Bacterial characteristics and genetics Flashcards
What is the endotoxin of Gram-negative bacteria?
Lipopolysaccharide
What is the pathogenetic part of the gram-positive bacteria?
Teichoic acid
Peptidoglycan is composed of long
polysaccharide chains made up of two
main sugars:
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
The NAG and NAM units alternate
and are linked together by?
β(1→4)
glycosidic bonds
What is the function of the peptydoglycan?
structural support, protection, and shape maintenance.
In how many stages does biosynthesis of peptidoglycan take place?
3:
1) synthesis of UDP-N-acetylmuramyl-pentapeptide and UDP-N-acetylglucosamine.
2) Intermediate lipid precursor is synthesized.
3) Polymerization of the newly synthesized disaccharide - peptide units.
what are microaerophilic bacteria?
they grow well in low O2 concentrations, but are killed by high O2 concentrations.
beta-hemolysis?
colonies of blood agar plates are surrounded by a zone of complete clearing ( lysis of red blood cells )
alpha-hemolysis?
partial blood hemolysis, surrounded by a greenish halo ( due to the transformation of hemoglobin to methemoglobin.
Gamma-hemolysis?
no change of the surrounding
vertical transmission of bacterial genetic material?
distribution to daughter cells following cell division
Horizontal transmission of bacterial genetic material?
with an unidirectional mechanism from a donor cell to an acceptor cell
Mechanisms of horizontal transfer of genetic material:
Transformation, Transduction, Conjugation
The ability to take up the DNA from the environment is called?
Competence
types of plasmids?
Conjugative, Col plasmids, virulence plasmids, metabolic plasmids.
what are bacteriocins?
Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s).
Mobile genetic elements:
Insertion sequences and transposons
What are transposable elements?
genetic units that are able to replicate independently and mediate their own transfer from one chromosome to another, from one position on the same chromosome to another.
What are transposons?
these genes may code for antimicrobial resistance, substrate metabolism
What are insertion sequences?
simple transposable elements, its presence in the chromosome is hard to detect
What is bactericide?
a substance that kills bacteria. Bactericides are
disinfectants, antiseptics, or antibiotics
What is Bacteriostatic?
“bacteriostatic” means that the agent prevents the growth of bacteria (i.e., it keeps them in
the stationary phase of growth), and “bactericidal” means that kills bacteria.
What are the phases of bacterial growth in liquid medium?
Exponential (the highest rate of growth), stationary (the number of cells doesnt increase), death ( death of bacteria due to the lack of nutrients)
What is a LAG phase?
It is phase during which the bacteria do not grow yet as they were just introduced to the liquid media.
How can we obtain isolated colonies of single species of bacteria?
We can use a technique such as isolated spreading with the use of a Loop.
What is the limiting factor for bacteria metabolism and doubling?
Water
What chemicals gram-positive bacteria cannot withstand?
Bile salts, Crystal violet dye
What color does MacConkey agar turns in the presence of lactose fermenting bacteria?
Red or pink
why is there a greenish halo during the Alpha hemolysis?
it is due to the transformation of hemoglobin to methemoglobin.
what is the episomic state of the plasmid?
plasmid is free in the cytoplasm
what is the integrated state of the plasmid?
the plasmid genes are integrated into the bacterial chromosome
what can cells with F+ produce?
sexx pilus, through which the gene for sex pilus is transferred to the F- cell
what do invertible elements do?
they switch the genes
what are the types of transduction?
Generalized and Specialized
how can we induce the competence state?
by the use of cations or by electroporation.
what is generalized transduction?
is when the bacteria chromosomes get integrated into the capsid of the virus and eventually transferred to other bacteria (lytic cycle)
what is specialized transduction?
is when the bacteriophage gene takes up some of bacterial gene and then after lysis of the cell transfers it to other bacteria
