Pathogenesis Of Bacterial Infections

Question 1

Pathogenicity

Answer 1

Ability of microbial species to produce disease

Question 2

Virulence

Answer 2

Relative degree of pathogenesis,which may vary b/w diff strains of same organism

Question 3

Exaltation

Answer 3

Enhancement of virulence

Question 4

Attenuation

Answer 4

Reduction of virulence

Question 5

Route of transmission
•Streptococci
•Vibrio cholerae

Answer 5

•initiate infection by any route
•infective orally,not infective subcutaneously

Question 6

•Contact transmission
•Droplet

Answer 6

•MDR organisms in hospitals like S.aureus,E.coli,Klebsiella etc nd Bacillus anthracis
•Meningococcus,C.diphtheriae,Pneumococcus

Question 7

•Aerosol
•Ingestion
•Vector borne

Answer 7

•M.tuberculosis
•Salmonella nd Shigella, Vibrio nd diarrheagenic E.coli, Campylobacter, agents of food poisoning
•Rickettsiae,Borrelia

Question 8

•Sexual
•Vertical
•Birth canal

Answer 8

•Gonococcus, Chlamydia trachomatis, Treponema pallidum, Haemophilus ducreyi
• Treponema pallidum
•Listeria, Streptococcus agalactiae

Question 9

Infective dose
•factors on which it depends

Answer 9

Minimum inoculum size capable of initiating an infection
• Virulence-inverse relation
Host’s age and immune status
Ability of organism to survive in gastric acidity(Shigella✅ Vibrio❎)

Question 10

Low infective dose

Answer 10

•Shigella-as low as 10 bacilli
•E.coli O157-H7(<10 bacilli)
•Campylobacter jejuni-500 bacilli

Question 11

Large infective dose

Answer 11

•E.coli-10^6-10^8 bacilli
•Salmonella-10^3-10^6
•Vibrio cholerae-10^6-10^8

Question 12

Adhesion

Answer 12

Initial event in pathogenesis
Mediated by adhesins-that bind to specific host cell receptors
ADHERENCE- prevents bac from being flushed away in secretions,facilitate bacterial invasions

Question 13

•Fimbriae or pili
•Non pilus adhesins

Answer 13

• Bind to sugar residues(glycoprotein or glycolipids) on host cells
• M protein(Streptococcus pyogenes), lipoteichoic acid(gram positive cocci), cell surface lectin(Chlamydia)

Question 14

Biofilm formation

Answer 14

Strong adherence to structures like catheters,prosthetic implants,heart valves
•Biofilm-grp of bacterial cells which stick to each other on a surface and are embedded within layer(slime layer) of a self produced matrix of extra cellular polymeric substance called glycocalyx

Question 15

Invasion
•Highly invasive pathogens
•less invasive

Answer 15

Entry of bac into host cells
•spreading or generalised lesions (streptococcal infections)
•localised lesions (staphylococcal abscess)

*Pathogens causing fatal diseases but lack invasiveness , remain confined to site of entry, produce disease by elaborating a potent toxin(C.tetani)

Question 16

Virulence factors helping in invasion

Answer 16

•Virulence marker antigen or invasion plasmid antigen in Shigella
•Enzymes-Hyaluronidase,collagenase,streptokinase,IgA proteases

Question 17

Antiphagocytic factors (strategies to evade phagocytosis)

Answer 17

▪️Capsule-prevent phagocytes from adhering to bacteria
Produced by-Neisseria meningitidis
Streptococcus pneumoniae
Haemophilus influenzae
Klebsiella pneumoniae
▪️Cell wall proteins-help in invasion
•Protein A of Staphylococcus aureus binds to IgG nd prevents the activation of complement
• M protein of Streptococcus pyogenes
▪️Cytotoxins-interfere with chemotaxis or killing of phagocytes
S.aureus produces haemolysins nd leukocidins-lyse nd damage RBCs nd WBCs

Question 18

•Facultative intracellular bac
• Obligate intracellular bac

Answer 18

•Salmonella typhi,Brucella legionella,Listeria,Nocardia,Neisseria meningitidis, Yersinia mycobacterium tuberculosis

•Mycobacterium leprae,Rickettsia,chlamydia,Coxiella burnetti

Question 19

Endotoxins

Answer 19

•Lipid A portion of lipopolysaccharide
•integral part of cell wall of gram -ve
•released by cell lysis
•highly heat stable
•only large doses are fatal
•poorly antigenic
•no effective vaccine
•mode of action -⬆️IL-1 nd TNF-alpha

Question 20

Mode of action of endotoxins

Answer 20

•Macrophage activation
•Complement activation
•Endothelial activation
•coagulation pathway activation
•platelet activation
•mast cell activation
•gram -ve septicemia

Question 21

Exotoxins

Answer 21

•proteins
•secreted by both gram -ve nd gram +ve
•active secretion
• heat labile,destroyed at 60
•mostly enzyme like action
•more potent-small doses r fatal
•highly antigenic
•toxoid forms r used as vaccines

Question 22

Exotoxins

Answer 22

•High potency-eg Botulinum toxin is most potent
•Used for vaccine-converted to toxoids by treatment with formaldehyde
Toxoids-lack toxicity,retain antigenicity
•Specific action on particular tissue-eg tetanus toxin for CNS