Characteristics and Pathogenicity of Bacterial Species

Posted on Dec 12, 2024 in Biology

Gram-Positive Spore-Forming Bacillus

Gram-positive spore-forming Bacillus are aerobic, used for biological warfare. B. anthracis causes anthrax, and B. cereus causes food poisoning or intoxication.

Bacillus anthracis

Causes skin infections (malignant pustule), papules, vesicles, pustules, necrotic ulcers, and septicemia.

Bacillus cereus

Mobile, forms a swarming unlike B. anthracis. Causes food poisoning in two ways: related to fried rice (emetic) and with meats and sauces (diarrhea). It can also cause eye infections, keratitis, endophthalmitis, foreign bodies, endocarditis, osteomyelitis, and pneumonia through the use of invasive procedures.

Clostridium

They are straight or slightly curved bacilli, isolated, in pairs or chains. Peritrichous mobile or immobile flagella produce endospores, oval or spherical, that deform the bacillus (central, subterminal, or terminal). They are anaerobes and grow in GasPak, where O2 is removed and replaced with nitrogen and 10% CO2. They cause tetanus, botulism, gas gangrene, and pseudomembranous colitis.

  • Clostridium perfringens: Large colonies with regular edges and hemolysis.
  • Clostridium tetani: Colonies as a network of fine filaments.
  • Clostridium botulinum: Causes botulism. Toxigenic varieties A-G; A, B, E, and F are sometimes pathogenic to humans.
  • Clostridium tetani: Cause of tetanus. All share a common type O antigen (somatic) and all produce the same kind of tetanospasmin neurotoxin that is released when the bacterium is lysed.
  • Clostridium perfringens: Produces large amounts of toxins and enzymes that are conducive to the spread of the disease.
  • Alpha toxin type A: A lecithinase that splits cell membrane lecithin, transforming it into phosphorylcholine and diglycerides.
  • Theta toxin: Hemolytic and necrotizing but is not a lecithinase. Collagenase is found in subcutaneous tissue and muscle.
  • Clostridium difficile: Producer of pseudomembranous colitis.

Gram-Positive Non-Spore-Forming

Corynebacterium diphtheriae (Diphtheria)

Acute, contagious, febrile, characterized by local inflammation. The microorganism is in the form of a polypeptide. Diphtheritic raqueta toxin is thermolabile, with a 0.1ug/kg deadly dose.

Pathogenesis: Drops of secretions enter the mucous membranes or skin abrasions. Toxigenic bacilli begin to produce toxins.

There are 4 types: gravis, mitis, intermedius, and belfantis.

Listeria

Gram-positive short rods, unlike mobile diphtheroids (racquet). Serotypes Ib, I, IVb, the latter causing listeriosis associated with unpasteurized cheese.

Clinical data: Perinatal listeriosis (infantile septic granulomatosis) with sepsis and death in utero before and after childbirth. In adults, it causes meningoencephalitis and bacteremia (immunocompromised).

Erysipelothrix rhusiopathiae

The disease is called erysipeloid, which is a form of skin infection and cellulitis that affects fingers and toes, appearing on a cut inoculation (sealer’s finger, whale finger).

Lactobacillus

Has great resistance to vancomycin.

Streptococcus

  • Beta-hemolytic Streptococcus: Total hemolysis (pyogenes, agalactiae).
  • Alpha-hemolytic Streptococcus: Partial hemolysis (pneumoniae, viridans).

Streptococcus pyogenes A

Streptococcal pyrogenic exotoxins A, B, and C are related to streptococci and scarlet fever. TSST factor is a streptococcal superantigen. Streptolysin O is labile and highly immunogenic. Streptolysin S is not immunogenic.

Streptococcus agalactiae B

Agent of neonatal infections and female genital tract infections.

Streptococcus pneumoniae

The capsule is a virulence factor for bacteria.

Enterococcus

Natural resistance to cephalosporin generations 1, 2, and 3.

  • Streptococcus faecalis: Found in the mouths of adults.
  • Streptococcus faecium: Found in the feces of normal adults.

Non-Fermentative Gram-Negative

Pseudomonas aeruginosa

O antigen, H antigen, capsule polysaccharide (alginate), pili. Comprises 3 stages: fixation and bacterial colonization, local invasion, and dissemination and systemic disease.

Kingella

Normal oral flora.

Moraxella

Normal flora of the airways.

  • Enterotoxigenic: Labile toxin, heat-stable.
  • Enteroinvasive: Induces phagocytosis.
  • Enteropathogenic: Effacement of the villi.
  • Enteroaggregative: Adherence to mucosal damage.
  • Enterohemorrhagic: Verotoxin.

Serratia marcescens

Produces pigment marcescin or prodigiosin.

Shigella

Infection by 10 to 3 bacteria. The most frequent is S. flexneri. The most virulent is S. dysenteriae.

Salmonella typhi

105 to 108.

Pathogenesis: Ingestion of contaminated food or drink, propagation in the small intestine, immunosuppression invasion, cytotoxins, and enterotoxins.

Non-Fermentative Gram-Negative

Pseudomonas aeruginosa

O antigen, H antigen, capsule polysaccharide (alginate), pili. Comprises 3 stages: fixation and bacterial colonization, local invasion, and dissemination and systemic disease.

Kingella

Normal oral flora.

Moraxella

Normal flora of the airways.

  • Enterotoxigenic: Labile toxin, heat-stable.
  • Enteroinvasive: Induces phagocytosis.
  • Enteropathogenic: Effacement of the villi.
  • Enteroaggregative: Adherence to mucosal damage.
  • Enterohemorrhagic: Verotoxin.

Serratia marcescens

Produces pigment marcescin or prodigiosin.

Shigella

Infection by 10 to 3 bacteria. The most frequent is S. flexneri. The most virulent is S. dysenteriae.

Salmonella typhi

105 to 108.

Pathogenesis: Ingestion of contaminated food or drink, propagation in the small intestine, immunosuppression invasion, cytotoxins, and enterotoxins.