BACTERIA – THE CAUSATIVE AGENTS OF RESPIRATORY TRACT DISEASES

Microbiology, Virology & Immunology
Ass. Prof. E. O. Kravtsova

by a primary lesion, usually in the upper respiratory tract,

and more generalized symptoms resulting from the spread of bacterial toxin throughout the body.

by Hippocrates.
The bacteria was discovered in 1882 by Edwin Klebs.
F.Loeffler- 1884

–isolate in pure culture
E.Roux -1888- separate the toxin
G.Ramon – 1923- diphtheria toxoid

ends (volutin).
They have the characteristic of forming irregular, club-shaped

or V-shaped arrangements in normal growth. The cytoplasm is granular.
They do not form spores.
Outer layer of the cell wall forming a microcapsula.
Nonmotile.

organism. The club-shaped forms are long and slender with swollen

ends, especially when stained with methylene blue or Neisser's stain (this reveals intensely stained volutin granules). On a slide, these microbes often arrange in pairs at acute angles to each other (V, L, X-arrangements). The non-pathogenic and opportunistic corynebacteria (diphtheroids) are rods arranged in parallel (“fence-like”) clusters. These bacteria possess irregular swellings only at one end of the cell. NOTE

C
Grows readily on media with protein, sugar.
Serum agar
Blood agar
Roux's media

(coagulated horse serum)
Loeffler's media (serum, sugar broth)

on whose slope there is a creamy growth within 12

h. On blood tellurite agar (Klauberg agar) the three biotypes of C. diphtheriae - gravis, mitis, and intermedius - form different colonies. The gravis type forms relatively large, grayish flat, rough colonies with radial lines and wavy edges. Colonies of the mitis type are small, lustrous, black, with a smooth surface. The three biotypes also differ biochemically. If typical colonies are obtained, a pure culture is then identified by fermentative and toxigenic properties.

down urea
Indol «-» H2S «+»or «-»
Reduce nitrates to nitrites
Potassium tellurite

is also reduced

with radial lines and a wavy edges.
Colonies of the

mitis type are small, black, with a smooth surface.

antigen , group specific, thermostabile, somatic polysaccharide.
The diphtheria exotoxin is

a complex of more than 20 antigens.

for 1 year on coagulated serum, for 2 months at

room t, for several days on children's toys.
Cor. diphtheriae are killed by t=60-100ºC and by 1% phenol in 10 min.

enzymatic activity
B- is responsible for binding the toxin to the

cells

Is complex of more than 20 antigens

Is lable, destroyed easily by exposure to heat, light, O2.
Diphtheria toxin can cause myocarditis, polyneuritis, and other systemic toxic effects. 

the presence in it of corynephages (tox+), which act as

the genetic determinant controlling toxin production.
The diphtheria toxin acts by inhibiting protein synthesis.
The toxin causes local necrotic changes and the resulting fibrinous exudate, together with the disintegrating epithelial cells, leucocytes, erythrocytes and bacteria.

diphtheria in man are caused by the diphtheria exotoxin, and

only testing the organism for toxigenicity can definitively determine whether it is pathogenic or not. The diphtheria exotoxin is a polypeptide, which attaches to the cell membrane, allowing to enter the cells, where it catalyses a reaction that stops the synthesis of the polypeptide chains and the most profound effects are on the myocardium, peripheral nerves, and kidneys. C diphtheriae may have different portals of entry: they can colonize the pharynx (espessially the tonsillar regions), the larynx, the nose, the conjunctiva and occasionally the genital tract and the skin (wounds). After adhesion the microbes multiply locally without invading deeper tissues or spreading through the body. The microbe destroys epithelial cells with ulcer formation. This is covered with a necrotic exudate forming a “false membrane.”

by an air-droplet route.
Transmission by various objects (toys) and foodstuffs

(milk) contaminated with Cor. diphtheriae is also possible.

on other parts of the body, e.g., the skin, is

the result of an inflammatory reaction to the presence of multiplying C.diphtheriae. This film soon becomes dark and malodorous, and bleeding occurs on attempting to remove it from tonsils surface. When the larynx is involved, it can result in life- threatening respiratory obstruction. The microbe produces exotoxin that passes into the bloodstream and the lymphatics. This toxemia causes severe generalized effects: myocarditis, polyneuritis, nephritis and suprarenal failure.

inside the nostrils. Almost no toxin is absorbed from this

site, so there is no danger to life and complications are rare.
2. Tonsillar diphtheria - the most common type, in which the infection is limited mostly to the tonsillar region. Most patients recover if properly treated with diphtheria antitoxin.
3. Nasopharyngeal diphtheria - the most often fatal form, in which the tonsillar infection spreads to the nose and throat structures, sometimes completely covering them with the membrane and causing toxemia.

of the infection downward from the nasopharynx to the larynx.
5.

Extra-respiratory diphtheria, consisting of those forms of the infection that affect parts of the body other than the respiratory tract – ex. the skin and wound. 

suspected lesions must be obtained.

-
Gram-positive rods.
The club-shaped long and slender cells with

swollen ends, cells arranged in pairs at acute angles to each other (V, L, X-arrangements).

(Klauberg medium)
2. Subculture on coagulated serum medium
3.

Identification of pure culture and differentiation from the diphtheroids
4. Determination of toxigenicity (IHA, ELISA, precipitation test)

and it can do so only before the toxin reaches

and damages tissue cells. Therefore, it must be given as soon as possible after C. diphtheriae begins to multiply in a patient's throat, on clinical suspicion, and before bacteriological confirmation. C. diphtheriae is nearly always sensitive to penicillin or to erythromycin. These will rid the patients of the organisms. Almost carriers can be cleared with antibiotics.
Active immunity.
The diphtheria toxoid is usually given, along with the tetanus and pertussis vaccine, as DPT (diphtheria -pertussis-tetanus vaccine) to infants between 3 and 6 months old. The usual course is three doses. A booster dose of the diphtheria tetanus (DT) vaccine is given at school entry. Passive immunity. Contacts of a patient may be protected by antitoxin. This may be useful when there is a danger of cross-infection in a ward from a missed case, or in home contacts of a patient.

about 50 species that are normally environmental saprophytes, although some

species cause opportunistic disease of animals and man. The group of pathogenic mycobacteria includes M.leprae that causes leprosy, and the tubercle bacilli. There are three species of tubercle bacilli: M.tuberculosis, the human tubercle bacillus; M. bovis, the bovine tubercle bacillus; M. africanum, a rather heterogeneous type found in Equatorial Africa.

bacterium. It is characterized by a very high content of

lipids, many of which have important biological functions. Surface peptidoglycolipids (mycosides) determine cultural properties and interaction with bacteriophage and serotype. Some glycolipids, especially cord-factor (trehalose dimycolate) and sulpholipids, are toxic. These lipids, together with peptidoglycan, are powerful adjuvants involved in granuloma formation. Lipoarabinomannan interferes with the processing of antigen and its presentation to T cells and may therefore suppress protective immune responses. It also triggers the release of the tumour necrosis factor from activated macrophages.

site of implantation of the bacillus (the lung, skin, or

alimentary tract). Bacteria are ingested by phagocytes, migrate to the draining lymph nodes where secondary lesions develop. The initial pulmonary lesion, the Ghon focus, together with the lymphadenopathy, forms the primary complex . The characteristic lesion of tuberculosis is the granuloma. The primary complex often heals with calcification. Some bacilli are disseminated through lymphatics and blood, leading in some cases to non-respiratory tuberculosis: lymph-node tuberculosis, genitourinary tuberculosis, bone and joint disease, tuberculous meningitis, abdominal tuberculosis, and tuberculous pericarditis.

screw-capped glass or plastic pots. At least three sputum samples,

preferably early-morning samples, should be collected. Bronchoscopy enables specimens to be obtained from abnormal areas of the lung by brushing, bronchoalveolar washing, and by bronchial or transbronchial biopsy. In cases of non-respiratory location of the tuberculosis process, other specimens could be obtained.

extremely specific, sensitive, and rapid diagnosis. Mycobacteria are detectable in

clinical specimens by PCR and by the demonstration of tuberculostearic acid by mass spectroscopy. However, these techniques are not yet widely available.
BACTERIOSCOPICAL EXAMINATION. After drying and heat fixing, the smear is stained by the Ziehl-Neelsen method (Acid-Fast staining). Smears may be stained and examined by fluorescence microscopy. Both methods depend on the acid-fastness of mycobacteria. Microscopy is also used to detect acid-fast bacilli in the urine, pleural, peritoneal, and cerebrospinal fluid after centrifugation, and in homogenates or histological sections of tissue.

they are readily overgrown by fungi or other bacteria in

the specimen. This may be avoided by treating the specimen with an agent, usually an acid or alkali that will preferentially kill organisms other than mycobacteria. The Lowenstein-Jensen medium is the most widely used. It is solid and contains eggs, glycerol, and mineral salts. Specimens are incubated at 35oC-40oC for 4-8 weeks. The following tests allow division of the tubercle bacilli into individual species: reduction of nitrate to nitrite (nitratase test), oxygen preference (aerobic strains grow on the surface of semisolid agar media, while micro-aerophilic strains form a band deep in the medium), susceptibility to different chemicals. On glycerol-containing media, colonies of M. tuberculosis are usually large and heaped up and produce nicotinamide while those of M. bovis are small and flat.

the bacteriological diagnosis of tuberculosis. Samples of sputum, pus, urine,

lavage waters, etc. are spread in a thick layer on the sterile slide glass. After the preparation is dried and manipulated with sulfuric acid, it is placed into a vial with citrate blood. After 3 to 4 days of incubation, the preparation is retrieved, fixed, and then stained with the Ziehl-Neelsen stain. Microcolonies in the preparation appear as rope-like microcolonies termed cords. Cord formation is regarded as a marker of the presence of a specific “cord-factor” in the microcapsule of the pathogen.
BIOLOGICAL EXAMINATION. M. tuberculosis causes disease in a wide range of mammals. This microbe is virulent for the guinea-pig. M. bovis causes infection in cattle and badgers and, less frequently, in deer and other wild or feral mammals. Experimentally, M. bovis is highly virulent to rabbits.

Mantoux test, tuberculin, the solution containing a known number of

international units of mycobacterial antigen - purified protein derivative (PPD) - is injected intradermally. The diameter of the induration is read 48 to 72 h later. The induration of up to 10 mm-15 mm is usually regarded as positive and may indicate previous exposure to mycobacterial antigens through infection with one of the tubercle bacilli or to BCG vaccination. (That is because of type IV hypersensitivity which develops three to eight weeks after the primary infection). Tuberculin reactivity does not correlate with protective immunity.

predominantly cell-mediated, and detection of antibody rising is not of

great importance in diagnosis. Thus, tuberculin conversion usually occurs 3 to 8 weeks from the time of infection.

are isoniazid, rifampicin, and pyrazinamide. Ethambutol and streptomycin are valuable

additional drugs. Reserve drugs, which may be used when first-line treatment has failed, are ethionamide or prothionamide, kanamycin, etc. All M. tuberculosis strains contain drug-resistant mutants.

Bacillus Calmette-Guerrin (BCG), was supposedly derived from a strain of

M. bovis. It is now prepared as a freeze-dried live vaccine for intradermal injection. The booster vaccination should be performed only in those negative on tuberculin testing (the Mantoux test).