Bacterial pathogens Flashcards
Gram + cocci
Staphylococcus aureus
Streptococcus pyogenes
Streptococcus agalactiae
Gram - cocci
Neisseria meningitidis
Neisseria gonorrhoeae
Gram + bacilli
Bacillus anthracis
Clostridium difficile
Listeria monocytogenes
Corynebacterium diptheriae
Gram - bacilli
Salmonella typhi Shigella spp Escherichia coli Proteus ssp Yersinia pestis
Gram - coccobacilli
Haemophilus
Bordetella
Brucella
Pasteurella
Spiral bacteria
Helicobacter Campylobacter Borrielia Leptospira Treponema pallidum
Cell structure
Gram + have thicker cell wall than Gram -
Gram + thick wall retains blue black colour of stain
Stain colour
Gram + = Blue black
Gram - = pinky red
Cell shape
Cocci are circular
Bacilli are flattened oval
Why do bacteria cause infections
Host factors, Bacterial factors, opportunity
Host factors
Immune system, devices
Bacterial factors
Virulence, resistance, ability to survive in environment
Opportunity
Exposure, normal flora
E.Coli and UTI’s
- Part of normal bowel flora in most humans
- Colonisation of urethral meatus
- Able to adhere to uroepithelial cells and triggers inflammatory response in bladder
- develops resistance to antibiotics
S. AUREUS and skin infections
- Carried in nasal carriage in up to 50% of people
- Adheres to damaged skin
- Produces exoenzymes and toxins that damage tissue
Staphylococccus aureus features
- Causes skin/soft tissue infections
- Bacteraemia, septicaemia
- Endocarditis, pneumonia
Staphylococcus epidermis
- opportunistic pathogen
- Most people carry on skin
- Causes infection with foreign bodies such as catheters etc
- Adheres to plastic/metals using glycocalyx (slime)
Streptococcus pyogenes
- Commonest cause of bacterial sore throat
- Scarlet Fever, necrotising fasciitis and other SSTI’s
- Invasive infections such as pneumonia
Streptococcus pneumoniae
- commonest cause of bacterial pneumonia
- Commonest cause of bacterial meningitis
- can cause other common childhood infections like otitis media
Streptococcus agalactiae
- also known as group B strep
- Commonest cause of bacterial meningitis and sepsis in neonates (3 months and under)
Streptococcus milleri complex
- 3 closely related species of pus-forming streptococci
- Associated with abscesses - dental, lung, liver, brain and others
Viridans streptococci
- Collective name for a number of species of haemolytic streptococci that inhabit the URT
- cause sub-acute bacterial endocarditis
Streptococcus gallolyticus
- Type of alpha-haemolytic streptococcus in bowel flora
- This organism can cause bacteraemia due to colonic malignancies
Listeria monocytogenes
- Gram + bacillus
- rare but significant cause of sepsis and meningitis during pregnancy and neonates
- Zoonosis - able to grow at low temps
- unpasteurised milk can be a cause
Corynebacterium species
- Gram + bacillus
- Most of the species are commensals of the skin and URT
- Corynebacterium diphtheriae causes diphtheria
Propionibacterium acnes
- Gram + bacillus
- Now called Cutibacterium acne - causes acne
Enterobacteriaceae (coliforms)
- A number of species of gram - bacteria found in bowel flora
- include Escherichia coli, Enterobacter cloacae
E.coli
- Commonest cause of UTI
- commonest cause of bacteraemia
- Cause of nosocomial infections - pneumonia, wound infections
- certain toxigenic strains associated with severe diarrhoea and HUS
Pseudomonas aeruginosa
- Multi-resistant Gram - bacteria
- Can cause respiratory infections, UTI’s and other infections
- produces green pigment
Neisseria meningitidis
- Gram negative diplococcus
- causes meningococcal sepsis (meningitis)
- Classic presentation is a non-branching rash
Neisseria gonorrhoeae
- Gram - diplococcus
- Causes gonorrhoeae
- Rarely causes secondary invasive infection
Haemophilus influenzae
- Gram - bacillus
- normal RT flora
- causes respiratory tract infections such as pneumonia
- The vaccine only prevents type B infections
Anaerobes
- Clostridium species (c.difficile, c.tetani etc)
- Often part of polybacterial infections
Mycobacterium species
- Do NOT stain using gram stains
- referred to as Acid fast Bacilli
- Mycobacterium tuberculosis - TB
- Atypical Mycobacteria cause respiratory infections
Bacteria without a conventional cell wall
- Chlamydia species, C. trachomatis - common STI
- Mycoplasma species M. pneumoniae - common cause of RTI
Spirochaetes
- Treponema pallidum - causes syphilis
- Other species cause Leptospirosis and Lyme disease
