Bacterial Infections MCQ

This module is about the specific bacteria that reach the dental chair. They fall into three groups: the organisms dentistry can set loose (oral viridans streptococci seeded into the blood, and the polymicrobial flora of odontogenic infection), the systemic infections that announce themselves with oral signs you must recognize and refer (syphilis, tuberculosis, scarlet fever), and the organisms that shape infection control (Pseudomonas in waterlines, tetanus, Clostridioides difficile after the antibiotics we prescribe). Sorting bacteria by the Gram stain and by whether they damage tissue with an exotoxin or with cell-wall endotoxin keeps the list manageable.

Gram-Positive Cocci: Streptococci and Staphylococci

• Viridans streptococci (such as S. sanguinis, S. mutans) are alpha-hemolytic oral commensals. Released into the blood by chewing, brushing, and dental procedures, they can settle on damaged or prosthetic heart valves and cause infective endocarditis.
• Streptococcus pyogenes (Group A, beta-hemolytic) causes pharyngitis and can be followed by rheumatic fever (with rheumatic heart disease) or scarlet fever, whose oral signs include a strawberry tongue and palatal petechiae.
• Streptococcus pneumoniae is an encapsulated organism causing pneumonia and otitis media; the capsule is its key antiphagocytic virulence factor and the target of vaccines.
• Staphylococcus aureus is coagulase-positive and causes abscesses, wound infections, and impetigo, and contributes to angular cheilitis; methicillin-resistant S. aureus (MRSA) is an important resistant strain, and drainage is central to treating staphylococcal abscesses.

Odontogenic Infections and Actinomycosis

• Odontogenic infections (periapical abscess, fascial-space infection) are polymicrobial: early facultative viridans streptococci give way to obligate anaerobes such as Prevotella, Fusobacterium, and Peptostreptococcus, which produce foul-smelling pus.
• The cornerstone of treatment is source control: drainage and removing or treating the offending tooth. Antibiotics are added for spreading infection, systemic signs, or an immunocompromised patient.
• Actinomyces israelii is a filamentous, anaerobic Gram-positive organism that causes cervicofacial actinomycosis (lumpy jaw): a chronic, indurated swelling with draining sinus tracts that exude yellow sulfur granules, often after extraction or trauma.
• Actinomycosis is treated with prolonged antibiotics (classically a long course of penicillin) along with surgical drainage, because the organism is walled off in chronic abscesses.

Gram-Negative and Other Notable Bacteria

• Pseudomonas aeruginosa is an opportunistic Gram-negative organism that thrives in water and forms biofilms, including in dental unit waterlines, posing a risk to immunocompromised patients; waterline maintenance and quality testing are the controls.
• Haemophilus influenzae type b once commonly caused epiglottitis, a true airway emergency; the Hib vaccine has made it rare in children.
• Neisseria species include the meningococcus (meningitis) and gonococcus (which can cause a pharyngitis); Neisseria are Gram-negative diplococci.
• Escherichia coli and other enteric Gram-negative rods are common causes of urinary and abdominal infection and carry LPS endotoxin, though they are not primary oral pathogens.

Spirochetes and Mycobacteria: Syphilis and Tuberculosis

• Treponema pallidum, a spirochete, causes syphilis. Primary syphilis is a painless chancre (which can be on the lip or in the mouth); secondary syphilis brings mucous patches and a rash; oral lesions are highly infectious, and congenital syphilis can produce notched (Hutchinson) incisors and mulberry molars.
• Mycobacterium tuberculosis causes tuberculosis; beyond the lungs it can rarely produce a chronic, non-healing oral ulcer (often on the tongue), so a persistent ulcer that does not heal warrants biopsy and referral.
• Both are recognized chiefly by their oral and clinical patterns; the dentist's role is to recognize, protect with standard (and, for active TB, airborne) precautions, and refer for diagnosis and treatment.
• Spirochetes also drive oral disease in ANUG (Fusobacterium with oral Treponema species) and in periodontitis (Treponema denticola), connecting this module back to the oral biofilm.

Toxin-Mediated and Antibiotic-Associated Infections

• Exotoxins are proteins secreted by living bacteria (often very potent and able to be made into toxoid vaccines), whereas endotoxin is the lipopolysaccharide of the Gram-negative wall, released as the cell dies.
• Clostridium tetani, from a contaminated wound, produces tetanospasmin, causing tetanus with trismus (lockjaw) and risus sardonicus; persistent trismus with a wound history is a red flag, distinct from the common odontogenic causes of limited opening.
• Clostridioides difficile overgrows when antibiotics disturb the gut flora, causing antibiotic-associated diarrhea and colitis; clindamycin and other broad agents used in dentistry are recognized triggers.
• Corynebacterium diphtheriae produces a toxin and a gray pharyngeal pseudomembrane; it is now rare because of vaccination but remains a classic toxin-mediated infection.