Human Pathogens & Lifestyle

Human Pathogens & Lifestyle

1. Bacterial morphology

   • determined by - growing bacteria on agar & light microscopy

2. microscopy

   • gram-positive bacteria
     • have a cell wall with 90% peptidoglycan and with teichoic acid, this makes it rigid
   • gram-negative bacteria
     • cell wall made up 10% of peptidoglycan and has lipopolysaccharides and lipoproteins, has no teichoic acid, thus not as rigid

3. causing disease by bacteria

   • the bacteria finds a host
     • it adheres to the host cells
       • then colonises the host cell surfaces and grows
         • it then multiplies within the host through binary fission
           • and overcomes the host's defences to survive

4. adhesion - first step in colonisation

   • may be specific or non-specific
     • specific adhesion
       • adherence to certain cells in host
       • a receptor and a ligand are essential
         • the ligand is called adhesin
           • adhesins are chemical components of capsules, cell walls and pili
         • host cell receptors are usually glycoproteins

5. bacterial multiplication

   • DNA replication through binary fission
     • cytoplasmic membrane elongates and DNA molecules are separated
       • the cross wall forms and membrane invaginates
         • after complete formation of the cross walls, the daughter cells form

6. multiplication in liquid

   • lag phase - no increase in population number
   • log phase - exponential increase in population number
   • stationary phase - cell death approximately equal to division
   • death phase - exponential decrease in population number

7. bacteria associated with food

   • food poisoning - pathogenic bacteria
     • gram-negative rods
       • enterobacteriaceae
       • pseudomonads
     • gram-positive rods
       • clostridia
       • bacilli
   • in general
     • bacillus cereus
     • listeria
     • campylobactar
     • vibrio
   • cultured bacteria
     • gram positive rods
       • lactobacilli

8. Viral Human Pathogens & Lifestyle

   • virus morphology - have RNA and DNA
     • icosahedral, head-tail, filamentous
     • determined by (usually) only
       • electron microscopy
       • genetic make-up - RNA/DNA
       • size
   • viral capsid
     • composed of capsomers arranged to form wall around nucleic acid core
       • two types of symmetry - icosahedral and helcial
   • viral structure
     • DNA or RNA & capside
       • this is in a nucleocapsid for a naked capsid virus
     • nucleocapsid & lipid membrane glycoproteins
       • this envelopes the virus
   • viral pathogens
     • HIV, influenza, ebola, adenovirus, coronavirus
   • virus life cycle
     • metabolically inactive stage
       • particulate transmission virion stage
         • involves nucleic acid, capsid, and nuclear envelope
       • entirely dependent on external physical factors for chance movement - spreading
     • infectious stage
       • note that they can be isolated from all kinds of living things
         • fungi, bacteria, animal, plants
     • attachment, penetration, uncoating,, biosynthesis, maturation & assembly, and lysis and release
       • biosynthesis involves macromolecular replication and transcription and macromolecular protein synthesis
   • bacteriophage - virus that infects and replicates in virus
     • lytic phage - virulent
       • lytic life cycle
         • firstly the phage attaches to host cells and injects DNA
           • the phage DNA circularises and enters lytic cycle
             • new phage DNA is now formed - proteins are synthesised and assembled into virions
             • cell lyses and releases phage virions
     • lysogenic phage - temperate
       • phage attaches to host cell
         • phage DNA circularises and enters lysogenic cycle
           • the phage DNA integrates within the bacterial chromosome by recombination - it becomes a prophage
             • lysogenic bacterium reproduce
               • occasionally though, the prophage may excise from the bacterium chromosomes
                 • this leads to the lytic cycle being initiated by another recombination event
   • PATHOGENS ARE OFTEN ZOONOTIC