IC1 eL Flashcards
Possible source of normal flora
- Maternal genital tract
- Skin
- Mouth and pharynx
- Air-borne organisms
- Environment & food
Normal sterile sites
- CNS
- CVS
- Lower respiratory tract
- Bone, Joint
- Genitourinary tract, except urethra & vagina
Common pathogens for bacterial meningitis
- Streptococcus pneumoniae
- Neisseria meningitidis
- Haemophilus influenzae
- Streptococcus agalactiae
- Listeria monocytogenes
Common pathogens for sinusitis
- Streptococcus pneumoniae
- Haemophilus influenzae
Common pathogens for otitis media
- Streptococcus pneumoniae
Common pathogens for community-acquired pneumonia
- Streptococcus pneumoniae
- Haemophilus influenzae
- Staphylococcus aureus
3 categories of community-acquired pneumonia
- Community acquired
- Atypical
- Tuberculosis
Common pathogens for sexually transmitted diseases
- Chlamydia trachomatis
- Neisseria gonorrhoea
- Treponema pallidum
- Ureaplasma urealyticum
- Haemophilus ducreyi
Common pathogens for Upper resp tract infection
- Streptococcus pyogenes
- Haemophilus influenzae
Common pathogens for urinary tract infection
- E. coli
- other Enterobacteriaceae
- Staph. saprophyticus
- Pseudomonas aeruginosa
6 types of lab diagnostics
- Microscopy e.g. gram stain, acid-fast
- Culture e.g. broth/ agar/ growth condition
- Biochemistry e.g. specific nutrients/ enzymes
- Serologic/ immunologic diagnostics e.g. to detect antigen/ antibodies
- Molecular/ nucleic acid-based diagnostics e.g. PCR
- Mass spectrometry
Usual timeline from specimen collection to identification, culture and susceptibility results
Day 1: Gram stain
Day 2-3: Culture bacteria
Day 3-4: Identify bacteria & AST
Macroscopic appearance for Pseudomonas aeruginosa
blue-green colonies, grape-like odour
Macroscopic appearance for Staphylococcus aureus
golden colonies
What is MacConkey’s Agar used for?
To isolate gram negative enteric bacteria and differentiates lactose fermenting and non-lactose fermenting gram negative bacteria.
Colour for lactose vs non-lactose fermenting colonies
Lactose: Pink
Non-lactose: Colourless
Examples of lactose fermenting colonies
- E.coli
- Enterobacter spp.
- Klebsiella spp.
Which streptococcus causes complete haemolysis?
beta-haemolytic streptococcus
Which streptococcus causes partial haemolysis?
alpha-haemolytic streptococcus
Which streptococcus causes no haemolysis?
gamma-haemolytic streptococcus
Example of gram positive cocci in clusters
Staphylococcus spp
Example of Gram positive diplococcus
Streptococcus pneumoniae
Example of Gram positive cocci in chains
Streptococcus
Example of Gram negative rod
E. coli
Colour for gram-negative and gram-positive
Gram-positive: Purple
Gram-negative: Pink
Key steps in gram stain
- Fixation
- Crystal violet
- Iodine treatment
- Decolourisation
- Colour stain with Safranin
Examples of non-fermenters
Pseudomonas aeruginosa, Acinetobacter baumanii
What do fermenters mean?
refers to ability to ferment sugar/carbohydrate
Which bacteria would test catalase +ve?
Staphylococcus
How to differentiate btw S. aureus and S. epidermidis?
Coagulase test.
- Coagulase +ve staphylococcus (S. aureus)
- Coagulase –ve staphylococcus (S. epidermidis)
Observation for a coagulase -ve test
Bacteria remain dispersed and no clumping
How to differentiate btw P. aeruginosa and E. coli?
Oxidase test.
Oxidase +ve GNR (eg P. aeruginosa) Vs
Oxidase -ve GNR (eg E. coli)
Observation for oxidase +ve result
Purple colour appears
Principles of Minimum inhibitory concentration (MIC)
The lowest concentration of an antimicrobial that prevents visible growth of an organism
How is MIC determined?
Carry out agar e.g. E-test/ broth dilution test
Another method for AST apart from MIC
Kirby-Bauer disk diffusion method
How is the Kirby-Bauer disk diffusion method carried out?
- organism is streaked onto the agar
- Antibiotics are added to the plate
- incubate
- zone of inhibition observed is used to determine susceptibility
Diameter of zone of inhibition corresponds/ correlates with antimicrobial activity
What are breakpoints?
Critical concentrations which predict susceptibility/resistance (interpretive criteria for S,I,R)
MIC > breakpoint -> S/ I/ R?
R
MICs of different drugs against a particular organism are not directly comparable (Y/N)
Y
Lowest MIC on a AST report indicate the best treatment option. (Y/N)
not necessarily
