A finding of “Gram Positive Flora” on a urine test indicates the presence of a specific type of bacteria, identified using a common laboratory staining technique. This preliminary result broadly classifies the bacteria, guiding medical providers on the next diagnostic steps. While often a benign result of external contamination during sample collection, it can also signal a true urinary tract infection (UTI) caused by Gram-positive organisms. Interpreting the result requires considering the patient’s clinical symptoms and the concentration of bacteria found.
Understanding the Gram Stain Method
The Gram stain method is a foundational procedure in microbiology used to categorize bacteria based on the structure of their cell walls. This differential stain uses multiple dyes to produce a color difference between two large groups of bacteria. The process begins by applying the primary purple dye, crystal violet, followed by iodine, which forms a complex within the bacterial cells.
The crucial step is the application of a decolorizer, typically alcohol. Gram-positive bacteria have a thick, mesh-like layer of peptidoglycan. When the decolorizer is added, this thick layer shrinks, trapping the large purple complex inside the cell. Consequently, Gram-positive bacteria retain the primary dye and appear purple or deep violet when viewed under a microscope.
The Microbiome of the Urinary Tract
The urogenital tract possesses a complex, diverse microbiome and is not completely sterile, especially the lower portion and the external opening of the urethra. Bacteria from the surrounding skin and genital areas can easily colonize this region, leading to their presence in a collected urine sample.
These normal inhabitants, or commensal organisms, include several Gram-positive species often detected in laboratory analysis. Examples include Lactobacillus species, which are dominant in the female urogenital tract, and common skin colonizers like Coagulase-negative Staphylococci (Staphylococcus epidermidis) and various Corynebacterium species. The presence of these organisms often represents colonization rather than an active infection, particularly if the colony count is low.
Differentiating Contamination from Infection
Distinguishing between a genuine infection and simple contamination is the primary challenge in interpreting Gram-positive flora results. Contamination occurs when bacteria from the surrounding skin mix with the urine during collection, which is why a clean-catch midstream technique is recommended. Laboratory analysis uses several criteria for distinction, the most important being the colony count, measured in colony-forming units per milliliter (CFU/mL).
A low count (less than \(10^4\) CFU/mL) or the presence of multiple bacterial types often suggests external contamination, especially if the patient has no symptoms. Conversely, a true urinary tract infection (UTI) is typically characterized by a high count of a single organism, traditionally \(\ge 10^5\) CFU/mL in an asymptomatic patient.
A lower threshold may be significant if the patient has classic UTI symptoms like painful urination (dysuria), frequent urges, or flank pain. The presence of white blood cells (pyuria, defined as \(\ge 10\) white blood cells per microliter) is also a strong indicator of inflammation and likely infection. Certain Gram-positive organisms are known uropathogens, causing infection even at lower counts. For example, Staphylococcus saprophyticus causes uncomplicated UTIs in younger women, and Enterococcus species are significant Gram-positive pathogens often seen in hospital-associated UTIs.
Identification and Next Steps
Following the initial finding of Gram-positive flora, the next step is typically a formal urine culture and sensitivity test (C&S). The urine culture is the gold standard for diagnosing a UTI because it allows the lab to grow and count the bacteria, confirming the concentration and purity of the growth. This procedure definitively identifies the species or genus, determining if the Gram-positive finding is a benign colonizer or a known pathogen.
If the culture confirms a significant count of a pathogenic species, the laboratory performs an antibiotic susceptibility test (AST). This test determines which antibiotics are effective against the identified bacteria. Results are categorized as susceptible, intermediate, or resistant, guiding the healthcare provider in selecting targeted treatment.
Clinical management depends on the correlation between lab results and the patient’s symptoms. If the patient has no symptoms, a high bacterial count may be diagnosed as asymptomatic bacteriuria and usually does not require antibiotic treatment. If a true Gram-positive UTI is confirmed by a significant count, symptoms, and pyuria, targeted antibiotic therapy based on sensitivity results is initiated.