Microbiology Notes on Pathogens

Overview of Microbial Pathogens

Cronobacter sakazakii

  • Colony Morphology
    • Produces yellow pigment.
  • Clinical Significance
    • Associated with meningitis and bacteremia in neonates, linked to contaminated powdered infant formula.
    • Also isolated from brain abscesses, respiratory infections, and wound infections.
    • Example: On BHI agar, colonies exhibit mucoid, yellow-pigmented appearance.

Serratia Species

  • General Characteristics

    • Exception: S. fonticola.
    • Positive for ONPG (slow lactose fermenter).
    • Produces extracellular DNase.
    • Recognized as opportunistic pathogens in healthcare settings.

  • Colony Morphology

    • Colonies produce pink-to-red pigment (prodigiosin) when incubated at room temperature.
    • Pigment production is notable in environmental strains.

  • Biochemical Reactions

    • IMVIC reactions: - - + +

  • Antimicrobial Susceptibility

    • Highly resistant to antimicrobials.
    • Serratia marcescens is the most clinically significant species.

Virulence Factors of Klebsiella spp.

  • Key Features
    • Presence of a polysaccharide capsule that helps in avoiding phagocytosis and some antimicrobials.
    • Biochemical profile includes:
    • Potassium cyanide broth negative.
    • No H2S production.
    • Variable motility.
    • Generally urease negative.
  • IMVIC Reactions
    • Results vary, few hydrolyze urea slowly; general notation: --++ (few exceptions on indole).
  • Notable Species
    • K. pneumoniae: Most common isolate; moist, gray, mucoid colonies on BAP.
    • Historical context: Frequent cause of respiratory infections in hospitalized and immunocompromised patients.
    • Antimicrobial Resistance: Severe due to K. pneumoniae carbapenemase.

Klebsiella pneumoniae Subspecies

  • K. pneumoniae subsp. ozaenae
    • Isolated from nasal secretions; linked to atrophic rhinitis.
    • Antimicrobial resistance from plasmid-mediated ESBLs, leading to hospital-acquired infections.
  • K. pneumoniae subsp. rhinoscleromatis
    • Predominantly found in Africa and South America.

Other Escherichia Species

  • E. hermanii & E. vulneris
    • Both produce yellow-pigmented colonies.
    • Clinical relevance: isolated from cerebrospinal fluid, wounds, and blood.
    • Associated with E. coli O157:H7 outbreaks.
  • E. albertii
    • Newest species; linked to diarrheal disease in children.

General Characteristics of Enterobacteriaceae Family

  • Members found in intestinal tracts of humans and animals.
  • Also present in free-living environments like soil and water.
  • Primarily linked to opportunistic and nosocomial infections.

Biochemical Tests and Identification

  • Key Tests associated with Klebsiella species:
    • Urease
    • Indole
    • Methyl Red
    • Voges-Proskauer
    • Citrate (Simmons)
    • Gelatin at 22°C
  • Table of Differentiation: Includes specific biochemical reactions for species identification (K. pneumoniae vs K. oxytoca vs K. ozaenae).

Conclusion

  • Understanding the biodiversity and clinical impacts of these bacterial pathogens is crucial for effective diagnosis and treatment in microbiology.