The results of the current study indicated the interference of both environmental and contagious agents in the goat’s mastitis and E. coli as an environmental bacterium was the most frequent isolated pathogen in the milk samples (29.1%). Bradley and Green (2001), reported E. coli as the predominant pathogen isolated from the six studied herds in Somerset in all the months of the year (Bardley and Green, 2001).
The other bacteria were detected in the present study included T.pyogenes, S.aureus, Mycoplasme spp., S. agalactiae, CoNS and C. pseudotuberculosis respectively. Generally, the most important pathogens of mastitis are Staphylococcus, Streptococcus, Mannheimia haemolytica, Mycoplasma agalactiae, Trueperella pyogenes, and coliforms (Esmaeili and Hamedi, 2019).
It has been approved that bacterial agents such as Staphylococcus spp., Streptococcus spp., and E. coli are the main causative organisms of mastitis in goats (Zhao et al., 2014). In the study of Goncagul et al (2021) in Turkey, non-aureus staphylococci and E.coli were respectively the most frequent bacteria in mastitis cases in Saanen breed (18.9%). The authors found S. aureus, S. agalactiae, and S. epidermidis as the other isolated bacteria from apparently healthy goats (Goncagul et al., 2021).
Mastitis is a multifactorial diseas in which the farm's sanitary condition, environmental factors and animal status are involved (Balemi et al., 2021). It is evident that isolation of various pathogens from goat herds is strongly associated with the unsuitable herd's hygiene status and its incompetence management system (McDougall et al., 2002). Moreover, the prevalence of contagious and environmental pathogens which we have isolated with high percentage, is associated with contaminated bed with faces and urine (Radostis et al., 2007). Isolation of different pathogens should be considered as a serious warning in industrial farms. Therefore, as eradication is not rational, implementation of biosecurity plans, hygiene and proper disinfection are the most cost-effective ways to control mastitis.
Our study evaluated the frequency of mastitis bacteria in Saanen and Alpine breeds for the first time in Iran and meanwhile antibiotic resistance of each bacteria was assessed in both breeds. According to the results, the difference in antibiotic resistance between Saanen and Alpine was merely seen in the case of amoxicillin (Table 2). The Alpine goats were significantly more resistance to amoxicillin compare to the Saanens. Resistance to amoxicillin was seen in C.pseudotuberculosis, but amoxicillin and florfenicol were the best choices against CoNS and S. aureus. Jabbar et al. (2020) in Pakistan found the same results and they considered amoxicillin as the choice drug against Staphylococcus (Jabbar et al., 2020). In the study of Balemi et al. (2021) in Ethiopia, S.aureus was the most prevalent agent among other bacteria in goats and it was 100% resistant to penicillin G and spectinomycine, but it showed 100% sensitivity to doxycycline, ceftriaxon, and vancomycine (Balemi et al., 2021).
By contrast S. aureus sensitivity to amoxicillin in the current study, this bacterium was highly resistant to streptomycin and lincomycin (100%), but in case of CoNS, 100% resistance was seen towards penicillin, gentamicin, lincomycin and streptomycin. In the study of Goncagul et al. (2021), E.coli was 100% sensitive to amoxicillin (Goncagul et al., 2021), while our investigation identified penicillin, gentamicin and tulathromycin as the antibiotic choices for E. coli. Furthermore, an in vitro study in 2010 showed that generally gentamicin is more effective against mastitis bacteria (Ali et al., 2010).
Contrary to the current evaluation, in the study of Begum et al. (2016) tetracycline was identified to have the highest efficacy against mastitis bacteria in goats (Begum et al., 2016). We identified oxytetracycline as one of those antibiotics which S. agalactiae, T. pyogenes and C. pseudotuberculosis showed the most resistance against. Similarly, Ramprabhu (2019) found the isolated bacteria from subclinical mastitis milk of goats are relatively resistant to tetracycline and amoxicillin. The researcher claimed that it might be as a result of variation in the level of usage of these drugs (Ramprabhu, 2019). Excessive administration and lack of supervision over oxytetracycline usage by farmers in small ruminants is one of the important causes of increasing bacterial resistance to this antibiotic in Iran.
Antibiotics are routinely used in the treatment of mastitis. However, the more occurrences of mastitis happen in a farm, the more unconscious use of antibiotics in infected animals takes place. It eventually leads to an increase in the risk of antibiotic resistance which the presence of them in milk particularly S.auerus is hazardous for public health (Rainard et al., 2018). Therefore, precise diagnosis and identification of the etiological agents causing mastitis and the use of effective antibiotics are necessary to determine treatment strategies.
Based on the obtained data and high multidrug resistance of the microorganisms, using antibiogram test by clinician is necessary in the treatment of mastitis. Avoidance from applying numerous and unnecessary antibiotics, especially since mastitis is one of the recurring causes of removal of animals from the farm, is another important proceeding. In addition, after determination of bacterial susceptibility against antibiotics, the results of the usage of specific antibiotics should be monitored. In conclusion, sampling of a larger range of animals and identification of subclinical cases, faster diagnosis and treatment of the disease which prevents mastitis progression and further economic damages are strictly recommended. We showed significantly higher resistance to amoxicillin in Alpine breed so further studies are needed to evaluate the issue of antibiotic resistance in this breed.