WILRIJK, Belgium, July 8 (UPI) -- Months after scientists in China identified a gene making bacteria resistant to the last-resort antibiotic colistin, a second gene was found by scientists in Europe that may be able to spread among bacteria more easily.
The mcr-2 gene was found in E. coli bacteria in pigs and cows in Belgium and appears to transfer between animals more frequently, suggesting it could pose a bigger threat than the gene discovered last year, scientists at the University of Antwerp report.
In November, scientists in China discovered the mcr-1 gene during a study on antibiotic resistance of E. coli in pigs raised for food.
Chinese scientists posited at the time, after finding the bacteria in both animals and humans, that the bacteria had evolved to resist colistin -- an antibiotic generally used only after all other antibiotics have failed to work -- because it is often fed to pigs there.
Thirty countries around the world have reported detection of the mcr-1 gene, including the United States, where it was detected in the urine of a woman in Pennsylvania in May.
The fear with mcr-1 and mcr-2 is their movement on plasmids, tiny pieces of DNA that can be traded between bacteria -- either the same or different families -- suggesting they can be transferred to bacteria that may infect humans. The higher prevalence of mcr-2 in the European animals, compared to levels of mcr-1 the scientists detected, suggests the newly found gene poses a greater danger.
"Identification of plasmid-mediated colistin resistance represents a paradigm shift in colistin-resistance mechanisms, which until recently were restricted to chromosomal mutations and vertical transmission," scientists wrote in the study, which is published in the journal Eurosurveillance.
After Chinese scientists detected mcr-1 last November, scientists in Belgium screened 105 colistin-resistant E. coli bacteria isolated in 2011 and 2012 from 52 calves and 53 piglets raised in different parts of the country. Scientists detected mcr-1 in 12.4 percent of the animals -- six calves and seven piglets.
Starting with 10 random E. coli samples from animals that exhibited colistin resistance but did not have mcr-1, scientists identified another form of the gene, mcr-2, in samples from three animals. While the overall prevalence among samples was lower for mcr-2 than mcr-1 -- 11.4 percent of all 105 samples tested positive -- 11 piglets had the second form of colistin-resistant E. coli, a marked increase among porcine E. coli.
The scientists say more research is needed, as is an increase in screening for the resistant bacteria, because of the potential for it to spread.
"There are more of these guys out there, including different flavors," Dr. Barry Kreiswirth, a researcher at Rutgers University, told STAT. "This is what you expect when people start looking."