Dissecting the Latest Super Bug

The report of a highly resistant E.coli bacterium isolated from a urinary tract infection that occurred in a 49 year old Pennsylvania woman (in April of 2016) has temporarily stolen the headlines from Zika. This colistin-resistant E.coli was uncovered via a Department of Defense program in which bacteria that meet certain criteria are automatically forwarded on for further study. While there has been much written about this event and its implications, there are a lot of misconceptions in the headlines.

A few facts about this phenomenon:

1. Plasmid-mediated colistin resistance is a very bad development.

Colistin resistance has existed before, but usually is conferred through changes in the genes of the bacterial chromosome delimiting spread to other bacteria. Indeed, I've seen many colistin resistant bacteria. When resistance is present on a plasmid, which is a mobile piece of genetic information, it can more easily disseminate to neighboring bacteria. The mcr-1 plasmid is such a mechanism for transmission of resistance. Colistin, a drug well known to infectious disease physicians, was a drug put on the shelf decades ago because of toxicity concerns. Today, it is often a drug of last resort and taken off the shelf in special situations in which resistance makes its use necsessary. Losing it through the dissemination of plasmid-resistance, first described in China, would be very problematic. Of note, the woman, who recovered from her infection, had no travel in the 5 months prior to the infection and it will be important to investigate her close contacts (animal and human) to attempt to pinpoint how the strain was acquired.

2. This E.coli isolate was, thankfully not totally drug resistant.

Though this bacterium deserves the "superbug" moniker, given it was both colistin-resistant and harbored an extended-spectrum beta-lactamase (ESBL), it was not resistant to all antibiotics known to man -- something I have battled against twice (Klebsiella pneumonia, Pseudomonas aeruginosa) not too successfully. Cabapenem (it's not a CRE), aminoglycoside, and nitrofurantoin (!) susceptibility was present in the strain leaving the patient with options. 

3. The isolation of an E.coli bearing the mcr-1 plasmid in a pig intestine sample is highly significant.

The aspect of the story -- which hasn't garnered as much attention with the notable exception  Maryn McKenna, one of the best infectious disease journalists -- is a puzzling development as colistin is not an antibiotic used in agriculture. Tracing the origin of the pig intestine to the farm in which the pig it belonged to resided will be important as will sampling other animals -- and humans -- on the farm.

Antibiotic resistance is the norm--it is what bacteria do naturally to survive. The discovery of this strain in the US is not surprising in the least. This event, however, should serve to underscore the need to treat antibiotics as the precious resources they are and not squander them through injudicious use whether in the hospital, the pediatrician's office, or the urgent care center. Additionally, infectious disease medicine must meet these challenges with less reliance on broad-spectrum non-specific antimicrobials and more with targeted therapies such as monoclonal antibodies, bacteriophages, lysins, and virulence factor disruptors and sophisticated and fast companion diagnostics.