Gangrenous mastitis in dromedary camels in UAE caused by Streptococcus agalactiae

Assessment of mastitis in camel using high-throughput sequencing

Camel milk is recognized as a functional food with significant economic value. Mastitis is one of the most common and costly diseases in the dairy industry. Mastitis, which is caused by pathogens such as bacteria, viruses, fungi, and algae, has an impact on the quality and quantity of milk produced as well as animal health and welfare. There is a paucity of data on the etiological factors that cause camel mastitis. This study reports the bacterial and fungal community involved in clinical camel mastitis using Illumina amplicon sequencing. A total of 25 milk samples were analyzed, including 9 samples with mastitis and 16 healthy samples. The bacterial community in healthy samples was significantly more diverse and abundant than in mastitis samples. The fungal population in mastitis samples, on the other hand, was more diverse and abundant. As compared to healthy samples, the genera Staphylococcus, Streptococcus, Schlegelella, unclassified Enterobacteriaceae, Lactococcus, Jeotgalicoccus. and Klebsiella were found to be abundant in mastitic milk. However, the genera Corynebacterium, Enteractinococcus, unclassified Sphingomonadaceae, Atopostipes, Paenibacillus, Pseudomonas, Lactobacillus, Sphingomonas, Pediococcus and Moraxella were reduced. In the fungal community, mastitis caused a significant increase in the relative abundance of the majority of taxa, including Candida, Phanerochaete, Aspergillus, Cladosporium and unclassified Pyronemataceae, while Penicillium and Alternaria showed a decline in relative abundance. In the bacterial and fungal communities, the discriminant analysis showed 19 and 5 differently abundant genera in healthy milk and mastitic milk, respectively. In conclusion, this study showed a microbiome dysbiosis linked to clinical camel mastitis, with opportunistic pathogens outgrowing commensal bacteria that were reduced. These findings are essential in designing an appropriate control program in the camel dairy herd, as well as in preventing and treating camel mastitis.

Risk factors associated with subclinical mastitis and its effect on physico-mineral features of camel milk

This study was carried out to determine the risk factors implicated in camel subclinical mastitis as well as the physico-mineral features of camel milk, there by examining the effect of this disease on those parameters. Milk samples were obtained from 125 lactating multiparous she-camels (aged 10-12 years) during early lactation from December 2020 to April 2021. The samples were screened for the presence of subclinical mastitis using the somatic cell count (SCC) test. In total, 73 (58.4%) samples showed the presence of subclinical mastitis, whereas the remaining 52 (41.6%) samples showed negative results for subclinical mastitis. Standard methods were used to appreciate the pH and mineral composition of the milk samples, such as Ca, Na, Cl, and K contents. In camels, unhygienic udder condition was identified as the major risk factor for the incidence of subclinical mastitis. Calf mortality and increased herd size were associated with a higher prevalence of subclinical mastitis. Tick infestations were also significantly associated with increased disease risk. Use of antisuckling devices, increase in milk yield, and weakness of body condition were identified as main risk factors and were primarily associated with the disease. However, udder lesions and deformities, milking frequency, and owner visits had no significant influence on the occurrence of subclinical mastitis. The overall mean pH value was 6.54 ± 0.01 and the mean values of Ca, Na, Cl, and K contents were 148.24 ± 2.55, 53.83 ± 1.52, 124.99 ± 1.80, and 240.22 ± 3.80 mg/100 g, respectively. When the level of milk from healthy animals and that from camels with subclinical mastitis (SCC > 2.4 × 10⁵) were compared, it showed that Na and Cl contents were significantly increased (p < 0.05) with the increase in SCC (56.52 vs.50.07 and 128.26 vs.120.40 mg/100 g, respectively). In contrast, there were no notable changes (p > 0.05) in the Ca, K, and pH values. In conclusion, udder hygiene, calf mortality, herd size, tick infestations, use of antisuckling devices, higher milk yield, and body condition were identified as the major risk factors that predispose the camels to subclinical mastitis. Furthermore, an increase in the Na and Cl levels in camel milk was observed along with udder inflammation. Consequently, the elevated Na and Cl levels in milk can be a sign of subclinical mastitis in camels.

Bacterial species-specific modulatory effects on phenotype and function of camel blood leukocytes

Background

Recent studies have reported pathogen-species-specific modulating effects on the innate immune system. Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae are important pathogenic bacteria responsible for different infectious diseases in several animal species. In the present study, a whole blood culture with S. aureus, E. coli, or S. agalactiae and flow cytometry were used to investigate, whether stimulation with different bacterial species induces different immunomodulation patterns in camel leukocytes. The expression of different cell surface myeloid markers and cell adhesion molecules on monocytes and neutrophils was investigated. In addition, the capacity of monocytes and neutrophils to produce reactive oxygen species (ROS) was analyzed.

Results

Stimulation with either of the bacterial species resulted in the expansion of the camel CD14^highMHCII^high monocyte subset with a reduced fraction of CD14^highMHCII^low monocytes. For the CD14^lowMHCII^high monocytes, however, only stimulation with S. aureus or S. agalactiae increased their fractions in blood. Although all bacterial species elicited the upregulation of cell surface MHC class II molecules on granulocytes, the increase was, however, highest on cells stimulated with S. aureus. The expression levels of the two adhesion molecules, CD11a and CD18, on neutrophils and monocytes were differently affected by bacterial stimulation. Functionally, E. coli failed to stimulate ROS production in monocytes, while induced a strong ROS production response in granulocytes. S. agalactiae elicited a week ROS production in granulocytes when compared to the other two pathogens.

Conclusions

The different responsiveness of monocytes and granulocytes toward different bacterial species indicates different host-pathogen interaction mechanisms for the two cell populations. In addition, the phenotypic and functional differences between cells stimulated with E. coli, S. aureus, or S. agalactiae suggests pathogen-species-specific modulating effects of the bacterial pathogens on the camel innate myeloid cells.