Bacterial Diseases of the LowerRespiratory System

Dr. Shler Ghafour Raheem

BSc., MSc., PhD Medical Microbiology

shler.ghafour@tis.edu.iq

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