Micro L6

Medical Bacteriology Overview

Key Terms

• Gonorrhea: A sexually transmitted infection caused by Neisseria gonorrhoeae.

• Adrenal hemorrhage: Bleeding into the adrenal glands.

• Epiglottitis: Inflammation of the epiglottis, often caused by Haemophilus influenzae.

• Pertussis: Also known as whooping cough, caused by Bordetella pertussis.

• Localized aggressive periodontitis: A severe form of gum disease often seen in adolescents.

• Enteric fever: Includes typhoid fever caused by Salmonella species.

• Bacillary dysentery: Intestinal inflammation caused by bacteria such as Shigella.

• Nosocomial infection: Infections acquired in healthcare settings.

• Cholera: Caused by Vibrio cholerae and characterized by severe diarrhea.

• Actinobacillus, Porphyromonas, Prevotella: Genus of bacteria associated with periodontal diseases.

Neisseriaceae Family

• General Characteristics:

  • Gram-negative, aerobic diplococci (some are capnophilic).

  • Includes Neisseria and Moraxella genera.

Neisseria gonorrhoeae

• Habitat: Urogenital tract, mouth, rectum, nasopharynx.

• Transmission: Sexual intercourse.

• Characteristics:

  • Non-motile and non-capsulated.

  • Causes gonorrhea leading to septicemia, arthritis, PID, and sterility in women.

• Virulence Factors:

  1. Pili

  2. IgA protease

  3. β-lactamase

  4. Cytotoxin (damages fallopian tubes).

• Treatment: Cephalosporins are the best treatment option.

Neisseria meningitidis

• Habitat: Nasopharynx.

• Transmission: Respiratory droplets.

• Characteristics:

  • Non-motile but capsulated.

  • Endotoxin is the main virulence factor causing meningitis or adrenal hemorrhage.

• Treatment: Penicillin and cefotaxime are drugs of choice.

Moraxella

• Characteristics: Gram-negative cocci.

• Habitat: Respiratory tract; opportunist causing endocarditis, otitis media, sinusitis, and meningitis.

Veillonella

• Characteristics: Gram-negative, anaerobic cocci found in the oral cavity (especially dental plaque).

• Function: Convert lactic acid to weaker acids, reducing enamel degradation.

• Important species: V. dispar, V. atypica, V. parvula.

Parvobacteria Group

• Includes: Haemophilus, Brucella, Bordetella, Pasteurella, Francisella, Aggregatibacter, Gardnerella, Eikenella.

Haemophilus influenzae

• Characteristics: Gram-negative, aerobic coccobacilli, non-sporing, non-motile, some capsulated.

• Habitat: Upper respiratory tract, requiring X factor (hematin) and V factor (NAD).

• Infections: Meningitis, osteomyelitis, epiglottitis, arthritis.

• Virulence Factors:

  1. IgA protease

  2. Capsule

  3. Endotoxin.

• Treatment: Ampicillin recommended; Hib vaccine for prevention.

Bordetella pertussis

• Characteristics: Gram-negative, capsulated bacilli.

• Habitat: Respiratory tract; transmitted via respiratory droplets.

• Disease: Causative agent of pertussis (whooping cough).

• Virulence Factors:

  1. Fimbrial antigen

  2. Endotoxin

  3. Tracheal cytotoxin.

• Treatment: Erythromycin is the drug of choice; DPT vaccine for prevention.

Actinobacillus (Aggregatibacter) actinomycetemcomitans

• Characteristics: Gram-negative, aerobic bacilli (star-shaped).

• Habitat: Oral cavity (supragingival sites).

• Disease: Localized aggressive periodontitis in adolescents, rapidly destructive periodontitis in adults.

• Virulence Factors:

  1. Endotoxin

  2. Leukotoxin

  3. Collagenase

  4. Cytolethal distending toxin (CDT)

  5. Epitheliotoxin

  6. Protease.

• Treatment: Tetracycline is the drug of choice.

Eikenella corrodens

• Characteristics: Gram-negative, capnophilic coccobacilli.

• Habitat: Intestinal and oral cavity.

• Diseases: Abdominal and brain abscesses, peritonitis, meningitis, endocarditis, osteomyelitis.

Capnocytophaga

• Characteristics: Gram-negative, capnophilic fusiforms.

• Habitat: Subgingival area.

• Virulence Factors: IgA protease.

• Causative Agent: Gingivitis and systemic infections, especially in immunocompromised patients.

Enterobacteriaceae Family

• Characteristics: Gram-negative, facultative anaerobes; many have flagellum, pilus, and capsule.

• Habitat: Gastrointestinal tract.

• Transmission: Tainted food and fecal-oral route.

• Virulence Factors: Endotoxin (LPS); includes lipid A responsible for endotoxic shock (fever, hypotension, DIC).

• Treatment: Broad-spectrum antibiotics (ampicillin, amoxicillin, cephalosporins, trimethoprim, chloramphenicol, aminoglycosides, ciprofloxacin).

Escherichia coli

• Habitat: Human intestinal tract.

• Infections: Urinary tract infections, neonatal meningitis, diarrhea (four types: EHEC, EIEC, ETEC, EPEC), each with different mechanisms.

Salmonella spp.

• Habitat: Intestinal tract and poultry products.

• Infections: Enteric fever (typhoid fever), gastroenteritis, septicemia.

• Vaccine: A typhoid vaccine is available.

Shigella spp.

• Habitat: Human intestine.

• Important Species: S. dysenteriae, S. sonnei, S. flexneri, S. boydii.

• Disease: Bloody diarrhea (bacillary dysentery), marked by significant neurotoxin production.

• Treatment: Electrolyte therapy recommended.

Klebsiella pneumoniae

• Habitat: Intestinal, respiratory tract, and oral cavity.

• Disease: Pneumonia and urinary tract infections (UTIs).

• Virulence Factors: Capsule.

Additional Genera

• Enterobacter, Serratia marcescens, Proteus spp., Yersinia pestis: causative agents of various infections, particularly UTIs, neonatal fatal infections, and plague.

Pseudomonas aeruginosa

• Characteristics: Gram-negative, aerobic bacilli with motility.

• Habitat: Human intestine, moist surfaces, and dental unit water lines.

• Virulence Factors: Protease, elastase, LPS, exotoxin, antiphagocytic extracellular slime layer.

• Treatment: Aminoglycosides, piperacillin, polymyxin, cephalosporins are preferred.

Vibrios

• Characteristics: Gram-negative, curved bacilli with high motility.

• Habitat: Contaminated water.

• Important Species: V. cholerae (causes cholera) and V. parahaemolyticus (causes mild diarrhea).

Campylobacters

• Characteristics: Gram-negative, curved and motile bacilli.

• Habitat: Animals, contaminated food, and milk.

• Important Species: C. jejuni (causes gastroenteritis), C. fetus (strong enterotoxin), C. rectus (periodontal diseases).

Helicobacter pylori

• Disease: Causative agent of gastritis, duodenal ulcers, and gastric cancers, treatable with antibiotics.

Wolinella

• Characteristics: Gram-negative bacilli with motility, found in the oral cavity, especially gingival sulcus.

• Medically Important Species: W. succinogenes; potential contributor to periodontal diseases.

Bacteroides fragilis

• Characteristics: Gram-negative, anaerobic bacilli.

• Habitat: Intestine.

• Virulence Factors: Capsule, endotoxin, proteases cause intra-abdominal infections, liver abscesses, and peritonitis.

• Treatment: Metronidazole and clindamycin are drugs of choice.

Tannerella forsythia

• Characteristics: Gram-negative, anaerobic bacilli.

• Habitat: Subgingival sites.

• Virulence Factors: Fatty acids, endotoxin, methylglyoxal secretion.

• Disease: Causative agent of periodontal diseases.

Porphyromonas gingivalis

• Characteristics: Gram-negative, anaerobic coccobacilli.

• Virulence Factors: Capsule, fimbriae, endotoxin, collagenase, phospholipase, fibrinolysin, proteases.

• Disease: Aggressive periodontal disease, regarded as a consensus periodontal pathogen.

Prevotellae

• Characteristics: Gram-negative, anaerobic bacilli.

• Normal Habitat: Oral cavity (subgingival sites).

• Prototype: P. melaninogenica; P. intermedia causes periodontal diseases, others are found in healthy gingival sites.

• Virulence Factors: Similar to P. gingivalis.

References

• Samaranayake L. (2024). Essential Microbiology for Dentistry. (6th edition). Churchill Livingstone Inc., London, United Kingdom. 424 p.

• evolve.elsevier.com