How can I obtain (isolate) Enterobacter aerogenes and Staphylococcus epidermidis?

How to Obtain Enterobacter aerogenes and Staphylococcus epidermidis

These organisms can be obtained from clinical specimens, commercial culture collections, or environmental sources, with S. epidermidis readily isolated from human skin and E. aerogenes from hospital environments or gastrointestinal sources.

Clinical Specimen Sources

Staphylococcus epidermidis Isolation

• S. epidermidis is a normal skin commensal and can be isolated from skin swabs, particularly from areas with high sebaceous gland density 1
• The organism colonizes medical devices including intravenous catheters and cardiovascular implantable devices where it produces biofilm 2
• For catheter-related specimens, use the Maki roll-plate method (rolling catheter tip on agar) or Brun-Buisson quantitative method (sonication/vortexing in solution) with thresholds of 15 CFU or 10³ CFU/mL respectively 1
• S. epidermidis grows readily on routine culture media including blood agar and brain heart infusion agar 1

Enterobacter aerogenes Isolation

• E. aerogenes is an opportunistic pathogen found in hospital environments, gastrointestinal tract, and contaminated medical solutions 3, 4, 5
• The organism has been isolated from blood cultures in healthcare-associated infections and can be recovered from environmental surfaces in hospital settings 4, 5
• E. aerogenes grows on standard enteric media and can be identified using automated systems like VITEK II or 16S rRNA sequencing 4
• Stool or rectal swabs can be cultured on selective media for gram-negative organisms 1

Commercial and Research Sources

• Both organisms can be obtained from the American Type Culture Collection (ATCC) or other commercial culture repositories 6
• Research investigators and academic institutions maintain bacterial strain collections that can be accessed for non-pathogenic laboratory strains 6
• When obtaining strains for laboratory work, use Biosafety Level 1 (BSL-1) non-pathogenic strains for training purposes 6

Laboratory Culture Techniques

Basic Plating Methods

• Use aseptic technique with sterile work surfaces to prevent contamination 6
• Streak-plating on appropriate agar media isolates single colonies for pure culture 6
• Pour-plating or spread-plating methods enumerate viable bacterial colonies 6
• For S. epidermidis, standard blood agar or nutrient agar at 35°C for 24 hours is sufficient 1
• For E. aerogenes, use MacConkey agar or other enteric selective media 3

Specimen Collection Principles

• Submit only high-quality specimens to ensure clinically useful results 7
• Avoid contamination from normal flora by proper site preparation and collection technique 1
• Transport specimens promptly in appropriate media to maintain organism viability 7

Important Caveats

• S. epidermidis is frequently a contaminant in clinical cultures; confirmation requires at least two positive specimens with identical organisms or correlation with clinical findings 1
• E. aerogenes is a multiresistant pathogen in healthcare settings; handle with appropriate biosafety precautions 3, 5
• Both organisms form biofilms that require specialized techniques (sonication, vortexing) for optimal recovery from device surfaces 1, 2
• When working with clinical isolates rather than laboratory strains, follow institutional biosafety protocols and use biosafety cabinets for BSL-2 organisms 6