False-positive Gram-stained smears of sterile body fluids due to contamination of laboratory deionized water

Test Characteristics of Cerebrospinal Fluid Gram Stain to Identify Bacterial Meningitis in Infants Younger Than 60 Days

“…Falsepositive CSF Gram stains have been described after bacterial contamination of the staining reagants. 11 In addition, CSF Gram stain results rely on subjective interpretation by laboratory staff after direct inspection, which could be falsely positive. 12 Alternately, CSF cultures could be falsely negative owing to low inoculum volume or variability in culture technique.…”

“…However, approximately one third of infants with a positive CSF Gram stains did not have a positive bacterial culture, even after excluding infants pretreated with antibiotics. False-positive CSF Gram stains have been described after bacterial contamination of the staining reagants 11 . In addition, CSF Gram stain results rely on subjective interpretation by laboratory staff after direct inspection, which could be falsely positive 12 .…”

Survival of Staphylococcus pseudintermedius in modified Romanowsky staining solutions

“…3 Gram-stained clinical samples of cerebrospinal fluid resulted in false positive diagnosis of Gram-negative bacilli due to bacterial contamination of the piped deionized water that was used to make the Gram stain solutions. 4 Previous studies also have highlighted misdiagnosis and unnecessary therapy following contamination of other media, including Gram-negative bacilli in Amies transport medium used for the transport of swabs, 5 and fungal contaminants in Hanks' solution. 6 Staphylococcus pseudintermedius is the most common cutaneous pathogen in the dog, regularly isolated from cases of pyoderma and otitis externa.…”

“…For example, fungal contamination of Grocott light‐green counterstain solution led to the misdiagnosis of yeast infections in two separate cases . Gram‐stained clinical samples of cerebrospinal fluid resulted in false positive diagnosis of Gram‐negative bacilli due to bacterial contamination of the piped deionized water that was used to make the Gram stain solutions . Previous studies also have highlighted misdiagnosis and unnecessary therapy following contamination of other media, including Gram‐negative bacilli in Amies transport medium used for the transport of swabs, and fungal contaminants in Hanks’ solution …”