First Report of a Human Isolate ofErwinia persicinus

Bacterial strains.The strains used in this study are listed in Table 1. All were maintained at −70°C in defibrinated sheep blood. All strains were passed twice on Trypticase soy agar with 5% sheep blood (Becton Dickinson Microbiology Systems, Sparks, Md.) before being used.

Media and biochemicals.The biochemical tests were performed on conventional media by the methods of Ewing (4) and by using some of the modifications described by Farmer et al. (5) and by Hickman and Farmer (7). Incubations were at 35°C, and test results were read at 24 h, 48 h, and 7 days, unless otherwise noted. Commercially available media were used whenever possible.

Antimicrobial susceptibility.Antimicrobial susceptibility profiles were determined for seven strains by the Kirby-Bauer disk diffusion method (8). MICs were determined by using a broth microdilution method and cation-supplemented Mueller-Hinton broth (9).

DNA methods.The preparation, isolation, and purification of labeled and unlabeled DNA, the method used for DNA reassociation, and the method used to separate single-stranded and double-stranded DNAs on hydroxyapatite have been described elsewhere (1, 2). The DNAs were labeled enzymatically in vitro with [³²P]dCTP by using a nick-translation reagent kit (Bethesda Research Laboratories, Inc., Gaithersburg, Md.) as directed by the manufacturer.

Results and discussion.Labeled DNA from E. persicinus 9108-82^T was shown to be 81 to 100% related (average, 87%) to unlabeled DNA from four other confirmedE. persicinus strains tested in 60°C reactions (Table 1). Divergence within the related sequences averaged 3%, and the degree of relatedness in reactions at 75°C was 76 to 98% (average, 86%).E. persicinus was 62% related to the type strain ofErwinia rhapontici, 50% related to a second E. rhapontici strain, and 49% related to Pantoea agglomerans. The percent divergence to these three strains was 10.0 to 10.5. The degree of relatedness of labeled DNA from E. persicinus 9108-82 to that of the human strain (strain 4073-83) was 95% at 60°C, with 3.5% divergence, and 86% at 75°C. The type strain showed a similar level of relatedness to the strain isolated from tuna (strain 839-82). These relatedness values leave no doubt that the human and tuna strains are E. persicinus.

The biochemical profiles of the two newly identified strains are characteristic of the profiles found for E. persicinusstrains (Table 2). Reactions that differ from those of the type strain include the methyl red, Voges-Proskauer, Simmons citrate, rhamnose, esculin, melibiose, and galactose reactions. Partial differentiation from other Enterobacter species,E. rhapontici, and Pantoea species is presented in Table 3. Accurate identification ofE. persicinus in the clinical laboratory may not be possible without the use of the extended set of conventional biochemicals listed in Table 2. Hao et al. (6) reported that all five strains in their study produced a water-soluble pink pigment when grown on peptone yeast agar supplemented with 1% glucose at 20, 25, and 30°C. Of the seven strains that we studied, strains 9108-82^T and 4073-83 produced pigment at 25°C and strain 9109-82 produced pigment at both 25 and 30°C on this same medium.

Strain 4073-83 was isolated from the urine of an 88-year-old female who presented with a urinary tract infection. The clinical history of the patient was extremely sparse; however, she had a history of atherosclerotic coronary vascular disease with congestive heart failure, hypertension, and diabetes mellitus. Her diagnoses also included a lower leg hematoma and stasis dermatitis. Her medications included indomethacin (Indocin; 25 mg three times daily [t.i.d.]), methyldopa (Aldomet; 250 mg t.i.d.), chlorpropamide (Diabinese; 250 mg daily), dipyridamole (Persantine; 25 mg t.i.d.), digoxin (Lanoxin; 0.25 mg every 3rd day), hydrochlorothiazide-triamterene (Dyazide; twice daily), furosemide (Lasix; 40 mg t.i.d.), phenytoin (Dilantin; t.i.d.), and potassium chloride (Slow K; 600 mg t.i.d.) but included no antimicrobial agents. She had been receiving most of these medications for the previous 18 months. Data regarding the colony count associated with this isolate was unavailable, making its significance in this patient unclear.

Strain 839-82 was isolated from raw tuna in Berlin, Germany. The isolate produced histamine, but it is unknown if this strain was associated with a foodborne disease.

Antimicrobial susceptibility data are shown in Table4. All seven strains are susceptible to all 23 agents tested with the exception of ampicillin, ticarcillin, and cefazolin. The susceptibilities for these last three antimicrobial agents are at the threshold of the intermediate-resistance breakpoint.

Data for E. persicinus are not included in the database of any commercially available identification product. If inoculated into any of these products, the isolate would most likely be identified asP. agglomerans. Such isolates should be examined further to determine whether they are E. persicinus so that the full spectrum of disease associated with this species can be further defined.