Bacterial Gastroenteritis Flashcards
What are the oxygen requirements of the enterobacteriaceae?
Aerobic or facultative anaerobic
What is the structure of enterobacteriaceae? (4)
G- rods, 1-5 microm, inner and outer membrane, peptidoglycan
What are the virulence factors of enterobacteriaceae? (3)
Flagella (H antigen)
Capsule (K or Vi)
LPS (O antigen)
What are the 3 medically important enterobacteriaceae species?
Salmonella enterica
Shigella sonnei, flexneri
Escherichia coli
Are most enterobacteriaceae motile or non-motile?
Motile (generally have peritrichous flagella)
What enterobacteriaceae species are non-motile?
Yersinia, Klebsiella, Shigella (although most are motile)
What morphological characteristic of enterobacteriaceae aids in host cell attachment and horizontal gene transfer?
Fimbriae (pili)
What virulence factor of enterobacteriaceae is the lipid A component of LPS and can lead to septic shock in the blood stream?
Endotoxin
What virulence factor of enterobacteriaceae protects from phagocytosis and activation of host immune system (complement) (although not all enterobacteriaceae have it)?
Capsule
What virulence factor present in a lot of G- species helps move proteins across the membrane?
T3SS (type three secretion systems)
What are the oxygen requirements of salmonella species?
Facultative anaerobe
What are the 2 salmonella species?
Salmonella bongori and salmonella enterica
What are the primary methods of transmission/ sources for salmonella?
Ingestion of contaminated food or water (poultry, organic vegetables)
What are the secondary methods of transmission/ sources for salmonella?
Pet reptiles/ birds, backyard poultry flocks, direct person to person
How do you distinguish between different salmonella species?
Serotyping, based on flagellar (H) and LPS (O) antigens (they are unique)
What organism is often the cause of foodborne gastroenteritis and then subsequent bacteremia?
Non-typhoidal salmonella
What does it mean that S. Typhimurium is a generalist infection?
Infects a variety of hosts
cases self-limiting gastroenteritis in humans
What salmonella species is the most common clinical isolate but presents with an indistinguishable disease?
Salmonella enterica serovar Enteritidis
What feature of ALL Salmonella invades epithelial cells and acts as a virulence factor?
SPI1 (type three secretion system)
Once salmonella invades the epithelial cells, how is the host cell damaged?
Actin cytoskeletal changes and engulfment of bacterium
target actin and host cell signaling cascades
What it the final step of the salmonella life cycle?
Transit epithelial layer and gain access to systemic sites
What is the most important Escherichia species?
E. coli (should be included with Shigella)
Which E.coli strains are pathogenic and have acquired virulence traits?
ETEC (enterotoxigenic E.coli)
EHEC (enterohemorrhagic E.coli)
EIEC (enteroinvasive E.coli)
Shigella species
What organism is the common in young children or travelers and is acquired via contaminated food and water?
ETEC (enterotoxigenic E.coli)
Pt presents with watery diarrhea and intestinal cramps (3-5 days then clears). What are you concerned about?
ETEC (enterotoxigenic E.coli)
1-2 days post exposure
What are the 2 toxins of ETEC (enterotoxigenic E.coli)?
LT1 (heat liable toxin) and STb (heat stable toxin)
Which ETEC (enterotoxigenic E.coli) toxin binds to the same receptor as cholera toxin, activates host adenylate cyclase increasing cAMP levels and results in watery diarrhea from secretion of chloride ions from the cell and water flow into lumen of intestine?
LT1 (heat liable toxin)
Which ETEC (enterotoxigenic E.coli) toxin binds to the guanylate cyclase receptor on intestinal epithelial cells which leads to increased cGMP levels and secretion of fluids from cells?
STb (heat stable toxin)
What Escherichia species is a common cause of foodborne intestinal illness and aka STEC (Shiga toxin producing E. coli)?
EHEC (enterohemorrhagic E.coli)
For which Escherichia species are cattle an important reservoir?
EHEC (enterohemorrhagic E.coli)
What is the most common serotype of EHEC (enterohemorrhagic E.coli)?
O157:H7
Once salmonella invades the epithelial cells effectors lead to actin cytoskeletal changes which. This allows it to gain access to the systemic sites causing what?
SX of salmonella (gastroenteritis)
Is E. coli gram + or gram - ?
Gram-
ETEC is acquired via consumption of contaminated food and water? What is it aka?
Traveler’s diarrhea (watery diarrhea and cramps lasting 3-5 days)
What are the virulence factors of EHEC and Shigella? (3)
- STX (shiga like toxin) - (A-B toxin, binds only in human intestines, released after bacteriophage lyses in response to stresses on the bacterial cell)
- Intimin (adhesions, aid in bacteria binding to intestines)
- Tir (Acts as receptor for intimin w/in epithelial cells, will cause cell death)
What does the A-B toxin do?
B binds to receptor, A is internalized, stops protein synthesis –> cell death
What E. coli infection is very similar to shigella, processes no flagella or adherence factors, and causes profuse bloody diarrhea and dysentery?
EnteroInvasive E. coli (EIEC)
Is shigella gram + or gram- ?
Gram-
What differentiates shigella from other pathogenic E. coli?
Lac-
Shigella initially presents with watery diarrhea but can progress to what sx?
Severe diarrhea w/ blood and mucous (dysentery)
Where does shigella replicate?
Inside macrophages (then kills the cell to be released)
What happens once shigella is released from lysed macrophage?
invades basolateral membrane of epithelial cells which allows it to spread cell to cell and damage the mucosal layer or the GI tract
What Shigella organism is the only to produce shiga toxins?
S. dysenteriae (causes more severe disease)
What are the 2 shiga toxins release by S. dysenteriae?
Shiga toxin 1 (very potent, identical to shiga like toxin O157:H7)
Shiga toxin 2, same mechanism as 1 but different structure and immunogenicity
What toxins are produced by other shigella species (not S. dysenteriae)?
ShET1 and ShET2
- Less severe than shiga toxins
What is the virulence factors of Shigella?
Shigella toxins
What is unique about the shiga toxin being ended for on the STx phage?
Can be transferred via horizontal gene transfer and thus can be presents on many types of bacteria)
E. coli O157:H7 is essentially the same as what other organism?
Shigella dysnteriae
How are shigella, E. coli and Salmonella transmitted?
Fecal-oral transmission (primarily from contaminated food/water)
Why is Salmonella rarely spread from person to person?
Because it requires a very high does to be infective
What are shigella and EHEC more common infections vs. salmonella?
Because they only need a low dose to be infectious 9as few as 10 cells) vs salmonella which needs a high dose
Shigella and EHEC can easily be spread person to person via what? (4)
Food handlers
Improperly chlorinated pools
Oral/anal sex
Handashake
How do you DX shigella, salmonella, and e. coli
From stool sample on MacConkey or SS agar
Shigella and salmonella are Lac- or Lac+ ?
Lac-
Is E. coli Lac- or Lac+ ?
Lac+
E. coli and Shigella are H2S+ or H2S- on SS agar?
H2S- (H2S = hydrogen sulfide)
Is salmonella H2S+ or H2S- on SS agar?
H2S+ (H2S = hydrogen sulfide)
Are ABX used in the tx of Shigella, E. coli and/or Salmonella?
NO! May prolong signs of infection by disrupting normal flora –> worse infection
Unless pt is IMC, the you tx w/ ABX based on serotype and resistance status of causative agent
What is the first line tx for Shigella, E. coli and/or Salmonella?
Sx care, mainly hydration
Do you recommend that a pt w/ Shigella, E. coli and/or Salmonella use anti-diarrheal medication?
No. May prolong sx
Why are tx options for Shigella, E. coli and/or Salmonella becoming limited?
High drug resistance
- Some strains of salmonella at resistant to more than 5 drugs, including fluoroquinolines. (this can lead to V. severe form of diarrhea)
What ABX is enterobacteriaceae resistant to?
Carbapenem, 3rd gen cephalosporins
Diarrheal Hemolytic Uremic syndrome (D+ HUS) is damage to the enothelial cells in capillaries by the shiga toxin and/or LPS. What can make this worse?
Inappropriate use of ABX: resistant organism or given more than 4 days after start of diarrhea –> renal dysfunction, thrombocytopenia, anemia
When in doubt about pathogen or onset of sx DON’T get ABX
What are the preventative measures for Shigella, E. coli and/or Salmonella? (6)
- WASH hands!
- Avoid people w/ diarrhea
- cook meat/eggs thoroughly
- Don’t let food left out for more than 2 hrs
- Cut food into small pieces for quicker cooling before storing in refrigerator
- Pay attention to food recalls (human and pet food)
What organism is sensitive to acid so large numbers must be ingested for infection?
Vibrio cholerae
What does vibrio cholerae produce after adherence to epithelial cells of small intestine and establish infection>
Cholera toxin (A-B toxin)
What does high cAMP result in with vibrio cholerae? (4)
Cells secrete Cl- ions, Na and other ions follow, water follows, outpouring from cells
Pt presents with profuse watery diarrhea (rice water stool), vomiting, severe muscle cramps. What are you concerned for?
Vibrio cholerae
Severe dehydration seen with Vibrio cholerae can lead to what?
Organ failure and death
What is the most common source of Vibrio cholerae?
Fecally contaminated water
How is Vibrio cholerae diagnosed?
Culture of stool specimen
What is the primary treatment for Vibrio cholerae?
Oral rehydration therapy
IV fluids/ abx if severe
How is Vibrio cholerae controlled/ prevented?
Sanitation and safe water supplies
2 vaccines but ineffective
C. diff disease ranges widely in severity from diarrhea to what (being life threatening)?
Colitis, pseudomembranous colitis
What is the morphology of C.diff?
G+ obligate anaerobic rod
What does C. diff produce that makes it resistant to disinfectants and environmental conditions?
Endospores (non-replicative)
What do the A and B toxins produced by C. diff result in?
Disrupt host cell actin and cell signaling, cause formation of pseudomembranes
Who is typically infected with C. diff?
Hospitalized pts on abx therapy (opportunistic pathogen, infection when normal microbiota disrupted)
How are infectious endospores of C.diff spread?
Shed in feces
65+ on abx, extended hospital/ nursing home stayes, IMC or previous infection are RFs for what?
C. diff
Why are re-infections post abx therapy common with C.diff?
Endospores
What non-pharmacologic tx is common for C.diff?
Fecal transplant (healthy microbiota outgrows C.diff)
How are C.diff endospores effectively killed?
Autoclave
Campylobacter pathogens are microaerobic and require what to grow?
Special gas concentrations (CO2, N2, O2)
What morphology is indicative of Campylobacter on microscopy?
Spiral rods
What is the most common cause of bacterial gastroenteritis in the US?
Campylobacter jejuni
What are the virulence factors of campaylobacter?
Adhesions and capsule
What size dose is needed to cause a campylobacter infection?
Low infectious dose (500-1000) cells
Campylbacter is acquired by eating what?
Raw chicken
Campylbacter causes diarrhea and severe abdominal pain that is elf limited and will last about 1 wk. Chronic infections can occur in what populations?
IMC, particularly HIV
Campylbacter has an lipopolysaccharide (LOS) that resembles human neuronal ganglosides, this can result in what disease?
Guillain barre syndrome (due to cross-reactive Ab)
How is Campylbacter dx? (2)
- Presents of S shaped organism in stool sample
- commercial Ab kit that looks for campy antigens
(Culture is difficult because Campylbacter requires specific growth conditions)
H. pylori is very similar to what other organism?
Campylbacter
What organism is motile, spiral shaped, produces urease and is oxidase and catalase positive?
H. pylori
How does H. pylori survive in the stomach?
Produces urease which produces a local alkaline environment for the bacteria to survive
What pathogen has lifelong colonization and can lead to gastric ulcers and gastric cancer?
H. pylori
What are the virulence factors of H. pylori?
- Vacuolating cytotoxin (VacA) - initiates inflammatory response
- Cytotoxin-associated gene A (CagA)
What does H. pylori strains that are CagA+ causes?
More severe disease (vs. CagA-) and have higher incidence of gastric cancer
How is H. pylori dx? (3)
- Antigen detection (most common) in stool sample
- Gastric biopsy test for urease
- Histologic examination of gastric biopsy
When and how do you tx H. pylori?
Tx only if symptomatic using multi drug therapy
Why don’t you tx all H. pylori infections (sx or asx)
Treating asx pts can disrupt normal flora resulting in the potential for a C. diff infection
What self-limiting gastroenteritis is due to ingestion of a toxin produced by the pathogen contaminated meat?
Clostridium perfringens
Allowing food to cool below 60˚ C allows for spore germination of what pathogen? How do you kill the enterotoxin?
Clostridium perfringens. Reheat food to 75˚C
What pathogen species is ubiquitous, produced large, dry ,crusty colonies and is used to produce antimicrobial compounds?
Bacillus species
What is shape, gram stain, oxygen requirements, clustering formation, and spore forming status, of Bacillus species?
Gram - rod, aerobic or facultative anaerobe, forms chains and produces spore
What bacillus species causes both emetic and diarrheal gastroenteritis?
Bacillus cereus
Is the emetic disease caused by b. cereus due to a heat stable or heat labile enterotoxin?
Heat stable (not killed by heat)
Is the diarrheal disease caused by b. cereus due to a heat stable or heat labile enterotoxin?
Heat labile (killed by heat)
Causes severe, watery diarrhea
How does the b. cereus enterotoxin that produces the emetic disease become infective?
Ingestion of contaminated rice. (heat does not kill the toxin)
Disease course is <24 hrs, no fever or diarrhea
How does the b. cereus enterotoxin that produces the diarrheal disease become infective?
Ingestion of contaminated vegetables
Disease courses lasts 2-3 days
Do you treat infections caused by b. cereus ?
No. They are self limited.
ABX will make diarrheal disease worse
What is shape, gram stain, motility status, oxygen and temperature requirements of Staphylococcus species?
Gram+ cocci, non-motile, facultative anaerobe. Prefers 30-37˚C, but can grow from 15-40C
What test will distinguish Staphylococcus species from other Gram+ cocci?
Catalase positive (staph is + )
Staph Gastroenteritis has staphylococcal superantigens produce enterotoxins (SEA, SEB… SER) that are resistant to what? (2)
Heat and gastric enzymes
Consumption of deli meat or potato salad can lead to infection w/ what pathogen?
Staphylococcal Gastroenteritis
Onset w/in 4 hrs, severe diarrheal, vomiting, abd pain w/o fever
Infections will cause what sx? Are they usually treated?
Cause fever
Intoxication will not cause a fever. Do you treat with ABX?
No
