Classification Of Bacteria

Question 1

Estimate of the currently identified pathogens responsible for causing human dz is

Answer 1

Fewer than 10%

Question 2

Infectious agent is specifically adapted to

Answer 2

A particular mode of transmission,
Mechanism to grow in human hosts,
Mechanism to cause disease.

Question 3

Practical use of classification scheme is

Answer 3

Identification

Question 4

Cause of haemolytic uremic syndrome (HUS) in infants

Answer 4

E. Coli

Question 5

Strains of E. Coli can be distinguished by

Answer 5

Antibody reactivity with their O- and H- antigens.

Question 6

Linnaean taxonomic hierarchy

Answer 6

Kingdom, phylum, class, order, family, genus, and species.

Question 7

Eschericheria coli O157:H7 taxonomic hierarchy

Answer 7

Prokaryote, gracilicutes, scotobacteria, eubacterials, enterobacteriaceae, E. coli.

Question 8

Most bacterial pathogens can be isolated on media?

Answer 8

Solid agar containing media

Question 9

Complex media

Answer 9

Includes agar, carbon source, acid hydrolysate or enzymatically degraded source of biologic material eg casein.

Question 10

Nonselective media

Answer 10

Used to distinguish among various bacteria in a clinical sample containing many different organisms.
Eg: blood agar, chocolate agar.
Media intended to cultivate as many species as possible.

Question 11

Selective media

Answer 11

Sample site: skin, respiratory tract, intestines, vagina.
Used to eliminate the large number of irrelevant bacteria in these specimens.
Basis: incorporation of an inhibitory agent that specifically selects against the growth of irrelevant bacteria, eg:
sodium azide- selects gram +ve over gram -ve,
Bile salts- select for gram -ve enteric bacteria and inhibit gram - ve mucosal & gram+ve bacteria,
Colistin and nalidixic acid- inhibit growth of gram -ve bacteria.
Eg: MacConkey agar that selects for enterobacteriaceae, CNA blood agar that selects for staphylococci and streptococci.

Question 12

Differential media

Answer 12

Some bacteria produce characteristic pigments, others can be differentiated on the basis of their complement of extra cellular enzymes, activity of these enzymes can be detected as zones of clearing surrounding colonies grown in presence of insoluble substrates.
Enterobacteriaceae members have ability to metabolise lactose. Lactose fermenting members of enterobacteriaceae form red or pink colonies.
Biochemical identification.

Question 13

Gram stain

Answer 13

Divides bacteria based on their differences in structure of cell wall.

Question 14

Factor differentiating enterobacteriaceae from other gram -ve rods.

Answer 14

Presence or absence of a respiratory enzyme, cytochrome C, lack of which differentiates enterobacteriaceae from other gram -ve rods.

Question 15

Test used to distinguish organisms on the basis of the presence or absence of a respiratory enzyme.

Answer 15

Oxidase test.

Question 16

Catalase activity

Answer 16

Differentiate between gram +ve cocci,
the species staphylococci are catalase +ve implying the species can be subdivided by coagulase test into staphylococcus aureus i.e. coagulase +ve and staphylococcus epidermitidis i.e. coagulase-ve;
the species streptococci are catalase -ve.

Question 17

Cause of some traits to be highly variable within a biologic group or within a specific taxonomic group is

Answer 17

Genetic instability.

Question 18

Common microbial biochemical tests used to differentiate among bacteria are

Answer 18

Carbohydrate breakdown
Catalase production
Citrate utilisation 
Coagulase 
Decarboxylase & deaminase
Hydrogen sulphide 
Indole
Nitrate reduction 
O-Nitrophenyl-beta-D-galactoside (ONPG) breakdown 
Oxidase production 
Proteinase production 
Urease production 
Votes-Proskauer production.