Sputum Culture

Sputum is a thick fluid mucus that is produced in the lungs and the lower respiratory tract. Sputum usually occurs in the respiratory tract infections or a different lung disorder. Sputum culture is done to identify the  causative microorgansim of infection. If your sputum culture test is resulted as positive it means there are bacteria in your respiratory tract and another laboratory test “ antibiotic sensitivity test” is done to find the most effective antibiotics to that bacteria. (See. Antibiotic sensitivity test)

Purpose; why the sputum culture is done?

Sputum culture is done to identify the causative bacteria and to find the correct antibiotic for treatment also sputum culture may be done to check the success of treatment.

Your doctor may request sputum culture if you have lung-chest infection symptoms like;

  • Persistent coughsputum-culture-bacteria
  • Fever
  • Chest pain
  • Rapid heartbeat
  • Muscle pain
  • Joint pain
  • Fatigue
  • Chills
  • Coughing up yellow-green sputum (mucus) sometimes blood in it
  • Headache
  • Difficult or fast breathing
  • Cyanosis (blue color around the lips)
  • Sweating
  • Loss of appetite

The cause of these symptoms may be lung infections or conditions like these diseases;

  • Bronchitis; chronic and acute bronchitis
  • Pneumonia
  • Tuberculosis (See.What is Tuberculosis?)
  • COPD ( chronic obstructive pulmonary disease)
  • Cystic fibrosis
  • Pleurisy
  • Pseudomonas lung infection
  • SARS ( severe acute respiratry syndrome)
  • MRSA lung infection
  • Lung abscess

Sputum culture sample collection

Sputum sample is needed for culture. Sputum sample is commonly collected in mornings.  A sterile culture sample cup will be given to you and you’ll be requested to collect sputum sample inside. You’ll be asked to cough deeply to bring the sputum from your lungs and spit into the sample cup but the culture sample must be sputum; only saliva samples are not suitable for sputum culture test. Laboratory technician may request you to rinse your mouth before sputum sample collection to remove food remains or extra saliva. Someone may tap on your chect or back gently to loosen the sputum and to move up easier in your respiratory tract.

Sputum may be in different color and appearance in some conditions;

  • Rusty color- Lobar pneumonia; an entire lob of may be affected
  • Dark brown- Amebic liver abscess rupture into bronchus; amebiasis may cause abscess in the liver and sometimes may cause a rupture of the abscess into the pleural space or lungs
  • Red jelly look-Klebsiella pneumonia
  • Red color without blood- serartia marcescens
  • Black color- Bacteria melaninogenicus pneumonia ( a type of bacteria that is found in normal flora of upper respiratory tract)
  • Green- pseudomonas infections
  • Milky- bronchioalveolar carcinoma; a type of lung cancer that may be found in non-smokers especially in eastern Asians and women
  • Yellow- jaundice

 How the sputum culture test is done?

Sputum sample is placed in a special culture media to provide bacteria growth. Blood agar, eosin methylene blue agar and chocolate agar are used for bacteria growth. Also Lowenstein jensen is used for tuberculosis. If there are bacteria in your lungs they will start to grow in these culture media within 1-2 days or more according to the bacteria type. For this reason you may take your  sputum culture result in a few days or more. Fungi may take more time for growth.cul

Evaluation of sputum culture test results

Negatif: Sputum culture test result is normal; means that there are no causative bacteria growth in sputum sample.

Positive: Pathogenic-harmful bacteria or fungi growth in the sputum culture.

If the sputum culture test is positive then antibiotic sensitivity test is done to find the effective antibiotic for that bacteria.

These are some bacteria types that may be found in a positive sputum culture test;

  • Streptococcus pneumonia
  • Moraxella influenzae
  • Heamophilus influanze
  • Klebsiella pneumonia
  • Streptococcus pyogenes

Factors that may affect sputum culture test result

  • Antibiotic usage recently
  • Sputum sample may be contaminated
  • Sputum sample may be inadequate
  • Saliva collection instead of sputum
  • Sputum sample may be waited too long before taking to the laboratory


Leave a Reply