BACTERIA MORPHOLOGY

Question 1

Groups of actinomycetes

Answer 1

Actinomyces: are anaerobic, non-acid-fast; fragment into short coccal and bacillary forms; do not form spores (conidia); e.g. Actinomyces israeli.

• Nocardia: similar to Actinomyces except that they are aerobic and acid-fast, e.g. Nocardia farcinica.

• Streptomyces: have vegetative mycelium and form conidia from aerial hyphae; do not fragment into short forms; over 500 species are recognized, many of which produce antibiotics, e.g. Streptomyces griseus (produces streptomycin).

Question 2

NON-FILAMENTOUS BACTERIA

Answer 2

They are simple unicellular organisms that never form mycelia.

Question 3

THE COCCI

Answer 3

• These are classified according to the mode of cell grouping and according to the Gram stain.
  • Streptococcus: The cells adhere in chains (of 4-20 cells) due to successive cell divisions along the same plane
  • They are Gram-positive, e.g. Streptococcus pyogenes (agent of pyogenic infections).
• Staphylococcus: The cells adhere in irregular clusters due to successive divisions in three planes irregularly
  • They are Gram-positive, e.g. Staphylococcus aureus

– Sarcina: The cells adhere in cubical packets of 8 (or multiples of 8) due to successive divisions in three planes regularly
– They are Gram-positive, e.g. Sarcina ventriculi (found in the stomach of humans and other monogastric animals).

– Neisseria: cells adhere in pairs (i.e. diplococcus) due to division along the same plane.
– They are Gram-negative, e.g. Neisseria gonorrhoeae and N. meningitides.

Question 4

THE BACILLI

Answer 4

Diplobacilli
• Streptobacilli
• Rods side by side or in X, V or Y figures

Question 5

Categories of THE BACILLI

Answer 5

Acid-fast Bacilli: Only members of the genus Mycobacterium are acid-fast and can be distinguished by the Ziehl-Neelsen stain, e.g. M. tuberculosis.

2. Gram-positive spore-forming Bacilli: These belong to two genera:
   • Bacillus: these are aerobic sporeformers, e.g. B. cereus
   • Clostridium: these are anaerobic sporeformers, e.g. C. tetani
3. Gram-positive non-spore-forming Bacilli: flagellated and highly motile; tend to grow in chains, e.g. Lactobacillus lactis.
4. Gram-negative Bacilli: comprises the coliforms or enteric bacteria (enterobacteria), such as Escherichia, Salmonella, Shigella, Klebsiella, Proteus, etc., and other bacilli such as Brucella, Bordetella, Pasterurella, Pseudomonas etc.

Question 6

FILAMENTOUS BACTERIA

Answer 6

They are all gram-positive organisms that form branching filaments (mycelia) resembling fungi