stain of the organism showed the presence of gram-nega- tive rods with subterminal endospores (Figure 1). The isolates were susceptible to penicillin G (MIC = 0.064 µ g/mL), clindamycin (MIC = 0.064 µ g/mL), and metronidazole (MIC = 0.032 µ g/mL) by Etest. Despite intense efforts, no other microorganisms were isolated from the blood or liver abscess specimens. Antimicrobial therapy was subsequently switched to intravenous ceftri- axone and metronidazole. After marked clinical improve- ment, the patient was discharged home on oral therapy. Conclusions Similar to certain members of the genus Clostridium (e.g., C. clostridioforme and C. ramosum), the organism has a propensity to stain gram negative (3). Subterminal, oval-to-round endospores may be visible. Strains may or may not be motile. Colonies are usually 3 mm in diameter after 72 hours of incubation and are nonhemolytic, grayish-white, opaque, convex, round, shiny, and have a slightly irregular margin (3), similar to our observations (Figure 2). Isolates are typically saccharolytic and ferment a variety of carbohydrate compounds but fail to hydrolyze gelatin or urea, reduce nitrate, or produce indole, lecithi- nase, or lipase (3). Although these phenotypic tests can possibly distinguish this organism from closely related species, these methods are too cumbersome and time-con- suming for routine use in the clinical setting. However, the increasing ease, availability, and affordability of identifica- tion methods that use DNA sequencing have identified uncommon microbial pathogens that are difficult to identi- fy and often encountered in the clinical microbiology lab- oratory. The 16S rRNA gene (≈1,500 bp in size) is ubiquitous in all eubacteria and has served as the principal target of bacterial identification protocols that are sequence-based. Each unique bacterial species has a dis- tinctive 16S rRNA gene sequence profile (signature); hence, the signatures of unknown bacteria can then be compared to publicly available or commercial sequence databases to determine if the organism belongs to a partic- ular known species. Although the sequence profile of our isolate (GenBank accession no. AY552788) was 99% identical to the type strain of C. hathewayi reported by Steer et al. (3) (GenBank accession no. AJ311620), the two sequences are believed to be completely identical since the 1% difference in the sequence profiles was attributed to uncharacterized bases in the sequence reported by Steer. C. hathewayi dis- plays the closest phylogenetic relationships with C. cel- erecresens and C. sphenoides (Figure 3), which may be found as part of the normal human colonic microflora (3,4). However, the natural habitat of C. hathewayi is not known. To the best of our knowledge, human infection caused by this bacterium has not been previously reported. Clostridium hathewayi Human Infection Figure 1. Gram strain of Clostridium hathewayi from growth on solid agar media. Note the gram-negative staining characteristics and presence of subterminal endospores. Magnification 1,000x. The two isolates described by Steer et al. (3) were recov- ered from a phytic acid-degrading, organism enriching chemostat that had been injected with human feces from healthy donors. In contrast, the isolation of C. hathewayi from our patient’s blood and hepatic abscess fluid speci- mens is convincing evidence of its clinical importance, although this finding needs to be corroborated by animal studies. The finding is not surprising, given that Clostridium spp. are not uncommonly implicated in cases of acute cholecystitis and associated bacteremia (5). Our Figure 2. Colonial morphology of Clostridium hathewayi on brucel- la blood agar media after 48 hours of anaerobic incubation. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 11, November 2004 1951