Prevalence and risk factors associated to multidrug-resistant Gram-positive bacteria isolated from dromedary camel milk in Tunisia

This study focuses on the carriage and antibiotic-susceptibility profiles of Gram-positive bacteria in dromedary camel milk. A total of 103 milk samples were collected from apparently healthy female dromedaries in southern Tunisia. Bacterial growth was observed only in 82 of these samples, yielding 86 Gram-positive bacterial isolates. <i>Staphylococcus</i> was the most frequently isolated genus (54/86, 62.8%) with 13% of coagulase-positive staphylococci (CoPS) represented by <i>S. aureus</i> and <i>S. intermedius</i> and 87% of coagulase-negative staphylococci (CoNS) (<i>n</i> = 47) identified as <i>S. simulans, S. xylosus, S. warneri, S. hominus1, S. capitis, S. sciuri</i> and <i>S. equorum. Cellulomonas</i> spp. (16, 18.6%), <i>Lactococcus lactis</i> subsp. <i>lactis</i> (8, 9.3%), <i>Aerococcus viridans</i> (7, 8.5%) and <i>Kocuria rosea</i> (1, 1.1%) were also identified. <i>Staphylococcus</i> species showed the highest resistance to chloramphenicol (50% of samples), followed by clindamycin (42.6% of samples), neomycin and nalidixic acid (40.7% each). No resistance genes were detected for the low levels of resistance to penicillin, oxacillin and cefoxitin. <i>Cellulomonas</i> spp., <i>L. lactis</i> subsp<i>. lactis</i> and <i>A. viridans</i> isolates exhibited moderate frequency of resistance, particularly to aminoglycosides and tetracycline. However, resistances to sulphonamide-trimethoprim, ciprofloxacin, nitrofurantoin, tylosin and rifampicin were rarely detected. Multidrug-resistant (MDR) bacteria were identified in 11.7% of the total isolates, with the higher rates observed for <i>L. lactis</i> subsp<i>. lactis</i> (25% of samples), <i>A. viridans</i> (14.2% of samples) and <i>Cellulomonas</i> spp. (6.25%), while 11% of <i>Staphylococcus</i> isolates were MDR, significantly more in CoPS (28.5%) than CoNS (8.5%). Additionally, MDR rate was higher in older female (<i>p</i> = 0.042) and those raised alongside ruminants (<i>p</i> = 0.030). All tested MDR bacteria exhibited significant combinations of resistance genes, including <i>aph3-IIIa</i> and <i>ant6-Ia</i> for aminoglycosides, <i>cat(pC221)</i> for chloramphenicol, <i>ermA</i> for erythromycin and clindamycin, <i>tetK</i> for tetracycline and <i>drfA</i> for trimethoprim-sulphonamide. Further, comprehensive studies are needed to understand MDR bacteria emergence within camel milk.