-
What is the cell wall of a prokaryote made of?
- proteins
- lipids
- peptidoglycans
-
What function does peptidoglycan serve?
- provides rigidity
- 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?
safranin
-
What is the gram-negative cell envelope made of?
- lipopolysaccharides
- lipoproteins
-
Which type of differential media doesn't allow gram-positive bacteria to grow?
MacConkey agar
- supports growth of coliform bacteria
- differentiates lactose fermentors
-
What bacteria does Thayer-Martin medium allow to grow?
Neisseria only
-
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?
- bacteroides
- clostridium
- peptostreptococcus
- fusobacterium
- prevotella
- propionibacterium
-
What bacteria are gram-negative?
- moraxella
- neisseria
- chlamydia
- bordetella
- brucella
- campylobacter
- francisella
- helicobacter
- hemophilus
- legionella
- citrobacter
- enterobacter
- escherichia
- klebsiella
- morganella
- proteus
- providencia
- salmonella
- serratia
- shigella
- acinetobacter
- burkholderia
- pseudomonas
- stenotrophomonas
- pasteurella
- vibrio
- bacteroides
- fusobacterium
- prevotella
- pneumococcus
-
What bacteria are gram-negative anaerobes?
- bacteroides
- fusobacterium
- prevotella
-
What bacteria are spiral organisms?
- borrelia
- leptospira
- treponema
-
What bacteria is facultative?
S. aureus
-
What is alpha hemolysis?
- partial hemolysis
- produces a small clear zone on blood agar
- S. pneumoniae
- Viridans gp streptococci
-
What is beta hemolysis?
- complete hemolysis
- produces a large clear zone on blood agar
- S. pyogenes (A)
- S. agalactiae (B)
- S. bovis (D)
- Enterococcus
-
What is gamma hemolysis?
- no hemolysis
- no clear zone on blood agar
-
What types of biochemical tests are used to differentiate bacteria?
- coagulase test
- catalase test
- Lancefield serogroup test
- oxygen requirements
- respiration
- hemolysis
-
What is serologic testing?
testing the host for antibodies against the pathogen
-
What bacteria are serologic tests available for?
- Legionella pneumophila
- Treponema pallidum
- Chlamydia psittaci
- Chlamydia pneumoniae
- Chlamydia trachomatis
- Mycoplasma pneumoniae
-
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?
- Chlamydia trachomatis
- neisseria gonorrhoeae
- Coccidioides immitis
- Histoplasma capsulatum
- Blastomyces dermatitidis
- Mycobacterium tuberculosis
- Mycobacterium avium complex
-
What bacteria grow in clusters of gram-positive cocci?
Staphylococcus
-
What bacteria grow in chains of gram-positive cocci?
Streptococcus
-
What bacteria grow in pairs of gram-positive cocci (diplococcus)?
-
What bacteria are gram-positive bacilli?
- Bacillus
- Corynebacterium
- Gardnerella
- Actinomyces
- Lactobacillus
- Listeria
- Nocardia
- Rhodococcus
-
What bacteria are gram-negative bacilli?
- Escherichia
- Klebsiella
- Enterobacter
- Serratia
- Citrobacter
- Proteus
- Providencia
- Morganella
- Salmonella
- Shigella
- Enterobacteriaceae
- Aeromonas
- Vibrio
- Pasteurella
- Pseudomonas
- Acinetobacter
- Haemophilus
- Campylobacter
- Legionella
-
What bacteria are coliform gram-negative bacilli?
- Escherichia
- Klebsiella
- Enterobacter
- Serratia
- Citrobacter
-
What bacteria are non-coliform gram-negative bacilli?
- Proteus
- Providencia
- Morganella
- Salmonella
- Shigella
-
What bacteria are gram-negative bacilli fermentors?
- Enterobacteriaceae
- Aeromonas
- Vibrio
- Pasteurella
-
What bacteria are gram-negative non-fermentors?
-
What bacteria are fastidious gram-negative bacilli?
- Haemophilus
- Campylobacter
- Legionella
-
What bacteria are gram-negative cocci?
-
What bacteria are atypical?
- Chlamydia
- Mycoplasma
- Legionella
-
What makes Chlamydia atypical?
cell wall is similar to gram-negatives, but no peptidoglycan present
-
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?
yeasts
-
How do yeasts reproduce?
blastoconidia formation or fission (budding)
-
What fungi form hyphae?
moulds
-
What type of hyphae penetrate medium (grow down)?
vegetative hyphae
-
What type of hyphae grow upward and bear reproductive bodies?
aerial hyphae
-
-
-
What fungi are dimorphic?
- Blastomyces
- Histoplasma
- Coccidioides
-
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?
18-24h
-
How long does it take to determine an MBC?
36-48h
-
What are the methods for determining an MIC?
- macro-bath dilution
- micro-broth dilution
- agar dilution
- Kirby-Bauer disk-diffusion
- epsilometer strip ("E test")
- automated systems
-
Why is a true 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
- S. aureus
- S. pneumoniae
-
What is a secondary pathogen?
- cause disease more readily in individuals with underlying chronic disease or in those otherwise compromised
- P. aeruginosa
- C. albicans
-
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?
- fimbriae/pili
- lectins
- lipids
- mechanical
-
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
- P. aeruginosa
- S. epidermidis
-
What are the mechanisms used to evade host defenses and remain viable?
- production of antiphagocytic capsule
- production of toxins
- production of destructive enzymes
- stealth
-
What is a antiphagocytic capsule?
- polysaccharide capsules discourage antibody recognition and retard complement fixation
- N. meningitidis
- 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?
- intracellular
- 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?
- lipopolysaccharides
- 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?
- bacteriophages
- plasmids
- transposons
- 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
- non-compliance
- patient self-medication
- 3. Widespread antimicrobial use in food production industry
-
What are the types of antimicrobial resistance?
-
What is primary resistance?
- naturally occurring
- prior antimicrobial exposure not required
- predictable
- also called inherent, intrinsic, or native
- E. coli to Vancomycin
-
What is secondary antimicrobial resistance?
- develops following antimicrobial exposure
- not predictable
- also called acquired
-
What are the two methods of developing secondary antimicrobial resistance?
- selection of resistant subpopulations
- genetic alteration
-
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?
- Conjugation: transfer between bacteria that are in cellular contact
- Transduction: transfer via bacteriophage (virus)
- Transformation: 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?
- Plasmid-mediated
- Transposon-mediated
-
What are the characteristics of plasmid-mediated resistance?
- extrachromosomal double-stranded DNA (circular)
- self-replicating
-
What are the characteristics of Transposon-mediated resistance?
- DNA fragments
- 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?
- beta-lactamases
- aminoglycoside resistance modifying enzymes
- chloramphenicol acetyltransferase
- erythromycin esterase
-
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?
- Enterobacter
- Citrobacter freundii
- Serratia marcescens
- Pseudomonas aeruginosa
-
What agents are potent inducers of beta-lactamases?
- cefotaxime
- ceftriaxone
- ceftazidime
- imipenem
- clavulanate
-
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
- K. pneumoniae
- E. coli
-
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
- K. pneumoniae
- Enterobacter
- Citrobacter freundii
- M. morganii
- Serratia marcescens
- P. aeruginosa
-
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
- DNA gyrase: P. aeruginosa resistance to ciprofloxacin
-
What alterations in bacterial cell membranes cause antimicrobial resistance?
- porin channels
- transport proteins
- efflux pumps
-
What are porin channels?
- portals through the bacterial cell wall
- aqueous interior
- facilitate transport of hydrophilic molecules into the cell
- change in number or size can cause resistance
-
What microbes use efflux pumps?
- E. coli: TCNs, FQs
- S. aureus: TCNs, FQs
- P. aeruginosa: FQs
- S. pneumoniae: macrolides
- N. gonorrhoeae: TCNs
- Candida: azoles
-
What drugs can be used for MRSA?
- vancomycin (DOC)
- bactrim
- minocycline
- linezolid
- daptomycin
-
What can be used to treat VISA?
bactrim
-
What genes convey MRSA and VRSA?
-
What agents is penicillin-resistant pneumococcus resistant to?
- PCNs
- Cephs
- macrolides
- bactrim
- TCNs
-
What drugs is enterococcus resistant to?
- cephs
- bactrim
- PCNs (static)
- vancomycin (static)
- AGs
-
What genes confer resistance to vancomycin?
- vanA: inducible, high-level resistance to vanco and teicoplanin
- vanB: inducible resistance to vanco, susceptible to teicoplanin
- vanC: 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?
- patient education
- knowledge of local susceptibility patterns
- prescriber education
- develop guidelines for appropriate antimicrobial usage
- vaccination
- hand washing
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