Accurate identification of organisms, along with antibiotic susceptibility testing is a crucial part of UTI testing, diagnosis and treatment. It may be even more significant for sufferers of recurrent UTI that have a history of frequent antibiotic use that has not eradicated the infection.
UTI testing companies use different approaches to antibiotic susceptibility testing and it’s important to discuss these potential differences with a knowledgeable clinician.
Antibiotic Susceptibility Testing FAQ
Simply put, antibiotic susceptibility is a measure of how sensitive a particular type of bacterium is to a particular antibiotic, or to a range of different antibiotics. You can think of it as a question: If the antibiotic is applied to the bacteria, will it have any effect?
Antibiotic susceptibility testing assesses whether a particular antibiotic is likely to treat an infection caused by a particular bacterium. A test is conducted in vitro (outside the body) to physically apply specific antibiotics to bacteria and then measure the impact of the antibiotic on those bacteria. An antibiotic susceptibility test can help clinicians choose which antibiotic to recommend to their patients.
Yes, antibiotic susceptibility testing and antibiotic sensitivity testing refer to the same process.
It can be. When fungi are found, antimicrobial sensitivity testing may also be done to determine which antifungal is most likely to treat a fungal infection.
Antimicrobial susceptibility test results generally report the minimal inhibitory concentration (MIC) in micrograms per milliliter. MIC refers to the lowest concentration of the antibiotic that inhibits the growth of the bacteria. Results may also include an interpretation of the level of susceptibility. The levels classifies the bacterium’s susceptibility to each tested antibiotic as one of the following: susceptible (S), intermediate (I), resistant (R), sensitive-dose dependent (SD), or no interpretation (NI).
Antibiotic resistance refers to the ability of bacteria to survive exposure to antibiotics whose purpose is to kill or stop the growth of those bacteria. Antibiotic resistance occurs in nature but it can also occur as a result of exposure to antibiotics. When this happens, the bacteria develop antibiotic resistance genes that enable them to resist the effect of the antibiotic and continue to multiply.
In the same way that our own human genes dictate certain characteristics, bacteria can carry genes that dictate whether they have the ability to resist the impact of certain antibiotic mechanisms. Once a bacterium has such a gene, it can actually transfer this genetic information to other bacteria, providing them with the same ability to resist the antibiotic mechanism.
It’s important to note that the standard procedure for antibiotic susceptibility testing is to isolate each type of bacterium identified. This does not account for the possible interactions between different bacteria, and their ability to protect the intermingled bacterial community via the transfer of antibiotic genes or other protective mechanisms.
Can Viruses and Sexually Transmitted Infections Cause UTI Symptoms?
Although viruses are identified in a portion of UTI samples, at this stage, the clinical significance of these viruses is not completely understood. It may be the case that a virus is a contributing or causative factor for UTI symptoms in some people.
Some Sexually Transmitted Infections (STIs) are known to cause UTI-like symptoms, so it’s often a good idea to rule this possibility out. Commonly tested UTIs include:
- Chlamydia trachomatis
- Neisseria gonorrhoeae
- Trichomonas vaginalis
The Limitations Of PCR Testing
Most companies that use PCR technology set a minimum threshold for detection of pathogens, and will not report on organisms detected at levels below that. This same issue is found in the threshold set in standard urine cultures.
Typical PCR thresholds reported on are:
- < 10,000 cells/mL
- 10,000-49,999 cells/mL
- 50,000-99,999 cells/mL
- ≥100,000 cells/mL
It’s also important to understand a few other points about PCR testing:
- PCR testing only tests for the organisms included in the pre-selected panel.
- If the organism causing your infection is not listed on the PCR panel, the test will not be able to inform you whether the organism was present or not.
- Because PCR testing looks for specific organisms only, it is unable to provide a picture of how these microorganisms are represented within the total urinary microbiome – it can’t see what it isn’t looking for.
Testing For Recurrent UTI Sufferers
Why do we share information about testing options on Live UTI Free? One of the most common questions we receive goes something like this…
“I tested positive for a UTI, then got treatment but my symptoms didn’t go away. Now my urine culture is negative and my doctor says I don’t have an infection. What can I do? I still feel like I have a UTI.”
These questions highlight something that science has now proven many times over: the standard UTI test is inaccurate in as many as 50% of cases.
If the question above, or any of the experiences below are familiar to you, and you want to take another shot at finding answers, providers of enhanced UTI testing methods may be able to help:
- Multiple rounds of antibiotics, with UTI symptoms always returning
- Negative urine test results despite symptoms of a UTI
- UTIs as frequently as every month, regardless of home remedies or medication
- An escalation of symptoms over time, and a fear that there is no solution
- Constant pain in the urinary tract, with little or no relief
To find a clinician who is experienced in diagnosing and treating recurrent and chronic UTI, you can get in touch with our team.
Testing For Interstitial Cystitis (IC)
Many clinicians who use enhanced testing methods for IC patients report receiving positive results in a significant number of cases. This means that many IC patients may have an infection as the root cause of their symptoms. You can learn more about how interstitial cystitis is diagnosed in our expert video series.
With the identification of causative pathogens comes the possibility of UTI treatment options. This is a step in the right direction for anyone diagnosed with IC.
|“We see patients with vague irritative urinary symptoms where their work up has been negative by standard testing. I suspect the infection has been there all the time but just not detected. We also see that people previously diagnosed with IC are now finding infection with these tests. I think in a lot of cases, IC is a misdiagnosis due to lack of adequate testing. After all, it’s a diagnosis of exclusion, but we now have more accurate tests that may show an infection cannot be ruled out.”
Testing For Clinicians
An unsuccessfully treated UTI is frustrating for sufferers, but it’s also frustrating for clinicians who want to help.
We often hear from clinicians seeking answers for patients that:
- Have taken multiple rounds of antibiotics with little or no improvement, and have experienced other health issues due to overuse of antibiotics
- Receive test results that identify one or more pathogens and antibiotic sensitivity, yet the recommended treatment is ineffective
- Receive negative urine culture results despite obvious symptoms of a urinary tract infection
- Have urinary tract infections caused by antibiotic resistant bacteria
If you’re a practitioner with a patient who has not responded to previous approaches, you can find more information about enhanced testing approaches by downloading our clinician resource and UTI testing directory.
Standard Urine Culture vs. Enhanced Testing
We talk about the inadequacies of the standard urine culture a lot on Live UTI Free. It’s one of the reasons we present information about UTI testing alternatives.
At the heart of it, the standard urine culture is incredibly inaccurate for a test that is so heavily relied on and considered the gold standard.
And this isn’t just our opinion. Studies show that standard urine culturing may miss more than 50% of infections, leaving many people with false negative results.
If you experience UTI symptoms but have received negative culture results, now could be the time to read up on this. We’ve covered UTI testing options in great detail here.
To understand why genetic sequencing technologies may be superior to the standard culture, we need to look at the limitations of culture:
- The standard urine culture was developed in the 1950s, but was never intended to be used in the diagnosis of lower urinary tract infection. It has not been updated since.
- Standard culture is typically conducted over no more than 24-48 hours. This is insufficient as many bacteria take up to 5 days to grow, and some fungi more than 20 days.
- Some bacteria, such as anaerobes (bacteria that will only grow in an oxygen free environment) will not grow at all unless an anaerobic culture is requested.
- Results are often biased towards easy to grow microorganisms, while others are completely missed.
- Uncommon microorganisms are often considered contamination rather than potential causes of infection.
- Bacteria that have been living in a biofilm, are less likely to grow in a culture than free-floating bacteria (see more on chronic bladder infection).
- Antibiotic susceptibility testing conducted via the standard method looks at isolated bacterial strains, rather than at the bacterial community as a whole, and therefore ignores the possibility of shared antibiotic resistance.
Antibiotic Susceptibility Testing That Treats The Bacterial Community As A Whole
If you read our antibiotic susceptibility testing FAQs at the start of this article, you’ll already have an understanding of how this works in theory.
The question we’re asking here is, is the antibiotic sensitivity of a bacterial species the same when it’s on its own as when it is part of a bacterial community.
The direct answer is no.
It has been shown that bacteria work together in many ways. One of these ways is to share antibiotic resistance characteristics with each other, strengthening the level of resistance of the community as a whole.
Can A UTI Be Caused By More Than One Type Of Bacteria?
When more than one causative bacterium is found in a urine sample, it is referred to as a polymicrobial infection, so we’ll use that term here.
Research results differ when it comes to what percentage of UTIs are caused by polymicrobial infection.
One of the issues with any research based on urine culture is that the standard culture is just not able to pick up many organisms. And in a clinical environment, when multiple organisms ARE detected by culture, they are often dismissed as sample contamination.
Why Treating The Bacterial Community As A Whole Is Important For UTI
Bacterial communities thrive in ways that a single bacterial species on its own cannot. Polymicrobial infections create an environment in which each organism can impact each other organism’s:
- Proliferation rate
- Virulence potential
- Overall survival in the presence of antibiotics
This means that interactions between organisms affect antibiotic tolerance and one bacterial strain can protect the entire population of bacteria.
If antibiotic recommendations ignore bacterial interactions, the UTI antibiotic treatment may be mis-targeted and have a lower chance of success.
Interpreting Antibiotic Recommendations
Along with antibiotic sensitivity information, you’ll also see a few other notes in reports provided by testing companies:
Formulations: How this antibiotic is delivered, which may be IM (Intramuscular), IV (Intravenous), PO (taken orally) or a combination of options.
MIC Results (ug/mL): This refers to the concentration in micrograms per milliliter (ug/mL) of antibiotic at which the bacterial community becomes susceptible.
Information To Take To Your Doctor
We’ve created a clinician resource and testing directory that you can download and take to your doctor. At the link you’ll also find some materials to help you prepare for your next appointment.
As always, if you have any questions or comments, we’d love to hear from you. And if you’d like to sign up for our mailing list, you can do so below.
To get answers to commonly asked questions about chronic and recurrent UTI, visit our FAQ page.