Microbiology Case Study: A 54 Year Old Woman with Fever

Patient History

A 54 year old woman is seen by her oncologist with complaints of rigors and fevers for the past two months. Her past medical history is significant for Stage IV Follicular Lymphoma. Previous treatment included rituximab and bendamustine that was completed a year prior. Currently her therapeutic plan is to receive rituximab maintenance therapy every two months (her most recent dose was 2 days prior to this visit) via a port. She has two dogs, both of which had a diarrheal illness three months prior. She has chickens and spent the summer RV camping around New England. She has not had diarrhea or noticed any rashes. Her travel history includes a trip to Europe  4 years prior. A blood culture was collected due to her fevers and rigors and was found to be positive 29 hours post incubation.

Gram stain of the blood culture bottle showed small, faintly staining gram negative, curved rods (Image 1). The patient was started on ciprofloxacin and referred to the infectious disease clinic. After 3 days of incubation, small slightly mucoid yellow gray colonies grew on 5% sheep blood and chocolate agar (Image 2). There was no growth on the MacConkey agar. Initial Gram stain revealed similar gram negative rods to the Gram stain performed on the blood culture media. MALDI-TOF identified the organism as Campylobacter jejuni. The patient was asked to stop taking ciprofloxacin and start azithromycin. She also had her port removed on this day. Four days after her oncology visit, the patient’s blood was negative for organisms. Her fever and rigors resolved as well. Susceptibility testing showed the organism to be resistant to ciprofloxacin and susceptible to azithromycin.

Image 1. Gram stain from the blood shows faintly staining curved gram negative rods.
Image 2. Growth on chocolate agar after 3 days (Not in a microaerophilic environment).


Campylobacter jejuni is a small, gram negative, curved rod. It is the most common cause of bacteria-mediated diarrheal disease globally (1). In immunocompromised patients, it can cause a variety of extraintestinal diseases: septicemia, meningitis, septic arthritis, and endocarditis (2). Infection can also lead to Guillain-Barre syndrome. This is an autoimmune disease of the peripheral nerves that is thought to be due to antigenic cross reactivity between the surface lipopolysaccharides of the bacteria and the patient’s peripheral nerve gangliosides (3). Of patients diagnosed with Guillain-Barre syndrome, 20-40% will have had a history of Campylobacter jejuni infection (2).

Campylobacter jejuni grows best at 42°C in a microaerophilic environment (5% O2,10% CO2, and 80% N2). It displays a darting motility in broth and will not grow in 3.5% NaCl. Almost all are oxidase and catalase positive. On Campy-BA, a selective blood agar plate for Campylobacter jejuni, colonies will be peach colored. This media is made up of a Brucella agar base, sheep red blood cells, and various antibiotics that suppress the growth of normal fecal flora(2).

Macrolides (erythromycin, azithromycin) are considered the treatment of choice, however it has been reported that resistance approaches 1.7% (1 and 2). Fluoroquinolones like ciprofloxacin can be used, however resistance is higher due to widespread use of this drug in medical and veterinarian practices and agricultural businesses.


  1. Yang W, Zhang M, Zhou J, Pang L, Wang G, Hou F. The Molecular Mechanisms of Ciprofloxacin Resistance in Clinical Campylobacter jejuni and Their Genotyping Characteristics in Beijing, China. Foodborne Pathog Dis. 2017;14(7):386-392.
  2. Tille P. Bailey & Scott’s Diagnostic Microbiology. Fourteenth Edition. Elsevier;2017.
  3. Murray P. Medical Microbiology. Seventh Edition. Elsevier; 2013.

-Angela Theiss, MD is a 3rd 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.

Microbiology Case Study: A 14 Year Old Female with 3 Day History of Abdominal Pain

Case History

A 14 year old Caucasian female was transferred to the pediatric emergency department from an outside hospital due to a 3 day history of abdominal pain. The pain was concentrated in the right lower quadrant and was accompanied by nausea and two episodes of vomiting. Her vital signs were normal and physical exam demonstrated tenderness and guarding upon palpation of the right lower quadrant of the abdomen. Her white blood cell count was elevated at 21.1 TH/cm2 and showed 91% neutrophils. Abdominal ultrasound was unremarkable and CT scan was inconclusive for appendicitis. The patient was taken to surgery for an exploratory laparotomy and her appendix was removed.

Laboratory Identification

Image 1. Microscopic review revealed a female nematode with characteristic cephalic inflations, numerous eggs in the uterine cavity, and an intestinal cavity at the posterior end (H&E, 20x).
Image 2. Numerous oval shaped eggs with a thick shell that are slightly flattened on one side were observed (H&E, 200x). The eggs measured 55 x 25 um in dimension.

Gross examination of the appendectomy specimen showed an unremarkable appendix that measured 5.7 cm in length by 0.7 cm in diameter. There was no evidence of perforation. On sectioning, a small, white, “worm-like” structure (0.6 x 0.1 cm) was identified at the tip of the appendix and submitted for histologic examination. Microscopic review identified a female nematode with many eggs characteristic of Enterobius vermicularis. There was no acute inflammatory process identified upon microscopic review of the appendix.


Enterobius vermicularis, commonly referred to as pinworm, is a nematode infection that frequently presents as perianal itching in young children or those living in crowded settings, with symptoms most prominent in the evening and night time. Adult female worms reside in the cecum of the large intestine and migrate to the perianal area during the night to lay eggs, resulting in irritation. Often, infections can be asymptomatic as well. E. vermicularis is one of the most common helminthic infections in the United States.  

Humans are the only known host of E. vermicularis and become infected by ingesting embryonated eggs from feces or handling contaminated materials such as clothing, bed linens or from bathroom surfaces. Pinworm has a direct lifecycle and the larvae hatch in the small intestines and develop into adult worms that occupy the colon. It takes about one month from ingestion of infective eggs for E. vermicularis eggs then to be shed on the perianal folds.

Laboratory identification of E. vermicularis is usually made by using a piece of scotch tape or an adhesive paddle applied to the perianal skin in the morning and then visualizing the eggs microscopically. The eggs of pinworm are oval in shape & are flattened on one side with a thick capsule and measure between 50-60 x 20-30 um in size.On occasion, the eggs can be seen on pap smears as well. E. vermicularis worms can sometimes be visualized during colonoscopy, gastrointestinal & pelvic surgeries, and are capable of being identified by histology. Histologic sections of adult E. vermicularis worms usually show prominent lateral alae on the outer surface, testis or ovaries depending on the sex of the worm, and the intestinal tract. In gravid female worms, the characteristic eggs are numerous and can be helpful in the identification. 

Treatment options of an E. vermicularis infection include an initial dose of albendazole, mebendazole,or pyrantel pamoate followed by a second dose two weeks later to prevent possible reinfection. Family members and other close contacts may be treated as well ensure eradication. In the case of our patient, her post-surgical course was uneventful and her white blood cell count trended down to 7.0 TH/cm2 after surgery. She was discharged home the following day. 

-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 Clinical Pathology as well as the Microbiology and Serology Laboratories.  Her interests include infectious disease histology, process and quality improvement, and resident education.

Microbiology Case Study: A 31 Year Old Man with History of IV Drug Use

Case History

The patient is a 31 year old man with a history of intravenous drug use with last reported use nine months previous, who reports low back pain. The patient’s symptoms started as a mild pain and progressively worsened over two weeks to the point that he was unable to stand or ambulate. He also developed intermittent radiation of pain to the bilateral lower extremities and associated symptoms of chills and diaphoresis. Blood cultures were sent. MRI showed an epidural abscess at the level of L5-S1. The patient underwent lumbar spinal decompression surgery, and intra-operative cultures were sent for evaluation.

Laboratory Identification

Gram smear of blood cultures showed gram negative bacilli (Image 1). Culture of the abscess specimen and blood cultures showed growth on chocolate, blood, and MacConkey agar; growth on MacConkey plates did not show lactose fermentation (Image 2,3). MALDI-TOF identified this organism as Serratia marcescens.

Image 1. Gram stain of blood culture showing gram negative rods.
Image 2. Blood agar showing large colonies without hemolysis.
Image 3. MacConkey agar showing non lactose fermenting colonies.


Serratia marcescens is a motile, facultatively anaerobic, gram negative bacillus of the Enterobacteriaciae family. Some strains of Serratia produce a distinctive brick red pigment, prodigiosin (Image 4), although non pigmented strains are frequently isolated from human infection sites. Serratia marcescens is one of the few Enterobacteriacea that produces DNAse, lipase, and gelatinase. It does not usually ferment lactose. This species is widely present in the environment, including in animals, insects, plants, water, and soil, but unlike other Enterobacteriaciae species it is not a typical component of normal human fecal flora.

Image 4. Colonies of Serratia marcescens producing red pigment. Photo from the CDC Public Health Image Library (https://phil.cdc.gov/Details.aspx?pid=10544).

Eight species of Serratia have been found to cause infections in humans. Of these, >90% are caused by Serratia marcescens (1). This is a rare cause of infection in immunocompetent hosts but can cause opportunistic nosocomial infections, especially following invasive procedures such as such as intravenous catheterization, respiratory intubation, and urinary tract manipulations. The most common infections caused by Serratia marcescens are urinary tract infections, pneumonia,surgical wound infections, eye infections, and bacteremia. Multiple hospital outbreaks of Serratia have been reported, with sources of infection including tap water, soap, blood transfusion products, and injected medications (2). It has also been described as a cause of endocarditis in injection drug users (3).

Serratia is intrinsically resistant to ampicillin, ampicillin-sulbactam, and 1st and 2nd generation cephalosporins due to an inducible, chromosomal AmpC beta-lactamase. Resistance to later-generation cephalosporins may be induced through exposure to these antibiotics, despite not being detected on initial antibiotic susceptibility tests. Thus, susceptibility testing is misleading and thirdgeneration cephalosporins (such as ceftazidime, ceftriaxone, and cefpodoxime) should be avoided for the treatment of Serratia species regardless of in vitro susceptibility.


  1. Laupland KB, Parkins MD, Gregson DB, Church DL, Ross T, Pitout JD. Population-based laboratory surveillance for Serratia species isolates in a large Canadian health region. Eur J Clin Microbiol Infect Dis. 2008; 27: 89–95.
  2. Mahlen SD. Serratia infections: from military experiments to current practice. Clin Microbiol Rev. 2011; 24:755.
  3. Mills J., Drew D. Serratia marcescens endocarditis: a regional illness associated with intravenous drug abuse. Ann Intern Med. 1976; 84:29–35.

-Erica Worswick is a pathology student fellow 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.

Microbiology Case Study: A 54 Year Old Male with Shortness of Breath

Case History

A 54 year old male presented in the emergency room with worsening of shortness of breath and chest pain. He has a history of a bicuspid aortic valve that was treated with bio-prosthetic aortic valve replacement seventeen years ago and a second aortic valve replacement seven years ago. The patient’s echocardiogram showed severe aorticstenosis and moderate to severe mitral regurgitation. During hospital stay he started to show signs of low cardiac output syndrome and an intra-aortic balloon pump was placed. During sternotomy for aortic valve replacement and mitral valve repair they discovered a severely calcified and stenotic valve with additional debris that could be consistent with endocarditis. Tissue culture was sent.

Gram stain showed pink strings that could be gram negative rods, but could also be tissue debris due to tissue grinding (Image 1). After 3 days of incubation, some colonies grew on 5% sheep blood (Image 2) and chocolate agar plates with no growth on MacConkey selective medium.

Colony Gram stain made from these colonies (Image 3) was compared with the initial gram stain and showed similar type of pleomorphic gram negative rods. MALDI-TOF identified this organism as Cardiobacterium hominis.

Image 1. Tissue Gram stain showing pleomorphic gram negative rods or tissue debris (difficult to say which).
Image 2. Growth of organism after 3 days on 5% sheep blood agar.
Image 3. Colony Gram stain from shows same pleomorphic forms seen on primary tissue Gram stain, which is consistent with Cardiobacterium hominis.


Cardiobacterium hominis is a fastidious, pleomorphic, non-motile, gram negative bacillus and member of the HACEK group which comprises Haemophilus species, Aggregatibacter, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae. C. hominis is present as normal flora of the oropharynx in most individuals but it has also been attributed to cause infective endocarditis.

C hominis is a fastidious bacterium that grows best in the presence of increased levels of CO2 and high levels of humidity and often takes several days to grow on solid media (1). It can be distinguished from other HACEK members by a positive oxidase reaction, the production of indole and the absence of catalase activity and nitrate production.

Some of the risk factors leading to C hominis endocarditis include dental work, structural cardiac abnormalities, previous valve replacement, dilated cardiomyopathy and past history of rheumatic heart disease and endocarditis (2). The illness usually follows a sub acute course with symptoms lasting for weeks or months (1). Patients will often report fever, myalgia, anorexia, and weight loss. C. hominis tends to form large, friable vegetations associated with cerebral embolization or mycotic aneurysm formation and this might be responsible for atypical presentation of endocarditis(1). The overall prognosis of endocarditis due to C. hominis is quite favorable, despite the frequent need fo rvalve replacement (3).

Third generation cephalosporin (ceftriaxone) is considered the drug of choice for C. hominis endocarditis. Ampicillin can be used after susceptibility testing. Ampicillin-sulbactam or ciprofloxacin are alternative therapeutic options.


  1. Currie, Codispoti, Mankad, et al. Late aortic homograft valve endocarditis caused by Cardiobacterium hominis: a case report and review of the literature. Heart 2000;83:579–581.
  2. Walkty A. Cardiobacterium hominis endocarditis: A case report and review of the literature. The Canadian Journal of Infectious Diseases & Medical Microbiology. 2005;16(5):293-297.
  3. Fazili T, Endy T, Javaid W, Amin M. Cardiobacterium Hominis Endocarditis of Bioprosthetic Pulmonic Valve: Case Report and Review of Literature. J Clin Case Rep. 2013;3:286.

-Kiran Manjee, MD, is a 1st year anatomic and clinical pathology resident at University of Chicago (NorthShore).

-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois. Follow Dr. McElvania on twitter @E-McElvania. 

Microbiology Case Study: A 21 Year Old With Chronic Kidney Disease

Case History

The patient is a 21 year old male with a history of developmental delay and chronic kidney disease secondary to posterior urethral valves, status post kidney transplant at age 14, who presents for a routine office visit with his pediatric nephrologist. In the past year, he has had chronic antibody-mediated transplant rejection despite immunosuppression. In addition, he drinks 1-1.5 gallons of water daily, self-catheterizes every three hours, and has an indwelling Foley at night. During the office visit, he denies any urinary symptoms, including dysuria, hematuria, cloudy urine, reduced output, or fever. However, given his significant risk factors for urinary tract infection, his provider orders a urinalysis and urine culture.

Laboratory Identification

The urine was noted to be cloudy, was positive for nitrites and leukocyte esterase, and had 11-50 white blood cells per high-powered field. 

Urine culture demonstrated the growth of two organisms, one of which was identified to be greater than 100,000 CFU of Proteus miribalis, and the second of which grew 10,000-100,000 CFU, was isolated, and is shown below:

Image 1. Appearance of the second organism’s growth on blood agar after the bile solubility test.
Image 2. Gram stain showing gram positive diplococci.

Mass spectrometry by MALDI-TOF confirmed that this second organism is Streptococcus pneumoniae, a bile-soluble gram positive diplococci. 


S pneumoniae is implicated in a number of diseases, but it is an uncommon pathogen in the urine. Several case-series and case reports have been published demonstrating a predilection of pathogenic urinary S pneumoniae for pediatric patients with urinary tract abnormalities. In one series, 26 urine cultures from 18 patients were identified as growing S pneumoniae, with CFU counts ranging from 100 to 100,000. Sixteen of the 26 cultures grew only S pneumoniae. Of the 18 patients, only six were adults, eight had had a kidney transplant, and four others had chronic problems with their kidneys (1). In another series of three pediatric cases, one patient had congenital bilateral duplication of the renal collecting system, one had a “congenital imperforate anus (high type 1A) with a rectovesical fistula and grade 4 bilateral vesicoureteral reflux,” and the third had bilateral renal dysplasia (2). Neither case series was able to identify a specific serotype of S pneumoniae responsible for these infections.

As discussed by Choi et al, the altered flow dynamics of the abnormal urinary systems in these patients may be compromising normal host immune clearance mechanisms, thereby increasing the susceptibility to infection (2, 3). However, it is unclear why S pneumoniae infections have a predilection for congenital urinary tract abnormalities, as opposed to all urinary tract abnormalities. Choi et al postulate that some of the gene polymorphisms known to predispose individuals to UTI or pneumococcal infections could be genetically linked to genes responsible for urinary tract abnormalities, thus increasing the probability that an individual with a congenital urinary tract abnormality would have an S pneumoniae urinary tract infection (2,4).

Given the patient’s history and risk factors, the presence of S pneumoniae in his urine was found to be significant. Treatment of both organisms and appropriate follow-up was recommended.


  1. Burckhardt, Irene, Jessica Panitz, Mark van der Linden, and Stefan Zimmermann.  “Streptococcus pneumoniae as an agent of urinary tract infections – a laboratory experience from 2010 to 2014 and further characterization of strains.”  Diagnostic Microbiology and Infectious Disease.  2016; 86: 97-101.
  2. Choi, Rihwa, Youngeun Ma, Kyung Sun Park,  Nam Yong Lee, Hee Yeon Cho, and Yae-Jean Kim.  “Streptococcus Pneumoniae as a uropathogen in children with urinary tract abnormalities.”  The Pediatric Infectious Disease Journal.  2013; 32(12): 1386-1388.
  3. Bogaert, D, R de Groot, PWM Hermans.  “Streptococcus pneumoniae colonization: the key to pneumococcal disease.”  The Lancet Infectious Diseases.  2004; 4(3): 144-154.
  4. Yuan, Fang Fang, Katherine Marks, Melanie Wong, Sarah Watson, Ellen de Leon, Peter Bruce McIntyre, John Stephen Sullivan.  “Clinical relevance of TLR2, TLR4, CD14, and Fc gamma RIIA gene polymorphisms in Streptococcus pneumoniae infection.”  Immunology and Cell Biology.  2008; 86(3): 268-270.

-Fritz Eyerer, MD is a first 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.

Microbiology Case Study: A 44 Year Old Man with Severe Back Pain

Case History

A 44 year old male presented to the emergency department with severe, throbbing back pain in his mid-thoracic spine. He states the pain began a couple weeks ago and noted no recent fevers or night sweats, but does admit to chills. His past medical history is significant for end stage renal disease requiring dialysis, insulin dependent diabetes mellitus, and multiple amputations. On physical examination, there was tenderness to palpation along spine in mid-thoracic region. Lab work showed a normal white blood cell count, C reactive protein of 0.90 mg/dL (0.00 – 0.50 mg/dL), and an erythrocyte sedimentation rate of 60.0 mm/hr  (0.0 -10.0 mm/hr). MRI of the spine was consistent with discitis and osteomyelitis at T7-8 with compression fractures causing spinal stenosis and cord compression. Given the concern for an infection process, blood cultures were collected and interventional radiology performed a bone biopsy. The specimen was sent for bacterial, fungal, and AFB cultures as well as for histology.

Laboratory Identification

Image 1. Discrete, creamy colonies growing on blood agar (left) and Sabouraud dextrose agar (right) after 48 hours of incubation at 35°C.
Image 2. Fragments of bone with focal necrosis, foci of acute and chronic inflammation with clusters of yeast forms and pseudohyphae consistent with a Candida spp. infection.

The organism grew as discrete, creamy colonies growing on blood agar and Sabouraud dextrose agar after 48 hours of incubation at 35°C and resembled a yeast. MALDI-TOF mass spectrometry identified the isolate as Candida parapsilosis.  Similarly, the surgical pathology specimen showed necrotic bone with inflammation and yeast forms and pseudohyphae consistent with a Candida spp. infection. Blood cultures were negative. On chart review from an outside hospital, it was discovered the patient had an episode of candidemia ten months ago which was thought to be related to his dialysis port.


Yeasts are ubiquitous in the environment and make up the normal microbiota of human skin as well as the oral cavity, gastrointestinal tract and genitourinary tract. In general, when Candida spp. cause infections it is thought to an opportunistic infection acquired endogenously and due to exposure to prolonged antibiotics, suppressed immune system, or as a result of intravascular catheters. Those with diabetes mellitus, mucositis, bowel perforations, and intravenous drug users are most susceptible. Infections with Candida parapsilosis are becoming more common, and have the potential to cause invasive disease, such as fungal endocarditis and severe infections in the neonatal population. 

In the microbiology laboratory, C. parapsilosis grows rapidly as discrete, creamy colonies on a variety of agars. On cornmeal-Tween 80 agar, C. parapsilosis grows as short, curved pseudohyphae with blastoconidia arranged singly or in small clusters at points of constriction. The arrangement is sometimes described as resembling a sage bush. C. parapsilosis is germ tube negative and is negative for urease. In many laboratories currently, identification is achieved by automated methods, such as Vitek 2, or mass spectrometry, allowing for more rapid and accurate identification.  

Anti-fungals, such as echinocandins, azoles, and amphotericin B, are all potential therapeutic options to treat C. parapsilosis infections. CLSI C.parapsilosis specific breakpoints exist for fluconazole, voriconazole,micafungin, caspofungin, and anidulafungin in the M27-S4. Susceptibility testing should be performed on significant isolates from normally sterile sites.

In the case of our patient, infectious disease was consulted and he was started on IV micafungin and then transitioned to oral fluconazole. He had a transesophgeal echo and eye exam performed to ensure he didn’t have endocarditis or an invasive eye infection due to hematogenous spread of the yeast. He was discharged home on long term oral fluconazole.  

-Rim Alkawas, MD, is a second year Anatomic and Clinical Pathology resident at the University of Mississippi Medical Center. 

-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 Clinical Pathology as well as the Microbiology and Serology Laboratories.  Her interests include infectious disease histology, process and quality improvement, and resident education.

Microbiology Case Study: A Young Adult with A Skin Lesion

Case History

A young adult female presents to an urgent care clinic with the chief complaint of a “bump and surrounding redness” on her right medial thigh. The patient reports the bump had been present without change for 1 year. Approximately 2 days prior to presenting at the urgent care clinic the patient states she nicked the bump while shaving, and subsequently the bump became tender with surrounding erythema and produced purulent drainage. The patient denies any similar prior lesions and denies any significant past medical history. On physical exam, the lesion measured 1 cm with the surrounding erythema measuring 5cm. The urgent care physician performed an incision and drainage and noted a scant amount of white purulent material within the lesion. A cyst wall was identified and was removed as much as possible. A swab of the purulent material was collected and submitted to microbiology for culture.

Laboratory Identification

The primary gram smear of the swab specimen was interpreted as no bacteria or polys seen. Routine culture media including blood, chocolate, MacConkey, and CNA agar were inoculated and incubated aerobically. Following incubation, the blood agar showed few gram positive cocci consistent with usual skin flora and few single morphology of medium to large sized gray colonies without hemolysis. On the MacConkey agar, few single morphology non-lactose fermenting colonies were identified. The gray colonies identified on the blood agar gram stained as gram negative bacilli with unremarkable morphology. An oxidase test was performed and the bacteria was found to be oxidase positive. The key biochemical and physiologic characteristics of the isolate included: good growth on thiosulfate citrate bile salts and sucrose (TCBS) agar with yellow colonies, good growth in 6% NaCl nutrient broth, and no growth in 0% NaCl nutrient broth. The organism was identified by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) as Vibrio alginolyticus.

Image 1. Blood agar isolate of medium sized gray colonies.

Image 2. MacConkey agar with non-lactose fermenting colonies.


Vibrio spp. are water organisms commonly found in marine or brackish water environments. These organisms are gram negative bacilli which classically have “comma” shaped morphology on gram smear, though this is not an absolute. On sheep blood agar, these organisms are variably beta hemolytic medium to large gray colonies and on MacConkey agar are non-lactose fermenting (with the exception of Vibrio vulnificus)Vibrio spp. are oxidase positive, ferment glucose, and readily grow on most isolation media with growth being enhanced with the addition of 1% NaCl to the media. The growth characteristics on media containing different concentrations of NaCl can be used in differentiating the different Vibrio spp. Thiosulfate Citrate Bile Salts and Sucrose (TCBS) agar is both selective and differential for Vibrio spp. with sucrose fermentation being detected as yellow colony formation.

Vibrio angiolyticus typically causes extraintestinal infections, with wound infections and otitis externa being the most frequent. Transmission frequently occurs via traumatic aquatic injuries in contaminated water. Vibrio angiolyticus rarely causes intestinal disease and is isolated in less than 5% of stool cultures in patients with Vibrio associated diarrhea. Growth characteristics of Vibrio alginolyticus include yellow colonies on TCBS due to its ability to ferment sucrose and good growth on 6% NaCl and no growth on 0% NaCl. Additional key biochemical characteristics of Vibrio alginolyticus include oxidase positivity, nitrite positivity, negative for myo-Inositol fermentation, negative for arginine dihydrolase, positive for lysine decarboxylase, and variable positivity for ornithine decarboxylase. Most wound infections due to Vibrio alginolyticus are non-severe, and most mild infections will clear without antibiotic therapy.


  1. Procop GW, Koneman EW. Koneman’s Color Atlas and Textbook of Diagnostic Microbiology, North American Edition. LWW; 2016.
  2. Morris, J., Calderwodd, S., and Bloom, A. Minor Vibrio and Vibrio-like species associated with human disease. In: UpToDate, Post, TW (Ed), UpToDate, Waltham, MA, 2017.


-Justin Rueckert, DO is a 3nd 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.