MDL 237
Clinical Bacteriology
Spring 06’
Rhoads
Introduction - summary
Characteristics of bacteria (vs Eukaryotes)
Distinguishing bacteria: via 1. anatomy/morphology
2. physiology
Relationships with other critters on planet Earth
Bacterial virulence & pathogenicity
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I hope to give you the opportunity to learn more this semester.
That’s more for your money! Good news!
Note: Take good notes on this presentation. If I say you don’t
need to know it then you don’t need to know it, but…
Bacteria vs the other guys
Kingdom Prokaryotae (Monera)
Prokaryotes: cyanobacteria (blue-green algae)
archae
bacteria – here is our focus
Note: facts in the next 2 slides are sometimes used to state
differences in prokaryotes (vs eukaryotes) and other times
to distinguish bacteria from everybody else. The latter is not
really proper, but since we are only interested in bacteria we
will do this.
Bacteria vs the other guys
no “life cycle”: “vegetative” cells
endospores (maybe) Clostridium, etc.
small: 0.1 – 10uM range, but….
binary fission: simple = rapid exponential growth
harder to stop / kill? bacteriastatic vs bacteriacidal
simple intracellular organization: no organelles
proximity of mRNA to ribosomes
more is better? simple = harder to stop / kill?
disadvantages?
organization of DNA:
DSCCC haploid chromosome plus plasmids
VS
multiple linear diploid chromosomeS cont….
Bacteria vs the other guys
envelope:
cell wall composed of peptidoglycan
exceptions: Mycoplasma,Mycobacterium,etc.
membrane(s): cytoplasmic and maybe another
“Gram” stain: Gram (+) vs Gram (-)
other differences:
nucleic acid homology
ribosome size / structure
huge metabolic diversity!!!
others that I cant think of at the moment or is
not worth discussing
Distinguishing bacteria: anatomy / morphology
Morphology is very important in classification,
characterization & identification of bacteria:
1. colony morphology
2. cellular moropholgy
3. Gram stain – not really morphology, but it is a 1st step
1. Colony morphology:
what is a colony?
how do you go about seeing a colony?
what is growth “media”? what are the types?
what are the basic differences in colony appearance?
can colonial morphology differ based upon the medium,
culture conditions, age, other? cont….
Streak plate for isolation – “isolated” colonies
No, you don’t need to know this for me
Distinguishing bacteria: anatomy / morphology
2. Cellular morphology:
a) size: Chlamydia (0.3uM) vs Bacillus (5uM)
b) shape:
rod: varies a lot! see 2 slides
other: spirochetes type of rod? see 1 slide
cocci: round round is round, but…. see 1 slide
c) arrangement: chains see cocci slide
clusters
other
Rod shape variations
Bacillus cereus with endospores
Escherichia coli
Pseudomonas aeruginosa
fusiform, ex: Fusobacterium
spirochaete, ex: Borrelia
Trepomena
Coryneform rod = club-shaped
ex: Corynebacterium
spirillum, ex: Helicobacter
coccobacillus, Ex: Haemophilus
Curved or comma-shaped, ex: Vibrio
clusters, ex: Staphylococcus
chains, ex: Streptococcus
diplococci, ex: Neisseria
Streptococcus - notice the shape – round?
Cocci
Arrangement - rods
Singles & pairs – most rods
Chains - Bacillus Corynebacterium – L shaped from “snapping
& “palisade” or Chinese letters
notice polyphosphate (volutin) granules
Distinguishing bacteria: anatomy / morphology
3. Gram stain: based on thickness of peptidoglycan cell wall
Gram (+): thick = retains CV during decolorization
Gram (-): thin = loses CV during decolorization
Gram variable: Mycobacterium
Mycoplasma
Other ways to determine?
presence or absence of lipopolysaccharide, etc.
Distinguishing bacteria: anatomy / morphology
Differential stains:
Gram stain Acid fast stain: Mycobacterium
Nocardia
other
Motility:
presence or absence of flagella
motility soft agar deep
Distinguishing bacteria: anatomy / morphology
Presence of absence of a capsule
Presence or absence of endospores
Distinguishing bacteria: physiology
Metabolism:
aerobic respiration
fermentation:
presence or absence of oxygen = aerotollerant
OR
only under anaerobic conditions
anaerobic respiration – using something other than
oxygen as a terminal electron acceptor
photosynthesis (but we are not concerned about that)
Tests: O/F glucose, oxygen requirements, other
Distinguishing bacteria: physiology
Oxygen requirements: overlaps with metabolism
obligately aerobic: Pseudomonas must have O2 so…
microaerophile: Campylobacter loves a little oxygen
facultative (anaerobe): Staphylococcus, all enterics lots
aerotollerant anaerobe: Streptococcus vs anaerobes?
obligately anaerobic: Clostridium, Bacteroides,
Fusobacterium, etc.
More than 1 reason why anaerobic
Degree of sensitivity varies: Clostridium not strict vs…
Culture requirements: gas pak, other
Distinguishing bacteria: physiology
Differential carbohydrate catabolism:
ability to utilize glucose: Phenol red broth
MR/VP
O/F glucose
ability to utilize lactose: MacConkeys
EMB
ability to utilize citrate: Simmon’s citrate
ability to utilize mannitol: Mannitol salt agar
etcetera, etcetera, etcetera….
Tests based upon pH changes with pH indicators in most
cases.
Distinguishing bacteria: physiology
1. Selective media: growth or no growth
2. Differential media: appearance differs
vs
differential hemolysis on blood agar CAMP test
MacConkey agar EMB agar mannitol salt agar
Distinguishing bacteria: physiology
Antimicrobial susceptibility testing:
Kirby Bauer
MRSA
MIC
Note: new FDA approved product IDI-MRSATM identifies
MRSA in 1hr using automated DNA analysis. ?????
Distinguishing bacteria: physiology
NUMEROUS other tests of many types! Please don’t do
something crazy like learning this list!
cytochrome C oxidase test
catalase test
nitrate reduction test
sulfate reduction test
amino acid decarboxylation test
phenylalanine deamination test
tryptophan hydrolysis test (indole)
starch hydrolysis test (amylase)
egg yolk lecithinase hydrolysis test (lipase)
gelatin hydrolysis test (protease)
and on and on it goes…….
About bacteria
Relationships with host (“definitive”)
mutualistic
commensal
parasitic = pathogens “Parasitology”?
Pathogen VS “opportunistic” pathogen VS non-pathogen
So, is an “infection” a bad thing? Some are, but most are not!
Are the pathogens even helping you most of the time?
Where are they on planet Earth? EVERYWHERE!
What do they do? LOTS!
Is Bacteriology synonymous with Medical Bacteriology? NO!
Bacterial virulence & pathogenicity
Pathogen: disease causing microorganism
Pathogenicity: ability to cause disease
Virulence:
1. severity: …of condition, …of damage
2. infectivity: effectiveness of initiating infection
Bacterial virulence & pathogenicity
Invasion: how do they get in
how do they pass barriers, defenses
Survival: evading defenses
nutrition
Pathology: physical / mechanical? Not likely vs fungi
intracellular disrupt cellular homeostasis
Rickettsia Chlamydia Mycobacterium others
toxins page 29 next slide →
Bacterial toxins
a) exotoxins: Gram (+) & Gram (-)
extracellular products disseminate → systemic
mechanism & severity varies:
S. aureus enterotoxin vs C. diptheriae, C. tetani, C.botulinum
good news: most are proteins so they….
are heat labile
can be destroyed by proteases
b) endotoxin: Gram (-) only they are all the same
outer membrane component – NOT a product
only disseminates as cell fragments
lipopolysaccharide (LPS)
pyrogen - hypothalamus