Septicemia and bacteremia. and Respiratory tract infections (Throat Swab and Sputum sample). Unit V DMLT II Semester.

SEPTICEMIA AND BACTEREMIA

The presence of viable bacteria in the blood is called bacteremia. In the initial stage, it is asymptomatic. It does not cause any serious complications in healthy individuals. Bacteremia becomes a bloodstream infection if the body's immune system fails to control bacteria in the bloodstream. Bloodstream infection due to bacteria and their toxins is also known as Septicemia or blood poisoning. In septicemia, the body releases chemicals to fight germs and toxins that develop several changes inside the human body. They trigger inflammation, multiple organ system failure, and even death. Septicemia and sepsis are used as synonyms. But both are not the same. A serious complication of septicemia is called sepsis. eg. Staphylococcus aureus, Streptococcus pneumonia, Streptococci Viridans Salmonella typhi, Neisseria meningitis, Escherichia coli. Haemophilus influenzae.

Laboratory diagnosis of Septicemia and bacteremia:

• i. Culture: Blood agar culture media is used to diagnose bacteria in blood. They support the growth of both aerobic and anaerobic culture media. eg. thioglycolate broth, brain heart infusion broth, triptone soya broth, etc. Two culture bottles are used one aerobic and the other anaerobic.

• ii. Specimen collection: 10 to 20 ml of blood is collected as a sample. Normally 1:10 to 1:20 dilution of blood sample is sufficient to neutralise antibodies and antibacterial component in a blood sample. Blood sample is equally distributed in aerobic and anaerobic blood culture media.

• iii. Inoculation: The blood sample is immediately inoculated just after its collection to avoid clotting. Culture media is incubated at an optimum temperature 37 degrees C. The incubation period is 24 hours. If bacterial growth occurs after 24 hours then they are subcultured on 2nd day and 7th day. Gram stain is used to stain blood culture.

• iv. Subculture on 2nd day:

  • a. MacConkey Agar for aerobic incubation

  • b. Blood agar for anaerobic incubation

  • c. Chocolate agar for carbon dioxide incubation.

• v. Report: Submit a report of the gram stain result. Identify bacteria with their antibiotic sensitivity and biochemical tests.

RESPIRATORY TRACT INFECTIONS

Respiratory tract infections are divided into two groups. These are upper respiratory tract infections and lower respiratory tract infections.

• A. Upper respiratory tract infection includes

  • 1. Sore throat or pharyngitis caused by Streptococcus pyrogens

  • 2. Diphtheria caused by Corynebacterium diphtheria

  • 3. Acute epiglottises in children caused by H. influenza

  • 4. Oral thrush in young children, diabetics, and immune-compromised persons caused by Candida albicans.

• B. Lower respiratory tract infection includes

  • 1. Pneumonia caused by Streptococcus. pneumonia

  • 2. Influenza caused by H. influenzae, Staphylococcus aureus, Streptococcus pyogens.

  • 3. Chest infection caused by H. influenzae.

  • 4. Atypical pneumonia caused by Mycoplasma pneumoniae

  • 5. Tuberculosis caused by Mycobacterium tuberculosis.

Laboratory diagnosis of infectious diseases in Upper Respiratory Tract Infections (Throat Swab)

Throat swab:

• 1. Specimen collection: The medical practitioner nurse or experienced medical laboratory technologist should collect the throat swab. The following precautions should be observed during specimen collection:

  • i. Collect specimens under proper light conditions.

  • ii. Collect specimens before the start of antibiotic therapy and before the use of antiseptic gargles (mouthwash).

  • iii. Use a sterile spatula or sterile spoon to depress the tongue then use a sterile swab to collect specimens from exudates or inflamed areas or pus.

  • iv. Collect two such throat swabs.

  • v. Avoid saliva collection on the swab.

  • vi. Keep this throat swab carrying sample in the sterile container and use it within two hours.

  • vii. Avoid throat swab collection from pediatric patients. It may child’s respiratory tract or may cause spasms in the tongue or upper respiratory tract.

Procedure:

First day: Prepare a smear of the specimen on the slide. Gram stain to examine pus cells and Gram-negative spirochetes. Look for pleomorphic rods (variation in size and shape of bacteria) in diphtheria suspected. Stain smear with Albert’s stain if diphtheria is suspected.

• i. Inoculate specimen in blood agar plates. Incubate it at 37o C for 24 hours.

• ii. Inoculate specimen in Tellurite blood agar plate (TBA Culture) if diphtheria is suspected. Incubate it at 37o C for 24 hours.

• iii. Inoculate specimen in Sabouraud blood agar plate if Candida infection is suspected. Incubate it at 37o C for 24 hours.

Second day:

• i. Examine blood agar plate for the presence of β hemolytic streptococci.

• ii. Examine the TBA culture plate for the presence of Corynebacterium diphtheriae.

• iii. Examine Sabouraud blood agar plate for the presence of Candida albicans.

• iv. Perform biochemical tests to identify and confirm the pathogen present in a specimen.

Reports: Submit a report as per examination, identification, and confirmatory biochemical tests about the presence of the pathogen

Dr Pramila Singh

Laboratory diagnosis of infectious diseases in Upper Respiratory Tract Infections (Sputum sample):

Sputum sample

• 1. Specimen collection: Instruct patient to gargle and wash oral cavity by using water. It will reduce the number of contamination of sputum by microbes present inside the oral cavity. Instruct patient to expel sputum from lower respiratory tract. Collect expelled sputum in a dry clean, wide-mouth, leakproof container. Sputum should be free from saliva. Use the sample for laboratory investigation immediately.

• 2. Procedure: Carry out all activities by putting specimens under the safety cabinet.

  • i. Note down the sputum appearance. It may be mucoid, mucociliary, green looking (purulent), green appearance with pus and mucus (mucopurulent), and presence of blood in sputum.

  • ii. Reject specimen, if its most part is saliva.

  • iii. Prepare sputum smear and stain it Gram staining technique. Gram staining is performed to identify Gram-positive diplococci such as S. pneumoniae, Gram-positive cocci such as S. aureus, Gram-negative rods such as H. influenza, etc.

  • iv. Mix one drop of alkaline eosin with one drop of sputum. Examine it for the presence of eosinophilic granules.

  • v. Mix sputum with 10g/dl KOH or NaOH solution to examine the presence of fungal infection

  • vi. Inoculate sputum in blood agar plate and chocolate agar plate. Incubate blood agar plate under aerobic conditions and chocolate agar plate in carbon dioxide atmosphere for 24 hours. Use L. J. Slope (Lowestein-Jensen slope) as culture media for pulmonary tuberculosis.

  • vii. Examine the blood agar plate and chocolate agar plate for the presence of Strepto.pneumoniae, Staph. aureus. K. pneumonia H. influenza. Examine L. J. Slope after 6 to 8 weeks for the presence of Mycobacterium tuberculosis.

  • viii. Confirmatory tests are biochemical tests.

Dr Pramila Singh