J . Kristie Johnson, Ph.D., D(ABMM - PowerPoint Presentation

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J. Kristie Johnson, Ph.D., D(ABMM)University of Maryland School of Medicine

A CASE OF MISTAKEN IDENTITY

Patient HistoryA 39-year-old previously healthy Amish woman was admitted to the burn unit after sustaining burns on 56% of her body. Because the patient’s immune system was suppressed and she developed a high grade fever, she was treated empirically with 2 broad spectrum antimicrobial agents: piperacillin/

tazobactam

and vancomycin

.Five days after antimicrobial therapy was introduced, the patient reported moderate abdominal pain and bloody diarrhea; her temperature was 103.6°F.A stool sample was sent to the lab.

Photo Credit: J. Kristie Johnson, Ph.D., D(ABMM)

Common Causes of Diarrhea BacterialCampylobacter jejuniSalmonella spp.Shigella

spp.

Escherichia coli

Yersinia enterocoliticaVibrio choleraeClostridium difficileViralNorovirusRotavirusCytomegalovirus Parasitic Giardia lambliaCryptosporidium

Processing a Stool Sample for Bacterial Pathogens

Stool samples are sent to the microbiology

laboratory.

Stool samples are plated onto selective media for bacterial pathogens in a biological safety

hood.

After incubation, plates are examined for bacterial

pathogens.

Photos show growth that might be observed following plating of stool

samples.

Photo Credit: J. Kristie Johnson, Ph.D., D(ABMM)

Microbiology Laboratory ResultsAll cultures were negative for common bacterial pathogens that cause diarrhea.In fact there was no growth of any of the types of bacteria found in “normal stool”But the non-selective agar plate (MacConkey agar) was full of mucoid pink colonies!

The clinical microbiologist reported this unusual finding to the patient’s physician.

Antibiotic Associated Hemorrhagic Colitis (AAHC) caused by K. oxytoca

Klebsiella

oxytoxaGram-negative rod.Encapsulated (colonies appear mucoid).Pink colonies indicate the organism ferments lactose.Often associated with urinary tract, wound, or bloodstream infections.Not considered a common cause of bacterial diarrhea.

Gram-negative rod on Gram Stain

Mucoid lactose-fermenting colonies on

MacConkey

agar

Diagnosis!

Photo Credit: J. Kristie Johnson, Ph.D., D(ABMM)

More on the diagnosis…. Klebsiella oxytocaSeveral studies have documented a strong association between K.

oxytoca

in stool

and antibiotic-associated hemorrhagic colitis (AAHC) in C. difficile-negative patients.Toxin production by K. oxytoca is the key pathogenic factorToxin is a cytotoxin that is chromosomally encodedCytotoxin is weak compared to C. difficile toxin A (tcdA, resulting in antibiotic-associated colitis (AAC)).

Explanation of DiagnosisK. oxytoca AAHC vs C. difficile AACImportant characteristics distinguishing K. oxytoca

AAHC and

C. difficile AAC

Adapted from Green, NM et al. 2009. Clin. Microbiol. Newsletter. 31: 111-116. Provided by Nicole Green, Ph.D., D(ABMM).

Characteristic

Klebsiella

oxytoca

– AAHC

Clostridium difficile - AAC

Pseudomembrane

No

YesBloody diarrheaYesNo

Antibiotic class associationΒ-lactams

Β-lactams

TreatmentWithdraw antibiotic

Requires additional antibiotics

Complications

MinimalToxic

megacolon, intestinal perforation, deathOutbreak-associated

No

Yes

Patient OutcomeBroad spectrum antimicrobial therapy inhibited the growth of normal stool bacteria and allowed the K. oxytoca to grow (e.g., “selected for” K. oxytoca).

Antimicrobial therapy was

discontinued

and the patient recovered.The clinical microbiologist was instrumental in diagnosing this unusual cause of diarrhea!

J. Kristie Johnson, Ph.D., D(ABMM)

Dr. Johnson is an Associate Professor at the University of Maryland School of Medicine, Departments of Pathology and Epidemiology and Public Health and Microbiology and Immunology and the Interim Director of the Clinical Microbiology and Virology Laboratories at the University of Maryland Medical Center

. Dr

. Johnson is a Diplomate of the American Board of Medical Microbiology and has expertise in public health and medical microbiology. Dr. Johnson’s research focuses on the detection, transmission, and control of antimicrobial resistant organisms concentrating on methicillin resistant Staphylococcus aureus (MRSA) and resistant Gram-negative bacteria to include multi-drug resistant

Enterobacteriaceae (KPC, ESBLs, and plasmid mediated AmpC), Acinetobacter baumannii, and Pseudomonas aeruginosa.

Photo Credit: J. Kristie Johnson, Ph.D., D(ABMM)