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Cardiobacterium hominis

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A Microbial Biorealm page on the genus KopeckyB


Higher order taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Cardiobacteriales; Cardiobacteriaceae; Cardiobacterium (17)


Cardiobacterium hominis (17)

NCBI: Taxonomy

Description and significance

Cardiobacterium hominis most literally means bacterium of the human heart. In 1962, C. hominis was first isolated from a patient with endocarditis (12). In 1964, Slotnick and Dougherty (16) described the bacteria and gave it the current name. C. hominis was recently classified in the Cardiobacteriaceae family due to 16S rRNA sequence studies (12). Two main distinguishing characteristics of C. hominis are its colonial morphology, slow growth rate, and its production of indole (2). C. hominis is a member of the HACEK group (Haemophilus aphrophilus, Actinobacillus actinomycetemcomitans, C hominis, Eikenella corrodens, and Kingella kingae), all Gram-negative bacilli, normally residing in the respiratory tract with a heightened capacity to produce endocardial infections. It is differentiated from the other four due to its positive oxidase reaction, production of indole, and absence of catalse activity and nitrate production. It grows optimally around 37°C and at a pH range of 7, which is fitting because it occurs in nasal flora in humans who run an internal temperature of about 37°C and a pH of 7 (1). In humans, it is also a part of the normal pharyngeal flora as it was found in the nose or throat in 68 out of 100 people as examined by Slotnick et al. (1964). Along with being found in the respiratory tract, C. hominis is occasionally found in the uterine, cervical, and vaginal cultures of women (3). C. hominis is important in the world of medicine as it is found in the blood of patients stricken with endocarditis, the inflammation of the inner membrane of the heart (11).

Genome structure

C. hominis has linear DNA and RNA with a genome size of 2,578,897 base pairs, where 59% of the genome codes for proteins (4, 5, 6). The gene trpC is notable in its genome as it codes for the protein indole-3-glycerol phosphate synthase, which is key in its characteristic ability to produce indole (7). Currently, little research has been done documenting the encoding of the genome, as it is a very rare human pathogen.

Cell structure and metabolism

C. hominis is a fastidious, Gram-negative, non-motile, facultatively anaerobic, indole-positive bacillus ranging from .5 – 2.25μm in length (13). It is oxidase-positive, therefore containing the enzyme cytochrome oxidase, catalase-negative, classifying it as an anaerobe, and urease-negative, therefore lacking the enzyme urease. It is actually pleomorphic but the media it is grown in determines the degree of pleomorphisism. Although it is a rod it expresses bulbous swelling of both ends and is characteristically grouped in chains, clusters, or rosettes. The metabolism classifies it as chemoorganotrophic for it strictly uses fermentation, producing lactic acid as the major product of glucose fermentation. It has been found to grow from blood in a number of different media under both aerobic and anaerobic conditions. However, it is defined as a facultative anaerobe because it will grow poorly in aerobic conditions unless the humidity is increased - similar to the environments of the human mouth and heart. Its growth is actually inhibited by the presence of riboflavin or flavin mononucleotide (1).


C. hominis is a pathogenic bacteria found naturally only in humans, as indicated by its name. However, studies have been done on animals by injecting large numbers of microorganisms only to observe very low virulence. The five HACEK bacteria are grouped together due to their shared ability to cause endocardial infections, they collectively cause about 5-10% of all valve endocarditis, or inflammation of heart tissue, associated with morbidity or mortality (11). C. hominis tends to form large, friable vegetations on the inner surface of the heart which are associated with significant cerebral embolisation in 30% of cases (2). Individually, C. hominis accounts for merely 0.1% of all cases of endocardits in the U.S., 90 reported cases to date (10), with 75% of these cases occurring in patients with abnormal valves. It has been found to target the mitral and aortic valves showing neither age nor sexual predilection (3). One study has shown that 44% of C. hominis endocarditis patients had a history of dental procedure or oral infection (2). These statistics describe the bacterium as a weak pathogen because individuals infected by it were already at a predisposition due to heart valve abnormalities, prosthetic valves, previous dental procedures, or poor dental hygiene. However, it is an opportunistic pathogen because upon mucosal disturbance, it can become invasive and pathogenic. Infection by C. hominis causing endocarditis is distinguished by its chronic course, averaging 169 days, the lack of infection outside the blood stream, and high sensitivity to treatment with penicillin (2). Common symptoms of C. hominis infections include fever, splenomegaly, peripheral embolic phenomenon, petachiae, and clubbing. If caught early, endocarditis by C. hominis can be treated with antibiotics, such as penicillin or ampicillin, but may need surgery (8). Cases have been reported where these antibiotics are ineffective due to a β-lactamase producing strain of C. hominis, in which case vancomycin is administered (9). However, if untreated, endocarditis can lead to permanent valve damage, embolism, stroke, or death. (3).

Current Research and or Application to Biotechnology

In 2011, a report was received of a new case of infectious endocarditis due to C. hominis except this time Wallet et al. were able to use a new, faster method of identification. C. hominis is not necessarily difficult to identify, it just takes a while to incubate if isolated from blood (5-6 days). At the University of Lille Nord de France, researchers eliminated the need to incubate culture for a long period of time and were able to confirm the identity of C. hominis in 50 hours by improving the automated detection system. Improvements were made by first isolating the Gram-negative bacillus in a blood culture then smearing a thin layer of the strain on a MALDI-steel plate. Using the MALDI-TOF (Matrix-Assisted Laser Desorption Ionization-Time of Flight) Mass Spectrometry automated sequencer, a 16S rDNA bacterial fragment was amplified from the bacteria and sequenced. In comparison with known C. hominis strain 6573 it showed 98% identity. This method proved to retain accuracy while being much faster than conventional methods of identifying C. hominis as the causative agent of endocarditis (12). I could be useful in the future as it decreases the diagnosis period allowing for sooner treatment and, in turn, recovery.

Hajjaji, Mansencal, and Dubourg performed another new method of identification of C. hominis endocarditis in last year as well. In December, 2011, a paper was submitted to the International Journal of Cardiology documenting the usefulness of positron emission tomography in diagnosing patients with C. hominis endocarditis. The case involves a 55 year-old man, with a history of heart valve surgery, admitted to the Ambroise Pare Hospital in France with suspected endocarditis. In its inauguration, a fluorine-18 fluorodeoxyglucose PET scan was performed. Resulting images of the initial portion of the aortic graft showed a circumferential and diffuse uptake, resulting in the diagnosis of infective endocarditis by C. hominis. In cases such as this, where the patient shows no signs of endocarditis in the blood or in echocardiography examinations, the PET scan may be useful to physicians in helping to diagnose infectious endocarditis (14).

In 2002, an interesting case study was published documenting C. hominis infecting a bioprothsetic heart valve to cause endocarditis to cause symptoms of septic arthritis. The patient was an 82 year-old man with ischemic cardiomyopathy who had a history of heart procedures and a bioprothsetic mitral valve replacement ten years earlier. The patient showed symptoms of immobilizing, painful swelling in the knee, aggressive night sweats, and a loss of 25 pounds in the month before admission. After a week in the hospital and numerous tests, the causative organism was identified as C. hominis. Doctors speculated that the infection was caused by a transient bacteremia from the gastrointestinal or upper respiratory tract. This was the first described case of C. hominis endocarditis presenting as septic arthritis. The case is worthy of noting because it shows this weakly pathogenic bacterium manifesting in a condition usually caused by highly virulent organisms (15).


1) Dewhirst, Floyd E. "Genus I. Cardiobacterium." Bergey's Manual of Systematic Bacteriology. By Bruce J. Paster. 2nd ed. Vol. II. New: Springer Science & Business Media, NY. 123-26. Print.

2) Wormser, G., and E. Bottone. "Cardiobacterium Hominis: Review of Microbiologic and Clinical Features." National Center for Biotechnology Information. U.S. National Library of Medicine, 1983. Web. 10 May 2012. <>.

3) Cleveland, Kerry O., Pierre Dorsainville, Burke Cunha, and Michael Gelfand. "Cardiobacterium." Medscape Reference, Aug. 2011. Web. 09 May 2012. <>.

4) "Cardiobacterium Hominis ATCC 15826." MiST2: Bacterial Genomes. Web. 09 May 2012. <>.

5) "Cardiobacterium Hominis Strain ATCC 15826 16S Ribosomal RNA, Partial Sequence." National Center for Biotechnology Information. U.S. National Library of Medicine. Web. 09 May 2012. <>.

6) "Cardiobacterium Hominis Strain ARUP UnID 195 16S Ribosomal RNA Gene, Partial Sequence." National Center for Biotechnology Information. U.S. National Library of Medicine. Web. 09 May 2012. <>.

7) Becker-Rudzik, M., BL Marrs, and DA Young. "Sequence of the Indoleglycerol Phosphate Synthase (trpC) Gene from Rhodobacter Capsulatus." National Center for Biotechnology Information. U.S. National Library of Medicine. Web. 09 May 2012. <>.

8) Brusch, John L., and Steven A. Conrad. "Infective Endocarditis." Medscape Reference, 29 Nov. 2011. Web. 09 May 2012. <>.

9) Po-Liang, Li, Hsueh Po-Ren, Hung Chien-Ching, Teng Lee-Jene, Jang Tsrang-Neng, and Luh Kwen-Tay. "Infective Endocarditis Complicated with Progressive Heart Failure Due to β-Lactamase-Producing Cardiobacterium Hominis." Journal of Clinical Microbiology. American Society for Microbiology, Feb. 2000. Web. 9 May 2012. <>.

10) Chentanez, Teera, Thana Khawcharoenporn, Nalurporn Chokrungvaranon, and James Joyner. "Cardiobacterium Hominis Endocarditis Presenting as Acute Embolic Stroke: A Case Report and Review of the Literature." Heart & Lung: The Journal of Acute and Critical Care 40.3 (2011): 262-69. Sciverse. Web. 9 May 2012. <>.

11) "Endocarditis." U.S. National Library of Medicine, 18 Nov. 0000. Web. 10 May 2012. <>.

12) Wallet, Frederic, Caroline Loiez, Christophe Decoene, and Rene Courcol. "Rapid Identification of Cardiobacterium Hominis by MALDI-TOF Mass Spectrometry during Infective Endocarditis." University of Lille Nord De France (2011): 327-29. Web. 9 May 2012. <>

13) Weaver, Robert E. "Genus Cardiobacterium." Bergey's Manual of Systematic Bacteriology. 1st ed. Vol. 1. Baltimore: Williams & Wilkins, 1984. 583-85. Print

14) Hajjaji, Imane, Nicolas Mansencal, and Olivier Dubourg. "Diagnosis of Cardiobacterium Hominis Endocarditis: Usefulness of Positron Emission Tomography." International Journal of Cardiology (2011). Sciverse, Jan. 2012. Web. 10 May 2012. <>.

15) Apisarnthanarak, Anucha, Raymond Johnson, Alan Braverman, William Dunne, and J.Russle Little. "Cardiobacterium Hominis Bioprosthetic Mitral Valve Endocarditis Presenting as Septic Arthritis." International Journal of Cardiology (2002). Sciverse, Jan. 2002. Web. 10 May 2012. <>.

16) Slotnick, I.J. and Dougherty, M. “Further characterization of an unclassified group of bacteria causing endocarditis in man: Cardiobacterium hominis” gen. et sp. n. Antonie van Leeuwenhoek, 30, 261–272. 1964.

17) "Cardiobacterium Hominis." U.S. National Library of Medicine. Web. 10 May 2012. <>.

Edited by Benjamin Kopecky, student of Dr. Lynn M Bedard, DePauw University