Answer: Community-acquired pneumonia caused by Acinetobacter baumannii. The Gram-positive rods seen on the initial Gram stain from the blood culture broth were later identified as Acinetobacter baumannii. A. baumannii is a strictly aerobic, nonfermenting, oxidase-negative, catalase-positive coccus/coccobacillus that grows well on both blood agar and MacConkey agar. In Gram-stained preparations, it typically appears as Gram-negative diplococci with an arrangement resembling that of Neisseria spp. (1). It is well recognized that some Acinetobacter isolates tend to retain crystal violet and resist decolorization (2) and may initially appear as Gram-positive cocci in direct smears prepared from positive blood culture bottles (3). This may explain the Gram-positive appearance of the original Gram-stained smear. Of note, there was a similar report of A. baumannii presenting as Gram-positive bacilli in a bronchial washing specimen from a patient with fulminant A. baumannii community-acquired pneumonia (4). However, the mechanism by which this phenomenon occurs remains unclear. The unusual bacillary appearance may be contributed to by the growth phase of the organism as well as the presence of antibiotic in the blood. It was reported that Acinetobacter spp. are plump rods measuring 0.9 to 1.6 by 1.5 to 2.5 μm during exponential growth and become coccoid after entry into the stationary phase (2). The organisms seen on the original Gram stain, however, measured up to 6 μm in length. This morphological change is likely caused by the presence of sub-MIC levels of β-lactam antibiotic in the blood, amoxicillin in this case. This effect has been described to occur in various Gram-negative bacilli in the presence of β-lactam antibiotics, which were proposed to inhibit septum formation, resulting in the elongated morphology (5, 6). The subsequent Gram-stained smear of the isolate from sheep blood agar showed Gram-negative diplococci, in contrast to the Gram-positive bacilli seen in the original smear. The isolate was identified as A. baumannii by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS; Bruker). The Vitek 2 system (GN ID card) and an API 20 NE strip identified the organism as a member of the Acinetobacter baumannii-Acinetobacter calcoaceticus complex. A. baumannii is ubiquitous in freshwater and soil. It is an opportunistic pathogen that plays a significant role in nosocomial infections and hospital outbreaks. It is also an uncommon cause of severe community-acquired pneumonia. While health care-associated A. baumannii is often multidrug resistant, strains of A. baumannii causing community-acquired pneumonia are usually susceptible to multiple antibiotics. The strain in this case tested susceptible to ampicillin-sulbactam, piperacillin-tazobactam, cefepime, gentamicin, ciprofloxacin, and imipenem via disk diffusion testing. The patient was empirically treated with intravenous amoxicillin-clavulanate and oral clarithromycin, which were subsequently changed to ampicillin-sulbactam on the basis of susceptibility testing. However, on the third day of admission, he developed a fever, and a repeat chest X-ray showed progression of consolidation. Repeat cultures were negative, and he was treated with piperacillin-tazobactam. He completed 10 days of antibiotics in total and returned home in a stable condition. This case illustrates that A. baumannii can present with unusual Gram stain findings in clinical specimens. Both laboratory and clinical personnel should be aware that in the appropriate clinical settings, A. baumannii infection should be considered a differential diagnosis despite seemingly incongruent Gram stain findings. (See page 2797 in this issue [doi:10.1128/JCM.02551-13] for photo quiz case presentation.)