Microbiology Part 3

GENETICS

-          A normal bacterial cell is HAPLOID

Note:

1.    REPLICATION- accurate duplication of chromosomal DNA which enables the formation of two identical daughter cells

2.    TRANScRIPTION- info from DNA to RNA, 1^st of two steps necessary to produce proteins.

   Simplistically, RNA polymerase locates the beginning of the gene (promotor ) , and

this area undergoes localized unwinding to allow RNA polymerase to t ranscr ibe

RNA (called mRNA) from the DNA template. The RNA is not processed, as in

eukaryotes. There are no introns and exons, no capping of the 5′ end, and no

polyadenine tails added to the 3′ end.

 

3.    TRANSLATION- processing of genetic info to synthesize proteins. Before transcription is completed, the ribosome will attach to the 5’ end of the message.

 70 s bacter ial ribosome is composed of two subuni ts, 30s and 50s. The r ibosome

t ranslates the message into protein by reading the t r iplet codon ( three

nucleot ides) which code for a speci fic amino acid. This amino acid is car ried to the

si te by t ransfer RNA ( tRNA) and pai rs wi th the codon by an ant icodon. Amino

acids are joined, and the r ibosome moves to the next codon. This cont inues unti l the

complete protein is synthesized.

4.    REGULATION-

5.    Other methods of DNA transfer

a.    RECOMBINATION- transfer genetic material from the donor chromosome to a recipient chromosome for those only that have similar nucleotide sequences. 3 mechanisms:

a.    TRANSFORMATION- involves the recipient cell taking up cell-free, fragmented(I.e naked) DNA and recombining genetic elements

                                                  i.    PRIMITIVE, occur in few genera

                                                ii.    Requires “leaky bacterial cell wall”

                                               iii.    Associated with CLONING or Recombinant DNA technology

1.    CLONING- splicing a gene into a plasmid DNA (vector)

b.    CONJUGATION: is an important means of gene transfer, particularly among GRAM NEGATIVEs.

a.    Involves mating types the donor (f+) and the recipient (f-)cells and the sex factor (f factor)

b.    TRANFER through the SEX PILUS /PILI into the recipient cell

c.    TRANSDUCTION- transfer of genetic material by BACTERIOPHAGES (or viruses the infect bacteria)

TRIVIA: Unique bacteria

A.   Chlamydia

a.    Cannot generate ATP

b.    2 phase life cycle

B.   RICKETTSIA- transmitted by ARTHROPODS

a.    Generate ATP but instead use the host cell products

C.   MYCOPLASMA- smallest bacteria

a.    Lack cell wall

b.    Plasma membrane contains sterols for added strength

c.    Mycoplasma pneumonia- Atypical pneumonia or walking pneumonia

 

 

VIRUSES

Table 9-1. The Multiplication of Animal Viruses

1 Attachment

(adsorption)

Virus attaches to a protein or polysaccharide

molecule (receptor) on the surface of a cell

 

2 Penetration

 Entire virus enters the cell, in some cases because it was phagocytized by the cell

3 Uncoating

Viral nucleic acid escapes from the capsid

4 Biosynthesis

 Viral genes are expressed, resulting in the production of pieces or parts of viruses (i.e.,viral DNA and viral proteins)

5 Assembly

Viral pieces are assembled to create complete virions

6 Release

Complete virions escape from the bacterial cell by budding or lysis

 

TRANSMISSION OF INFECTIOUS AGENTS

Ø  Human reservoirs

a.    Diseases that are obligate human pathogens

b.    If humans are reservoir—they are CARRIERs

                                                  i.    Asymptomatic Carriers- harbors infection but no symptoms

                                                                                                  i.    As part of their NORMAL FLORA

                                                                                                ii.    Streptococcus pyogenes

                                                ii.    Symptomatic carriers- obvious signs and symptoms

Ø  Animal reservoirs- primary host is animal

Ø  Environmental reservoir- soil lake plants

MECHANISM OF TRANSMISSION

Contact	a.    Direct contact- physical contact between infected ndividual and a susceptible individual (STD) b.    Indirect contact- come in contact with contaminated surface n  Fomites (doorknobs, counters etc)
Droplet transmission	Cough and sneezes Come in contact with the mucous membrane of the individual nose mouth eyes Ex measles
Airborne transmission	Small contaminated dust particles or the residue of the DRIED DROPLETS remain suspended in the air for long periods of time. Ex. Influenza TB pneumonia
Food and water contamination	Ex. Fecal oral route
Vectors	Animals capable of transmitting disease Most common: mosquito (malaria)
Entry into a Host	Wound, ingestion, injection

 

MECHANISMS OF PATHOGENECITY

Ø  Virulence factor- characteristic of an organism that allow it to either damage the host or evade host defences

ü  Exotoxins- secreted either into the environement or aster olonization of host

ü  Exotoxins secreted into the water or foodà ingested by host--.cause INTOXICATION (Botuism, Staphylococal food poisoning)

ü  Exotoxins produce after infection interfere with the cell fxn or physically damge the cell (Brodetella pertussis, Corynebacterium diphtheria, Vibrio cholerae)

ü  ENDOTOXINS- Gram negative organisms; found in their outer membrane. Induce fever and shock in the host

ü  CAPSULES- used for adherence to host surfaces and help the bacteria evade phagocytosis by the host cell

Ø   

INFECTION

Infection: sufficient to cause disease for some microorganism. Ex: pneumonia. I

            Infection may be followed by toxin production as in diphtheria