Lactobacillus is a rod-shaped bacterium that is the part of the normal flora of the human genitourinary and digestive tracts but may cause urinary tract infections, UTI, in individuals with reduced immunity. However, the diagnosis of lactobacillus UTI is often challenging as this bacterium commonly occurs as a contaminant in the urine samples of many patients, especially women. Repeated isolation of the bacteria in the laboratory is essential confirm the diagnosis.
The clinical specimen for all suspected cases of UTIs is a clean catch, early morning urine sample. Since the first part of the urine tends to flush out urethral contaminants, a mid-stream urine sample is collected in a screw-capped, sterile plastic bottle.
If lactobacilli are isolated from the urine sample, a repeat test is ordered to rule out contamination and to confirm true lactobacillus infection. An article published in the November 1999 issue of "Nephrology Dialysis Transplantation" recommends direct aspiration of the urine sample from the urethra or the suprapubic region using a needle to rule out contamination in such cases.
Urinalysis is often the first test that is performed in a doctor's office to check for the presence of UTI and involves three steps. According to MedlinePlus, the first step involves visual examination of the urine sample for color and clarity. This is followed by a preliminary microscopic examination that detects the presence of pus cells, mucus and other substances. The third step is a chemical analysis that involves dipping a special stick coated with chemicals into the urine sample. These chemicals change color when they encounter substances of interest such as glucose or creatinine. If the urinalysis reveals anything suspicious, the patient's sample is sent to the laboratory for further testing.
A small amount of the urine sample is placed on a glass slide, stained with dyes such crystal violet and basic fuchsin and observed under the microscope. According to "Mackie and McCartney's Manual of Practical Medical Microbiology," the presence of purple-colored, rod-shaped bacteria provides a preliminary diagnosis of lactobacilli.
A small amount of the urine sample is placed on growth medium plates, which consist of gels that promote the growth of the bacteria. The plates are then incubated at 37 degrees Celsius for 18 hours. The presence of bacterial colonies on the plates indicates infection. The colonies are then confirmed to be lactobacilli using an array of biochemical tests such as gas chromatography.
In case of lactobacilli and other contaminating commensals, the proof of a UTI requires the demonstration that the bacteria is present in the urine in numbers greater than those likely to result from contamination. Mackie and McCartney's Manual of Practical Medical Microbiology states that the presence of significant number of bacteria in the urine is known as significant bacteriuria and is indicated by the presence of greater than 100,000 bacteria/ml of urine.
Antimicrobial assays are performed to identify the antibiotic susceptibility pattern of the strain of lactobacilli that is causing the UTI. A small amount of the bacterial culture is placed on a growth medium plate, and paper discs impregnated with antibiotics are placed on it. The plates are then incubated. The absence of growth around a disc indicates that the lactobacilli are susceptible to that particular antibiotic.
- "Nephrology Dialysis Transplantation"; Common errors in diagnosis and management of urinary tract infection; I: Pathophysiology and diagnostic techniques; Martina Franz and Walter H. Hörl; November 1999.
- Medline Plus: Urinalysis
- "Mackie and McCartney's Manual of Practical Medical Microbiology"; J. G. Collee, A. G. Fraser, B. P. Marmion and A. Simmons; 1996.