Grame positive and negative cell membrane

(layers and molecules)

• Gram-positive bacteria - cytoplasmic membrane with membrane proteins, peptidogylcan (polymer of sugar residues, usually 'l-lysine-type' in gram positive bacteria, teichoic acids (high variable anionic polymers) embedded within the peptidogylcan 
• Gram-positive bacteria - same as gram-positive (except with 'm-DAP type' peptidoglycan). Unique outer membrane formed by lipid bilayer with inner phospholid leaflet and outer LPS leaflet (allows production of outer membrane vesicles and is target of MAC)
• LPS consists of Lipid A (endotoxin), O antigen (highly variable, allows smooth LPS) and core sugars linking the two components

Important bacterial structures

• Capsule - high molecular weight polymers, structurally diverse, can employ molecular mimicry, resistance to phagocytosis/lysis
• Flagella - allows motility through rotation - made up of basal body(motor complex energised by protons), hook (comprised of FlgE, conserved length( and filament (flagellin subunits, can self assemble and has variety of morphologies)
• Pili - filamentous structure, variable length, pilin polymer, allows adhesion

• Type I, II, V - through IM and OM - allows movement of substances out of bacterial cell
• Types III, IV and VI - allows pumping of internal molecule across host membrane
• Type VII - movement of molecule across IM and mycomembrane
• Type III consists of cytoplasmic sorting platform, basal body between IM and OM, single needly protein, and a heterotrimer translocon protein that can insert through the host membrane
• Facilitates cell entry, attachment, anti-phagocytosis, replication and toxin injection

• Antigenic variation is the mechanism by which a pathogen can alter surface proteins to evade host response
• Phase variation is a method of dealing with rapidly varying environments without requiring random mutations - variation of portein expression within different parts of bacterial population

• Blood agar - shows whether bacteria can undergo α (green), β (clear) or γ (unchanged) haemolysis
• Chocolate agar - green colouration of agar if bacteria produce hydrogen peroxide 
• MacConkey's agar - growth of gram negative bacteria. Those that utilise lactose make agar acidic and turn the agar pink, those that can't will form ammonia and turn the agar white/colourless
• XLD agar - bacteria that can ferment xylose turn colonies yellow (Coliforms) and black on metabolising of thiosulfate (Salmonella)

• Bacterial cells can be coccus, staphylococcus (grouped), streptococci (chain), bacillus, streptobacilli (chain), vibrio (kidney shaped), spirochete, corkscrew 
• Bacterial cell colonies can be circular, irregular, filamentious, rhizoid (branching), flat or raised

• Cell morphology - cocci seperated by oxidase test (+ Neisseria, - no pathogen), rods seperate with growth bile salt (+ use indole test to determine E. coli +, from Klebsiella -)
• Bile salt negative rods - pseudomonas are + for oxidase, proteus + for urease, salmonella + for H₂S, and Shigella - for all. 

• If rods, use atmosphere - anaerobic is Clostridia, aerobic is Bacillus, facultative anaerobes are Corynebacteria and Lactobacillus
• Cocci, use catalase test, + is micrococcus or staphylooccus, use coagulase test to determine Staph (+ is aureus, - is epidermidis)
• - catalase is step., plate on blood agar (gamma haemolysis is not a pathogen, beta needs lancefield typing, alpha can be pneumonia (+optichin sensitive) or viridans (-optichin sensitive)

• Virulence is the severity or harmfulness of a pathogen
• Bacteraemia is the presence of bacteria in the blood
• Septicaemia is the poisoning of the blood due to the presence of bacteria
• Septic shock is hypotension caused by sepsis

• The phenotype or property under investigation should be associated with pathogenic strains of the species (and not non-pathogenic strains)
• Specific inactivation of the gene associated with the virulence trait should result in a measurable loss of pathogenicity
• Reversion of allelic replacement of the gene should lead to restoration of pathogenicity

Gram positive bacteria 

(syllabus required)

• Step. pneumoniae (primary lobar pneumonia)
• Step. pyogenes (pharyngitis, cellulitis, rheumatic fever, glomerulonephritis
• Staph. aureus (surgical wounds, burns, food poisoning)
• MRSA
• Clostridium difficile and tetani 

Enteric O-antigen possessing gram negative bacteria

(syllabus required)

• E. coli (EHEC - enterohaemorrhagic, EPEC -enteropathogenic) Shingella spp., Salmonella spp. - travellers diarrhea, dysentery, enteric feverm food poisoning

Mycobacteria, NOAP gram negative bacteria and common hospital acquired infections

(syllabus required)

• Mycobacterium tuberculosis (tuberculosis)
• NOAP - Neisseria gonorrhoeae, Neisseria meningitides
• Staph aureus, mRSA, C. dif, Tuberculosis