Why is it important to work with a pure culture? Pure culture is defined as a population containing only a single species or strain ofbacteria. It is important to work with a pure culture because in order to study the cultural, morphological and physiological characteristics of an individual species it has to be pure.

A pure culture is usually derived from a mixed culture (one containing many species) by transferring a small sample into new, sterile growth medium in such a manner as to disperse the individual cells across the medium surface or by thinning the sample manyfold before inoculating the new medium.

Isolation of Pure Cultures from a Mixed Population

1. First, the mixture must be diluted until the various individual microorganisms become separated far enough apart on an agar surface that after incubation they form visible colonies isolated from the colonies of other microorganisms.
2. Then, an isolated colony can be aseptically “picked off” the isolation plate.

1. Using the streak plate method of isolation, obtain isolated colonies from a mixture of microorganisms. 2. Pick off isolated colonies of microorganisms growing on a streak plate and aseptically transfer them to sterile media to obtain pure cultures.

In the study of microorganisms, a mixed culture is one that contains more than one type of organism growing in a sterile medium, such as agar. The mixed culture can include multiple species of viruses, bacteria and parasites, which may or may not live in harmony with one another, sharing the available resources.

A pure culture contains only one single type; a mixed culture contains two or more different bacteria. Microbiologists use subculturing techniques to grow and maintain bacterial cultures, to examine cultures for purity or morphology, or to determine the number of viable organisms.

Because “mixed flora”* means that at least 2 organisms are present in addition to the identified organism, such a urine culture does not meet the criteria for a positive urine culture with 2 organisms or less.

Abstract. Urine cultures that contain more than one organism are usually considered contaminated. The frequency with which such growth truly represents mixed infection is unknown. Surprisingly few studies have evaluated the clinical significance of polymicrobial growth from urine.

When 3 or more types of bacteria grow and no single one predominates (i.e., none is present at >100,000 CFU/mL), the results may be reported as “mixed bacterial flora.”

If the urine is not collected in a sterile manner the urine sample may be ‘contaminated’ by bacteria that originate from the skin or genital area, and not from the urinary tract. This is often described by the clinical laboratory as ‘mixed growth bacteria’.

“Mixed Growth” is used to indicate contamination with vaginal, skin or bowel organisms. The presence of epithelial cells on microscopy also indicates contamination. If pyuria (> 40 WBC) is present, and the specimen culture suggests contamination a repeat sample is advisable, if clinically indicated.

A “positive” or abnormal test is when bacteria or yeast are found in the culture. This likely means that you have a urinary tract infection or bladder infection.

Although a variety of bacteria can cause UTIs, most are due to Escherichia coli (E. coli), bacteria that are common in the digestive tract and routinely found in stool….Other bacteria that commonly cause UTIs include:

• Proteus.
• Klebsiella.
• Enterobacter.
• Staphylococcus.
• Acinetobacter.

Urinary tract infections are caused by microorganisms — usually bacteria — that enter the urethra and bladder, causing inflammation and infection. Though a UTI most commonly happens in the urethra and bladder, bacteria can also travel up the ureters and infect your kidneys.

Normal urine varies in color from almost colorless to dark yellow. Some foods, such as beets and blackberries, may turn urine red. Usually, glucose, ketones, protein, and bilirubin are not detectable in urine.

If your urine culture shows you don’t have a UTI, you’ll need further testing to find out the cause of your symptoms.” In rare cases, a person with symptoms similar to a UTI, but with repeated negative cultures (meaning they don’t show a bacterial infection) may in fact have bladder cancer.

Commonly known as UTI, urinary tract infections can be induced by stress. Feeling highly stressed is not the direct cause, but it leads to high levels of cortisol, which reduce the effect of the immune system.

It’s also possible that the symptoms may not be caused by a bladder infection, but instead may be caused by an infection in the urethra, the tube that allows urine to pass out of the body. Or, inflammation in the urethra might be causing the symptoms, rather than bacteria.

Although burning during urination is a telltale sign of a UTI, it can also be a symptom of a number of other problems such as a vaginal yeast infection or certain sexually transmitted diseases (STDs). These include chlamydia, gonorrhea, and trichomoniasis.

Painful Bladder Syndrome (PBS) PBS is not caused by an infection, but it can feel like a bladder infection like a urinary tract infection or UTI. Painful bladder syndrome is also referred to as bladder pain syndrome and interstitial cystitis. In the past, doctors thought PBS was rare and difficult to treat.

Interstitial cystitis, or IC, is a mysterious, painful bladder condition with no known cause or cure. Patients typically experience symptoms resembling those of a urinary tract infection, minus the actual infection: the burning, the urgency, the constant need to pee, the overall pelvic pain and discomfort.

The Difference Between a UTI and IC “In women who have interstitial cystitis, urine culture results will be negative, meaning that no bacteria are found in the urine as with a urinary tract infection.” With IC, women may also experience pain during sexual intercourse, another symptom not commonly associated with a UTI.