Manure from dairy cows has been defined as an increasing source of bacteria that can become resistant to antibiotics. These findings are the result of the work of Fabienne Wichmann and colleagues at Yale University in New Haven, Connecticut. The research was published in the April 22, 2014, edition of the journal mBio®.
Bacteria that are antibiotic resistant reach the food chain of humans through the use of cow manure as fertilizer. The manure may or may not contain bacteria that are antibiotic resistant. If the manure does contain an antibiotic resistant strain of bacteria then there is a potential for transmission to humans that eat food that was fertilized with cow manure. The food plants can even become a source of antibiotic resistance due to the phenomenon of gene exchange between species.
A more prominent and more likely transfer of new antibiotic bacterial species to humans is through infection of cow farmers by new bacterial strains. The dairy cow farmers can transmit a new disease directly to other humans through physical contact or through airborne distribution during coughing or sneezing. The more humans that come into contact with a potentially antibiotic resistant type of bacteria increases the probability that the bacteria will become resistant to antibiotics due in part to the high level of use of antibiotics by humans.
The researchers found that only five samples of cow manure contained 80 unique and functional antibiotic resistance genes. The scientists created a laboratory cultured strain of Escherichia coli that was resistant to one of the four major types of antibiotics used to treat humans from the 80 genes. The scientists also found a never before known family of antibiotic resistant genes that conferred resistance to the same group of antibiotics.
A primary source of antibiotic resistant bacteria origination is the use of antibiotics to keep cattle healthy. The potential for transfer of antibiotic resistance to humans through food crops depends on whether the cow manure has antibiotic resistant bacteria or genes. It is possible that a new antibiotic resistant disease could be contracted by people simply by using cow manure as fertilizer for their house plants or home garden.