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Journal of Clinical Microbiology, June 2003, p. 2752-2754, Vol. 41, No. 6
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.6.2752-2754.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
R. M. Alden Research Laboratory,1 Infectious Diseases Division,2 Microbiology Laboratory, St. John's Hospital Health Center, Santa Monica, California 904043
Received 26 December 2002/ Returned for modification 27 January 2003/ Accepted 26 February 2003
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View this table: [in a new window] |
TABLE 1. Characteristics of 16 cases of Desulfovibrio infections in humansa
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The two sets of blood cultures collected by the emergency department were flagged positive by the BACTEC 9240 blood culture system (Becton Dickinson) in anaerobic Lytic-10 medium after 60 h of incubation. Gram stains revealed gram-negative spiral bacilli, and wet mounts made from centrifuged concentrates showed that the organisms were motile. The contents of positive vials were subcultured to chocolate and blood agars incubated at 35°C in 6% CO2, to MacConkey agar incubated aerobically at 35°C, and to CDC anaerobic blood agar incubated anaerobically at 35°C. After 4 days, small translucent colonies appeared on the anaerobic media; the aerobic plates remained negative. The isolate was sent to the R. M. Alden Research Laboratory for identification. It was categorized as a Desulfovibrio species on the basis of morphology, motility, obligate anaerobic requirements, the lack of saccharolytic activity, a positive desulfoviridin test, and the production of H2S (5). Identification of the species was performed by Quest Diagnostics (San Juan Capistrano, Calif.) with a MicroSeq 500 16S ribosomal DNA sequencing kit (Applied Biosystems, Foster City, Calif.), which sequences the first 500 bp of the 16S rRNA gene. The DNA was first amplified by PCR, purified, and then sequenced by the dideoxy chain termination cycle sequencing method. The sequenced products were purified and resolved by capillary electrophoresis on an ABI 3700 DNA sequencer and analyzed with ABI Sequencing Analysis software. The resulting DNA sequence was compared by means of MicroSeq analysis software to Applied Biosystem's library of 16 ribosomal DNA bacterial sequences. In addition, the sequences were also compared against those in public databases. The isolate was identified as D. desulfuricans.
Our isolate was beta-lactamase positive (per testing with nitrocefin), and the indicated MICs of the following antimicrobial agents for this isolate were determined by using the NCCLS agar dilution method (11): penicillin, >4 µg/ml; amoxicillin-clavulanate, 0.5 µg/ml; ampicillin-sulbactam, 1.0 µg/ml; piperacillin-tazobactam, 64/4 µg/ml; ticarcillin-clavulanate, 2/2 µg/ml; ceftriaxone, 16 µg/ml; cefoxitin, >128 µg/ml; levofloxacin, 0.5 µg/ml; moxifloxacin, gatifloxacin, and metronidazole, 0.125 µg/ml; clindamycin, 0.25 µg/ml; chloramphenicol, 8 µg/ml; and imipenem and ertapenem, 0.25 µg/ml. By the Etest, doxycycline had an MIC of 0.38 µg/ml for the isolate. The Etest was used for doxycycline because we did not have powder for the agar dilution test. The Etest was easy to read and could be used to test other agents as needed.
Desulfovibrio is infrequently the cause of human or veterinary infection (2, 4, 6, 7, 9, 10, 12, 13, 14, 15). To date, this organism has been found to have been the sole isolate in five cases of bacteremia. In three of these cases, the organism was determined to be D. fairfieldensis, in one case the organism was D. desulfuricans, and in one case the organism was identified only to the genus level. One of the cases of bacteremia was associated with a multibacterial abdominal infection from which a genetically identical D. fairfieldensis strain. Most reports do not identify the species, so scant data on the relative rates of occurrence of the different Desulfovibrio species are available. Loubinoux et al. (7) have suggested that while Desulfovibrio may be a weak, opportunistic pathogen, it appears that D. fairfieldensis "may possess a higher pathogenic potential than other Desulfovibrio species" since it has accounted for the majority of monobacterial isolations, mostly from bacteremic cases. Our case is the second report of D. desulfuricans bacteremia as a monobacterial infection, which suggests that this species also exhibits pathogenic potential. Eight of the 16 isolates (50%) have been obtained from patients with appendicitis and/or intra-abdominal abscesses, and in six other cases, the suspected source was an intra-abdominal process. Our case was associated with a diarrheal disease that occurred approximately 10 days prior to the onset of illness, but no gastroenterological symptoms were present immediately prior to the bacteremia, which suggests that there was a possible intestinal colonization and subsequent invasion.
One case of D. desulficans bacteremia was reported for a 2.5-year-old Labrador retriever with a fever of 105°F, anorexia, a tense abdomen, and rear-limb stiffness (14). The dog was treated and cured with doxycycline. An abdominal source of infection was suspected but not proven.
The optimal antimicrobial therapy for Desulfovibrio infection remains undetermined. In the cases reported, diverse therapeutic regimens have been used. Patients have been treated with multiple antimicrobials, including metronidazole, doxycycline, ceftriaxone, cefotaxime, ciprofloxacin, and ampicillin. Lozniewski et al., using an agar dilution method with supplemented Brucella agar as the basal medium and reading the results at 48 h (8), reported the in vitro susceptibilities of 16 clinical isolates of Desulfovbrio species. Loubinoux et al. (7) used Wilkins-Chalgren agar and read results at 96 h because of the "slow growth of the organism." They noted that all isolates were susceptible to imipenem (MIC at which 90% of the isolates were inhibited, 0.5 µg/ml; range, 0.125 to 1 µg/ml) and metronidazole (MIC at which 90% of the isolates were inhibited, 0.25 µg/ml; range, 0.125 to 1 µg/ml) but that penicillin G, piperacillin (with and without tazobactam), and cefoxitin were "devoid of significant antimicrobial activity." Six isolates had a positive nitrocefin test, which suggests that class A beta-lactamase may be produced in some strains but that more than one mechanism of beta-lactamase resistance may be operative. Most isolates were susceptible to ciprofloxacin, chloramphenicol, and clindamycin. Our patient was treated empirically with doxycycline, to which the isolate was susceptible, and had a good response, as did the Labrador retriever (14). Lozniewski et al. (8) suggested that either imipenem or metronidazole should be the agent of choice to treat infections with Desulfovibrio spp., especially as these species were often isolated from mixed aerobic-anaerobic infections.
Motile, strictly anaerobic gram-negative rods are infrequently encountered in clinical specimens, especially in blood cultures. Several isolates of Anaerobiospirillum succiniciproducens have been referred to our lab during the past 20 years. These bacteria have a corkscrew shape and a jerky motility; ferment glucose, maltose, lactose, and sucrose; are desulfoviridin negative; and are sensitive to the 10-µg colistin disk. Desulfovibrio spp. are curved rods with a rapid, progressive motility; they are resistant to colistin, asaccharolytic, and, most importantly, desulfoviridin positive. Other saccharolytic, desulfoviridin-negative motile genera include Butyrivibrio, Succinimonas, Succinivibrio, Anaerovibrio, and Selenomonas. Asaccharolytic, desulfoviridin-negative genera include Wolinella and Campylobacter. Growth of the species of these two genera is stimulated by the addition of a formate-fumarate supplement to the broth media (5).
Desulfovibrio infections are an infrequent cause of human disease and are often associated with an intra-abdominal source. Empirical antimicrobial therapy with either imipenem or metronidazole should be considered.
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