Bacterial Infections of the Respiratory Tract (PDF)

Bacterial infections of the respiratory tract (I) Nur Adilla binti Zaini M. Sc. (Medical Microbiology) - Manchester Lecturer Unit of Microbiology, FoM [email protected] Nur Adilla Zaini Topic outcomes Objectives The objective of this lecture is to...

Bacterial infections of the respiratory tract (I) Nur Adilla binti Zaini M. Sc. (Medical Microbiology) - Manchester Lecturer Unit of Microbiology, FoM [email protected] Nur Adilla Zaini Topic outcomes Objectives The objective of this lecture is to discuss the common bacterial causes of respiratory infections, host factors predisposing to infections; pathogenesis; laboratory diagnosis. Topic Outcomes At the end of the lecture, students should be able to: 29.1 Explain the host factors that predispose a person to respiratory infections. 29.2 Relate the various types of bacterial respiratory tract infections with the common bacteria causing it. 29.3 Describe the morphology, virulence factors, pathogenicity and clinical features of infections caused by Streptococcus pneumoniae, Haemophilus influenzae and Klebsiella pneumoniae. (Recall the lecture on Gram-positive cocci in the Musculoskeletal system) Nur Adilla Zaini Respiratory tract infections Infections of parts of the body involved in breathing, such as the sinuses, throat, airways, or lungs. Nur Adilla Zaini Nur Adilla Zaini Nur Adilla Zaini Predispose factors Nur Adilla Zaini Nur Adilla Zaini  Sinusitis The most common bacterial agents responsible for 1 acute sinusitis are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. Other, including Staphylococcus aureus, 2 Streptococcus pyogenes, Gram-negative organisms and anaerobes have also been recovered. Chronic sinusitis -a mixed infection of aerobic and 3 anaerobic Nur Adilla Zaini Common symptoms Runny nose Stuffy nose Facial pain or pressure Headache Mucus dripping down the throat (post-nasal drip) Sore throat Cough Bad breath Nur Adilla Zaini  Otitis Most common causative bacteria are Streptococcus 01 pneumoniae, Hemophilus influenzae and beta-lactamase producing Moraxella catarrhalis. Otitis externa, the skin flora such as Staphylococcus epidermidis, 02 Staphylococcus aureus, diphtheroids and occasionally an anaerobic organism, Propionibacterium acnes. 03 Moist and warm environment, a diffuse acute otitis externa (Swimmer's ear) may be caused by Pseudomonas aeruginosa, along with other skin flora. Nur Adilla Zaini (Image courtesy: Michael Hawke, MD) (Image courtesy: Karen McKoy, MD) Nur Adilla Zaini  Pharyngitis, tonsillitis Group A beta-hemolytic streptococcus or Streptococcus 01 pyogenes are the most important bacterial agent associated with acute pharyngitis and tonsillitis. 02 Corynebacterium diphtheriae causes occasional cases of acute pharyngitis. Mycoplasma pneumoniae and Mycoplasma hominis also have been associated with acute pharyngitis. 03 Outbreaks of Chlamydia pneumoniae (TWAR agent) causing pharyngitis or pneumonitis have occurred in military recruits. Nur Adilla Zaini (Image courtesy: Biophoto Associates) (James et. al, 2019) Nur Adilla Zaini Laryngitis Laryngitis is inflammation of the larynx (voice box). Nur Adilla Zaini  Bronchitis Bronchitis is usually preceded by an upper respiratory tract infection 01 or forms part of a clinical syndrome in diseases such as influenza, rubeola, rubella, pertussis, scarlet fever and typhoid fever. Chronic bronchitis is caused by smoking, environmental factors, and 02 bacterial infections with H. influenzae and S. pneumoniae, leading to a persistent cough and sputum production. Nur Adilla Zaini  Bronchiolitis 01 Bronchiolitis is a viral respiratory disease of infants and is caused primarily by respiratory syncytial virus. 02 Occasionally M. pneumoniae is known to cause bronchiolitis. Nur Adilla Zaini Pneumonia Pneumonia is an infection that affects one or both lungs. It causes the air sacs, or alveoli, of the lungs to fill up with fluid or pus. Bacteria, viruses, or fungi may cause pneumonia. Nur Adilla Zaini Nur Adilla Zaini Streptococcus pneumoniae Nur Adilla Zaini  Streptococcus pneumoniae ❑ Streptococcus pneumoniae causes pneumonia, bacteremia, meningitis, and infections of the upper respiratory tract. ❑ S. pneumoniae is also known as the pneumococcus. ❑ Pneumococci are gram-positive lancet-shaped cocci arranged in pairs (diplococci) or short chains. ❑ Pneumococci possess polysaccharide capsules of more than 85 antigenically distinct types. Nur Adilla Zaini ❑ Specific antibody to the capsule opsonizes the organism, facilitates phagocytosis, and promotes resistance. ❑ Such antibody develops in humans as a result either of infection (asymptomatic or clinical) or of administration of polysaccharide vaccine. ❑ Capsular polysaccharide elicits primarily a B-cell (i.e., T-independent) response. ❑ Another important surface component of S. pneumoniae is a teichoic acid in the cell wall called C-substance (also known as C-polysaccharide). ❑ It is medically important not for itself, but because it reacts with a normal serum protein made by the liver called C-reactive protein (CRP). Nur Adilla Zaini ❑ CRP is an “acute-phase” protein that is elevated as much as 1000-fold in acute inflammation. ❑ CRP is not an antibody (which are γ-globulins) but rather a β-globulin. (Plasma contains α-, β-, and γ-globulins.) ❑ Note that CRP is a nonspecific indicator of inflammation and is elevated in response to the presence of many organisms, not just S. pneumoniae. ❑ Clinically, CRP in human serum is measured in the laboratory by its reaction with the carbohydrate of S. pneumoniae. ❑ The medical importance of CRP is that an elevated CRP appears to be a better predictor of heart attack risk than an elevated cholesterol level. Nur Adilla Zaini  Pathogenesis and epidemiology 01 Humans are the natural hosts for pneumococci; there is no animal reservoir. Because a proportion (5%–50%) of the healthy population 02 harbors virulent organisms in the oropharynx, pneumococcal infections are not considered to be communicable. 03 Resistance is high in healthy young people, and disease results most often when predisposing factors are present. Nur Adilla Zaini The most important virulence factor is the capsular polysaccharide, and anticapsular antibody is protective. Lipoteichoic acid activates complement and induces inflammatory cytokine production, contributes to the inflammatory response and to the septic shock syndrome that occurs in some immunocompromised patients. Pneumolysin, the hemolysin that causes α-hemolysis, may also contribute to pathogenesis. Nur Adilla Zaini Pneumococci produce IgA protease that enhances the organism’s ability to colonize the mucosa of the upper respiratory tract. Pneumococci multiply in tissues and cause inflammation. When they reach alveoli, there is outpouring of fluid and red and white blood cells, resulting in consolidation of the lung. During recovery, pneumococci are phagocytized, mononuclear cells ingest debris, and the consolidation resolves. Nur Adilla Zaini  Clinical findings 01 Pneumonia often begins with a sudden chill, fever, cough, and pleuritic pain. Sputum is a red or brown “rusty” color. 02 Prominent cause of otitis media, sinusitis, mastoiditis, conjunctivitis, purulent bronchitis, pericarditis, bacterial meningitis, and sepsis. 03 Leading cause of sepsis in patients without a functional spleen. (Channa et. al, 2021) Nur Adilla Zaini Laboratory diagnosis 01 In sputum, pneumococci are seen as lancet- shaped gram-positive diplococci in Gram-stained smears. 02 They can also be detected by using the quellung reaction with multitype antiserum. 03 On blood agar, pneumococci form small α- hemolytic colonies. The colonies are bile-soluble and growth is inhibited by optochin. Nur Adilla Zaini Klebsiella pneumoniae Nur Adilla Zaini  Klebsiella pneumoniae 01 Klebsiella usually opportunistic pathogens that cause nosocomial infections, especially pneumonia and urinary tract infections. 02 K. pneumoniae is an important respiratory tract pathogen outside hospitals as well. 03 Has a very large polysaccharide capsule, which gives its colonies a striking mucoid appearance. Nur Adilla Zaini  Pathogenesis and epidemiology 01 K. pneumoniae is most likely to be a primary, non- opportunistic pathogen; this property is related to its antiphagocytic capsule. Although this organism is a primary pathogen, patients with 02 K. pneumoniae infections frequently have predisposing conditions such as advanced age, chronic respiratory disease, diabetes, or alcoholism. 03 The organism is carried in the respiratory tract of about 10% of healthy people, who are prone to pneumonia if host defenses are lowered. Nur Adilla Zaini Clinical findings 01 Pneumonia caused by Klebsiella, which produces a thick, bloody sputum (“currant-jelly” sputum) and can progress to necrosis and abscess formation Nur Adilla Zaini Laboratory diagnosis 01 Lactose fermenter colonies. Nur Adilla Zaini Haemophilus influenzae Nur Adilla Zaini  Haemophilus influenzae 01 The use of the highly effective “conjugate” vaccine has greatly reduced the incidence of meningitis caused by this organism. 02 It is still an important cause of upper respiratory tract infections (otitis media, sinusitis, conjunctivitis, and epiglottitis) and sepsis in children. 03 Also causes pneumonia in adults, particularly in those with chronic obstructive lung disease. Nur Adilla Zaini  Important properties 01 Small gram-negative rod (coccobacillus) with a polysaccharide capsule. Serologic typing is based on the antigenicity of the capsular polysaccharide. Type b causes most of the severe, invasive diseases, such 02 as meningitis and sepsis. Unencapsulated strains can also cause disease, especially diseases of the upper respiratory tract such as sinusitis and otitis media, but are usually noninvasive. 03 Growth of the organism on laboratory media requires the addition of two components, heme (factor X) and NAD (factor V), for adequate energy production. Nur Adilla Zaini  Pathogenesis and epidemiology 01 Infects only humans; there is no animal reservoir. Enters the body by the inhalation of airborne droplets 02 into the respiratory tract, resulting in either asymptomatic colonization or infections such as otitis media, sinusitis, or pneumonia. 03 The organism produces an IgA protease that degrades secretory IgA, thus facilitating attachment to the respiratory mucosa. 04 After becoming established in the upper respiratory tract, the organism can enter the bloodstream (bacteremia) and spread to the meninges. Nur Adilla Zaini Pathogenesis and epidemiology Meningitis is caused primarily by the encapsulated 05 strains, but non-encapsulated strains are frequently involved in otitis media, sinusitis, and pneumonia. 06 Pathogenesis of H. influenzae involves its antiphagocytic capsule and endotoxin; no exotoxin is produced. 07 Most infections occur in children between the ages of 6 months and 6 years, with a peak in the age group from 6 months to 1 year. Nur Adilla Zaini Nur Adilla Zaini Nur Adilla Zaini Nur Adilla Zaini  Clinical findings a Acute epiglottitis with swelling and 01 Sinusitis and otitis media. cherry-red coloring of the Rarely, epiglottitis, which can obstruct the epiglottis (anterior view). 02 airway, occurs. A swollen “cherry-red” epiglottis is seen. b Acute Pneumonia in elderly adults, especially epiglottitis with 03 those with chronic respiratory disease, can swelling and be caused by un-typeable strains of H. cherry-red influenzae. coloring of the epiglottis (superior view) Nur AdillaImage Zaini courtesy : Schröder et al., 2018 Laboratory diagnosis 01 Isolation of the organism on chocolate agar with two growth factors required for bacterial respiration; factor X (a heme compound) and factor V (NAD). 02 An organism that grows only in the presence of both growth factors is presumptively identified as H. influenzae; other species of Haemophilus, such as Haemophilus parainfluenzae, do not require both factors. Nur Adilla Zaini Laboratory diagnosis 03 Definitive identification can be made with either biochemical tests or the capsular swelling (quellung) reaction. 04 Additional means of identifying encapsulated strains include fluorescent antibody staining of the organism and counter immunoelectrophoresis or latex agglutination tests, which detect the capsular polysaccharide. Nur Adilla Zaini All presentation’s materials; words, tables, figures, and designs are cited and adapted from the reference given and the internet. Nur Adilla Zaini