BIOL 260 Microbiology   spring 2017

Seattle Central College

Lauren Yasuda, Ph.D. 

Mon 6/12-Tues 6/13:  Ch.19-20

Tues 6/13 at 2:30:  Review session (rm 104)

Weds 6/14 at 1:00:  Exam IV (Ch.14-16, 18, 19-20)

Ch.16 Host-microbes interactions handout answer key

Ch.19 Epidemiology handout answer key

Results of disc diffusion antibiotic susceptibility tests

Course evaluation links (due by Fri 6/16):  lab 1, lab 2 

Ch.20 study questions notes:

SQ#2 - Selective toxicity of an antimicrobial drug refers to a drug's ability to cause more harm to microorganisms than to the human host.  ß-lactam antibiotics (e.g., penicillin) harm bacteria by inhibiting peptidoglycan synthesis, which damages the cell walls.  Since human cells don't have peptidoglycan, these antibiotics can harm the bacteria without harming the host.

SQ#3 - The therapeutic index (TI) of a drug is the ratio of the minimum dose toxic for patients to the minimum dose effective for therapy (e.g., treating an infection).  A drug with a high TI is safer than a drug with a low TI.  For example, a drug with a TI of 100 has a toxic dose 100x higher than the effective dose, BUT for a drug with TI of 2, the toxic dose is only twice the effective dose.  

A drug treatment with bacteriostatic effect inhibits bacterial growth, whereas a drug treatment with a bacteriocidal effect kills bacteria.

SQ#8 - Selective toxicity of antibiotics (abx) that inhibit bacterial ...

cell wall synthesis:  targets are proteins in the bacterial cell wall; human cells lack these proteins 

protein synthesis:  targets are components of bacterial ribosomes; human cells have ribosomes, but with different components

DNA or RNA synthesis:  targets are enzymes involved in bacterial DNA replication & transcription; human cells do these processes, but use different enzymes 

folate synthesis:  targets are enzymes in bacteria used for folate synthesis; human cells don't synthesize folate therefore lack these enzymes

SQ#10 - The minimum inhibitory concentration (MIC) of an abx is the lowest concentration of the drug that inhibits growth of a certain type of bacteria.  The MIC can be determined by an abx dilution series:  The bacteria can grow in the presence of abx concentrations lower than the MIC.   For a bacteria, if the MIC of an abx is lower than a standard value, the bacteria is susceptible (sensitive) to that abx.  If the MIC is higher than this value, the bacteria has intermediate susceptibility or is resistant to that abx.

 The minimum bacteriocidal concentration (MBC) of an abx is the lowest concentration of the drug that kills a certain type of bacteria.  Prescribing an abx at this dose would be appropriate for immunocompromised patients or patients with life-threatening infections (e.g., endocarditis, meningitis, etc).  Preferably, the MBC of the abx would be low, in order to avoid toxicity to the patient.

BIOL 260 links

"Unseen Enemy" - CNN film 

Center for Disease Dynamics, Economics & Policy

TEDTalks: How our microbes make us who we are

The Scientist - human microbiome

National Ctr for Emerging & Zoonotic Diseases (NCEZID)

World Health Organization (WHO)

Science Global Health 9/14

Sequencing to track Ebola's spread