Microbiology Lecture Notes

Enterobacteriaceae: Shigella

• Closely related to Escherichia, with distinct differences.

• Non-motile and an invasive pathogen.

• Check the PowerPoint on Blackboard for questions about invasiveness, normal flora, pathogen type, toxin production, and capsule presence.

• Invasive nature often leads to bloody diarrhea, unlike enteroinvasive E. Coli, which causes blood after the diarrhea.

• Colonizes host tissues and spreads easily, making it a primary suspect in diarrhea outbreaks.

• Transmission: Person-to-person contact or fecal-oral route.

• Humans are the only known reservoir, which indicates potential human carriers without symptoms.

Shigellosis (Bacillary Dysentery)

• Presence of blood, pus, and mucus in the stool, accompanied by abdominal pain and cramping.

• Usually from contaminated food or water and is highly infectious.

• Infection initiated by ingesting fewer than 200 cells, contrasting with enterotoxigenic E. Coli (11,000,000 cells) and enteroinvasive E. Coli (millions of cells).

• Low pH of the stomach, then attach to specific host cells via invasins.

• Invasins are proteins on the end of pili and fimbriae that help the cells attach to the host cell.

• In the case of Shigella, are coated for plasmids.

• Invade and penetrate epithelial cells lining the large intestine.

• Additional cell death is caused by the Shiga toxin (shigalatoxin).

• Shiga toxin: A cytotoxin acting as an enterotoxin in the intestinal tract, destroying epithelial cells lining the large intestine.

• Incubation period: Before 48 hours.

• Symptoms: Fever, abdominal pain, and bloody diarrhea.

Bacteremia

• Not a second disease of Shigella but a complication of untreated or undertreated shigellosis in immunocompromised patients.

• Bacteremia: Bacteria enter the bloodstream.

• Can lead to septicemia and septic shock.

Salmonella

• Another frank pathogen typically not carried as normal flora.

• Most strains carried by animals, except Salmonella typhi, which is carried by humans.

• Implicated in many cases of food poisoning due to toxin production or cell presence.

• Birds and reptiles carry it as part of their normal intestinal flora.

• Handling birds or reptiles (live or dead) increases the risk of contracting Salmonella.

• Easily found in food products, leading to recalls.

Salmonellosis (Gastroenteritis)

• Gastroenteritis: Inflammation of the entire digestive tract (stomach and intestines).

• Enteritis: Inflammation of the intestinal tract only.

• Exposure is frequent, but requires ingesting a high number of cells (1,000,000 to 100,000,000).

• Bacteria survive the low pH in the stomach and colonize both the small and large intestine, invading the intestinal epithelium.

• Symptoms begin after 12 to 48 hours: Low-grade fever, abdominal pain, and non-bloody diarrhea.

• May include vomiting early on.

• Usually self-limiting, with the immune system eliminating it in 2 to 5 days.

• Common strains in the U.S.: Salmonella typhimurium and Salmonella enteritidis.

• Pregnant women are more likely to be diagnosed because symptoms mimic listeriosis, leading to medical intervention.

Septicemia (Enteric Fever)

• Caused by Salmonella paratyphi, similar to typhoid fever.

• Symptoms: Vomiting, diarrhea, abdominal pain, and cramping; blood in the stool is possible but not typical.

• Most people survive enteric fever unless they have underlying health concerns.

Typhoid Fever

• Caused by Salmonella typhi, through ingestion of contaminated food or drink from an infected host or asymptomatic carrier.

• Salmonella typhi is carried only by humans.

• Transmission: Person-to-person contact or fecal-oral route.

• Infection begins in the small intestine and invades the lymphoid tissue and the bloodstream.

• Incubation time: One to two weeks.

• Symptoms: High fever, headache, myalgia (pain without a known cause), and gastrointestinal distress.

• Vomiting and diarrhea are common.

• Rose-spotted rash on the abdomen indicates bacteria in the blood damaging capillaries and blood vessels.

• Blood cultures are positive early in the infection, while stool tests are more likely to be positive as the infection progresses.

• Chronic state: Organism resides in the gallbladder, secreting Salmonella typhi cells with bile, leading to potential transmission through bowel movements.

• Organism is encapsulated with the K antigen (Vi antigen) as a main virulence factor, a capsule.

• Gram-negative, producing lipopolysaccharide (LPS) as part of the O-specific antigen.

• Does not produce other toxins.

Typhoid Mary

• Story of Mary Mallon, an Irish immigrant and asymptomatic carrier of Salmonella typhi.

• Worked as a cook for various families in the New York area in the early 1900s.

• Linked to multiple outbreaks of typhoid fever.

• Was forcibly quarantined twice on North Brother Island, spending nearly three decades in isolation.

• Cultural and socioeconomic factors, including anti-Irish sentiment and miasma theory, influenced her treatment.

• Raises ethical questions about public health versus individual rights.

Yersinia

• Another frank pathogen.

• 11 species exist, all are not normal flora in humans but can be in other animals.

Yersinia enterocolitica

• Causes symptoms of disease that mimics appendicitis.

• Swine are an indirect reservoir for the disease, including waste form domesticated and wild pigs.

• Contracted via the fecal to oral route and easily spread from person to person.

Yersinia pestis

• Causative agent of bubonic and pneumonic plague, historically known as the "Black Death".

• Transmitted through an insect vector (fleas) from rodents (black rats - Rattus rattus).

• Black rats would have fleas. The fleas, when they would get hungry, would jump off and bite whatever mammal was around, and if they the fleas bit a human, a human could get bubonic pneumonic plague.

• The disease devastated Europe and the world from 1349 to 1500, resulting in an estimated one-fourth of the world population.

Forms of Yersinia pestis Infection

1. Cutaneous

• Begins with a flea bite, injecting bacteria directly into the bloodstream.

• An open wound with blackened edges develops near the bite site, does not scab over, similar to cutaneous anthrax.

• Progresses to the next stage in about 80% of cases

2. Bubonic

• Organism moves through the bloodstream through our lymph nodes.

• Macrophages replicate and causes the lymph nodes to get larger and larger.

• Enlarged lymph node called bubos.

• Once the lymph node ruptures, the bacteria is now carried throughout the bloodstream to any part of the body.

3. Pneumonic

• Most severe form, affecting the respiratory system.

• Typically, people would either suffocate and/or have hemorrhaging in their lungs and drown in their own blood.

Opportunistic Pathogens

• These can cause Urinary Tract Infections (UTIs) and Upper Respiratory Tract Infections.

Citrobacter

• Normal intestinal flora.

• Not considered an enteric pathogen.

• Can cause urinary tract infections, pneumonias, and intra-abdominal abscesses if there's a leakage of intestinal contents into the abdominal cavity

Klebsiella

• Second organism in this family that is nonmodal.

• K antigen was named for Klebsiella.

• Able to produce a heat-stable enterotoxin.

• Causes nosocomial infections, like wounds, bacteremia, pneumonia, and urinary tract infections.

• Infections are typically only seen in hospitalized patients and in immunocompromised hosts.

• Increasing antibiotic resistance.

Enterobacter

• It is normal flora of us, but also for most mammals, and so it's very common to find this in soil, even in, like, well water.

• Does not typically cause too much harm.

• Some species cause urinary tract and respiratory tract infections.

• Two strains: Enterobacter aerogenes and Enterobacter cloacae

• Enterobacter oblomerans causes septicemia due to biofilm contamination in saline bags.

Serratia

• It is another member of our normal flora. We typically see it in hospital acquired infection.

• They produce that red pigment prodigiosin.

• Found in hospital related infection of the urinary or respiratory tracts.

• Burn victims are prone to this because they do not have intact skin. Intact skin is the bodies defense.* Contamination of antiseptic soulition can lead to epidemic or Septic Arthritis.

• Burn victims are prone to this because they do not have intact skin, so their defense is broken.

Proteus

• Is an opportunistic pathogen, either normal flora for 50% of the population.

• Can cause urinary tract and hospital acquired respiratory infections.

• Highly mortal. The problem with cultivating it is they tend to swim over the surface of the plate.

Edwardsiella

• There's only three and Edwardsiella tarda is more likely to be isolated.

• Very similar to E. Coli.

• Usually found in aquatic animals and reptiles, so you can get from eating raw or improperly cooked fish.

• These are all very rare.

Providencia

• Very Rare.

• Associated with hospitall or nosocomial infection for urinary tract, and antimicrobial resistance.

• Providentia alcalifaceans has been associated with some cases of diarrhea in children.