4Mycobacterium tuberculosis Infection of the lungs with M. tuberculosis causes pulmonary tuberculosis.Tuberculosis is the commonest HIV-related, causing about 30% of deaths in AIDS patients.The development of tuberculosis in HIV co-infected persons accelerates progression to full-blown AIDS.Tuberculosis is difficult to diagnose by sputum examination in those co-infected with HIV when there is marked immunosuppression resulting in diffuse infiltration without cavitation.When immune responses are less suppressed, typical pulmonary caseating granulomas and cavities form, and AFB can usually be detected in sputum.
5Bacteria that cause respiratory tract infection S. pneumoniae and H. influenzae are the commonestcauses of acute respiratory tract infections in tropicalcountries.S. pneumoniae causes lobar pneumonia andbronchopneumonia in young children (especially whenmalnourished), in those co-infected with HIV (majorHIV-related pathogen), the elderly, the bed-ridden andother debilitated persons.
6Bacteria that cause respiratory tract infection S. aureus, S. pyogenes, and H. influenzae are often secondary invaders in patients with influenza virus pneumonia. H. influenzae is associated with acute and chronic bronchitis and chest infections in post-surgical patients and the elderly. S. aureus can produce a severe pneumonia (with a tendency to form abscesses), especially in children and following influenza.
7Bacteria that cause respiratory tract infection P. aeruginosa is more commonly found in patients withchronic lung cavities or as a complication of treatmentwith immunosuppressive drugs.● K. pneumoniae may be found with E. coli and yeasts as a complication of antibiotic therapy.● Moraxella catarrhalis can cause upper and lower respiratory tract infections, mostly in adults with pre-existing respiratory disease and those with immunodeficiency.
8Bacteria that cause respiratory tract infection Y. pestis (highly infectious) can be found in the sputum of patients with pneumonic plague. The specimen maycontain blood.● Mycoplasma pneumoniae ( M. pneumoniae) causes primary atypical pneumonia.● Legionella pneumophila (L. pneumophila) causes Legionnaire’s disease, a severe and often fatal form of pneumonia.
9Bacteria that cause respiratory tract infection Eosinophils can be found in the sputum of patients with allergic respiratory conditions such as asthma.CommensalsSputum as it is being collected passes through thepharynx and the mouth. It therefore becomes contaminated with small numbers of commensalorganisms from the upper respiratory tract andmouth.
10COLLECTION AND TRANSPORT OF SPUTUM Sputum for microbiological investigation is collected and transported as follows:In a hospital with a microbiology laboratory1 Give the patient a clean (need not be sterile), dry, wide-necked, leak-proof container, and request him or her to cough deeply to produce a sputum specimen.
11COLLECTION AND TRANSPORT OF SPUTUM Caution: When a sputum specimen is being collected, adequate safety precautions must be taken to prevent the spread of infectious organisms and to avoid contaminating the outside of the container. Use a phenol-containing disinfectant to wipe the outside of the container after collecting the specimen.Important: The specimen must be sputum, not saliva. Sputum is best collected in the morning soon after the patient wakes and before any mouth-wash is used.When pulmonary tuberculosis is suspected, up to three specimens may need to be examined to detect AFB.Mucopus aspirated from the nasopharynxWhen it is not possible to get sputum from childrenwith suspected pneumonia or bronchopneumonia,pathogens can often be isolated from mucopus aspiratedfrom the nasopharynx.
12COLLECTION AND TRANSPORT OF SPUTUM 2-Label the container, and complete a request3- When pneumonia or bronchopneumonia is suspected, deliver the sputum to the laboratory with as little delay as possible because organisms such as S. pneumoniae and H. influenzae require culturing as soon as possible.Note: Specimens for the isolation of S pneumoniae and H. influenzae must never be refrigerated.
13When pneumonic plague is suspected: Deliver the sputum to the laboratory as soon as possible. Make sure the specimen is marked HIGH RISK.
14In a health centre for dispatch to a microbiology laboratory 1 Collect the sputum in a container supplied by the microbiology laboratory .Follow the technique and observe the precautions mentioned under the hospital collection of sputum.2 To ensure the survival of pathogens such as S. pneumoniae and H. influenzae, transfer a purulent part of the sputum to a cotton-wool swab, and insert it in a container of Amies transport medium. Label the container using a lead pencil.Amies medium will help the pathogens to survive andavoid the overgrowth of fast-multiplying commensals.3 Send the sputum specimen and swab with a request form to reach the microbiology laboratory within 6 hours.
15LABORATORY EXAMINATION OF SPUTUM sputum specimens should be examined in a biological safety cabinet1- Describe the appearance of the specimenDescribe whether the sputum is:Purulent: Green-looking, mostly pusMucopurulent: Green-looking with pus and mucusMucoid: Mostly mucusMucosalivary: Mucus with a small amount of salivaWhen the sputum contains blood, this must also bereported.
16LABORATORY EXAMINATION OF SPUTUM When the sputum is mostly saliva, report the specimen as ‘Unsuitable for microbiological investigation’ and request another specimen.Note: Before culturing sputum, many laboratories examine a wet preparation or Field’s stained smear microscopically for cells. When large numbers of squamous epithelial cells (oftencovered with bacteria) are present and only a few or no pus or macrophage cells, this indicates that the specimen is unsuitable for culturing.
172- Examine the specimen microscopically Gram smear Using a piece of stick, transfer a purulent part of the sputum to a glass slide, and make a thin smear. Allow the smear to air-dry in a safe place. Fix Examine the smear for pus cells and predominant bacteria. Look especially among the pus cells for: ● Gram positive diplococci (capsulated) that could be S. pneumoniae . The
18● Gram positive cocci in groups that could be S ● Gram positive cocci in groups that could be S. aureus , but not often seen. ● Gram negative rods and cocco-bacilli that could be H. influenza, particularly when these are the predominant organisms. ● Gram negative capsulated rods that could be K. pneumoniae, but not often seen. ● Gram negative diplococci in and between pus cells that could be M. catarrhalis
19Gram stained smears of sputum must be reported with caution Gram stained smears of sputum must be reported with caution. Cocci, diplococci, streptococci, and rods may be seen in normal sputum because these organisms form part of the normal microbial flora of the upper respiratory tract. Note: When pus cells are present but no bacteria are seen in a Gram stained smear, this may indicate the presence of microorganisms such as M. tuberculosis, Chlamydophila pneumoniae, Mycoplasma pneumoniae, Legionella pneumophilia or viruses.
20Ziehl-Neelsen smear to detect AFB the NaOC1 concentration technique is also safer for laboratory staff. Because NaOC1 kills M. tuberculosis,
21Eosin preparation when an allergic condition requires investigation Transfer a small amount of sputum to a slide. Add a small drop of alkaline eosin solution, mix, and cover with a cover glass. Using the 10 and 40 objectives with the condenser iris closed sufficiently to give good contrast, examine the preparation for eosinophils*. *Eosinophils can be easily differentiated from pus cells because they contain bright red-staining granules and a bilobed nucleus. Free eosinophilic granules may be seen in the preparation and occasionally elongated refractile Charcot Leyden crystals (formed from the material of dead eosinophils). Large numbers of eosinophils in sputum can also be found with paragonimiasis.
22Giemsa or Wayson stained preparation when pneumonic plague is suspected Fix the sputum smear with methanol for 5 minutes. Stain using Giemsa technique or rapid Wayson’s technique Bipolar Caution: Y. perstis is highly infectious (Hazard Group 3 pathogen), therefore handle specimens with great care. Laboratory-acquired infections can occur following accidental inoculation or inhalation of the organisms. Minimize procedures that create aerosols and whenever possible carry out procedures in a safety cabinet.
23Culture the specimenTo obtain as pure a culture as possible of a respiratorypathogen it is necessary to reduce the numberof commensals inoculated. Ways of reducing commensalnumbers include washing the sputum freefrom saliva or liquefying and diluting it. The techniqueusing saline-washed sputum is described. Thedilution technique requires a liquefying agent suchas dithiothreitol (Sputolysin, Sputasol ) which isexpensive and unstable.
24The procedure for the routine liquefaction of sputum is as follows: The sputum is expectorated into a sterile Universal container or other wide mouthed screw-capped bottle Add approximately 5 times the volume of 0.85% saline and agitate to free the sputum from adherent saliva. Remove the saline with a sterile Pasteur pipette. To the washed sputum, add an equal volume of Sputasol solution Shake the mixture well, place in a 37°C water bath and incubate, with periodic shaking, until liquifaction is complete Inoculate on to a suitable culture medium. For the total cell count, place a drop of the liquefied sputum in a haemocytometer for enumeration. For a differential cell count, fix a dried smear in methyl alcohol and stain with haematoxylin and eosin or with Lieshmann stain. The working solution of Sputasol will remain stable for at least 48 hours stored at 2-8°C. An investigation into the survival of respiratory pathogens in specimens that had been stored for 48 hours at 4°C following homogenisation using Sputasol, showed that the organisms remained viable and, when necessary, treated specimens could be successfully re-cultured8.
25Blood agar and chocolate agar – Wash a purulent part of the sputum in about5 ml of sterile physiological saline.– Inoculate the washed sputum on plates of:● Blood agar, see No. 16● Chocolate (heated blood) agar, see No. 16Inoculation technique to reduce commensal numbers:Using the technique described in subunit 7.4 (to inoculatea whole plate of agar), flame the loop in between eachspread. This will help to obtain a pure growth of thepathogen in the areas of the 3rd and 4th spread.– Add an optochin disc to the blood agar platewithin the area of 2nd spread. This will help toidentify S. pneumoniae (see subunit ).
26Availability: Optochin discs can be purchased economically from Mast Diagnostics (see Appendix 11) in vials of100 discs, code D-42. They have a shelf-life of about 2 years.– Incubate the blood agar plate aerobically and thechocolate agar plate in a carbon dioxideenriched atmosphere (see subunit 7.4).ADDITIONALCulture of sputum for M. tuberculosisCulturing and susceptibility testing of M. tuberculosisare usually undertaken in a Tuberculosis ReferenceLaboratory, mainly for surveillance purposes, todetermine levels of drug resistance, and to managetreatment failures and relapses (see also subunit).Culture of sputum when pneumonic plagueis suspectedIsolation of Y. pestis is described in subunit