Research points to potential shortcoming of antibiotic lab tests

July 6, 2018 by Jacqueline Mitchell, Beth Israel Deaconess Medical Center

To determine which antibiotics reliably treat which bacterial infections, diagnostic laboratories that focus on clinical microbiology test pathogens isolated from patients. As multidrug-resistant organisms continue to emerge, these tests—called antibiotic susceptibility assays—are increasingly critical. Clinicians depend on reliable results when choosing the right drug to treat patients.

A recent study revealed that one aspect of these tests may fall short and not be stringent enough.

To obtain consistently reliable results, researchers conducting antibiotic susceptibility assays follow national guidelines with standardized methods, including the use of a specific number of organisms—or "inoculum—that is added to each assay. There is a target inoculum, and then a range of an allowable inoculum, or acceptable upper and lower bounds around the target inoculum.

"Our question was whether this wiggle room impacts results," said co-author James Kirby, MD, Director of the Clinical Microbiology Laboratory at BIDMC. "Our findings were clear: inoculum matters." Kirby and his colleague Kenneth Smith, Ph.D. published their findings in Antimicrobial Agents and Chemotherapy May 21.

The investigators examined pathogens cited by the US Centers for Disease Control and Prevention and the World Health Organization as urgent and concerning drug resistance threats. "We found that the susceptibility determination against two big gun drugs—meropenem and cefepime—were dramatically affected by inoculum differences within the allowable range of inoculum," said Kirby. "Although we have no idea about how often clinical labs deviate even beyond the allowable range, we expect this happens with some frequency and would further skew results."

Kirby and Smith's findings indicate that laboratories must hit the target inoculum pretty much on the nose to obtain reliable testing results for multidrug-resistant pathogens.

Explore further: Simple method tests hard-to-treat bacteria's susceptibility to different antibiotics

Related Stories

Simple method tests hard-to-treat bacteria's susceptibility to different antibiotics

July 14, 2016
The recent emergence of bacterial infections that are resistant to many existing antibiotics is driving an urgent need for tools to quickly identify the small number of therapies that are still effective for individual patients. ...

Screening method uncovers drugs that may combat deadly antibiotic-resistant bacteria

April 29, 2016
In recent years, hospitals have reported dramatic increases in the number of cases of the highly contagious, difficult-to-treat, and often deadly antibiotic-resistant bacteria carbapenem-resistant Enterobacteriaceae (CRE). ...

Avoid piperacillin-tazobactam when treating BSI cause by ceftriaxone-resistant pathogens

April 22, 2018
The antibiotic combination treatment piperacillin-tazobactam was significantly less effective than meropenem when treating potentially fatal bloodstream infections (BSI) caused by ceftriaxone-resistant Escherichia coli and ...

Researchers make FAST work of antibiotic resistance

June 26, 2018
Researchers from The University of Western Australia have showcased exciting results from a screening test to detect antibiotic resistance and to ensure the right antibiotics can be prescribed quicker.

Quick identification of multidrug-resistant pathogens

June 1, 2018
If doctors diagnose a patient with blood poisoning, the patient will immediately be administered a broad-spectrum antibiotic. In many cases, however, the drug is ineffective. Multidrug-resistant pathogens are often the reason ...

Recommended for you

Drug overdose epidemic has been growing exponentially for decades

September 20, 2018
Death rates from drug overdoses in the U.S. have been on an exponential growth curve that began at least 15 years before the mid-1990s surge in opioid prescribing, suggesting that overdose death rates may continue along this ...

Anti-cancer drugs may hold key to overcoming antimalarial drug resistance

September 20, 2018
Scientists have found a way to boost the efficacy of the world's most powerful antimalarial drug with the help of chemotherapy medicines, according to new research published in the journal Nature Communications.

Probiotic use may reduce antibiotic prescriptions, researchers say

September 14, 2018
Use of probiotics is linked to reduced need for antibiotic treatment in infants and children, according to a review of studies that probed the benefits of probiotics, say researchers in the U.S., England and the Netherlands.

Recalled blood pressure drugs not linked to increased short term cancer risk

September 12, 2018
Products containing the withdrawn blood pressure drug valsartan are not associated with a markedly increased short term risk of cancer, finds an expedited analysis published by The BMJ today.

Sugar pills relieve pain for chronic pain patients

September 12, 2018
Someday doctors may prescribe sugar pills for certain chronic pain patients based on their brain anatomy and psychology. And the pills will reduce their pain as effectively as any powerful drug on the market, according to ...

A new approach for finding Alzheimer's treatments

September 11, 2018
Considering what little progress has been made finding drugs to treat Alzheimer's disease, Maikel Rheinstädter decided to come at the problem from a totally different angle—perhaps the solution lay not with the peptide ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.