Chronic diarrhea is a substantial contributor to morbidity in patients with human immunodeficiency virus (HIV) infection. Even after extensive evaluation, a pathogen often cannot be identified [1]. Recent studies of patients with diarrhea associated with the acquired immunodeficiency syndrome have described histopathologic findings of enteroadherent bacteria that produced attaching and effacing (AE) lesions on the intestinal cell [2, 3]. Such lesions are virulent characteristics expressed by the chromosomally encoded eaeA gene cluster of enteropathogenic Escherichia coli (EPEC). None of the bacteria recovered in these studies carried the eaeA gene [2, 3].

We report the isolation of an unusual EPEC-like strain in an HIV-infected man with a 10-month history of chronic, intermittent diarrhea and a weight loss of 9 kg. When diarrhea began, the patient's CD4 count was less than 100 cells/mm³. He had been receiving a combination of zidovudine and didanosine and treatment for presumptive disseminated Mycobacterium avium complex disease and antipneumocystosis prophylaxis. Examination of an ileal biopsy specimen showed intracellular Enterocytozoon bieneusi sporoblasts and spores. Examination of a colonic biopsy specimen showed multiple superficial V-shaped mucosal ulcers containing aggregates of small bacillary organisms. Some of these clearly produced AE lesions, as shown by electron microscopic examination (Figure 1). A stool sample was guaiac negative, and cultures yielded predominant non-lactose-fermenting, indole-negative E. coli. The latter could not be typed and was nonmotile. Strong evidence supports the pathogenic role of the isolate: 1) Molecular studies showed that the isolate was positive for eae by polymerase chain reaction (PCR) or colony hybridization and was negative for the EPEC-specific locus of the EPEC adherence factor and bundle-forming pilus gene or with the E. coli-specific enterotoxin probes [4]; 2) the fluorescent actin stain assay showed the AE interaction between the nonlactose-fermenting isolate and HCT-8 cells; and 3) the patient's diarrhea resolved promptly after treatment with oral ciprofloxacin (no treatment was given for the microsporidia).

View larger version (163K): [in this window] [in a new window]   Figure 1. Transmission electron µgraph showing attaching and effacing lesions on the surfaces of colonic mucosal epithelial cells. Small rod-shaped bacteria tightly adhere to the surfaces of epithelial cells, which have lost their microvilli. Other bacteria are present in endocytotic vacuoles within the epithelial cells. (Original magnification x 7000.).

Further prospective studies are needed to elucidate the role of potentially diarrheagenic E. coli organisms in chronic diarrhea and the related wasting syndrome seen in HIV-infected patients.