Bacterial Diseases Part 2

Cholera

• caused by vibrio cholerae

• produces enterotoxin → cholera toxin

  • binds to intestinal epithelial cells

  • stimulates hyper secretion of water and electrolytes into gut lumen (w/o) damaging mucosal lining

• resulting profuse watery diarrhea (rice water stools) causes severe dehydration and hypovolemic shock

• organism can contaminate water and the shellfish in it

• Vibrio parahaemolyticus results in a milder form of the disease → vibriosis

  • associated with raw or undercooked seafood

  • more common cause of gastroenteritis

• cholera vaccines are available

Enteroinvasive E. coli strains

• invades mucosal cells

• gains access to the submucosa of the large intestine

• causes inflammation and dysentery

• mechanism of invasion similar to that of Shigella

Enterotoxigenic E.coli strains

• make enterotoxins carried on plasmids

• toxins stimulate increased fluid secretion in the small intestine

  • results in watery diarrhea and severe dehydration

• common cause of traveler’s diarrhea

Enterohemorrhagic E. coli strains

• produce a Shiga-like toxin → referred to as the Shiga-toxin producing E. coli

• most common serotype is E. coli O157:H7

• infection leads to bloody diarrhea

• complication: Hemolytic Uremic Syndrome (HUS) → life threatening condition involving the kidneys

• reservoir: gastrointestinal tract of cattle

E. coli carried in our intestines can…

cause opportunistic infections outside the gut

Campylobacter Gastroenteritis (Campylobacteriosis)

• leading bacterial gastroenteritis worldwide

• mainly caused by Campylobacter jejuni

• found in undercooked chicken and unpasteurized milk

• diarrhea, severe abdominal pain, nausea, vomiting, and fever

• most cases are self-limiting

• C. fetus is less common but can cause systemic infection in high risk patients

• rare complication: Guillain-Barre syndrome (GBS) → post-infectious autoimmune disease

Yersinia Gastroenteritis (Yersiniosis)

• intestinal infection caused by eating raw/undercooked pork with Yersinia enterocolitica

• produces an enterotoxin

• can survive and grow at refrigerator temps

• diarrhea, fever, and abdominal pain

• older patients → pain can mimic appendicitis

• disease is generally self-limiting

Clostridium difficile

• gram-positive, anaerobic endospore forming rod

• major cause of antibiotic-associated colitis and pseudomembranous colitis

• vegetative cells produce exotoxins → causes tissue damage and diarrhea

• transmission is fecal-oral in healthcare setting

• infection risk increases after broad-spectrum antibiotic use

• relapse of infection can occur due to endospore germination

Peptic Ulcers

• caused by Helicobacter pylori

  • spiral shaped bacteria

  • survives in acidity of the stomach by producing urease: neutralizes gastric acid locally

  • multiplies in gastric mucosa

• leads to ulcers

• 90% of ulcers can be cured by antibiotic treatment

• chronic H. pylori infection is linked to gastric cancer

bactremia

bacteria present in the blood

septicemia

bacteria present and multiplying in the blood

sepsis

the body’s systemic, harmful response (organ dysfunction and inflammation) to an infection

Puerperal Fever (Puerperal Sepsis or childbirth fever)

• serious infection involving Streptococcus pyogenes (GAS)

• after vaginal delivery → uterine wall becomes irritated

  • organisms enter this site and get into the blood stream

• now uncommon due to improved antiseptic obstetric practices and antibiotics

Group B Streptococci (GBS)

• refers to Streptococcus agalactiae → cause of neonatal sepsis with meningitis as a complication

• newborns contaminated through colonized birth canal

• pregnant women routinely screened for GBS so that they can be treated before it affects the newborn

Rheumatic Fever

• Streptococcus pyogenes causes Strep Throat

  • once symptoms go away → subsequent immune response to that infection develops

• antibodies generated against the organism (ex: M protein) mistakenly target and attack the body’s own healthy tissues

  • due to molecular mimicry

• leads to rheumatic fever → damages heart valves and joints

  • accompanied by fever, rash, and arthritis

Anthrax

• caused by Bacillus anthracis → spore-forming bacterium

• found in soil

• primarily infects grazing animals

• endospores enter body through skin, inhalation, or ingestion 

  • leads to three forms of the disease: cutaneous, pulmonary, and gastrointestinal

• produces two exotoxins (lethal factor and edema factor) and a protective capsule

  • lead to severe illness and death if untreated

  • edema factor: causes fluid accumulation and disrupts immune cell function → weakens defenses and causes swelling

  • lethal factor: causes cell death and tissue necrosis → leads to shock and organ failure

• prevention by vaccination

• classified as a potential bioweapon for bioterrorism

Gas Gangrene

• severe, rapidly progressing condition characterized by death of body tissues

• caused by Clostridium perfringens

  • gram-positive

  • endospore forming

  • anaerobe

• infection occurs when bacteria enter deep contaminated wounds

  • anaerobic environment allows them to thrive → produces toxins and enzymes

    • cytotoxins produced that destroy blood cells and damage tissue (necrosis and gas formation)

• bacteria eventually enters bloodstream

• infection can be fatal without prompt surgical debridement and antibiotic therapy

Plague

• caused by Yersinia pestis

• rare in US

• survive and replicate in macrophages

• found in wild rodents

• transmission occurs when infected flea bites a person

• travels through lymphatic system → causes swollen lymph nodes (buboes)

• if enters bloodstream → causes septicemic plague

• pneumonic plague affects lungs → spread from person to person via respiratory droplets

  • lethal

• vaccines available in some countries

• early antibiotic therapy is crucial for survival

Lyme Disease

• caused by Borrelia burgdorferi

• reservoirs: deer and rodents

• ticks can transfer the organism to humans

• “Bull’s Eye Rash” → telltale sign of the disease, but not everyone develops it

• early antibiotic treatment necessary to avoid late-stage complications

  • includes neurological symptoms, carditis, and chronic arthritis

• systemic disease

  • spirochetes can disseminate through bloodstream to affect multiple organs and tissues

Rickettsia Systemic Diseases

• emerging diseases

• caused by Rickettsia species 

  • small gram-negative obligate intracellular bacteria

• transmitted to humans through arthropod vectors

• invade and damage endothelial cells of blood vessels

• cause fever, headache, rash, weakness, and enlargement of liver and spleen

• treated with antibiotics

• often remains latent

Typhus Fever

• caused by Rickettsia typhi and Rickettsia prowazekii

• Epidemic Typhus caused by Rickettsia prowazekii

  • transmitted from bites of body louse

  • lice feed → excrete bacteria in feces

  • scratching bite allows organism to enter skin

• organism spreads easily in overcrowded and unclean environment

• no vaccine available but can be treated with antibiotics

• Brill-Zinsser disease: recurrence due to reactivation of latent organism

  • causes milder symptoms

Rocky Mountain Spotted Fever (RMSF)

• caused by Rickettsia rickettsii

• transmitted by ticks

• infects vascular endothelium

• leads to systemic vasculitis, characteristic petechial rash, and damage to organs

• antibiotics treat the infection but can become rapidly fatal if untreated

Bacterial Meningitis

infection of the meninges

Pneumococcal meningitis

• caused by Streptococcus pneumoniae

• bacterium colonizes nasopharynx of healthy individuals without symptoms

• causes pneumonia

• virulence factors: capsules and pneumolysin

• vaccines available

Meningococcal meningitis

• caused by Neisseria meningitidis

• gram-negative bacterium

• colonizes nasopharynx asymptomatically in healthy individuals

• virulence factors: capsule: endotoxin, and pili

• symptoms come on rapidly

• treatment must begin promptly to prevent death

• vaccines available against common serogroups in the US

Haemophilis influenzae type B (HiB)

• live asymptomatically in the upper respiratory tract → esp in unvaccinated children

• now rare

• before vaccine → leading cause of meningitis in young children and cause of pneumonia

Group B Streptococcus (GBS), Listeria monocytogenes, and E. coli are

the leading causes of bacterial meningitis in newborns

Listeriosis

• foodborne infection caused by Listeria monocytogenes → found in many foods and is capable of growing at refrigeration temps

• bacteria is gram positive rod

• starts in the GI tract as a foodborne illness

• survives and replicates inside macrophages

• mild and asymptomatic in healthy adults and children

  • flu-like or gastrointestinal symptoms

• becomes a severe NS disease (septicemia or Listerial meningitis) → more common in immunocompromised and the elderly

• pregnant women → bacterium can cross the placenta

  • lead to fetal loss or neonatal septicemia and meningitis

Tetanus

• caused by Clostridium tetani

  • anaerobic endospore bacterium

• spores can infect a puncture wound → spores germinate into vegetative cell → release neurotoxin

• neurotoxin blocks inhibitory signals in NS

  • leads to sustained muscle contraction (spastic paralysis)

• symptom: Lockjaw

• can be fatal is untreated

• preventable with vaccine containing tetanus toxoid

  • DTaP → T in this

    • protects against diphtheria and tetanus (toxoid based), then pertussis (acellular bacteria)

Botulism

• rare but serious illness caused by Clostridium botulinum

  • anaerobic endospore bacterium

  • produces one of the most potent toxins → neurotoxin carried on a prophage

    • prevents muscle from contracting by blocking nerve signals to muscles → flaccid paralysis

• foodborne in canned food where anaerobic conditions allow spore germination

• if infants eat honey contaminated with endospores → can germinate in infant gut

  • can form toxin producing vegetative cells → leads to “floppy baby syndrome” (Infant botulism)

• endospores can contaminate anaerobic wounds → can germinate into vegetative cells producing the toxin 

  • causes wound botulism