Systematic Bacteriology 2 Flashcards
Give an example of gram negative cocci
Neisseria spp
What are two types of aerobic gram negative cocci and how do they appear?
Neisseria gonorrhoeae - most common cause of bacterial meningitis
Neisseria meningitidis - causes gonorrhoea (STD)
Appear in pairs (diplococci) on Gram film
What are coliforms?
Gram negative large aerobic bacilli; many are part of normal bowel flora (as long as in GI tract)
Look like E.coli on gram film and when cultured on blood agar
How do coliforms grow and how are they differentiated?
Grow best aerobically; can grown anaerobically
Differentiated from each other by biochemical reactions and by the antigenic structure of their walls: O antigen (cell wall) and H antigen (flagella)
What are gut commensal coliforms? Give examples
Normal bowel flora:
Most strains of E.coli
Give examples of gut pathogens
Salmonella spp.
Some E.coli strains produce toxins (Verotoxin producing E.coli - VTEC)
How do coliforms cause infection?
Coliforms cause serious infection in normally sterile sites, like UTIs, peritonitis, bilary tract (gall bladder) infection
How are coliform infections treated?
Gentamacin - 1st line antibiotic for coliform infections
How does sepsis due to coliform infection occur?
Bacteria die releasing ENDOtoxin from gram negative cell wall.
Lipopolysaccharide is taken up by cells like macrophages that release cytokines
Sets off inflammatory response and sepsis pathway
Give examples of other aerobic gram negative bacilli
Pseudomonas aeruginosa - strict aerobe that is not very pathogenic but is intrinsically resistant to antibiotics - most strains still resistant to genatomicin
What does (cocco)bacillus mean and give an example?
Look like cocci but are bacilli .
Haemophilus influenzae are gram negative aerobic coccobacillus
Give examples of spiral or curved gram negative aerobic bacilli
Vibrio cholerae (causes cholera)
Give examples of strict anaerobes
Clostridium spp.
Bacteroides spp.
What are clostridium spp. and how do they function? Give an examples
Gram positive anaerobic bacilli that are part of normal bowel flora
Produce spores that can survive outside body
Produce EXOTOXINS causing severe tissue damage
Clostridium difficile - causes antibiotic-associated diarrhoea (antibiotics wipe out normal bowel flora)
What are bacteroides, regions and treatment?
Gram negative anaerobic bacilli, many species are part of normal bowel flora (usually non-pathogenic; cause porblems in sterile sites like peritoneum)
Metronidazole - 1st line treatment
What are mycobacterium? Give an examples
Thick waxy coat does not take up gram stain.
Stained by ACID FAST BACILLI (AFB) or acid-alcohol fast bacilli (AAFB) - gives blue/green background
Myobacterium tuberculosis causes TB
What are spirochaetes? Give examples
Spiral-shaped bacteria; do not take up gram stain
Treponema pallidum - causes syphilis
Borrelia burgdorferi - causes Lyme disease
What types of DNA do bacteria have?
Chromosome
Extrachromosomal like plasmids (double-stranded, encode genes for antibiotic resistance - genetic advantage)
Importance of bacterial genetic variation and how it occurs?
Mutation
Gene transfer
Resistance to antibiotics develops and spreads rapidly as a result of genetic variation
How do mutations result in genetic variation?
Rapid bacterial growth increase chance of mutations
Failure in accurate replication of DNA
Leads to new variants of organism - many fail to survive, rare strains may be successful
Methods of gene transfer between bacteria?
Transformation - DNA released from dead bacteria taken up by living bacteria; incorporated into plasmids or bacterial chromosome
Conjugation - sex pilus produced by a bacteria through which plasmid DNA can be transferred (bacterial “sex”)
Transduction - viruses infect bacteria and transfer pieces of DNA between them
Describe how antibiotics can result in antibiotic resistance
Unnecessary, sub-therapeutic or exposure to low conc. of antibiotic in environment encourages devlopment of resistant strains
Mechanisms of resistance?
Produce enzymes that destroy antibitoics
Altered antibiotic binding sites
Alteration of cell wall porins - stop entering into cell
Up-regulation of efflux pumps (pump unwanted things out of cell)
Enzymes that destroy antibiotics?
Beta-lactamase - early penicillins, like amoxicillin. Destroys beta-lactam ring in nucleus
Extended spectrum beta-lactamase (ESBL) - all penicillins and cephalosporins
Carbapenemase (CPE) - all penicillins, all cephalosporins and carbapenems (antibiotics of last resort)
What does the beta lactam ring look like?
Square with one N atom and a double-bonded O atom
How does altering antibiotic binding sites result in resistance?
Genetic mutation alters binding site
Antibiotic cannot bind and has not effect on bacteria
This is what causes MRSA (methicillin-resistant Staph. aureus) as penicillin binding protein on Staph. aureus is altered
Antibiotic resistance due to change in cell wall porins?
Channels in bacterial cell that transport molecules from outside to inside cell
Changed result in bacterial call wall becoming impermeable to antobiotic
Antibiotic resistance due to up-regulation of efflux pumps?
Pump molecules out of cells
Up-regulation of pumps results in antibiotic being removed from cell before it can act
Common mechanism of resistance in fungi, like Candida spp
