Lec 5: Diversity of Gram +ve bacteria

Question 1

Classification of gram +ve

Answer 1

Bergey’s manual

Based on nucleic acid sequence

Groups: low G+C, high G+C

Mol% G+C= ([G+C]/ G+C+A+T) x 100

Question 2

Low G+C Gram positive bacteria

Answer 2

Phylum: firmicutes, tenericutes

Question 3

Genus Clostridium

Answer 3

Phylum Firmicutes

Rod-shaped

Anaerobe

Form endospores (resistant to heat, drying, chemicals, radiation)

Fermentative -> gain energy

Catalase -ve

In soil, human intestinal tract

Question 4

Clostridium botulinum

Answer 4

Causes botulism (food poisoning)

Common source of infection: insufficiently heated home-canned food -> endospores not killed -> germinate -> produce toxin

If food in adequately cooked -> toxin remains -> disease

Botulinum toxin: a neurotoxin -> paralysis

Question 5

Clostridium tetani

Answer 5

Causes tetanus

Endospores in soil -> enter wound -> germinate

Question 6

Clostridium perfringens

Answer 6

Cause food poisoning, diarrhoea

Cause gas gangrene

Spores from soil or bowel flora enter wounds from abortions, war, car accidents etc

Toxin destroys tissue, H2 gas from fermentation, tissue necrosis

Question 7

Genus Bacillus

Answer 7

Phylum Firmicutes

Low G+C

Gram +ve

Rod shaped

Aerobic or facultative anaerobe (can grow in presence or absence of O2)

Forms endospores

Catalase positive

Some species produce antibiotics

Question 8

Bacillus subtilis

Answer 8

Type species (typical bacillus). Well studied and understood

Question 9

Bacillus cereus

Answer 9

Food poisoning

Question 10

Bacillus thuringiensis

Answer 10

Insecticidal protein crystal toxic to caterpillars form next to endospore

Question 11

Genus listeria

Answer 11

Phylum firmicutes

Gram positive rods

Facultative anaerobes

Question 12

Listeria monocytogenes

Answer 12

Cause listeriosis

Contaminates soft cheeses, paté, deli meats, hot dogs

Risk to pregnant women, immunocompromised individuals

Neonatal sepsis (blood poisoning), death, stillbirths

Question 13

Genus Lactobacillus

Answer 13

Phylum firmicutes

Gram +ve rods

Facultative anaerobes

Ferment sugars -> lactic acid

Used in production pickles, wine, cheese etc

Inhabit gastrointestinal and genital tracts

Question 14

Genus Staphylococcus

Answer 14

Phylum Firmicutes

Gram +ve cocci

Irregular clusters ‘bunch of grapes’

Facultative anaerobes

Catalase positive

Associated with skin, mucus membranes of vertebrates

Question 15

Staphylococcus epidermidis

Answer 15

Common skin resident

Coagulase negative

Question 16

Staphylococcus aureus

Answer 16

Major human pathogen: ‘golden staph’

Cause boils, abscesses, pneumonia, food poisoning, toxic syndrome

Coagulase positive -> enzyme clots blood plasma

Question 17

Genus Streptococcus

Answer 17

Genus Firmicutes

Gram +ve cocci

In pairs or chains

Facultative anaerobes

Catalase -ve -> distinguishes Steptococcus from Staphylcoccus

2 grouping systems: lancefield grouping (based on structural variations in cell wall), type of haemolysis on blood agar plates

Question 18

Streptococcus pyogenes

Answer 18

Group A streptococci (GAS)

Major human pathogen (sore throat, rheumatic fever, ‘flesh eating’ disease)

Beta-haemolysis (zone of complete lysis of rbc around colony on blood agar)

Question 19

Streptococcus Agalactiae

Answer 19

Cause of sepsis & meningitis in newborn

Beta haemolysis

Question 20

Streptococcus pneumoniae

Answer 20

Pneumonia

Alpha haemolysis (partial lysis of rbc) -> greenish colour (biliverdin: by-product of haemoglobin degradation)

Question 21

Streptococcus mutans

Answer 21

Dental caries, plaque

Alpha haemolysis or non haemolytic

Question 22

Genus mycoplasma

Answer 22

Phylum Tenericutes

Lack cell walls

Bounded by cell membrane (contain sterols from host as cholesterol)

Variable shape: pleomorphic, spherical to pear-shaped, colonies ‘fried egg’ appearance

In soul, water, animals, plants

Question 23

Mycoplasma pneumoniae

Answer 23

Cause atypical pneumonia

Mild form of pneumonia

Question 24

Phylum actinobacteria

Answer 24

High G+C

Gram +ve bacteria

Question 25

Actinomycetes

Answer 25

Gram +ve

Aerobic

Form branching filaments or hyphae and asexual spores

Many resemble fungi in morphology

Soil inhabitants (few human, animal & plant pathogens)

Produce most of medically useful antibiotics

Question 26

Genus Corynebacterium

Answer 26

Phylum Actinobacteria

Gram +ve rods

Straight, curved or club-shaped cells

Angular arrangement of cells (chinese letters or palisade)

Form volutin (polyphosphate granules) inside cytoplasm -> energy & phosphate reserve

Question 27

Corynebacterium diptheriae

Answer 27

Diphtheria: respiratory infection

Characteristic pseudomembrane on respiratory mucosa (diphtheria toxin)

Endocritis (heart damage): possible side effect of diphtheria

Question 28

Genus Mycobacterium

Answer 28

Phylum Actinobacteria

Gram +ve rods: sometimes branch or form filaments

Grow slowly (up to 40 days -> colony)

Cell wall: high lipid content, outer layer: mycolic acids and other lipids, waxy & hydrophobic, cells impermeable to most stains, acid-fast

Needs special stains (Ziehl-Neelsen stain)

Question 29

Mycobacterium Tuberculosis

Answer 29

Global problem

Tubercules (nodules) in lung ->

Latent: infection dormant

Active: fever, cough, infectious, death if untreated

Disseminated: systemic (spread throughout body), death

Question 30

Mycobacterium leprae

Answer 30

Leprosy (Hansen’s disease)

Bacteria invades skin & nerve cells

Obligate intracellular pathogen

Can be disfiguring

Question 31

Genus Streptomyces

Answer 31

Phylum Actinobacteria

Gram +ve rods

Extensively branched filaments

Aerial (stick out) hyphae with chains or spores (not endospores)

In soil: odour of moist earth due to its volatile substances

Synthesise numerous antibiotics (streptomycin, tetracycline)