A Man with a Saccular Aneurysm of the Left Common Iliac Artery: (Answer on pages 945–7)

Figure 2. Gram stain of a blood culture showing a gram-negative rod with bipolar staining, giving the cell a distinctive " safety pin " appearance (original magnification, ϫ1000). Figure 1. Magnetic resonance angiography showing a mycotic aneu-rysm of the left common iliac artery caused by Burkholderia pseudomallei. Diagnosis: A mycotic aneurysm due to Burkholderia pseudomallei. Laboratory and radiographic investigations (figure 1) suggested an infectious aneurysm, and cultures of blood and an artery tissue specimen grew a gram-negative bacillus that was identified as B. pseudomallei, confirming a mycotic aneurysm. Members of the family Enterobacteriaceae (Klebsiella and Yersinia species), Pasteurella, and Bacteroides demonstrate bi-polar staining on gram-stained smears [1]. Yersinia pestis exhibit bipolar staining, which gives it a " safety pin " appearance, and it is nonmotile. B. pseudomallei and Pseudomonas stutzeri should be considered when a nonfermentative, wrinkled colony is isolated. B. pseudomallei is a gram-negative rod that exhibits bipolar staining in Gram stains; it is described as having a safety pin appearance (figure 2). B. pseudomallei is a strict aerobe, it is motile, and it oxidizes glucose and lactose (P. stutzeri does not use lactose) [2]. It was identified on the basis of a positive blood and artery tissue culture result within 48 h after the samples were obtained, Gram stain findings, colonial morphology , biochemical characteristics, and 16S mRNA sequenc-ing results (figure 3). Whitmore and Krishnaswami [3] described an infective disease in Rangoon (Burma) in 1912. This disease, termed me-lioidosis by Stanton and Fletcher in 1932 [4], was caused by a gram-negative environmental bacterium that has been named Bacillus pseudomallei, Bacillus withmorii, Pseudomonas pseu-domallei, and, since 1992, B. pseudomallei [5]. B. pseudomallei is an important pathogen in humans and in a wide variety of animal species in areas of endemicity, including horses, sheep, cattle, goats, pigs, cats, and dogs [6]. Pneumonia is the most common clinical presentation of infection in humans [7]. Melioidosis is endemic in Southeast Asia and Northern Australia. The incidence in most African countries is unknown, because diagnosis requires bacteriologic confirmation by culture, which is a technique that is not available Figure 3. Wrinkled colonies of Burkholderia pseudomallei visible after incubation at 37؇C for 72 h on chocolate agar. everywhere. Melioidosis is underdiagnosed, and unconfirmed cases have been reported from Burkina Faso (Upper Volta) [8]. Mycotic aneurysms are most frequently caused by Staphylococcus aureus and non-Typhi serotypes of Salmonella [9]. Me-lioidosis presenting as mycotic aneurysm is …