Microbiology Flashcards
Define pathogen
An organism that causes or is capable of causing disease
Define commensal
An organism which colonises a host but causes no disease under normal conditions
Define opportunistic pathogen
A microbe that only causes disease if the host’s defenses are compromised
Define virulence/pathogenicity
The degree to which a given organism is pathogenic
Define asymptomatic carriage
When a pathogen is harmlessly carried at a tissue site where it causes no disease
What is a bacillus
rod shaped
What is a cocci
round
What does purple suggest
Gram positive
What does pink suggest
Gram negative
What is a diplococcus
Two cocci
What is a vibrio
A curved rod
What is a spirochaete
A spiral rod
What are the sterile sites in the body
Lungs, gall bladder, bladder, kidneys
In what form is bacterial DNA found
Double stranded circular DNA
What stain is needed to identify TB and why
Zeill Neeson as the TB has a thick waxy surface
What causes toxic shock
When the inate immune system acts against lypolysaccharide
How long can spores last and what temperatures can they survive in
50years in water and 120 degrees heat
What is dessication
A state of extreme drying
What temperatures can bacteria tolerate
-80 to 80
What pH can bacteria tolerate
4 to 9
How do bacteria divide
binary fission
What is an endotoxin
From gram negative LPS cell wall, weak non specific antigen. Heat stable and cant be converted to toxoid
What is an exotoxin
A protein secreted by mainly gram positive, specific action with high antigenicity. Heat labile and can be converted tot toxoid
What is a toxoid
A toxin which has been treated so that it loses it’s toxicity but retains it’s antigenicity
What is used for transformation
Plasmid
What is used for transduction
phage
What is used for conjugation
sex pillus (between recipient and donor)
What genes does a plasmid contain
Transfer promotion, plasmid maintenance and antibiotic or virulence determining genes
Which bacteria cant be cultured artificially
Obligate intracellular bacteria
Which shaped bacteria are tested with ZN stain
Rods
What is a bacteriaphage
Where one bacteria phages another and steals DNA by transduction
Examples of obligate intracellular bacteria
Rickettsia, chlamydia, coxiella
Bacteria with no cell wall (mollicutes)
Mycoplasma pneumoniae
Bacteria which grow as filaments
Actinomyces, streptomyces
Why is gonorrhoea more painful in men
As they have a longer urethra
What does large gram positive rods suggest
Clostridia
What stain is used at first in gram staining
Crystal violet
What is added in gram staining to fix the cell wall
Iodine
What is used to decolourise in gram staining
Ethanol or acetone
What is used to counterstain in gram staining
Safronin (pink)
What are gram positive clusters
Staphlococci
What are gram positive chains
Streptococci
Why do gram positive stain purple
1 cell wall. Decolouriser dehydrates cell, CV-1 gets stuck in peptidoglycan. The counterstain isnt taken so the cell stays purple
Why do gram negative stain pink
Decolouriser interacts with lipid and causes loss of CV-1 and outer LPS membrane. Cell appears pink with counter stain
Anaerobic gram negative cocci
Veillonella
Aerobic gram negative cocci
Neisseria
Anaerobic gram positive cocci
Peptostreptococcus
Aerobic gram positive cocci
Staphylococcus or streptococcus
Name a commensal of the skin
Staphylococcus epidermidis
Alpha haemolytic streptococcus
S. pneumoniae, S. oralis, S. milleri
Lancefield A beta haemolytic streptococcus
S. pyogenes
Lancefield B beta haemolytic streptococcus
S. algalactiae
What does S. algalactiae cause
UTI or meningitidis
Non haemolytic streptococcus
S. bovis
Enterococcus Streptococcus
E. faecalis (Lancefield D)
What is catalase testing
Distinguishs strep and staph. Catalase converts H2O2 from flavoproteins into water and oxygen
Positive catalase test result
Staph, gram negatives and funghi
Negative catalase test result
Strep
What is coagulase testing
Distinguishes staph. Coagulase activates prothrombin and therefore fibrin to fibrinogen
How is free coagulase detected
tube coagulase test
How is bound coagulase detected
Slide coagulase test
What is a positive coagulase test
Clot formation, Staph aureus
What is a negative coagulase test
Clear, staph epidermidis
How is reduced sensitivity to penicillin detected
Oxacillin disc
What does a positive latex test suggest
Staph aureus
What is haemolysis
Ability of bacteria to break down red blood cells on blood agar. Used for differentiating streptococci
Alpha haemolysis
Green due to hydrogen peroxide production
Which bacteria cause alpha haemolysis
S. pneumoniae, S. oralis, S. milleri
Beta haemolysis
Clear/white due to blood cell lysis by haemolysin
Which bacteria cause beta haemolysis
S pyogenes and S algalactiae
Gamma haemolysis
No haemolysis
Which bacteria cause gamma haemolysis
E. faecalis and S. epidermidis
Which bacteria is sensitive to optochin disc
Strep pneumoniae
What does tetanus cause
Muscle locks due to over stimulation of nerves
What does botulin cause
Muscle relaxes, blocks nerves
What type of infection is caused by pseudomonas
Oppurtunistic
ZN positive mycobacteria
M tuberculosis, M leprae, M avium intracellulare
Gram positive anaerobic rods
Clostridium and proprioribacterium (p.acnes)
How to remember propriobacterium acnes as a anaerobic rod
No air to spots. Spots stop you procreating with your rod, and getting a positive pregnancy test.
Gram positive aerobic rods
Corynebacterium (C. diptheriae), listeria, bacillus, erysipelothrix
Gram negative anaerobic
Bacteriodes
Gram negative aerobic
Coliforms (Shigella, salmonella), pseudomonas, parvobacteria (H. influenzae), vibrio (V. cholera)
Selective indicator media for gram negative bacilli
MacConkey agar and CLED (cysteine, lactose, electrolyte deficient)
How is motility used to differentiate between bacteria
Flagella staining patterns
Positive lactose fermentors (g-ve anaerobes)
E coli, klebsiella, enterobacter, citrobacter
Negative lactose fermentors (g-ve anaerobes)
Salmonella and shigella
Positive oxidative test
Vibrio, helicobacter, pseudomonas
Negative oxidase test
Colioforms, parvobacteria
Why do gram positive bacteria take up the gram stain
They have a thick peptidoglycan wall
Antibiotic for staph auresu
Flucoaxacillin
Where are staphlococcus normally found
Nose and skin
What is coagulase
An enzyme produced by bacteria which helps fibrin clots form around bacteria, protecting them from phagocytosis
In which type of infections do staphaloccus coagulase negative species cause
Oppurtunistic infections
Which organism causes 90% of osteomyelitis
Staph aureus
which antibiotics is MRSA resistant to
Beta lactams, gentamicin, erythromycin and tetracycline
Staph aureus virulence factors
Pore forming toxins (alpha haemolysin, PVL), proteases (exfoliatin), toxic shock syndrome (stimulates cytokine release), protein A (binds to and immobilises IgG)
Pyogenic staph aureus associated conditions
Wound infections, abscesses, impetigo, septicaemia, osteomyelitis, pneumonia and endocarditis
Toxin staph aureus associated conditions
Scalded skin syndrome, toxic shock syndrome, food poisoning
Coagulase negative Staph conditions
Infected implants, endocarditis, septicaemia
Staph epidermidis associated infections
Oppurtunistic
Staph epidermidis virulence factors
Ability to form persistent biofilms
Who gets oppurtunistic infections
Debilitated, prostheses and catheters
Staph saprophyticus infection
Acute cystitis
Staph saprophyticus virulence factors
Haemogglutinin for adhesion, urease which causes kidney stones
How do (staph epidermidis) bio films work
Antibiotics struggle to get through and a layer of metabolically inactive cells at the base protect the remaining cells
Features of streptococcus pyogenes
Beta haemolytic, group A lancefield. Faculative anaerobe, penicillin sensitive
What happens in alpha haemolysis
H2O2 reacts with Hb, causes partial greening
What happens in beta haemolysis
Haemolysins O and S, complete lysis
What happens in gamma haemolysis
No lysis
What are the three ways in which streptococci can be classified
Haemolysis, lancefield typing, biochemical properties
What is lancefield typing
Categorises catalase negative, beta haemolytic strep according to baceterial carbohydrate cell surface antigens. Clumpy indicates recognition
Name a Lancefield group A
Strep pyogenes
Name a lancefield group B and the infections it causes
S. agalactiae, neonatal infections
Examples of strep pyogenes infections
Wound infections, tonsilitis, pharyngitis, otitis media, impetigo, scarlet fever
Complications of strep pyogenes infections
Rheumatic fever, glomerulonephritis (antiSLO test used to assesss severity
S pyogenes virulence factors, on surface
Capsule, M protein encourages complement degradation
S pyogenes virulence factors, enzymes
Hyaluranidase (for spreading), Streptokinase (breaks down clots), C5a peptidase (reduces chemotaxis)
S pyogenes virulence factors, toxins
Streptolysins O and S (bind cholesterol) reason for Beta haemolysis. Erythrogenic toxin SB(beta)eA
S. pneumoniae features
Rust coloured sputum, chest consolidation, draughtman colonies
What is sputum
Fluid from the lower respiratory tract
What can make s.pneumonia change from a normal commensal of the oropharynx to pathogenic
Hypogammaglobulinaemia and asplenia
Which infections are caused by s.pneumoniae
Pneumonia, otitis media, sinusitis and meningitis
S pneumoniae virulence factors, capsule
Polysaccharide (antiphagolyic), polyvalent vaccine (children under 2 have different surface proteins so are at a higher risk)
S pneumoniae virulence factors, inflammatory wall consitituents
Teichoric acid (chlorine), peptidoglycan
S pneumoniae virulence factors, cytotoxin
Pneumolysin
What is viridans strep
General name for oral strep. alpha or non haemolytic. They cause abscesses or infective endocarditis. Milleri group are the post virulent
Which alpha haemolytic strep is optochin sensitive
S. pneumoniae
What are irregular gram positive rods
Cornyebacterium diptheriae
What is the treatment for cornyebacterium diptheriae
Erythromycin and antitoxin
How is diptheria spread
Droplets
What does diptheria require for growth
Potassium telluite
What does diptheria toxin do
Inhibits protein synthesis
What does diptheria vaccine consist of
Toxoid
What is a feature of gram positive bacteria
More peptidoglycan
What is a feature of gram negative bacteria
Both inner and outer membranes
What are the three components of LPS endotoxin
Outer lipid A component, Core R oligosaccharide antigen and Somatic O antigen of repeating carbohydrate units
Which part of LPS is responsible for toxicity
Outer lipid A component
Why dont mycobacteria gram stain
Outer mycolic acid lipid layer
Why dont mycoplasms gram stain
No peptidoglycans
Why group are mycobacteria and mycoplasms in
Gram negative
Gram negative virulence factors
Colonisation factors (adhesins, invasins, nutrient acquisition and defense) and toxins (usually secreted proteins which cause damage and subversion)
What are gamma proteobacteria
Enterobacteria (colioforms)
Describe enterobacteria
Rods which are covered in flagella. some are intestinal parasite. Faculative anaerobes as the gut is largely anaerobic. Mac conkey is used to culture
Lac positive phenotype of macconkey (latose fermenters, macconkey pink)
Commensal EColi
Lac negative phenotype on macconkey (non-lactose fermenters, macconkey pale)
Salmonella, shigella, proteus
How to differentiate between salmonella and shigella
Serology, shigella has no H antigen as it has no flagella
What is an example of a serotype
H antigen on flagella
What is an example of a serogroup
O antigen on LPS
Where is K angtigen found
EPS (capsule)
Whats the difference between bacteraemia and sepsis
Sepsis is bacteraemia when theres symptoms
Diseases caused by E coli
Wound infections, UTIs, Gastroenteritis, travellers diarrhoea, bacteraemia and a meningitis
Which Ecoli target the small intestine and what is the result of this
ETEC and EPEC and cause watery diarrhoea
Which Ecoli target the large intestine and what is the result of this
EHEC and EIEC and cause bloody diarrhoea
Which Ecoli causes chronic diarrhoea and where does it target
EAEC (aggregatitive) and it targets the large intestine
Which Ecoli targets the urinary tract and can cause cystitis
UPEC
Which toxins are produced by ETEC
Heat labile and heat stable toxin
What is the action of Heat labile toxin
Modifies Gs protein and locks it into the active GTP state, it permanently activates adenyl cyclate= more cAMP= more phosphorylation of CFTR ion transporter= more Cl- excretion= water cotransported= diarrhoea
What is the action of Heat stabile toxin
Mimics guanylin peptide hormone, activates GC-2C receptor causing more cGMP and CTFR activity etc. But has a smaller effect than heat labile
How do EHEC and EPEC work
Induce pedestal formation, adhere turn on TTSS. Microvilli rearrange into pedestal allowing the entry of the bacteria
Dysentry is a version of which bacteria
Shigella
Shigella has pathology like which Ecoli
EIEC
Symptoms of shigella
Severe bloody diarrhoea, frequent passage of stools, small volume. blood and pus, cramps and pain
Shigella infectiivty
Acid tolerance good so only a small infective dose is needed. Person to person spread of via contaminated food/water. It overlies lymphoid follicles in peyers patches
How does shigella cause disease (exciting)
Induces apoptosis and reinfects adjacent cells from the basolateral membrane, host actin monomers are polymerised into actin rockets to propel through the cytoplasm. Apoptotic macrophages release cytokines and cause inflammation
Which Ecoli also produces shigella toxin
EHEC
What are the virulence features of shigella
Catalytic (glycoside which cleaves N-adenosine band in RNA) and receptor binding region
Which is the main type of salmonella
Salmonella enteritica
Which infections are caused by salmonella
Gasteroenteritis, enteric fever (typhoid, systemic disease) and bacteraemia rarely
How is salmonella caught
Ingested contaminated food/water
Describe the mechanism of salmonella infection
Invasion of small intestine epithelium, infalmmatory response, transcytosed to the basolateral membrane, enters submucosa, intracellular replication, membrane ruffling, systemic infections due to dissemination with m φs
Where are peyers patches
ileum
Describe the mechanism of gastroenteritis
Bacteria mediated endocytosis, induction of chemokine release, neutrophil recruitment and migration, neutrophil induced tissue injury. Inflammatory necrosis of mucosa. Fluid+electrolyte loss=diarrhoea
Enteric fever mechanism
Bacterial mediated endocytosis, transcytosis to basolateral membrane, survival in M φ, systemic spread. Initially little damage to the gut mucosa
What is a key feature of typhoid fever
Inflammation and ulceration of peyers patches
What is klebsiella
An environmental, oppurtnistic hospital acquired infective agenet which colonises the GI tract and oropharynx
Describe the stools in cholera
Rice water stools
How is cholera acquired
Faeco-oral route, high dose required (optimum ph 8)
Describe the appearance of cholera
Curved road with a single polar flagellum
Virulence factors of cholera
TCP pilli needed for colonisation, cholera toxin causes uncontrolled cAMP production causes Cl-, Na+ and therefore water loss
3 examples of localised acute infections
Burns/wounds, UTIs, keratitis
Systemic acute infections
Bacteraemia
Acute infection in ICU patients
Nosocomial penumonia
What does nosocomial mean
Originating in hospital
Who gets chronic infections
Cystic fibrosis patients
How is H. influenzae spread
nasopharyngeal carriage
Which H influenzae strains cause infections
Capsulate strains
Who gets H influenzae infetions
Children or smokers
How do you culture H influenzae
Chocolate agar as requires haem and NAD
H influenzae virulence factors
Pilli, capsule (can penetrate nasopharynx), type B main cause of meningitis- Hib vaccine. LPS causes inflammation
What is pseudomonas aeruginosa
Oppurtunistic pathogen found in many locations, notoriously difficult to treat
Legionella pneumophillia where is it found
Aquatic environments
Describe the pathogenicity of legionella pneumophilia
Bacteria take over macorphages, covers in ribosomes using the ER, using this as camouflage and evading phagocytosis
What causes symptoms in legionella pneumophilia
Upregulated inflammatory immune response caused by taken over macrophage. Causing more proinflammatory genes and excessive influx of neutrophils into the lungs
Causes of low neutrophil count
Leukaemia, chemotherapy and AIDS
Describe bordatella pertussis
Coccobacilli, fastiduous, low infective dose
Where does bordatella pertussis effect
upper respiratory tract, it adheres to the cilliated epithelium
Bordatella pertussis virulence factors
Pertussis toxin- locks Gi in off state which stops inhibition of adenylate cyclase= more cAMP. CγA toxin also increases cAMP
Which is the only gram negative cocci
Neisseria
Describe neisseria
Non flaggelated diplococci
Where can Neisseria be found during infection
CSF or urethral discharge
Name two neisseria
N. meningitidis (meningococcus) and N. gonorrhoeae
Describe meningococcus
Found in nasopharynx, aerosol transmission, crosses nasopharyngeal epithelium causes bacteraemia and if it crosses the BBB it causes meningitis
Which rash is distinctive of N. meningitidis
non blanching, petechial or purpuric rash
