MLAB 2434 – CLINICAL MICROBIOLOGY
SUMMER, 2005
CECILE SANDERS & KERI BROPHY
Chapter 1
- Bacterial Cell Structure, Physiology,
Metabolism, & Genetics

Taxonomy

Kingdom, Division, Class, Order, Family,
Tribe, Genus and Species
• Family = “Clan”; has “–aceae” ending
• Genus = “Human last name”
• Species = “Human first name”


When in print, genus and species are
italicized. (Staphylococcus aureus)
When written, genus and species are
underlined. (Staphylococcus aureus)
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Staphylococcus sp. is used when
referring to the genus as a whole
when the species is not identified.
 “sp.” – singular (Staphylococcus sp.)
 “spp.” – plural (Staphylococcus spp.)
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)
Bacteria Identification – test each
bacterial culture for a variety of
metabolic characteristics and
compare the results with known
results.
 All organisms are either
“prokaryotes”, “eukaryotes”, or
“archaeobacteria”

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

EUKARYOTES fungi, algae, protozoa,
animal cells, and plant
cells


Cells have nuclei
that contains DNA
and are complex
Most cells do NOT
have a cell wall
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

PROKARYOTES bacteria



Do not have a
membrane-bound
nucleus
DNA is a single
circular chromosome
Have both cell
(plasma) membrane
AND cell wall.
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Archaeobacteria
Resembles eukaryotes
 Found in microorganisms that grow
under extreme environmental
conditions


See chart on page 6 for
comparisons of Prokaryotes and
Eurkaryotes
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Bacterial Cell Wall
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Gram Positive (G+) Cell Wall





Very thick protective peptidoglycan layer
Many G+ antibiotics act by preventing
synthesis of peptidoclycan
Consists of cross-linked chains of glycan
Also contain teichoic acid and liptoeichoic
acid
Unique structure makes these bacteria G+
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Gram Negative (G-) Cell Wall
Two layers; inner is much thinner
than G+ cell walls
 Outer wall contains several
molecules, including Lipid A which is
responsible for producing fever and
shock in infections with G- bacteria

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)


G+ cocci in
clusters→
G- bacilli (rods)→
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Acid Fast Cell Wall – mainly
Mycobacteria and Nocardia
Have a G+ cell wall structure but
also a waxy layer of glycolipids and
fatty acids (mycolic acid)
 Waxy layer makes them difficult to
gram stain
 Can be decolorized by acid-alcohol,
hence the name “acid fast”

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Absence of Cell Wall – mainly
Mycoplasma and Ureaplasma


Lack of cell wall results in a variety
of shapes microscopically
Some bacteria produce slime layers
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Some bacteria
produce a capsule


Protect the
bacteria from
phagocytosis
Capsule usually
does not stain,
but can appear as
a clear area
(halo-like)
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Cell Appendages

Flagella – exterior protein filaments
that rotate and cause bacteria to
be motile
• Polar
• Peritrichous

Pili (fimbriae) – hairlike projections
that aid in attachment to surfaces
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Microscopic Shapes




Cocci (spherical)
Bacilli (rod-shaped)
Spirochetes (helical)
Groupings





Singly
Pairs
Clusters
Chains
Palisading
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Size and length
Short
 Long
 Filamentous
 Fusiform
 Curved
 Pleomorphic

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Common Bacterial
Stain


Gram Stain – to
be covered in lab
Acid-fast
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Acridine Orange –
stains nucleic acid of
both G+ and Gbacteria, either
living or dead; used
to locate bacteria in
blood cultures and
other specimens
where background
material obscures
gram stains
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Methylene Blue – stain for
Corynebacterium diphtheriae to
show metachromatic granules and as
counter-stain in acid-fast stain
procedures
 Lactophenol Cotton Blue – fungal
stain
 Calcofluor White – fungal stain
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

India Ink – negative stain for
capsules
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Microbial Growth and Nutrition
Needs
Source of carbon for making cellular
constituents
 Source of nitrogen for making
proteins
 Source of energy (ATP) for cellular
functions
 Smaller amounts of other molecules

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Nutritional Requirements for
Growth

Autotrophs (lithotrophs)
• Able to grow simply, using only CO2,
water and inorganic salts
• Obtain energy via photosynthesis or
oxidation of inorganic compounds
• Occur in nature and do not normally
cause disease
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Heterotrophic
• Require more complex substances for
growth
• Require an organic source of carbon and
obtain energy by oxidizing or
fermenting organic substances
• All human bacteria fall in this category
• Within this group, nutritional needs
vary greatly
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Types of Growth Media
Minimal medium – simple; not usually
used in diagnostic clinical
microbiology
 Nutrient medium – made of
extracts of meat or soy beans
 Enriched medium – nutrient medium
with extra growth factors, such as
blood

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)
Selective medium – contains
additives that inhibit the growth of
some bacteria while allowing others
to grow
 Differential medium – contains
additives that allow visualization of
metabolic differences in bacteria
 Transport medium – holding medium
to preserve those bacteria present
but does not allow multiplication

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Environmental Factors Influencing
Growth
pH – most media is between 7.0 and
7.5
 Temperature – most pathogens grow
at body temperature; grown at 35°
C in the lab

Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Gaseous composition
• Obligate aerobes – require oxygen
• Obligate anaerobes – cannot grow in the
presence of oxygen
• Facultative anaerobes – can grow with
or without oxygen
• Capnophilic – grow better with extra
CO2
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Bacterial Growth



Reproduce by binary fission
Can be fast (as little as 20 minutes for E.
coli) or slow (as long as 24 hours for M.
tuberculosis)
Determination of Numbers



Direct counting under microscope
Direct plate count
Density measurement
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Bacterial Biochemistry and Metabolism


Metabolic reactions cause production of
energy in form of ATP
Identification systems analyze unknown
specimens for:
• Utilization of variety of substances as a source
of carbon
• Production of specific end products from
various substrates
• Production of acid or alkaline pH in the test
medium
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Fermentation and Respiration
(Oxidation)

Fermentation
• Anaerobic process in obligate and
facultative anaerobes
• The electron acceptor is an organic
compound
• Does NOT require oxygen
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Oxidation
• More efficient energy-generating
process
• Molecular oxygen is the final electron
acceptor
• Aerobic process in obligate aerobes and
facultative anaerobes
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Metabolic
Pathways – main
one is EmbdenMeyerhoff

Convert glucose
to pyruvic acid, a
key intermediate
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

From pyruvic acid:







Alcoholic fermentation (ethanol)
Homolactic acid fermentation (lactic acid)
Heterolactic acid fermentation (lactic
acid, CO2, alcohols, formic and acetic acids
Propionic acid
Mixed acid fermentation (lactic, acetic,
succinic, and formic)
Butanediol fermentation
Butyric acid fermentation
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)


Main oxidative pathway is the Krebs
Cycle, resulting in acid and CO2
Carbohydrate Utilization & Lactose
Fermentation



“Sugars” = carbohydrates
Lactose fermentation – key component in
identification schemes
Lactose is converted to glucose, so ALL
lactose fermenters also ferment glucose
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Genetic Elements and Alterations

Plasmid
• Extra piece of DNA
• Code for antibiotic resistance and
other virulence factors are often found
on plasmids
• Sometimes passed from one bacterial
species to another
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Plasmid replication
Chapter 1
- Bacterial Cell Structure,
Physiology, Metabolism, & Genetics (cont’d)

Mutations
Changes that occur in the DNA code
 Results in changes in the coded
protein or in the prevention of its
synthesis
