Dromedary camel milk probiotics and their antimicrobial properties

Dromedary camel or Arabian camel (Camelus dromedarius) is an important part of many communities' lifestyles, particularly in dry areas of the Middle East including Saudi Arabia. According to the Ministry of Environment (2018), Water and Agriculture in Saudi Arabia, the number of camels is estimated at more than 1.39 million heads.

Camels are characterized by their remarkable abilities to adapt to harsh weather conditions, limited agricultural areas and low rainfall. They are used in transportation, sports, and as a source of meat and milk. As a result, camels help to boost the economy and ensure human food security.

In 2020, the GCC camel dairy market was about US$ 502.3 million and is expected to be US$ 661.2 Million by 2024. Camel dairy products are speedily getting popular among health-conscious consumers due to its higher nutritional values and health-improving properties.

Raw dromedary camel milk is an integral part of the nomadic diet due to its antimicrobial properties in relation to many diseases and its high concentration of vitamins, minerals, antimicrobial factors and antioxidants when compared to other animal species. Camel milk contains a wide array of biologically-active compounds including peptides that benefit a variety of bioprocesses such as metabolism, immunity and growth. It has anti-diabetic, anti-hepatitis and bactericidal properties. The presence of biomolecules such as the lactoperoxidase/thiocyanate/hydrogen peroxide system, lactoferrins, lysozyme, immunoglobulins and free fatty acids, protect mammalian milk against microbial contamination to varying degrees. According to the animal species and lactation stage the concentration and activity of antimicrobial substances vary.

Furthermore, immunoglobulin, lactalbumin, serum albumin, peptidoglycan recognition protein and lactophorin are among the proteins found in camel whey. Whey supplementation in the diet may aid wound healing by cellular antioxidant activity.

One of the most common virulent bacterial agents is S. aureus that can survive on dry environmental surfaces for months and causes many serious diseases such as septic arthritis, endocarditis, pneumonia and mastitis. S. aureus infections can spread through skin-to-skin contact or interaction with the pus from an infected wound due to production of hyaluronidase enzyme, which damage tissues and contact with the materials used by an infected person such as towels, sheets, clothing, or athletic equipment.

Escherichia coli is a Gram negative bacilli (Enterobacteriaceae) found as a commensal in the intestinal tract. However, pathogenic strains (pathotypes) of this organism are distinguished from normal flora in that they possess virulence factors such as exotoxins.

The widespread use of antibiotics has increased the emerging of antibiotic-resistant pathogenic microorganisms, limiting the effectiveness against infections. For example, the irresponsible use of the antibiotics, penicillin from the beta-lactam family, which was formerly highly effective against S. aureus. It has developed microbial resistance due to the lactamase producing pathogens, which inactivates lactam antibiotics. According to FAOSTATS, 5 million human deaths were attributed to antibiotics-resistance worldwide in 2019 and the number is increasing annually.

As a result, novel alternative antimicrobials to control bacterial pathogens are urgently needed. It is broadly acknowledged that nutritional components including camel milk and its derivatives decrease the risk of worsening human diseases. Camel milk is becoming more popular for human consumption due to its distinct composition and unique functional properties.

camel milk has been reported with the substantial inhibitory effects against S. aureus and E. coli and decreased their total bacterial count in tissues of rats. Camel milk possesses antimicrobial activity attributed to Lactoferrin, Lysozyme, Lactoperoxidase and short peptidoglycan recognition protein.

Lysozyme is an enzyme, which has an antibacterial activity against Gram-positive bacteria by lysing their cell wall (peptidoglycan layer), disrupting bacterial membranes and activating autolytic enzymes in the bacterial cell wall. Lysozyme exists in camel's milk at a higher concentration (two times more) than in cow's milk. Interestingly, owing to the high content of lysozyme, camel's milk can be kept at room temperature for a long period compared to other animal milks.

Lactoferrin is an iron-binding glycoprotein that exists in camel’s milk at high concentration (0.59–5.10 mg mL⁻¹). It contributes to the initial defense activity against pathogens that enter the body through mucosal tissues. It has the ability to bind free iron, which is one of the elements required for bacterial growth, hence, inhibits the proliferation of many pathogens including Gram-positive and Gram-negative bacteria, protozoa and fungi and viruses. In addition, some of the microorganisms found with surface receptors for the N-terminal region of lactoferrin and Lactoferrin bind to these receptors causing cell death in Gram-negative bacteria due to cell wall disruption and subsequent release of lipopolysacharide, resulting in decreased permeability and increased sensitivity to lysozyme and other antimicrobial agents. Lactoferrin confers the positive charge to the surface and the lipid layer has negative charge which develops electrostatic interaction therefore Gram-positive bacteria are killed due to membrane permeability.

Lactoperoxodase is a heme peroxidase enzyme found in camel's milk, as well as in tears and saliva. It has a profound bactericidal activity, particularly against Gram-negative bacteria. It is thought that its primary function of milk is to protect the udder from microbial infections. Furthermore, lactoperoxidase has been shown to promote general growth, have anti-tumor activity, and play a functional role in catecholamine degradation.

According to the National Health Service in the UK, probiotics are "live bacteria and yeasts which promotes different health benefits. Yoghurts and food products are supplemented with these probiotics and are often described as "good" or "friendly" bacteria". Various microbial groups including beneficial bacteria inhabit camel's milk. In our recent metagenomics study, we have highlighted the existence of beneficial microbiota such as Allobaculum and Akkermansia from fermented and pasteurized camel milk (Sheikh et al., 2022). Additionally, the total cholesterol level was decreased in the fermented camel milk given mice group than in the other milk groups. There are many kinds of research that state the camel milk’s potential against several diseases such as diabetes, allergy, gastrointestinal ulcers, liver disorders etc,. One of our recent study (Khalifa et al., 2022) mentioned probiotic enriched camel milk attenuated Colitis disease in mice model. Many probiotic bacterial groups including Lactic acid bacteria inhabit camel's milk owning to its ideal composition for microbial growth. Lactococcus lactis, a lactic acid bacterium exists in camel's milk and displays abilities to produce hydrogen peroxide, which has been shown to inhibit the growth of pathogenic microorganisms. This effect, however, could be caused by the hydrogen peroxide produced or by activated Lactoperoxodase from the H₂O₂ production in the milk.

Furthermore, some of the studies reported with the use of camel milk in treating hypertension and cardiovascular disorders due to its content of angiotensin-I-converting enzyme (ACE)-inhibiting peptides. ACE is a dipeptidyl carboxypeptidase that converts angiotensin I to active angiotensin II, which is an effective vasoconstrictor. Angiotensin II increase the blood pressure by raising salt levels. ACE inhibitor drugs are frequently prescribed to the individuals having hypertension or other cardiovascular disorders.

camel milk contains IgG immunoglobulin which is the most prevalent Immunoglobulins in the passive immunity of newborns. It is produced 100 g/L in colostrum however, it is declined to 10 g/L during lactation period.

Overall, camel's milk includes numerous health-promoting substances, including bioactive peptides, lysozymes, lactoferrin, Lactoperoxodase and Angiotensin-Converting Enzyme (ACE) inhibiting peptides. Whey from camel's milk is high in nutrients and bioactive peptides. These bioactive peptides have significant antimicrobial, Angiotensin-Converting Enzyme (ACE) inhibitory and antihypertension activities.

Great appreciation should go to Al Bilad Bank Scholarly Chair for Food Security in Saudi Arabia, the Deanship of Scientific Research, Vice Presidency for Graduate Studies and Scientific Research, King Faisal University, Al-Ahsa, Saudi Arabia, for supporting this project grant No CHAIR89.