Introduction to microbiology: Bacteria Flashcards
List the subjects of microbiology
- bacteria
- viruses
- fungi
- Protozoa
Define microbiology
The study of organisms and agents too small to be seen by the unaided eye ie microorganisms
List some applications of microbiology
- food industry
- agriculture
- medicine
What type of microbiology are light microscopes able to see
Bacteria
What type of microscopes are able to see viruses
Electron microscopes
What scale of microorganisms are harmful
Small amount
How large are viruses
10-1000 nanometers (smallest)
What size are bacteria
0.1-5 micrometers
What size are Protozoa
5-200 micrometers (largest 1/4 of a mm)
What is the name of the virus which causes flu
Influenza A
What is the name of the bacteria which is a normal skin resident found throughout the body
Staph aureus
Which microorganism can cause MRSA
Staphylococcus aureus
What does MRSA stand for
Methicillin resistant staphylococcus aureus
What is the name of the antibiotic that MRSA is resistant to
Methicillin
Which bacteria is the most common cause of bacterial conjunctivitis
Staphylococcus aureus
What type of organism is acanthamoeba
Water Bourne organism
What is acanthamoeba found in
Domestic water supplies in the UK
What can acanthamoeba cause
Corneal infection of contact lens wearers who wash their contact lenses in tap water
What two things do infectious diseases cause
- morbidity
- mortality
What does morbidity cause
Harm & disease
What are infectious diseases caused by
Pathogenic microorganisms such as bacteria, viruses, parasites or fungi
Which two ways can the diseases be spread by from person to person
Directly or indirectly
Which infectious disease is the biggest killer
Acute respiratory infection
How much amount of deaths do infectious diseases cause worldwide and are leading cause of death
One-third
Why are one third of all deaths caused by infections
Because of disease in developing countries
How much percent of deaths are from infectious diseases caused by a handful of diseases
90%
Name a viral ocular infection
Herpes simplex keratitis
Name a bacterial ocular infection
Bacterial keratitis
Name a chlamydial ocular infection
Trachoma
Name a protazoal ocular infection
Acanthamoeba keratitis
Name a fungal ocular infection
Fungal keratitis
Which is the same virus which causes cold sores
Herpes simplex
What is the meaning of keratitis
Inflammation of the cornea caused by a virus
What type of ulcer does herpes simplex keratitis cause on the cornea
Dendritic (multiple branching pattern)
Which type of patients is bacterial keratitis more common in
Contact lens wearers (90% who got the infection wear cl’s)
Which part of the eye does the chlamydial infection trachoma affect
Conjunctiva
It is a conjunctival infection
What can trachoma be treated with
Antibiotics
What does a chlamydial infection do to the eye to cause corneal scarring
Turns eyelashes towards the eye
And produces a poor ocular surface
What is the treatment following the protazoal infection, acanthamoeba keratitis
Corneal graft due to the scarring
What infection causes a corneal inflammation by a fungus
Fungal keratitis
What are the two ways of fighting infection
- vaccination
- antibiotics
What do the majority of present day vaccination programmes use and why
Active vaccines containing pathogen-specific antigens to elicit a protective immune response in the recipient
What effect does repeated vaccination have
Enhances the effectiveness of the antibody response and for some vaccines
It also elicits cell mediated responses
Which infections were a major killer before there was vaccination
Measles
Mumps
Reubella
What vaccine was a combined vaccine for measles, mumps and reubella
MMR vaccine
During which period did antibiotics come about
1940’s
What microorganism is antibiotics useful for and hopeless against
Useful for bacteria
& hopeless against viruses
How do antibiotics cure diseases
By killing or interfering with the growth of bacteria
How are antibiotics non toxic compounds
They have selective toxicity because bacteria synthesise their DNA differently to body cells
What are narrow spectrum antibiotics
Antibiotics which selectively act on a few specific bacteria
What are broad spectrum antibiotics
Antibiotics which target a wider range of bacteria
What do bacteria synthesis differently to normal human (eukaryotic) cells
DNA & protein
What does a bacteria cell have in addition to a cell wall
A cell membrane
How does antibiotic resistance arise
By the drug killing the defenceless bacteria and selecting those that can resist it
When was resistance to penicillin identified and how long was that after the mass production
1943
4 years after mass production
What is the term superbug often used to refer to
Healthcare associated infections eg
- methicillin resistant staphylococcus aureus (MRSA)
&
- clostridium difficile (c.difficile)
Are resistant to commonly used antibiotics
What is clostridium difficile
A gut organism
Is usually a small amount but can cause death
What is an epidemic most commonly used to describe
An outbreak of an illness or disease in which the number of individual cases exceeds the usual or expected number of cases in any given population
What is a pandemic describe
An epidemic which occurs in more than one country or population simultaneously
Give an example of a disease which has reached pandemic proportions
AIDS/HIV virus
when did AIDS begin
early 1980’s
when was AIDS identified around
1984
when was an anti body for AIDS found to test for the disease
1986
where in the world is AIDS most common
africa 5% so 1 in 20 people in Africa had AIDS
what is a pathogen
a disease causing organism
with what cells are there more of bacteria compared to
human cells
how many types of species of bacteria are there on the body
800
what are commensals
microorganisms that derive benefit from the host and in turn protect the body from the disease (limit the growth of harmful disease)
how many % of organisms are commensals in the body
90%
state the order of which microorganisms are pathogenic and non pathogenic
- very few microbes are always pathogenic (e.g. bacteria which causes TB)
- many microbes are potentially pathogenic (in particular circumstances)
- most microbes are never pathogenic (won’t cause disease)
what are bacteria usually classified according to
- morphological appearance (size and shape)
- staining characteristics
- growth requirements
recent developments have established a - genotype classification (genetic makeup)
list the three types of shapes of bacteria
- cocci, diplococci
- bacilli, coccobacilli
- spirochetes
which shape of bacteria are round
cocci & diplococci
what is the difference between cocci and diplococci bacteria
cocci are individual round shapes and diplococci are pairs of round shape bacteria cells
which shape of bacteria are rod-shaped
bacilli
what is the difference between bacilli and coccobacilli
bacilli are rod shaped and coccobacilli are more oval shaped (in-between rod and round)
which shape of bacteria are spiral
spirochetes
what do bacteria cells lack
a membrane bound nucleus
&
sub-cellualar organelles
what are prokaryotes
a cell with a nucleus what doesn’t have a nuclear membrane but does have DNA loose within the cytoplasm
eg bacteria
how is the DNA organised in a bacteria cell
as a fibrous mass in the cytoplasm
what type of ribosome does a bacteria prokaryotic cell have
70s
consisting of 30s and 50s sub-units
what type of ribosomes does a eukaryotic cell have
80s
which ribosomes protein synthesis does the antibiotic inhibit
70s
what does a bacteria cell envelope consist of
a plasma membrane and a cell wall
what does the bacteria plasma membrane and cell wall contain
a special polymer called peptidogylcan
what is a peptidoglycan
a repeating disaccaride unit which produces the cell wass
what do some bacteria which have inclusion bodies act as
an energy store
what are two sub-divisions of bacteria distinguished according to
their ability to retain a crystal violet iodine dye complex
describe the method of using a gram stain on bacteria
- place bacteria on a slide
- air dry it at room temperature
- stain the slide with crystal violet
- treat the slide with iodine
- decolourise with ethanol
what do the different staining characteristics of bacteria by crystal violet iodine dye complex relate to
differences in the cell wall
what is a bacteria which has retained the dye after ethanol has been placed on it called
gram positive
what is a bacteria which has decolourised after ethanol has been placed on it
gram negative
how to gram positive bacteria retain the gram stain
as it becomes incorporated in the thick peptidoglycan layer that surrounds the organism
what type of peptidoglycan layer do gram negative organisms have
a reduced/thin peptidoglycan layer
what do peptidoglycan consist of a backbone of
alternating units of:
- N-acetyl glucosamine (NAG)
&
- N-acetyl muramic acid (NAM)
what type of compounds are N-acetyl glucosamine (NAG & N-acetyl muramic acid (NAM)
disaccharides assembled together which form two repeating sugar proteins
what are gram positive bacteria further characterised by with the presence of
teichoic & teichuronic acids bonded to the peptidoglycan layer
what is a major component of the outer membrane of gram negative bacteria
lipopolysaccharide (incorporating lipid A endotoxin)
what do certain gram positive and gram negative bacteria have and what is it for
a capsule external to the cell wall
this protects the bacterium and may confer resistance to intracellular killing by phagocytosis (protective capsule is resistance to phagocytosis)
what is present on a bacterial cell which allows for locomotion (move around in fluid)
flagella
what may gram negative organisms be covered in and why
fine hairs called fimbriae
which mediates attachment to the host
what component of a bacterium cell can attach bacterial cells and for what reason
pili
to attach bacterial cells together or/and to transfer genetic information which can be associated with resistance (sex pili)
what can almost all bacteria survive on and why
simple organic compounds e.g. glucose
because they need little nutrients in order to survive (they have a simple metabolism)
which ways are energy production achieved for bacteria
- glycolysis
- TCA cycle
- oxidative phosphorylation
what is the alternative pathway which can be used to produce energy for bacteria
pentose phosphate pathway
in which conditions can facultative organisms live in and what does this determine
aerobic
or
anaerobic conditions
determines if the bacteria either only uses glycolysis or glycolysis & krebs cycle
how are facultative organisms very adaptable
they can live with or without oxygen or it can even utilise oxygen
how does bacteria in the absence of oxygen (anaerobes), produce energy
the glycolytic pathway (fermentation yielding) which goes to pyruvate, which turns into lactate or ethanol
what do aerobes require
oxygen
where are bacterial genes located
both within the bacterial chromosomes and extrachromosomal plasmids
where are many antibiotic resistance genes located
on plasmids
what can the transfer of genetic information occur through
- transformation
- transduction
- conjugation
how does the transfer of genetic information occur via transformation
bacteria can take up the plasmid (simple loop of DNA) and they become incorporated
how does the transfer of genetic information occur via transduction
a phage (bacterial virus) is able to transfer genetic information from one bacterial cell on to another
how does the transfer of genetic information occur via conjugation
a pilus connects bacterial cells together & plasmids can transfer across the pilus
what are bacterial spores and what do they do
spores are highly resistant structures which are an inactive form of bacterial cells which will activate when they are ready, and a few bacteria have the ability to produce them.
spores resist a range of environments and protect against heat, radiation or desiccation
give some examples of spore forming bacteria
- clostridium tetani
& - bacillus anthracis
what spore does clostridium tetani produce
tetanus
what spore does bacillus anthracis produce
anthrax
what does the body act as a host to a large number of
microorganisms (commensals)
how do commensals protect against infection
by competing with potential pathogens for nutrients
or
preventing pathogens from colonising epithelial surfaces
what may trigger pathogenic damage and give an example
alterations in homeostasis.
eg a non harming staphylococcus aureus on the eyelid are harmless but if they go into the eye from a cataract surgery they can cause bad effects which can be sight threatening
name an example of a bacteria which is entirely adapted to the pathogenic way of life in humans and are never part of the normal flora
M. tuberculosis
what do some bacteria which are part of the normal flora acquire, and what do they make them, give an example
extra virulence factors making them pathogenic
eg S. epidermidis
what can many free-living bacteria and components of the normal flora cause in immunocompromised patients, and what if introduced to something particular, give an example
disease especially if introduced into deep tissues
eg acinetobacter
what does the virulence mean
degree of pathogenicity (ability to cause damage to our body cells)
what does virulence factors mean and give examples of what triggers this
factors that trigger pathology e.g.
- adherence
- invasion
- toxicity
name the steps of bacterial virulence factors
- exposure (first must be exposed to pathogens)
- adherence (bacterial cell must bind to skin or mucosa to cause harm)
- invasion (through epithelium, but is not always the case as sometimes through the toxins that those bacterial cells induce you can still have an external infection & harm comes from what bacterial cells are excreting)
- colonisation and growth (a direct damage to tissue = production of virulence factors)
can either go on to: - toxicity (toxic effects are local or systemic)
or - invasivness (further growth at original site and distant sites)
both cause tissue damage & disease
explain how bacterial cells cause harm in blepharitis
blepharitis has an infective component but the bacterial cells on the eyelash doesn’t cause the blepharitis, but the toxins they release does, which produces the harm
many bacteria synthesise toxins that serve as…
virulence factors, inducing damage to the host
what mechanisms do toxins cause damage by
- inhibiting protein synthesis
- damaging cell membranes
name the two types of bacterial toxins
- endotoxins
- exotoxins
how do endotoxins work
they are bound to the bacterial cell surface (become a component of the bacterial cell wall) and the toxin induces damage on contact
the do exotoxins work
they are excreted or released onto surrounding tissues during bacterial lysis
list the pathogenic mechanisms of staphylococcus species
- protein A activates complement and induces inflammation (local inflammatory response) and inhibits opsonisation
- leukocidin (toxins) kills neutrophils (cells which protect us) and macrophages
- alpha toxin causes membrane damage to many types of cell
what do antimicrobial agents do
kill or inhibit bacterial growth by interfering with
- cell wall synthesis
- DNA synthesis
- protein synthesis
- folic acid metabolism
which antimicrobial agent kills bacterial growth by interfering with protein synthesis
chloramphenicol
which antimicrobial agent kills bacterial growth by interfering with cell wall synthesis
penecillin
when do we test for antibiotic susceptibility
when broad spectrum anti biotic doesn’t work
what is the most common test for antibiotic susceptibility in clinical laboratories
disk diffusion test (kirby-bauer)
how is the disk diffusion test carried out
- a bacterial isolate is inoculated uniformly onto the surface of an agar plate
- a filter disk is impregnated with a standard amount of antibiotic is applied to the surface of the plate
- the antibiotic is allowed to diffuse into the adjacent medium
how do we test for antibiotic susceptibility from disk diffusion test
- zones of inhibition of bacterial growth may be present around the antibiotic disk
- the size of the zone of inhibition is dependent on the degree of sensitivity of the bacterium to the antibiotic
