2. Introduction To Microbes Flashcards
What are the microorganisms that cause human disease in order of increasing size?
– Viruses
– Bacteria
– Fungi
– Parasites
What is the structure of viruses?
- nucleic acid (DNA or RNA, double or single stranded)
- protein coat
- lipid envelope
- attachment proteins
Give an example of a single stranded, non-enveloped DNA virus?
Parvovirus 19
Give 4 examples of a double stranded, non-enveloped DNA virus
- Adenovirus
- BK virus
- Human papilloma virus
- JC virus
Give 4 examples of Double-stranded, Enveloped DNA viruses
• Herpes viruses
- cold sores (human herpes simplex type 1)
- chicken pox
- epstein barr virus
- Hepatitis B
- Molluscum
- contagiosum
What are the 4 types of RNA viruses?
- Single-stranded, positive strand, icosahedral, non-enveloped
- Single-stranded, positive strand, icosahedral or helical, enveloped
- Single-stranded, negative strand, helical, enveloped
- Double stranded, icosahedral, non-enveloped
What are bacteriophages?
Viruses that invade bacteria
How can we use bacteriophages?
Can be used to treat bacterial infections
How are DNA viruses classified?
- Single stranded non-enveloped DNA virus
- Double stranded non-enveloped DNA virus
- Double-stranded enveloped DNA virus
Examples of single stranded, positive strand, icosahedral, non-enveloped RNA viruses?
Coxsackievirus Echovirus Enterovirus Hep A,E Norovirus
Examples of ss, positive strand, icosahedral or helical, enveloped RNA viruses?
HIV Hep C Rubella Encephalitis viruses Yellow fever West Nile
Examples of ss, negative strand, helical, enveloped RNA viruses?
Ebola Lassa Marburg Measles Mumps Influenza Parainfluenza Respiratory syncytial virus
Example of double stranded icosahedral, non enveloped RNA virus?
Rotavirus
What are the main common features in the structure of bacteria
- circular DNA
- no nuclear membrane around DNA
- transmissible circular plasmids (contains genes for virulence factors and resistance)
- plasma membrane
- cell wall
- capsule
- pili
- flagellum
What are the 3 main bacteria shapes
- Coccus/cocci
- Bacillus/ rods
- Spirillus
What are the two different types of bacteria?
Eubacteria and Archaebacteria
What is the main type of bacteria that is seen clinically?
Eubacteria
What are the 2 arrangements of cocci
Cluster (staphylococcus)
Chains (streptococcus)
What can plasmids carry?
Antibiotic resistance genes - worrying as plasmids can be transferred from bacteria to bacteria
Can carry multiple antibiotic resistance genes for a wide range of antibiotics
Define PDR?
Pan drug resistant (bacteria)
How does HIV increase your susceptibility to TB?
Weakens your immune system
Differentiate between gram positive and gram negative bacteria
• Gram-positive bacteria are bacteria that give a positive result in the Gram stain test whilst gram negative bacteria give a negative result.
These 2 bacterial groups have different cellular structures:
• Whilst they each have a plasma membrane, periplasmic space and a peptidoglycan layer; the gram negative bacteria also has an extra outer membrane (lipopolysaccharide and protein) layer. The two membranes( plasma membrane and lipopolysaccaride outer membrane) are separated by the periplasmic
space, which contains the peptidoglycan layer in the middle. in contrast to gram-positive cells, the peptidoglycan layer is thin and the cells are therefore more susceptible to damage
• Gram-positive bacteria have thick, multi-layered, peptidoglycan cell walls that are exterior to the cytoplasmic membrane .
what colour are the gram positive and negative bacteria on the gram stain?
Gram positive bacteria stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells are stained with.
Alternatively, Gram negative bacteria stain red, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decoloring process.
What is gram staining?
Gram staining is a common technique used to differentiate two large groups of bacteria based on their different cell wall constituents.
What are aerobes?
This refers to any bacteria that can survive in the presence of oxygen.
There are obligate aerobes that need oxygen for survival
What are Anaerobes?
This refers to bacteria that can survive in the absence of
oxygen
what are Obligate anaerobes?
require an oxygen-free environment for survival (unless they’re able to form spores) and are poisoned by oxygen.
How do obligate anaerobes survive?
In order to allow their survival in our oxygen rich environment they have to move about in spores.
Describe the use of the capsule around bacteria
- Sticky, viscous to allow cells to adhere to surfaces
- Protects bacteria from antibodies and phagocytosis
- Act as diffusion barriers against some antibiotics
- Protect against desiccation or drying
List the 4 main encapsulated bacteria
Neisseria meningitidis (meningococcus)
Hemophilus influenzae type b (Hib)
Streptococcus pneumoniae (pneumococcus)
Group B streptococcus (GBS)
Which organ is important in recognising encapsulated bacteria?
The spleen is especially important in recognising these bacteria and dealing with them. If a patient does not have a spleen then they are at an increased risk of infections from these bacteria. Such patients will commonly need to be immunised against these bacteria and/or receive prophylactic antibiotics.
How are bacteria, fungi and parasites named?
- Genus + species (Surname(capital) then first name(lower case))
- —> Linnaean taxonomy
- E.g. Staphylococcus aureus
- Some are supplemented by adjectives describing growth, typing or antimicrobial susceptibility characteristics
- E.g. E. coli 0157 and MRSA (meticillin resistant Staph aureus)
What do cell walls of prokaryotes contain?
peptidoglycan
What is present in eukaryote plasma membranes that is lacking in prokaryotes?
Sterols and carbohydrates
Give examples of gram positive cocci
Staph aureus Coagulase negative staph Alpha-haemolytic streptococci Beta-haemolytic streptococci including Strep pyogenes Streptococcus pneumoniae Enterococcus faecalis
Give examples of gram positive bacilli
Listeria monocytogenes
Bacillus anthracis
Bacillus cereus
Give examples of gram negative cocci
Neisseria meningitidis
Neisseria gonorrhoeae
Moraxella catarrhalis
Acinetobacter baumannii
Give examples of gram negative bacilli
Escherichia coli Klebsiella pneumoniae Proteus species Salmonella typhi Pseudomonas aeruginosa Haemophilus influenzae
What are 2 mechanisms of bacterial pathogensis
• Virulence factors
– Host entry (e.g. polysaccharide capsule
– Adherence to host cells (e.g. pili and fimbriae)
– Invasiveness (e.g. enzymes such as collagenase)
– Iron sequestration (siderophores)
• Toxins
– Exotoxins (e.g.diphtheria toxin)
– Endotoxins (lipopolysaccharide)
Give the 2 different types of fungi and attach examples of each
• Yeasts (single-celled)
- Candida albicans
- Cryptococcus neoformans
- Pneumocystis jiroveci
• Molds (multicellular)
- Aspergillus species
- Dermatophytes (ringworm, athlete’s foot)
Skin fungi
Give the 2 different types of parasites and attach examples of each
• Protozoa (single-celled)
- Giardia lamblia
- Cryptosporidium parvum
- Plasmodium falciparum
- Trypanosoma cruzi
• Helminths (worms, multi-cellular)
- Roundworms (e.g Enterobius vermicularis)
- Tapeworms (e.g. Taenia saginata)
- Flukes (e.g. Schistosoma mansoni)/ can cause bloody urine
What is agar and what properties does it have?
Polysaccharide derived from seaweed
Melts when heated to around 85 degrees, but when cooled it does not solidify to gel until 34-42 degrees
Clearer than gelatin and resists digestion by bacterial enzymes
Allows the creation of a medium that can be inoculated at 40 degrees in its cooled molten state yet incubated at 60 degrees without melting
What do agar plates contain?
Proteins, sodium chloride, red due to the addition of blood
What type of bacteria will only grow if blood cells in the medium have been lysed to release their extracellular nutrients?
Haemophilus influenza - lysed blood is a darker brown colour and is called chocolate agar
What does the cell envelope of bacteria contain?
Cell wall
Cytoplasmic membrane
Capsule/ glycocalyx
What is the difference between a capsule and a glycocalyx?
If the material is tightly bound to the cell and has an organised structure it is a capsule
If the material is loosely bound and amorphous, it is called a slime layer/ glycocalyx
What are the two types of appendages bacteria can have?
Flagella and pili
What are flagella?
- Long, semirigid, helical, hollow tubular structures composed of several thousand molecules of the protein flagellin
- Allow movement
- Anchored in the cell membranes by a basal body which rotates the flagellum
- Highly antigenic
How do bacteria with flagella act on an agar surface?
Do not form compact colonies but instead swarm over the surface if it is wet enough to produce a scumlike mat
What are pili?
- Shorter and thinner than flagella
- Attachment structures that promote specific cell to cell contact between bacteria cell and another bacteria cell/ the host cell
How does a gram stain work?
If a specimen is treated with a solution of crystal violet and then iodine, the bacterial cells will stain purple
If the stained cells are treated with a solvent e.g. alcohol, gram-positive organisms retain the stain whereas gram-negative species lose the stain to become colourless
Addition of the counter stain safranin stains the clear gram-negative bacteria pink/red
Need a lot of microorganisms
How do fungi reproduce?
sexually and asexually
Do viruses have a cell wall?
No, they contain a protein coat surrounding nucleic acid
Where do viruses reproduce?
Contain the genetic information needed to direct their own replication but require the host cells cellular structures and enzymes to do this
How does antibiotic resistance occur?
1) high number of bacteria and a few of them are resistant to antibiotics
2) antibiotics kill bacteria causing the illness, as well as good bacteria protecting the body from infection
3) the resistant bacteria now have preferred conditions to grow and take over
4) bacteria can even transfer their drug-resistance to other bacteria causing more problems
Why is antibiotic resistance a problem?
- Genetic mutations make some bacteria naturally resistant to an antibiotic.
- If the bacteria can survive, its more likely to reproduce and cause more infection.
- Can lead to the antibiotic resistant allele to be passed onto offspring (natural selection).
symptoms of influenza? What is its exposure?
chills, fever, headache, muscle aches, cough, swollen throat, runny nose, vomiting, diarrhoea
Person to person - droplets
Symptoms of chickenpox and what is its exposure?
Itchy, rash, small fluid filled blisters
Inhalation - aerosol
Symptoms of MRSA and what is its exposure?
Red swollen skin, slow healing wounds, boils/pus filled abscesses, fever, tiredness, headache
Direct contact
Define prions
Proteinaceous infectious particles
Self replicating - but no nucleic acid
How features of prions make they similar to microorganisms?
Have element of infectious behaviour:
- replicate (cause misfolding of normal proteins)
- transmissible (development of CJD after neurosurgery due to contamination by prions of medical tools)
What are obligate intracellular parasites?
Cannot reproduce outside their host cell, meaning that the parasite’s reproduction is entirely reliant on intracellular resources.
e.g. viruses, some bacteria (chlamydia), fungi and protozoa
Take over host cells metabolic machinery allowing it reproduce.
What is one structural difference between obligate intracellular bacteria and normal bacteria? give examples of OIB.
Obligate intracellular bacteria are smaller in size compared to other bacteria.
e.g. chlamydia, mycoplasma, rickettsiae.
Order microorganisms from smallest to largest.
prions < proteins < viruses < OIB < mitochondria < bacteria < eukaryotic cells (yeast, protozoa, human cells) < worms
Why is it difficult to produce anti fungal drugs?
Fungi are eukaryotes like humans
- similar biological and physiological processes
What is the difference between enveloped and non-enveloped viruses?
Enveloped viruses have lipid bilayer around the virus, whereas non-enveloped do not.
- enveloped viruses are relatively easier to kill.
What is the cell wall in bacteria made of and what is its function?
Peptidoglycan layer (cross-linked polymeric mesh)
The molecular structure of this layer helps render the bacterial wall resistant to host peptidases such as those in the intestine. This helps the bacteria survive in a hostile environment.
What is the capsule in bacteria made of and what is its function?
Usually a polysaccharide.
Allows cells to adhere to surfaces, protect bacteria from antibodies and phagocytosis, and act as diffusion barriers against some antibiotics, thus contributing to the organisms’ pathogenicity. Capsules can also protect bacteria against desiccation, or drying, which facilitates transmission.
How can the outer cytoplasmic membrane in bacteria be identified?
The outer membrane is distinguished by the presence of embedded lipopolysaccharide (LPS) The polysaccharide portion of LPS (O polysaccharide) is antigenic and can, therefore, be used to identify different strains and species. The lipid portion (called lipid A) is embedded in the membrane and is toxic to humans. Because lipid A is an integral part of the membrane, it is called endotoxin.
