MICROBIOLOGY 3

MICROBIOLOGY 3

1. Diversity of Bacteria

   • Helical
     • Treponema pallidium
   • Gram positive cocci
     • Staphylococci
       • Catalase positive
       • Staphylococcus aureus is positive in the coagulase test unlike other Staphylococci
     • Streptococci
       • Catalase negative
       • Further differenced by growth on fresh blood agar (beta haemolytic = completely clear zone, alpha haemolytic = green halo
   • Gram positive bacilli
     • Clostridia
       • produce spores
       • Clostridium perfringens selected for by Nagler test
     • Bacillus
       • Produce spores
   • Gram negative cocci
     • Neisseria gonorrhoeae
       • Also tested for by the oxidase test (turns purple)
     • Neisseria meningitidis
   • Gram negative bacilli
     • E coli
   • Yersinia pestis caused the Plague and is spread by rats
   • Honeymoon cystitis is caused when the skin bacterium Staphylococcus saprophyticus

2. Bacterial Identification

   • Artificial growth
     • Non viable cells may be present
     • Growth medium may not support growth
     • Growth conditions may not support growth
   • Pre treatment of acid or alkali eliminates bacteria that cant grow at extreme pH
     • Temperature and oxygen levels may also be manipulated
   • MacConkey agar contains bile salts
     • Salt selects for Staphylococci
   • VPAT agar select for Campylobacters and Neisseria gonorrhoeae
   • Exploits morphology and chemical composition, culture characteristics, metabolic characteristics, pathogenicity tests, antigenic structure identification and genome fingerprinting
   • Size and position of spores can aid identification
   • Haemophilus influenzae requires two growth factors, the X factor (haem) and the V factor (NAD). This bacterium causes respiratory infections and meningitis in small children
   • The enzyme catalase releases oxygen bubbles from a dilute solution of hydrogen peroxide in the catalase test (distinguishes between Staphylococci and Streptococci
   • Plasmid fingerprinting based on analysis of the 16S ribosomal RNA of bacteria

3. Mycobacterial Infections

   • Gram positive bacteria
     • Mycobacteria have waxy outer envelope so resist staining. The Zeihl Neelson staining protocol is used instead
       • Degrades waxy membranes
   • Mycobacterium laprae
     • Rod shaped bacterium
     • Causes leprosy
       • Damages peripheral nerves
       • Treatment involves multiple drug therapy for a year
     • Cant be cultured in the lab
   • Mycobacterium scrofulaceum, Mycobacterium avium-intracellulare and Mycobacterium tuberculosis cause scrofula
     • Infection of the skin of the neck and cervical lymph nodes
   • Mycobacterium tuberculosis was discovered by Robert Koch
     • Tuberculosis is considered a pulmonary disease but it can spread to many parts of the body
     • Also a form of meningitis
     • Can be cultured on an egg based medium
     • Lesions found in the upper portions of the lungs as it is an obligate aerobe

4. Bacterial Structures

   • 0.2-8um. Smaller than fungi but not smaller than viruses
     • Small bacteria - bordetella pertussis, Treponema pallidum and mycoplasma species (smallest)
     • Medium bacteria - Bacillus subtilis, E coli and Staphylococcus aureus
     • Large bacteria - Anabaena, Beggiatoa gigantean, Thiomargarita nambiensis, Epilopscium fishelsoni
   • Prokaryotes don't posses a nuclear membrane, organelle such as mitochondria and chloroplasts and have 70S ribosomes
   • Gram stain reaction
     • Crystal violet iodine complex retained by Gram positive
       • Gram positive bacteria have many layers of peptidoglycan and teichoic acid
     • CVI is removed by alcohol or acetone from Gram negative, which is then further stained red
       • Gram negative bacteria have one or two layers of peptidoglycan but this is surrounded by an outer membrane
         • Outer membrane: typical phospholipid appearance, proteins that allow transport, lipopolysaccharides and Lipid A (endotoxin)
         • May have fimbriae to stick to surfaces or pili for DNA transfer
   • Capsules may be produced to delay phagocytosis
   • Bacillus (aerobes)and Clostriudium (anaerobes) species produce spores to protect against heat, desiccation and irradiation