Theme 1: Lecture 1- Bacterial pathogens Flashcards
Which bacteria have thicker walls - gram +ve or -ve?
+ve
What colour do gram +ve cells turn following a gram stain and why?
blue/ purple
thicker wall allows colour to be retained
What colour do gram -ve cells turn following a gram stain and why?
red/pink
thin outer membrane does not retain the blue colouring
What factors allow certain bacteria to cause infections?
- Host factors - devices, immune system
- Opportunity - exposure, normal flora
- Bacterial factors - virulence, resistance, environmental survival
Why is E.coli the most common cause of UTIs?
- able to adhere to uroepithelial cells/ urinary catheter materials
- triggers host inflammatory response
- able to develop resistance to antibiotics
How would S.aureus cause skin infections?
- nasal carriage in up to 50% of people
- able to adhere to damaged skin
- produces exoenzymes and toxins that can damage tissues and provoke host response e.g pus formation
Is staphylococcus aureus gram +ve or -ve?
+ve
What infections can S.aureus cause?
- skin/soft tissue infections - commonest
- more severe infections - bacteraemia, septicaemia
- osteomyelitis/ septic arthritis
- rarely- endocarditis, pneumonia, UTI and meningitis
What are opportunistic pathogens?
microorganisms that do not usually infect healthy hosts but produce infections in hospitals, to immunosuppressed persons or those patients presenting underlying diseases
What is staphylococcus epidermis?
- gram +ve
- opportunistic pathogen
- most people carry on skin
- causes infection in association with ‘foreign bodies’ e.g catheters, prosthetics
- adheres to plastics/metals using glycocalyx (‘slime’)
What is the commonest cause of bacterial sore throat?
streptococcus pyogenes
What is another word for streptococcus progenies and what conditions can it cause
- group A strep
- scarlet fever, necrotising fasciitis, other SSTIs, pneumonia, puerperal sepsis, glomerulonephritis
what is puerperal sepsis?
infections in lower reproductive tract after women has given birth
Which bacteria is responsible for causing ‘strawberry tougue’ presentation in scarlet fever?
streptococcus pyogenes
How can you tell apart staph infections from strep infections under a microscope?
"staphylo" = 'bunch of grapes' "strepto" = 'chain'
What is the commonest cause of bacterial pneumonia and bacterial meningitis?
streptococcus pneumonia
What is the commonest cause of bacterial meningitis and sepsis in neonates?
streptococcus agalactiae a.k.a ‘group B strep’
Which gram +ve species of pus-forming streptococci is associated with abscesses? (dental, lung, liver, brain etc)
streptococcus milleri complex
What is viridans streptococci?
- gram +ve
- collective name for number of α-haemolytic streptococci that inhabit the upper respiratory tract e.g S.oralis, S.mitis
- classic caușe of sub-acute bacterial endocarditis
What condition is S.mitis associated with?
rotting teeth/dental care
What is streptococcus gallolyticus? a.k.a streptococcus bovis
- a type of α- haemolytic streptococcus that forms part of bowel flora
- bacteraemia with this organism can be associated with colonic malignancies
What is zoonosis?
diseases that can be passed from animals to humans
What is listeria monocytogenes?
- gram +ve bacillus
- rare but significant cause of sepsis and meningitis in pregnancy, neonates and immunosuppressed patients
Which gram +ve bacteria is associated with consuming cheese made from unpasteurised milk and other foodstuffs?
listeria monocytogenes
Which gram +ve bacteria is a classic cause of diphtheria?
corynebacterium species - cornyebacterium diptherisae
are corynebacterium species gram +ve or -ve? what shape are they?
gram +ve bacilli
What is propionibacterium acnes?
- gram +ve bacillus
- cutibacterium acnes
- associated with acne
What are enterobacteriaceae?
collective term for species of gram -ve bacilli found in bowel flora
includes E.coli, klebsiella pneumonia, enterobacter cloacae
What gram -ve bacteria is the commonest cause of UTI and bacteraemia?
E.Coli
What is a nosocomial infection?
hospital acquired infection
What is the most common strain of E.coli and what is it associated with?
O157
- associated with severe diarrhoea and haemolytic uraemia syndrome
- associated with farm work and unpasteurised dairy products
What is pseudomonas aeruginosa?
- multi resistant gram -ve bacillus
- opportunistic pathogen
- can cause respiratory infections, UTI, SST’s in vulnerable patients
Which gram -ve bacterial infection often produces a characteristic green pigment?
pseudomonas aeruginosa
what is neisseria meningitidis?
gram -ve diplococcus
-causes meningococcal sepsis and/or meningitis
What is the classic presentation of neisseria meningitidis?
purpuric non-blanching rash
when you press against the rash, the rash lesions don’t disappear
What bacteria causes gonorrhoea?
neisseria gonorrhoea
-gram -ve diplococcus
What condition is seen in neonates infected with neisseria gonorrhoea?
ophthalmia neonatorum
What is haemophilus influenzae and what infections can it cause?
- gram -ve bacillus
- forms part of normal respiratory tract flora
- can cause respiratory tract infections e.g pneumonia, COPD
- capsulated types e.g type b - associated with meningitis and epiglottis
What are anaerobes?
organisms that grow in the absence of oxygen
What are clostridium species?
anaerobes / often spore-forming (spore forming allows them to survive better in environments, especially hospital environments)
What is C.difficile infection?
antibiotic associated diarrhoea/colitis
-anaerobe
Which anaerobe is the classic cause of gas gangrene?
C.perfringens
Which anaerobe is the cause of tetanus?
C.tetani
Which anaerobe is the cause of botulism?
C.botulinum
What is another word for mycobacterium species and how do they react using conventional gram staining?
- acid fast bacilli (AFBs)
- do not stain using conventional gram staining
What is the cause of TB?
Mycobacterium tuberculosso
Give 4 bacteria that do not have a conventional cell wall
- chlamydia species
- C.trachomatis
- mycoplasma species
- M.pneumoniae
What bacteria is the commonest cause of STI?
C.Trachomatis
Which bacteria is the commonest cause of respiratory tract infection?
M.pneumoniae
Which spirochetes causes syphillis?
treponema pallidum
What infections, other than syphilis, can spirochetes cause?
- leptospirosis - associated to rats and sewage work
- Lyme disease - tick bites
What is the commonest cause of skin infection?
staphylococcus aureus
Which bacteria is the most common ST?
Chlamydia trachoma’s
Name the 6 types of bacteria that can cause meningitis?
- Neisseria meningitidis
- Streptococcus pneumoniae
- Listeria monoctogenes
- Streptococcus agalactiae
- Haemophilus influenzae
- Staphylococcus aureus
What is the leading cause of preventable blindness in developing countries?
chalmydia trochomatis
