Quizlet exported flaschards Dr.S-C

• Study notes on fermentative proteobacteria have been given.

Overview of Proteobacteria

• Four phyla of Bacteria encompassing over 90% of characterized genera and species include Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes.
• Proteobacteria are categorized into five clusters: Alpha, Beta, Gamma, Delta, and Epsilon Proteobacteria.
• Proteobacteria are well-studied due to their relative ease of culturing.
• All Proteobacteria are Gram-negative.

Enterobacteriales (Gamma Proteobacteria)

• Key genera within the Enterobacteriales class include Escherichia, Enterobacter, Klebsiella, Proteus, Salmonella, Serratia, and Shigella.
• Enteric bacteria characteristics:
  • Gram-negative
  • Facultative anaerobes
  • Motile or non-motile
  • Possess peritrichous flagella
  • Nonsporulating rods
  • Cytochrome c oxidase (negative) and catalase (positive)
  • Ferment sugars
  • Some are pathogenic
• Salmonella (S.typhi) causes typhoid fever.
• Salmonella is associated with poultry and can withstand dry conditions.
• Escherichia (E.coli) acts as both a commensal organism and a pathogen in gastrointestinal infections.
• Shigella (S.dysenteriae) causes bloody diarrhea and is closely related to E.coli.
• Yersinia (Y.pestis) is responsible for causing the plague.
• Klebsiella can live in soil or water, fix nitrogen, and cause pneumonia.
• Serratia produces a red pigment called prodigiosin.
• Erwinia is a common plant pathogen.
• Photobacterium exhibits bioluminescence.

Classification Based on Fermentation

• Enteric bacteria can be classified by fermentation products during anaerobic respiration: Mixed Acid Fermenters and 2,3-Butanediol Fermenters.
• Mixed acid fermenters produce acetic, lactic, and succinic acids.
• In addition to acids, mixed acid fermentation yields ethanol, CO2, and H2.
• Examples of mixed acid fermenters are E.coli, Salmonella, Shigella, Citrobacter, Proteus, and Yersinia.
• 2,3-butanediol fermentation primarily produces butanediol, ethanol, CO2, H2, and trace amounts of acids.
• Mixed acid fermenters cannot produce 2,3-butanediol.
• Examples of butanediol fermenters are Enterobacter aerogenes, Klebsiella, Erwinia, and Serratia.

Specific Enteric Bacteria

• Escherichia: A universal inhabitant of the intestinal tract, synthesizes vitamin K; pathogenic strains can cause diarrhea, UTIs in women, gastrointestinal infections, and foodborne diseases.
• Salmonella: Closely related to Escherichia, pathogenic, immunologically characterized by surface antigens, causes typhoid fever and gastroenteritis.
• Shigella: Closely related to Escherichia, pathogenic, causes bacillary dysentery.
• Proteus: Rapidly motile with swarming motility, colonies form concentric rings, cause UTIs in humans, and produce urease.
• Enterobacter aerogenes: Found in water, sewage, and the intestinal tract of warm-blooded animals; may cause UTIs.
• Klebsiella: Found in soil and water, most strains fix nitrogen, and can cause pneumonia.
• Serratia: Found in soil, water, and the intestinal tract of insects, vertebrate animals, and sometimes humans; may cause nosocomial infections and forms prodigiosins (red pigments).
• Cronobacter: Discovered in 2007, causes meningitis (kills babies).

Coliforms

• Coliforms are facultative aerobic, Gram-negative, non-spore-forming, rod-shaped bacteria that ferment lactose within 48 hours at 36 degrees Celsius.
• The presence of coliforms like E.coli in water indicates contamination and inadequate treatment to remove fecal contaminants.

Serovars and Antigens

• Serovars are variations within a species of bacteria or virus, based on surface antigens.
• Salmonella has over 2500 distinct serovars.
• Salmonella's three cell surface antigens are O, H, and Vi.
  • O antigen: Cell wall (somatic) antigen
  • H antigen: Flagellar antigen
  • Vi antigen: Outer polysaccharide antigen, associated with typhoid fever
• Some Escherichia strains form the K-antigen (capsular polysaccharide), allowing attachment and colonization of the small intestine and producing enterotoxins that cause diarrhea.
• Shigella produces both an endotoxin (enterotoxin) and a neurotoxin, causing gastroenteritis.

Biochemical Tests for Enteric Bacteria

• Methyl Red Test: Determines if enteric bacteria are mixed acid fermenters when supplied with glucose.
  • Positive result: Content turns red due to acid production.
  • Negative result: Content remains yellow as no acids are produced.
• Voges-Proskauer Test: Detects acetoin and Cytochrome c oxidase in bacterial broth culture.
  • Reagents used: KOH (potassium hydroxide) and naphthol.
  • Positive result: Cherry red color.
  • Negative result: Yellow-brown color.
  • Positive results indicate the presence of Enterobacter and Klebsiella and other butanediol fermenters.
• Triple Sugar Iron Test (TSI): Tests a microorganism's ability to ferment sugars and produce H2S.
  • Salmonella and Shigella show a positive test.
  • Sugar supplies used: Glucose, lactose, and sucrose.
  • Sulfur source: Sodium thiosulphate.
  • Iron source: Ferrous sulphate.
  • Positive result: Acids produced change the phenol red to yellow.
• Urease Test: Identifies organisms that hydrolyze urea to produce CO2 and NH3 (due to the urease enzyme).
  • Proteus, Yersinia, and Klebsiella usually give a positive result.
  • Positive result: Red/magenta color.
  • Negative result: Yellow color.
• Indole Test: Determines an organism's ability to cleave tryptophan using tryptophanase to produce indole and pyruvate.
  • Escherichia coli, Enterococcus, Klebsiella, and Aeromonas show positive results.
  • Positive result: Red or red-violet color at the surface of the broth.
  • Negative result: Yellow color at the surface of the broth.
• Motility Test: Uses a motility test agar that is semisolid to detect bacterial motility.
  • Motility is detected by diffused growth moving from the central stab line.
  • Proteus, Salmonella, and some Escherichia exhibit motility.
• Gas Production from Glucose Test:
  • Positive result: Color change from red to yellow (acid production) and large gas production.
  • Escherichia coli shows a clearer positive result (Proteus may not).
• Citrate Utilization Test:
  • Positive result: Color change from green to blue.
  • Negative result: Color remains green.
  • Escherichia coli gives a negative result.
  • Enterobacter, Salmonella, and Proteus give positive results.
• Oxidase and Nitrate Reduction Tests:
  • Oxidase test and nitrate reduction to nitrite (denitrification) are key tests to distinguish Enterics from other bacteria of similar morphology.
  • Enterics are oxidase-negative.
  • Enterics cannot reduce nitrates to nitrogen gas.

Pseudomonadales and Vibrionales

Key Genera

• Key genera in the group Pseudomonadales and Vibrionales include Alivibrio, Pseudomonas, Vibrio, and Photobacterium.

Pseudomonadales Morphology:

- Gram-negative
- Polarly flagellated
- Aerobic

• Physiology: Cytochrome c oxidase positive and catalase positive.
• Metabolism: Chemoorganotrophs.
• Ecology: Found in soil; some respire anaerobically with nitrate as an electron acceptor.
• Pathogenicity: Opportunistic pathogens causing plant and animal diseases.
• P.aeruginosa can cause respiratory infections (cystic fibrosis), wounds (burns), and UTIs.
• P.syringae and P.marginalis are plant pathogens.
• Treatment Complications: Carry R plasmids that remove antimicrobial drugs from cells.
• Most pseudomonads are naturally resistant to antibiotics.

Vibrionales Morphology:

- Gram-negative
- Curved rods
- Facultative anaerobes
- Polar or peritrichously flagellated.

• Metabolism: Fermentative metabolism.
• Ecology: Aquatic (marine/brackish/freshwater habitats).
• Pathogenicity: Causes cholera in humans and gastroenteritis.
• Physiology: Oxidase positive.

Bioluminescence

• Several Vibrionales species emit light- bioluminescence but only at high population densities

Biofilms

• Biofilms: A community of microbes encased in a sticky matrix and associated with a surface.

Biofilm Formation Steps:

- Free-swimming bacteria settle on a surface.
- Cells synthesize a sticky matrix (extracellular polymeric substances).