Bacteriology Quiz: Key Bacterial Species

Prokaryotes: Domains Bacteria and Archaea

• Prokaryotes have one circular chromosome, not enclosed in a membrane
• They lack organelles
• Their cell walls contain peptidoglycan
• They reproduce by binary fission

Proteobacteria

• A large taxonomic group named after the Greek god Proteus, known for changing shape
• Gram-negative bacteria
• Chemoheterotrophic metabolism
• Five classes: Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Epsilonproteobacteria

Alphaproteobacteria

• Can grow with very low nutrient levels
• Some have stalks or buds known as prosthecae
• Include important pathogens:
  • Rickettsia: Obligate intracellular parasites, cause spotted fevers (e.g., Rocky Mountain spotted fever, epidemic typhus) transmitted by ticks and insects.
  • Ehrlichia: Transmitted by ticks, cause ehrlichiosis
  • Bartonella: Human pathogen, B. henselae causes cat-scratch disease
  • Brucella: Obligate parasite of mammals, survives phagocytosis, causes brucellosis

Betaproteobacteria

• Include non-motile rods like Bordetella pertussis, which causes whooping cough
• Contains Neisseria gonorrhoeae and N. meningitidis which cause gonorrhoea and meningococcal meningitis respectively

Gammaproteobacteria

• Includes several subclasses:
  • Pseudomonadales: Opportunistic pathogens (nosocomial infections), diverse metabolism, often found in soil, and includes Pseudomonas aeruginosa (wound and urinary tract infections), Moraxella lacunata (conjunctivitis), Acinetobacter baumanii (respiratory pathogen, antibiotic resistant)
  • Vibrionales: Found in aquatic habitats, includes Vibrio cholerae (cholera) and V. parahaemolyticus (gastroenteritis).
  • Enterobacteriales: Commonly called enterics, found in the intestinal tract, ferment carbohydrates, facultative anaerobes (can live with or without oxygen) with peritrichous flagella; Escherichia coli (indicator of fecal contamination, foodborne illness, UTI infections), Salmonella (wide range of foodborne illnesses, especially Salmonella typhi causing typhoid fever), Shigella (bacillary dysentery), Klebsiella pneumoniae(pneumonia), Serratia (red pigment production, nosocomial infections), Proteus (swarming motility; colonies show concentric rings), Yersinia pestis (plague, transmitted via fleas). Various Enterobacter species are also found in this class.
  • Pasteurellales: Pathogens of domestic animals, e.g., Pasteurella multocida; Haemophilus influenzae is involved with meningitis, earaches, and epiglottis

Deltaproteobacteria

• Contains Bdellovibrio: Attacks other gram-negative bacteria

Epsilonproteobacteria

• Helical or curved shape, microaerophilic
• Includes Campylobacter jejuni (foodborne intestinal disease) and Helicobacter (cause peptic ulcers and stomach cancer)

The Nonproteobacteria (Gram-Negative Bacteria)

• Diverse group including Chlamydiae, Bacteroidetes, Cytophaga, and Fusobacteria
  • Chlamydiae: Lack peptidoglycan, grow intracellularly; Chlamydia trachomatis (trachoma, urethritis), Chlamydophila psittaci (respiratory psittacosis), and Chlamydophila pneumoniae (pneumonia).
  • Bacteroidetes: Anaerobic, found in the mouth and large intestine; Cytophaga degrades cellulose.
  • Fusobacteria: Anaerobic, found in the mouth, cause dental abscesses.

Cyanobacteria (The Oxygenic Photosynthetic Bacteria)

• Carry out oxygenic photosynthesis (2H₂O + CO₂ → (CH₂O) + H₂O + O₂)
• Many contain heterocysts for nitrogen fixation
• Possess gas vesicles for buoyancy
• Unicellular or filamentous

The Phyla Chlorobi and Chloroflexi (The Anoxygenic Photosynthetic Bacteria)

• Carry out anoxygenic photosynthesis (2H₂S + CO₂ → (CH₂O) + H₂O + 2S°)
• Include green sulfur bacteria (Chlorobi), green nonsulfur bacteria (Chloroflexi), purple sulfur bacteria, and purple nonsulfur bacteria.

Spirochaetes

• Coiled bacteria that move via axial filaments.
• Includes Treponema pallidum (syphilis), Borrelia (relapsing fever, Lyme disease), and Leptospira (excreted in animal urine).

Deinococcus-Thermus

• Deinococcus radiodurans: Extremely resistant to radiation.
• Thermus aquaticus: Found in hot springs, a source of Taq polymerase.

The Gram-Positive Bacteria

• Divided into Firmicutes, Tenericutes, and Actinobacteria based on G+C ratios.

Firmicutes

• Low G + C ratio, Gram-positive
  • Clostridiales: Endospore-producing, obligate anaerobes; Clostridium botulinum, C. perfringens, C. difficile and C. tetani
  • Bacillales: Endospore-producing rods; Bacillus anthracis (anthrax), B. thuringiensis(insect pathogen), B. cereus(food poisoning)
  • Lactobacillales: Aerotolerant anaerobes, produce lactic acid; Lactobacillus (colonize body, food production), various Streptococcus species (spherical in chains; S. pyogenes(tissue destruction), S. pneumoniae and S. mutans(alpha-hemolysis, dental caries, and respiratory infections) -Enterococcus: Found in the intestinal tract; hospital contaminants; E. faecalis, and E. faecium; Listeria monocytogenes (food contaminants)

Tenericutes

• Low G+C ratio, lack a cell wall, pleomorphic; Mycoplasma pneumoniae (mild pneumonia).

Actinobacteria

• High G+C ratio, Gram-positive, often pleomorphic, branching filaments, important inhabitants of soil
  • Corynebacterium diphtheriae (diphtheria),
  • Propionibacterium acnes (acne),
  • Gardnerella vaginalis (vaginitis),
  • Streptomyces (antibiotics),
  • Actinomyces (mouth and throat tissue destruction)
  • Nocardia asteroides (pulmonary infections).

Diversity Within Archaea

• Extremophiles (halophiles, thermophiles, methanogens)
• Lack peptidoglycan.

Microbial Diversity

• Bacteria have a wide size range
• PCR determines the large number of bacterial species
• The majority of bacterial species haven't been identified or cultured and are part of interlinked, complex food chains.