Culture And Susceptibility, Aerobic (Manual method)

Bacterial/ Viral

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No Fasting Required

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Identifies bacteria & antibiotic susceptibility.

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Culture And Susceptibility Aerobic (Manual Method)

Why is it done?
- Identifies and isolates aerobic bacteria from clinical specimens such as blood, urine, wound exudates, cerebrospinal fluid, respiratory samples, and other body fluids or tissues
- Determines antibiotic susceptibility patterns of isolated organisms using manual methods such as disk diffusion (Kirby-Bauer method) or E-strip testing
- Diagnoses bacterial infections and guides appropriate antimicrobial therapy selection
- Performed when patients present with signs and symptoms of bacterial infection such as fever, wound infection, urinary tract infection, pneumonia, bacteremia, or meningitis
- Typically performed urgently when infection is suspected and sample collection has been completed; results usually available within 24-72 hours depending on organism growth rate
Normal Range
- No growth of aerobic bacteria on culture media (reported as 'No growth' or 'Sterile')
- Normal interpretation: Absence of pathogenic aerobic bacteria indicates no active bacterial infection in the sampled specimen
- Growth of normal flora only: May be reported separately and generally considered normal for specimens from skin or mucous membranes
- Susceptibility results expressed as: 'Sensitive' (S), 'Intermediate' (I), or 'Resistant' (R) for each antibiotic tested, based on measured inhibition zone diameters compared to CLSI or EUCAST standards
- Minimum inhibitory concentration (MIC) values may also be reported, measured in micrograms per milliliter (µg/mL)
Interpretation
- Bacterial growth identification: Any growth of pathogenic aerobic bacteria indicates active bacterial infection; organism type guides initial treatment decisions
- Susceptibility interpretation - Sensitive (S): Indicates organism will likely respond to standard doses of the antibiotic; preferred choice for treatment
- Susceptibility interpretation - Intermediate (I): Organism shows moderate resistance; antibiotic may be effective at higher doses or for infections at specific anatomical sites with good drug penetration
- Susceptibility interpretation - Resistant (R): Organism unlikely to respond to therapy; alternative antibiotics should be selected
- Mixed flora: May indicate contamination of sample during collection, though significant mixed flora from normally sterile sites suggests polymicrobial infection
- Factors affecting interpretation: Collection site, specimen quality, timing of culture collection, recent antimicrobial therapy, and proper specimen handling influence results
- Clinical significance: Results directly influence choice of empiric or targeted antibiotic therapy, helping minimize unnecessary antibiotic use and reduce antimicrobial resistance
Associated Organs
- Organ systems affected: Respiratory tract (pneumonia, bronchitis), urinary tract (cystitis, pyelonephritis, urosepsis), cardiovascular system (bacteremia, endocarditis), central nervous system (meningitis, ventriculitis), gastrointestinal tract (peritonitis, intra-abdominal infections), skin and soft tissues (wound infections, cellulitis, abscesses)
- Common aerobic pathogens: Staphylococcus aureus (including MRSA), Streptococcus species, Enterococcus species, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Proteus species
- Conditions commonly diagnosed: Sepsis, hospital-acquired infections (HAI), healthcare-associated infections, community-acquired infections, catheter-related infections, surgical site infections
- Potential complications of untreated bacterial infections: Systemic inflammatory response syndrome (SIRS), septic shock, multi-organ failure, death, chronic sequelae including scarring and tissue damage
- Antimicrobial resistance concerns: Inappropriate antibiotic selection may lead to treatment failure, increased morbidity and mortality, and further selection of resistant organisms
Follow-up Tests
- Repeat culture: Recommended if clinical response is inadequate after appropriate therapy or if initial culture was negative but clinical suspicion remains high
- Extended susceptibility testing: Additional antimicrobials may be tested if first-line agents show resistance; extended spectrum beta-lactamase (ESBL) or carbapenemase testing for resistant gram-negative organisms
- Anaerobic culture and susceptibility: If mixed flora suspected or if culture site suggests anaerobic involvement (abdominal infections, human bite wounds, aspiration pneumonia)
- Fungal culture: Ordered simultaneously or subsequently if fungal infection suspected, particularly in immunocompromised patients
- Gram stain: Often performed on initial specimen and culture to provide preliminary organism identification while awaiting culture results
- Blood cultures: If bacteremia suspected and initial specimen is blood; paired bottles (aerobic and anaerobic) collected at separate sites within 5 minutes
- Imaging studies: Chest X-ray, ultrasound, CT scan, or MRI may be ordered concurrently to localize infection and assess complications
- Clinical monitoring: Routine follow-up with vital signs, complete blood count (CBC), comprehensive metabolic panel (CMP), procalcitonin, or C-reactive protein (CRP) to assess treatment response
Fasting Required?
- No fasting required for culture and susceptibility testing
- Patient preparation depends on specimen source:
- • Blood cultures: Collected after antiseptic skin preparation with chlorhexidine or 70% alcohol; do not collect through existing IV lines if possible; two sets from separate venipuncture sites recommended
- • Urine cultures: Clean-catch midstream collection or catheterized specimen; patient should void naturally before collection for clean-catch samples
- • Wound cultures: Specimen collected with sterile swab or syringe; non-healing wounds should be cleaned of surface debris before culturing
- • Respiratory samples: Sputum collection early in morning after throat clearing; specimens must be purulent not saliva
- Do not allow collection tubes to contaminate with antiseptics or non-sterile materials
- No specific medication restrictions; however, if possible, avoid collecting cultures while patient is on antibiotics or collect before antibiotic initiation for better culture yield
- Specimen transport: Must be rapid and appropriate; sterile specimens kept at room temperature or 35-37°C to maintain viability; refrigeration generally avoided except for certain specimens like CSF which should be kept warm

How our test process works!