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

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. Staphylococcus was the most frequently isolated genus (54/86, 62.8%) with 13% of coagulase-positive staphylococci (CoPS) represented by S. aureus and S. intermedius and 87% of coagulase-negative staphylococci (CoNS) (n = 47) identified as S. simulans, S. xylosus, S. warneri, S. hominus1, S. capitis, S. sciuri and S. equorum. Cellulomonas spp. (16, 18.6%), Lactococcus lactis subsp. lactis (8, 9.3%), Aerococcus viridans (7, 8.5%) and Kocuria rosea (1, 1.1%) were also identified. Staphylococcus 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. Cellulomonas spp., L. lactis subsp. lactis and A. viridans 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 L. lactis subsp. lactis (25% of samples), A. viridans (14.2% of samples) and Cellulomonas spp. (6.25%), while 11% of Staphylococcus isolates were MDR, significantly more in CoPS (28.5%) than CoNS (8.5%). Additionally, MDR rate was higher in older female (p = 0.042) and those raised alongside ruminants (p = 0.030). All tested MDR bacteria exhibited significant combinations of resistance genes, including aph3-IIIa and ant6-Ia for aminoglycosides, cat(pC221) for chloramphenicol, ermA for erythromycin and clindamycin, tetK for tetracycline and drfA for trimethoprim-sulphonamide. Further, comprehensive studies are needed to understand MDR bacteria emergence within camel milk.