gi infections and food poisoning

gi tract

- contaminated food and water are common vesicles for transmission
- low pH of stomach provides strong selective pressure
- dense and diverse microbiota

diarrhea

- water content, volume, or frequency of stools
- important to consider patient history, symptoms, medication use, and underlying conditions

infection

- longer incubation time (24-48 hours)
- inflammation and presence of WBCs
- longer duration, may systemic
- self limiting or more serious
- can be mediated by enterotoxins

intoxication

- shorter incubation time (1-6 hours)
- little to no inflammation
- shorter duration
- typically localized
- typically self limiting
- caused by enterotoxins

enterobacteriaceae

- gram neg
- bacilli or coccobacilli
- facultative anaerobes
- capable of glucose fermentation
- referred to as enterics
- o, h, k antigen
- virulence is adhesions, toxins, and secretion systems

o antigen

- lipopolysaccharide

h antigen

- flagellum

k antigen

- capsule

mac agar

- lactose fermentatione

eosin y-methylene blue agar

- lactose & sucrose fermentation

hektoen enteric agar

- lactose, sucrose, salicin fermentation
- h2s indicator
- lactose non fermenters = green (shigella)

- xylose-lysine-deoxycholate

- xylose fermentation
- h2s indicator
- salmonella make red colonies with black centers (h2s production)

triple sugar iron agar slant

- glucose, lactose, sucrose fermentation
- h2s indicator

e coli

- different diseases associated with distinct strains
- acquisition and expression of different virulence factors
- causes UTIs
- septicemia and meningitis (most common cause among neonates)

enterotoxigenic e coli

- travelers diarrhea
- etec

enterohemorrhagic e coli

- 0157:H7
- ehec

klebsiella pneumoniae

- common cause of pneumonia, especially among hospital patients
- wound infections and UTIs
- capsule, mucoid colonies
- multidrug resistances

salmonella

- lactose non fermenters (colorless on mac)
- h2s producers
- pathogenic enterica
- o, h, vi antigens for serotyping

salmonella gastroenteritis

- common in poultry, milk, eggs, pets
- infectious dose 10^6 cells
- 8-36 hours after ingestion of contaminated foods
- self limiting
- antibiotic treatment can promote carrier state

salmonella typhi

- humans are the only known reservoir and source of infection
- prevalent in tropical and sub tropical areas
- acid tolerant and invasice
- causes typhoid fever
- colonization of small intestine, lymph nodes, blood, and systemic spread to other organs

shigella

- genetically similar to e coli
- delayed lactose fermentation (48 hours)

bacillary dystentery

- low infectious dose (

vibrio

- gram neg pleomorphic bacilli
- curved comma shape
- aquatic sources (associated w shellfish)
- facultative anaerobes
- motile, single, polar flagellum
- non spore forming
- catalase pos
- oxidase pos
- halophilic

vibrio cholerae

- causative agent of acute diarrheal disease cholera
- vomiting, diarrhea, severe dehydration
- rice water stool containing mucus
- oral rehydration therapy
- toxin-coregulated pilus is required for colonization

cholera toxin

- water rushes outside of the cell into the lumen causing diarrhea

vibrio parahaemolyticus

- second most common vibrio spp causing gastroenteritis
- raw or undercooked seafood
- halophilic

vibrio vulnificus

- septicemia
- consumption of raw seafood
- wound infections

thiosulfate citrate bile salt sucrose agar

- selective media for isolation of vibrio
- sucrose fermenters = yellow
- non fermenters = green

campylobacter

- gram neg curved rods
- seagull wing appearance
- microaerophilic
- oxidase pos
- motile - "darting"
- asaccharolytic

campylobacter jejuni

- commonly associated with poultry
- gastrointestinal disease
- cramps and bloody diarrhea
- diagnosis on campy blood agar
- incubation at 42C
- microaerophilic atmosphere

helicobacter pylori

- gram neg rod
- microaerophilic
- colonizes stomach
- urease is virulence factor
- causes gastric infections
- ulcers
- gastrointestinal carcinoma

urea breath test

- radioactive carbon isotope is ingested
- goes into the lungs and binds to bacteria
- bacteria convert it to co2 and nh3

listeria monocytogenes

- gram pos bacillus
- motile at room temp
- non spore forming
- widespread in environment
- beta hemolytic
- catalase pos
- cold enrichment
- camp+ = block phenomenon

listeriosis

- pregnant women: may lead to spontaneous abortion or still birth
- neonates: manifests as meningitis
- immunocompromised: CNS infections and endocarditis
- foodborne illness in healthy adults

entamoeba histolytica

- 3rd most common cause of death resulting from parasite
- invasive pathogen
- asymptomatic, amebic dysentery, extraintestinal amebiasis
- "bulls eye" nucleus
- detection of ulcers in liver

giardia duodenalis

- most common intestinal parasite in US
- travelers diarrhea
- contaminated water
- tear shaped with falling leaf motility

norovirus

- member of calciviridae
- single stranded rna viruses
- most common infectious gastroenteritis
- food and water borne + person to person transmission
- nausea, vomiting, diarrhea
- short lived immunity, multiple infections

rotavirus

- member of reoviridae
- double stranded rna viruses
- most common cause of viral gastroenteritis in children
- dehydration
- green stool
- fecal oral route
- elisa and latex agglutination for fecal material