Microbiology Flashcards
Diagnostic methods for microbiology
Cel culture
Antigen or antibody detection
PCR
3 bacterial shapes
Cocci (round)
Bacillus (rod-shaped)
Spirochaetes (spirals)
What colour are gram stains?
Purple - positive
Pink - negative
Organisms that don’t stain well with gram stain
TB (waxy coat)
Factors required for bacterial growth
Food
Moisture
Correct temperature
Correct pH
3 types of atmosphere bacteria can grow in
Aerobic
Microaerophikic
Anaerobic
What is an exotoxin?
Produced inside cell and then exported from it
Mainly gram positive
What is an endotoxin?
Part of cell wall
Mainly gram negative
Role of toxins in sepsis
Cause damage to red and white blood cells causing them to become leaky. This causes BP drop affects blood clotting which can lead to sepsis
Gram positive bacilli that can form spores
Clostridium (e.g. C. diff)
Bacillus sp. (e.g. anthrax)
What are spores?
Inactive hardy forms of bacteria that cannot replicate but can survive adverse conditions
Which organism is haemolysis used to classify?
Streptococcus
What is alpha haemolysis?
Partial haemolysis
Enzymes denature haemoglobin side red blood cells causing greenish discolouration round the colony
What is beta haemolysis?
Complete haemolysis
Enzymes breakdown red blood cell causing complete clearing round the colony - most pathogenic
What is gamma haemolysis?
No haemolysis
What is strep pneumonia?
Gram positive cocci
Commonest cause of pneumonia, also causes meningitis
Part of normal upper respiratory tract flora in many people
Majority of UK strains are still sensitive to penicillin
What is streptococcus viridans?
Gram positive cocci
Group of species which are common come sales
Can cause endocarditis (infection of heart valves)
What is group A strep (strep pyogenes)?
Most pathogenic of all strep.
Cause tonsillitis, necrotising fasciitis, puerperal sepsi
All strains are still sensitive to penicillin
What are group B strep (strep. Agalactiae)?
Most common cause of newborn infections
Examples of non-haemolytic strains?
Enterococcus
Not particularly pathogenic
Common cause of UTI
Most sensitive to amoxicillin (but not penicillin)
What are prion proteins?
Infectious protein that have no DNA or RNA
Cannot be sterilised or cleaned off
What test distinguishes staph aureus from other staph organisms?
Coagulase test
Staph aureus - positive - golden
What are coagulate negative staphylococci?
Common skin commensals
Do not produce toxins
Common causes of prosthetic joint and prosthetic heart valve infection and catheter infection - difficult to treat with antibiotics
What is staph aureus?
Produces both exotoxins (enzymes that damage cells) and endotoxins (toxins that act on the gut - food poisoning)
Strains sensitive to flucloxacillin - MSSA
Strains resistant to flucloxacillin - MRSA (also resistant to penicillins +!cephlaosporins)
Infections caused by staph aureus
Commonest cause of skin, soft tissue and wound infection
Commonest causes of bone and joint infection
Food poisoning (enterotoxjn producing strains)
Flucloxacillin is treatment of choice for MSSA
What is Staph. aureus bacteraemia?
Infection in the blood stream
Leads to sepsis
Can spread to other sites in the body
Many are hospital acquired
Examples of gram positive strict anaerobes
Clostridium
What is clostridium?
Part of normal bowel flora
Produces spores
Produces exotoxins
First line treatment for clostridium
Metronidazole (first line treatment for infections caused by anaerobes)
What does C. diff cause?
Antibiotic associated diarrhoea esp. in the elderly
What is C. perfrigens?
Gas gangrene
Severe soft tissue infection following wound contamination
(e.g. Gunshot wound)
What is C. tetani?
Causes tetanus, usually fatal paralytic illness
Examples of gram negative strict anaerobes
Legionella
Pseudomonas
Examples of aerobic gram negative cocci?
Neisseria meningitides & Neisseria gonorrhoeae
Examples of small gram negative aerobic bacilli?
Bordetella pertussis & Haemophilis influenzae
What are coliforms?
Species of gram negative bacilli that look like E. coli
2 main subtypes of aerobic gram-negative coliforms?
Gut commensals
Gut pathogens
Examples of gut commensals?
Most strains of E. coli
Klabsiella spp.
Enteronacter spp.
Proteus spp.
Examples of gut pathogen commensals
Salmonella spp.
Shigella spp.
Verotoxin
E. coli 0157 (outbreaks in nurseries & care homes)
First line treatment for coliforms?
Gentamicin
Examples of gram-negative microacrophilic bacilli (spiral)?
Vibrio cholerae, Campylobacter sp. & Heliconacter sp.
What does Helicobacter pylori cause?
Gastritis & duodenal ulcers
Examples of gram-negative strict anaerobes?
Bacteroides spp.
First line treatment for anaerobes?
Metronidazole
What are mycobacteria?
Thick waxy coat doesn’t gram stain
Acid fast bacilli or acid-alcohol fast bacilli
Examples of Spirochaetes?
Treponema pallidum (causes syphilis) Borrelianburgdorferi (causes Lyme disease)
Methods of gene transfer in bacteria
Transformation (dead bacteria DNA taken up by living bacteria)
Conjugation (bacteria sex)
Transduction (viruses transfer DNA from one bacteria to another)
General signs of infection
Local symptoms - pain, redness, swelling, heat, loss of function
Systemic symptoms - fever, sweats rigors
Investigations for infection
WCC (non-specific) Culture - blood - urine - stool - psoutum PCR Blood for serology (antibodies/antigen)
What causes sepsis?
Cytokines cause blood vessels to become leaky
Lower blood volume requires heart to work harder to maintain oxygenation a of tissues
Blood supply to less essential organs (skin, kidneys liver) is hut down to try maintain blood supply to brain
Blood clotting system is activated causing blood clotting in tiny vessels -> uses up clotting factors -> increased risk of haemorrhage
Difference between bactericidal & bacteriostatic?
Bactericidal - kill bacteria
Bacteriostatic - inhibit bacterial growth
Where in bacteria can antibiotics act?
Bacteria wall
Bacterial ribosome
Bacterial DNA
Examples of antibiotics that act on bacterial cell walls?
Penicillins
Cephalosporins
Glycopeptides
Examples of glycopeptides
Vancomycin, teicoplanin
Need to be administered IV
Types of antibiotics that inhibit protein synthesis
Macrolides (erthromycin' clarythromycin & azithromycin) Amino glycosides (Gentamicin IV) Tetracyclines (doxycycline)
Types of antibiotics that act on bacterial DNA
Metronidazole
Trimethoprin
Fluroquinolones (Ciprofloxacin)
