Microbiology Flashcards
What are common techniques in the detection of microorganisms?
Microscopy - electron, ultraviolet, light
PCR - amplification of DNA to look at genome
Gram stain - ability of dye to penetrate the cell wall
Culture - spread on agar plates and grown
Serological methods - looking for antigens or antibodies
What is the process for gram staining?
Add crystal violet dye
Add iodine
Add decolouriser/acetone - gram positive will stain purple
Counterstain with safranin - gram negative will stain pink
Why do bacteria stain gram positive or gram negative?
Gram positive - has a peptidoglycan layer that can retain the dye = purple
Gram negative - has a lipopolysaccharide layer on membrane that prohibits penetration of dye = pink
What are examples of gram positive bacteria?
Cocci - staph, strep, enterococci
Bacilli - clostridium, diphtheria, bacillus, lactobacillus, listeria
What are examples of gram negative bacteria?
Cocci - neisseria
Bacilli - legionella, e.coli, klebsiella, salmonella, pseudomonas, enterobacter, shigella
What are the main 3 factors leading to infection?
Susceptible host
- Age, sex, genes, innate defence, behaviours, co-morbidities
Source/environment
- air, food, water, animals, travel
Pathogen
- microbial flora, virus, bacteria, parasites, helminths
What are Koch’s postulates in establishing pathogenicity (4)?
The same organism must be present in every case of the disease and not in healthy individuals
Organism must be isolated from the diseased host and grown in pure culture
Isolated organism must cause disease when inoculated into a healthy, susceptible animal
Organism must be re-isolated from the inoculated, diseased animal
(rules do not apply to normal human flora or uncultivable organisms)
What are basic bacterial classifications?
Gram stain - negative or positive
Microscopic morphology - cocci or bacilli
Atmospheric requirements - un/aerobic
Biochemical - expression of enzymes
Colonial characteristics - size, shape, colour
Antibiotic susceptibility
Why are some bacteria more virulent than others?
Characteristics of successful pathogens
- motility - enable pathogen to reach site
- adhesins - to attach to host cells
- ability to form biofilms
- ability to produce toxins that have adverse effects on host cells
Opportunistic pathogens - can only cause disease individuals whose host defences are compromised
What are examples or healthcare associated infections?
Infections that occur as a result of contact with the healthcare system - from nursing home care, primary or secondary care.
- MRSA - Clostridium difficile - ESBL - HAP
What are examples of community acquired infection?
Infections that are contracted outside of a hospital or diagnosed within 48 hours of admission
- Flu - CAP - Norovirus
What are the main causes of antibiotic resistance?
Over-prescription of antibiotics
Patients not finishing the entire course
Overuse of abx in livestock and fish farming
Poor infection control
Poor hygiene and sanitation
Absence of new antibiotics being discovered
What are the 4 main drug-resistant superbugs?
- MRSA
- Staphylococcus aureus
- Resistant to methicillin - fluclox, penicillin
- Found in catheters
- Clostridium difficile
- Anaerobic bacterium lives in the gut
- Overgrows from broad spectrum antibiotics or PPIs and overgrow causing pseudomembranes and colitis
- ESBL - Extended Spectrum Beta-Lactamases
- Gram negative bacteria resistant to all penicillin based antibiotics
- Complicate urinary catheters and in situ drains
- VRE - Vancomycin-resistant enterococcus
- Normally occurs inside the hospital
- Can cause infections of the urinary tract, bloodstream, wounds associated with catheters and surgical procedures
What are basic infection prevention and control methods?
Institutions
- food preparation regulations, aseptic practices, screen blood, ventilation, cleanliness of equipment, laundry management, ANTT
Health care staff
- education, sharps disposal, PPE, screening health workers, vaccinations, post exposure prophylaxis
Clinical Practice
- antibiotic stewardship, aseptic technique, preoperative prophylaxis, screening patients, immunisation
What are responses to infection for control and prevention purposes?
Surveillance to detect outbreaks and microbial resistance Reporting of notifiable diseases Isolation Reservoir control Vector control
What is the role of the infection control team within a hospital setting?
Follow up with audit results and check they are implemented
Checking people following infection prevention rules
Surveillance to detect outbreaks and antimicrobial resistance
Reporting of notifiable disease
What are the main preoperative measures of safeguarding patients against infection?
ANTT - aseptic techniques Sterile equipment Handwashing PPE Operating theatre air quality - HEPA Filter Antibiotic prophylaxis
What are procedure related risks of post-op infections?
Pre-existant sepsis
Poor skin preparation - shaving
Nonviable tissue in wound - haematoma
Foreign material - drains and sutures, dead space
What are patient related risks of post-op infections?
Host resistance Age Malnutrition, diabetes, steroids, obesity Immunosuppresion Hypovalaemia
What are the main principles of infection prevention?
Remove sources - containing the infected
Block routes of transfer
Enhance natural resistance - vaccination, nutrition
Offer antimicrobial prophylaxis
What are the 3 routes of transmission of bacteria and viruses in hospitals?
Airborne - droplets
Direct Contact
Faecal-Oral
What are main differentiations between viral and bacterial infections?
Viral:
- Non-productive cough
- Symptoms last 7-10 days
- Sore throat normally virus except strep
- Lymphocytes and monocles
Bacterial:
- Higher fever
- Productive cough
- Symptoms persist longer
- Neutrophils
What is the presentation in sepsis?
Low BP <100 Increased RR >22 Fast pulse Altered mental state Low oxygen sats Fever turns to hypothermia
What is the sepsis 6 management?
Within the first hour…
Take 3:
- Bloods, measure urine output, serial lactase
Give 3:
- Antibiotics, IV fluids, Oxygen
What viral disease has classic triad presentation of fever, pharyngitis and lymphadenopathy with a rash, splenomegaly and is transmitted through saliva?
Mononucleosis - Epstein Barr virus
What are malignant complications of Epstein Barr virus?
Burkitt’s lymphoma
Lymphoproliferative disease
Nasopharyngeal carcinoma
CNS lymphoma
What viral disease presents with fever, sore throat, cough, abdominal pain, diarrhoea for 3-4 days followed by a rash on palms of hands and soles of feet, trunk and sores on oral mucosa in children under 10?
Hand, foot and mouth disease
What are the 2 types of herpes simplex virus?
Herpes Simplex Type 1: Cold sores on lips
Herpes Simplex Type 2: Genital ulcers - more common
What are the clinical features of herpex simplex and how is it treated?
Skin and mucous membrane lesions - mouth/genitals
- Prodromal - tingling or burning before blisters appear - Cluster of small, painful fluid-filled blisters that ooze and ulcerate + heal within a few weeks
Dysuria in women
Lymphadenopathy
Can infect nail bed
Antivirals - aciclovir
Why is there an increased risk of developing HIV with herpes simplex?
Breaches in the mucosal barrier as a result of genital ulcers
What viral disease commonly presents with warts and what is the malignant serotype?
HPV
- 1 and 4 - feet common warts
- 2, 3, 10 - finger common warts
- 6 and 11 - genital warts
- 16 and 18 - cervical cancer
What are common bacteria/virus causing GI infections?
E.coli Salmonella Campylobacter Norovirus Clostridium difficile
What are common bacteria causing infective endocarditis?
Staphylococci sanguini
Streptococci
What are diagnostic modalities available in primary care for the diagnosis of infection?
PCR Wound swabs, pus Urine samples Scraping Rapid antigen tests FBC - wcc, crp, platelets Serology - antigens/antibodies
What are the 6 steps for the mechanism of viral infection?
Attachment - specific receptors Penetration - fusion of viral envelope Uncoating - release genomic material Replication - production of mRNA Assembly - make viral protein on ribosome Release - virus can bud off or cytolysis
What is the management of a needle-stick injury?
Encourage wound to bleed
Wash wound using running water and soap
Do not scrub
Dry and cover wound
Document and inform appropriate people and OH
Blood tests for both the source and recipient
PeP if necessary
What factors determine travel-related risks?
Mode of transportation Destination Season of travel Duration of travel Standards of accommodation Food hygiene Sanitation Behaviour of traveller Underlying health of traveller
What are viral and bacterial causative agents of gastroenteritis?
Viral
- Rotavirus
- Norovirus
- Astrovirus
Bacterial
- Camplyobactor jejuni
- E.coli
- Salmonella
- Shigella
What are the 2 types of enterically transmitted hepatitis viruses and what are the general presentation?
Hepatitis E - waterborne
Hepatitis A - spread in faeces
Tiredness, fever, nausea, vomiting, abdominal pain, jaundice, loss of appetite, dark urine, pale faeces, itchy skin
What are arthropod-associated travel infections?
Malaria Dengue fever Crimean-congo haemorrhagic fever Yellow fever Zika virus Tick-borne encephalitis Japanese encephalitis
How can mosquito-borne viral infections be controlled and prevented?
Draining stagnant water Insecticides Mosquito nets Wearing long sleeves and trousers DEET
How does slapped cheek present, what is the causative viral agent, who is it most dangerous to and how is it spread?
Parvovirus B19
Dangerous in pregnancy - anaemia, intrauterine death
Slapped cheek appearance, low grade fever, arthralgia, non-specific influenza symptoms, reticular erythematous eruptions predominantly on extremities
Can be spread via direct contact and respiratory droplets + vertically
What is shingles?
Herpes zoster infection is an acute, unilateral, painful blistering rash caused by reactivation of the varicella-zoster virus (VZV), following initial primary infection of VZV causing chickenpox, virus lies dormant in the dorsal root or cranial nerve ganglia
What is the presentation of shingles?
Prodromal period - burning period over affected dermatome for 2-3 days, may experience fever, headache, lethargy
Followed by rash - erythematous, macular rash, itchy, vesicular well enclosed in dermatome
What viral disease presents with high temp, loss of appetite, swollen eyelids and lymph glands in the neck… followed by a rash of pinkish-red spots over the chest, tummy and back that spreads to limbs and face, not itchy?
Roseola, Sixth disease
Human herpes virus 6
Spread through respiratory secretions
What viral disease presents with prodromal stage of fever, malaise, conjuctivitis, cough… followed by small red/white spots in mouth(koplik spots), erythematous and maculopapular rash starting at head and spreads to trunk and limbs for 3/4 days, fever stops once rash appears?
Measles
Spread by airborne of droplet transmission
What is a common respiratory disease in children under 2?
Respiratory syncytial virus
Cough, wheeze, hypoxia, croup, URTI, bronchiolitis
What viral disease presents similarly to EBV but is usually asymptomatic with possible flu-like symptoms the first time?
Cytomegalovirus
What is tertiary syphillis?
Reactivated syphilis
Affects neurological and cardiovascular
What are clinical features of syphillis?
Enlarged inguinal lymph nodes
Painless genital ulcers
Mouth ulcers
Flu-like illness
Alopecia
Mucosal ulceration and erosions on genitalia
What are clinical features of gonorrhoea?
Men - pirulent discharge, pain on urination
Women - often asymptomatic - PID, infertility
What are clinical features of chlamydia?
Women - vaginal discharge, abornmal bleeding, friable cervix
Men - penile discharge, conjunctivitis, Reiter’s syndrome - late
C.trachomatis - serotype D-K
How do STIs in children present?
conjunctivitis
sticky discharge from eyes
