Microbiology Flashcards
what is s. aureus an example of
a classic pathogen
what does s. aureus cause
oral diseases such as angular cheilitis, mucositis and bone infection
what is angular cheilitis
inflammation of the corners of the mouth
what is the pathway following suspected infection of s. aureus causing angular cheilitis
- sample with a sterile swab moistened with sterile water
- rub swab on blood agar
- incubate the bacteria at an appropriate temperature
- look at the colony morphology to identify s. aureus
- can then do a gram stain, and look at the clumping factor detection
how does s. aureus appear on gram stains
as black dots, resembling very closely to a bunch of grapes
what does s. aureus contain that allows it to clump in serum
coagulase positive virulence factor
what is an example of non selective agar
blood agar
what are the benefits of using blood agar
grows everything on the sample, which can give a good overal impression of the bacteria
what are the negatives of using blood agar
grows everything which can make it difficult to pick out pathogens of interest
what is an example of selective agar - in the context of s. aureus
mannitol salt agar
what do the elements of mannitol salt agar involve
the mannitol is a sugar that when fermented changes pH and can indicate the presence of s. aureus. the salt inhibits the growth of lots of different types of bacteria while still allowing s. aureus to grow if you play around with the concentration.
how is s. aureus characterised
its clumpy grape gram stain appearance
what is the process of testing the presence of s. aureus in a sample on mannitol salt agar
- the salt suppresses the growth of other bacteria beside s. aureus
- s. aureus ferments mannitol, which lowers the pH within the agar, making it acidic
- the pH indicator in the mannitol salt agar changes the colour of the agar from pink to yellow
what other species of staph are there
s. epidermis
how can you differentiate between s. aureus and s. epidermis.
s. epidermis does not ferment mannitol and therefore will not change the colour of the agar. s. epidermis also lacks the coagulent factor and will not clump in serum, whereas the s. aureus will.
how can colony morphology aid in the identification of s. aureus
when s. aureus is present it has a round, convex shape and can also be characterised by its size and sharp odor
what is found on the cell wall of s. aureus
clumping factor and protein A
break down the name of s. aureus
staphyloccocus aureus
- staphyl is the genus, and is related to the grape shape it adopts on gram stains
- coccus is related to the round shape
- aureus is related to the gold colour on blood agar
is s. epidermis coagulase negative or coagulase positive
coagulase negative
what is another antimicrobial testing method that can be used to identify presence of s. aureus
minimum inhibitory concentration
what is minimum inhibitory concentration
measures how much antibiotic is required to inhibit the bacteria - helps with prescribing
what does minimum inhibitory concentration highlight the importance of
taking specimens for identification and susceptibility training
what is present in mannitol salt agar that presents a colour change
pH indicator
what changes the pH in mannitol salt agar
the fermentation of the mannitol by the s. aureus
what is a bacterial endotoxin
toxic substances bound to the bacterial cell wall that are released when the bacterium ruptures or disintegrates
how do prions lead to a spongiform appearance in the affected brain
they affect signalling processes, damaging neurons and leading to the spongiform
what is spongiform encephalopathy
- spongiform = sponge like. brain tissue degenerates, where the healthy tissue become cysts and the brain looks like a sponge.
- encephalo (brain) pathy (disease process) - cause is the accumulation of misfolded proteins called prions
what are prions
misfolded proteins
what does fomite mean
objects or materials which are likely to carry infection, such as clothes, utensils, and furniture
what does SICP stand for
standard infection control precautions
what is the ecological plaque hypothesis used to explain
the disease process for caries and periodontal disease
what is the ecological plaque hypothesis
a theory that dental plaque induced diseases are not caused by specific species, but by changes in the environment that lead to an imbalance in the normal oral microflora
break down the ecological plaque hypothesis
- stress such as increased sugar intake leads to increased acid production
- this leads to an environmental shift, where the neutral pH falls to a lower pH level
- this changes the ecological environment, which leads to disease, like caries
what does the understanding of the difference between host and bacterial cells also help with
insight into disease diagnosis and treatment
what are the key anatomical elements to bacterial cells
- outer capsule and protective layers
- other bacterial components
- genome, which is a circular strand of DNA
what are examples of virulence factors
fimbriae, pili, fibrillae, and colonisation factors
what is virulence
the severity or harmfulness of a disease
what contributes to how harmful a disease is
adhesion and antiphagocytics
what are the first steps in pathogenesis
exposure and adhesion
what is an adhesin
a protein or glycoprotein found on the surface of a pathogen that attaches to receptors on the host cell
what pathogen causes dental caries
streptococcus mutans
what is the adhesin of s. mutans
adhesin p1
where does adhesin p1 attach to
teeth
what is chemotaxis
the movement of an organism or entity in response to chemical stimulus
what does aerobic bacteria require
oxygen
what does capnophilic bacteria require
carbon dioxide
what does facultative bacteria require
with and without oxygen
what does anaerobic bacteria require
no oxygen
what does microaerophilic bacteria require
small amounts of oxygen
how do bacteria grow
binary fission
what does binary fission describe
the way in which bacteria grow
what is another way of describing the way in which bacteria grow
exponential growth
what illustrates binary fission of bacteria
cell number growth curves
what are the different phases of a growth curve of bacteria
- lag phase
- exponential growth phase
- stationary phase
- death curve
what occurs in the lag phase
the bacteria are inoculated into a system, and the bacteria acclimatise to their new surroundings
what occurs in the exponential growth phase
binary fission - rapid reproduction of bacteria
when is it thought that exponential growth occurs in the body
during infection
what is the stationary phase
this is when production is equal to death
what is the death curve
this is when the bacteria death rate is greater than bacterial reproduction
what is managing infection about in regards to the cell number growth curve
discourgaing the growth phase and encouraging the death curve
what is the purpose of a gram stain
visualising bacteria
why do we not just use a microscope to visualise bacteria
the bacteria are too thin and the light will shine right through them
why can gram stains be used if someone is infected
if you look at the specimen using special stains under the microscope to visualise the bacteria, you can then make a judgement call on the best antibiotic to use for treatment
what are the different classifications of bacteria in gram stains
gram positive and gram negative
what is within the cell wall material of gram positive cells that allows the crystal violet dye to stick
peptidoglycan
how are bacteria classified as being either gram positive or gram negative
based on the difference in the structure of their peptidoglycan cell wall
what is the main role of peptidoglycan
gives strength to the outer structure of the organism
how is peptidoglycan vital for binary fission
when the bacteria divide themselves into two, the peptidoglycan in the cell wall must grow as the bacterium elongates before dividing. and then when it has split, the cell wall must reform so the two new cells are both enclosed
what is the series of events of using a gram stain to visualise bacteria
- specimen added to film
- chemical called crystal violet is added to film
- all cells take up the dye
- flood film with lugols iodine
- all cells appear blue black
- decolourise with acetone
- gram pos cells retain dye complex
- gram neg cells are decolourised
- counterstain with a red dye
- gram pos appear blue black
- gram neg appear red
how do penicillin binding proteins link to the importance of peptidoglycan and gram positive cells
PBP are enzymes involved in the cross linking of the peptidoglycan layer of the cell wall
how do penicillin binding proteins link with antibiotics
they are targets for penicillin based antibiotics and stop further linking of peptidoglycan side chains
what are exotoxins
toxins secreted by bacteria. they are produced by both gram pos and gram neg bacteria
what exotoxin is produced by clumps of s. aureus
panton valentine leukocidin - kills white blood cells
what do high concentrations of panton valentine leukocidin cause
pmn lysis
what does pmn lysis mean
polymophonuclear leukocytes are phagocytes that consume s. aureus, but some s. aureus strains are able to cause lysis of these cells after being consumed
what is the issue with PMN lysis
causes an inflammatory response and eventually tissue necrosis (cell death)
what is an example of an endotoxin
lipopolysaccharides
what are lipopolysaccharides
large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. they are potent biochemical molecules
what is the clinical relevance of endotoxins
they cause localised disease like chronic periodontitis and can trigger sepsis
what does cocci mean
round shaped
what does bacilli mean
rod shaped
why are spiral forms of bacteria of dental relevance
cause acute ulcerative gingivitis
why are spiral forms of bacteria difficult to visualise using conventional gram staining
they have very thin cell walls
what kind of bacteria is an exception to gram stains
mycobacteria - they have a thick, waxy cell wall whcih makes gram stains difficult to penetrate
how can mycobacteria be visualised
using fluorescent microscopy
what is a clinical example of mycobacteria
the mycobacteria abscessus infection that had an outbreak in georgie in a dental practice to children who had a pulpotomy. it was caused by contaminated water being used during the pulpotomies
what is m. abscessus
a rapidly growing, non tuberculosis mycobacterium found in the environment in water, soil and dust
what is an example of a gram positive cocci bacteria
streptococcus mutans, which occur in chains and cause dental caries
what is an example of a gram positive bacilli bacteria
clostridium tetani which has a rice shape and causes spinal contraction
what is an example of a gram negative cocci bacteria
diplococci antiphagocytic such as neisseria meningitidis which causes meningitis
what is an example of a gram negative bacilli
prevotella intermedia which causes periodontal disease - black pigmented anaerobic rods
what is an endotoxin
a toxin present inside a bacterial cell wall that is released wehn the bacteria disintegrates
where are the lipopolysaccharides
the outer membrane of gram negative bacteria
what do endotoxin lipopolysaccharides cause
fever, inflammation and septic shock
which type of bacterial cells are endotoxins found in
only gram negative bacteria
why are endotoxins found only in gram negative bacteria
gram positive bacteria lack an outer membrane so they cannot produce endotoxins
what is the key difference between endotoxins and exotoxins
endo are released when the cell dies, exo are released while the cell still lives
what is an exotoxin
a toxin released by a living bacterial cell
what is an example of an exotoxin
panton valentine leukocydin, which is released from s. aureus
what does PVL do
causes lysis of the white blood cells neutrophil polymorphonuclear cells. some strains of s. aureus have the enhanced ability to cause PMN lysis after phagocytosis
what is the cell wall of gram positive cells like
a thick peptidoglycan cell wall containing teichoic acid
what is the cell wall of gram negative bacteria like
a thin peptidoglycan cell wall with no teichoic acid
what is teichoic acid
a polymer of ribitol or glycerol phosphate
what is a major difference in the cell walls of gram positive cells and gram negative cells
gram positive cells do not have an outer membrane and therefore lack the endotoxin lipopolysaccharide
what colour do gram positive cells go in a gram stain
purple
what colour do gram negative cells go in a gram stain
red
why do gram stains differ depending on gram positive and gram negative bacteria
gram positive bacteria have a single thick layer of peptidoglycan above their plasma membrane that can retain the dye.
gram negative bacteria have a thin layer of peptidoglycan sandwhiched between the surface membrane and the plasma membrane so it cannot retain the dye
what structural properties do bacteria have that aid them in moving and attaching to other cells
pili and fimbriae which are hairlike structures that allow them to attach to the other cells.
flagella are whip like processes that allow them to move
what are the functions of the bacterial plasma membrane
- acquire nutrients
- eliminate waste
- maintain a constant, organised state
what does pleomorphic mean
there are multiple layers
what are the functions of the cell wall of bacteria
protect the bacteria and maintain the shape
what are some bacteria also surrounded by
a capsule that acts as a shield, and protects the bacteria against phagocytosis, and helps to adhere to surfaces.
what are the different shapes of bacteria
cocci is round shaped
bacili is rod shaped
spirilla is spiral shaped
