Bacterial Diseases of the LowerRespiratory System
Dr. Shler Ghafour Raheem
BSc., MSc., PhD Medical Microbiology
Bacterial Pneumonias
Physicians describe pneumonias according to the:
Affected region of the lungs: Lobar pneumonia involves entirelobes of the lungs
Organism causing the disease: Mycoplasmal pneumonia
Location of acquisition: Healthcare-associated pneumonia(pneumonia acquired in any health care setting, is a common illness among the elderlyand immunosuppressed patients).
Bacterial pneumonias are the more serious and common in adult andStreptococcus pneumonia is the most common type of bacterial pneumonia.
Bacterial Pneumonias
Causes
Streptococcus pneumoniae
Mycoplasma pneumoniae
Klebsiella pneumoniae
Haemophilus influenzae
Staphylococcus aureus
Yersinia pestis
Chlamydophila psittaci and C. pneumoniae
• Virulence factors: Vary among pathogens but include attachment molecules, capsules, inhibitors of phagocytosis, and lipid A.
• Portal of entry
Inhalation, also via blood in case of Yersinia
• Signs and symptoms
• Dry, unproductive cough, headache, fever, chills, and chest pain. Bloody mucoid sputum with Klebsiella; frothy bloody sputum with Yersinia
• Prevention
washing hands frequently, stop smoking, and, in the case of C. psittaci, avoid infected birds.
Vaccines against S. pneumoniae and H. influenzae are available.
Susceptibility
• Pneumococcus: immunocompromised individuals
• M. pneumoniae: high school and college students
• K. pneumoniae: hospitalized individuals
• H. influenzae: infants and young children
• S. aureus: very young and patients with respiratory diseases
• C. pneumoniae: most common in school-aged children
• C. psittaci: individuals in close contact with birds.
General characteristics
Gram positive
Lancet-shaped diplococci
Non motile
Encapsulated
α hemolytic
Optochin sensitive
Lysed by bile
• If an etiology is identified, therapy should be de-escalated and directed at that pathogen
Sputum gram-stain showing the typical lancet-shaped gram positive diplococci of S. pneumoniae
Alpha hemolytic streptococcus
S. pneumoniae
https://microbiologyinfo.com/biochemical-test-and-identification-of-streptococcus-pneumoniae
• Reservoir: Human upper respiratory tract
• Transmission: Respiratory droplets
- Not considered highly communicable
- Often colonizes the nasopharynx without causing disease
Predisposing Factors• Influenza or measles infection
•Chronic obstructive pulmonary disease (COPD)
• Congestive heart failure ( CHF)
• Alcoholism (dominant cause of pneumonia)
Pathogenesis
• Polysaccharide capsule is the major virulence factor
- Antiphagocytic
- Antigenic and opsonized by host antibodies
• IgA protease enhances the organism’s ability to colonize the mucosa of the URT
• Pilli
• Teichoic acid
• Pneumolysin: hemolysin/cytolysin
-Damages respiratory epithelium- Inhibits leukocyte respiratory burst and inhibits classical complement fixation
Diseases
• Typical pneumonia
- Most common cause (especially in sixth decade of life)
- Shaking chills, high fever, lobar consolidation, blood-tinged, "rusty" sputum
• Adult meningitis
- Most common cause
- CSF reveals high WBCs (neutrophils) and low glucose, high protein
• Otitis media and sinusitis in children
• Bacteremia/sepsis
Laboratory Diagnosis
• Direct Gram staining
• Optochin sensitive (P disk)
• Hemolysis (α)
• Catalase (-ve)
• Bile solubility test (+ve)
• Lancefield (none)Streptococcus pneumoniae
• Quellung reaction
- Using specific anti-capsular antisera- Capsule fixed and swells- Capsular swelling is visible
microscopically
• Latex particle agglutination - Detection of capsular antigen Quellung reaction
Treatment
• Bacterial pneumonia: Macrolides
• Adult meningitis: Ceftriaxone or cefotaxime. Vancomycin is added if penicillin resistant S. pneumoniae has been reported in the community
• Otitis media and sinusitis in children: amoxicillin, erythromycin for allergic individuals
Prevention: Antibody to the capsule (over 80 different capsular
serotypes) provides type-specific immunity
• A 65-year-old man presents at his physician’s office with fever,cough, and evidence of pneumonia. Sputum and blood culturesare collected for analysis. α-Hemolytic colonies grew on bloodagar, and a Gram stain of the colony material reveals Gram-positive cocci in pairs. What is the most likely organism?
A. Klebsiella pneumoniae
B. Neisseria meningitidis
C. Staphylococcus aureus
D. Streptococcus pneumoniae
E. Moraxella catarrhalis
Tuberculosis
• Tuberculosis (TB) is the leading disease killer in the world,though its importance to people in industrialized countries has declined as a result
of successful surveillance and the use of effective antimicrobial drugs.
• Tuberculosis (TB) is caused by bacteria (Mycobacteriumtuberculosis) that most often affect the lungs. Tuberculosis iscurable and preventable.
Genus: Mycobacterium
Medically important species
M .tuberculosisM. leprae
M. avium complex
General characteristics
long , Slender
Weakly gram positive
Strongly acid fast
Strictly aerobic rods
Facultative intracellular organism
Grow slowly. Generation time(8-24)hr.
Acid fast stains
M. tuberculosis
https://letstalkrespiratory.com/tuberculosis
Cell wall
Complex
Contains Mycolic Acid
Lipids account for 60% of Cell Wall Weight
Waxy cell surface
Making them resistant toDisinfectants
Detergents
Common antibacterial agents
Traditional stains https://letstalkrespiratory.com/tuberculosis
Epidemiology
Worldwide; a third of the world population is infected with this organism
Transmitted in respiratory aerosols
Occasionally from animals (e.g. milk)
Populations at greatest risk for disease are
Immunocompromised patients (particularly those with HIV)
Drug or alcohol abusers
Homeless persons
Individuals exposed to diseased patients
Virulence factors
The virulence of M. tuberculosis rests
With its ability to survive and grow within host cells
They do not produce demonstrable toxin
Bacterial sulpholipids inhibit the fusion of phagocytic vesicle with lysosomes
Pathogenesis
Inhaled aerosols
Engulfed by alveolar macrophagesBacilli multiply
Infected macrophages migrate local lymph nodes
Develop Ghon’s focus Primary complex
Cell mediated immune response
Diseases caused by M. tuberculosis
The initial pulmonary focus is the middle or lower lung fields, where thetubercle bacilli ca multiply freely
The patient cellular immunity is activated, and mycobacterialreplication ceases in most patients within 3-6 weeks after exposure tothe organism
Non specific symptoms
Malaise
Weight loss
Cough
Night sweats
Sputum may be scant or bloody and purulent
Sputum production with hemoptysis is associated with tissue destruction (e.g., cavitary disease)
Laboratory diagnosis
1. Microscopy
Acid-fast staining of sputum or otherspecimens is the usual initial test. Either theKinyoun version of the acid-fast stain or the older
Ziehl-Neelsen version can be used.
2. culture
culture on special media such as Lowenstein-Jensen agar, for up to 8 weeks. It will not grow on a blood agar plate
3- Positive skin test reactivity
Treatment
Multiple – drug regimens and prolonged treatment are required
Isoniazid (INH)
Ethambutol
Pyrazinamide
Rifampin
References
• Robert W. Bauman, Todd P. Primm. 2018. Microbiology with Diseases by Body System. Fifth edition, Pearson. P: 672-687.
• Kaplan. 2018. USMLE™ Step 1 Lecture Note. Immunology and Microbiology
• Patrick R. Murray, Ken S. Rosenthal, Michael A. Pfaller. 2020. Medical Microbiology. Elsevier.
• Warren E. Levinson, Peter Chin-Hong, Elizabeth Joyce, Jesse Nussbaum, Brian Schwart. 2018. Review of Medical Microbiology & Immunology, 15th edition. McGraw-Hill Education.
• Hedia M, Marie-Antoinette L. and Mamadou D. Mycolic Acids: Structures, Biosynthesis, and Beyond. Chemistry & Biology 21, January 16, 2014 Elsevier. doi.org/10.1016/j.chembiol.2013.11.011.
• https://www.who.int/news-room/fact-sheets/detail/tuberculosis