With a population of many million animals, camels represent a major livestock species in the Horn of Africa. The diet of people living in semiarid and arid regions in the Horn of Africa is to a large extent based on raw camel milk. Therefore, the health status of the camel and specifically of its mammary glands is important for human nutrition in the region. The mapping of capsular types, clinical complexes, and antimicrobial resistance to specific MLST generated sequence types revealed interesting insights into the molecular epidemiology of GBS from camels. We identified three clonal complexes/populations within the camel GBS (Figure 1). The biggest population comprising 64 isolates encompassed four capsular types and isolates from diseased and healthy animals. Abscesses and wound infections accounted for the majority of clinical isolates within this population. The second largest population consisted of 26 isolates, which all belonged to the ST-616 and were of capsular type III only. This population consisted of clinical isolates only, originating from milk of mastitic camels. This population showed the least diversity in terms of capsular types, and clinical complexes and is of most importance to the livestock keeper, since mastitis is the main constraint for productivity of camels. The third population detected in this study contains ST-609 and ST-614. When compared to human isolates, the four camel isolates accounting for STs ST-609 and ST-614 clustered in one population with human GBS isolated in Kenya. The four human isolates belonged to ST-26 and to capsular type V. These isolates represent hybrids of mixed ancestry (Figure 3), pointing towards a high plasticity of S. agalactiae and the possible occurrence of genetic exchange . Nevertheless, only three alleles are shared between the camel and human strains within this population, and camel strains are clearly distinct from human strains on the phylogenetic tree (boostrap values on Figure 2). Another study showed that, even if bovine and human strains share all seven alleles of the MLST scheme, they represent distinct lineages, as demonstrated by including more housekeeping genes . Therefore, our data do not provide evidence of cross-species transmission of camel GBS to humans or vice-versa. Nevertheless, GBS from people in intimate contact with camels or camel products should be collected and compared to these strains in order to completely rule out such a possibility.
In order to advise animal holders, caretakers and veterinarians on the best options to treat GBS infections in camels we investigated the susceptibility to 23 anti-microbial drugs used in veterinary and human medicine. Clinical breakpoints which are animal species and disease specific  are unfortunately not available for camels. However, the CLSI clinical breakpoints available for streptococci from animal species other than camels  as well as the high MIC90 values for tetracycline (64 mg/L) and gentamicin (32 mg/L) indicated resistance to these antimicrobials. While the resistance to gentamicin is genus specific and hence expected we additionally detected resistance to tetracycline in 34% of all camel GBS tested. According to EUCAST ECOFF values the MIC90 value for tetracycline was high above the cut-off supporting the finding of acquired resistance to tetracycline. Two previous reports based on relatively low numbers of isolates and antimicrobials tested via agar diffusion sensitivity testing reported a higher prevalence of tetracycline resistant isolates (44% to 53%) which might be attributed to the low number of isolates tested, the method used or the sampling scheme . Resistance to tetracycline was detected in three different STs within the two large clonal complexes/populations. Interestingly, not all isolates from any of the three STs were resistant. Most resistant isolates (71%) belonged to the mastitis causing isolates of ST-616. We showed that resistance was conferred by the gene tetM. The latter has been reported to be characteristic for resistance against tetracycline especially in human GBS . Interestingly, the presence of the tetM gene in three different STs, which represent two distinct populations, suggests a repeated acquisition of the tetM gene via transposition by a Tn916-like element as indicated by our PCR results . Our current data do not provide a conclusive picture on the source of tetracycline resistance genes detected in camel GBS. Sequence analysis of the flanking regions of tetM via full genome sequencing might help in answering this question .
Tetracycline is a broad spectrum antimicrobial commonly used to treat bacterial infections in animals in the Horn of Africa. The use of tetracycline and other antimicrobials is not as regulated and closely monitored as in the industrialized world and the entry of antimicrobial residues into the food chain is therefore difficult to control. Our findings show that mastitis in camels caused by GBS should be treated with antimicrobials other than tetracycline to prevent the further spread of tetracycline resistant clones. Alternative drugs are increasingly available in pastoralist regions of East Africa and should be favoured to tetracycline for treatment of mastitis caused by GBS. However, it has to be noted in this respect that one camel GBS isolate of our study revealed an increased MIC to β-lactam antibiotics, assumingly a first step to resistance, indicating that use of this kind of antibiotics in the region might also lead to resistance problems.
Given the increasing importance of camels as dairy animals, and the limitations and risks of parenteral and intra-mammary antibiotic treatments for camel mastitis, long term research into alternative disease control options such as vaccination combined with specific point of care diagnostic tests is highly desirable and timely. In this respect, antigens of capsular type III GBS are a good starting point  and require further characterization regarding their potential use in glycogonjugated vaccines or as diagnostics molecules. A vaccine against all camel capsular types would be desirable but is likely to be even more challenging.
Camel GBS should be added to pangenome studies of GBS since they are more distantly related to human strains than livestock species such as cattle given the number of shared alleles . Whole genome sequencing and analysis of camel GBS might reveal supplementary biochemical pathways and functions that are not essential for bacterial survival but which might explain the origin of antibiotic resistance genes or reveal colonization factors necessary to infect the camel. In addition, genome data will allow to identify molecular targets specific to camel GBS for diagnostic tool development.
Camel GBS sequence types (STs) were distinct from STs reported from other hosts so far. Most mastitis causing GBS were associated with ST-616. Widespread resistance (34%) to tetracycline was most prominent in ST-616 and associated with acquisition of tetM carried on a Tn916-like element. The presence of tetM within different MLST clades suggests acquisition on multiple occasions. Wound infections and mastitis in East African camels associated with GBS should be treated with antimicrobials other than tetracycline in East Africa.