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-Respiratory infections caused by bacteria are quite so many. They can be differentiated by placing them into where they actually cause disease in the respiratory system or tract. Some bacteria cause disease in the upper respiratory tract whilst others affect the lower respiratory tract. The upper respiratory tract comprises the nasal cavity, pharynx and the larynx, whilst the lower respiratory tract is made up of the trachea, primary bronchi and the lungs.
When it comes to aetiology, the respiratory infections caused by bacteria can be compared and contrasted as follows:
Legionnaires disease is caused by the bacteria Legionalla pneumophila, which is a rod shaped, motile and gram negative, fastidious bacteria. Legionnaires disease is one of the most common causes of atypical pneumonia in hospitalized patients. It is the second most common cause of community-acquired bacterial pneumonia and travel-acquired pneumonia.Legionelloses can occur both sporadically and in epidemics. And over the past decade, Legionnaire’s Disease cases have increased. This is so because of the common use of central air conditioning, especially in office hotels, buildings and hospitals.
In contrast to Legionalla pneumophila, Haemophilus influenzae is a nonmotile, but is also a fastidious, Gram-negative, rod-shaped bacterium like L. pneumophila. Non capsular type b H. influenzae causes is associated with acute exacerbations of chronic bronchitis. Disease is e much more common in children than older age groups..
Haemophilus influenzae can cause infection in the respiratory tract, which can spread to other organs. Many species of Haemophilus are normal residents in the upper airways of children and adults and rarely cause disease. Usually, Haemophilus influenzae can cause infections in children and sometimes in adults who have a chronic lung disorder or a weakened immune system.
Diphtheria, which is an acute infectious bacterial disease primarily involving the mucous membrane of the upper respiratory tract (nose, tonsils, pharynx, and larynx), is caused by Corynebacterium diphtheriae.
In comparison to L pneumophila and H influenzae, Corynebacterium diphtheria, is a also rod shaped but non motile like H influenza, and in contrast, is gram positive and non fastidious.
Normally, streptococcus pneumoniae is a inhabitant of the human upper respiratory tract., but it causes infections like pneumonia, bacteremia, otitis media, meningitis, sinusitis, peritonitis and arthritis. Streptococcus pneumoniae cells are Gram-positive, coccus bacteria. Usually, they are seen as pairs of cocci (diplococci), but they may also occur singly and in short chains.They can be aerobic or anaerobic and are often capsulate.
Streptococcus pneumoniae is known in medical microbiology as the pneumococcus, referring to its morphology and its consistent involvement in pneumococcal pneumonia. Streptococcus pneumonia caused pneumonia can be divided into two forms, bronchial pneumonia (100%), most prevalent in infants, young children and aged adults and and lobar pneumonia (80%), which is common in younger adults
Streptococcus pyogene, a gram positive cocci, non motile and non spore forming bacteria, causes streptococcal pharyngitis, which is popularly known as strep throat. Strep throat is characterized by a painful, red throat with white patches on tonsils, and is accompanied by swollen lymph nodes, fever, and headache. Streptococcus pyogenes is considered to be an opportunistic pathogen. This is so because it is part of the normal flora of the respiratory tract in many people, not causing any complications until the person’s natural defenses become immunocompromised.
Mycobacteruim tuberculosis, are rods, gram positive, acid fast and obligate aerobic bacteria. They cause the disease Tuberculosis (TB) whose importance has been compounded by the emergence of AIDS and the appearance of multiple drug-resistant (MDR) strains of M. Tuberculosis. TB most commonly affects the lungs but also can involve almost any organ of the body. There is a vaccine against Tb called Bacille Calmette Guérin, also known as BCG, which is a vaccine given throughout many parts of the world.
TB is one of the most serious infectious disease of the resource poor world. It is persistent wherever poverty, malnutrition and poor housing prevail. It affects the apparently healthy as well as being a serious disease of the immunocompromised, as it is particularly with patients with HIV/AIDS. TB is primarily a disease of the lungs, but may spread to other sites
Bordetella pertussis, the small gram negative coccobacilli, are slow growing and fastidious bacteria. They cause a disease called whooping cough, whose name is because of the characteristic sound produced when affected individuals attempt to inhale; the whoop originates from the inflammation and swelling of the laryngeal structures that vibrate when there is a rapid inflow of air during inspiration.
Wooping cough is characterised in three main phases. The first stage of whooping cough is known as the catarrhal stage, in which symtoms are runny nose, sneezing, low-grade fever, mild, occasional cough, similar to the common cold. The cough gradually becomes more severe, and after one to two weeks, the second stage begins.
It is during the second stage (the paroxysmal stage) that the coughing is most severe. A series of closely spaced coughs occurs, followed by a `whoop` as air is inhaled. Vomitting may be stimulated by the coughing process. Coughing can occasionally be so severe as to rupture blood vessels in the eye or meninges.
The third stage of whooping cough is the recovery or convalescent stage, where there is a marked decrease in vomiting and paroxysms becomes less frequent and the child sleeps better. And towards the end of this phase, the coughing stops.
Whooping cough commonly affects infants and young children but can be prevented by immunization with pertussis vaccine
L. pneumophila is not acquired through a person to a person transmission. The bacteria, thus the disease is acquired by inhalation of contaminated water from showers, Respiratory therapy equipment,air conditioning systems as well as cooling towers. And the bacteria will usually cause respiratory disease in humans after a susceptible host inhales aerosolized water containing the bacteria or aspirates water containing the bacteria.
Legionnaires disease is one of the causes of atypical pneumonia and even after inhalation of the bacteria, disease is not obvious. There are therefore,e risk factors which are associated with one getting Legionnaires disease. These are, cancer, usually pulmonary or hematological malignancy, Smoking, Surgery,Diabetes, HIV/AIDS ,Chronic cardiopulmonary disease, Advanced age and Alcohol abuse
Haemophilus influenza is a normal habitat of the upper respiratory tract of humans and other animals. The infective bacteria are transmitted from person to person, by air borne route. This is typically through sneezing, coughing, or touching.
Corynebacterium diphtheria is a normal habitat of human nasopharynx and occasionally, the skin. Therefore, the disease Diphtheri,a is transmitted from the infected to others via airborne respiratory droplets or by direct contact with nasopharyngeal secretions or skin lesions. Quite, rarely, it can be spread by objects which are contaminated by an infected person. The spread of diphtheria is increased by overcrowding and poor living conditions. Raw milk has served as a vehicle. Infected individuals may develop symptoms of diphtheria, or they may become carriers of the bacteria with no symptoms (asymptomatic carriers). These asymptomatic carriers can serve as reservoirs for active infection and may transmit the disease to other individuals
Streptococcus pneumonia is a normal habitat of the human respiratory tract. Therefore, the spread of the bacteria is primarily via droplet spread or aerosol or through contact with nasal secretions of the infected person. It is therefore. a transmission of person to person.
Streptococcus pyogenes is a normal habitat of the human upper respiratory tract as well as the skin. The respiratory disease caused by these bacteria, Streptococcal pharyngitis is acquired by inhaling aerosols emitted by infected individuals. Spread is therefore by air-borne droplets, through sneezing and coughing and by contact.
M. tuberculosis has the ability to survive in the environment due to the waxy outer coat and this is what aids the transmission of bacteria through air borne droplet spread because they can survive for long periods of time in air and house dust. Therefore, a person can become infected with M. tuberculosis when they inhale minute particles of infected sputum from the air. TB is acquired by inhalation of Mycobacterium tuberculosis in aerosols and dust. Air-borne transmission of TB is every effective because infected people release enormous numbers of mycobacterial into the environment, when they cough, sneeze, shout, or spit.
In the transmission of TB, social and environmental factors as well as genetic predisposition have a role to play.
B. pertussis causes whooping cough, which is a highly contagious disease and is spread among people by direct contact with the nose or mouth fluids from of infected people. People may contaminate their hands with respiratory secretions from an infected person and then touch their own mouth or nose. Another way is that small bacteria-containing droplets of mucus from the nose or lungs enter the air during a cough or sneeze and people can become infected by breathing in these drops. And in vaccinated populations, B.pertussis is brought home by an older person, like even a parent, then spread to the vulnerable population of children.
Once L. pneumophila bacterium is in inhaled, infection will begin. The bacteria virulence factors are unclear, but the bacteria have a way of surviving in the alveolar macrophages. The infection though, will be obvious, if the person has other predisposing risk factors like smoking, cancer, HIV/AIDS, surgery, advanced age, alcohol abuse and diabetes.
About 2-9 days after inhaling the bacteria, symptoms will involve headaches, fever chills and a cough which is nonproductive but may become productive as disease progresses. There will also be other symptoms involving the gastrointestinal tract like vomiting, nausea and diarrhea Arthralgias and myalgias are the musculoskeletal symptoms often experienced.
And when the L.pneumophila bacteria get to the alveoli, they are attacked by the alveolar macrophages. These alveolar macrophages, will take the bacteria into the food vacuole inside the cell. Most often, the infection will progress because instead of the bacteria being destroyed by the macrophages, the bacteria will instead stop the fusion of the lysosome and monocyte. This will result in the bacteria to multiply inside the macrophage, and they eventually lyse the cell as well as infect other cells. Disease will progress from here.
H. influenza interfers with the local expression of the immune response in tissues. Therefore, it does not interfere with the development of an immune response, but will just actively interfere with its expression in tissues. This bacteria liberates a protease that cleaves human IgA antibogy. H. influenza is a resident or invades mucosa where IgA antibodies operate.
H. influenzae has a polysaccharide capsule which is an important virulence factor. This is because the capsule allows the bacteria to resist digestion by phagocytosis. These capsules also protect the bacteria when taken up by the lung macrophages.
Diphtheria, the disease is due to production of diphtheria toxin which is controlled by the tax gene, which is integrated into the bacterial chromosome on a lysogenic phage. The toxin`s mode of action is the blocking of protein synthesis in the host epithelial cells by inactivating the elongation factor.
The signs and symptoms of respiratory diphtheria, which begin after a 2-5 days incubation period, are because of the bacterium’s ability to cause a localized inflammatory reaction of the cells lining the upper respiratory tract. The initial symptoms will be moderate fever, malaise, hoarseness, difficulty in breathing and swallowing and a sore throat. Later the complications may be cardiac, neurologic, infectious, like lung, bone and blood infection and death.
So, when respiratory diphtheria progresses, the infected individual may also develop a gray membrane (pseudomembrane) which will form over the lining tissues of the tonsils and/or nasopharynx. In severe disease, patients may also develop neck swelling and enlarged neck lymph nodes. The extension of the pseudomembrane into the larynx and trachea can eventually lead to obstruction of the airway with subsequent suffocation and death. Immunization is the best prevention against diphtheria.
The clinical symptoms of S. pneumoniae caused pneumonia include sudden onset of high fever, chest pains, dyspnea and a cough productiveof bloody sputum. In adults though, on set may be less sudden with shortness of breath, fever and altered mental status being the first symptoms of pneumonia. In young children and infants, vomiting, convultions and fever may be the first signs.
Pnuemococcal pneumonia is one of the important causes of death in the elderly and infants. And the ones at high risk are those with chronic conditions and with immune deficiencies. Other complications that can arise from infection can be acute respiratory distress syndrome, septic shock, and empyema.
S pneumoniae is a typical extracellular bacterial pathogen, which has a capsule that protects it from phagocytosis. Therefore, its pathogenicity requires adherence to host cells as well as the ability to replicate evade phagocytosis. It is in this effect that the organism must then gain access to areas where it can manifest infection, either through direct extension or lymphatic or hematogenous spread.
Through direct extension, organisms may gain access to areas of the upper and/or lower respiratory tracts (sinuses, bronchi, eustachian tubes) after the colonization. Normally, in a healthy host, anatomic and ciliary clearance mechanisms will prevent clinical infection. But, clearance may be reduced by chronic (bronchitis, smoking, allergies,) or acute (viral infection, allergies) factors, which can lead to infection.
Alternatively, by hematogenous spread and after mucosal invasion, pneumococci may reach normally sterile areas, such as the blood, peritoneum, cerebrospinal fluid, or joint fluid
Symptoms of strep throat are sore throat, high fever, coughing, swollen lymph nodes and tonsils and a fiery red appearance to pharyngeal tissues which is du to tissue erosion.
The M protein enhances the pathogenicity of S. Pyogenes. This protein, which is anchored in the cell wall and cell membrane, encourages adherence to the pharyngeal tissue and retards phagocytosis of the bacteria by the phagocytic cells of the host. Host immunity to Streptococcus pyogenes results from the development of antibodies specific to M protein. Over 80 specific types of M protein have been identified and complete immunity to streptococcal disease requires that a person produce antibodies against all 80 types.
In developing countries, TB is a major cause of death and disability. In all cases, the disease begins with exposure to an infectious human source, thereafter, subsequent infection usually goes without notice.
The first stage which is called primary infection causes no outward clinical manifestations. In this stage, the bacteria are engulfed by the alveolar macrophages where they can both survive and multiply. Primary TB is often mild and asymptomatic and often in 90% of cases, it does not proceed further. But clinical manifestations develop in the remaining 10% leading to active tuberculosis. and it may take several months from the time the infection initially gets into the lungs until the symptoms develop. In active TB infection, the usual symptoms are a generalized tiredness or fever, weight loss, weakness, and night sweats. And if the infection in the lung worsens then, chest pain, coughing, coughing up of sputum and/or blood, and shortness of breath may be experienced. In the event that there is spread of infection beyond the lungs, the symptoms will depend upon the organs involved.
M. tuberculosis is an intracellular pathogen, meaning, it is capable of surviving within macrophages. It is capable of surviving intra-cellularly through the inhibition of phagosome-lysosome fusion. Cell mediated immunity alos comes into effect, which causes infiltration of macrophages and lymphocytes with development of granulomas (tubercles)..
Much of the pathology of TB is due to host immune responsiveness rather than to direct bacterial toxicity. And at times, the body’s immune system becomes weakened, and the TB bacteria break through the scar tissue and can cause active disease, referred to as reactivation tuberculosis or secondary TB. Like the immune system can be weakened by old age, chemotherapy, HIV/AIDS and certain other medications.
B.pertussis usually colonizes the ciliated respiratory epithelium of the trachea-bronchial tract. This colonization prevents the cilia from eliminating materials from the respiratory tract and it is this accumulation of materials which stimulates the coughing. It has been seen that capsulation of the bacteria canvplay a role in the successful colonization.
A variety of virulence factors of B. pertussis have been demonstrated which are:
The Pertussis toxin known for causing death
Adenylate cyclise toxin play a role in inhibiting s the defensive functions of neutrophils
Tracheal cytotoxin which kills the tracheal epithelial cells and causes local inflammation
And the Endotoxin
Pathogenesis of B. pertussis is that it colonizes an area which is normally bacteria-free i.e the respiratory epithelium and then disrupts or destroy the first line defense mechanism i.e the cilia The infection is promoted by the bacterium..
Legionella pneumophila can be diagnosed in the lab by the following ways,
The specimens are bronchial washings and bronchoalvealor lavage which are better collected before commencement of antibiotic therapy.
Legionellae are fastidious organisms requiring cysteine and other essential
growth promoting factors for their successful isolation and need 48 hours incubation before growth is visible for up to five days or more. A negative culture is not an obvious exclusion the diagnosis of legionellosis.
Ideally, paired sera collected as soon as possible after the onset of illness and 3 to 6 weeks later should be tested.
Direct Fluorescent antibody (DFA)
Legionellae can be detected in respiratory secretions by DFA for several days after the start of antimicrobial therapy. DFA staining has also been used for serologic identification of Legionella isolates.
Urine Antigen Detection
Urinary antigen testing has helped in the recognition of outbreaks of Legionnaires’
disease allowing for a rapid public health response. Also urine antigen helps make an early diagnosis thus the initiation of appropriate antibiotic therapy.
immunochromatographic (ICT) membrane assay. This is a very simple test, not needing special laboratory equipment, giving results within 15 min.
Nucleic acid based tests
Poymerase Chain Reaction (PCR) tests that have been developed for legionellae
Diagnosis of H. influenzae pneumonia is made by successfully culturing, isolation and identification of the bacteria. Identifying H. influenzae needs a sample to be taken from infected tissue and be confirmed by laboratory tests.
The specimen is usually grown on culture with the following conditions:
On chocolate blood agar ( which is prepared by adding blood to an agar base at 80oC)
Incubated at 35-37oC with optimal pH of 7.6.
under aerobic conditions or under slight CO2 tension (5% CO2
The diagnosis of diphtheria is confirmed by isolation of the bacterium Corynebacterium diphtheriae. Specimens are taken from the nose and throat in any individual suspected of having diphtheria, as well as their close contacts.
For culture, Corynebacterium diphtheriae, can be isolated (and diphtheria can be diagnosed) using the following conditions:
Using blood culture-identification is aided by a selective medium on which characteristic black colonies form within 48 hrs at 35 degrees celcius .
Biochemically, it is catalase positive and reduces nitrate.
The Elek test is used to demonstrate toxin production of the bacteria.
Polymerase Chain Reaction (PCR) is also used for the identification of the toxin gene
Streptococcus pneumoniae can be isolated and identified using culture and biochemical tests.
The specimen is usually grown on culture with the following conditions:
By use of at 5% blood agar which will grow colonies that characteristically produce a zone of alpha (green) hemolysis, and this differentiates S. pneumoniae from the group A (beta hemolytic) streptococcus,
Biochemically, S. pneumoniae is catalase negative and is distinguished from other streptococci by inulin fermentation, optochin sensitivity and bile test.
PCR is also available for diagnosis as well as for screening for S.pnumoniae by using respiratory samples or feces
When cultured on blood agar, they are alpha hemolytic. Individual cells are between 0.5 and 1.25 micrometers in diameter. They do not form spores, and they are nonmotile. Like other streptococci, they lack catalase and ferment glucose to lactic acid. Unlike other streptococci, they do not display an M protein, they hydrolyze inulin, and their cell wall composition is characteristic both in terms of their peptidoglycan and their teichoic acid
S.pyogenes caused Strep throat can be diagnosed through a throat culture or a rapid strep test. The throat culture will be grown on an enriched medium containing blood. S. pyogenes is fermentative, is a facultative anaerobe and is a catalase-negative
TB can be diagnosed by a skin test for delayed hypersensitivity with tuberculin. A positive test does not necessarily indicate active disease; merely exposure to the organism
Staining and microscopic exam of sputum specimens for the presence of acid-fast bacteria is a rapid test for tuberculosis.
When cultured, M. tuberculosis grows very slowly, meaning culture results may delay commencing of treatment for the patient. Culture also requires the use of complex media.
Polymerase Chain Reaction (PCR) can also be used to diagnose TB. This test detects the genetic material of the bacteria, it is extremely sensitive (it detects minute amounts of the bacteria) as well as specific (it detects only the TB bacteria). Results are usually ready within a few days.
Culture of the bacterium Bordetella pertussis from nasal secretions can establish the diagnosis of whooping cough. Since there are difficulties in obtaining the adequate sample, swabs should be inoculated directly onto media at the patients` bedside. It is better to get both post and peri nasal swabs.
B. pertussis fails to grow on routine blood agar and only requires enriched medium. Therefore, special media are used for isolation of B. pertussis, and these are Bordet Gengou medium and Lacey`s medium and it needs 3-7 days incubation in moist atmosphere. B.pertussis is then identified on colony appearance basis using the proper medium as well as agglutination tests.
Polymerase Chain Reaction (PCR) has been used to successfully identify the bacterium and diagnose whooping cough. This test can identify genetic material from the bacterium in nasal secretions
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