What is peptidoglycan and what is the difference in regard to it in G+ vs G- organisms?
It is a heteropolymer consisting of N-acetylglucosamine and N-acetylmuramic acid.
Provides rigidity and determines shape of bacteria.
G+ have many cross-linkages in the peptidoglycan (thick layer)
G- have far fewer cross-links (thin layer)
What is the cell wall of prokaryotes composed of?
What does the cell wall of fungi consist of?
mannans & glucans (polysaccharides)
What is the cell membrane of prokaryotes made of?
What is a gram-stain used for?
To classify bacteria as G+ or G- on the basis of stain retention of cell peptidoglycan
G+ stain purple
G- stain red
What are 2 different types of media and what do they help determine?
Differential - identity of an organism (e.g. MacConkey agar inhibits growth of G+ bacteria and supports growth of G- orgs, esp those that normally grow in the GIT; CHROM agar differentiates betw diff candida spp)
Selective - select specific bacteria from mixed cultures (e.g. Thayer-Martin medium allows neisseria to grow)
Purpose of the coagulase test
differentiates between Staph aureus and other Staph spp (Staph aureus is coagulase positive)
Purpose of the catalase test
distinguish between streptococci (catalase-negative) and staph (catalase-positive)
Purpose of the lancefield serogroup
group various streptococcal species
Examples of different oxygen requirements and examples of bacteria that grow under these conditions
Aerobic (Pseudomonas aeruginosa)
Anaerobic (Bacteroides fragilis)
Facultative (S. aureus)
What does a respiration test tell us about bacteria?
Fermentation tells us if bacteria can utilize glucose or lactose as a substrate. This use produces acid or alcohol. (e.g. Pseudomonas and Acinetobacter are non-fermenting)
What does hemolysis testing tell us about bacteria?
If the bacteria is Alpha, Beta, or Gamma
Alpha hemolytic do partial hemolysis - clear a small zone (e.g. S pneumoniae, viridans group, streptococci)
Beta hemolytic do complete hemolysis - clear a large zone (e.g. S. pyogenes, S. agalactase, enterococci)
Gamma have no clear zone (no hemolysis)
What do serologic tests detect?
Nonspecific or specific antibodies
Presence and quantity can aid in identification of pathogen
Tests available for: legionella pneumophila, Treponema pallidum, Chlamydia psittaci, C. pneumoniae, C. trachomatis, Mycoplasma pneumoniae
What are genetic tests/how are they used?
DNA probe hybridization: chemiluminescent sigle-stranded DNA probes bind to complementary rRNA of the target microorganism
Commonly used to detect Chlamydia trachomatis, neisseria gonorrhoeae, Coccidioides immitis, Histoplasma capsulatum, Blastomyces dermatitidis, Mycobacterium tuberculosis, and Mycobacterium avium complex
If an unknown bacteria is a cluster of G+ cocci, what test might be used to determine the identity?
A coagulase test.
If + they'd probably be Staph aureus
If - they'd probably be Staph epidermidis
If an unknown G+ bacteria is cocci in pairs or chains, what is its likely identity?
Streptococci or Enterococcus
If they are Streptococci, they could be Alpha or Beta hemolytic.
If Alpha, likely identity is S. pneumoniae or Viridans group
If Beta, Group A may be S pyogenes, Group B may be S. agalactiae, Group D may be S. bovis, or others
Gram + bacilli are unusual, but what are some of the more likely of this type of bacteria we may encounter?
Bacillus spp (B. anthracis)
Corynebacterium spp (C. diptheriae)
Gram - bacilli are usually what type of bacteria?
Name some of the coliform enterobacteriaceae (G- bacilli)
Name some of the non-coliform enterobacteriaceae (G- bacilli)
Name some G- bacilli that are aerobic and fermentors
Name some G- bacilli that are aerobic and non-fermentors
Name some G- bacilli that are aerobic and fastidious
Haemophilus (H. influenzae, H. ducreyi, H. parainfluenzae)
Name some aerobic G- cocci
Neisseria spp (N. gonorrhoeae, N. meningitidis)
Name some G+ anaerobes
Clostridium spp (C. botulinum, C. difficile, C. perfringens, C. tetani)
Name some G- anaerobes
Bacteroides fragilis (inherently resistant to antibiotics)
Name 3 atypical bacteria and the reason they're considered atypical
Chlamydia spp - cell wall similar to G- but lack peptidoglycan
Mycoplasma spp - lack a cell wall
Legionella spp - G- but difficult to stain; difficult to grow on standard media; use serologic testing to identify
How are fungi classified?
According to morphology
Describe yeasts and moulds
Yeasts are unicellular and reproduce by formation of blastoconidia or fission (budding)
Moulds are characterized by formation of hyphae. Vegetative hyphae penetrate medium and aerial hyphae bear reproductive bodies.
Name some common yeasts
Candida spp (C. albicans, C. glabrata, C. krusei, C. lusitaniae, C. parapsilosis, C. tropicalis)
Name some common moulds
Aspergillus spp (A. flavus, A. fumigatus)
What does dimorphic mean and name some organisms that would be classified as dimorphic
Can grow as either a yeast or a mould
minimum inhibitory concentration - the lowest concentration of an agent that inhibits the visible growth of an organism
The lowest concentration of an agent that results in a 99.9% reduction in colony forming units
What are three types of tests for the evaluation of antimicrobial activity?
6 methods for determining MICs
1. Macro-broth dilution
2. Micro-broth dilution
3. Agar dilution method
4. Kirby-Bauer disk diffusion
5. Epsilometer strip method or "E test"
6. Automated systems
What is a MIC50? An MIC90?
This is the MIC that will inhibit 50% (or 90%) of the population tested
When doubling dilutions (0.5, 1, 2, 4, etc.) if the MIC is read as 4, what is the true MIC?
It would be somewhere between 2 and 4
Who determines breakpoint values for interpreting MICs and what is it based on?
Based on: drug p'kin and p'dyn, distribution of MICs of a population of bacteria, clinical efficacy
What does SIR stand for when talking about breakpoint values?
What is an antibiogram?
A table that tells what percent of a group of bacteria is susceptible to a particular antibiotic
What type of table helps to make formulary decisions regarding antimicrobials and what info is included?