Antibiotic resistance in Streptococcus agalactiae isolates from dairy camels in Kenya

Sammanfattning: Camels (Camelus dromedarius) are the most valuable livestock species in the arid and semi-arid lands in the Horn of Africa where the majority of the human population adopts a pastoralist lifestyle with extensive animal husbandry. Camels provide an important food source, milk, which is considered to be the most important commodity, and a source of income for the pastoralists. The health of the camel, and especially the udder health, is therefore very important for the pastoralist communities living in the arid areas in Kenya that do not support other livestock. Streptococcus agalactiae (SRA) is considered to be a zoonotic bacterium that can cause disease in both humans and animals but its zoonotic potential is not entirely clarified. It is a highly contagious udder-bound pathogen most known as a cause of mastitis, particularly in cattle, but also in camels. A few studies have also isolated SRA in apparently healthy camels, suggesting the bacteria could be a commensal. Antibiotic resistance (ABR) is a serious health threat to both humans and animals as well as a threat to food security, global development and economies worldwide. Antibiotic resistance in bacteria causing disease in camels can potentially be transmitted to people consuming camel products or handling these animals. The two antibiotic classes that are most frequently used in livestock production are tetracyclines and β-lactams. Tetracycline resistance has been observed in SRA isolates derived from camels in Kenya, but little resistance to β-lactams has been found. The prevalence of resistant and possibly multi-resistant bacteria in camels in Kenya is not known to a great extent. The aim of this study was to investigate if phenotypic ABR and possibly multiresistance is present in SRA isolates from dairy camels in Laikipia County, Kenya. The overall objective was to increase the knowledge of ABR among SRA in dairy camels in order to prevent further resistance development. In this study, six camel herds were selected for sampling; ranches (n=3), pastoralist (n=1) and smallholders (n=2). From each herd all lactating dams and their respective calves were sampled. In total, 179 individuals were sampled; 89 lactating camels and 90 calves. In lactating camels, milk samples were collected from lactating dams with a California Mastitis Test score of 2 or higher and swabs were taken from the nasal and vaginal mucosa; in their respective suckling calves from the nasal, oral and rectal mucosa. Primary identification of SRA in milk and swab samples was performed by bacterial culturing and confirmed by Matrix assisted laser desorption ionization-time of flight (MALDI-TOF). Antimicrobial susceptibility testing was performed by broth microdilution method to determine antimicrobial susceptibility in SRA isolates. In this study, SRA was isolated from 27% of the sampled individuals. The bacterium was found at all sampling sites, except for vaginal swabs, in both healthy and CMT-positive lactating dams as well as in apparently healthy calves, supporting the suggestion that SRA is a commensal and an opportunistic pathogen in camels. The overall prevalence of tetracycline-resistant SRA isolates was high (57%) in the six herds, especially in the pastoral and ranch managed systems. No resistance to penicillin was detected. Tetracycline-resistant SRA isolates were found at all SRA-positive sampling sites. All SRA isolates from milk samples were resistant to tetracycline. A few camels and calves were SRA-positive in more than one sampling site and resistance to tetracycline could be found in one, two or none of these isolates. The results in this study, in combination with earlier results from Kenya, shows that a shift from the use of tetracycline to penicillin when treating diseases in camels would be favourable as there is a risk that tetracycline would be ineffective. Bacteria that already have acquired resistance genes will however continue to spread within and between herds. Hence, finding a resistant bacterial isolate in a camel does not per se mean that the bacterium has become resistant due to antibiotic treatment. To avoid further development of resistant bacteria, prevention of disease is the most important objective. Healthy animals do not require antibiotic treatment.