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
