)
- Treatment: amoxicillin for 2-3 weeks
Surgical wound cleansing in first 48h
Use sterile saline for wound cleansing up to 48 hours after surgery.
Advise patients that they may shower safely 48 hours after surgery.
Use tap water for wound cleansing after 48 hours if the surgical wound has separated or has been surgically opened to drain pus.
Management of 1st/2nd/3rd trimester acquisition of genital herpes (>28 weeks)
1st/2nd trimester:
- Initial episode treated acicolvir 400 mg TDS for 5 days
- Following 1st or 2nd trimester acquisition, daily suppressive aciclovir 400 mg TDS from 36 weeks of gestation reduces HSV lesions at term and hence the need for delivery by caesarean section
3rd trimester:
Initiate acicolvir 400 mg TDS and continue until delivery
C-section delivery is advised if 1st episode of HSV (within 6 weeks of delivery)
If opt for SVD, avoid interventions like ARM and give intrapartum IV acyclovir
Pregnant woman non-immune to rubella- advice re: vaccination timing?
Post-natally, can be whilst breast feeding.
When is the transplacental transmission from mother to foetus greatest for toxoplasma gondii?
26-40 weeks
Although risk of transmission is lower in earlier pregnancy, if infection does occur, particularly <10 weeks, complications are typically more severe
How many pregnancies does CMV infection affect?
0.2-2.2% (1 in 50 to 1 in 500)
What is the mortality rate associated with disseminated neonatal herpes?
30% (even if treated)
What type of virus is HIV?
Lentivirus (retrovirus)
Gram positive cocci
- Staphylococcus
- Streptococcus
(Both facultative anaerobes)
Gram positive bacilli/ rods
- Corynebacterium (Facultative anaerobe)
- Listeria non-spore forming (Facultative anaerobe)
- Bacillus spore forming (Facultative anaerobe)
- Clostridium spore forming (Obligate anaerobe)
- Actinomyces spore forming (Facultative anaerobe)
Gram negative cocci
-Nisseria gonorrhoeae
- Neisseria meningitidis
- Moraxella catarrhalis
All obligate aerobes
Gram negative intracellular organism
C. trachomatis
Gram negative bacilli/ rods
(Facultative anaerobes- with or without O2)
Hemophilus influenzae
Klebsiella pneumoniae
Escherichia coli
Proteus mirabilis
Enterobacter cloacae
Helicobacter/Compylobacter (spiral rod)
Salmonella
(Obligate aerobes- need O2)
Legionella pneumophila
Bacteroides
Pseudomonas aeruginosa
Gram negative spirochaetes (spiral shaped)
Treponema pallidum
Borrelia burgdorferi (considered diderm rather than gram neg or positive)
What increases/ decreases the risk of HIV transmission?
Increases: presence of inflammatory STD (increased risk of acquiring HIV of 1.5 –> 2.2). Risk effect greater for men than women.
Decreases: male circumcision
% of neonates with congenital CMB that are symptomatic at birth
10-15%
Treatments for genital warts and those that shouldn’t be used in pregnancy
- Trichloracetic acid
- Liquid nitrogen cryotherapy
- Imiquimod 5% cream
- LASER treatment
- Podophylline paint (teratogenic)
- 5-fluorouracil (teratogenic)
Non-treatment also an option (one third of patients will clear warts spontaneously)
Soft non-keratinised warts respond well to podophyllotoxin and trichloroacetic acid (TCA). Keratinised lesions may be better treated with physical ablative methods such as cryotherapy, excision, TCA or electrocautery.
Imiquimod is suitable treatment for both keratinised and non-keratinised warts.
People with small numbers of low volume warts, irrespective of type, can be treated with ablative therapy or topical podophyllotoxin from the outset. Very large lesions should be considered for surgical treatment
Treatment options for toxoplasmosis gondii in pregnancy
Spiramycin ASAP if fetus not infected or status of the fetus not known. This reduces risk of transplacental infection. This is continued until term, or until fetal infection is documented. Most effective if initiated within 8 weeks of seroconversion.
Pyrimethamine, sulfadiazine and folinic acid where fetal infection is known e.g. positive amniotic fluid PCR. Monitoring for haemotoxicity required.
Pyrimethamine should be avoided in the 1st trimester as teratogenic
Which congenital infection most commonly causes congenital hearing loss?
CMV
What disease does Borrelia cause?
Lyme disease
What percentage of women develop antibodies to HPV following infection?
50-60%
Risk of transmission of HIV for the following exposures:
Receptive anal intercourse
Insertive anal intercourse
Receptive vaginal intercourse
Insertive vaginal intercourse
Receptive oral sex (giving fellatio)
Insertive oral sex (receiving fellatio)
Blood transfusion
Needle stick injury
Sharing injecting equipment
Mucous membrane exposure
Receptive anal intercourse 1.11 %
Insertive anal intercourse
0.06%
Receptive vaginal intercourse
0.1%
Insertive vaginal intercourse
0.082%
Receptive oral sex (giving fellatio)
0.02%
Insertive oral sex (receiving fellatio)
0%
Blood transfusion
90-100%
Needle stick injury
0.3%
Sharing injecting equipment
0.67%
Mucous membrane exposure
0.63%
HPV genotypes 6 and 11 are associated with what lesions of the cervix?
Low grade squamous intraepithelial lesions of the cervix (LSIL)
What virus family does zika belong to?
How is it transmitted?
Management if couple planning conception
Flaviviridae
Transmitted by aedes mosquito
If male partner has travelled to Zika area the couple should delay trying to conceive ie avoid UPSI for 3 months after return.
If only female partner has travelled then should avoid UPSI for 2 months after return.
Which organism is the most common cause of puerperal sepsis?
Group A streptococcus
Risk of developing chlamydia when had sexual intercourse with asymptomatic chlamydia positive partner
65% (2/3)
What organism causes lymphogranuloma venereum?
Chlamydia trachomatis L1-L3
Which type of white cell is elevated in acute CMV infection?
In which cells can CMV lie dormant?
Lymphocytes/ Monocytes
Monocytes
Chance foetus will be affected if fetal CMV infection confirmed
10% symptomatic at birth
What strain of streptococcus is responsible for the majority of GBS infections?
Strep agalactiae (aerobic and gram positive)
Which pathogen underlies late congenital infection during childhood and presents with eight nerve deafness, interstitial keratitis and abnormal teeth?
Treponema pallidum pallidum (ventral syphilis)
Congenital infection most associated with hydrops
Parvovirus B19 (causes fetal anaemia)
Causes of ophthalmia neonatorum
Chlamydia (most common, can also cause pneumonia)
Gonorrhoea
HSV
S. Aureus
Rate of stillbirth in UK (2016), how does BMI > 30 affect this?
1 in 225/ 4.4 per 1000
1 in 100
Tests for late IUD
FBC, U&Es, LFTs, Bile Acids, Clotting, CRP
(Sepsis, abruption, PET, cholestasis, DIC)
Kleihauer for all women (not just those RhD negative)
(Presence of FMH, quantify need for extra Anti-D)
Thrombophilia screen
(Most tests are not affected by pregnancy – if abnormal, repeat at 6 weeks)
HbA1c, random glucose, TFTs
(DM, thyroid dysfunction)
Microbiology: Serology (if tropical travel test for malaria)
(Toxoplasma, Rubella, CMV, HSV, Parvovirus, Syphilis; compare virology against booking serum)
Microbiology: Blood cultures, Swabs (Cx, HVS); MSU
(GBS, E. Coli, Listeria, Chlamydia spp. etc)
Parental genetics
(Aneuploidy or single gene disorders)
Fetal and Placenta Histology; written consent required
(Cord/cardiac blood; fetal and placental swabs
Fetal skin/placenta for karyotyping/single gene Post-mortem: external (e.g. Dysmorphic, SGA/IUGR), limited autopsy/X-rays; full autopsy; placenta only)
Management of varicella exposure in pregnant woman
If not sensitised (VZV IgG negative) and within 10 days of exposure, give VZIG
Is symptomatic, acyclovir treatment (if present within 24h of onset of rash)
Vertical transmission rate of Hep B/ Hep C and how this can be reduced (Hep B)?
Vertical transmission is 90% for hep B and 5% for hep C
Can be reduced by:
1. Hep B vaccine at birth (70% reduction)
2. Hep B vaccine and anti-hep B immune globuline (HBIG)- 90% reduction
Congenital syphilis syndrome
Teeth
Snuffles
Saddle nose
Hepatosplenomegaly
Osteochondritis
Gumma
Blindness/ deafness
FTT, IUFD
Effect of Abx in pregnancy
Penicillin’s, cephalosporin’s, macrocodes, clindamycin = Safe.
Sulphonamides = hyperbilirubinemia and kernicterus
Tetracyclines = Fetal/infant stunting of growth, discoloration of teeth, and hypoplasia of dental enamel
Aminoglycosides (Streptomycin) = congenital deafness ; may cause neuromuscular blockade if low calcium/Mg
Nitrofurantoin = Cause neonatal haemolysis
Quinolones (ciprofloxacin) = arthropothies
What percentage of women with untreated bacteria develop pyelonephritis?
28%
Causes of TSS (bacteria), mechanism and mortality/ treatment
S. Aureus (Coagulase positive)–> enterotoxin type B
Streptococcus –> strep pyogenes –> strep pyrogenic exotoxins
Mechanism is via T cell superantigen stimulation (toxins act as super antigen)
Mortality in S. Aureus is 3%, but 30-70% with strep
Treated with flucloxacillin & clindamycin (Vanc instead of fluclox if pen allergic)
Oncogenic viruses and cancer they cause
EBV –> Burrito’s lymphoma, nasopharyngeal carcinoma, Hodgkin’s disease
HPV –> cervical ca, skin ca
Hep B/C –> liver ca.
HTLV1 –> T cell leukaemia
HSV2 –> Cervical ca.
Ebola haemorrhagic fever:
1. Mortality rate if pregnant
2. Spontaneous abortion rate
3. How long can men transmit the virus in semen after recovery?
- 95.5%
- 66%
- 7 weeks
Surgical wound classifications
Clean: an incision in which no inflammation is encountered in a surgical procedure, without a break in sterile technique, and during which the respiratory, alimentary or genitourinary tracts are not entered.
Clean-contaminated: an incision through which the respiratory, alimentary, or genitourinary tract is entered under controlled conditions but with no contamination encountered.
Contaminated: an incision undertaken during an operation in which there is a major break in sterile technique or gross spillage from the gastrointestinal tract, or an incision in which acute, non-purulent inflammation is encountered. Open traumatic wounds that are more than 12 to 24 hours old also fall into this category.
Dirty or infected: an incision undertaken during an operation in which the viscera are perforated or when acute inflammation with pus is encountered (for example, emergency surgery for faecal peritonitis), and for traumatic wounds if treatment is delayed, there is faecal contamination, or devitalised tissue is present
Post op wound cleansing
- Use sterile saline for wound cleansing up to 48 hours after surgery.
- Advise patients that they may shower safely 48 hours after surgery.
- Use tap water for wound cleansing after 48 hours if the surgical wound has separated or has been surgically opened to drain pus.
How is hepatitis D transmitted? What is its structure?
Via blood products and sexual transmission/ vertical transmission
Requires co-infection with Hep B for propagation
RNA virus
Associated with chronic liver disease
Structure of HSV
dsDNA virus
Ebola virus binds to which cell surface protein
Cholesterol transporter protein
Which virus causes molluscum contagiosum?
Poxvirus
On MacConkey agar, what colour do the following organisms appear?
1. E.Coli/ Enterobacter/ Klebsiella
2. Salmonella, proteus, pseudomonas aeruginosa, shigella
- Pink (produce acid, lowering pH of agar)
- Undyed/ clear
Which organisms contain ribosomes, do not have a rigid cell wall but cannot be grown on inanimate culture?
Chlamydia
If MSRA is suspected when treating SUO- what Abx should be added to the regime?
Vancomycin or teicoplanin
Risk of neonatal herpes is SVD at time of active infection
41%
