S1B5 - Enterobacteriaceae Flashcards
What does infection from Proteus spp. usually cause?
Proteus spp. are responsible for nosocomial urinary tract infections (UTIs), such as pyelonephritis, and can lead to sepsis.
What organism is the most common cause of urinary tract infections in women?
E. coli is the most common cause of urinary tract infections in women.
Why are the other species of Shigella (not. S. dysenteriae) not as virulent?
Other species include S. flexneri, S. boydii (India), and S. sonnei, which have decreased virulence because of the lack of toxin production.
What is another bacterial species that can lead to hemolytic-uremic syndrome besides E. coli?
Some strains of S. dysenteriae produce a Shiga toxin that can lead to Hemolytic-Uremic Syndrome (HUS).
What method is used to diagnose Escherichia coli infection?
Diagnosis of E. Coli is made by stool culture on blood agar plate and differential media.
MacConkey’s agar is a differential media on which E. Coli grows pink colonies because it ferments lactose.
Eosin methylene blue (EMB) agar is a differential media on which E. Coli appears to have a dark metallic green sheen because it ferments lactose. Salmonella and Shigella do not ferment lactose and are colorless on EMB agar.
Urinalysis, urine culture, and urine microscopy are used to diagnose urinary tract infection.
Is S. dysenteriae motile or non-motile?
S. dysenteriae is non-motile (vs. motile Salmonella), however note that S. dysenteriae polymerizes actin to travel from enterocyte to enterocyte.
What is the morphology, gram staining, urease positive/negative and oxygen requirement of Klebsiella pneumoniae?
Klebsiella pneumoniae is an encapsulated, urease-positive, gram-negative, facultative anaerobic bacillus.
How is secondary pneumonic plague acquired?
Secondary pneumonic plague is a complication of Y. pestis infection, acquired by hematogenous spread of Y. pestis from a bubo to the lungs.
Serologic testing in Yersinia pestis infection might find elevated antibody titers to what Y. pestis antigen?
Serological testing may demonstrate a rise in antibody titers to the F-1 antigen of Y. pestis. Rapid antibody tests are available in endemic areas.
How will Yersinia pestis infection appear with Wayson staining?
Wayson stain demonstrates a typical “safety pin” appearance (bipolar staining).
What lung findings would you find on physical exam and lab testing in Klebsiella pneumoniae pneumonia?
Physical exam and laboratory testing of K. pneumoniae pneumonia are consistent with single lung consolidation, known as lobar pneumonia in cases of community-acquired pneumonia. Patients may also present with a patchy or diffuse infiltrate, known as bronchopneumonia in cases of nosocomial pneumonia.
A 29-year-old woman presents with diarrhea several hours after eating a chicken sandwich that she thinks may have been undercooked. Which of the following suggests Salmonella gastroenteritis?
A) Gram negative rods producing Shiga-like toxin
B) Comma-shaped organisms expressing oxidase
C) Gram negative lactose fermenters that produce hydrogen sulfide
D) Gram negative, motile, lactose nonfermenters
E) Gram positive obligate anaerobes
Gram negative, motile, lactose nonfermenters
Answer Explanation
Salmonella are gram-negative, lactose nonfermenters who produce hydrogen sulfide (H2S) and possess flagellar motility.
Comma-shaped organisms causing diarrhea that produce oxidase are suggestive of either Vibrio spp. or Campylobacter spp. GNR producing Shiga-like toxin is enterohemorrhagic E. coli (O157:H7). Gram-positive obligate anaerobes that cause diarrhea are C. difficile.
How would Klebsiella pneumoniae appear on MacConkey’s agar?
K. pneumoniae is lactose-fermenting, growing pink colonies on MacConkey’s agar. It is a non-motile enteric like Shigella. Lactose-fermenting enterics (“KEE”) include Klebsiella, E. coli, and Enterobacter, while enteric non-lactose fermenters (“SSP”) include Salmonella, Shigella, and Proteus.
What is the morphology, gram staining, lactose fermenting/non-fermenting, and oxygen requirement of Escherichia coli?
Escherichia coli is a lactose fermenting, gram-negative, facultative anaerobic bacillus.
How does the disease caused by Salmonella paratyphi differ from the disease caused by Salmonella typhi?
Salmonella paratyphi causes paratyphoid fever, and like typhoid fever it is also referred to as enteric fever. The course of paratyphoid fever resembles typhoid fever, but presents with a more abrupt onset, milder symptoms, and a shorter course.
What distinguishes Uropathogenic E. Coli (UPEC) from other serotypes of E. Coli? .
Uropathogenic E. Coli (UPEC) adheres with type I fimbriae and P pili, contains hemolysin and other toxins, and is the major cause of urinary tract infections (UTIs).
What diseases does Klebsiella pneumoniae cause?
K. pneumoniae causes
- Nosocomial and community-acquired pneumonia
- Nosocomial urinary tract infections
- Liver abscesses
What are some of the characteristics of Yersinia pestis - Morphology? - Gram-stain? - Motile/non-motile? - Sporulating/nonsporulating? - Intracellular/extracellular?
Yersinia pestis is a nonmotile, pleomorphic, nonsporulating, facultative intracellular, gram-negative bipolar staining bacillus (coccobacillus) that belongs to the Enterobacteriaceae family.
Describe the pathogenesis behind the formation of staghorn calculi in Proteus spp. urinary tract infection.
The urease that Proteus spp. possesses functions to split urea in the urinary tract to form ammonium hydroxide, ultimately resulting in an increased pH. The increase in pH precipitates ammonium magnesium phosphate, leading to struvite calculi that often form large staghorn calculi.
Does S. dysenteriae produce H2S?
S. dysenteriae does not produce H2S (vs. Salmonella, which produces H2S).
What type of diarrhea does S. dysenteriae cause? What are the initial manifestations?
Patients present early with non-bloody, voluminous diarrhea caused by enterotoxin in the small intestine. Dysentery occurs within hours to days and involves frequent, small, bloody, mucoid stools with abdominal cramps and tenesmus.
What distinguishes Enteroaggregative E. coli (EAEC) from other serotypes of E. Coli (toxins and GI symptoms)?
Enteroaggregative E. Coli (EAEC) uses aggregative adherence fimbriae (AAF) to make a biofilm of bacterial clusters on the intestinal wall. It causes diarrhea with mucus.
summarize this picmonic
What groups of individuals have a higher susceptibility to Salmonella infection?
Sufficiently large amounts of bacteria are needed to cause Salmonella infection (high ID50), since many bacteria are destroyed in the stomach upon ingestion. For this reason, individuals that are at high risk of infection include
- Individuals with impaired gastric acid secretion (bypassing destruction of bacteria by gastric acid)
- Individuals with sickle-cell due to autosplenectomy
- Young children
- The elderly
- Immunosuppressed individuals
What disease does Salmonella enteritidis cause?
Salmonella enteritidis causes gastroenteritis.
What are the three different forms of plague?
Y. pestis causes three different forms of plague:
- Bubonic plague
- Septicemic plague
- Pneumonic plague
What is the virulence factor in Yersinia pestis that functions to prevent phagocytosis and acts to generate the antibody response?
Y. pestis produces a capsular F1 antigen that functions to prevent phagocytosis and generate the antibody response.
What toxin does S. dysenteriae produce? What is the mechanism of this toxin? What is the organism that produces a similar toxin?
S. dysenteriae produces Shiga toxin, which inactivates 60S ribosomes. This is similar to the Shiga-like toxins produced by EHEC.
What is the morphology, gram staining, lactose fermentation ability, and presence of oxidase in Shigella dysenteriae?
Shigella dysenteriae is a non-lactose fermenting, oxidase negative, gram-negative bacillus.
How is enterohemorrhagic Escherichia Coli (EHEC) infection usually acquired?
EHEC is contracted by consuming beef or foods contaminated with cow feces.
What is the clinical presentation of bubonic plague caused by Yersinia pestis?
Bubonic plague presents with sudden onset of fever, chills, weakness, and headache, followed by intense pain and swelling in lymph nodes, usually in a region draining from the inoculation site. These swollen lymph nodes are called buboes. Some patients may have eschars, pustules, or necrotic lesions after being bitten by an infected flea.
An intubated patient develops ventilator-associated pneumonia. The gram stain of a sputum sample reveals a gram-negative encapsulated rod. What is the most likely organism?
A) Streptococcus pneumoniae
B) Klebsiella sp.
C) Staphylococcus aureus
D) E. coli
E) Pneumocystis jiroveci
Klebsiella spp.
Answer Explanation
All of the answer choices potentially cause pneumonia, especially nosocomial pneumonia. The gram stain reveals gram-negative rods. Thus, strep and staph can immediately be eliminated as answer choices, as well as pneumocystis, which is a yeast. Strep forms chains and staph forms clusters.
E. coli are also gram-negative rods, but lack the prominent polysaccharide capsule. Strep pneumo is a gram positive diplococcus, typically described as appearing “lancet shaped”. S. aureus is gram-positive cocci. Pneumocystis jiroveci (formerly known as P. carinii) is a yeast and is best visualized using a silver stain.
Where is Klebsiella pneumoniae naturally found in the human body?
K. pneumoniae is part of the intestinal flora.
A stool sample from a patient suffering from gastroenteritis is plated on Hektoen enteric agar, and the next day black colonies appear. What is the causative organism, and what does the black colonies signify?
Salmonella spp. produce hydrogen sulfide, which appears as black colonies when plated on Hektoen enteric agar.
What are the symptoms of Salmonella enteritidis related gastroenteritis?
Individuals infected with S. enteritidis present with
- Nausea
- Vomiting
- Fever
- Inflammatory diarrhea
- Cramping
How is Escherichia coli transmitted?
Escherichia coli that is virulent is transmitted by a fecal-oral route, and often is commonly associated with “traveler’s diarrhea.”
Who is at risk for Klebsiella pneumoniae infection?
K. pneumoniae pneumonia occurs more commonly in people in long-term healthcare settings (hospital, nursing homes), and in people with impaired immune defenses, especially diabetics and alcoholics (particularly via aspiration). K. pneumoniae is uncommon in otherwise healthy people.
What is the most common cause of urinary tract infections (UTIs) and resulting sepsis in a hospital setting? What measure can be taken to help prevent this from happening?
E. Coli (MOST COMMON) UTI and sepsis can be prevented by prompt removal and switching of urinary Foley catheters. Other pathogens include Pseudomonas, Proteus, Providencia, Enterobacteriaceae, Morganella and Enterococci.
What behaviors increase the risk of Escherichia coli gastrointestinal infection?
Consuming uncooked foods and unfiltered water increases the risk of acquiring gastrointestinal E. Coli infection. E. coli can survive in water and on surfaces of foods
How are Escherichia Coli urinary tract infection diagnosed?
Urinalysis, urine culture, and urine microscopy are used to diagnose urinary tract infection.
Compare the following characteristics of Salmonella and Shigella: - Flagella - Hydrogen sulfide production - Infective Dose (large/small)
It is important to know the differences between Salmonella and Shigella
Flagella
- Salmonella - yes
- Shigella - no
H2S production
- Salmonella - yes
- Shigella - no
Infective dose
- Salmonella - Large
- Shigella - Small
How is Salmonella transmitted?
Transmission of Salmonella occurs via a fecal-oral route from food that contains traces of animal feces that contain the causative organism.
What distinguishes Enterotoxigenic E. Coli (ETEC) from other serotypes of E. Coli in terms of secreted toxin?
Enterotoxigenic E. Coli (ETEC) uses fimbriae to attach to epithelial cells and secretes cells with heat labile toxin (LT), related to cholera toxin, and heat stable toxin (ST). ETEC is the most common cause of watery traveler’s diarrhea (think ETEC for Travelers).
To establish an infection with Shigella, a patient needs to be inoculated with how many organisms? Is Shigella acid-labile or acid-resistant?
S. dysenteriae is transmitted via a fecal-oral route and is acid-resistant, and only a small inoculum (10-100 organisms) is needed can overcome gastric acid defense.
How is primary pneumonic plague, Yersinia pestis, acquired?
Pneumonic plague can be primary or secondary. Primary pneumonic plague is rapidly fatal and is acquired by inhaling aerosolized droplets. Primary pneumonic plague presents with sudden onset of dyspnea, fever, pleuritic chest pain, and cough, sometimes with bloody sputum.
Describe the location and process by which Shigella causes infection.
Shigella invades the distal ileum and colon through specialized epithelial cells (M cells) that overlie mucosal lymphoid follicles. S. dysenteriae then replicates intracellularly and spreads cell-to-cell and release Shiga toxin.
What is the Weil-Felix test?
The Weil-Felix test is an old diagnostic test that uses Proteus vulgaris antigens to diagnose Rickettsia. The Proteus antigens cross-react with a patient’s serum antibodies against Rickettsia.
An alcoholic is brought in by ambulance. On arrival he is febrile and disoriented, with a blood alcohol level of 0.33. While undergoing detoxification, he coughs up thick, bloody sputum. What is the likely organism?
A) Pseudomonas aeruginosa
B) Klebsiella
C) Chlamydophila pneumoniae
D) Streptococcus pneumoniae
E) Mycoplasma pneumoniae
lebsiella
Answer Explanation
An alcoholic with bloody, commonly described as “red currant jelly,” sputum suggests Klebsiella pneumonia. Klebsiella is a common cause of pulmonary infection, in particular with alcoholics.
The other choices are causes of pneumonia, but are not as likely in this clinical scenario. Mycoplasma pneumonia causes an atypical, interstitial pneumonia with a non-productive cough most commonly in younger age groups.
Pseudomonas is more likely to cause lung infection in patients that are mechanically ventilated or that have cystic fibrosis.
Streptococcus pneumoniae can cause pneumonia, but the sputum is more likely to be a “rusty-brown” color.
Chlamydophila pneumoniae can cause pneumonia similar to the presentation of Mycoplasma, however has a higher incidence in elderly adults.
What regions of the genitourinary tract does Klebsiella pneumoniae affect?
K. pneumoniae urinary tract infection (UTI) is uncommon compared to other bacterial UTIs, but it is particularly associated with use of urinary catheters. K. pneumoniae can cause upper or lower urinary tract inflammation such as
- Cystitis
- Pyelonephritis
- Renal abscesses
What proteins are injected by Yersinia pestis through its type III secretion system. What is the function of these proteins?
Y. pestis also contains a type III secretion system, allowing the organism to inject Yersinia outer proteins (Yops) that aid in inhibiting phagocytosis and cell signaling.
How is Yersinia pestis infection treated?
Treatment for plague includes streptomycin or gentamicin. Doxycycline and tetracycline are alternative treatments for patients who cannot tolerate aminoglycosides.
How is the spread of Yersinia pestis pneumonic plague prevented in healthcare settings?
In order to prevent the spread of respiratory infection, patients suspected of having Yersinia pestis infection are placed on droplet precautions until pneumonic plague has been ruled out.
Chest x-ray of patients with Klebsiella pneumoniae pneumonia may mimic what other pulmonary process?
Chest x-ray of K. pneumoniae pneumonia usually demonstrates right upper lobe inflammation and cavitation, which can be confused with active secondary pulmonary tuberculosis.
Why are sickle cell patients more susceptible to Salmonella typhi related osteomyelitis?
Sickle cell patients are functionally asplenic and have trouble clearing the Vi-encapsulated S. typhi, predisposing them to Salmonella osteomyelitis.
How is Klebsiella pneumoniae transmitted?
K. pneumoniae is transmitted via direct person-to-person contact (fecal-oral, fomites, and aspiration). Nosocomial infection is spread by healthcare workers or contamination of objects in the environment, such as catheters and ventilators.
How does Escherichia Coli appear when grown on MacConkey’s agar?
MacConkey’s agar is a differential media on which E. Coli grows pink colonies because it ferments lactose.
summarize this picmonic
What are some diagnostic tests that can be used for a suspected Proteus spp. infection?
Diagnosis can be made by
- Swarming motility and inability to metabolize lactose (on MacConkey) on agar
- Urease test positive
- Alkaline urine
Where are most cases of Yersinia pestis in the United States found?
The majority of human cases of Y. pestis infection in the United States have occurred in Southwestern states and the Pacific coast (Arizona, California, Colorado, New Mexico, and Texas).
How is Yersinia pestis infection diagnosed?
Diagnosis is made via culture, Gram staining, and Wright-Giemsa staining of sputum, cerebrospinal fluid, bubo aspirate material, or blood.
What are the treatment options for S. dysenteriae infections?
Treatment for S. dysenteriae should initially include fluoroquinolones. Other antibiotics that can be used include azithromycin and trimethoprim-sulfamethoxazole.
What are possible treatment options for a Proteus spp. related uncomplicated cystitis?
Treatment for Proteus spp. related uncomplicated UTI infection (cystitis) can include trimethoprim-sulfamethoxazole or a fluoroquinolone.
What are the three ways by which Yersinia pestis can be transmitted to humans?
Y. pestis can be transmitted:
- Flea bite (flea carries Y. pestis from infected animal to human host)
- Respiratory droplets from infected host
- Direct contact with infected tissue or fluid from human or animal host
What is the morphology, gram staining, anaerobe/aerobe, motile/non-motile and oxidase positive/negative, lactose fermenter/non-fermenter of Salmonella spp.?
Salmonella is a genus of motile, facultative anaerobic, oxidase-negative, lactose non-fermenting, gram-negative bacilli.
How are E. Coli infections treated for: - Diarrhea? - UTI? - Meningitis? - Sepsis?
Prognosis is favorable.
- Treatment is rehydration for diarrhea;
- trimethoprim-sulfamethoxazole or oral penicillin for UTI;
- third-generation cephalosporin (ceftriaxone) for meningitis and sepsis.
What distinguishes enteropathogenic Escherichia Coli (EPEC) from other types of E. Coli?
Enteropathogenic E. Coli (EPEC) produces no toxin and adheres to intestinal epithelium using bundle forming pili and destroys microvilli, leading to malabsorption. EPEC usually presents as diarrhea in children (think EPEC for Pediatrics).
An 18-year-old male presents with a fever to 103.1F, chills, muscle aches, and abdominal pain. On examination he is diaphoretic, has a readily palpable spleen, a liver edge 3 cm beneath his right costal margin, and a few salmon-colored spots on his trunk. He reports having had mild diarrhea 4 days prior to onset of these new symptoms. What is the likely infectious agent?
A) Paragonimus westermani
B) Vibrio cholerae
C) Clonorchis sinesis
D) Salmonella typhi
E) Salmonella enteriditis
Salmonella typhi
Answer Explanation
The history of recent, mild diarrhea (prodrome) followed by abdominal pain and high fevers strongly suggests typhoid fever, which is caused by Salmonella typhi. The finding of hepatosplenomegaly and rose spots further clinches the diagnosis.
S. enteritidis causes normal salmonellosis, without abdominal pain, rose spots, and hepatosplenomegaly. P. westermani is the Oriental lung fluke whose primary S/Sx include hemoptysis and cough. Clonorchis sinensis is a liver fluke that can cause pigmented gallstones, cholangiocarcinoma, and hepatomegaly but has a more chronic time course. V. cholerae causes cholera marked by large volume, watery diarrhea.
What is the morphology, gram staining, oxidase positive/negative, urease positive/negative, and lactose fermenter/non-fermenter of Proteus spp.?
Proteus spp. (most notably Proteus mirabilis) is genus of oxidase-negative, lactose non-fermenting, urease-positive, gram-negative bacilli.
What can be found in stool samples of patients infected with S. dysenteriae?
Fecal leukocytes present in stool (as in Salmonella and C. difficile diarrhea).
What do H antigen, K antigen, and O antigen represent in regards to Escherichia coli?
E. Coli is divided into serotypes based on their
- H antigen (flagella)
- K antigen (capsule)
- O antigen (polysaccharide component LPS endotoxin)
What antibiotic is used for prophylactic treatment for people who may have been exposed to Yersinia pestis?
Post exposure prophylaxis includes doxycycline or tetracycline, and is administered to individuals with close contact to individuals with untreated Yersinia pestis.
What are the normal reservoirs for S. dysentariae?
Humans are the only carriers.
What are the treatment options for typhoid fever?
Treatment of typhoid fever includes ciprofloxacin for uncomplicated illness or azithromycin for suspected quinolone-resistance.
Which strain of Escherichia Coli proliferates in enterocytes and destroys the epithelium?
Enteroinvasive E. Coli (EIEC) uses a Type III secretion system to invade enterocytes, proliferate, and destroy the epithelium. It causes watery or bloody diarrhea, but milder than EHEC.
What property of Salmonella typhi allows survival within phagocytes?
The capsular Vi polysaccharide of Salmonella allows survival in phagocytes of Peyer’s patches.
What other infections can Klebsiella pneumoniae cause besides urinary tract infections and pneumonia?
Other clinical K. pneumoniae infections include pyogenic liver abscess and both superficial and deep-skin and soft-tissue infections.
What are two complications of Yersinia pestis?
Two complications of Y. pestis infection includes meningitis or disseminated intravascular coagulation.
What are the reservoirs for Salmonella typhi and what risk factors put individuals at high risk for transmission?
S. typhi survives only in humans. Because humans are the only reservoir, individuals with history of travel to settings where sanitation is poor are at high risk.
What is the treatment for Klebsiella pneumoniae infection?
The antibiotic regimen for Klebsiella is highly dependent on susceptibility testing. The typical first-line treatment is a first or second generation cephalosporins for non-drug-resistant Klebsiella pneumoniae.
What can some strains of Klebsiella pneumoniae produce to confer antibiotic resistance?
Some emerging strains produce extended spectrum beta-lactamases and carbapenemases that make them resistant to all cephalosporin generations and carbapenems.
What are three treatment options for a Proteus related uncomplicated pyelonephritis?
Treatment for Proteus spp. related acute uncomplicated pyelonephritis can include
- Fluoroquinolones
- Gentamicin with ampicillin
- Ceftriaxone
Where are Proteus spp. normally found in the body? How does infection commonly occur?
Proteus spp. are part of the human intestinal flora and can cause infection upon leaving this location, a common example is via a contaminated catheter into the urinary tract.
What diagnostic tests can be performed and what positive tests show for a suspected Klebsiella pneumoniae infection?
Diagnosis is made by
- Gram stain showing gram-negative organisms
- Microscopy of fluid sample from the infection site (sputum, blood, urine, peritoneal fluid)
- MacConkey agar (differential media for lactose-fermenting)
- Positive Quellung reaction
What disease does Salmonella typhi cause?
Salmonella typhi causes typhoid fever (enteric fever).
During a Salmonella infection, what are the results of the following tests: Urease, indole, lactose fermentation, H2S production?
Diagnosis of Salmonella infection is made by culture in the setting of a compatible clinical illness. Diagnostic test results for Salmonella include the following:
- Urease negative
- Indole negative
- Lactose fermentation negative
- H2S production positive
What diagnostic study distinguishes EHEC from other serotypes of E. Coli? What other disease processes is associated with EHEC?
Enterohemorrhagic E. Coli (EHEC) also known as STEC (Shiga-like producing E. coli), produces Shiga-like toxin (SLT) that kills enterocytes. SLT is functionally similar to Shiga toxin, and both act to inactivate the 60S ribosome. O157:H7 is the most common serotype in the United States and can cause hemolytic uremic syndrome (HUS), a triad of
- Anemia
- Thrombocytopenia
- Acute renal failure
EHEC presents with dysentery from inflammation caused by Shiga-like toxin. EHEC does not ferment sorbitol, which distinguishes it from other E. coli.
Describe the carrier state in Salmonella typhi infection.
Individuals infected with S. typhi may enter a carrier state where organisms are stored in the gallbladder, especially in gallstones. Organisms may reenter the bowel lumen, facilitating further spread via feces (in the early 1900s, Typhoid Mary was a cook who was jailed after a Salmonella outbreak was traced to her kitchen).
What is treatment for Salmonella enteritidis?
Treatment for S. enteritidis is supportive, as the illness is usually self-limited.
What are common sources associated with Salmonella enteritidis?
Pet reptiles/amphibians (such as turtles), along with uncooked chicken are common sources of S. enteritidis.
How does Klebsiella pneumoniae pneumonia present clinically?
K. pneumoniae pneumonia typically presents with fever, pleuritic chest pain, dyspnea, and “currant-jelly” bloody sputum.
Describe the 3-week progression of symptoms in untreated typhoid fever.
Patients with untreated typhoid fever present with symptoms 5 to 21 days after ingestion of S. typhi from contaminated food or water. Symptoms include
- Fever and bacteremia during the first week.
- Abdominal pain and “rose spots” (faint salmon-colored macules on the trunk and abdomen) during the second week. Constipation or “pea soup” diarrhea with abdominal distention may occur.
- Hepatosplenomegaly, intestinal bleeding, and perforation from Peyer’s patches hyperplasia during the third week.
What enteric disease-causing bacteria ferments lactose and will grow in dark green metallic colonies on eosin methylene blue (EMB) agar?
Eosin methylene blue (EMB) agar is a differential media on which E. Coli appears to have a dark metallic green sheen because it ferments lactose. Salmonella and Shigella do not ferment lactose and are colorless on EMB agar.
What locations put one at risk for Yersinia pestis infection? What practices put one at risk for Yersinia pestis infection?
Exposure to rodents (such as prairie dogs) and fleas put one at risk for Y. pestis infection. High-risk occupations include veterinarians, researchers, and people living in endemic areas like Central Africa and Madagascar. In order to prevent the spread of Y. pestis in endemic regions, rodent control, flea control and insect repellants may be used.
What is the clinical presentation of septicemic plague caused by Yersinia pestis?
Septicemic plague presents with nonspecific fever, gastrointestinal illness, and pain. Buboes are not present, making this a difficult condition to diagnose.
In this motility test, one tube contains Shigella sp. and the other contains E. coli. Which is which?
In this citrate utilization test, one tube contains Klebsiella and Salmonella, and the other tube contains E. coli and shigella. Which is which?
In this urease test, tube 1 is the negative control.
Which tubes contain:
- K. pneumoniae
- E. coli
- P. mirabilis
- P. mirabilis is rapidly positive - bright pink throughout.
- K. pneumoniae - delayed (+)ve (pink color along the slant).
- E. coli - negative (no pink color).
In this Indole test, which tube contains E. coli?
E. coli has a positive Indole test. It will be in tube A with the red ring.
On this MacConkey agar plate, what color is the lactose fermenter? What color is the lactose non-fermenter?
MacConkey agar
- Lactose fermenters are pink
- Lactose non-fermenters are yellow/white
On this EMB agar, which streaks are:
- Lactose negative
- Lactose positive
- E. coli
EMB agar
- Purple colonies are lactose positive.
- Purple colonies with metallic green sheen are E. coli
How does Yersinia enterocolitica cause gastrointestinal symptoms?
Y. enterocolitica localizes in the terminal ileum, appendix, and right colon and secretes Yst enterotoxin to give diarrhea. Additionally, Y. entercolitica invades and causes local inflammation that can spread to the colon, leading to ulceration and producing dysentery-like symptoms.
How does Yersinia enterocolitica cause mesenteric adenitis?
Y. enterocolitica can be carried to mesenteric lymph nodes, replicating and causing swelling of mesenteric lymph nodes (mesenteric adenitis).
A child with gastroenteritis has a stool culture taken. Laboratory tests reveal gram-negative, non-lactose fermenting organisms that show motility only at 22 degrees Celsius. What is the most likely organism?
A) Yersinia enterocolitica
B) Shigella flexneri
C) Salmonella enteriditis
D) Salmonella paratyphi
E) Shigella sonnei
Yersinia enterocolitica
Answer Explanation
Motility in Yersinia enterocolotica is via flagella, enhancing its ability to invade cells. It becomes motile at lower temperatures.
Salmonella possess flagella as well, however Salmonella are motile at all times.
Shigella is motile within cells via actin-based motility.
What is the virulence factor in Yersinia enterocolitica that aids in inhibiting phagocytosis and cell signaling?
Y. enterocolitica also contains a type III secretion system, allowing the organism to inject Yersinia outer proteins (Yops) that aid in inhibiting phagocytosis and cell signaling.
Describe the motility of Y. enterocolitica.
Y. enterocolitica is motile at 22°C.
What diseases does Yersinia enterocolitica cause?
Y. enterocolitica causes yersiniosis, which is a type of enterocolitis (bloody diarrhea), and mesenteric adenitis.
How is Yersinia enterocolitica infection diagnosed?
Diagnosis of Y. enterocolitica is made with stool cultures.
What are typical symptoms of infection with Yersinia enterocolitica?
Patients typically present with diarrhea, abdominal pain, and fever, which may be accompanied by nausea, vomiting, and pharyngitis.
What is the morphology, gram staining, oxygen requirement, and lactose-fermenting status of Yersinia enterocolitica?
Yersinia enterocolitica is a facultative anaerobic, non lactose-fermenting gram-negative coccobacillus.
What toxin does Yersinia enterocolitica synthesize and what is its function?
Y. enterocolitica secretes a heat-stable enterotoxin called Yst in environmental conditions similar to the mammalian ileum. Yst induces diarrhea and prolongs fecal shedding of the organism via cGMP synthesis in the intestinal brush border, leading to an overall effect of fluid loss and lack of fluid absorption.
How should enterocolitis caused by Yersinia enterocolitica be treated?
Y. enterocolitica enterocolitis has a self-limited course in previously healthy hosts. Treatment is supportive, and doxycycline or TMP-SMX maybe given for complicated gastrointestinal infections.
How do symptoms of Yersinia enterocolitica enterocolitis vary by age group?
The clinical manifestations can vary by age group.
- Children under 5 years present with bloody diarrhea
- Children over 5 years present with bloody diarrhea and appendicitis-like pain
- Adults present with bloody diarrhea and arthritis
How is Yersinia enterocolitica transmitted?
Yersinia enterocolitica is transmitted via a fecal-oral route from ingestion or contact with animals and animal products. This could include ingestion of contaminated raw pork, other meats, milk, and untreated water. It often occurs in daycare centers.
What are the most common post-infectious sequelae of Yersinia enterocolitica infection?
The most common sequelae of Y. enterocolitica infection are reactive arthritis (associated with HLA-B27+ status) and erythema nodosum.
Which urease test tube contains Klebsiella?
Tube 2
Klebsiella is urease positive.
(CHuck Norris hates PUNKSS)
Which citrate test tube contains Klebsiella?
The blue tube.
Klebsiella is citrate positive.
Which urease test tube contains Proteus mirabalis?
Tube 2
Proteus mirabalis is urease positive.
(CHuck Norris hates PUNKSS)
A bacteria grows on MacConkey agar with a swarming pattern. What bacteria is it?
Proteus spp. grow in a swarming pattern on MacConkey agar.
Where is bacteroides fragilis normally found?
Bacteroides fragilis is part of the GI tract normal flora.
Bacteroides fragilis produces what vitamin?
Bacteroides fragilis produces vitamin K.
What does bacteroides fragilis do if it gets into tissues?
Bacteroides fragilis can create gas as they proliferate. This can cause tissue death and a characteristic gas gangrene.
What is a symptom of intestinal infection with bacteroides fragillis?
Gastrointestinal abscess
This is a collection of bacterial proliferation which has been walled off from the body’s immune system. Often filled with pus, the patient can present with systemic signs of infections and characteristic findings on abdominal CT scan.
Are bacteroides sensitive or resistant to penicillin?
Bacteroides are penicillin resistant.
These organisms are resistant to penicillin by virtue of production of beta-lactamase.
What antibiotic treatments are given for bacteroides infections?
Clindamycin or Metronidazole
Clindamycin is an antibiotic often used for anaerobic species. It is bacteriostatic and works similar to macrolides by inhibiting ribosomal translocation.
Metronidazole is an antibiotic that works against anaerobic bacteria which is also anti-protozoal and amebicide. The drug is taken up and converted into a product which causes oxidative damage to the organism.
What is the appearance of bacteroides fragilis on Bile Esculin agar?
What is the key identifier for Serratia marcescens?
Serratia marcescens produces red-pigmented colonies.
Think red marashino cherries.
