WEEK 1: MICROBIAL DIVERSITY AND PATHOGENESIS Flashcards
What 4 things does Archaea have in common with bacteria?
- Anucleate cells (Cells without nucleus)
- Cell envelope
- Generally has a single chromosome (but some exceptions)
- Varies in shape and size
What 3 things does Archaea have in common with eukaryotes?
- DNA replication, transcription and translation more like eukarya
- HISTONES in DNA
- Share similar enzymes in DNA replication of eukaryotes (DNA polymerase ,primase etc)
What process that contributes to the greenhouse gas effect are species of archae involved in?
- Methane production from Cows!
What are the 4 basic shapes of bacteria?
- Spherical (Cocci)
- Rod-shaped (Bacilli)
- Spiral (Spirochaete)
- Curved (Commas)
What is an example of a spiral shaped bacteria?
- Helicobacter pylori
What is an example of a curved shaped bacteria?
- Cholera
What are the 5 specialised structures of MOST (but not all) bacteria?
- Cell wall
- Outer membrane
- Capsule
- Flagella
- Endospores
Which part of the bacteria can contain the pathogenic aspect?
- The outer membrane
Which feature of bacteria determines the shape?
- The cell wall
In general, how thick is the gram positive layer of peptidoglycan?
- It is thick
- 20-80nm thickness
Which two secondary cell polymers are attached to the peptidoglycan in a gram positive bacteria?
- TEICHOIC ACID: Joined by phosphate groups
- LIPOTEICHOIC ACID: Extends to the surface of peptidoglycan
What charge does a gram positive bacteria cell wall possess?
- Negative charge
What is the peptidoglycan layer made up of?
- Peptido
- Glycan
What does Peptido in the peptidoglycan layer consist of?
- Four amino acids (tetrapeptides)
- Both D and L amino acids
What does the Glycan in the peptidoglycan layer consist of?
- TWO alternating sugars
- NAG (N-acetyl glucosamine)
- NAM (N-acetylmuramic acid)
Which molecule NAG and NAM similar to structurally?
- Glucose
Which type of amino acids are ONLY unique to the bacterial cell wall?
- The D amino acids
What are 6 functions of the cell wall in gram positive bacteria?
- Maintains SHAPE of bacteria
- Provides STRUCTURAL SUPPORT
- Contributes to PATHOGENICITY
- Site of action of some antibiotics
- Attachment
- Peptidoglycan provides RIGIDNESS to cell
How thin is the peptidoglycan sheet in gram negative bacteria?
- The thin sheet of peptidoglycan –> 1-3nm
What does the thin peptidoglycan layer in gram -ve bacteria do?
- Allows bacteria to have GREATER flexibility
- Makes it SENSITIVE TO LYSIS
How many periplasmic spaces are there in gram negatvie bacteria?
- 2!
What percentage of lipid makes up the OM of gram negative bacteria?
- 15%
What are 4 things that the OM in gram negative bacteria contains?
- Protein (porin peroteins)
- Lipoprotein (Brauns Lipoprotein)
- Phospholipid (membrane bilayer)
- LPS in uppermost layer
What are the two components of the LPS layer?
- Lipid A
- O specific Polysaccharide side chain –> O ANTIGEN
What does Lipid A function as in the LPS layer of gram negative bacteria?
- An endotoxin
- Released in salmonella to cause nasty immune responses
Which part of the LPS is used to evade immune defenses via antigenic variation?
- Glycan O antigen —> Molecular mimicary and evasion
What are 3 positive things that LPS does for BACTERIA?
- Helps with the structural integrity of OM and allows certain chemicals in (permeability)
- Increases the negative charge of cell membrane + stabilises the membrane structure
- ESSENTIAL FOR BACTERIAL SURVIVAL
What are examples of bacteria that COMPLETELY lack peptidoglycan?
- Chlamydiae (STI) and Planctomycetes
- Also intracellular parasites –> c.f. RIckettsia and Mycoplasma
- They maintain their shape despite having no peptidoglycan
- Stain gram negative
Are the bacteria that completely lack peptidoglycan sensitive to Penicillin and beta-lactam antibiotics?
- NO
- They are INSENSITIVE
What is an example of bacteria that naturally lack a cell wall and 3 features of them?
Mycoplasmataceae
- VERY SMALL (0.1-0.5 microm)
- Pleomorphic (Ability to alter shape and size) e.g. coccus, donut shaped, filamentous
- INSENSITIVE to Penicillins or other Beta lactams (because of no peptidoglycan)
What types of diseases can strains of Mycoplasmataceae cause?
- Pelvic inflammatory disease as some are sexually transmitted
- Cause atypical pneumonia in humans
What is the name for bacteria with a unique atypical outer membrane?
- Acid Fast Bacterial Cell Wall
What types of lipids are contained in the Acid Fast Bacterial Cell Wall?
- Mycolic acid (main one) or Cord Factor (found in Mycobacterium TB)
What does the waxy nature caused by the lipids of the Acid fast cell wall cause it to be?
- Hydrophobic
- Impenetrable to most organic molecules + antibiotics
- HIGH resistance to chemicals and dyes
Which component of the acid fast cell wall contributes to the pathogenicity? -
- The mycolic acid as it gives it the waxy component
Which 5 things does the bacterial cytoplasm comprise of?
- Cytosol
- Nucleoid–> Chromosome
- Ribosomes (cell wall production)
- Inclusion (endospores)
- Cytoskeletal components
Which type of bacterial ribosome does antibiotics target and why doesn’t it kill our own cells?
- Targets the 70S ribosomes to STOP protein synthesis
- Doesn’t kill our cells because they have 80S ribosomes
What sequence does the 16S rRNA bind to?
- The Shine-dalgano sequence
What is the 16S rRNA a component of and what is it the scaffold for?
- Component of the 30S ribosome unit in prokaryotes
- Scaffold for the protein component
Does the 16S rRNA have BOTH conserved and variable sections? **
- YES
Is the 16 rRNA conserved in bacteria?
- YES
If bacteria contains capsules are you supposed to heat fix when staining?
- NO!
- Could denature the protein layers (glycoprotein)
What do the bacterial capsules (glycocalyx) contain?
- Loose polysaccharide or protein layers on OUTER surface of cell wall of SOME bacteria whether they are gram +ve or -ve
What are 4 functions of bacterial capsules?
- Protects against dessication
- Prevents bacteriophages from attachment and infection
- Protects against phagocytosis
- Mediate bacterial attachment to solid surfaces
What do the capsules of Strep. Pneumoniae and Klebsiella pneumoniae cause?
- Prevent their destruction in the respiratory tract and cause pneumonia
Are uncapsulated strains of Step.Pneumoniae and Klebsiella pneumoniae pathogenic?
- NO
- Basis of vaccines
What are some characteristics of bacterial flagella?
- Long, whip like structures that extend beyond the surface of the bacterial cell
- Aid cell motility
What are 3 things things that flagella enable bacetria to do?
- Flee from harmful environments
- Move towards favorable environments
- Move bacteria forward or backward -depending on direction of flagella motor
What are pili/fimbriae (what are they composed of) and what are their functions?
- Hairlike structures on the outside of bacteria
- Smaller than flagella
- Higher number than flagella
- Composed of pilin (protein subunuits)
- AID IN BACTERIAL ADHESION AND IMPORTANT VIRULENCE FACTORS–> Sex pili (transfer of genetic material)
- also virulence factors to host cells –> E.coli
What are bacterial endospores?
- Dormant, tough, NON-REPRODUCTIVE structure in cytoplasm of certain bacteria (Bacillus and Clostridium)
How many bacterial cells does one spore give rise to?
- ONE!!!
What are bacterial spores resistant to?
- UV radiation
- Dessication
- Heat
- Freezing
- Chemical Disinfectants
When are spores produced?
- When environmental conditions become unfavorable
What is normal flora defined as?
- The mixture of microbes present on a healthy human
What is resident flora termed as?
- Organisms consistently found at a given site (normally) and are always present there
What is transient flora termed as?
- Not always present at a given site
In utero, are there microorganisms colonising the fetus’ skin?
- No that only happens after birth
- Different microflora based on type of birth
What are the two most common bacteria present in ALL humans?
- Staphylococcus epidermis
- Escherichia coli
What are 5 characteristics of the Staphylococcus genus?
- Gram Positive cocci
- Form IRREGULAR clusters-divide in multiple planes (grapes)
- NON-motile
- Facultative anaerobes (grow in presence OR absence of O2)
- Catalase positive
What does the presence of E.coli in the gut supress?
- Suppresses the growth of harmful bacteria
When can E.coli cause disease? (2 things)
- In debilitated and immunosuppressed people
- When GI barriers are violated
What bacteria is the most common cause of a UTI?
- E.coli
In a healthy human, are the internal tissues such as brain, CSF, blood, kidneys and liver?
- YES!
- But not in all cases
What is mutualism defined as and what is an example?
- Two independent organisms living together to theri MUTUAL BENEFIT
- e.g. E.coli in colon produces Vit K and some B vitamins
- bacteria break down WASTE
- BACTERIA benefit by having food supply and sheltered environment
What is commensalism defined as?
- Normal flora that NEITHER hurt, harm, nor benefit the carrying host
- e.g. normal flora (residents, commensals)
What is paratism defined as?
- Where one organism benefits at the EXPENSE of the other
What kind of relationship with us is normal flora considered to be? (2 types)
- Commensalistic or Mutualistic
When are normal flora considered to be in a parasitic relationship?
- When they cause infection
e. g. Opportunistic pathogens
e. g. E.coli, Strep pneumoniae, Candida albicans
What is the carrier defined as in terms of bacteria-human relationship?
- Infected individual who is not diseased (potential source of infection)
What are the two types of acute carrier and what is an explanation?
- Incubatory –> incubating the pathogen but not ill yet
- Convalescent–> Recovered but has LARGE NUMBERS OF PATHOGEN
What is a chronic carrier of a disease?
- Harbors pathogen for LONG PERIODS
- Multiplication and shedding occur at LOW levels
- Capable of transmitting infection
- SOMETIMES THERE IS ABSENCE OF SYMPTOMS OF DISEASE
What is an asymptomatic carrier defined as and what is an example?
- Harbors pathogen for LONG PERIODS
- Multiplication and shedding occur at LOW levels
- Capable of transmitting infection
- COMPLETE ABSENCE OF ANY SYMPTOMS OF DISEASE
e. g. Typhoid Mary
What is one thing that normal flora on the skin do?
- Produce FAs
What are 6 things that gut bacteria can do that is beneficial for us?
- Aid digestion (dietary fibre)
- Ferment unused energy substrates
- Produce bacteriocins and colicins (antibacterial) 3=
- Synthesize and excrete vitamins (B12)
- train immune system
- Boost immunity (antigenic stimulation by gut flora)
What is the role of vaginal lactobacilli and what kind of environment is it ?
- Acid envrionment suppresses growth of other bacterial inhabitants
- Thought to decrease thrush
What process do adults eliminate 3E13 microorganisms daily via?
- Peristalsis
What makes skin an inhospitable environment for some microorganisms?
- Slightly acidic pH
- HIGH CONCENTRATION of NaCl
- Lots of areas LOW INMOISTURE (a part from underarms where tinea fungus can grow)
Which inhibitory substances does skin contain?
- Lysozymes
- Cathelicidins
Where is the normal flora of the nose found?
- Just inside the nostrils
Which enzyme does nasal mucous contain?
- Lysozyme
What are the main bacteria found in the nose?
- Staphylococcus spp. (Epidermis and aureus)-main one
- Aerobic corynebacteria (DIPTHEROIDS)
- SMALL NUMBERS OF : Strep. pneumoniae, Neisseria meningitidis and haemophillus influenzae in NASOPHARYNX
Are there normally microbiota in the lower respiratory tract (trachea, bronchi, bronchioles and alveoli-lungs)?
- NO!!
- Cilia produce mucous which removes them
- Macrophages
Why is saliva not a good culture medium?
- Because it contains antibacterial substances like lyzozymes
What is Glycoxalyx?
- A glycoprotein and polysaccharide layer that covers surface of epithelial cells
What are two types of baceria that are acid tolerant and thus found in the stomach?
- Lactobacilli
- Streptococci
Which part of the small intestine contains the most bacterial numbers per gram which is indicated as moderate?
- The ileum
More similar to the colon microbiota as pH more alkaline
Which part of the gut contains the largest number of bacteria?
- The large intestine
Which class of bacteria predominates the oxygen depleted area in the large intestine?
- The anaerobes–> 95-99% (Bacteriodes) and facultative anaerboes (E.coli)
What is disease defined as?
- When the body no longer functions properly
- Due to genetic, metabolic, deficiency, or infection
What is infection defined as and what is the time frame?
- When bacteria or microorganisms penetrate the host defenses
- Invade tissues
- Multiply
- Time-frame is WEEKS e.g. Hepatitis- 14 days
What is intoxication and what is the timeframe?
- When the bacteria produce toxins due to food/chemicals present
- Can occur within 30mins-2hrs of consumption
What are pathogens defined as?
- MICROORGANISM WITH THE POTENTIAL TO CAUSE DISEASE
- Bacteria that are never part of the normal flora e.g. Mycobacerium TB
- Or can be normal flora that acquire virulence or antibiotic resistance determinants (E.coli or Staph.aureus)
What is pathogenicity defined as?
- The CAPACITY of an organism to enter a host and CAUSE DISEASE
What is virulence defined as?
- A measure of pathogenicity
- The degree of intensity of pathogenicity –> the MORE virulent, the MORE damage is caused
What is a virulence factor required by an organism to cause?
- Virulence factor is required by the organism to cause disease
What processes do virulence determinants which are expressed by pathogens mediate to cause disease?
- Adhesion (ligands for cells)
- Anti-phagocytic (Capsule)
- Damage (Toxin)
What are the 4 general steps in bacteria causing disease?
- Exposure (to pathogens)
- Adherence (to skin or mucosa)
- Penetration/Invasion (through epithelium)
- Colonization and Growth (Production of virulence factors)
What are the two types of sources where an infectious agent is acquired?
- Inamimate
2. Animate
What are examples of Inamimate sources of infection?
- Food, soil, water
- inanimate objects (fomites) –> hospital/industrial equipment, soiled linen, dressings
What are examples of animate sources of infection?
- Animals (zoonosis) –> Pets, food source
- Insects
- Humans –> patients, family members, staff, casual contacts (carriers)
What are the 3 types of transmission between humans?
- Respiratory or salivary spread (aerosol, saliva)
- Faecal-oral spread (good public health hygiene)
- Venereal Spread (sexually and difficult to control)
What are the 3 types of anthropod-borne infections and zoonoses?
- Vector (biting anthropod)e.g. malaria,typhus, sandfly
- Vertebrate reservoir e.g Rabies
- Vector-vertebrate reservoir e.g. Plague, yellow fever
What are the 4 general modes of transmission of pathogens?
- Airborne
- Contact
- Vehicle
- Vector borne
What is the droplet spread for airborne transmission and which particle is an important route of transmission, and how large are the particles?
- Travels LONG distances
- MORE than 1m
- Dust particles
- Particles are SMALL (1-4microm)
What is the droplet spread for contact transmission, and how large are the particles?
- Travel LESS than 1m
- Particles are LARGE (more than 5microm)
What are fomites in vehicle transmission of pathogens?
- Common vehicles like surgical instruments, bedding, eating utensils
What are nosicomal infections?
- HOSPITAL acquired infections e.g. biofilms from own flora, catheders
- Major source of morbidity and mortality
What are biofilms composed of?
- “…microorganisms attached to the surface and encased in a hydrated polymeric matrix of their own synthesis”
What are the majority of hospital acquired infections due to?
- Biofilms
What are 3 examples of HAI (hospital acquired infections-nosocomial)?
- Staphylococcal infections
- Hospital acquired Legionnaires disease (from cooling towers)
- UTIs
What are the three sources of infection for nosocomial (HAI)?
- Self infection
- Staff/patient or patient/patient
- Environment
Which bacterium is the major cause of nosocomial HAI?
- S.aureus –> golden Staph
Which people does S.aureus manly manifest itself in?
- In immuno-compromised people
What is the MRSA S. aureus resistant to?
- Methicillin –> this is a semi synthetic penicillin (antibiotic)
What is the VRSA S.aureus resistant to?
- Vancomycin antibiotic
