Why is in vitro (test tube) culture still relevant in the medical field?

Why In Vitro Culture Remains Essential in Modern Medicine

In vitro culture is fundamental to clinical microbiology because it provides viable organisms necessary for antimicrobial susceptibility testing, enables outbreak detection through molecular subtyping, and remains the gold standard for diagnosing bloodstream infections despite advances in molecular diagnostics. 1, 2

Critical Functions That Cannot Be Replaced

Antimicrobial Susceptibility Testing

• Culture provides the only reliable method to determine which antibiotics will effectively treat a specific infection, as molecular methods detect nucleic acid but cannot perform susceptibility testing 1, 2
• Direct testing of viable pathogens remains necessary for susceptibility determination for the foreseeable future, even as molecular diagnostics advance 1
• This information directly impacts patient survival, as appropriate antimicrobial therapy significantly reduces mortality in sepsis and septic shock 1

Public Health Surveillance and Outbreak Detection

• Replacement of culture by culture-independent diagnostic tests (CIDTs) without preserving access to isolates impedes detection of dispersed outbreaks and reduces public health capacity to control and prevent them 1
• Molecular subtyping of bacterial strains through methods like pulsed-field gel electrophoresis and whole-genome sequencing requires cultured isolates, and this enhanced surveillance has prevented thousands of illnesses 1
• Specimens testing positive for bacterial pathogens by CIDT should be cultured either at clinical or public health laboratories to enable strain identification, serotyping, and subtyping 1

Definitive Diagnosis of Bloodstream Infections

• Blood culture remains the best approach to identify incriminating microorganisms when bloodstream infection is suspected and to guarantee adequate antimicrobial treatment 2
• For catheter-related bloodstream infections, definitive diagnosis requires positive blood culture results with concordant microbial growth from the catheter tip or catheter-drawn cultures meeting quantitative or differential time to positivity criteria 1, 3
• Quantitative blood cultures are the most accurate method to diagnose catheter-related bloodstream infections, with neither method requiring catheter removal 1

Essential Role in Low- and Middle-Income Countries

Practical Necessity in Resource-Limited Settings

• Culture media are fundamental in clinical microbiology laboratories in low- and middle-income countries (LMICs), where they are mostly prepared in-house due to limited access to commercial alternatives 1
• The WHO Essential Diagnostics List includes culture media as essential products that must be quality assured, creating political will and manufacturer commitment 1
• Professional societies like CLSI authorize pragmatic approaches such as using well-characterized clinical organisms for quality control instead of expensive culture collection strains, making culture feasible in resource-limited settings 1

Cost-Effective Diagnostic Strategy

• A tiered identification system with basic genus-level identification on-site using culture and referral to reference laboratories for species identification reduces costs while maintaining diagnostic capability 1
• Adapted culture media such as glucose-topped MacConkey agar for urine cultures and blood-free media for large-colony hemolytic streptococci provide cost-effective alternatives in remote settings 1

Advances Enhancing Culture Relevance

Technological Improvements

• Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) revolutionized identification of microorganisms from cultures, dramatically reducing time to results 2
• Modern automated blood culture systems like BACT/ALERT VIRTUO significantly shorten time to detection compared to previous systems, with median detection times of 11.6 hours versus 13.3-13.5 hours for competitors 4
• Optimized culture media, detection methods, and microaerophilic atmospheres have dramatically decreased Mycobacterium tuberculosis culture time 5

Expanding Capabilities

• Pure bacterial culture remains essential for studying virulence, antibiotic susceptibility, and genome sequencing to facilitate understanding and treatment of diseases 5
• Shell vial procedures and amoebal coculture techniques have enabled discovery of new bacterial species and culture of previously unculturable fastidious organisms like Tropheryma whipplei and Coxiella burnetii 5
• Addition of antioxidants in culture media under aerobic atmosphere now allows growth of strictly anaerobic species, optimizing anaerobe culture in routine laboratories 5

Integration with Molecular Methods

Complementary Rather Than Competitive

• Culture-independent methods including multiplex molecular panels serve clinical diagnostic needs but must be complemented by culture to provide subtyping information and antimicrobial susceptibility data 1
• The Infectious Diseases Society of America recommends both culture-independent and culture-dependent diagnostic testing when clinically indicated, recognizing the complementary value of each approach 1
• Blood cultures should be obtained before initiation of antimicrobial therapy in all patients with suspected sepsis, as this remains the diagnostic gold standard 1

Common Pitfalls to Avoid

• Do not rely solely on molecular diagnostics without considering the need for susceptibility testing and public health surveillance 1
• Avoid assuming that detection of nucleic acid by molecular methods is equivalent to detection of viable organisms by culture, as clinical significance may differ 1
• Do not neglect proper culture technique including appropriate skin antisepsis with alcohol, alcoholic chlorhexidine (>0.5%), or tincture of iodine rather than povidone-iodine, which has higher contamination rates 1, 3
• Ensure adequate drying time for antiseptics to prevent contamination of blood cultures 3