Prevalence and Characterization of Cefotaxime-Resistant Microbes in Animal Farms

Introduction: Antimicrobial resistance is a growing concern in animal and public health. The number of antibiotic resistant microorganisms (ARMs) is increasing and will continue to increase due to the slow development of new antibiotics and lack of alternative therapies for bacterial diseases. Extended spectrum β-lactamase (ESBL) producing microorganisms, which are resistant to third-generation cephalosporins, present a new challenge to the food animal industry.

Purpose:  The purpose of this study was to identify the origin of cefotaxime-resistant microorganisms and decipher the mechanisms of ESBL transmission in food animals.

Methods: Cattle fecal swab samples from nine locations and were collected, plated on MacConkey agar plates containing cefotaxime (4 mg/l), and incubated at 37°C for 48 hours to isolate cefotaxime-resistant colonies. After colony purification, 16S rRNA gene sequencing was conducted to identify the resistant microorganisms using the 16S universal primers (27F and 519R).

Results : We isolated cefotaxime-resistant microorganisms in farm animals, which have never been exposed to antibiotics through their entire life span. The prevalence of cefotaxime-resistant microorganisms in cattle was varying among farms, ranging from 5.2% to 100%. Animals reared in loose housing systems show lower prevalence of ARMs compared to animals in intensive housing systems, indicating animal-to-animal transmission plays a key role in ARM transmission. Seventeen different species of microbes including animal, human and plant pathogens as well as soil bacteria were identified by 16S rRNA sequencing.

Significance:  This study reports the first occurrence of cefotaxime resistance in animals. The development of cefotaxime resistance microorganisms might have originated from nature as well as the use of antibiotics.