Staphylococcus nepalensis, a commensal of the oral microbiota of domestic cats, is a reservoir of transferrable antimicrobial resistance

Tenebrio molitor as a model system to study Staphylococcus spp virulence and horizontal gene transfer

Invertebrates can provide a valuable alternative to traditional vertebrate animal models for studying bacterial and fungal infections. This study aimed to establish the larvae of the coleoptera Tenebrio molitor (mealworm) as an in vivo model for evaluating virulence and horizontal gene transfer between Staphylococcus spp. After identifying the best conditions for rearing T. molitor, larvae were infected with different Staphylococcus species, resulting in dose-dependent killing curves. All species tested killed the insects at higher doses, with S. nepalensis and S. aureus being the most and least virulent, respectively. However, only S. nepalensis was able to kill more than 50% of larvae 72 h post-infection at a low amount of 105 CFU. Staphylococcus infection also stimulated an increase in the concentration of hemocytes present in the hemolymph, which was proportional to the virulence. To investigate T. molitor's suitability as an in vivo model for plasmid transfer studies, we used S. aureus strains as donor and recipient of a plasmid containing the gentamicin resistance gene aac(6')-aph(2″). By inoculating larvae with non-lethal doses of each, we observed conjugation, and obtained transconjugant colonies with a frequency of 1.6 × 10-5 per donor cell. This study demonstrates the potential of T. molitor larvae as a reliable and cost-effective model for analyzing the virulence of Staphylococcus and, for the first time, an optimal environment for the plasmid transfer between S. aureus carrying antimicrobial resistance genes.

ANTIMICROBIAL SUSCEPTIBILITY OF STAPHYLOCOCCUS SPP. ISOLATED FROM FELIDS AND CANIDS IN BELO HORIZONTE ZOO, BRAZIL

The epidemiology of Staphylococcus spp. has become a major concern among humans and animals due to increasing antimicrobial resistance and frequent reports of infection. Despite the importance of animals as reservoirs for staphylococci, little is known about the epidemiology of Staphylococcus spp. in most nondomestic species, including canids and felids. This study evaluated the frequency, distribution, and patterns of antimicrobial resistance of staphylococcal species isolated from captive felids and canids from Belo Horizonte Zoo, Brazil. Rectal, oral, and nasal swabs from apparently healthy maned wolves (Chrysocyon brachyurus, n= 7), a lion (Panthera leo, n = 1), jaguars (Panthera onca, n = 3), and one swab of a cougar (Puma concolor) with an ear infection were streaked onto mannitol salt agar. Colonies identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry, polymerase chain reaction for the Staphylococcus intermedius group (SIG), and 16S rRNA gene sequencing. Isolates were subjected to antimicrobial susceptibility tests and Staphylococcus pseudintermedius strains were subjected to multilocus sequence typing. Staphylococcus species were isolated from 24 of the 34 samples (70.6%). Among the isolated strains, S. pseudintermedius and Staphylococcus felis were the most frequent species (41.7 and 25%, respectively). Five novel sequence types were identified among the S. pseudintermedius isolates. Resistance to tetracycline (7/24, 29.2%) or penicillin (6/23, 26.1%) was significantly higher than the other antimicrobial agents tested (P < 0.05). One isolate, Staphylococcus nepalensis, was positive for mecA and resistant to five antimicrobials, and was thus classified as multidrug-resistant. The present work suggests that maned wolves are natural hosts of SIG and also reports the isolation of S. felis in sick and healthy, captive, nondomestic carnivores. The isolated staphylococci were susceptible to most classes of antimicrobials tested. However, the multidrug-resistance capability of an S. nepalensis strain reinforces the hypothesis that felids and canids act as reservoirs of pathogens with antimicrobial resistance.