Preliminary Evaluation of Survival of Tubercle Bacilli in Heat-Fixed Sputum Smears
Laboratory personnel study and examine specimens using a variety of laboratory instruments and equipments like binocular compound microscopes. Laboratory personnel are at risk of getting infected by the pathogens they are examining, as derived from the original article.
One of the specimens they are examining using binocular compound microscopes is heat-fixed sputum smears which they then identify as being positive o negative to acid fast bacilli, the pathogen that causes tuberculosis.
Tuberculosis is known as a disease of the lung but may also attack almost any part of the body. If living germs enter the lungs and get a foothold there, they grow fairly rapidly, at least for a time. These germs are microscopic and can only be seen using microscopes such as binocular compound microscopes. Tuberculosis germs are passed form person to person in numerous ways. They can be blown about and breathed in by other persons or the germs may be left in eating utensils, whistles, pencils, etc. and the germs carried to another person’s mouth. When tubercle bacilli get into the body, they may be coughed or sneezed out before they do any serious damage. If swallowed, they may be killed by stomach acid. If they get into the blood, they may be destroyed by the white blood cells. But if they still elude these defenses, they are likely to find a lodging place, often in the lungs. Symptoms and signs of tuberculosis include body malaise, tiredness, sharp chest pain, low-grade fever, cough, and in some cases, blood spitting.
In some scientific studies, it was demonstrated that the tubercle bacilli can survive heat-fixed sputum smears, as narrated in the original article. Prior studies have not confirmed or proven the length of time the tubercle bacilli can survive the heat-fixed sputum smear. The original article describes how the researchers found out and evaluated the length of time the tubercle bacilli can survive the heat-fixed sputum smear.
How did they go about in making the experiment? The researchers, according to the original article, used the slide culture technique right after air drying and heat-fixing (0h, 24H, 48H, 72H, and after 7 days post heat-fixation) the sputum smears specimens in order to reveal the tubercle bacilli. Thirty different specimens were derived from patients being treated for pulmonary tuberculosis. These patients have already been found positive for tubercle bacilli in smear and culture tests. Sputum was spread in the smear over a 25 x 10 mm area of a 76 x 13 mm glass slide with the use of a 10 microliter disposable loop, according to the article. They are then air-dried in a safety cabinet. A culture of the duplicates of the positive controls and pests were made by placing each slide in a 16 x 150 mm tube that contains 8 mL of selective lysed blood medium. The duplicates are then left to incubate for seven days at a temperature of 37°C. After the incubation period, the slides were removed, rinsed in distilled water briefly, and then neutralized using 5% sodium hypochlorite. The slides are then stained with Ziehl-Neelsen stain in order to easily identify the tubercle bacilli. The slides are then examined using binocular compound microscopes.
The results revealed that 50% of the sputum specimens have tubercle bacilli surviving heat fixation. Two specimens are positive after 0H, five specimens are positive after 48H, 3 specimens are positie after 72H, and 5 specimens were positive after 7 days. In conclusion, the article states that tubercle bacilli that remained in heat-fixed sputum smears are infection risks for the laboratory staff and personnel.
