Tag: microbiology

Case History  

A 36 year old Caucasian male presented to the hospital with symptoms of a bowel obstruction.  His past medical history was significant for a gunshot wound to the abdomen followed by the development of colon cancer with metastasis to the liver. Recently, he had an intestinal stent placed in order to relieve an obstruction from tumoral growth. During the current admission, he was taken to the operating room for a diverting colostomy and two days later developed a fever of 101.1°F and increasing abdominal pain. Due to a concern for sepsis, blood cultures were collected and piperacillin-tazobactam was added to his antibiotic therapy regimen which already included vancomycin and ciprofloxacin.

Laboratory Identification

The blood culture signaled positive after less than 24 hours on the automated instrument and Gram stain revealed gram negative rods (Image 1). The organism grew as mucoid colonies on blood, chocolate and MacConkey agars after 24 hours of incubation at 35°C in 5% CO₂ (Image 2). When the blood agar plate was examined with a light source, the organism clearly illustrated beta hemolysis (Image 3). Rapid biochemical testing was positive for catalase, oxidase and indole. The Vitek II identified the isolate as Aeromonas veronii bv. sobria.

Discussion 

Aeromonas spp. are facultative anaerobic gram negative rods. They are inhabitants of aquatic ecosystems and as such can cause wound infections in people exposed to polluted lakes or brackish water with fresh breaks in their skin. Additionally, gastroenteritis is common with Aeromonas spp. and are often acquired through ingestion of unpurified water or to a lesser extent by consumption of contaminated meats, fresh produce or dairy products. Extraintestinal infections, including sepsis and meningitis, can result by spread from GI sources or wound infections. Interesting, medicinal leeches, used in the post-operative setting to increase blood flow to the surgical site, are colonized with Aeromonas spp. (most commonly Aeromonas veronii bv. sobria) and can result in systemic infections in the patient.

In the laboratory, Aeromonas spp. grow readily from stool, wound and blood sources on commonly used media and exhibits beta hemolysis on blood agar. In addition, Aeromonas spp. will grow on CIN agar (at room temperature as well as incubator temperature) as colonies with a pink center surrounded by a white apron and are indistinguishable from Yersinia spp. Aeromonas spp. is positive for catalase, oxidase and indole by rapid testing. In most cases, identification of Aeromonas spp. to the complex level can be accomplished by biochemical testing (esculin, VP), automated instrumentation or MALDI-TOF mass spectrometry. The three clinically relevant complexes include: A. hydrophila complex, A. caviae complex and A. veronii complex.

With regards to susceptibility testing for Aeromonas spp., the CLSI M45, 3^rd edition provides guidelines for the three complexes discussed above. Third or fourth generation cephalosporins, fluoroquinolones and trimethoprim-sulfamethoxazole are recommended as antibiotics for primary testing for isolates from extraintestinal sites. Aeromonas spp. are uniformly resistant to ampicillin, amoxicillin-clavulanate and cefazolin and many strains may possess various inducible beta lactamases.

In the case of our patient, with the laboratory identification of Aeromonas veronii bv. sobria, his gram negative coverage was switched to ciprofloxacin for a 10 day course. His PICC was removed and on further imaging studies he was found to have a large abdominal abscess which required surgical drainage. Subsequent cultures from the abdominal abscess were negative.

-Lisa Stempak, MD, is an Assistant Professor of Pathology at the University of Mississippi Medical Center in Jackson, MS. She is certified by the American Board of Pathology in Anatomic and Clinical Pathology as well as Medical Microbiology. She is the director of the Microbiology and Serology Laboratories. Her interests include infectious disease histology, process and quality improvement, and resident education.

Case History

The patient is a 79 y/o male with past medical history of rheumatic heart disease, permanent atrial fibrillation, mechanical aortic and mitral valves (2004), status post single chamber pace maker for bradycardia (2010), and prostate adenocarcinoma treated in 2000. He had new MRI compatible pace maker placed on Oct 19, 2017. During follow-up he was noted to have a hematoma over the incision site. He had a revision done on Nov 3, 2017. At that time, the blood from the incision site was sent for culture. 

Laboratory Identification

Gram stain showed moderate amount of polys with no bacteria seen. The isolate was a gram-negative rod that was identified on the MALDI-ToF as Burkholderia multivorans.

Discussion

The Burkholderia genus appears as gram-negative medium-sized straight rods, with the exception being B. mallei which is a coccobacillus. The will grow on blood, chocolate, and MacConkey agar. Oxidative-fermentative-base-polymyxin B-bacitracin-lactose (OFPBL) agar can be used to isolate B. cepacia and Ashdown medium can be used to isolate B. pseudomallei. They are non-lactose fermenters on MacConkey, but B. cepacia can turn into a dark pink to red due to oxidation of lactose after 4-7 days.

B. multivorans is a species within the Burkholderia genus, which are normal to plant, soil, and water, but not normally considered common human flora. Formerly of the Pseudomonas genus, B. cepacia, B. mallei, and B. pseudomallei are the most commonly seen as infections in humans. Further, B. cepacia and B. mallei are not typically human pathogens in a healthy human host. Because of the rarity of this genus to infect humans, their pathogenicity is not well known; but, importantly, they are intrinsically resistant to many antibiotics and can thus be associated with hospital acquired infections.

Of this genus, very little literature is present on B. multivorans specifically, and of the literature that does exist, most of it is in relation to cystic fibrosis patients. Taxonomic advances has shown that B. cepacia complex is a cluster of nine closesly related genomic species or genomorvars (1).  B. multivorans represents genomorvar II. Hospital acquired clinical infections from this complex (but perhaps not specifically from this particular genomorvar) has been seen following catheterization, cystoscopy, heart surgery, and with contaminated ventriculoatrial shunt (2). B. multivorans biochemically is oxidase positive, catalase positive, lipase positive, nitrate-reducing, urease positive, resistant to colistin, and can grow at 42C (3, 4).

A recent comparative genomic study showed that B. multivorans is a highly evolutionarily preserved genome with genomic characteristics from the environment and isolated from cystic fibrosis patients to be similar, and that isolates from different continents are also similar (5). Further, a murine model for pulmonary infections showed that B. multivorans could persist in the host by establishing an intracellular presence within macrophages, which could explain the persistence of this pathogen in cystic fibrosis patients (6). Importantly though, due to the conserved and common genomic structure, there rests a possibility for potential vaccination for cystic fibrosis patients against B. multivorans.

The patient was prescribed a single dose of oral Bactrim and then advised to come into the hospital for admission for IV antibiotics. IV ceftazidime was started with pending blood cultures, which are negative at the time of this documentation.

References:

1. Coenye T. et al. Taxonomy and identification of the Burkholderia cepacia complex. J Clin Microbiol 2001;39:3427-3436.
2. Pallent LJ. et al. Pseudomonas cepacia as contaminant and infective age. J Hosp Infect 1983;4:9-13.
3. Henry DA. et al. Phenotypic methods for determining genomovar status of Burkholderia cepacia complex. J Clin Microbiol 2001;39:1073-1078.
4. Vandamme P. et al. Occurrence of multiple genomovars of Burkholderia cepacia in patients with cystic fibrosis and proposal of Burkholderia multivorans sp. nov. Int J Syst Bacteriol 1997;47:1188-1200.
5. Peeters C. et al. Comparative genomics of Burkholderia multivorans, a ubiquitous pathogen with a highly conserved genomic structure. PLoS One. 2017, 21; 12 (4): e0176191.
6. Chu KK. et al. Persistence of Burkholderia multivorans with the Pulmonary Macrophage in the Murine Lung. Infect Immun 2004; 72 (10): 6142-6147.

-Jeff Covington, MD, PhD, is a 1^st year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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

Case history

A middle-aged male presented to the hospital emergency room with the complaints of malaise, shaking and chills for the last two days. He denied any runny nose, cough, abdominal pain, nausea, vomiting, headache or known sick contacts. His past medical history was significant for alcohol use disorder. Imaging of the abdomen revealed an ill-defined region of decreased attenuation in the right lobe of the liver measuring 4.8 x 4.7 x 2.2 cm. The Gram stain of the abscess showed 4+ WBCs (PMNs) and 4+ gram negative rods with a very large capsule surrounding them (Image 1).  The organisms grew very mucoid colonies on 5% sheep blood, chocolate, and MacConkey agars (Image 2).  A string test performed on the mucoid bacterial colonies was >5 mm (Image 3).

Discussion

The organism was identified as Klebsiella pneumoniae by MALDI-TOF MS.  Based on the mucoid capsule and positive string test, this organism was further identified as hypermucoviscous K. pneumoniae.

Hypermucoviscous K. pneumoniae is a relatively newly recognized hypervirulent variant of K. pneumoniae. It was first described in the Asian Pacific rim and is now increasingly recognized in Western countries. Defining clinical features include serious, life-threatening community-acquired infection in younger healthy hosts, an unusual feature for enteric gram negative bacilli in the non-immunocompromised population. It can cause a variety of diseases including, but not limited to liver abscess, pneumonia, meningitis, osteomyelitis, necrotizing fasciitis and endophthalmitis.

Intestinal colonization, appears to be a critical step leading to infection. It is seen mostly in Asians, raising the issue of a genetic predisposition vs. geospecific strain acquisition.  The increased virulence might be due to the ability to more efficiently acquire iron and perhaps an increase in capsule production, which confers the hypermucoviscous phenotype to the organism. The vehicles for acquisition and subsequent colonization appear to be food and water, person-to-person transmission (e.g., close contacts such as family members or sexual partners) or animal-to-person transmission (e.g., between pets and their owners).

To date, most strains of hypermucoviscous K. pneumoniae have been very susceptible to antimicrobials except ampicillin.  However, in recent literature, propensity for hypermucoviscous Klebsiella pneumoniae to become multi-, extreme or pandrug-resistant, including the acquisition of extended-spectrum β-lactamases (ESBL) and carbapenemases has been reported. Since hypermucoviscous K. pneumoniae strains often cause abscesses, source control is a major aspect of the overall management plan and a need to drain abscesses and closed space infections is essential for optimal outcome.

References

1. Alyssa S. Shon, Rajinder P.S. Bajwa and Thomas A. Russo; Hypervirulent (hypermucoviscous) Klebsiella pneumonia: A new and dangerous breed; Virulence 4:2, 107–118; February 15, 2013; 2013 Landes Bioscience
2. Bonnie C Prokesch, Michael TeKippe, Jiwoong Kim, Prithvi Raj, Erin McElvania TeKippe, David E Greenberg; Primary osteomyelitis caused by hypervirulent Klebsiella pneumonia; The Lancet Infectious Diseases , Volume 16 , Issue 9 , e190 – e195

-Muhammad Ahmad, MD is a 2^nd year anatomic and clinical pathology resident at University of Chicago (NorthShore) program based at Evanston Hospital, Evanston, IL. His academic interests include breast pathology and cytopathology.

-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois.

Case History

A 28 y/o female with a past medical history of chronic eosinophilic pneumonia, chronic persistent asthma, and elevated IgE status post Xolair therapy presented with a cough. She is a former smoker and a former IV drug user. She has been having a productive cough since March and has not improved despite multiple courses of antibiotic therapy. She coughs mostly in the morning and describes her sputum as thick and greenish. She does not have any associated fevers and does not feel that her rescue inhalers help much. She was given a course of doxycycline for 10 days, and sputum was sent for culture.

Laboratory Identification

One of the gram negative rods was identified by the MALDI-ToF as Pasteurella multocida.

Discussion

The genus Pasteurella consists of multiple identified species with the one most commonly seen in the clinical setting as Pasteurella multocida. As a genus, they are typically gram-negative straight bacilli that are nonmotile, oxidase-positive, catalase-positive, nitrate reducing, and ferment glucose. They will grow on blood and on chocolate agars, but importantly will not grow on MacConkey. Their colony morphology on blood agar is generally convex, smooth, and nonhemolytic.

Infections with Pasteurella are classically associated with animal bites, such as from a dog or cat. However, prior cases in the literature have shown that pulmonary infection with Pasteurella can be associated with other chronic pulmonary diseases such as COPD (1). The choice for using doxycycline is supported in the literature and was specifically discussed in a prior case with improvement (2).

References:

1. Klein NC. et al. Pasteurella multocida pneumonia. Semin Respir Infect 1997; 12 (1): 54-56.
2. Bhat S. et al. A case of lower respiratory tract infection with canine-associated Pasteurella canis in a patient with chronic obstructive pulmonary disease. J Clin Diagn Res 2015; 9 (8): DD03-DD04.

-Jeff Covington, MD, PhD, is a 1^st year anatomic and clinical pathology resident at the University of Vermont Medical Center.

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