Mountain Falls Pulmonary Clinic, Cheyenne Regional Medical Center, Cheyenne, Wyoming Division of Pulmonary and Critical Care Medicine, University of Connecticut School of Medicine, Farmington, Connecticut, USA.
Respirology. 2011 Jan;16(1):86-9. doi: 10.1111/j.1440-1843.2010.01855.x.
The increasing incidence of respiratory infections due to methicillin resistant Staphylococcus aureus has resulted in increased empirical use of antibiotics active against this pathogen. There are limited data available as to whether the Gram stain of respiratory tract secretions accurately predicts growth of S. aureus. We theorized that the distinctive morphology of S. aureus would allow rapid, accurate identification of the organism in respiratory secretions.
The authors reviewed all available Gram stains of tracheal aspirates sent to our hospital's microbiology laboratory between 1 April 2008 and 31 October 2008, while blinded to the culture result, and recorded the presence or absence of organisms with a morphology consistent with S. aureus. These results were correlated with the semiquantitative culture result.
Among 136 tracheal aspirates studied, 50 (37%) grew S. aureus. The Gram stain was read as positive for organisms consistent with S. aureus in 34 of these. Among 86 samples that did not grow S. aureus, the Gram stain was read as negative in 62. Therefore, the Gram stain had a sensitivity of 68%, a specificity of 72%, a negative predictive value of 80% and a positive predictive value of 59% for culture of S. aureus. False negative Gram stains were more likely when the culture revealed only rare or small growth of S. aureus (P = 0.01).
In this study, the tracheal aspirate Gram stain read by an experienced clinician who was not a microbiologist, was not accurate enough to reliably predict the growth of S. aureus.
耐甲氧西林金黄色葡萄球菌引起的呼吸道感染发病率不断上升，导致对抗这种病原体的抗生素经验性使用增加。关于呼吸道分泌物的革兰氏染色是否准确预测金黄色葡萄球菌生长的相关数据有限。我们推测金黄色葡萄球菌的独特形态学特征将允许快速、准确地识别呼吸道分泌物中的病原体。
作者回顾了 2008 年 4 月 1 日至 2008 年 10 月 31 日期间送往我们医院微生物实验室的所有可用的气管抽吸物的革兰氏染色，同时对培养结果进行盲法处理，并记录形态与金黄色葡萄球菌一致的生物体的存在或缺失。这些结果与半定量培养结果相关联。
在 136 例气管抽吸物中，50 例（37%）生长金黄色葡萄球菌。在其中 34 例中，革兰氏染色呈阳性，提示存在与金黄色葡萄球菌一致的生物体。在 86 例未生长金黄色葡萄球菌的样本中，62 例革兰氏染色呈阴性。因此，革兰氏染色对金黄色葡萄球菌培养的敏感性为 68%，特异性为 72%，阴性预测值为 80%，阳性预测值为 59%。当培养物显示金黄色葡萄球菌的生长仅为罕见或少量时，革兰氏染色的假阴性结果更有可能（P = 0.01）。
在这项研究中，由一位非微生物学家的经验丰富的临床医生读取的气管抽吸物革兰氏染色结果不够准确，无法可靠地预测金黄色葡萄球菌的生长。
