1- General Microbioogy

Question 1

Penicillin binding proteins ?

Answer 1

Transpeptidases and carboxypeptidases

Question 2

The toxic portion of lipopolysaccharide ?

Answer 2

Lipid A

Question 3

The outer membrane of gram -ve bacteria is comprised of ?

Answer 3

1- LPS :
O-antigen
Core
Lipid A

2- Porin

3- Lipoprotein

4- Outer membrane protein

Question 4

Peptidoglycan is comprised of ?

Answer 4

NAG and NAM connected by tetrapeptides in which the first 2 amino acids may vary among different organisms , the the third amino acid in the peptide must contain an amino group which forms the cross link with the fourth peptide ( D-alanine from another chain )

Question 5

The carrier for the NAG-NAM-peptide unit ?

Answer 5

Bactoprenol

Question 6

How the individual unit is added to the peptidoglycan ?

Answer 6

Through transglycosylases which use the pyrophosphate link between the unit and the bactoprenol as energy to drive the reaction , the cross linking is catalyzed by the transpeptidases and carboxypeptidases by removing the terminal D-alanines

Question 7

Bacitracin mechanism of action ?

Answer 7

Interferes with recycling of the pyrophosphobactophrenol back to phosphobactophrenol

Question 8

Beta-lactams mechanism of action ? Resistance ?

Answer 8

Target the PBPs

Resistance by :
Decreased binding of the antibiotic to the PBPs
Decreased concentration of antibiotics at target
Beta-lactamases

Question 9

Vancomycin mechanism of action ? Resistance ?

Answer 9

Binds to D-ala-D-ala to block the transpeptidation reaction

Van-A and Van-B genes change the pentapeptide terminus so vancomycin will no longer bind

Question 10

Mechanism of resistance of endospores ?

Answer 10

New enzymes
Increases or decreases in other enzymes
Dehydration ( Ca dipicolinate in core )
Keratin spore coat

Question 11

Bacteria adherence to cell surface mechanisms ?

Answer 11

1- pili/fimbriae in gram -ve cells
2- teichoic acids in gram +ve cells
3- adhesins : colonizing factor adhesins , pertussis toxin and hemagglutinins
4- IgA protease which make it easier for pathogens to colonize
5- biofilms ( a mechanism of partial adherence to inert materials ) in staph epidermidis , streptococcus mutans , Pseudomonas aeruginosa

Question 12

Mechanisms of avoiding immediate destruction by host defense system ?

Answer 12

1- anti-phagocytic surface components as Capsules/Slim layers :
Streptococcus pyogens M protein
Neisseria gonorrhoeae pili
Staph aureus A protein

2- IgA proteases :
Neisseria
Haemophilus
Strept pneumoniae

Question 13

Antigenic variation mechanisms ?

Answer 13

1- changing surface antigens to avoid immune destruction
2- N. gonorrhoeae pili and outer membrane proteins
3- T. b. rhodesiense and T. b. gambiense phase variation
4- enterobacteriaceae : capsular and flagellar antigens may or may not be expressed
5- HIV , Influenza : antigenic drift

Question 14

Type lll secretion systems are found in ?

Answer 14

E coli 
Salmonella 
Yersinia 
Pseudomonas 
Chlamydia