Abstract

Background:
Streptococcus pluranimalium is an emerging zoonotic pathogen. Its overall low isolation rate has contributed to the paucity of available data. However, data on its antimicrobial resistance (AMR) profile, particularly from swine in China, remain scarce. The escalating global challenge of AMR underscores the urgent need to elucidate resistance mechanisms in zoonotic veterinary pathogens.

Aim:
To the best of our knowledge, this is the first comprehensive characterization of AMR phenotypes and genotypes in S. pluranimalium isolates from diseased pigs in China, with an emphasis on identifying novel resistance gene combinations and evaluating their potential for cross-species dissemination.

Methods:
The AMR profile of 17 S. pluranimalium isolates was determined using minimum inhibitory concentration testing against a panel of antimicrobials. Next-generation sequencing was used to comprehensively investigate the genetic determinants of resistance, and a comparative analysis was conducted incorporating 5 publicly available genomes.

Results:
All 17 isolates were multidrug-resistant. They exhibited high resistance rates to sulfamethoxazole (100%), azithromycin (94.12%), tylosin tartrate (70.59%), and tetracycline (76.47%) but remained susceptible to penicillin, amoxicillin, ceftizoxime, and vancomycin. Genomic analysis identified 20 antimicrobial resistance genes. Notably, we report for the first time the co-occurrence of five aminoglycoside resistance genes (aad(6), aph(3')-IIIa, sat-4, aph(2'')-Ia, and patB) in this species, along with the simultaneous detection of lnuB and lnuC.

Conclusion:
Our next-generation sequencing analysis identified diverse and novel combinations of antibiotic resistance genes in porcine-derived S. pluranimalium, positioning it as a potential reservoir for AMR dissemination. These findings offer critical molecular insights into the AMR landscape in Chinese swine, emphasizing the risk of cross-species transmission and the need for integrated surveillance of this pathogen.

Key words: Antimicrobial resistance; Streptococcus pluranimalium; Pig.