Core Microbiology Pathology Flashcards
Why do Certain Bacteria Cause Particular Infections?
3 Factors:
Host factors (Immune system and devices)
Opportunity (Exposure and Normal flora)
Bacterial Factors ( Virulence, Resistance, Environmental survival)
Where are E.coli & UTIS found what happens?
Part most peoples NORMAL bowel flora.
•Colonise urethral meatus & surrounding area e.g. perineum.
•Females- short urethra.
•Use pili to adhere to uroepithelial cells/ urinary catheter materials triggers host inflamm response (infec).
•Can develop resistance to antibiotics that treat UTIs.
Where are S.aureus &; Skin Infecs found, what happens?
- In NASAL CARRIAGE in 50% people.
- Can adhere to damaged skin e.g. eczma, surgical wound, burn etc.
- Makes exoenzymes &; toxins damage tissues &a provoke host inflamm response (pus formation by WBCs).
What is Staphylococcus aureus? What does it cause?
- Gram +ve coccus.
- Primary pathogen.
- 30-50% carry in nose.
- Causes skin/ soft tissue infecs- commonest; of surgical site infecs.
- Can get into blood stream.
- Bacteraemia/ septicaemia.
- Osteomyelitis/ septic arthritis.
- Endocarditis
- Pneumonia
- UTI
- Meningitis
What is Staphylococcus epidermidis? What does it cause?
- Opportunistic pathogen.
- SKIN commensal.
- Most people carry it on skin as part of normal flora.
- Is a ‘coagulase –ve staphylococci’ (coagulase lab test).
- Causes infec in association with ‘foreign bodies’ which it sticks to e.g. intravascular catheters, Prosthetic joints, prosthetic cardiac valves.
- Adheres to plastics/ metals using glycocalyx (slime), forming biofilms.
- Causes inflamm response.
- Over time joint loosens rocks pain.
What is Streptococcus pyogenes? What does it cause?
•‘Group A Strep’.
•Strawberry tongue
•In chains (not clump- see pic )
•Commonest cause of bacterial sore throat (pustular appearance of tonsils).
•Also causes;
o Scarlet Fever
o Necrotising fasciitis (‘flesh eating bug’)
o Other SSTIs (skin & soft tissue infecs)
o Invasive infecs, such as pneumonia
o Puerperal sepsis (lower genital tracts of females that’ve just delivered)
• Also associated with 2ndry immunological presentations e.g. glomerulonephritis.
What is Streptococcus pneumoniae? What does it cause?
- Commonest cause of bacterial pneumonia & bacterial meningitis (except in neonates).
- Also causes resp tract infeccs & other childhood infecs e.g. otitis media.
What is Streptococcus agalacitae? What does it cause?
- ‘Group B strep’.
* Commonest cause of meningitis & sepsis in neonates (babies under 3 mnths).
What is the Streptococcus milleri complex ?
- 3 closely related species of pus-forming streptococci.
- Normal flora in bowel & upper resp tract.
- Trigger pus formation
- Associated with abscesses; dental, lung, liver, brain & others.
What is Viridans streptococci?
- Collective name for a number of species of α-haemolytic streptococci that inhabit the upper respiratory tract e.g. S. oralis, S. mitis
- Can invade mucosal surfaces into the bloodstream = infec damaged heart valves.
- Classic cause of sub-acute bacterial endocarditis (sub acute as present over couple of weeks e.g. with tiredness etc)
What is Streptococcus gallolyticus?
- Formerly known as Streptococcus bovis
- A type of α- haemolytic streptococcus that forms part of bowel flora
- Bacteraemia with this organism can be associated with colonic malignancies (lower GI malignancies)
What is Listeria monocytogenes?
- Gram +ve bacillus.
- Rare but signinf cause of sepsis & meningitis in pregnancy, neonates & immunosuppressed patients.
- Zoonosis (can be transmitted to humans from animals), able to grow at low temps.
- Associated with consuming cheese from unpasteurised milk &; other foodstuffs
What is Corynebacterium species ?
- Gram positive bacilli
- A number of species are commensals of skin &upper respiratory tract
- Occasional opportunistic infecs associated with devices & trauma
- Corynebacterium diphtheria- classic cause of diphtheria
- Rarely seen now in UK because of immunisation
What is Propionibacterium acnes?
- Gram positive bacillus
- Associated with acne
- Can also cause device-associated & post-procedural infections
What is Enterobacteriaceae (‘coliforms’) ?
- A collective terms for diff gram –ve bacilli species found in bowel flora.
- Gram –ve stain pink & bacilli more sausage shaped.
- Common species; Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae
What is E.Coli?
- Commonest cause of UTI & bacteraemia (sources include urinary (e.g. catheters), biliary (e.g. gallstones) & intra-abdominal)
- Cause of nosocomial (originate in hospital) infecs e.g. line infections, pneumonia, wound infections
- Certain toxigenic strains (e.g. O157) associated with severe diarrhoea & haemolytic uraemic syndrome (HUS)
- Growing resistance to antibiotics
What is Pseudomonas aeruginosa?
- Multi-resistant gram negative bacillus
- Opportunistic pathogen (can’t cause infec in healthy, needs immunosuppression)
- Can cause resp infecs, UTIs, soft-tissue and other infecs in vulnerable patients
- Often produces characteristic green pigment
What is Neisseria meniingitidis?
- Gram –ve diplococcus
- Causes meningococcal sepsis and/or meningitis
- Classic presentation- purpuric non-blanching rash (sepsis)- can do glass test to help i.d. rash
- Reduction in cases after vaccine intro
What is Neisseria gonorrhoeae?
- Gram –ve diplococcus
- Causes gonorrhoea
- Ophthalmia neonatum (in babies whose mother has gonorrhoea).
- Rarely causes invasive infecs (e.g. septic arthritis) 2ndry to primary sexually transmitted infec
What is Haemophilius influenzae?
- Gram negative bacillus
- Part of normal respiratory tract flora
- Can cause resp tract infecs (e.g. pneumonia, infective exacerbations of COPD)
- Capsulated types (e.g. type b) associated with meningitis & epiglottitis (can obstruct airway).
- Only type b infecs prevented by HIb vaccine
What are anaerobes?
• Grow in absence of oxygen.
• CLOSTRIDIUM species- many are spore-forming;
o C. difficile – antibiotic-associated diarrhoea/colitis
o C. perfringens – classical cause of gas gangrene
o C. tetani – cause of tetanus
o C. botulinum – cause of botulism
• Bacteroides species, Fusobacterium species, Prevotella species and many others
• Often part of polybacterial infecs (with other organisms) e.g. dental infecs, lung abscesses, colonic abscesses, post-trauma skin/soft tissue infecs
What is Mycobacterium species?
- Often referred to as ‘Acid Fast Bacilli’ (AFBs)
- Do NOT stain using conventional gram staining (has slightly diff cell wall)
- Mycobacterium tuberculosis – cause of TB
- Other Mycobacterium species sometimes called ‘Atypical Mycobacteria’ &; cause resp infecs in those with chronic lung disease or opportunistic infecs in immuno-compromised patients e.g. AIDS, transplant patients, etc
What are Bacteria without a conventional cell wall
- Not going to stain with gram stain.
- Chlamydia species
- C. trachomatis – commonest cause of STI
- Mycoplasma species
- M. pneumoniae – common cause of resp tract infecs
What is Spirochaetes? What does it cause?
• Treponema pallidum- causes syphilis
• Other species of spirochaetes that can cause important infecs:
oLeptospirosis (in contaminated water/ rats).
oLyme Disease (tic bites you reactive skin lesions).