Card Set Information
Microbiology Overview PHPR523
What is the cell wall of a prokaryote made of?
What function does peptidoglycan serve?
determines the shape of the bacteria
What is the difference between the peptidoglycan of gram-positive and gram-negative bacteria?
very few cross-linkages in gram-negatives
What dyes are used to classify gram-positive bacteria?
What dyes are used to classify gram-negative bacteria?
What is the gram-negative cell envelope made of?
Which type of differential media doesn't allow gram-positive bacteria to grow?
supports growth of coliform bacteria
differentiates lactose fermentors
What bacteria does Thayer-Martin medium allow to grow?
What use does CHROM agar have?
differentiates between Candida species
What is a coagulase test?
tests for an extracellular protein that binds to prothrombin to form staphylothrombin
Only S. aureus is coagulase positive
What is a catalase test?
distinguishes between streptococci and staphylococci
strep is catalase negative
staph is catalase positive
determined by dropping hydrogen peroxide on a colony (bubbling indicates a positive result)
What is the purpose of the Lancefield serogroup test?
to group various streptococcal species based on serologic reactivity of the cell wall polysaccharide
What bacteria are anaerobic?
What bacteria are gram-negative?
What bacteria are gram-negative anaerobes?
What bacteria are spiral organisms?
What bacteria is facultative?
What is alpha hemolysis?
produces a small clear zone on blood agar
Viridans gp streptococci
What is beta hemolysis?
produces a large clear zone on blood agar
S. pyogenes (A)
S. agalactiae (B)
S. bovis (D)
What is gamma hemolysis?
no clear zone on blood agar
What types of biochemical tests are used to differentiate bacteria?
Lancefield serogroup test
What is serologic testing?
testing the host for antibodies against the pathogen
What bacteria are serologic tests available for?
What is genetic testing for bacteria?
DNA probe hybridization (single-stranded DNA probes bind to complementary rRNA of target microbes)
What bacteria can be tested for using genetic testing?
Mycobacterium avium complex
What bacteria grow in clusters of gram-positive cocci?
What bacteria grow in chains of gram-positive cocci?
What bacteria grow in pairs of gram-positive cocci (diplococcus)?
What bacteria are gram-positive bacilli?
What bacteria are gram-negative bacilli?
What bacteria are coliform gram-negative bacilli?
What bacteria are non-coliform gram-negative bacilli?
What bacteria are gram-negative bacilli fermentors?
What bacteria are gram-negative non-fermentors?
What bacteria are fastidious gram-negative bacilli?
What bacteria are gram-negative cocci?
What bacteria are atypical?
What makes Chlamydia atypical?
cell wall is similar to gram-negatives, but
What makes Mycoplasma atypical?
no cell wall
What makes Legionella atypical?
gram-negative, but difficult to stain
difficult to grow on standard media
Which fungi are unicellular?
How do yeasts reproduce?
blastoconidia formation or fission (budding)
What fungi form hyphae?
What type of hyphae penetrate medium (grow down)?
What type of hyphae grow upward and bear reproductive bodies?
What fungi are yeasts?
What fungi are moulds?
What fungi are dimorphic?
What is a conidiophore?
the stem of an aerial hyphae
What is a phialide?
row of cells along the vessicle of an aerial hyphae
What is a conidia?
a bud of an aerial hyphae
What is the Minimum Inhibitory Concentration (MIC)?
the lowest concentration required to inhibit the visible growth of an organism
What is the Minimum Bactericidal Concentration (MBC)?
the lowest concentration required to kill 99.9% of colony forming units
What is tolerance?
when the MBC is 4-8x greater than the MIC
How long does it take to determine an MIC?
How long does it take to determine an MBC?
What are the methods for determining an MIC?
epsilometer strip ("E test")
Why is a
MIC rarely determined?
dilutions are performed by doubling
0.5, 1, 2, 4...
an MIC of 4
actually somewhere between 2 and 4
What are the limitations of MICs?
don't provide information regarding rate or extent of killing
conducted with a standard inoculum
media does not contain plasma proteins or complement
don't take site of infection into account (affects drug penetration, distribution, and protein binding)
What is the advantage of time-kill curves?
rate and extent of killing can be determined
regrowth can also be determined
How is a time-kill curve determined?
broth is inoculated with a test isolate at a standard inocula and a known amount of antibiotic
samples are removed from the testing containers at predetermined time-points and plated on agar
What is virulence?
a quantitative measure of pathogenicity or the likelihood that it will cause disease
What are virulence factors?
factors that enable a microbe to establish itself on or within a host and enhance its potential to cause disease
What is a primary pathogen?
regularly cause disease in susceptible individuals with apparently intact defense systems
What is a secondary pathogen?
cause disease more readily in individuals with underlying chronic disease or in those otherwise compromised
What must a pathogen do to cause disease?
colonize the host
gain access to the host (break down defenses or wait for trauma)
find a niche within the host
evade host defenses
multiply within the host
How do microbes adhere to the host?
What is a biofilm?
matrix-enclosed bacterial populations that adhere to a surface, interface, and each other
increase resistance to microbials
help evade host defenses
What are the mechanisms used to evade host defenses and remain viable?
production of antiphagocytic capsule
production of toxins
production of destructive enzymes
What is a antiphagocytic capsule?
polysaccharide capsules discourage antibody recognition and retard complement fixation
S. agalactiae (B)
What are toxins?
diverse microbial products that allow the pathogen access to their niche in the host
provide a means for environmental signaling between bacteria
protect the bacteria from clearance by the host
many are actually enzymes with specific intracellular targets within host cells
often comprised of a binding domain (B subunit) and an enzymatic domain (A subunit) that is responsible for the toxic effects once inside the cell
What are the two major types of toxins?
What is an exotoxin?
bacterial products that are protein in nature
released by the bacterium during exponential growth
toxic to target cells
What is an endotoxin?
cell-associated toxic components of gram-negative bacteria
How are toxins classified?
cellular or tissue site of action (tetanus neurotoxin)
mechanism of action (adenylate cyclase toxin)
intracellular target (protein toxin)
major biologic effect (hemolytic toxin)
producing organism (cholera toxin)
What is the most common type of toxin?
membrane bound virulence factor produced by some gram-negative bacteria
commonly referred to as LPS or endotoxin
triggers humoral enzymatic mechanisms involving the complement, clotting, fibrinolytic, and kinin pathways
How are bacterial genetic materials transferred?
transformation via fragments of chromosomes
What factors contributed to the emergence of antimicrobial resistance?
1. Inappropriate antibiotic use by clinicians
overuse of broad-spectrum agents
used for tx of non-bacterial infections
inappropriate antimicrobial prophylaxis
2. Lack of patient education or ineffective education
failure to complete regimens
3. Widespread antimicrobial use in food production industry
What are the types of antimicrobial resistance?
What is primary resistance?
prior antimicrobial exposure not required
also called inherent, intrinsic, or native
E. coli to Vancomycin
What is secondary antimicrobial resistance?
develops following antimicrobial exposure
also called acquired
What are the two methods of developing secondary antimicrobial resistance?
selection of resistant subpopulations
What are the types of genetic alterations for antimicrobial resistance?
spontaneous mutations (point mutations)
acquisition of new genetic material
What are the methods of acquiring genetic material for antimicrobial resistance?
: transfer between bacteria that are in cellular contact
: transfer via bacteriophage (virus)
: uptake and incorporation of exogenous DNA (S. pneumoniae)
What are the types of exogenous DNA that can by used for genetic transformation for antimicrobial resistance?
What are the characteristics of plasmid-mediated resistance?
extrachromosomal double-stranded DNA (circular)
What are the characteristics of Transposon-mediated resistance?
relies on host bacteria or plasmids for replication (not self-replicating)
intra- or inter-species
What are the mechanisms of antimicrobial resistance?
antibiotic inactivating enzymes
alteration of target or active site
alterations in bacterial cell membranes
What are common antibiotic inactivating enzymes?
aminoglycoside resistance modifying enzymes
How do beta-lactamases work?
split the amide bond of the beta-lactam ring
can be constitutive (constant) or inducible
What bacteria have inducible beta-lactamases?
What agents are potent inducers of beta-lactamases?
What are Extended-spectrum beta-lactamases (ESBLs)?
active against all beta-lactams except cephamycins (cefotetan and cefoxitin), cefepime, and carbapenems
inhibited by beta-lactamase inhibitors (sulbactam, clavulanate, tazobactam)
genes are located on plasmids
What are AmpC-type-beta-lactamases?
active against all beta-lactams except cefepime and carbapenems
not inhibited by beta-lactamase inhibitors
genes found on chromosomes and plasmids
may be inducible
What are the strategies to overcome beta-lactamase mediated resistance?
administer large doses of beta-lactams to overhelm beta-lactamases
combine beta-lactams with beta-lactamase inhibitors (tazobactam, clavulanate, sulbactam)
How do aminoglycoside resistance modifying enzymes work?
modification as the AG is transported across the cell wall of the microbe
commonly observed among Enterococci exhibiting hig-level AG resistance
What targets or active sites are altered for antimicrobial resistance?
Penicillin-binding proteins (PBP)
: S. aureus resistance to beta-lactams
Ribosomal binding sites
: Strep resistance to gentamicin
Cell wall precursors
: Enterococcal resistance to vancomycin
: P. aeruginosa resistance to ciprofloxacin
What alterations in bacterial cell membranes cause antimicrobial resistance?
What are porin channels?
portals through the bacterial cell wall
facilitate transport of hydrophilic molecules into the cell
change in number or size can cause resistance
What microbes use efflux pumps?
: TCNs, FQs
: TCNs, FQs
What drugs can be used for MRSA?
What can be used to treat VISA?
What genes convey MRSA and VRSA?
What agents is penicillin-resistant pneumococcus resistant to?
What drugs is enterococcus resistant to?
What genes confer resistance to vancomycin?
: inducible, high-level resistance to vanco and teicoplanin
: inducible resistance to vanco, susceptible to teicoplanin
: constitutive resistance to vanco (may be low level), may be susceptible to teicoplanin
What are the treatment strategies for resistant enterococci?
vancomycin, linezolid, daptomycin,a nd streptogramins
intermittent vs continuous infusions of beta-lactams and vanco
traditional vs once-daily aminoglycosides
What are the strategies for preventing the spread of antibiotic resistance?
knowledge of local susceptibility patterns
develop guidelines for appropriate antimicrobial usage