Infection 3) Bacterial pathogenesis Flashcards
Describe the envelope structure of gram positive bacteria
Thick peptidoglycan layer
Lipoteichoic and trichroic acid
Describe the envelope structure of gram negative bacteria
Outer membrane of lipopolysaccharide, proteins and pores
Thin peptidoglycans
Inner membrane
Give an example of bacteria that need an aerobic environment
Staph.aureus
Give an example of a bacteria that needs an anaerobic environment
Clostridium species
Give an example of a facultative anaerobe bacteria
E.coli
What is a facultative anaerobe bacteria?
Bacteria that can switch between aerobic and anaerobic metabolsim
Describe the consequence of alpha haemolytic streptococci on agar
Cause partial haemolytic of blood agar and produce a greenish colour
Describe the consequence of beta haemolytic streptococci on agar
Complete haemolysis so agar becomes transparent
What is serological typing?
Type of cell-surface antigens present, antibodies to expressed antigens
What is genotyping
Genes encoding those antigens
Replacing serotyping
What is a commensal?
Something which is probably not causing disease when identified from clinical sample
Living in a relationship in which one organism derives food or other benefits from another organism without hurting or helping it
What is a pathogen?
Something that causes disease
What 3 things determine an organism’s pathogenicity?
Organism’s virulence
Site
Immune state of patient
Describe the 2 types of site
Sterile - blood and urine
Unsterile - stool and throat
Give examples of gram positive cocci
Staphylococci - s.aureus - coagulase negative staphylococci Streptococci - group A streptococcus (S.pyogenes) - group B, C, G - group D (enterococcus) - S.pneumoniae - viridans type streptococci Peptococcus / peptostreptococcus
Give examples of gram positive rods (bacilli)
Bacillus e.g. B.cerus and B.anthracis Corynebacterium Propionibacterium Listeria monocytogenes Clostridium e.g. C.difficle
Give examples of gram negative cocci
Neisseria
- n.meningitis
- N.gonorrhoea
Moraxella (branhamella) catarrhalis
Give examples of gram negative rods
Haemphilus influenza Enterobacteriaceae - salmonella and shigella - eschericia coli - klebsiella and enterobacter - proteus Pseudomonoas e.g. P.aeruginosa Bacteroides e.g. B.fragilis Campylobacter and helicobacter Vibrio cholera Bordatella pertussis Legionella
What infections does S.aureus cause?
Furunculosis
Staph abscess
Impetigo
Sepsis - line, splenic abscess, lung abscess
Toxin mediated - toxic shock, scalded skin, food poisoning
Bacteraemia - endocarditis, osteomyelitis, septic arthritis
Describe S.aureus virulence
Coagulase enzyme
Adhesions
Protein A
Toxins
What toxins does S.aureus have?
Cytotoxins
Exfoliative toxins
Enterotoxins
What cytotoxin does S.aureus have?
PVL (pantun-valentine leukocidin)
Describe scalded skin syndrome
Exfoliative toxins Outbreaks in nurseries Local infection Distant bullae Sheet-like desquamation
Why is coagulase negative staphylococci less virulent?
Doesn’t make coagulase
Give examples of alpha haemolytic streptococci
S.milleri
S.mitis
S.anguis
S.pneumoniae
Give examples of beta haemolytic streptococci
S.pyogenes
S.equi, S.canis
What superficial infections can streptococci cause?
Pharyngitis
Cellulitis
What deep infections can streptococci cause?
Severe soft tissue infection
Myositis
Necrotising fasciitis
Describe the clinical signs of necrotising fasciitis
Pain out of proportion to physical signs Bruising and blistering Generalised toxaemia Renal impairment Very high inflammatory response (CRP) Raised creatine kinase
Describe the structure and virulence of streptococci
Fibronectin-binding proteins Collagen binding proteins C5a peptidase M protein Capsule, wall, membrane Exotoxins
What is M protein?
Major antigenic determinant of S.pyogenes
Binds serum factor H to prevent opsonisation
Alpha-helical coiled coil protein
What is molecular mimicry?
Structural similarity of microbial antigenic determinant and host proteins resulting in cross creativity of antibody and T-cell responses to microbial antigens with self antigens
What exotoxins does streptococci produce?
Superantigens Streptococcal inhibitor of complement Haemolysis DNAses Hyaluronidase Streptokinase
Give examples of non-bacterial pathogens
Fungal organisms
Yeasts, moulds, dimorphic fungi
Candida species
Aspergillus species
What infections can enterobacter cause?
Klebsiella Enterobacter Citrobacter Wound infections, biliary infections Hospital acquired pneumonia Meningitis
What are the 4 main virulence mechanisms of E.coli?
Adhesions
Siderophores
Capsule
Toxins
Describe the adhesions of E.coli
P fimbria - binds uroepithelial antigens
Non-fimbral GI adhesions causing diarrhoeal diseases
Describe the siderophores of E.coli
Enterobactin
Powerful iron chelators
Describe the toxins produced by E.coli
Endotoxin
Exotoxin
Verotoxins
