*Corynebacterium diphtheriae* causes diphtheria by producing a potent diphtheria toxin. This toxin forms a thick, grayish pseudomembrane in the throat of infected patients, leading to tissue swelling, severe breathing difficulties, and other life-threatening symptoms if left untreated.

Pathogenicity of *Corynebacterium diphtheriae*

An accumulation of grayish exudate consisting of dead host cells, pus, red blood cells, fibrin, and infectious bacteria results in the formation of a pseudomembrane. The pseudomembrane can cover mucous membranes of the nasal cavity, tonsils, pharynx, and larynx. As the disease progresses, the pseudomembrane can enlarge to obstruct the fauces of the pharynx or trachea and can lead to suffocation and death.

Signs and Symptoms of Diphtheria 

Diagnosis of diphtheria is primarily based on the clinical symptoms (i.e., the pseudomembrane) and vaccination history, and is typically confirmed by identifying bacterial cultures obtained from throat swabs. The diphtheria toxin itself can be directly detected in vitro using polymerase chain reaction (PCR)-based, direct detection systems for the diphtheria tox gene, and immunological techniques like radial immunodiffusion or Elek’s immunodiffusion test.

Diagnosis of Diphtheria 

Broad-spectrum antibiotics like penicillin and erythromycin tend to effectively control C. diphtheriae infections. Regrettably, they have no effect against preformed toxins. If toxin production has already occurred in the patient, antitoxins (preformed antibodies against the toxin) are administered. Although this is effective in neutralizing the toxin, the antitoxins may lead to serum sickness because they are produced in horses

Treatment of Diphtheria 

Diphtheria is caused by *Corynebacterium diphtheriae* and is a respiratory infection of the oropharynx but can also cause impetigo-like lesions on the skin. Although the disease can affect people of all ages, it tends to be most severe in those younger than 5 years or older than 40 years.

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The respiratory tract can be infected by many different types of bacteria, which cause many different diseases. The diseases that can be caused by bacteria include: 
- Streptococcal Pharyngitis (strep throat)
 - Scarlet fever
- Acute Rheumatic Fever
- Acute Glomerulonephritis
- Acute Otitis Media (AOM)
- Otitis Media with Effusion (OME)
- Bacterial Rhinosinusitis
- Diphtheria
- Tuberculosis
- Haemophilus Pneumonia
- Mycoplasma Pneumonia
- Chlamydial Pneumonias
- Health Care-Associated Pneumonia
- Pseudomonas Pneumonia
- Pertussis (Whooping Cough)
- Legionnaires Disease
- Q Fever
- Psittacosis

The Different Bacterial Infections of the Respiratory System

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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*Streptococcus pyogenes* causes several infections, including: 
 - Streptococcal Pharyngitis (strep throat)
 - Scarlet fever
 - Acute Rheumatic Fever
 - Acute Glomerulonephritis

Streptococcal Infections of the Respiratory System

Acute Otitis Media (AOM) is characterized by the formation and accumulation of pus in the middle ear. The pus builds up, resulting in moderate to severe bulging of the tympanic membrane and otalgia (ear pain). Inflammation resulting from the infection leads to swelling of the eustachian tubes, and may also lead to fever, nausea, vomiting, and diarrhea, particularly in infants.

Acute Otitis Media (AOM)

Otitis Media with Effusion (OME) can be caused by any blockage of the eustachian tubes, with or without infection, this can cause fluid to become trapped and accumulate in the middle ear. The accumulated fluid offers an excellent reservoir for microbial growth and, consequently, secondary bacterial infections often ensue. This can lead to recurring and chronic earaches, which are especially common in young children. 

Otitis Media with Effusion (OME)

Bacterial Rhinosinusitis often occurs as a secondary infection after a viral infection. Bacterial sinusitis involves infection and inflammation within the paranasal sinuses. The most common causes of bacterial rhinosinusitis include *S. pneumoniae,* *H. influenzae,* and *M. catarrhalis*

Bacterial Rhinosinusitis

Diphtheria

Tuberculosis (TB) is one of the deadliest infectious diseases in human history. Although tuberculosis infection rates in the United States are extremely low, the CDC estimates that about one-third of the world’s population is infected with *Mycobacterium tuberculosis*, the causal organism of TB,

Tuberculosis

Pertussis is commonly called whooping cough, and is caused by *Bordetella pertussis* The disease is characterized by mucus accumulation in the lungs that leads to a long period of severe coughing. Sometimes, following a bout of coughing, a sound resembling a “whoop” is produced as air is inhaled through the inflamed and restricted airway hence the name whooping cough.

Pertussis (Whooping Cough)

Legionnaires disease (also known as legionellosis) is an atypical pneumonia and is caused by an aerobic gram-negative bacillus *Legionella pneumophila.* infections typically occur from human-made reservoirs such as air-conditioning cooling towers, humidifiers, misting systems, and fountains.

Legionnaires Disease

Q fever is caused by a rickettsia, *Coxiella burnetii.* The primary reservoirs for this bacterium are domesticated livestock such as cattle, sheep, and goats. The bacterium may be transmitted by ticks or through exposure to the urine, feces, milk, or amniotic fluid of an infected animal. In humans, the primary route of infection is through inhalation of contaminated farmyard aerosols.

Q Fever

Psittacosis is a rare infection and is typically found in people who work with birds. *Chlamydia trachomatis,* the causative agent of the sexually transmitted disease chlamydia, can cause pneumonia in infants when the infection is passed from a person giving birth to a baby.

Psittacosis

Bacterial pneumonia is a prevalent, potentially serious infection; it caused more 50,000 deaths in the United States in 2014. There are several types, including: 
 - Haemophilus Pneumonia
 - Mycoplasma Pneumonia
 - Chlamydial Pneumonias
 - Health Care-Associated Pneumonia
 - Pseudomonas Pneumonia

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