Antimicrobial Testing–Are We Doing it Wrong?

Antibiotic resistance is a huge concern for microbiologists. In addition to stewardship programs and regulating agricultural use of antibiotics, is it time to re-examine clinical testing paradigms?

A recent study suggests that the typical way microbiologists test for antibiotic susceptibility–meuller-hinton plates and antibiotic disks–might be fallible. When his team tested Salmonella against polymyxin using typical methods, the organism tested sensitive; when the tested the same organism against the same antibiotic using medium that more closely resembled human cells, the organism tested resistant.

Bloomberg Business discusses the paper here. The article is worth your time, even if the info-graphic gives erroneous information (it mentions meuller-hinton broth instead of meuller-hinton agar plates).

An Interactive Tool to See Antibacterial Resistance Over Time

Do you need to know the percentage of Salmonella Typhi resistant to nalidixic acid in California in 2001? A resource now exists that can give you that answer.

The Centers for Disease Control (CDC) has released a tool called National Antimicrobial Resistance Monitoring System (NARMS) Now: Human Data, and it allows users to access antimicrobial resistance data based on year and geographical region. The interactive site tracks resistance for four bacteria that cause foodborne illness: Salmonella, Shigella, Campylobacter, and E. coli O157.

Using Evolution to Thwart Resistance

The very act of using antibiotics contributes to antibiotic resistance. Bacteria are exposed to an antimicrobial agent and develop genetic strategies to survive repeated exposures. But what if using antibiotics in a certain sequence could revert resistant strains to the wild type? Researchers from California and Washington DC tested that theory and discovered some promising results.

You can read the PLOS ONE study and the Scientific American article to learn more.

Livestock-Associated MRSA

Over at her new blog Germination, Maryn McKenna discusses a recent study in Clinical Infectious Diseases about livestock-associated MRSA and infections in farmers. For those clinical laboratory scientists who work in labs that serve a rural population, this is a must-read.



Kelly Swails, MT(ASCP), is a laboratory professional, recovering microbiologist, and web editor for Lab Medicine.


Illinois Summit on Antibiotic Stewardship

Last week, I attended the Illinois Summit on Antimicrobial Stewardship at Northwestern Memorial Hospital. While the target audience was physicians, nurses, pharmacists, and administrators, as a clinical laboratory scientist I found the presentations (with a few caveats, which I’ll get to in a moment) quite informative.

The morning sessions covered the relationship between antibiotic use and resistance patterns; interpretations and implementation of the national guideless for stewardship; and using behavioral science to increase compliance with stewardship programs. Participants spent part of the afternoon in small groups to discuss designing and implementing a stewardship program.

A few notes:

-50% of antibiotics for upper respiratory infections aren’t needed; 50% of antibiotics for inpatients aren’t needed, either

-antibiotics are the only drug where use in one person impacts it effectiveness in another

-based on the literature, antibiotic stewardship programs have at least a transient effect on antibiotic effectiveness—eventually, resistance numbers begin to climb again

-hospital antibiograms are the most widely available measure of resistant organisms, but we aren’t using them as effectively as we could. For example, we typically report that, say, “62.5% of E. coli isolates are resistant to ciprofloxacin,” but we don’t say where those isolates come from. Are they urinary tract infections or upper respiratory infections? What’s the rate of resistance for infected wounds?

-a weighted antibiogram might make empirical treatments for effective. For example, “what % of urinary tract infections are resistant to ciprofloxacin?”

-it’s important to note that the IT department, hospital information systems, and laboratory information systems play a huge role in stewardship programs

-stewardship programs depend on the “5 D’s” Diagnosis, drug selection, dose, duration, and de-escalation of use

-diagnostic uncertainty—driven by lack of early organism identification—drives a significant amount of antibiotic use

-when combined with stewardship, rapid bacterial identification methods such as MALDI-ToF platforms decrease parameters such as length of patient say, time to treatment, etc.

-we can use peer pressure to drive improvements. No one wants to perform worse than the doctor next door

-our efforts might be moot, anyway; other countries take a much laxer stance on antibiotic use

While the laboratory in general and clinical microbiology departments specifically were mentioned during the presentations, I must say they were only mentioned in the context of how little perceived impact we have on stewardship. (“Well, we know the laboratory isn’t going to give us any useful information for another three days…”) It wasn’t until I participated in the small group sessions in the afternoon that attendees at my table admitted that the laboratory is an important piece of the stewardship puzzle. We have mountains of data we can assimilate (antibiogram creation, anyone?). We can bring in new technologies to make identifications faster. We can work closely with the infectious disease doctors to help guide treatment. That brings up a good point—if microbiology labs aren’t in-house, then creating an antibiotic stewardship program becomes that much harder because results can be delayed.

If you’d like to see the powerpoints from the presentations, you can do so by clicking the “downloadable content” tab at Northwestern Memorial Hospital’s antibiotic stewardship page.


Kelly Swails, MT(ASCP), is a laboratory professional, recovering microbiologist, and web editor for Lab Medicine.

Go Outside And Play in the Dirt

Researchers may have made some headway in the fight against antimicrobial resistance. A paper published online in Nature today (abstract only unless you’re a subscriber) discusses a new method to grow bacteria that have previously been uncultivable. In doing so, researchers have discovered a new antibiotic they’re calling teixobactin that is active against gram-positive organisms (specifically, a precursor of peptidoglycan present in the cell wall). Initial tests suggest bacteria can’t form a resistance to this mode of action.

Maybe there’s something to the expression “throw some dirt on it and get back in the game” after all.

NPR and the Washington Post discuss this paper and its findings today, as well. It’s too soon to be excited, but I admit I’m cautiously optimistic.


Kelly Swails, MT(ASCP), is a laboratory professional, recovering microbiologist, and web editor for Lab Medicine.