Bacteriology Exam 1 Flashcards
basic roles of bacteria and fungi in health and disease
Host immunity
environment
organism pathogenicity
primary pathogen
normal host defenses overcome
opportunistic pathogen
sentinels of underlying problems with host management
prokaryote cell structure and organization
bacteria
no membrane bound organelles
70S ribosomes
DNA = singular circular chromosome, plasmid
no nuclear membrane/nucleolus
replicates via binary fission
haploid genome
no introns
polycistronic operons
eukaryotes cell structure and organization
fungi, protozoa, algae
membrane bound organelles
70 & 80S ribosomes
DNA linear chromosomes
nuclear membrane/nucleolus
replicates via mitosis
diploid genome
introns
monocistronic transcription (no operons)
what is a cell wall made up of? what is the difference between gram + and gram - cell walls?
peptidoglycan (murein) - a crosslinked polymer with repeating subunits of NAG & NAM
gram + has thick peptidoglycan layer
gram - has thin layer, doesn’t uptake gram stain as well
Cell wall structure: how do gram + and gram - bacteria differ?
gram +: thin cytoplasmic membrane + thick peptidoglycan layer
gram -: thin cytoplasmic membrane + thin peptidoglycan layer + outer bilipid membrane
What won’t a gram stain allow us to see?
spores
mollicutes (E.G. MYCOPLASMA)
What is different about Mycoplasma?
type of mollicute = no cell wall = cannot be stained via gram stain
obligate aerobe
must use O2 as terminal e- acceptor
aerotolerant anaerobe
don’t use O2 but can survive in the presence of O2 with help of superoxide dismutase & peroxidase
facultative anaerobe
prefer no O2, but can use it if present; many have catalase, SOD and peroxidase
obligate anaerobe
no enzymes dealing with O2
what protective enzymes do bacteria have to protect them from reactive oxygen species?
superoxide dismutase
peroxidase
catalase
Anaerobe
uses other terminal e- acceptor (SO4)
Koch’s Postulates
1.Microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
2.The microorganism must be isolated from a diseased organism and grown in pure culture
3.The cultured microorganism should cause disease when introduced into a healthy organism
4.The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent
limitations of Koch’s postulates
diseases may be caused by ingestion of a preformed toxin
many microorganisms are difficult to grow in culture
some agents require another factor (i.e. stress) to cause disease
there are carrier states for some microorganisms
exotoxins
gram + & gram - bacteria
proteins/polypeptides
pharmacologically-specific effects
distinct in structure
lethal in minute amounts
labile to heat/chemicals
convertible to toxoids
endotoxins
gram - bacteria
lipopolysaccharide (lipid A) - toxic
many effects
similar in structure
lethal in large amounts
stable in heat/chemicals
not convertible to toxoids
saprophytes
environmental organisms
commensals
colonize tissue without disease
symbionts
colonize host tissue but a mutually beneficial relationships exists
opportunists
colonize host tissue but cause disease with tissue injury or an environmental change
primary pathogens
infection directly causes disease, but host species predilections may exist
Thinking back to childbed fever in Semmelweis’s day, before we knew what bacteria were, what kinds of bacteria do you think actually caused the infections in the post-parturient women?
primary pathogens & opportunists
direct detection methods:
non-selective media
selective media
differential media
specific Ab
molecular detection of bacteria/fungal DNA
non-selective media: nothing added to inhibit microbes
selective media: additives to inhibit specific groups of microbes
differential media: additives to aid differentiation of microbial growth of microbial growth
MacConkey Agar
selective for gram - bacteria
differential for lactose fermentation
Pheylethyl alcohol agar
selective gram + bacteria
indirect detection methods
detection of host Ab directed against bacterial or fungal antigen
When would we want to choose a serological test versus culture?
serological test for…
pathogens with chronic carrier state
surveillance and control of regulatory diseases
difficult to-cultivate pathogens (e.g. neuro or ophtho)
When submitting a sample from a non-sterile site for culture, what other laboratory methods and clinical thinking are helpful in interpreting the significance of microorganisms isolated?
examples of cell wall disruptors (beta-lactams)
bactericidal or bacteriostatic
penicillins
cephalosporins
carbapenems
penicillins are bactericidal
examples of DNA synthesis inhibitors
bactericidal or bacteriostatic
sulfonamides - bacteriostatic unless combined with trimethoprim, then bactericial
nitroimidazoles - bactericidal
fluoroquinolones - bactericidal
examples of protein synthesis inhibitors
bactericidal or bacteriostatic
aminoglycosides - bactericidal
tetracyclins - bacteriostatic
macrolides/lincosamides - bacteriostatic
aceamides - bacteriostatic
what antibiotics should you NOT give food animals
chloramphenicol
metronidazole
which agents have at least some activity in all 4 quadrants?
carbapenems
macrolides/lincosamides
tetracyclines
acetamides
ampicillin
piperacillin
which agents have activity ONLY against intracellular bacteria and Mycoplasma
fluoroquinolones
tetracyclins
chloramphenicol
some macrolides
which protein synthesis inhibitors act on 30s ribosomes?
aminoglycosides
tetracyclines
which protein synthesis inhibitors act on 50s ribosomes?
macrolides/lincosamides
acetamides
which agents work only against both gram - and gram + obligate anaerobes
nitroimidazoles
which agents work only against both gram - and gram + aerobe facultatives
cephalosporins
sulfonamides/trimethoprim
fluoroquinolones
aminoglycosides
which agent works against everything except gram - aerobe facultative
benzylpenicillin
general mechanisms of antimicrobial resistance
- inactivation of drugs via bacterial enzymes
- modification of drug targets
- preventing access to cell
- efflux pumps
mechanisms of acquired resistance
transformation
transduction
conjugation
mutation
methods of antibiotic susceptibility testing (AST)
broth microdilutions (e.g. MIC)
Kirby-Bauer disc diffusion
What is exactly in an MIC and what does the laboratory observe to determine that value.
a two-fold dilution series of gorillacillin in Mueller-Hinton broth where a standard amount of bacteria of interest is added to each tube and then incubated at 35o for 16-24 hours
lowest dilution tested with no visible growth = MIC
