GI Bacteria Flashcards

Question

Vibrio cholera Diagnosis

Answer 1

**Fecal specimens** * Culture and isolation on _differential/selective media_ * **TCBS agar** * ID by biochemical reactions and agglutination assays w/ specific antisera * Key characteristics: **gram-****⊖****, comma-shaped rods, oxidase** ⊕**, motile** * All Enterobacteriaceae are oxidase ⊖ ⇒ distinguishing feature of Vibrio

Answer 2

* Natural infection → high degree of **resistance to reinfection by homologous strains** but not to a heterologous strain * **Bactericidal, antitoxin and agglutinating Ab** produced but exact role unclear * Local immunity due to **IgA antibodies** associated w/ immune state * Current vaccines provide some short-term protection

Answer 3

* **Fluid and electrolyte replacement** * Serious cases ⇒ **tetracycline, azithromycin, and ciprofloxacin** * _Current vaccines in development but not commercially available in the US_ * **Oral: heat-killed and genetically attenuated vaccines** * Current vaccines provide some short-term protection * Ongoing work on subunit vaccines, combinations * **Water purification, sanitation, and elimination of carriers**

Answer 4

**Halophilic marine organism** * **Major cause of diarrheal disease** in _Japan_ * **Outbreaks of diarrhea** in the _coastal areas of the USA and on cruise ships_ * Ass. w/ ingestion of **raw or undercooked seafood** * _Clinical disease:_ * Varies from **mild to severe watery diarrhea, N/V, abdominal cramps and fever** * Diarrhea is **occasionally bloody** * Self-limiting, lasts **~3 days**

Answer 5

**Halophilic marine organism** * Common in shellfish _along Gulf of Mexico coast_ * Less common along Atlantic and Pacific * **Severe skin and soft tissue infections** in _shellfish handlers_ * **Rapidly fatal septicemia** in _immunocompromised hosts_ * Chronic liver disease predisposes to severe infection * 50% fatality rate

Answer 6

* **Large, gram-**⊕**, spore-forming rod, obligate anaerobe** * Found in **soil** * Present in the colon of **2-4%** of **normal healthy individuals** * Carriage rate for hospital personnel up to 30%

Answer 7

* Major cause of **antibiotic-associated diarrhea** * Severe inflammation * Occasionally lethal * Almost always ass. w/ intense **antibiotic therapy** ⇒ imbalance in normal intestinal flora ⇒ overgrowth of resistant organisms (endogenous or exogenous) * **Mild, watery or bloody** **diarrhea** w/ abd cramping * May progress to **pseudomembranous colitis** * Pseudomembrane composed of fibrin, leukocytes and necrotic colonic cells * Can result in **perforations**

Answer 8

Two exotoxins (**glucosyltransferases**) ⇒ ⊗ Ras GTPase (Rho, Rac, Cdc42) ⇒ cell death * **Toxin A (TcdA)** ⇒ _enterotoxin_ * Causes **fluid secretion** and **hemorrhagic necrosis** * **Chemotactic** for PMNs, additional release of cytokines * **Toxin B** (**TcdB**) ⇒ _cytotoxin_ * Induces actin depolymerization/condensation ⇒ **disruption of cellular cytoskeleton** * Loss of cell shape, adherence and tight junctions ⇒ **cell rounding** * Subsequent **interference w/ protein synthesis**

Answer 9

* **Detection of toxins in stools** * Toxin B by tissue culture cell cytotoxicity assay * Toxins A and B by ELISA * **Endoscopy** * Culture and isolation (not routine)

Answer 10

* Mild cases ⇒ **discontinue implicated abx therapy** * Severe cases ⇒ **metronidazole or vancomycin** * **15-30% relapse or reinfection rate**

Answer 11

**“Facultative pathogens”** Enterobacteriaceae family ⇒ **Salmonella, Shigella, Yersinia** Vibrionaceae ⇒ **Campylobacter** * Attach to and invade epithelial cells * Can replicate intracellular & extracellularly * Most do not cause disseminated disease * Some exceptions

Answer 12

* **Enterobacteriaceae** family * Facultative intracellular pathogens * **True human pathogen** ⇒ no animal reservoir * 2° attack rates in families up to 40% * ***S. dysenteriae, S. boydii, S. flexneri, S. sonnei*** * 15-20k cases of Shigellosis/yr in US * Developed nations ⇒ ***S. sonnei*** and ***S. flexneri*** most common * **S. sonnei** ⇒ young children and adolescents * **Bacillary dysentery** * Acute diarrheal disease marked by mucous, blood and tenesmus

Answer 13

* **Shiga-toxin** [A-B toxin] * Heat labile, _cytotoxic_ S. dysenteriae _exotoxin_ * **⊗** **Protein synthesis** (chain elongation) by blocking AA-tRNA binding to acceptor site on rRNA * Affects **gut**, **renal endothelial cells**, and **CNS** * Similar to EHEC verotoxin (Shiga-like toxin) * Encoded by **lysogenic bacteriophage** * **Invasion plasmid antigens** * **Type III Secretion System** * Mediate attachment, penetration, escape from phagocytic vesicles, cell-to-cell spread via actin filaments, host cell apoptosis * **Endotoxin**

Answer 14

* Infectious dose: **100 bacteria** * Infection of _small intestine_: 1-4 days * invasion of _large intestine_: 3 to 4 weeks * Invasion and penetration of epithelial cells of mucosa * Penetration into lamina propria * Can invade resident MΦ * ⊕ Cytokine secretion or MΦ apoptosis * **Microabscesses and shallow, crater-like ulcers** * Can cause actin rearrangement ⇒ contiguous spread to adjacent epithelial cells * Invasion into the bloodstream and beyond lamina propria rare

Answer 15

* Sx begin w/ **fever and abdominal cramps** * **Diarrhea** common during _first 2-3 days_ * Afterwards **stools are low volume** * _In severe cases:_ **frequent, mucoid and bloody stools** w/ **tenesmus** (pain and strain on defecation) * Except for *_S. dysenteriae_* infection, **shigellosis** is self-limiting w/ low case fatality rates in untreated cases * Can be acute or chronic * Can be associated w/ sign. morbidity * Usu. tx w/ abx

Answer 16

* Found in developing countries * Produces a potent exotoxin * **Toxic megacolon**, intestinal perforation, hemolytic uremic syndrome, severe metabolic alterations

Answer 17

* Non-specific **methylene blue stain** for fecal leukocytes * Culture and isolation on **differential/selective media** * MacConkey’s agar * Eosin methylene blue agar * Salmonella/Shigella agar * ID by biochemical reactions * _Key characteristics:_ * **Gram-⊖ rod** * **Lactose non-fermenter** * Differentiate from E. coli which is a lactose fermenter * **Urease ⊖** * **H₂S ⊖ and non-motile** at both 25°C and 37°C * Differentiate from Salmonella which are H₂S ⊕ and motile

Answer 18

* _Supportive therapy_: **fluid and electrolyte replacement** * Abx may be given, particularly to young patient to shorten the duration of disease and carrier state * **Ciprofloxacin, ampicillin, tetracycline, trimethoprim-sulfamethoxazole** * **Sanitation and personal hygiene** to interfere w/ fecal-oral transmission

Answer 19

* **Enterobacteriaceae** family * _Historically 3 species recognized_ * ***Salmonella typhi****, **Salmonella choleraesuis, Salmonella enteritidis*** * Numerous named serotypes of *Salmonella enteritidis* * Undergo **antigenic variation** ⇒ mosaics of genes * Recombination, ∆ in length, gene duplications, point mucations * _2 species now recognized based on DNA:_ * ***Salmonella enterica*** (divided into 6 subspecies or serovars, medically relavent group) * ***Salmonella bongori*** * _Recommended nomenclature:_ * Salmonella enterica ser Typhi * Salmonella enterica ser Enteritidis * In practice, _named serotypes/subspecies referred to as species:_ * *S. typhi, S. paratyphi A, S. paratyphi B, S. typhimurium, S. enteritidis*

Answer 20

* **Facultative intracellular pathogens** ⇒ able to survive in phagocytic cells * **Invasins** * Adherence and penetration of intestinal epithelial cells * **Vi (virulence) antigen** * Antiphagocytic _capsular polysaccharide_ of S. typhi * **Endotoxin** * LPS w/ specific O polysaccharide chains that contribute to virulence * **Type III Secretion System**

Answer 21

* 1° enter via **oral route** * Infective dose: **10⁶-10⁸ bacteria** * Initiate infection by **attaching to epithelium of small intestine** * _Three main types of disease in humans:_ 1. **Typhoid fever** * S. typhi, S. paratyphi A, and S. paratyphi B ⇒ **enteric fever** (less severe form) 2. **Enterocolitis** 3. **Bacteremia w/ focal lesions**

Answer 22

Caused by ***Salmonella enteric ser Typhi*** *(S. typhi)* Severest form of the disease Restricted to humans * Organisms acquired by **fecal contamination of water, food or fomites** * Replication starts within **salmonella containing vacuoles (SCV)** * Taken up by MΦ and PMNs * S. typhi penetrates lamina propria → submucosal and serosal layers of intestinal wall → **systemic infection** * _First week:_ * **Lethargy, malaise, fever, aches, pain, constipation** * Multiply in **Peyer's patches** in small intestines * Disseminate to **regional lymph nodes, RES, bloodstream, liver and spleen** * _Second week:_ * **High fever, tender abdomen** and ± **rose spots** on the skin * ± **Diarrhea** * **Seeding of bloodstream** from different foci of infection * _Third week:_ * **Diarrhea**; **bloody stools** may develop * **Infection of biliary system**, **re-infection of intestines** from bloodstream * _Complications_**:** * Generalized infection w/ **metastasis to bone, joints, liver, and meninges** * **Carrier state** may develop w/ _excretion of organisms in feces for long periods_

Answer 23

* Caused most frequently by **S. enteritidis** and **S. typhimurium** * *Salmonella enterica ser Enteritidis, Salmonella enterica ser Typhimurium* * Associated w/ contaminated **poultry or poultry products** * Infects ovaries of healthy appearing hens and contaminate eggs before shells are formed * Enter via **oral route** * Infectious dose: **10⁵-10⁸ bacteria** * Organisms **invade mucosa of small and large intestines** * **Facultative intracellular pathogen** * Remains within a membrane bound vacuole ⇒ **salmonella containing vacuole (SCV)** * Bloodstream invasion is rare * **Nausea, vomiting and diarrhea** occur _8-48 hrs_ after ingestion * ± **Fever** and other constitutional sx * Organisms may be **isolated from stools** * ⊕ Fecal leukocytes, not usually bloody * **Self-limiting,** sx last ~**1-4 days** * Not usually treated * Similar presentation to Enteroinvasive E. coli (EIEC)

Answer 24

* 5-10% of Salmonella infections * Associated w/ *S. choleraesuis* (**Salmonella enterica ser Cholerasuis)** but may involve any NTS serotype * Oral ingestion → **early invasion of the bloodstream** * **Osteomyelitis**, **PNA, and meningitis** most common manifestations * **Sickle cell patients** at ↑ risk * Intestinal symptoms _often absent_ * **Blood cultures ⊕**

Answer 25

* _Specimens:_ * **Enterocolitis** * Stool * **Typhoid fever** * Blood (1^st and 2^nd weeks) * Stool (2^nd and 3^rd weeks) * Urine (4^th week) * Bone marrow cultures may be useful in certain circumstances * Culture and isolation on **differential/selective media** * ID by **biochemical reactions** and **agglutination tests** w/ specific sera * _Key characteristics:_ * **Gram-⊖ rod** * **Lactose non-fermenter** * **H₂S ⊕, motile** * Differentiates from Shigella which is H₂S ⊖, non-motile * **Widal test** * Agglutination test for **anti-Salmonella Ab** in serum * Paired serum samples must demonstrate rise in titer

Answer 26

* **Enterocolitis** * _Tx_: **supportive therapy**, fluid and electrolyte replacement * _Prevention_: adequate sanitation, immunization of domestic livestock and the proper cooking of poultry products and meat * **Typhoid fever** * _Tx_: **chloramphenicol, ampicillin or trimethoprim-sulfamethoxazole** * Replapses problematic * Chronic carrier rates high * _Prevention_: proper sanitation and personal hygiene * **S. typhi killed and attenuated vaccines** available but protection limited * Used as traveler’s vaccines * Boosters required * Potential for vaccination of hens vs non-typhi Salmonella

Answer 27

* **Causes 5-10% of all infectious diarrheas** * _Bimodal peak incidence:_ * **Infants \< 1 y/o** * Adolescents and young adults (**15-29 y/o**) * Found in **GI tract of wild and domestic animals** * Abx resistant infectious ass. w/ abx used in raising cattle, restricted by FDA * Transmitted by **contaminated food/drink** and **contact w/ infected animals** * Causes **chronic diarrhea** in up to _20% of HIV pts_ * Two other species: ***C. fetus*** and ***C. intestinalis*** implicated as a rare cause of **systemic infections** in _immunocompromised hosts_

Answer 28

* _Infectious dose:_ **several hundred bacteria** * _Incubation period_: **2-6 days** * **Enterocolitis** * Begins as **watery, foul smelling diarrhea** * Followed by **bloody stools**, **fever and abdominal pain** * **Locally invasive** ⇒ ⊕ for fecal leukocytes * No known enterotoxins or exotoxins * **Self-limiting** after **5-8 days** but sometimes continues for longer * Not usu. tx w/ abx unless severe or prolonged disease

Answer 29

* **Guillain-Barré Syndrome** * Autoimmune **acute demyelinating neuropathy** * Symmetical weakness over several days w/ recovery over weeks to months * Frequently _preceded by infection_ * CMV, Coxsackievirus, echovirus, Flu A, Zika virus, and Camplylobacter * **~40% of pts have culture or serologic e/o Camplyobacter infection** @ onset of neurologic sx * MOA: Ab vs _C. jejuni LPS core oligosaccharide_ **cross-react w/** _gangliosides of peripheral nerves_ * Molecular mimicry, type II hypersensitivity

Answer 30

* **Short, curved, gram-⊖ rods** * **Microaerophilic** (5-10% O₂) * **Grows at 42°C** on special media * Extended culture period (3-4 days, up to 1 wk) * **Oxidase ⊕** * All Enterobacteriaceae are oxidase ⊖ * Vibrio cholera oxidase ⊕ but have more episodes of diarrhea

Answer 31

_Three species of medical importance:_ * **Yersinia pestis** * Bubonic plague * ***Yersinia enterocolitica*** and ***Yersinia pseudotuberculosis*** * GI infections * Typhoid fever-like syndromes

Answer 32

***Yersinia enterocolitica*** and ***Yersinia pseudotuberculosis*** * **Enterobacteriaceae** family ⇒ **gram ⊖ rods** * Found in a wide variety of **wild and domestic animals** * Transmission by **contaminated water, food, and milk** or by **entry via skin break** * *Y. enterocolitica* affects **mostly children**

Answer 33

***Y. enterocolitica*** and ***Y. pseudotuberculosis*** * Initial infection of the **ileum** * **Gastroenteritis** (more typical infection) * **Fever, abd pain and diarrhea** * Clinically indistinguishable from Shigella or Salmonella gastroenteritis * **Enterotoxin** similar to _ST toxin_ of E. coli * May be responsible for fluid loss * Usually **self-limiting** * **I****nvasive infection** (less common) * **Mucosal destruction, enlargement of regional mesenteric lymph nodes,** **±** **ulceration** * _Complications:_ * **Extraintestinal infection of liver, joints** * **Generalized septicemia**

Answer 34

* _Diagnosis:_ * Definitive dx by isolation of Yersinia from **stool cultures** * ID by **biochemical tests** * Can grow at **4****°C** * _Treatment:_ * Y. enterocolitica usually self-limiting ⇒ **supportive tx** * Disease caused by either species ⇒ Tetracycline, ampicillin, cephalosporins or chloramphenicol

Answer 35

* **Gram-⊕ cocci** in **grape-like clusters** * _3 species of Staphylococcus of clinical importance:_ * **S. epidermidis** * Most commonly associated w/ infections related to cardiovascular and orthopedic prostheses, CSF shunts, vascular grafts and catheters * **S. saprophyticus** * Cause 10-20% of urinary tract infections in young, sexually active women * **S. aureus** * Normal flora of skin and nares in ~30-40% * May cause disease in nearly any tissue * _Staphylococcal disease divided into 3 general groups:_ 1. **Skin infections** 2. **Infections of hard and soft tissue** 3. **Toxic syndromes** * _Virulence factors varied and include:_ * **Surface antigens** (protein A) * **Extracellular enzymes** (coagulase, lipases, staphylokinase) * **Exotoxins** (enterotoxins, exfoliatin, TSST-1)

Answer 36

* **Gram-⊕ Cocci in Grape-Like Clusters** * **Catalase ⊕** * Differentiates staph (catalase ⊕) from strep (catalase ⊖) * **Coagulase ⊕** * Differentiates S. aureus (coagulase ⊕) from all other staph (coagulase ⊖) * Routinely cultured on blood agar plates * **Beta-hemolytic, yellow or golden colonies**

Answer 37

**Enterotoxins** * **18 serologically distinct types of enterotoxin (A-R)** * **A-D** associated w/ food poisoning * Heat stable and can resist boiling * Resistant to gastric enzymes and acidity * **Cytokine release, PMN infiltration, mast cell degranulation** * **Loss of brush border** * **⊕** **Intestinal peristalsis and diarrhea** * **⊕** **Vomit reflex** by interacting w/ neural receptors in upper GI tract * **±** **Superantigen activity** similar to Staph TSST-1 ⇒ excessive cytokine release

Answer 38

* Fairly common food borne illness * Caused by **ingestion of enterotoxin produced by S. aureus** * Enterotoxins produced by ~ ½ of all coagulase ⊕ S. aureus strains * Ham, processed foods, chicken salad, cottage cheese, etc. * Sx onset within **1-6 hours** s/p ingestion * **Nausea, abdominal cramps, vomiting, watery and non-bloody diarrhea, profuse sweating, headache** * Self-limiting, **recovery within 24-48 hours** * _Treatment:_ **fluid replacement; abx not indicated**

Answer 39

_2 medically important species in the genus Bacillus:_ * ***Bacillus anthracis*** ⇒ anthrax (1° a disease of sheep and cattle) * Man acquires disease accidentally, usu. in an agricultural or industrial setting * ***Bacillus cereus*** ⇒ food poisoning in man

Answer 40

* **Aerobic, large gram-⊕ rods** * **Spore-formers (endospores)** * Resistant to adverse chemical and physical environmental changes, withstand dry heat and certain disinfectants * Survive on **grain foods** (ex. rice) and in **some meat dishes** * Spores germinate when food is kept warm * *B. cereus* produces a **heat-stable** and a **heat-labile** **enterotoxin**

Answer 41

* _Resembles staph food poisoning_ * Short incubation period (**~ 4 hrs**) * **Nausea, vomiting, abdominal cramps and occasional diarrhea** * Mediated by a **heat-stable enterotoxin** * **Contaminated rice and grain dishes** * Usually self-limitin

Answer 42

* _Resembles clostridial gastroenteritis_ * Incubation longer, **up to 24 hrs** * Colonization of GI tract * **Profuse diarrhea, abd pain and cramps** * Mediated by **heat-labile enterotoxin** ⇒ ↑ cAMP production * Similar to E. coli and Vibrio cholera * **Contaminated meat, vegetables and gravy/sauces** * Generally self-limiting * Symptomatic treatment

Answer 43

**Anaerobic, gram-⊕, spore-forming rods** _Most commonly associated w/ human diseases:_ * **C. tetani:** causative agent of tetanus * **C. botulinum**: food-borne botulism, infant botulism, wound botulism * **C. perfringens**: myonecrosis, gas gangrene, anaerobic cellulitis, food poisoning * **C. difficile**: abx-associated diarrhea, pseudomembranous enterocolitis

Answer 44

* **Gram-⊕, spore-forming rod** * **Obligate anaerobe** * Found in **soil, pond and lake sediments** * Germination of spores and growth of vegetative form occur in **alkaline foodstuffs** (usually home canned) _when conditions are anaerobic_ * Also found in **Alaska** following **ingestion of home preserved fish**

Answer 45

**Neurotoxic exotoxin (botulinum)** _⊗_ _Release of ACh_ @ peripheral synapses ⇒ **flaccid paralysis** 8 antigenically distinct subtypes **(A-G)** of botulinum toxin [A-B toxin]

Answer 46

* **Ingestion of preformed toxin** in _home canned alkaline vegetables_ (string beans, mushrooms) * Not cooked enough to inactivate the toxin * Acidic foods do not support growth of C. botulinum * **Incubation 12-36 hrs** * **Nausea, vomiting, diarrhea or constipation** followed by **descending paralysis** * Ocular, pharyngeal, and respiratory muscles involvement → extensive voluntary muscle involvement * Mortality rate 60% untreated, 10% w/ treatment

Answer 47

* Occasionally organism can **multiply in wounds** * Same clinical picture food-borne **w/o GI sx** * **Incubation 4-14 days**

Answer 48

* **Most common form of botulism in the US** * Some ass. w/ feeding infants **honey containing C. botulinum spores** * In many cases, spores from **unknown environmental sources** * Incubation **3-30 days** * Organism grow in GI tract * _Produce toxins_ absorbed through intestinal wall into circulation * Babies w/ **constipation, weakness and flaccid paralysis** (**floppy infant syndrome**) * **Infants 1-8 months of age**, prior to establishment of normal GI flora

Answer 49

* **Clinical dx** (disease usually an **intoxication**) * **Serum and stool samples** from all suspected cases * Stool cultured anaerobically for organism * Toxin may be identified in serum * **Samples from suspected contaminated foodstuffs** * Test for both organisms and toxin

Answer 50

* Supportive care: **nutritional and respiratory** * _Assisted respiration_ most important determinant of outcome * **Penicillin is abx of choice**, only if organisms present * Abx not recommended for infant botulism b/c autolysis of organisms ⇒ ↑ [toxin] * **Equine antitoxins** * Trivalent (A, B, and E) and heptavalent (A-G) * For **food-borne and wound botulism** * Hypersensitivity rxn in 20% * Not recommended in infant botulism * **BabyBIG^®, Botulism Immune Globulin IV (BIG-IV)** * Human-derived botulism antitoxin Ab for tx of infant botulism types A and B

Answer 51

* Education to improve home canning methods, but cases are also restaurant acquired * All canned food should be **cooked at 100°C for 10 min** to inactivate toxin * **Bulging food containers** may contain gas produced by C. botulinum and should be discarded * **honey should not be given to children under 12 months of age**; however most cases of infant botulism are caused by unidentified sources * Anti-toxin is not recommended prophylactically in cases of suspected exposure

Answer 52

Notable cause of **myonecrosis** and **gas gangrene** in contaminated wounds **_Food poisoning_** * Ingestion of **meat dishes (stew, soup, gravy) contaminated w/ spores** of C. perfringens * Spores germinate in GI tract * Organisms **colonize ileum and large intestine** * Production of **heat-labile enterotoxin** * Onset of sx **within 18 hours** of ingestion * **Watery diarrhea w/ abd cramps and little vomiting** * Usually self-limiting * Supportive treatment

GI Bacteria Flashcards

(76 cards)