Microbiology 2 Flashcards
How do you classify microorganisms?
Appearance/Structural features
Growth Requirements
Enzyme/metabolic tests
Molecular tests
Wha are the different shapes of bacteria?
Cocci
Bacilli
Spiral shaped
Describe Streptococcus and Staphylococcus?
Strep = strips Staph = clusters
What colour stain do you get with gram negative and gram positive?
Negative = pink - single layer of peptidoglycan Positive = purple - huge layer of peptidoglycan
What organisms dont stain well with gram stain?
Mycobacterium TB - due to waxy cell wall that doesn’t take up cell wall
Treponema pallidum - causes syphilis (spirochaete organism)
What are the differences between aerobic and obligate aerobes?
Aerobic - grow in air/O2
Obligate = NEED O2
What is the difference between obligate anaerobes and facultative anaerobes?
Obligate = Killed by O2 Facultative = tollerate O2
What is a selective media?
A substance in which in the presence of it it permits growth of one organisms over another one.
What is a differential media?
The incorporation of chemicals produces visible changes in colonies that facilitate identification (differentiation)
Describe haemolysis?
Important in classification of streptococcus. Shows haemolysis of blood on blood agar plates.
Describe the different types of haemolysis?
Alpha = partial haemolysis - causes a greenish discolouration Beta = completely haemolysis - most aggressive organisms as they produce toxins that lyse the red blood cells on the plate Gamma = no haemolysis
What organisms are, alpha, beta and non-haemolytic?
Alpha = viridian's, pneumoniae Beta = Group strep A (strep. pyrogens) and B Non = enterococcus
Describe in more detail step. pneumonia?
Gram positive cocci in chans or pairs
Commonest cause of pneumonia, can also cause meningitis
Part of normal URT flora in many people
Describe strep Viridian’s in more detail?
Gram positive cocci in chains
Common commensals of URT, bowel and vagina, but can cause infection in a normally sterile site
Endocarditis can be caused by this
Describe strep (group A) aka strep pyogenes?
most pathogenic of all strep
causes tonsillitis, soft tissue and skin infections, sepsis (puerperal) (throat and skin infections)
Strains still sensitive to penicillin
Describe enterococcus?
non haemolytic strep
part of the normal bowel flora
Common cause of UTI
Describe staphylococcus?
Grows best in O2
Clusters positive cocci
Use the coagulase test to distngust between staph. aureus etc
Describe the coagulase test?
A test to distinguish staph aureus (common pathogen) from the other coagulase negative staph (common skin commensals)
What happens in the coagulase test?
Golden colour = staph aureus
White colour = coagulase negative staph
Describe the coagulase negative staph group?
Contains - staph epidermis, staph hominis etc
Common skin commensals that usually dont cause harm
Common cause of joint and prosthetic heart valve infection and IV injections
What can staph aureus cause?
Skin and wound infections
What is one of ht most commonest causes of bacteraemia?
Staph aureus
Bacteria in the blood spread
infection at any site may result in bacteria getting into the bloodstream - patient maybe become septic.
Infection may spread to other parts of the body (heart valves)
What do you treat MRSA resistant aureus with?
Flucloxacillin
What is fever?
Temperature higher than 38 degrees
How does fever fight infection?
When an infection is sensed ion the body, the prostaglandin E increased the body’s thermal set point, which causes the body to shiver, causing fever, which gives you an increased survival from infection
Describe sepsis
Small blood vessels become leaky and loose fluid in the tissues
Lower blood volume require the heart to work harder (increases HR)
Poor tissue oxygen perfusion means blood supply to organs decreases to keep blood flowing to the brain
the blood clotting system is activated causing blood clotting in tiny vessels - which uses up the clotting factors - increasing the risk of haemorrhage
