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bacterial properties

-external organelle

3 forms of bacteria

-small & unicellular
-no internal organelles (i.e. no chloroplasts, nucleus, ER or mitochondria)
-haploid DNA – only 1 form of each gene
-Some have flagella

3 forms of bacteria
cocci, bacilli, spirilli


Identifying Bacteria

Gram stain: distinguishes between 2 bacterial cell walls
1 - Bacteria are stained with a violet dye and iodine
2 - rinsed in alcohol
3 - stained with a red dye

-Gram +ve bacteria: have peptidoglycan in their cell wall which retains the dye --> deep violet
Have teichoic acid present in the membrane, Only 1 cell membrane

-Gram -ve bacteria: Dye is lost from thinner peptidoglycans --> absorb counterstain; pink
Have lipoproteins and 2 cell membranes

After Gram stain, other techniques to identify
+ classify bacteria:
-Culture and microscopy
-Biochemical and serological tests
-DNA techniques such as PCR
-Sensitivities to antibiotics


Pathogenic Bacteria

pathogenic Gram -ve bacteria:
o E a1, b2
o S a1,b1
o S
o V
o N a,b

pathogenic Gram +ve bacteria:
o S a 5
o S p 3
o S p 4

pathogenic mycobacteria:
o M t
o M l

bacterial pathogens work:

types of pathogens
- e.g. 4
is take up by
survive by
o e.g. 2
o e.g. 3
o e.g. 1

pathogenic Gram -ve bacteria:
o Escherichia Coli – EPEC causes diarrhoea, EHEC produces toxins, causing dysentery and kidney failure
o Salmonella – typhimurium causes food poisoning, while typhi causes typhoid
o Shigella – causes dysentery
o Vibrio cholerae – causes cholera
o Neisseria – the meningitidis causes meningitis, while the gonorrhoeae causes gonorrhoea

pathogenic Gram +ve bacteria:
o Staphylococcus aures – causes skin disease, endocarditis, bacteraemia, joint diseases and pneumonia
o Streptococcus pneumoniae – causes pneumonia, meningitis and otitis media (group of inflammatory diseases in the middle ear)
o Streptococs pyogenes – causes tonsillitis, necrotizing fasciitis, bacteremia (presence of bacteria in the blood) and scarlet fever

pathogenic mycobacteria:
o Mycobacterium tuberculosis – causes TB
o Mycobacterium leprae – causes leprosy

bacterial pathogens work:
o Colonize – involves using surface structures such as fimbriae and pili
o Persist – avoid, subvert or circumvent host defences in or outside cells
o Replicate – acquire nutrients such as iron and an energy source
o Disseminate within cells, tissues between organs and hosts – bacterial and host cell motility (ability to move spontaneously), through aerosols and faeces
o Cause disease – produce toxins that kill host cells, induce diarrhoea or dysregulate immune response

types of pathogens
-extracellular pathogens, such as staphylococcus, streptococcus, Yersinia and Neisseria
-intracellular pathogens (those found inside the body already), taken up by the phagosome / endosomes, survive by:
o Escape – bacteria such as Listeria and Shigella
o Prevent fusion with lysosomes - examples of these include salmonella, mycobacteria and chlamydia
o Survive in phagolysosomes – coxiella does this


Salmonella motility and invasion

in normal cells,

2) similar but

-also bacteria


in normal cells, actin polymerisation drives membrane ruffling

multi-protein machines:
1) Flagella for motility
2) Type III secretion system for invasion: similar to flagella machine but delivers virulence (harmful) proteins into host cells to induce actin polymerisation --> membrane ruffling --> internalisation

-Listeria also manipulates actin in cell membranes --> food poisoning (more serious diseases in immunocompromised/elderly/pregnant)

-Shigella also


Evolution of Bacteria
-genomes encode

-type gene received by
-replicate by:
a) e.g.
b) e.g.

-most from
-contributes to
-genetic diversity

-Genomes encode 500 - 4500 proteins
-40% core genes, rest accessory genes (i.e. gene repertoire, vary between diff. strains)

-Accessory genes received by binary fission & horizontal gene trasmission
-replicate by binary fission: loose chromosomes duplicate & growth of the cell --> division to two cells
-undergo horizontal gene transfer:
a) Transformation: uptake of natural dsDNA segments --> converted to ss segments --> homologous recombination to be taken up by chromosome. e.g. Neisseria + streptococcus
b) Transduction: e.g. lytic infection - phage DNA invades bacteria --> phage DNA replicate w/ bacterial DNA --> bacterial DNA packaged in phage heads --> bacterium lyses --> new phage particles released --> infected phage invades another cell; DNA fragment incorporated into new cell DNA e.g. many gram +/-ve bacteria
c) Conjugative transfer of self-transmissible plasmid - 2 bacteria cells form mating bridge --> exchange plasmid --> new plasmid being synthesised w/each half of new plasmid in each cell

-most accessory genes by horizontal transfer from unknown sources
-pathogenicity island: horizontally acquired DNA that contributes to virulence, driving force of evolution of bacterial pathogens, origin oft unknown
-genetic variation & rapid gen & selective pressures & years --> variety evolutionary pathways for bacteria ---> genetic diversity


Sources and routes of bacterial infection
-N e.g. 4
-M e.g. 3
-S e.g. 3
-S e.g. 12
-S e.g. 4
-L e.g. 4


a) Intrinsic:
-Nasal cavity and sinuses and Upper respiratory tract e.g. staphylococcus spp. , staphylococcus pneumoniae, H. influenza and B. catarrhalis
-Mouth e.g. lactobilli, actinomyces, fusobacterium
-Stomach e.g. lactobacilli, candida/ yeast, helicobacter pylori
-Small intestine/biliary tract and large intestine e.g. Escherichia coli, Bacteroides ap., proteus spp, klebsiella, Enterobacter spp, clostridium spp, peptostreptococcus, lactobacillus, enterococci, strep group B, candida/yeast, anaerobes
-Skin e.g. Staphylococcus epidermidis, staphylococcus aureus, propionobacterium acnes, Corynebacterium spp
-Lower genital tract (vagina) e.g. lactobacillus, enterococci, strep group B candida/yeast, anaerobes

b) Extrinsic


Portals of entry

expected and unexpected


Infections targeting upper respiratory tract:
-virus 6
-bacteria 5

--> 3
-other --> 4
-lower --> 4

Infections targeting upper respiratory tract:
-Usually extrinsically acquired; respiratory tract droplets / airborne
-Hand transmission as intermediate
o Viruses include:
Varicella (chicken pox) = VZV
Other herpes virus (HSV, EBV)
o Bacteria include:
Streptococcus spp (dental bacteria)
Streptococcus pneumoniae
Streptococcus pyogenes
Neisseria meningitides
Staphylococcus aureus (MSSA & MRSA)

--> pharyngitis, tonsillitis, sinusitis
-spread to adjacent tissues --> brain abscess, meningitis, empyema (build-up of pus in pleural space), pericarditis (inflammation of pericardium)
-Lower respiratory tract infections --> bronchitis, pneumonia, pneumonitis (inflammation of lung tissue), spread to bloodstream --> bacteraemia


urogenital tract
-Intrinsic infections from large intestine: 8
-Extrinsic infections infect the urinary tract: 2
-Intrinsic infections infect genital tract: 2
-Extrinsic infections infect the genital tract as sexually transmitted: 6

-consequences of urinary tract infections: 2
-consequences of pelvic infections and STDs: 3
-consequences also pregnancy related infections: 3

urogenital tract:
-both extrinsic & intrinsic sources
-Intrinsic infections from large intestine:
Escherichia coli
Basteroides ap
Proteus spp
Enterobacter spp
Streptococcus group B
-Extrinsic infections infect the urinary tract: Nosocomial infections (hospital acquired infections e.g. urinary catheters) e.g. Escherichia coli, klebsiella spp
-Intrinsic infections infect genital tract: streptococcus group B (pregnant women), Candida/yeast
-Extrinsic infections infect the genital tract as sexually transmitted e.g. Neisseria gonorrhoeae, chlamydia trachomatis, Trepome,a pallidum (leads to syphilis), HIV, HSV

-consequences of urinary tract infections: cystitis, pyelonephritis
-consequences of pelvic infections and STDs: gonococcal urethritis, pervic inflammatory disease, tubo-ovarian abscess
-consequences also pregnancy related infections: e.g. neonatal group B strep infection, Neonata gonococcal conjunctivitis, maternal endometritis (group A strep)


broken skin:
from 5

-s & m: 2
-recent 2
-s 3

consequences 7

broken skin:
-from surgery, pre-existing kin breaches: varicella burns, IVDA, bites (humans, animals, insects), i.v. cannulae (an intravenous portal of entry)

-Skin & mouth: staphylococcus aureus, streptococcus pyogenes
-Recent antibiotics/in hospital: MRSA, pseudomonas
-Surgery/bowel flora exposure: all above & more gram -ve
-Unusual pathogens: Pasteurella multocida from dog bites, aeromonas hydrophilia from medicinal leeches, clostridium perfringens from the soil

The consequences of infection via broken skin include:
Superficial infection
Gangrene/necrotic infection


gastro-intestinal tract (faeco-oral route)
-generally caused by
-viruses 3
-bacteria 7
-toxins 3
-parasites 2

-d 3
-b 5
-t 3

gastro-intestinal tract (faeco-oral route)
-generally caused by contaminated food + water
-Viruses: Hepatitis A, norovirus, hepatitis E
-bacteria: Escherichia coli, Campylobacter jejuni (causes food poisoning), sjigella spp (dysentery), vibrio cholerae, salmonella enterica, salmonella typhi, listeria monocytogenes
-Toxins: staphylococcal enterotoxins, botulinum toxin, shellfish & jellyfish toxins
-Parasites: amoebiasis, worms

-consequences of GI tract bacterial infection:
Diarrhoeal illnesses – diarrhoea, vomiting, dysentery (bloody diarrhoea)
Bacteremic/systemic infections – typhoid, Listeriosis and salmonellosis and septic arthritis, aortitis (inflammation of the aortic wall)
Toxin-mediated diseases may cause diarrhoea and vomiting, or neurological issues


-types: ab

affected by:
1) i - : 5
2) - : 4

i d - : 5

Pathogenicity: ability of organism to cause disease
(-Commensals – beneficial for the body and thus do not cause disease)
a) True – always cause the disease
b) Opportunistic – Only occur if condition met

affected by:
1) Infectivity – general features favouring initiation of infection such as:
Transmission to the host
Ability to colonise the host
Tropism – fins a unique niche inside or outside the cell
Immune evasion
2) Virulence – features enhance disease causation by promoting cell damage :
Toxin production
Enzymes that degrade host molecules
Interruption of normal host process
Complete immune evasion

infectious dose: no. of bacteria required to initiate an infection and can be affected by:
o Route of transmission
o Ability to colonise the host
o Tropism and motility
o Replication speed
o Immune evasion at site