Bacterial Gastroenteritis Workup

Author: Jennifer Lynn Bonheur, MD; Chief Editor: Julian Katz, MD more...

Updated: Apr 19, 2012

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Approach Considerations
Bacterial Cultures
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Approach Considerations

A stool pH of 5.5 or below or the presence of reducing substances indicates carbohydrate intolerance. This is usually transient in nature.

Enteroinvasive infections of the large bowel cause leukocytes, predominantly neutrophils, to be shed into stool. Absence of fecal leukocytes does not eliminate the possibility of enteroinvasive organisms; however, the presence of fecal leukocytes eliminates consideration of enterotoxigenic E coli, Vibrio species, and viruses. Shigella characteristically causes marked bandemia with variable total WBC count.

Examine any exudate found in the stool for leukocytes. Such exudates highly suggest inflammatory bowel disease, which could be infectious or of another origin.

Antilisteriolysin O (ALLO) is positive during the convalescent phase of bacterial gastroenteritis and when invasive disease has occurred.

Procedures

Identification of pseudomembranes in the colon by direct visualization is diagnostic for C difficile; however, the yield may be low.

Bacterial Cultures

Table 3, below, lists common bacteria and the optimal culture media for their growth.

Table 3. Common Bacteria and Optimum Culture Media (Open Table in a new window)

Organism	Detection Method	Microbiologic Characteristics
Aeromonas species	Blood agar	Oxidase-positive, flagellated GNB
Bacillus species	Blood agar	Facultatively aerobic, spore-forming GPR; beta hemolytic; reduces nitrates; ferments carbohydrates
Campylobacter species	Skirrow agar	Rapidly motile, curved GNR; Campylobacter jejuni 90% of infections, Campylobacter coli 5% of infections
C difficile	CCFE agar, EIA for toxin, LA for protein	Anaerobic, spore-forming GPR; toxin-mediated diarrhea; produces pseudomembranous colitis
C perfringens	None available	Anaerobic, spore-forming GPR; toxin-mediated diarrhea
E coli	MacConkey, EMB, or SM agar	Lactose-producing GNR
Listeria species	Blood agar	Flagellated GPB
Plesiomonas species	Blood agar	Oxidase-positive GNR
Salmonella species	Blood, MacConkey, EMB, XLD, or HE agar	Nonlactose, non–H2S-producing GNR
Shigella species	Blood, MacConkey, EMB, XLD, or HE agar	Nonlactose and H2S-producing GNR; verotoxin (neurotoxin)
Staphylococcus species	Blood agar	Heat-stable, preformed toxin-mediated GPC
Vibrio species	Blood or TCBS agar	Oxidase-positive, motile, curved GNB
Y enterocolitica	CIN agar	Nonlactose-producing, oval GNR
CCFE = cycloserine-cefoxitin-fructose-egg; CIN = cefsulodin-irgasan-novobiocin; EIA= enzyme immunoassay; EMB = e-methylene blue; GNB = gram-negative bacillus; GNR = gram-negative rod; GPB = gram-positive bacillus; GPC = gram-positive cocci; GPR = gram-positive rod; H2S = hydrogen sulfide; HE = Hektoen enteric; LA = latex agglutination; SM = Sorbitol-MacConkey; TCBS = thiosulfate-citrate-bile-sucrose; XLD = xylose-lysine-deoxycholate.

The following is a list of the different culture media used to isolate bacteria. A high index of suspicion is needed to choose the appropriate medium.

Blood agar - All aerobic bacteria and yeast; detects cytochrome oxidase production
MacConkey EMB agar - Inhibits gram-positive organisms; permits lactose fermentation
XLD agar and HE agar - Inhibit gram-positive organisms and nonpathogenic gram-negative bacilli; permit lactose fermentation and H2S production
Skirrow agar - Selective for Campylobacter species
SM agar - Selective for enterohemorrhagic E coli
CIN agar - Selective for Y enterocolitica
Thiosulfate-citrate-bile-sucrose agar - Selective for Vibrio species
CCFE agar - Selective for C difficile

Stool cultures are useful when positive, but the yield is usually low. Refrigerate stool that is not cultured within 2 hours of collection at 4°C, or place it in a transport medium. Always culture stool for Campylobacter, Salmonella, and Shigella species, especially if stool leukocytes or gross blood is found in the stool.

Serotype Salmonella for S typhimurium DT104, particularly if the gastroenteritis is associated with raw milk or cheese ingestion. S typhimurium DT104 is a multidrug-resistant organism, and antibiotic sensitivities are crucial to guide therapy.^{[15, 16]}

Preformed toxin from Bacillus or Staphylococcus species may cause rapid-onset gastroenteritis. In such cases, the bacteria may not exist in the gastrointestinal tract; therefore, culture the food ingested by the person.

Bloody diarrhea with a history of ground beef ingestion should raise the suspicion for enterohemorrhagic E coli. If E coli is found in the stool, type it to determine if it is O157:H7. Report cases of E coli O157:E7 gastroenteritis (and other infectious problems) to the state health department.

History of raw seafood ingestion or foreign travel should prompt additional screening for Vibrio and Plesiomonas species.

Proceed to Treatment & Management

Contributor Information and Disclosures

Author

Jennifer Lynn Bonheur, MD Attending Physician, Division of Gastroenterology, Lenox Hill Hospital

Jennifer Lynn Bonheur, MD is a member of the following medical societies: American Gastroenterological Association, American Society for Gastrointestinal Endoscopy, New York Academy of Sciences, New York Society for Gastrointestinal Endoscopy, and Sigma Xi

Disclosure: Nothing to disclose.

Coauthor(s)

Mukul Arya, MD Associate Professor of Internal Medicine, Weill Cornell Medical College; Assistant Director of Therapeutic Endoscopy, Department of Gastroenterology and Internal Medicine, Wyckoff Heights Medical Center

Mukul Arya, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Medical Association, and American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

M Akram Tamer, MD Professor, Program Director, Department of Pediatrics, University of Miami, Leonard M Miller School of Medicine

M Akram Tamer, MD is a member of the following medical societies: American Medical Association and Florida Medical Association

Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD Clinical Professor of Medicine, Drexel University College of Medicine

Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law, Medicine & Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility

Disclosure: Nothing to disclose.

Additional Contributors

Simmy Bank, MD Chair, Professor, Department of Internal Medicine, Division of Gastroenterology, Long Island Jewish Hospital, Albert Einstein College of Medicine

Disclosure: Nothing to disclose.

Richard E Frye, MD, PhD Assistant Professor, Departments of Pediatrics and Neurology, University of Texas Medical School at Houston

Richard E Frye, MD, PhD is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, Child Neurology Society, and International Neuropsychological Society

Disclosure: Nothing to disclose.

John Gunn Lee, MD Director of Pancreaticobiliary Service, Associate Professor, Department of Internal Medicine, Division of Gastroenterology, University of California at Irvine School of Medicine

John Gunn Lee, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, and American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

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Table 1. Stool Characteristics and Sources

Stool Characteristics	Small Bowel	Large Bowel
Appearance	Watery	Mucus and/or blood
Volume	Large	Small
Frequency	Increased	Increased
Blood	Possibly heme-positive but never gross blood	Possibly grossly bloody
pH	Possibly < 5.5	>5.5
Reducing substances	Possibly positive	Negative
White blood cell (WBC) count	< 5/high-power field (HPF)	Possibly >10/HPF
Serum WBC count	Normal	Possible leukocytosis, bandemia
Organisms	Preformed toxins: Bacillus species, Staphylococcus aureus	Invasive bacteria: E coli and Shigella, Salmonella, Campylobacter, Yersinia, Aeromonas, and Plesiomonas species
	Toxic bacteria: E coli, cholera, C perfringens, Vibrio species, Listeria monocytogenes	Toxic bacteria: C difficile
	Other causes: rotavirus, adenovirus, calicivirus, astrovirus, Norwalk virus, and Giardia and Cryptosporidium species	Other causes: Entamoeba species

Table 2. Symptoms and Their Characteristics

Organism	Incubation	Duration	Vomiting	Fever	Abdominal Pain
Aeromonas species	None	0-2 weeks	+/-	+/-	No
Bacillus species	1-16 hours	1-2 days	Yes	No	Yes
Campylobacter species	2-4 days	5-7 days	No	Yes	Yes
C difficile	Variable	Variable	No	Few	Few
C perfringens	0-1	1 day	Mild	No	Yes
Enterohemorrhagic E coli	1-8 days	3-6 days	No	+/-	Yes
Enterotoxigenic E coli	1-3 days	3-5 days	Yes	Low	Yes
Listeria species	20 hours	2 days	Few	Yes	+/-
Plesiomonas species	None	0-2 weeks	+/-	+/-	+/-
Salmonella species	0-3 days	2-7 days	Yes	Yes	Yes
Shigella species	0-2 days	2-7 days	No	High	Yes
S aureus	2-6 hours	1 day	Yes	No	Yes
Vibrio species	0-1 days	5-7 days	Yes	No	Yes
Y enterocolitica	0-6	1-46 days	Yes	Yes	Yes

Table 3. Common Bacteria and Optimum Culture Media

Organism	Detection Method	Microbiologic Characteristics
Aeromonas species	Blood agar	Oxidase-positive, flagellated GNB
Bacillus species	Blood agar	Facultatively aerobic, spore-forming GPR; beta hemolytic; reduces nitrates; ferments carbohydrates
Campylobacter species	Skirrow agar	Rapidly motile, curved GNR; Campylobacter jejuni 90% of infections, Campylobacter coli 5% of infections
C difficile	CCFE agar, EIA for toxin, LA for protein	Anaerobic, spore-forming GPR; toxin-mediated diarrhea; produces pseudomembranous colitis
C perfringens	None available	Anaerobic, spore-forming GPR; toxin-mediated diarrhea
E coli	MacConkey, EMB, or SM agar	Lactose-producing GNR
Listeria species	Blood agar	Flagellated GPB
Plesiomonas species	Blood agar	Oxidase-positive GNR
Salmonella species	Blood, MacConkey, EMB, XLD, or HE agar	Nonlactose, non–H2S-producing GNR
Shigella species	Blood, MacConkey, EMB, XLD, or HE agar	Nonlactose and H2S-producing GNR; verotoxin (neurotoxin)
Staphylococcus species	Blood agar	Heat-stable, preformed toxin-mediated GPC
Vibrio species	Blood or TCBS agar	Oxidase-positive, motile, curved GNB
Y enterocolitica	CIN agar	Nonlactose-producing, oval GNR
CCFE = cycloserine-cefoxitin-fructose-egg; CIN = cefsulodin-irgasan-novobiocin; EIA= enzyme immunoassay; EMB = e-methylene blue; GNB = gram-negative bacillus; GNR = gram-negative rod; GPB = gram-positive bacillus; GPC = gram-positive cocci; GPR = gram-positive rod; H2S = hydrogen sulfide; HE = Hektoen enteric; LA = latex agglutination; SM = Sorbitol-MacConkey; TCBS = thiosulfate-citrate-bile-sucrose; XLD = xylose-lysine-deoxycholate.

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