Bacteria Flashcards
what types of culture media are there?
liquid
solid
what does selective media do? aka enrichment media
suppress growth of a particular organism and enhance the growth of another
what is the difference between synthetic media and complex media?
synthetic media is chemically altered whereas complex media is an aquaeous solution of an animal or plant that already contain b vitamins carbs and hydrolysed proteins
why is trypsin favored over acids in hydrolysis?
because acids destroy amino acids more than trypsin
how are microorganisms differentiated in culture?
different fermentation patterns of different microorganisms help in identification
what are exacting microorganisms?
organisms that need blood, mill, or serum to grow
what are media requirements and their sources
protein → meat extract/milk/soya
proteolytic enzyme → trypsin
b vitamin → yeast extract
nutrients → glucose/carbs/satrch
asmotic pressure → NaCl
buffer → bicarbonate
agar → carb extract from seaweed
imparting low pH → lactic acid
define binary fission
process by which cell enlarges and elongates forming a cross wall that separates the cell into two or more cells equal compartments containing a copy of the genetic material, septum then forms to reduce connection until daughter cells separate
what is the bacterial cell composed of
- cell wall
- cytoplasm
- nucleus
- ribosomes
- inclusion granukes
what is the function of the cell wall in a bacterial cell
- maintenance of shape and integrity of bacterial cell
- withstand osmotic pressure caused by high concentrations of ions in the cell
the cell walls of bacteria is composed of peptidoglycan, what is peptidoglycan?
chains crosslinked by short peptide bridges composed of alternating residues of n-acetyl muramic acid and n-acetyl glucosamine
the N-acetly muramic acid (NAM) in the peptidoglycan is attached to a tetrapeptide, what is this tetrapeptide made up of?
- L-alanine
- D-alanine
- D-glutamic acid
these are crosslinked via (direct peptide linkage) & (peptide interbridges)
what is the antimicrobial target of bacteria?
the presence of DAP and 2 amino acids in the D-configuration
what’s the difference between gram positive and gram negative bacteria
in gram positive bacteria, what is techoic acid made up of
ribitol phosphate and glycerol phosphate connected by phosphodiester bridges hence the negative charge of the gram-positive bacteria
why does gram negative bacteria have a positively charged cell wall?
The lipopolysaccharides impart a strongly negative charge to surface of Gram-negative bacterial cells.
describe the regions of the lipopolysaccharides of the gram-negative bacteria
Lipid A: glucosamine phosphate + fatty acid in the outer leaflet of the membrane, responsible for toxic and pyrogenicity.
Core: connected to Lipid A by ketodeoxytonate (KDO)
O-specific polysaccharide: 6 carbon sugars and deoxysugar (abequose)
what is the function of the outer layer of gram negative bacterial cell wall?
- prevents enzymes in outer side the cytoplasm from diffusing away
- resists dissolution by detergents
what is the periplasm?
region between the outer surface of cytoplasmic membrane and inner surface of outer membrane
what is the function of the plasmic membrane in bacteria?
- energy generation
- nutrient transport
- electron transport
describe the structure of bacterial DNA
circular double stranded DNA
what is the unique antibiotic target in gram negative and positive bacteria?
negative: DNA gyrase
positive: topoisomerase IV
what are plasmids?
circular double stranded extrachromosomal DNA
what is the function of plasmids?
- autonomous replication
- antibiotic resistance
describe bacterial ribosomes
70s: dividedd into two subunits (50s & 20s)
what do inclusion granules of bacteria do?
repository of C/N/S/phosphorus for when nutrient depletion occurs
how are eukaryotic ribosomes different from bacterial ribosomes?
eukaryotic ribosomes are 80s divided into (40s-60s)
whereas bacterial ribosomes are 70s divided into (50s-30s)
what are the cell surface components of a bacterial cell?
flagella
fimbrae
pili
extracellular polysaccharides
what is the role of flagella in bacteria?
it provides motility, and flagellin protein allow flagellar motor movement
what is the function of fimbrae in bacteria
serve as adhesins that allow attachment to surfaces and initiate biofilm formation
it allows hemagglutination and cell clumping
what is the function of pili
allows the process of genetic exchange (conjugation)
what is therole of the S layer in bacteria
it serves as a permeabiliy barrier that increases the robust of cell
what is the composition of extracellular polysaccharides in bacteria
0.2% carbohydrates and 98% water
what types of extracellular polysaccharides are there in bacteria?
capsules: tight and rigid
slime: loose
what do slime and capsules do?
- provide barrier against antibodies
- protection against dissection
- protection against phagocytes
what are the extracellular polysaccharides of:
(1) pseudomonas aeruginosa
(2) leuconostoc mesenteroides
- alginate
- dextran
define biofilm
bacteria attached to surfaces forming multilayered communities
how do bacteria adhere to surfaces
via fimbrae and extracellular polysaccharides
how do biofilms form
cells grow and divide, produce microcolonies and coalesce
how are biofilms protected from antibiotics?
enveloping of attached cell in extracellular polysaccharide matrix which allows bacteria to stick together on the surface
how do biofilms get their nutrients if they are strung together?
EPS hold bacteria at distance to form pores that allow the passage of nutrients
true or false
biolfilms are impossible to eliminate from surfaces
true
define sporulation
profound biochemical change to give rise to a specialized structure (endospore)
which bacterial genera is capable of sporulation?
bacillus
clostridium
how are spores eliminated?
ethelyne oxide + heat
how is the vegetative cell different from the spore?
Spores are inactive and dormant structures. Vegetative cells are actively growing cells that form the endospore. They can tolerate stress like chemicals, heat and radiation. They cannot manage in stressful environments.
what layers surround the core of the spore?
outermost layer: proteins + spore coats
cortex: loosely crosslinked peptidoglycan
central core which holds the genome
what does the dipicolinic acid + calcium ions complex of the spore do?
plays a role in heat resistance, whereby it leaves the core dehydrated by retaining only 10-30% of water
what do the core specific proteins of the spore do?
bind to DNA to prevent damage to the cell
true or false
pH of the spore is 1 unit lower than that of the vegetative cell
true
how is sporulation started?
Ceasing protein synthesis and activation of spore genes
what are the spore genes responsible for the activation of sporulation
SPO
SSP
What do SPO & SSP do?
they produce proteins that catalyze the production of dry, metabolically inert, resistant spores. which takes hours to complete
how do spores go back to their vegetative form?
by removing the stress that caused the sporulation
Germination
what happens when the spore goes back to its vegetative form?
- loss of resistance
- loss of calcium diplionate cortex components
- degradation of core proteins
- water uptake
- new RNA + DNA
what is an opportunistic pathogen?
an organism that normally doesn’t cause harm but can cause disease when host’s resistance is low
what is an example of an opportunistic bacteria?
- staphylococcus epidermidis, it is present normally on the skin but can be fatal on the heart valve
- pseudomonas aeruginosa, lethal in immunocompromised
define bacterial toxins
bacteria products that cause host cell damage
what types of toxins are there
endotoxin: related to cell wall (Lipid A of LPS)
exotoxin (released extracellularly)
what types of exotoxins are there
- A-B toxins: most common, b subunit covalently bound to a subunit bound to host, mediate enzymatic activity responsible for toxicity (diptheria/cholera)
- cytolytic toxins: attack cell constituents causing lysis (phospholipases/haemolysins)
- superantigen toxins: stimulate immune response, releasing cytokines leading to massive inflammatory response (staphyloccocus aures) aka toxic shock
what type of toxins activate b lymphocytes, stimulate the complement cascade and the production of tumor necrosis factor
endotoxins
true or false
endotoxins are released from damaged cells
true
how long does E.coli take to multiply/divide?
45 minutes
how do gram positive and gram negative bacteria divide?
gram positive: develop a cross wall that divides into two due to the rigid cell wall
gram negative: constrict and fuse membrane, due to fragile cell wall
this process takes 15 minutes to complete
how is it possible for bacteria to grow/replicate every 15 minutes under optimal conditions
they replicate more than onxe every hour by initiating new rounds of DNA replication, therefore partially replicated chromosomes are separated into daughter cells thus making division quicker
how do rods/cocci/streptococci/staphyloccoci/sarcina increase their size?
rods → elongation
cocci → radial expansion
streptococci → parallel planes (successive division)
staphylococci → successive division
sarcina → rotate successive division
how do bacteria grow on solid surfaces?
creating a localized colony from moist and nutrients
how do bacteria grow on liquids?
by nutrients diffusing through the colony
what is solidified media?
broth that is solidified by agar below 45 celcius
what are the methods by which bacteria exchange genetic material?
- transformation
- transduction
- conjugation
what is transformation?
a process by which bacteria exchanges genetic material by absorbing small pieces of naked DNA from the environment and recombine it into their chromosomes
can lead to septic abscess
what is transduction?
a process by which bacteria exchanges genetic material by bacteriophages infecting bacteria by injecting viral DNA into their cell and incorporate into bacterial chromosomes creating a temperate phage
what is conjugation?
a process by which bacteria exchanges genetic material by generating defective viral DNA which is transcribed to produce viral elements that cannot assemble or lyse the host cell
true or false
conjugation evolved from transduction
true
what is the F-factor
simplest form of plasmid that generates f pilus in cell envelope (transfers DNA from one cell to another)
what does the f-factor do in conjugation
transfers a copy of DNA from one cell to another
what is the name of the integrated form of f factor
Hfr
what does bacterial growth depend on
- nutrients
- water
- partial pressure of oxygen
- temperature
- solute concentration
what is the optimal environment for the growth of gram negative and grame positive respectively
negative: aquatic environments
positive: arid environments (skin)
majority of bacteria are mesophiles, define mesophiles
grow at body temperature 37
how are bacteria able to grow in high temperatures?
high temperatures speed up the chemical reactions within the bacterial cell thus enzymaticc and growth action occur rapidly
most pathogens of medical significance grow at a pH of _____
(7.4-7.6)
why do gram negative bacteria favor aquatic environments for growth
because their cell envelope cannot withstand high internal osmotic pressures associated with rapid dehydration of dessication and they would be unable to grow in high concentrations of solutes
what is water activity Aw
vapour pressure of water in the space above the material relative to the vapour pressure above pore water at the same temp and pressure
what elements are the terminal electron acceptors in respiration
iron
oxygen
lactic acid
sulfur
what are obligate anaerobes
organisms toxicated by oxygen
what type of culture is used to grow anaerobes?
special media and anaerobic chambers
why are bacteroides and fusobacter found in the GI tract along with streptococci?
because the close proximity of strongly anaerobic and aerobic cells will create an anoxic microenvironment in whch the anaerobe can flourish
what causes stationary phase in bacterial growth?
the inability of oxygen to diffuse adequately into a liquid culture
fill in the blanks
what is the gram stain
a staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye. The cell walls of certain bacteria (denoted Gram-positive ) retain the first dye and appear violet, while those that lose it (denoted Gram-negative ) appear red.
what are the properties of the bacterial cytoplasmic membrane?
- 40% lipid (much in the form of phospholipids)
- 60% protein and small amounts of carbohydrates
- no sterols
- Semi-permeable. Generally, only low molecular weight materials can penetrate to the inside of the cell.
- has efflux proteins (vomit pumps)
- Contains many proteins/enzymes essential to the bacterium survival; e.g. the proton motive force that generates adenosine triphosphate (ATP; energy
Many bacteria form and store granules in their cytoplasm in the form of high molecular weight polymers. these are:
- glycogen: a storage form of both carbon and energy
- polymer of β-hydroxybutyric acid (storage form of both carbon and energy)
Protein crystals are sometimes found. Bacillus thuringiensis crystals are used as ____
insecticide
define bacterial growth
Change in the population rather than an increase in the size or mass of the individual bacterium
describe what happens in each phase of bacterial growth
Lag Phase
- Population remains temporarily unchanged.
- Bacterial cells may be growing in volume or mass, synthesizing enzymes, proteins, RNA, etc., and increasing in metabolic activity.
Exponential growth phase
- Expressed as generation time, or doubling time of the bacterial population.
Stationary Phase
population growth is limited
- Exhaustion of available nutrients
- Accumulation of inhibitory metabolites or end products
- Exhaustion of space
what happens in exponential growth phases?
One cell divides producing 2 (‘daughter’) cells. Increase in population is by geometric progression
Total population b at the end of a given period (starting with 1 cell) b = 1 x 2n
what is a chemostat?
Chemostat: bioreactor to which fresh medium is continuously added, while culture liquid is continuously removed to keep the culture volume constant
what is the optimal temperature for the growth of each of the following:
psychrophiles / mesophiles/ thermophiles
- Psychrophiles: 0-20ºC (optimum temperature: 15ºC)
- Mesophiles: 25-40ºC
- Thermophiles: >45ºC
Control of temperature is essential for the storage of pharmaceutical products. how is that acheived?
- deep freeze (-20ºC) Total Parenteral Nutrition, raw materials - 8-12ºC: reconstituted syrups and multi-dose eye drops (expiry date) - 80ºC for WFI (regrowth of Gram-negative and release of toxins)
explain how pH controls growth of bacteria
- extreme pH prevent microbial growth
- neutral pH: bacterial spoilage e.g. in antacid mixtures, flavoured mouth washes, distilled and deionised water -
- pH>8: spoilage is rare (soap-based emulsion)
- low pH: spoilage by moulds and yeast e.g. fruit juice flavoured syrups
true or false
The greater the solute concentration, the lower the water activity
true
Water activity of aqueous formulations can be lowered to decrease microbial growth, how can that be achieved in syrup?
Syrup BP: (Aw = 0.86)
list the nonsterile pharmaceutical products
• Preparations for topical use and for use in the respiratory trac
t • Preparations for oral and rectal administration
- Preparations for oral administration containing raw materials of natural origin
- Herbal remedies
define sterile pharmaceutical products
Preparations required to be sterile on the dosage form and other preparations labelled sterile, need to comply with test for sterility.
what are the acceptable counts for each pharmaceutical product
define colony count
The viable count referred as to the number of colony-forming units (cfu)
what Plate count methods are there
- pour plate
- spread plate
true or false
The Most Probable Number method is reserved for the enumeration of bacteria in situations where no other method is available.
true
what rapid microbiology methods (RMM) are there?
- growth based (OD)
- direct measurement (DEFT)
- cell component (NAAT)
what is phylogeny?
study of the evolution of organisms
why are the domains of life classified on the basis of rRNA?
because rRNA are present in all living cells
provide examples of biochemical profiling methods
- Example Fermentation of various sugars (acidity turn colour yellow)
- Production of oxidase (presence of cytochrome oxidase)
- Hydrogen sulphide production (production of H2S, will react with iron salts forming a black precipitate)
what does Serological testing use?
highly specific antibody (Ab) antigen (Ag) interaction
what is an example of a serological test?
Enzyme Linked Immunosorbent Assay (ELISA)
how does PCR work
Polymerase Chain Reaction (PCR) based techniques allow amplification of a known gene of interest for nucleic acid sequencing, which provide accurate identification of the genus
draw an endospore cell
what’s the difference between sporulation and germination?
Germination is the process by which a spore reverts into a (vegetative) bacterium.
sporulation is when the vegetative cell turns into a spore
true or false
Spores are used as biological indicators for sterility assurance of sterilization process.
true
The use of broad spectrum chemotherapeutic antibiotics is associated with an increased risk of developing ________
C. difficile associated disease (CDAD).
list 3 of each
5 broad spectrum antibiotics
5 low risk antibiotics
Chlamydia are obligate intracellular bacteria, what does that mean?
they lack the metabolic pathway to produce their own high-energy phosphate compounds (“energy parasites”)
chlamidya exist in two forms. what are they?
- the small (300-400nm) extracellular infectious elementary body (EB)
- the larger (800-1000nm) intracellular non-infectious reticulate body (RB)
describe the structure of chlamidya
Microbial structure
- internal and external membrane similar to Gram-negative bacteria
- no peptidoglycan layer
- lipopolysaccharide
- no flagella and non piliated
how is chlamydia treated?
Tetracyclines: doxycycline 100 mg bds; 7 days
- Macrolides: azithromycin 1g : single dose.
how do you prevent chlamydia?
- safe sex
- not sharing sex toys
- appropriate sanitary hygiene
draw the structure of mycobacterium tuberculosis
name one a characteristic of virulent strains of M. tuberculosis
cord formation
list risk patients of tuberculosis
1) close contacts of an infectious case
2) those who have lived in places where TB is still common
3) those whose immune system is weakened by HIV or other medical conditions
4) people who experience chronic poor health through lifestyle factors such as homelessness, alcoholism and drug abuse
5) young children and very elderly people are more susceptible
describe the structure of the cell wall of mycobacterium tuberculosis
Basic layer: peptidoglycan linked to an arabinogalactan wall (copolymer of arabinose and galactose) esterified to mycolic acid structure.
what is mycolic acid
High-molecular-weight (60-90 carbons) 3-hydroxy fatty acid found in mycobacteria
25% of the dry weight is free lipids located outside the outer layers.
what lipids exist in a mycobacterium cell?
- Lipids include waxes,
- species-specific mycosides (complex glycolipids and peptidoglycolipids),
- lipopolysaccharides
- cord factor (6,6”-dimycolate of trehalose)
Anti-TB drugs are always prescribed in combination, why?
to reduce the risk of the TB bacilli becoming resistant to one or more of them
It is vital that the medication is taken as prescribed. why?
taking anti-TB medication in the wrong dose, intermittently or for too short a time can result in the development of drug resistance
what are the first line of treatment in tb
isoniazid, rifampicin, pyrazinamide, ethambutol
how do you treat a newly diagnosed tb patient? and how do you re-treat a patient?
newly diagnosed
- initial phase: isoniazid + rifampicin + pyrazinamide + ethambutol (2 months) 2. continuation phase: isoniazid + rifampicin (4 months)
retreatment
- isoniazid + rifampicin + pyrazinamide + ethambutol and streptomycin (2 months) 2. ioniazid + rifampicin + ethambutol (5 months)
true or false
Treatment needs to be fully supervised (Directly Observed Therapy - DOT) in patients who cannot be relied upon to comply with the treatment regimen.
true
what are the manifestations of gonococcus
cervicitis
urethritis
neisseria genus is divided into two, what are they
gonorrhea → causing Epididymitis in mucosal epithelia
meningitidis → causing meningitis
what is pelvic inflammatory disease?
inflammation of uterus and fallopian tubes
what are complication of pelvic inflammatory disease
ectopic pregnancy
what immune response is capable of killing all gonococcus genus
complement system
how are gonococcus able to grow in large amounts in the blood stream?
they are surrounded by a capsule that enhances the organism’s ability to withstand complement mediated killing in the blood streaam
what do meningicocci shed?
lipopolysaccharides, which reduce the release of tumor necrosis factor in the blood and CSF
what is the main group of gram negative cocci?
neisseria
what are facultative anaerobes?
use nitrites as electron acceptors and grow anaerbically
which gonoccocus produces a respiratory disease
Moraxella catarrhalis
true or false
humans are the only resevoir for gonococcus
true
what would you need for gonococcus culture?
boiled blood
iron
vitamins
carbon dioxide
what factors aid gonococcus in attachment
pili
surface proteins
lipooligosaccharides
what is phase variation
genetic mechanism that enables bacteria to express or unexpress their surface adherence components/antigenic variation
what is the difference between pili and opa in gonococcus
Pili and colony opacity-associated proteins (Opa) are surface-exposed structures of Neisseria gonorrhoeae. Pili can extend several micrometers from the gonococcal cell surface, while Opa proteins are integral parts of the outer membrane.
how is pili of significance to gonococcus
Pili are inhibitory to phagocytosis of gonococci by polymorphonuclear cells
why do gonococcus invade non ciliated epithelial mucosa of the fallopian tubes
because non ciliated epithelia possess microvili which aids in attachment, ciliary stasis, internalization, intracellular replication leading to exocytosis of dead cell
what is gonorrhoea genital mucosal secretions composed of
- IgG → leakage of antibodies from serum to mucos surface
- IgA 1 / IgA 2 → help Neisseria evade opsonization not only by eliminating the presence of Fc fragments of IgA1 already bound but also by reducing the neutralizing ability of IgA1 antibodies by reducing their binding avidity.
which molecule in gonococcus kills ciliated cells of fallopian tubes
lipopolysaccharides
how is gonococcus internalized in the fallopian tubes?
microvili and nonciliated cells engulf bacteria by parasite directed endocytosis
why is it that gonorrhea is often asymptomatic in women, but symptomatic in men
cervical cells have a pilus-mediated association with complement receptor 3 (CR3) which invades events that lead to epithelial colonization, contrarily, male urethra does not have pilus associated defence, thus it can be inflammatory
what cells of the immune system kill gonorrhea and how?
complement → activating cr3
IgG/IgM antibodies → attack LOS of gonorrhea
how does gonococcus become resistant
when LOS is altered by addition of terminal sialic acid molecule on short core carbohydrate chain causing the microorganism to camoflage and protect itself from serum
