Medical Microbiology Foodborne and Waterborne Diseases

STAPHYLOCOCCAL FOOD INTOXICATION

• Causative Agent: Staphylococcus aureus; Gram-positive cocci in clusters

• Virulence Factors: Heat-stable enterotoxin (type I exotoxin; superantigen); survives boiling

• Symptoms: Acute nausea, vomiting, diarrhea, abdominal cramps; fever mentioned

• Incubation Period: 1–6 hours

• Reservoir: Human skin

• Mode of Transmission: Contaminated hands → food; bacteria multiply in improperly stored food and produce toxins

• Preventive Measures: Safe food handling; handwashing; correct temperatures/refrigeration

• Treatment: Supportive care; oral rehydration

• Predisposing Factors: Temperature abuse; poor food hygiene

• Diagnosis: N/A

• Additional Information: AKA food poisoning; intoxication from preformed toxin; antibiotics do not address ingested toxin. Slides 6–8

FOODBORNE BOTULISM

• Causative Agent: Clostridium botulinum; Gram-positive endospore-forming bacillus; obligate anaerobe

• Virulence Factors: Potent heat-labile neurotoxin (exotoxin); endospores

• Symptoms: Flaccid paralysis; respiratory or cardiac failure; potentially fatal

• Incubation Period: N/A

• Reservoir: Contaminated food

• Mode of Transmission: Canned food containing botulinum neurotoxin

• Preventive Measures: Proper/commercial canning; nitrites in meats

• Treatment: Respiratory assistance; antitoxins

• Predisposing Factors: N/A

• Diagnosis: Slide preparation: terminal endospore gives drumstick appearance

• Additional Information: Spores germinate under anaerobic conditions; neurotoxin affects nervous system. Slides 9–11

INFANT BOTULISM

• Causative Agent: Clostridium botulinum spores

• Virulence Factors: Spores germinate and produce neurotoxin in infant

• Symptoms: Floppiness/decreased muscle tone; feeding difficulty

• Incubation Period: N/A

• Reservoir: Honey (associated source)

• Mode of Transmission: Infant ingests spores, associated with honey

• Preventive Measures: N/A

• Treatment: N/A

• Predisposing Factors: Infants

• Diagnosis: N/A

• Additional Information: Distinct from foodborne intoxication: ingested spores, not preformed toxin. Slide 12

WOUND BOTULISM

• Causative Agent: Clostridium botulinum

• Virulence Factors: Spores germinate in anaerobic deep wounds and produce neurotoxin

• Symptoms: N/A

• Incubation Period: N/A

• Reservoir: Deep wounds

• Mode of Transmission: Growth of organism in deep puncture wounds

• Preventive Measures: N/A

• Treatment: N/A

• Predisposing Factors: IV drug use; deep wounds

• Diagnosis: N/A

• Additional Information: Additional form of botulism. Slide 12

C. DIFFICILE–ASSOCIATED DIARRHEA

• Causative Agent: Clostridium difficile; Gram-positive endospore-forming obligate anaerobic bacillus

• Virulence Factors: Exotoxins

• Symptoms: Mild diarrhea to colitis; severe ulceration/perforation; sometimes bloody diarrhea

• Incubation Period: N/A

• Reservoir: Primary: humans; secondary: contaminated medical equipment

• Mode of Transmission: Fecal-contaminated water; contaminated medical equipment

• Preventive Measures: Hospital gowns, gloves and disposable equipment

• Treatment: Metronidazole and vancomycin (as specified on slides)

• Predisposing Factors: Extended antibiotic use; health-care exposure

• Diagnosis: Stool PCR for genes producing toxins

• Additional Information: AKA C. diff colitis; slide cites ~500,000 U.S. infections in a 2015 CDC study. Slides 13–15

SALMONELLOSIS

• Causative Agent: Salmonella enterica serovar Typhimurium; Gram-negative motile facultative anaerobic bacillus

• Virulence Factors: Invades intestinal mucosa; multiplies in phagocytes → bacteremia

• Symptoms: Fever (not typically high), nausea, vomiting, cramps, diarrhea

• Incubation Period: 12–36 hours

• Reservoir: Contaminated meat, fruits/vegetables, raw eggs, pet reptiles

• Mode of Transmission: Contaminated food

• Preventive Measures: Avoid raw eggs; wash produce with clean water; avoid pet reptiles

• Treatment: Oral rehydration and antibiotics

• Predisposing Factors: N/A

• Diagnosis: PCR identification of serovar/strain in food

• Additional Information: AKA Salmonella gastroenteritis; carriers may shed bacteria for up to 6 months. Slides 16–18

TYPHOID FEVER

• Causative Agent: Salmonella enterica serovar Typhi; Gram-negative motile facultative anaerobic bacillus

• Virulence Factors: Multiplies in phagocytes → bacteremia

• Symptoms: Prolonged high fever (~104°F), headache, myalgia, cramps, diarrhea, rose spots; severe intestinal ulceration/perforation → bloody diarrhea

• Incubation Period: 2–3 weeks

• Reservoir: Humans

• Mode of Transmission: Fecal-contaminated food or water

• Preventive Measures: Handwashing/personal hygiene

• Treatment: Antibiotics and oral rehydration; chronic carriers may need weeks of treatment

• Predisposing Factors: N/A

• Diagnosis: Pathogen in blood/stool; symptoms including rose spots; serology mentioned in annotation

• Additional Information: 1–3% may become chronic fecal shedders; “Typhoid Mary.” Slides 19–21

SHIGELLOSIS

• Causative Agent: Shigella species (sonnei, boydii, dysenteriae, flexneri); Gram-negative facultative anaerobic bacilli

• Virulence Factors: Shiga toxin; multiply within GI epithelial cells

• Symptoms: Intestinal inflammation; ulceration; bloody mucous diarrhea (bacillary dysentery)

• Incubation Period: 12 hours–2 weeks

• Reservoir: Primary: water; secondary: humans

• Mode of Transmission: Fecal-contaminated water

• Preventive Measures: Handwashing/personal hygiene

• Treatment: Often antibiotics and oral rehydration

• Predisposing Factors: N/A

• Diagnosis: Stool PCR for Shiga-toxin gene; symptoms

• Additional Information: S. dysenteriae listed as most virulent. Slides 23–24

BACTERIAL GASTROENTERITIS (ETEC)

• Causative Agent: Enterotoxigenic Escherichia coli (ETEC), non-O157:H7; Gram-negative motile coliform bacillus

• Virulence Factors: Enterotoxin (exotoxin)

• Symptoms: Nausea, vomiting, diarrhea; milder than EHEC

• Incubation Period: N/A

• Reservoir: Human/animal GI tracts (coliform context)

• Mode of Transmission: Fecal-contaminated water

• Preventive Measures: Boil water before drinking

• Treatment: Oral rehydration; bismuth preparations / OTC antidiarrheals

• Predisposing Factors: N/A

• Diagnosis: N/A

• Additional Information: AKA travelers’ diarrhea; coliforms indicate fecal pollution. Slides 25–26

HEMORRHAGIC COLITIS (EHEC)

• Causative Agent: Enterohemorrhagic Escherichia coli (EHEC), O157:H7; Gram-negative motile coliform bacillus

• Virulence Factors: Shiga toxin; toxin genes discussed via horizontal gene transfer

• Symptoms: Colon inflammation, profound bloody diarrhea, intestinal ulceration; HUS/kidney damage; possible death

• Incubation Period: N/A

• Reservoir: Cattle

• Mode of Transmission: Fecal-contaminated food

• Preventive Measures: Meat inspection; cook meat/ground beef thoroughly

• Treatment: Oral rehydration and supportive care

• Predisposing Factors: N/A

• Diagnosis: Stool cultures; PCR/tests for Shiga toxin genes

• Additional Information: Slide states 50–500 deaths annually; distinguish from ETEC. Slides 27–30

CHOLERA

• Causative Agent: Vibrio cholerae O1 or O139; curved Gram-negative bacillus, single polar flagellum

• Virulence Factors: Powerful cholera exotoxin

• Symptoms: Profuse “rice-water” stools; extreme water/electrolyte loss (12–20 L/day), shock, circulatory collapse, organ failure/death

• Incubation Period: N/A

• Reservoir: Primary: water; secondary: humans

• Mode of Transmission: Contaminated water and seafood

• Preventive Measures: Boil water

• Treatment: Oral rehydration and electrolyte replacement

• Predisposing Factors: N/A

• Diagnosis: N/A

• Additional Information: Halophile in salty waters; endemic in parts of Asia; linked to natural disasters. Slides 31–32

BRUCELLOSIS

• Causative Agent: Brucella abortus; Gram-negative coccobacillus

• Virulence Factors: Multiplies within phagocytes

• Symptoms: Undulant recurring daily fever (~104°F), chills, night sweats

• Incubation Period: N/A

• Reservoir: Livestock and wild animals (cows, elk, bison)

• Mode of Transmission: Unpasteurized milk; contact with infected animals (zoonosis)

• Preventive Measures: Animal vaccination; pasteurize milk; protective clothing

• Treatment: Prolonged antibiotics

• Predisposing Factors: Dairy workers; animal-hide workers/leather makers; hunters

• Diagnosis: N/A

• Additional Information: AKA undulant fever; usually not fatal; rare in U.S. Slides 33–35

HEPATITIS A

• Causative Agent: Hepatitis A virus (HAV); nonenveloped single-stranded RNA virus

• Virulence Factors: Multiplies in intestinal epithelium → viremia and spread to liver, kidneys, spleen

• Symptoms: Children often asymptomatic; adults: anorexia, nausea, diarrhea, headache, fever, chills; late jaundice; symptoms 2–21 days

• Incubation Period: 2–6 weeks

• Reservoir: Primary: food/water; secondary: humans

• Mode of Transmission: Contaminated food and water; fecal–oral

• Preventive Measures: Inactivated HAV vaccine

• Treatment: Immunoglobulins (antibodies), per slides

• Predisposing Factors: N/A

• Diagnosis: Serology for antiviral IgM

• Additional Information: Acute shedding; surface persistence; chlorine resistance; nonchronic, low mortality, lifelong immunity after recovery. Slides 36–37

ROTAVIRUS GASTROENTERITIS

• Causative Agent: Rotavirus; double-stranded RNA virus

• Virulence Factors: N/A

• Symptoms: Low-grade fever, diarrhea and vomiting, lasting about one week

• Incubation Period: 2–3 days

• Reservoir: N/A

• Mode of Transmission: N/A

• Preventive Measures: Live oral vaccine

• Treatment: N/A

• Predisposing Factors: Children; daycare centers; winter season

• Diagnosis: Viral antigens detected in feces

• Additional Information: AKA stomach flu (not influenza). Slide 38

NOROVIRUS GASTROENTERITIS

• Causative Agent: Norovirus; single-stranded RNA virus

• Virulence Factors: Low infectious dose (low ID50), highly contagious

• Symptoms: Diarrhea and vomiting, lasting 2–3 days

• Incubation Period: 18–48 hours

• Reservoir: N/A

• Mode of Transmission: N/A

• Preventive Measures: Thorough handwashing; slide states no vaccine

• Treatment: N/A

• Predisposing Factors: Cruise ships and classrooms; outbreaks year-round

• Diagnosis: PCR

• Additional Information: AKA stomach flu; adults and children affected. Slide 38

POLIOMYELITIS

• Causative Agent: Poliovirus; nonenveloped RNA virus

• Virulence Factors: Multiplies in motor neurons, destroying them

• Symptoms: Usually asymptomatic; early sore throat/nausea; less than 1% paralytic: muscle wasting, lower-limb paralysis; respiratory failure/death

• Incubation Period: N/A

• Reservoir: Primary: water; secondary: humans

• Mode of Transmission: Fecal–oral, contaminated water

• Preventive Measures: Salk injected inactivated vaccine; Sabin live oral vaccine

• Treatment: No treatment stated

• Predisposing Factors: Common in children

• Diagnosis: N/A

• Additional Information: AKA paralytic polio; cases dropped 99% from 1988–2000, per slide. Slides 39–40

GIARDIASIS

• Causative Agent: Giardia intestinalis; flagellated protozoan (Protista)

• Virulence Factors: Multistage lifecycle: ingested dormant cysts → trophozoites attach to intestinal wall

• Symptoms: Prolonged diarrhea, hydrogen sulfide (rotten-egg) gas, weight loss, cramps

• Incubation Period: N/A

• Reservoir: Primary: water; secondary: humans

• Mode of Transmission: Water contaminated with cysts

• Preventive Measures: Boil water

• Treatment: Metronidazole or other antiprotozoal/antiparasitic drugs

• Predisposing Factors: Drinking contaminated stream/river water

• Diagnosis: Microscopic stool examination for cysts/trophozoites

• Additional Information: Trophozoite = active; cyst = dormant. Slides 41–42

AMOEBIASIS

• Causative Agent: Entamoeba histolytica; protozoan parasite (Protista)

• Virulence Factors: Multistage lifecycle: cysts → intestinal trophozoites

• Symptoms: Nausea, fever, cramps, intestinal ulceration/perforation, bloody mucous diarrhea; possible necrotic liver abscess

• Incubation Period: N/A

• Reservoir: Primary: water; secondary: humans

• Mode of Transmission: Water contaminated with cysts

• Preventive Measures: Boil water

• Treatment: Metronidazole or other antiprotozoal/antiparasitic drugs

• Predisposing Factors: N/A

• Diagnosis: Microscopic intestinal biopsy showing trophozoites containing ingested red blood cells

• Additional Information: AKA amoebic dysentery; slide states 10% mortality untreated. Slides 43–45

BEEF TAPEWORM INFECTION (TAENIASIS)

• Causative Agent: Taenia saginata; animal flatworm (Platyhelminthes)

• Virulence Factors: Multistage lifecycle: eggs → oncospheres → cysticerci larvae → adults; specialized hooks/suckers and reproductive proglottids

• Symptoms: Heavy adult-worm burden: abdominal pain, poor appetite, weight loss, fatigue

• Incubation Period: N/A

• Reservoir: Primary/definitive: humans; secondary/intermediate: cattle

• Mode of Transmission: Raw or undercooked beef containing cysticerci larvae

• Preventive Measures: N/A

• Treatment: Prolonged anthelminthic drugs; worm/eggs expelled over weeks

• Predisposing Factors: N/A

• Diagnosis: Stool eggs or proglottids

• Additional Information: Adult 4–8 m, 1,000–2,000 segments; humans definitive and cattle intermediate; cysticercosis discussed separately as larval infection. Slides 46–57

PRION DISEASES

• Causative Agent: Infectious misfolded proteins

• Virulence Factors: Highly resistant infectious protein

• Symptoms: Progressive brain degeneration / spongiform encephalopathy; fatal

• Incubation Period: Usually years

• Reservoir: Sheep, cattle, humans

• Mode of Transmission: Consumption of contaminated animal tissue

• Preventive Measures: Incineration

• Treatment: No treatment

• Predisposing Factors: N/A

• Diagnosis: N/A

• Additional Information: Examples: bovine spongiform encephalopathy (mad cow), human CJD, sheep scrapie. Slides 58–59