Bacteria Flashcards
Properties of a bacteria cell
Prokaryotic
◦ Organelles not membrane bound
◦ DNA is one circular molecule
Knowledge of the cell structure and function of a bacteria is important in _____ & _____
Diagnosis
Pathogenicity
The bacteria cell wall is made of
Peptidoglycan
Peptidoglycan cell wall is made up of Repeating _______ with ____ _____ in a side chain extending from each disaccharide
• This results in a ____ _____ ____ _____
Disaccharides
Amino acids
Stable cross linked structure
5 cell wall functions is to
• maintains cell shape
• acts as a barrier, protects cell contents from external environment
• maintains cell osmotic pressure in a hypotonic environment
• contributes to sensitivity to certain antimicrobial agents (penicillin) and the immune system (antibodies, phagocytes)
• determines reactivity to Gram stain
Characteristics of gram positive cell wall
peptidoglycan (60-90% of the cell wall)
Techoic acid – polysaccharide, antigenic (Important for serologic identification of some bacteria)
If peptidoglycan is digested away from the cell, gram positive cells lose their cell walls and become_____.
These must be maintained in _____ ______in order to survive.
protoplasts
Isotonic solutions
Characteristics of gram negative cell wall
Very thin peptidoglycan
No techoic acid
A unique outer cell membrane
• Periplasmic space
• An external layer of lipopolysaccharide (LPS)
The 3 unique cell membrane of the gram negative bacteria features
◦ excludes all hydrophobic molecules (This protects the bacteria from the action of bile salts and toxins of the gut)
◦ contain narrow, restrictive protein channels called porins which permits passage of low molecular weight hydrophilic molecules.
◦ Large antibiotic molecules penetrate the outer membrane slowly (antibiotic resistance)
The peiplasmic place exists where and contains what
between the cytoplasmic membrane and the outer membrane which contains digestive enzymes and other transport proteins
The external layer of lipopolysaccharide (LPS) consists of
• polysaccharide O antigens used in typing gram negatives
• lipid A or endotoxin. Endotoxin can trigger fever and septic shock in gram negative infections
• LPS also protects the cell from phagocytosis, penicillins and the antibacterial enzyme lysozyme
Flagella are long filaments extending from the cell surface, which enable them to move in their environment.
They are built of ______ and are strongly ____.
The ___ antigens are important targets of protective antibody response
Proteins
Antigenic
H
The flagella may be
_____ (single cell, restricted to the pole)
_____ (a tuft at one pole)
______ (one or more flagella at both ends of the cell
______ (distributed over the cell surface).
Polar
Lophotrichous
Amphitrichous
Peritrichous
Flagella can help in identifying certain types of bacteria e.g, _______ species show a rapid ‘______’ type of growth on solid media.
Proteus
Swarming
The bacteria capsule is
A gelatinous polysaccharide and/or polypeptide outer covering
The capsule may be firmly attached or loosely attached as a slime layer
Within the slime layer many cells can come together to form a ______, which may protect them from _____ & _____
Biofilm
Antibiotics and toxins
5 important Characteristics of the capsule
• Virulence factor, protecting bacteria from phagocytosis by immune cells e.g Streptococcus pneumoniae .
• Permit bacteria to adhere to cell surfaces and structures such as medical implants, catheters and so on. [Adherence is an important first step in colonization and sometimes leads to disease].
• Capsules can be a source of nutrients and energy to microbes. [Streptococcus mutans, which colonizes teeth, ferments the sugar in the capsule and the acid byproducts contribute to tooth decay.]
• Prevents cell from drying out (desiccation)
• Polysaccharides from certain capsules is antigenic and can elicit production of protective antibodies
[Included in vaccines
Such a vaccine is used against Hemophilus influenzae , Streptococcus pneumoniae and Neisseria meningitidis.]
In the nucleus of bacteria
the cytoplasm contains ___,which is typically a single circle concentrated in a nucleoid region and not membrane bound
Genetic information is carried in a long ____
_____ ____. This is the chromosome, which comprise genes.
Genetic information may also be extrachromosomal, present as ____
DNA
Double stranded DNA
Plasmids
Plasmids are?
Plasmids replicate _____ of the chromosome
carry genes that are not essential for cell survival but may give some advantage to an organism e.g?
Small, extrachromosomal DNA circles.
Independently
they can carry genes for antibiotic resistance and toxin production.
Pili Also project from the cell wall but are more rigid than the ____
Also called _____
They function in attachment to host
cells (act as ______)
They prevent ______
Flagella
Fimbriae
Adhesins
Phagocytosis
Pili are Present in many Gram negative bacteria
◦e. g ______ ______uses its fimbriae to attach to the lining of the genital tract and initiate an ___
Sex pili act to join bacterial cells for transfer of DNA from one cell to another known as ____
Negative
Neisseria gonorrhoea
STD
Bacterial conjugation
Fimbriae also act as ______ for viruses that infect bacteria called ________
• Fimbriae and cell walls of Streptococcus ____ are coated with ___ ______.
• M protein acts as an important virulence factor by _____ & _____
Receptors
Bacteriophages
Pyogenes
M protein
adhering to host cells and resisting phagocytosis
Ribosomes are
• Composed of ____ & ____
• the site of ______ in cells
• typically comprised of two subunits?
• Antibiotics inhibit protein synthesis at the subunits
• 50s subunit – – e g ?
• 30s subunit — e g ?
Protein & RNA
Protein synthesis
50s & 30s
Erythromycin
Tetracycline
Clinical importance
Gram positive thickly meshed peptidoglycan layer does not block diffusion of low molecular weight compounds so, some substances (antibiotics, dyes, detergents), can pass through
Antibiotics and chemicals that are able to attack the peptidoglycan cell wall () are unable to pass through the Gram negative cell wall
Crystal violet is trapped in the thick peptidoglycan layer, so the dark blue colour is retained
The outer cell membrane of the Gram negative cell wall is partially destroyed by alcohol, so crystal violet is washed out and a counterstain can be taken
Virulence of bacteria depends on certain cell structures
What makes up flagella
Flagellin
Sex Pili is also known as
F pili
Sub units of pili
Pilins
Which part of the bacteria has the most antigenic variation
The capsule
Drugs affecting 50s
Chloramphenicol
Macrolides
Clindamycin
Drugs affecting 30s subunit
Tetracyclines
Aminoglycosides
Based on oxygen dependence, bacteria is classified into
Obligate aerobes
Facultative aerobes
Microaerophilic eg H. pylori
Obligate anaerobes eg Clostridium, Bacillus
Hemolytic pattern
Explains how bacteria reacts in blood agar
Beta hemolysis
And example
Complete hemolysis. The bacterium can lyse of red cells
Clear areas of bacterium in culture
GBS
GAS
Group B & A streptococcus
Alpha hemolysis
Partially hemolysis of red cell
Green area around the bacteria in culture
Streptococcus viridans
Gamma hemolysis
Doesn’t lyse the rbc
Eg peptostreptococcus
Capsulated Bacteria(and one Fungus)
YES Some Nasty Killers Have Pretty Big Capsules.
Y - Yersinia pestis
E - Escherichia coli (Extraintestinal strains)
S - Salmonella typhi
Some - Streptococcus pneumoniae and pyogenes
Nasty - Neisseria meningitidis
Killers - Klebsiella pneumoniae
Have - Haemophilus influenzae
Pretty - Pseudomonas aeruginosa
Big - Bacillus anthracis and Bordetella pertussis
Capsules - Cryptococcus neoformans
Others: Francisella, Brucella, Pasteurella
Teichoic acud is present in the cell wall of
Gram +ve bacteria
Outer cell membrane is present in
Gram -ve bacteria
H antigens are components of
Flagella
O antigen are components of
Lipopolysaccharide
Erythromycin inhibits protein synthesis at
Tetracycline at?
50s subunit
30s subunit
