Microbiology Case Study: 38-Year-Old with Intermittent Straight Catheterization

Case History:

A 38 year old man with history of secondary progressive multiple sclerosis complicated by neurogenic bladder requiring intermittent straight catheterization presented with fevers, chills, and weakness. Clinical evaluation revealed hypotension and leukocytosis concerning for sepsis. His urinalysis was positive for 3+ blood, 1+ leukocyte esterase and nitrites. Urine was sent to our laboratory for culture and grew bacteria with the below gram stain and colony morphology.

Gram stain showing gram negative bacilli.
Gram stain showing gram negative bacilli.
Sheep blood agar growing nonhemolytic grey-yellow mucoid bacterial colonies.
Sheep blood agar growing nonhemolytic grey-yellow mucoid bacterial colonies.
MacConkey agar growing mucoid lactose fermenting (pink) bacterial colonies.
MacConkey agar growing mucoid lactose fermenting (pink) bacterial colonies.

 

Laboratory identification:

Klebsiella and Raoultella both are gram negative bacilli that form lactose fermenting, yellow, mucoid bacterial colonies. The bacterial colonies appear mucoid because of the bacteria’s polysaccharide capsule. Distinguishing these two types of bacteria requires molecular analysis as their morphology can be identical. In our initial identification process, only one type of bacteria was detected on the urine culture. Given the gram stain and colony morphology, our differential included Klebsiella, Enterobacter, and Roaultella. The bacteria was verified as Roaultella species using mass spectrometry. However, our laboratory also received two sets of blood cultures which showed the same morphology as above but the bacteria was identified as K. oxytoca. This prompted a review of the urine culture in which a subtle second bacterial colony morphology was seen and confirmed as K. oxytoca.

Discussion:

In summary, our patient had a urinary tract infection caused by Roaultella and Klebsiella which was the source of the patient’s sepsis. Only the Klebsiella was detected in his blood stream. Raoultella and Klebsiella are both gram negative, oxidase negative, non-motile, capsulated, facultative anaerobic bacilli within the Enterobacteriaceae family. Raoultella was initially classified within the Klebsiella genus, but reclassified based on comparative analysis of the 16S rRNA gene and rpoB gene which encodes the β subunit of bacterial RNA polymerase. Members of the Raoultella genus include R. electrica, R. terrigena, R. planticola, and R. ornithinolytica and are found in the environment, specifically in plants, soil, and water. Raoultella species are rare in human disease but have been documented to cause bacteremia, urinary tract infection, conjunctivitis and cholecystitis.

Klebsiella causes human disease much more frequently than Roaultella. Klebsiella are part of human oropharynx and gastrointestinal flora that act as opportunistic pathogens. Mode of transmission may occur endogenously or through person to person spread, hence nosocomial infections are common. K. oxytoca and K. pneumoniae are the most frequently implicated species in human disease and may cause a wide spectrum of infections such as urinary tract infections, respiratory infections, enteritis, meningitis and bacteremia.

For our patient, we reported antibiotic sensitivities that were susceptible to both types of bacteria. The patient was treated with ceftriaxone and then transitioned to cefpodoxime with resolution of his urosepsis. In general, Raoultella’s susceptibility to antimicrobial agents are not well studied and should be based on the antibiotic sensitivities of each strain. In contrast, Klebsiella is well documented to have increasing antimicrobial resistance. Most clinical strains are resistant to ampicillin, carbenicillin and ticarcillin as well as extended spectrum beta-lactam drugs. Resistance to beta-lactam drugs is the result of Klebsiella bacteria that harbor plasmids which produce beta-lactamase enzymes.

 

-Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

Wojewoda-small

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

 

 

Microbiology Case Study–35-Year-Old with a Puncture Wound

Case History:

A 35 year old healthy man presented with a puncture wound of the left hand. He was bit by his neighbor’s dog. Fluid expressed from the wound was sent to the microbiology laboratory with the following gram stain and colony morphology.

past1
Gram stain showing small gram negative coccobacilli.
Sheep blood agar with smooth, gray, non-hemolytic bacterial colonies.
Sheep blood agar with smooth, gray, non-hemolytic bacterial colonies.

 

Laboratory Identification:

Bacterial colonies, as shown above, grew on sheep blood and chocolate agars. No growth was present on CNA or MacConkey agars which in combination with the gram stain indicated a type of fastidious gram negative bacteria. Additionally, the bacterial colonies were oxidase positive, catalase positive and indole positive. These findings were consistent with Pasteurella species and confirmed to be P. multocida by mass spectrometry.

Discussion:

Pasteurella species are nonmotile, gram-negative, facultative anaerobic coccobacilli or rods. P. multocida is the most common species involved in human disease. P. multocida is part of the normal oropharyngeal flora in multiple animals including cats, dogs, cattle, horses, rodents and other animals. This bacteria has been reported in up to 70-90% cats and 40-60% of dogs. Humans who have frequent exposure to animals may also harbor P. multocida as part of their normal flora.

Pasteurella are opportunistic pathogens that require mechanical disruption of host barriers. The vast majority of P. multicida related diseases are wound infections and/or cellulitis as a result of a cat bite or scratch. Transmission of Pasteurella also occurs in partially healing wound or regions of poor skin integrity that are licked by a cat or dog. Pasteurella infections may be complicated by septic arthritis and osteomyelitis if wounds are deep and inoculate the underlying soft tissue. Patients who are immunocompromised may develop bacteremia with more widespread infections. The majority of Pasteurella species are susceptible to penicillin, cephalosporins and tetracycline. Our laboratory does not report antibiotic sensitivities for P. multocida for a few reasons: Pasteurella is rarely resistant to penicillin, and bite wounds are generally mixed infections.

 

-Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

Make the Diagnosis–A 58 Year Old Male with Abdominal Pain

A 58-year-old male presents with abdominal pain and bloody diarrhea which had a gradual onset over the last 3 weeks. He has lost 8 pounds during this period of time. A cecal biopsy is performed, and a representative section is shown here. What is the most likely diagnosis?

amoebiasis1

  1. Amoebiasis
  2. Ascariasis
  3. Candidiasis
  4. Cryptosporidiosis
  5. Giardiasis

The diagnosis in this case is amoebiasis. The most common cause of amebic enterocolitis is Entamoeba histolytica, an organism spread through ingestion of cysts in contaminated food or water. The trophozoite forms are round, and frequently show intracytoplasmic red cells.

Amoeba with intracytoplasmic red cells
Amoeba with intracytoplasmic red cells

Occasionally, the organisms invade other organs, such as the liver, lung, and heart. Most patients may be treated on an outpatient basis, unless there is severe colitis or extraintestinal disease.

The organisms frequently invade through the mucosa and into the submucosa, often with lateral extension.

"Flask-shaped" ulcer in amoebiasis
“Flask-shaped” ulcer in amoebiasis

Occasionally, the organisms invade other organs, such as the liver, lung, and heart. Most patients may be treated on an outpatient basis, unless there is severe colitis or extraintestinal disease.

Krafts

-Kristine Krafts, MD, is an Assistant Professor of Pathology at the University of Minnesota School of Medicine and School of Dentistry and the founder of the educational website Pathology Student.

Microbiology Case Study–Upper Thigh Pain

An 85 year old man presented with right medial upper thigh pain and swelling.  Imaging revealed a large pseudoaneurysm in the right superficial femoral artery with evidence of rupture. The patient was taken to the operating room for placement of a gortex stent graft. His postoperative course was complicated by development of a large hematoma at the surgical site. Incision and drainage of the hematoma was surgically performed and fluid from the hematoma was sent to the microbiology laboratory.

Gram stain with multiple gram negative bacilli.
Gram stain with multiple gram negative bacilli.
White-grey bacterial colonies growing on blood agar plate.
White-grey bacterial colonies growing on blood agar plate.
Grey semi-translucent non-lactose fermenting colonies growing on MacConkey agar.
Grey semi-translucent non-lactose fermenting colonies growing on MacConkey agar.

 

Laboratory Identification:

The gram stain and plates confirmed the bacteria were non-lactose fermenting, non-hemolytic gram negative bacilli which is consistent Salmonella. Salmonella species was confirmed by mass spectrometry. Another feature helpful in the identification of Salmonella is its ability to produce hydrogen sulfide. Although not performed in this case, Salmonella will produce colonies with black centers when grown on Xylose lysine deoxycholate agar (selective agar that has thiosulfate which Salmonella metabolize to hydrogen sulfide).

The bacterial isolates of Salmonella were forwarded to the public health laboratories where serotype is determined based on serologic reactions to O and H antigens. The O antigen is the most external component of the lipopolysacccharide of gram negative bacteria and the H antigen is the antigenic determinant that makes up the flagellar subunits . This Salmonella species was identified to be S. enteritidis. Two sets of the patient’s blood cultures also grew S. enteritidis.

Discussion:

Salmonella are motile, gram negative bacilli that are widely disseminated in nature. Various animals such as turtles, lizards, snakes and birds are associated with Salmonella. Salmonella may infect humans via ingestion of contaminated food products that are typically of poultry or dairy origin. Person to person transmission may also occur by fecal-oral route. Salmonella has multiple virulence factors that allow it to evade the immune system. One of its virulence factors is the polysaccharide capsule that surrounds the O antigen. The O antigen is highly immunogenic and shielding the O antigen prevents its recognition by antibodies. Additionally, Salmonella can periodically change its H antigen as another protective mechanism against antibodies.

 

Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

Wojewoda-small

Christi Wojewoda, MD, is certified by the American Board of Pathology in AP/CP and Medical Microbiology. She is currently the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

 

Microbiology Case Study–Abdominal Pain

A 60 year old man presented with abdominal pain and bloody diarrhea. He denied fever, chills, nausea, vomiting or recent travel. A stool culture was sent to the microbiology laboratory.

Colony Gram stain showing Gram-negative bacilli
Colony Gram stain showing Gram-negative bacilli
Grey-white bacterial colonies growing on a blood agar plate.
Grey-white bacterial colonies growing on a blood agar plate.
Fuschia colonies growing on CHROMagar O157.
Fuschia colonies growing on CHROMagar O157.

 

Laboratory Identification:

E. coli O157:H7 is most likely to be detected in the acute phase of illness and may be missed after 5-7 days from onset of symptoms. In general, laboratory identification is based on the detection of Shiga toxin-producing strains or detection of the O157:H7 serotype through various methodologies. In our laboratory, we identified E. coli O157 based on the above gram stain and colony morphology in combination with growth with the appropriate color on a selective plate for E. coli O157, CHROMagar O157. We used our automated microbial identification system, Vitek 2, which performs multiple biochemical reactions to confirm the bacteria as E. coli O157:H7. Additionally, we identified the presence of Shiga toxin through an immunochromatographic lateral flow rapid test using monoclonal antibodies specific to Shiga toxins.

 

Discussion:

E. coli are gram negative rods that are beta hemolytic, indole positive and lactose fermenters. E. coli is part of the normal colon flora but certain types of E. coli can cause disease depending on their virulence factors. Enterohemorrhagic E. coli (EHEC), also known as Shiga toxin producing E.coli (STEC), is one of six major groups of E. coli that causes diarrhea. EHEC produce a Shiga toxin that inhibits protein synthesis of intestinal epithelial cells via inhibition of the 60S ribosome. The most common serotype is E. coli O157:H7. Transmission occurs through ingestion of raw milk or uncooked ground beef. Hamburgers have been the cause of many outbreaks of infection in the United States although majority of E. coli O157:H7 infections are not associated with outbreaks.

Clinical manifestations from E. coli O157:H7 infection usually occurs at three days from time of exposure but may vary from one to eight days. Clinical symptoms typically begin with abdominal cramps, vomiting, and bloody diarrhea without fever. However, patients may experience a spectrum of disease ranging from asymptomatic infection (less common) to hemorrhagic colitis with progression hemolytic-uremic syndrome (HUS). HUS is the most common cause of acute renal failure in children and results from toxin-mediated damage of endothelial cells in the kidney. HUS is characterized by the triad of acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. Supportive therapy is recommended for treatment of E. coli O157:H7 infections. Antibiotics are not recommended because of the potential to increase Shiga toxin production. For this reason, we do not report antibiotic sensitivities for E. coli O157:H7.

 

Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

Wojewoda-small

Christi Wojewoda, MD, is certified by the American Board of Pathology in AP/CP and Medical Microbiology. She is currently the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

Hematology Case Study: 60-Year-Old Male with Hives

A 60-year-old male presents with hives, skin flushing, and headaches. After an appropriate preliminary work-up, a bone marrow biopsy is performed. A representative section from the bone marrow biopsy is shown here. What are the granulated cells at the center of this image?

mast

A. Megakaryocytes
B. Promyelocytes
C. Mast cells
D.Myeloma cells
E. Adenocarcinoma cells

The granulated cells in this image are mast cells, which are identified by their abundant, metachromatic granules. This patient was diagnosed with systemic mastocytosis, a clonal disorder of mast cells and their precursors.

Mastocytosis is actually a spectrum of rare disorders, all of which are characterized by an increase in mast cells. Most patients have disease that is localized to the skin, but about 10% of patients have systemic involvement, like the patient in this case. There is a localized, cutaneous form of mastocytosis called urticaria pigmentosum that happens mostly in children and accounts for over half of all cases of mastocytosis.

Clinically, the skin lesions of mastocytosis vary in appearance. In urticaria pigmentosum, the lesions are small, round, red-brown plaques and papules. Other cases of mastocytosis show solitary pink-tan nodules that may be itchy or show blister formation. The itchiness is due to the release of mast cell granules (which contain histamine and other vasoactive substances).

In systemic mastocytosis, patients have skin lesions similar to those of urticaria pigmentosum – but there is also mast cell infiltration of the bone marrow, lymph nodes, spleen and liver. Patients often suffer itchiness and flushing triggered by certain foods, temperature changes, alcohol and certain drugs (like aspirin).

Krafts

-Kristine Krafts, MD, is an Assistant Professor of Pathology at the University of Minnesota School of Medicine and School of Dentistry and the founder of the educational website Pathology Student.

Microbiology Case Study–Pleural Thickening in Lung Transplant Patient

Case history:

A 71-year-old man with a past medical history of idiopathic pulmonary fibrosis and asbestosis status post recent single lung transplant presented with worsening dyspnea. He had a right pleural catheter since the time of his lung transplant surgery five months ago. A chest CT scan was performed and revealed a right pleural effusion with pleural thickening. A sample of the pleural fluid was sent to the microbiology laboratory with the following gram stain and colony morphology:

Gram stain showing gram positive bacilli with subtle palisading arrangements and formations that resemble Chinese letters.
Gram stain showing gram positive bacilli with subtle palisading arrangements and formations that resemble Chinese letters.
Blood agar plate with gray-white, moist, smooth, non-hemolytic bacterial colonies.
Blood agar plate with gray-white, moist, smooth, non-hemolytic bacterial colonies.

 

Laboratory Identification:

The pleural fluid grew bacterial colonies on blood agar plates as shown above. No growth was present on MacConkey agar (selective for gram negative bacteria). The colony morphology and gram stain was suggestive of Corynebacterium species. Mass spectrometry confirmed the bacteria as Corynebacterium striatum.

Discussion:

Corynebacterium striatum are gram-positive bacilli that are normal skin and mucosal membrane flora. C. striatum is commonly regarded as a contaminant but may be an opportunistic pathogen in immunocompromised patients such as the patient presented in the above case. Transmission of C. striatum most likely occurs when the patient’s endogenous strain gains access to a normally sterile site of the body. C. striatum has also been documented to spread nosocomially in patients with severe chronic obstructive pulmonary disease. C. striatum is associated with a spectrum of diseases including infectious endocarditis, bacteremia, pneumonia, lung abscess, arthritis, chorioamnionitis and foreign medical device infections. Patients with C. striatum infections are empirically treated with vancomycin because the susceptibility to other antibiotics is variable. Additionally, removal of foreign medical device should be performed if indicated.

 

Jill Miller, MD is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.

Wojewoda-small

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.