Spore Forming and Non-Spore Forming Gram-positive Bacilli

SBM 2044

Medical Microbiology

Second year UG of BBiomedic Sc

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.

SF Bacteria- 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.

Bacillus anthracis

• 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

SF Bacteria- Bacillus

• Anthrax toxin is made up of three proteins:

• Protective antigen (PA), edema factor (EF) and lethal factor (LF).

• Treatment: ciprofloxacin, penicillin G along with gentamicin and streptomycin.

SF Bacteria- Bacillus

SF Bacteria - Clostridium

• Anaerobic, G+, motile rods

• Many decompose proteins of form toxins.

• Found in soil, animal faeces.

• Spores is placed centrally, subterminally or terminally; most species are motile with flagella.

SF Bacteria - Clostridium

• Many form colonies with a zone of haemolysis on blood agar. C perfringens typically produce multiple zones of haemolysis around colonies.

SF Bacteria - Clostridium

• C botulinum causes botulism• -Distinguished by antigenic type of toxin• Spores are resistant to 100C for many hours,

diminished at acid pH or high salt.• 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.

• Lethal dose to human 1-2 µg.

SF Bacteria - Clostridium

• Pathogenesis• Most cases, through ingestion of uncooked

food.• 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.

SF Bacteria - Clostridium

• ‘floppy baby’ = infant botulism. C botulinum spores in babies’ food.

• Treatment – antitoxins raised in horses.• Trivalent (A, B, E) antitoxin must be promptly

administered intravenously with precautions; plus adequate ventilations.

SF Bacteria - Clostridium

• Clostridium tetani cause tetanus. • Distinguishable by specific flagellar antigens.• Toxin binds to receptors on the presynaptic

membranes of motor neurons.

NSF 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

ActinomycesRhodococcus

Listeria

Lactobacillus

Clostridium

Bacillus

Corynebacterium diphtheriae• Infects nasopharynx or skin• Mostly grow aerobically, non-motile• Irregular swellings/clubbed-shaped; granules

within rod stained with aniline dyes.

Corynebacterium diphtheriae

• Blood agar+potassium tellurite, tellurite is reduced intracellularly

Corynebacterium diphtheriae

• In respiratory wounds, skin of infected person; spread by droplets or contact to susceptible individuals

• Diphtheria toxin (Dt) is a heat-labile

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.

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

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.

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.

• 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.

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.

References

• http://textbookofbacteriology.net/

• http://www.gsbs.utmb.edu/microbook/

• Brooks’ Jawetz Medical Microbiology

• Puan Intan Azura Shahdan

• Room F2/A/2/73

Pseudomonad, Pasteurella

• Pasteurella – short G- rods with bipolar staining. Animals are their natural hosts in most cases.

Vibrios

Helicobacter pylori

Gram-positive Gram-negative

Cocci

Bacilli

F=fastidious, SF=spore-forming