Clinical microbiology introduction to bacteriology cell structure

2.  The outermost component of bacterial cell that provides
structural support &maintains its characteristic shape.
 Multilayered structure. The inner layer is peptidoglycan
and there is an outer membrane.
 In the Gram+ve bacteria peptidoglycan layer is thicker with
fibers of teichoic acid penetrating it.
 Gm-ve have a complex outer layer consisting of
(lipopolysacchride,lipoprotein &phospholipid) a
periplasmic space and porine proteins.
 Mycobacteria have high concentration of lipids (mycolic
acid)result in inaility to be Gram stained.

3.  Peptidoglycan:
A complex interwoven network , surrounding the
cell ,compose of peptides and suger(glycan).
The carbohydrate backbone is alternating NAG
&NAM molecules connected with tetrapeptide bond.
Present only in bacterial cell but not human cell
(good target for antibiotics).
Lysozyme enzyme in human tears , mucus &saliva
can cleave it (natural protection).

4.  Lipopolysacchride(LPS):
Part of the outer membrane of Gm-ve bacteria. It is
an endotoxin responsible for fever , hypotension
&shock .
It comopose of a phospholipid (lipid A) responcible
for the toxic effect and polysacchride units used for
identification.
 Teichoic acid:
Fiibers of glycerol &ribitol phosphate in the outer
layer of Gm+ve bacteria only.
It can induce septic shock by the same
mechechanism of Gm-ve bacteria .

7.  A phospholipid bilayer similer to that of eukaryotic cell but
did not contain sterols
 Function:
a)active transport of molecules inside the cell.
b)Energy generation.
c)synthesis of precursor of cell wall.
d)secretion of enzymes and toxins.
Mesosome:
Invagination in the cytoplasm important during cell
division.

8.  The cytoplasm has two distinct areas:
a)an amorphus matrix contains
ribosomes, nutrient granules, metabolites
&plasmids.
b)an inner, nucleoid reigon contains the
DNA.

9.  The site of protein synthesis, it differs from
eukaryotes in size&chemical composition
 They are 70S in size with 50S&30S subunits,
while in human ribosomes are 80Sin size
with 60S & 40S subunits.
 This differerences is the base of selective
action of some antibiotics.

10.  Different types of granules , some for
storage , some have certain staining
characteristics others are high energy stores
.

11.  The area where DNA is located
 Prokaryotic DNA is single , circular contain
about 2000 genes.
 Tnucleiod contain no nuclear membrane , no
nucleolus , no mitotic spindles and no
histones.
 Bacterial DNA has no intrones where
eukaryotic DNA does.

12.  Extachromosomal double-stranded , circular DNA
molecules. Capable of replicating independently.
 Found in both Gm+ve &Gm-ve bacteria.
 Types: a)Transmissible can transfer from cell to cell by
conjugation.
b)Non transmissible, small present in many copies
per cell.
Plasmids carry genes for: Resistance to Antibiotic, heavy
metals , UV light. Genes for production of pili and
exotoxins ,bacteriocins e.g colicns of E.coli & pyocin of
Pseudomonas sp . Also nitrogen fixation enzyme ,
antibiotic production e.g Streptomyces.

13.  Pieces of DNA that moves readily between
DNS s of bacteria , plasmids and
bacteriophages. (jumping genes)
 Types: a)replicative transposons.
b)direct transposons.
Functions: can code for drug resistant
enzymes and toxins.
They are not capable for self-replication.

15.  A gelatinous layer covering the entire
bacterium. It compose of polysacchride,
variation in suger type from one species to
other.
 Importance:a)virulance factor
(antiphagocytic)
b)identification
c)vaccination
e)adherence

16.  Long whip-like appendages move bacteria
toward nutrients.
 It compose of a protien(flagellin),the energy
provided from ATP.
 Flagellated bacteria have different no. and
locations
 Medical importance:
a)flagella play role in pathogenesis
b) used in identification.

17.  Hair like filaments , shorter & straighter than
flagella , compose of subunits of pilin.
 Found mainly in Gm-ve bacteria.
 Importance:
a)attachment to specific recepters b)sex
pili for conjogation

18.  Slime layer of polysacchride coat secreated
by many bacteria.
 Allow firm adherance of bacteria to various
structures
 Glycocalyx producing bacteria are more
virulant.

19.  Highly resistant structures ,formed in adverse conditions by two
genera of medically imp. Gm+ve bacteria ,the genus Bacillus
and the genus Clostrridium.
 The spores formed inside the cell, contain DNA, small amount of
cytoplasm , cell membrane,peptidoglycan & v.little water
surrounded by a thick keratinized coat.
 It resistant to heat, dehydration, radiation and chemicals.
 It had no metabolic activity ,can remain dormant for years.
 Sterlization can not be achieved by heat.
 Autoclaving (steam heating under pressure at 121c for 30
minutes)is required.