1. Spore Forming and Non-Spore
Forming Gram-positive Bacilli
10th
January 2007
SBM 2044
Medical Microbiology
Second year UG of BBiomedic Sc
2. Spores
• Why do bacteria produce spores?
• Survival
• Classification
• Definition = a resting cell, highly resistant
to dessication, heat, and chemical agents;
when returned to favourable conditions
bacteria re-activated, the spores
germinate to produce single vegetative
cells.
4. Bacillus
• Aerobic, G+ rods in chains, spores are located in
center of the non-motile bacilli
• Found in soil, water, air and vegetation
• Spores are viable for decades.
• B. cereus – produce enterotoxin and cause food
poisoning.
• B. anthracis – infection in human through injured
skin (cutaneous anthrax), mucous membranes
(GI anthrax), or inhalation of spores into lung.
6. • Spores germinate in the tissue of entry,
and growth of vegetative organisms result
in formation of a gelatinous oedema and
congestion.
• Spread via lymphatics to bloodstream and
multiply freely in blood and tissues.
• Capsulated, poly-D-glutamic acid capsule
is antiphagocytic
Bacillus
7. • Anthrax toxin is made up of three proteins:
• Protective antigen (PA), oedema factor
(EF) and lethal factor (LF).
• Treatment: ciprofloxacin, penicillin G along
with gentamicin and streptomycin. Vaccine
with live spores and a toxoid used to
protect livestock in endemic areas.
Bacillus
8. Clostridium
• Anaerobic, G+, motile rods, typical tennis
racquet morphology is created by terminal
spores that swell the sporangium
• Clostridial diseases from wounds inc tetanus
(NM disease) and gas gangrene (soft tissue
infection that damages muscle)
• Found in soil, animal faeces.
• Spores is placed centrally, subterminally or
terminally; most species are motile with flagella.
9. Clostridium
• Many form colonies with a zone of haemolysis
on blood agar. C perfringens typically produce
multiple zones of haemolysis around colonies.
10. Clostridium botulinum
• C botulinum causes botulism, from eating poorly
preserved food (canned).
• Spores are resistant to 100°C for many hours,
diminished at acid pH or high salt.
• C botulinum is distinguished by antigenic type of
toxin
• Toxin - 7 antigenic varieties (A →G). A, B, E (F)
mainly harmful to human.
• Botulinum toxin is absorbed from gut and binds
to receptors of presynaptic nervous system and
cranial nerves.
11. Clostridium
• Toxin acts by blocking release of acetylcholine
at synapses and neuromuscular junctions →
flacid paralysis.
• Symptoms such as visual disturbances,
inability to swallow, speech problem; seldom
with no apparent GI symptoms; no fever.
• ‘floppy baby’ = infant botulism. C botulinum
spores ingested from babies’ food. Present
with weak sucking response, loss of tone and
respiratory complications.
12. Clostridium
• Treatment – antitoxins raised in horses.
• Trivalent (A, B, E) antitoxin must be promptly
administered intravenously with precautions;
plus adequate ventilations.
• Treatment to control the microbe’s growth and
toxin production.
• Clostridium tetani cause tetanus or lockjaw.
13.
14. Non-Spore Forming Bacteria
• Generally, members of normal flora of skin and
mucous membranes of humans.
Aerobic G+ with High
G+C content, irregularly
shaped
Aerobic G+ with lower
G+C content, regularly
shaped
Corynebacterium
Propionibacterium
Actinomyces
Rhodococcus
Listeria
Lactobacillus
Erysipelothrix
15. Corynebacterium diphtheriae
• Infects nasopharynx or skin
• Mostly grow aerobically, non-motile
• Irregular swellings/clubbed-shaped; granules
within rod stained with aniline dyes.
16. Corynebacterium diphtheriae
• Blood agar+potassium tellurite, tellurite is
reduced intracellularly which gives the
black/gray coloured appearance.
17. Corynebacterium diphtheriae
• In respiratory wounds, skin of infected person; spread
by droplets or contact to susceptible individuals
• Diphtheria toxin (Dt) is a single polypeptide chain,
62000 Mw; a heat-labile.
• Dt cleaved into two polypeptide fragments following
mild-digestion with trypsin and reduction under
denaturing conditions.
Transporting A into
cell
Inhibits polypeptide chain
elongation, by inactivating EF-2
(with NAD)
This abrupt arrest of protein
synthesis results in necrotizing
and neurotoxic effects of Dt.
A B
18. Corynebacterium diphtheriae
• Pathogenesis is based upon: (1) the ability of a
given strain of C diphtheriae to colonize in the
nasopharyngeal cavity and/or on the skin, and
(2) its ability to produce diphtheria toxin.
• Pathology: Dt absorbed into mucous
membranes, causing destruction of epith and
superficial inflammatory response. Necrotic
epith embedded in exuding fibrin+RBC+WBC=
grayish “pseudomembrane”
• Disease is principally result of the action of toxin
formed rather than invasion by the organism
19. Corynebacterium diphtheriae
• Vaccination confers protection against disease
by production of antibodies to the diphtheria
toxin. The vaccine is produced from purified
inactivated toxin from a strain of C. diphtheriae.
• Diphtheriae antitoxin (DTP) administered to
infants, and followed by boosters.
• Treatment rapid suppression of toxin-producing
bacteria by antimicrobial drugs at the earliest
diagnosis of diphtheria.
20. Listeria monocytogenes
• Small/Short, G+,peritrichous flagella, rod. Grow
on Mueller-Hinton agar (better in sheep blood-
small zone of haemolysis); facultative anaerobe,
motile at room temp, catalase +
• Listeriosis results from ingestion of
contaminated food such as cheese and vegie;
primarily affects pregnant women, newborns,
those with weakened immune system.
• Able to multiply at low temp,
hence accumulate in contami-
nated food stored in refrigerator.
21. • The bacterium apparently invades via the intestinal mucosa. It is thought to attach to
intestinal cells by means of D-galactose residues on the bacterial surface which adhere to
D-galactose receptors on susceptible intestinal cells The bacterium is taken up by induced
phagocytosis, which is thought to be mediated by a membrane associated protein called
internalin. Once ingested the bacterium produces listeriolysin to escape from the
phagosome. The bacterium then multiplies rapidly in the cytoplasm and moves through the
cytoplasm to invade adjacent cells by polymerizing actin to form long tails.
Steps in the invasion
of cells and
intracellular spread by
L. monocytogenes.
22. Actinomycetes
• Form chains or filaments, facultative
anaerobes (+CO2)
• Actinomycosis is a chronic suppurative
and granulomatous infection that
produces pyogenic lesions with
interconnecting sinus tracts that contain
granules. Most cases due to A israelii, A
naeslundii.
• Commonly affecting cervicofacial, thoracic
and abdominal actinomycosis.
