Lesson 4 Overview

Characteristics of Enterobacteriaceae

  • Gram-negative: Enterobacteriaceae are characterized by a gram-negative cell wall structure.
  • Fermentation: They can ferment glucose, a key metabolic feature.
  • Oxidase negative: Enterobacteriaceae do not produce oxidase.
  • Nitrate reduction: They reduce nitrate to nitrite.
  • Anaerobic respiration: They are facultative anaerobes, meaning they can survive with or without oxygen.
  • Motility: Most species within Enterobacteriaceae are motile; notable exceptions include:
    • Xenorhabdus
    • Yersinia

Infections Caused by Enterobacteriaceae

  • Diarrheal diseases: The primary infections caused by Enterobacteriaceae.
  • Urinary Tract Infections (UTIs): Also common infections associated with this group.
  • Normal flora: They are typically found in the intestines of humans and animals.

Extended Spectrum Beta-Lactamase (ESBLs)

  • Definition: ESBL stands for Extended Spectrum Beta-Lactamase, which are enzymes produced by some bacteria that confer resistance to a wide range of beta-lactam antibiotics.
  • Significant Organisms:
    • Escherichia coli (E. coli)
    • Klebsiella pneumoniae
    • Klebsiella oxytoca
    • Proteus mirabilis
    • Enterobacter species
  • Resistance to antibiotics: These organisms are resistant to:
    • Cephalosporins
    • Penicillins
    • Monobactams
  • Detection method: To determine if an organism is producing ESBL, clavaulanic acid can be added to an antibiotic susceptibility test. If there is susceptibility with the addition of clavulanic acid, this indicates the presence of ESBL.
  • Carbapenem-resistant Enterobacteriaceae (CRE):
    • Definition: Carbapenem-resistant Enterobacteriaceae refers to a group of bacteria that have developed resistance to carbapenem antibiotics, including Klebsiella pneumoniae.
    • Detection methods for CRE: The modified Hodge test or PCR (Polymerase Chain Reaction).

Examination of E. coli

  • Infections:
    • Diarrheal diseases
    • UTIs
  • Colony Morphology:
    • Appears as pink colonies on MacConkey agar (indicative of lactose fermentation).
    • On blood agar, they form large gray moist colonies.
  • Biochemical tests:
    • Indole: Positive
    • Methyl Red: Positive
    • Voges-Proskauer: Negative
    • Citrate: Negative
    • Phenylalanine deaminase: Negative
    • Urease: Negative
    • Hydrogen Sulfide (H2S): Negative
    • Triple Sugar Iron (TSI): Results in acid over acid (A/A).
    • Motility: Positive.

Examination of Klebsiella pneumoniae

  • Pathogenicity:
    • Causes respiratory infections, wound infections, and UTIs.
  • Colony Morphology:
    • Appears mucoid and pink due to lactose fermentation.
  • Biochemical tests:
    • Indole: Negative
    • Methyl Red: Negative
    • Voges-Proskauer: Positive
    • Citrate: Positive
    • Phenylalanine deaminase: Negative
    • Urease: Weakly positive.
    • H2S Production: Negative.
    • TSI: Result is acid over acid (A/A).
    • Motility: Negative.

Examination of Klebsiella oxytoca

  • Pathogenicity: Causes UTIs.
  • Colony Morphology: Mucoid, similar to Klebsiella pneumoniae.
  • Biochemical tests:
    • Indole: Positive
    • Methyl Red: Negative
    • Voges-Proskauer: Positive
    • Citrate: Positive
    • Phenylalanine deaminase: Negative
    • Urease: Negative.
    • H2S Production: Negative.

Examination of Enterobacter Species

  • Pathogenicity: Associated with UTIs.
  • Colony Morphology: Large gray mucoid colonies, less mucoid than Klebsiella.
  • Biochemical tests:
    • Motility: Usually positive
    • Indole: Negative
    • Methyl Red: Negative
    • Voges-Proskauer: Positive
    • Citrate: Positive
    • Phenylalanine deaminase: Negative
    • Urease: Negative.
    • H2S Production: Negative.
    • TSI: Results in acid over acid (A/A).

Examination of Serratia marcescens

  • Pathogenicity: Known for nosocomial infections, particularly UTIs and respiratory infections.
  • Colony Morphology: Frequently pigmented, notable for red pigmentation.
  • Biochemical tests:
    • Motility: Positive
    • Indole: Negative
    • Methyl Red: Negative
    • Voges-Proskauer: Positive
    • Citrate: Positive
    • Phenylalanine deaminase: Negative
    • Urease: Negative.
    • H2S Production: Negative.
    • TSI: Results in acid over acid (A/A) but can also be seen as a nonfermenter depending on growth conditions.

Examination of Citrobacter species (Fruendii and Koseri)

  • Pathogenicity: Often associated with UTIs.
  • Colony Morphology: Typically gray, large, and wet colonies, similar to Enterobacter.
  • Biochemical tests:
    • Motility: Positive (for both species)
    • Indole: Negative (Fruendii), Positive (Koseri)
    • Methyl Red: Positive (both species)
    • Voges-Proskauer: Negative (both species)
    • Citrate: Positive (both species)
    • Phenylalanine deaminase: Negative (Fruendii), Positive (Koseri)
    • Urease: Slow-positive (requires extended incubation time).
    • H2S Production: Variable results; Fruendii is generally positive, Koseri negative.

Study and Preparation for Upcoming Exam

  • Exam readiness: Aim to be prepared for the exam by next Thursday (the 9th). If readiness is not achieved, the date will be pushed to the following Tuesday (the 14th).
  • Next sessions: Continuing to delve into chemical reactions and addressing other lessons (specifically components related to urine and remaining material).
  • Follow-up: Plan to complete material in the immediate future, focusing on clarity and thorough knowledge of each organism's characteristics and tests.