*Microbiology 1 (Lecture 1 and 2) Flashcards
List of microorganisms in increasing size
Prion proteins Viruses bacteria fungi parasites
What type of names do all organisms have?
A genus name and a species name
What type of diseases does prion proteins cause?
Give an example.
Transmissible Spongiform Encephalopathies (brain infection)
Mad cow disease (Crutzefelt Jacob Disease)
Problem with prion proteins?
Cannot be reliably removed by sterilisation
What type of organism is a virus?
What is it surrounded by/
"obligate intracellular parasite" A capsomere (protein coat)
Diagnosis of viral infections?(3)
PCR
Cell culture
Serology
Difference between the genetic material contained within viruses and bacteria?
Viruses = DNA or RNA Bacteria = DNA and RNA (one double stranded chromosome with some genetic material sometimes stored within plasmids)
What surrounds a bacteria in terms of walls, etc.?
Plasma membrane
Cell wall
Capsule (+/-)
What does a bacteria use for adhesion and movement?
Adhesion: Pilli and fimbriae
Movement: Flagellae
Bacterial shapes? (3)
Coccus
Bacillus
Spirochaetes
Can spirochaetes be stained using the gram method?
No but they have a gram negative structure
Gram stain reactions?
Gram positive = purple
Gram negative = pink
Difference between gram positive and gram negative?
Gram positive cell wall contains a thick layer of peptidoglycan compared to a thin layer between the cytoplasmic membrane and outer membrane in gram negative bacteria
What 2 organisms do not stain well?
Mycobacterium tuberculosis (causes TB, has a waxy coat) Treponema pallidum (spirochaete that causes syphilis)
Where in the body is there a natural bacterial flora? (5)
URT Lower small intestine Large intestine Vagina Skin (resident and transient flora)
What is commensalism?
Where one organism benefits from the relationship without affecting the other (commensal is part of the normal flora)
Opportunistic pathogen?
An organisms that will cause infection in an immunocompromised individual
Virulence?
Degree of pathogenicity of an organism (i.e. how easily can an organism cause disease)
How does bacteria replicate?
What do they require to replicate? (4)
How quickly can bacteria replicate in ideal growth conditions?
Binary fission Food Moisture Correct temp. (usually 37 for human pathogens) correct pH (about 7.4) Every 20 minutes
3 main types of atmosphere?
Aerobic (growth in presence of oxygen, many aerobic organisms will also grow in anaerobic conditions but less well)
Microaerophillic (reduced O2 and enriched with CO2)
Anaerobic (no O2, “anaerobes” are strict anaerobes)
Why does bacteria make us ill?
2 types of these?
Many produce toxins (enzymes)
Exotoxin (mainly gram positive, produced side cell and exported out)
Endotoxin (mainly gram negative, part of GN cell wall)
What do toxins produced from bacteria do?
Interact with cells of the immune system causing release of cytokines
Damage RBCs and WBCs, make small blood cells ‘leaky”, decrease BP, affect blood clotting and eventually lead to sepsis and septic shock
What type of organisms tend to form spores?
2 examples
Gram positive bacilli (put DNA in thick coat = can’t replicate but can survive for long time)
Clostridium sp. (e.g. C. difficile)
Bacillus sp. (e.g. Bacillus anthracis)
How does a spore develop? (3 stages)
Chromosome condenses
Septum forms
Calcium dipliconate accumulates
Diagnostic methods for bacteria?
Microscopy (same day)
Culture (48 hours)
Detection of antigens (e.g. in urine)
Detection of antibodies (e.g. serology) - same day
PCR (same day)
NAATs (detection of DNA/ RNA through nucleic acid amplification tests
Streptococcus pneumoniae causes?
Pneumonia and meningitis
Streptococcus viridans?
Endocarditis
Streptococcus pyogenes (group A strep.)
Skin (e.g. necrotising fascitis), throat infecitons (e.g. tonsillitis - if rash present = scarlet fever), (peurperal sepsis = severe life threaten infection and pregnant and post natal women)
Group B strep.?
Neonatal meningitis
Enterococcus sp.
Gut infections, UTI
Staphylococcus aureus
Wound, skin infections, bone and joint, food poisoning etc.
Coagulase negative staphylococci e.g. Staph. epidermidis
Skin commensal, IV line infections
Corynaebacterium diphtheriae
Diptheria
Diptheroids
Skin commensal
Listeria monocytogenes
Meningitis
Bacillus cereus?
Food poisoning
Bacillus anthracis
Anthrax
Clostridium tetani
Tetanus
Clostridium perfingens
Gas gangrene
Clostridium difficile
Antibiotic related colitis
How long does a TB culture take?
4-12 weeks
2 types of fungi?
Moulds (produce spores and hyphae (allow them to invade organic tissues)
Yeasts (single cells that reproduce by budding)
Most common mould infection in humans?
Aspergillus spp (do not stain)
Most common yeast infection in humans?
Candida spp. (stain as large gram positive structures)
Difference between sterilisation and disinfection?
Sterilisation destruct and removes 99.9% of micro-organisms and spores
Used for anything that will come into contact with a normally sterile area of the body
Disinfection removes or destructs pathogenic micro-organisms enough to make an item safe
What might sterilisation not kill?
Prion proteins
Sterilisation methods?
Steam under pressure (autoclave)
Dry heat in oven at 160 degrees for greater than an hour
exposure to ethylene oxide gas
Irradiation
Disinfection methods (2)?
Hot water
Chemicals (e.g. hypochlorite, chlorohexidine, Povidone iodine)
What are the genus for bacteria that are gram positive cocci?
Streptococcus spp.
Enterococcus sp.
Staphylococcus spp.
Which out of streptococcus and staphylococcus and enterococcus grow in chains/ clusters?
Strep, entero. = chains
Staph. = clusters
How are streptococci and enterococcus differentiated?
Are they aerobic or anaerobic?
by type of haemolysis when grown on blood agar
Aerobic (although facultatively anaerobic)
Types of haemolysis?
Alpha/ partial
Beta/ complete
gamma/ non-haemolytic
What happens in alpha haemolysis
Enzymes denature haemoglobin inside RBC causing greenish discolouration around colony
What happens in beta haemolysis
Enzymes (exotoxins) lyse RBC = complete clearing (most pathogenic streptococci are beta)
Which species are alpha haemolytic
streptococcus pneumoniae aka “pneumococcus”
Streptococcus “viridans” (contains many different species)
Streptococcus pneumoniae:
Where is this part of the normal flora
What are the majority of UK strains of this sensitive to
URT
Penicillin
Where is streptococcus “viridian’s” part of the normal flora?
Vagina, bowel, URT
How to tell the difference between the 2 alpha haemolytic gram positive cocci?
Streptococcus pneumoniae tends to grow in pairs or short chains
Streptococcus “viridans” grows in chains
How are beta haemolytic streptococci differentiated
Based on cell wall antigenic structure
2 types of beta haemolytic streptococci?
Group A strep aka strep. pyogenes
Group B strep.
What is the most pathogenic of all the strep.
why
Group A strep.
Produces a range of exotoxins
What antibiotics are strep A sensitive to
Penicillin and amoxicillin
What is the non-haemolytic bacteria?
Enterococci e.g. enterococcus faecalis, enterococcus faecium
Where are enterococcus normally found
When do they cause problems
In the bowel flora
When they get into normally sterile sites
what are most strains of E. faecalis sensitive to
Amoxicillin
what are the antibiotic resistant strains of E. facium called
Vancomycin resistant enterococci
What test is used to distinguish staph. aureus from all the other staphlococci
Coagulase test
What does a positive coagulase test look like
Coagulase plasma clots in bottom of test tube = staph. aureus
Are coagulase negative staph. harmful
When do they cause harm
Not usually (don't tend to produce toxins) Produce slime (surface polysaccharide) which allows them to stick to artificial material in the body
Where does staph. aureus colonise in about 30% of patients
URT
What are 2 conditions staph. aureus can cause depending on exotoxin produced
Toxic shock syndrome
Panton-Valentine leukocidin (damages WBCs)
Condition staph. aureus can cause due to enterotoxins?
food poisoning
What are staph. aureus sensitive/ resistant to flucloxacillin called?
MSSA
MRSA (meticillin resistant staphylococcus aureus)
Treatment for MSSA?
Flucloxacillin
Bacteraemia?
Bacteria in the blood stream
One of the commonest causes of bacteraemia?
Staph. aureus
Microbiology tests for infection (6)
blood culture urine culture faeces culture swab for puss specimen for PCR Blood for serology
Fever?
Temperature greater than 38
In a fever, what is released to raise the body’s thermal set point
What WBC is involved in creating a fever
Prostoglandins
Macrophages
What happens during sepsis?
Small blood vessels become leaky and loose fluid
Lower blood volume means heart has to work harder
Poor tissue oxygen perfusion means blood supply to less essential organs (e.g. skin, kidneys, liver) is shut down
Blood clotting cascade activated = clotting in tiny vessels = uses clotting factors = increased risk of haemorrhage
Levels of sepsis
Sepsis
Severe sepsis
Septic shock
