Bacterial Infections

• Types of Skin Lesions

  • Macules
  • Papules
  • Plaques
  • Nodules
  • Urticaria
  • Vesicles
  • Pustules
  • Purpura
  • Ulcers
  • Eschar

  
• Pathogenic bacteria possess characteristics that enable them to circumvent the body's defenses and exploit its resources, resulting in infection
• Bacterial infections spread by a variety of mechanisms including direct contact, ingestion, and inhalation
• Staphylococcus aureus

  Gram-positive cocci usually arranged in pairs, short chains, or in grape-like clusters, found in the skin and the nasopharynx, produces enzymes and toxins that contribute to its virulence and pathogenicity

  
• Staphylococcus aureus


  • It spreads by direct contact with a person having purulent lesions, or through fomites like bed linens and contaminated clothing

  
• Clinical Findings of Staphylococcus aureus infections

  • Folliculitis
  • Furuncle
  • Carbuncle
  • Sty or hordeolum
  • Impetigo
  • Staphylococcal Scalded Skin Syndrome (Ritter's Disease)

  
• Staphylococcal Scalded Skin Syndrome (Ritter's Disease)


  Sudden onset of perioral erythema that covers the whole body within two days, caused by exfoliative toxin, skin becomes intact again in 7-10 days with no scarring

  
• Laboratory Diagnosis for Staphylococcus aureus

  • Microscopic examination: Gram-stained (gram-positive cocci)
  • Culture: gray to golden yellow colonies

  
• Treatment and Prevention for Staphylococcus aureus

  • Oxacillin (only penicillin-derived antibiotic active against S. aureus)
  • Incision and drainage

  
• Patient Care for Staphylococcus aureus infections

  • Standard Precautions for minor skin, burn, and wound infections
  • Contact Precaution if major, SSSS
  • Standard Precautions for MRSA infections
  • Contact Precautions if wounds cannot be contained by dressings

  
• Staphylococcus epidermidis


  Gram-positive bacteria that is part of the skin's normal flora, frequently linked to "stitch abscess", UTI, and endocarditis, causes infections in people who utilize prosthetic equipment

  
• Streptococcus pyogenes


  Gram-positive cocci that belong to group A beta-hemolytic, M protein is a major virulence factor, produces enzymes and toxins that contribute to pathogenesis

  
• Clinical Manifestations of Streptococcus pyogenes infections

  • Erysipelas (St. Anthony's Fire)
  • Cellulitis
  • Necrotizing Fasciitis

  
• Complications of Streptococcus pyogenes infections

  • Acute glomerulonephritis
  • Rheumatic fever

  
• Laboratory Diagnosis for Streptococcus pyogenes

  • Microscopy: Gram stain of infected tissue
  • Culture: Positive beta hemolysis in blood agar
  • Bacitracin test: Antibiotic susceptibility

  
• Treatment and Prevention for Streptococcus pyogenes

  • Drug of choice: Penicillin
  • Alternative for PCN allergy: Erythromycin or Cephalosporin
  • Drainage of pus and thorough debridement of infected tissues

  
• Patient Care for Streptococcus pyogenes infections

  • Standard Precautions for minor skin, burn, and wound infections
  • Contact or Droplet Precautions for major infections

  
• Pseudomonas aeruginosa


  Gram negative bacillus, arranged in pairs, encapsulated, an opportunist pathogen, common cause of nosocomial infections, resistant to most antibiotics, capable of producing water-soluble pigments like pyocyanin, virulence factors include adhesins, toxins, and enzymes

  
• Clinical Findings of Pseudomonas aeruginosa infections

  • Colonization of burn wounds with blue-green pus and sweet grape-like odor
  • Folliculitis
  • Secondary infection to acne and nail infection
  • Osteochondritis
  • Ocular keratitis in contact lens wearers, endocarditis and osteomyelitis in IV drug users
  • External otitis (swimmer's ear) in healthy people, and severe external otitis in diabetics
  • Respiratory failure in persons with cystic fibrosis
  • Extensive skin burns leading to sepsis

  
• Laboratory Diagnosis for Pseudomonas aeruginosa

  • Gram stain
  • Culture: Colonies with green pigmentation and sweet grape-like odor

  
• Treatment and Prevention for Pseudomonas aeruginosa

  • Preventing contamination of sterile hospital equipment and instruments
  • Preventing cross-contamination of patients by hospital personnel
  • Drug of choice: Cephalosporins (Cefepime)
• Clostridium perfringens


  Gram-positive rod-shaped bacilli that are anaerobic and rarely produce endospores, produces toxins including the most lethal alpha toxin, associated with soil and water contaminated with feces
• Clinical Findings of Clostridium perfringens infections

  • Soft tissue infections: Cellulitis, suppurative myositis, myonecrosis or gas gangrene
  • Gas gangrene (Clostridial Myonecrosis): Life-threatening infection characterized by massive tissue necrosis with gas formation, leading to shock, renal failure and death within two days
• Treatment and Prevention for Clostridium perfringens

  • Surgical wound debridement
  • High-dose Penicillin therapy
• Use Standard Precaution for Clostridium perfringens infections
• Bacteria are generally associated with many types of ocular infections, which if left untreated can harm the eye structures and result in blindness and visual impairment
• Types of Bacterial Eye Infections

  • Conjunctivitis
  • Keratitis
  • Keratoconjunctivitis
• Bacterial Conjunctivitis (Pink eye conjunctivitis)


  Inflammation or infection involving the conjunctiva, characterized by eye irritation, reddening of the conjunctiva, swelling of the eyelids, mucopurulent discharges, and sensitivity to light (Photophobia)
• Mode of Transmission for Bacterial Conjunctivitis

  • Human-to-human transmission via contact with eye and respiratory discharges
  • Contaminated fingers
  • Fomites like clothing, facial tissues, eye makeup, eye medications, ophthalmic instruments

  
• Etiologic Agents of Bacterial Conjunctivitis

  • Haemophilus influenzae biogroup Aegyptius (Koch-Weeks bacillus): Gram-negative rod shaped (coccobacillus), associated with acute, purulent conjunctivitis, virulence factor is pili
  • Streptococcus pneumoniae: Gram-positive diplococci, virulence factors include adhesin, capsule, toxin pneumolysin and IgA protease
  • Chlamydia trachomatis: Gram-negative obligate intracellular pathogen, drug of choice is sulfonamides
• Clinical Findings of Bacterial Eye Infections

  • Conjunctivitis ("swimming pool conjunctivitis"): Mucopurulent eye discharge, acquired through swimming in non-chlorinated or poorly chlorinated water, or genital to eye transfer
  • Inclusion conjunctivitis (Chlamydial Conjunctivitis, Para trachoma): Swelling of eyelids with mucopurulent discharge, keratitis, corneal infiltrates and vascularization
  • Trachoma (Chlamydia Keratoconjunctivitis): Follicular conjunctivitis with scarring leading to in-turned eyelids and corneal ulceration, scarring, and blindness
  • Neisseria gonorrhea (gonococcus): Redness, swelling of conjunctiva with purulent eye discharge, can lead to corneal ulceration, perforation and blindness if untreated
• Foodborne disease can arise from either infection or intoxication, and may lead to gastritis, enteritis, or colitis
• Neisseria gonorrhea (gonococcus)

  A kidney bean–shaped, Gram-negative diplococcus
• Neisseria gonorrhea (gonococcus)


  • Common cause of STD
  • In neonates- "ophthalmia neonatorum" – acquired upon passage in birth canal
  • In adults, transmitted through finger-to eye contact involving infectious genital secretions

  
• Signs and symptoms of Neisseria gonorrhea infection

  • Redness, swelling of conjunctiva with purulent eye discharge
  • If untreated – leads to corneal ulceration, perforation and blindness
• Prevention of Neisseria gonorrhea infection in neonates

  1. 1% silver nitrate (Crede's prophylaxis)

  2. 1% tetracycline eye ointments or 0.5% erythromycin eye ointments
• "In the struggle comes the learning"
• Foodborne Disease


  Can arise from either infection or intoxication
• Types of foodborne disease

  • Gastritis – inflammation of the mucosal lining of the stomach
  • Enteritis – inflammation of the small intestines
  • Colitis – inflammation of the colon (large intestines)
  • Gastroenteritis – inflammation of the mucosal lining of the stomach and intestine
  • Hepatitis – inflammation of the liver
  • Dysentery – low-volume, painful, bloody diarrhea
• Bacillus cereus


  A gram-positive aerobic rod or bacillus, mildly pathogenic, low virulence, an opportunist pathogen