Companion Pets Possible Reservoir for mcr-1–harboring E. coli

Colistin-resistance mechanism gene mcr-1 was initially identified in Escherichia coli isolates from food, food animals, and human patients in November of 2015. Reports soon followed regarding the detection of mcr-1 Enterobacteriaceae in humans and food animals in approximately 12 countries. An emergence of mcr-1 adds resistance to what could possibly be a “last resort” drug, leaving medical professionals without treatment options for their patients.

A letter recently published in the Centers for Disease Control and Prevention’s journal Emerging Infectious Diseases, reports possible transmission of mcr-1—harboring E. coli between companion pets and people. The findings were reported after samples from companion animals and one human patient showed mcr-1 in colistin-resistant E. coli.

According to the letter, “Three mcr-1—harboring E. coli clinical isolates were identified from specimens of 3 patients admitted to a urology ward of a hospital in Guangzhou, China. E. coli isolate EC07 was identified in the urine of a 50-year-old male patient with glomerulonephritis in October 2015. Isolate EC08 was cultured from the urine of a 48-year-old male patient with prostatitis in December 2015. Isolate EC09 was identified in the blood of an 80-year-old male patient with bladder cancer 3 weeks after EC08 was identified.”

Upon review of medical records, the patient carrying the E. coli isolate EC07 was identified as a pet shop employee. This finding led public health officials to collect fecal samples from a total of 53 animals—39 dogs and 14 cats–from the shop where the patient worked. Among these samples, six animals tested positive for mcr-1 — four dogs and two cats – all six isolates were resistant to colistin, polymyxin B, cephalosporin, gentamixin, and ciproflaxicin.

E. coli can also gain resistance to beta-lactam agents by the production of cephamycinase AmpC enzymes, according to a separate study on antimicrobial-resistant E. coli in the hospitalized companion animal. “This adds to the resistance burden within bacterial populations, because the use of one antimicrobial class could select for resistance to multiple other classes by favouring the spread of plasmids that confer multi-drug resistance (MDR — resistance to ≥three drug classes),” the study authors explained.

Antimicrobial-resistant infections can severely impact the welfare of companion animals and their caretakers, increasing morbidity and mortality. Additionally, these infections create an increased burden in the hospital setting, especially in animals undergoing treatment as compared to healthy animals.

Both studies conclude that companion animals can serve as a reservoir of colistin-resistant E. coli, and they may also act as a source of infection for new animals in the environment. This adds another layer to an already complex and ever-evolving epidemiology of plasmid-mediated colistin resistance in the community.

There is an urgent need for further studies that help determine what risk factors are present with environmental contamination and the spreading of antimicrobial-resistant bacteria. This will help healthcare, veterinary, and public health professionals implement effective programs and infection control measures.