الفهرس 
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Abstract
Mastitis in sheep and goats constitute an enormous animal health problem. The economic importance of mastitis in small ruminants is principality due to premature culling of animals with udder abnormalities, reduction in both milk quantity and quality. The present study was designed to study the phenotypic and genotypic characterization of some bacterial pathogens associated with SCM in sheep and goats.
The results of clinical examination of the udders of lactating ewes (n=125; 250 udder halves) and does (n=125; 250 udder halves) revealed that out of 500 examined udder haves, 481 halves were apparently normal; 242 in ewes and 239 in does, while 19 halves showed complete loss of function; 8 in ewes and 11 in does.
According to CMT applied in the current study, the overall prevalences of SCM in examined animals and udder HMSs level were 35.6 and 27.4%, respectively. The prevalences of SCM were 29.6 and 21.1% in sheep and udder HMSs levels, respectively. On the other hand, the prevalences were 41.6 and 33.9% at goats and udder HMSs levels, respectively.
The results of bacteriological examination of milk samples collected from lactating sheep and goats revealed that 71.9% of examined animals revealed positive bacterial isolation; 42.7% were single while 29.2% were mixed isolates. Regarding sheep, the percentage of bacterial isolation was 67.6%; 43.2% single and 24.3% mixed. Meanwhile in goats, the percentage was 75%; 42.3% single and 32.7% mixed. On the other hand, at individual HMSs level it was found that 70.5% of the collected HMSs samples revealed positive bacterial isolation; 45.5% single while 25% mixed isolates. Regarding sheep HMSs, the percentage of bacterial isolation was 66.7%; 41.2% single and 25.5% mixed. Meanwhile in goats HMSs, the percentage was 72.8%; 48.1% single and 24.7% mixed.
Results of isolation and identification of different bacterial pathogens recovered from subclinically mastitic animal milk samples (n=132) by traditional methods in addition to Vitek2 compact system showed that 126 bacterial isolates (95.5%) were recovered and identified. Of the isolates, 60 (45.5%) were single and 66 (50%) were mixed. S. aureus and CNS were the most prevalent isolates represented (24.2%, for each), followed by E. coli (19.7%), Streptococcus spp. (14.4%), Enterococcus spp. (7.6%), and P. aeruginosa (5.3%).
Regarding sheep milk isolates, 47 bacterial isolates out of 51 examined HMSs (92.2%) were identified. CNS was the most prevalent (25.5%), followed by S. aureus (21.6%), both of E. coli and Streptococcus spp. (15.7% for each), Enterococcus spp. (7.8%), and P. aeruginosa (5.9%).
Concerning goat milk isolates, a total of 79 bacterial isolates out of 81 examined HMSs (97.5%) were identified. S. aureus was the most prevalent (25.9%), followed by CNS (23.5%), E. coli (22.2%), Streptococcus spp. (13.6%), Enterococcus spp. (7.4%), and P. aeruginosa (4.9%).
Regarding CNS isolates (n=32), S. epidermidis was the most prevalent (6.8%) followed by S. xylosus (5.3%) and S. simulans (3.8%), S. chromogenes and S. haemolyticus (3% for each), S. auricularis (1.5%), and S. cohnii (1.5%).
Among Streptococcus isolates (n=19), S. agalactiae was the most prevalent (6.8%), followed by S. dysgalactiae (5.3%), and S. uberis (2.3%).
Concerning Enterococcus isolates (n=10), E. faecalis was the most prevalent (3.8%), followed by E. faecium (3%), and E. hirae (0.8%).
The results of haemolytic activity on sheep blood agar of different bacterial pathogens revealed that 75.4% of the bacterial isolates were haemolytic; 67.5% were β-haemolytic while 7.9% were α-haemolytic. Haemolysis was represented as 75, 71.9, 84.6, 100, 30 and 100% in CNS, S. aureus, E. coli, Streptococcus, Enterococcus and P. aeruginosa isolates, respectively, and they were mostly β-haemolytic.
The results of biofilm production on YESCA CR agar medium of different bacterial pathogens revealed that 57.9% of the bacterial isolates were biofilm formers; 46.8% strong biofilm formers while 11.1% intermediate. Biofilm production was represented as 53.1, 59.4, 46.2, 63.2, 70 and 87.5% in CNS, S. aureus, E. coli, Streptococcus, Enterococcus and P. aeruginosa isolates, respectively, and they were mostly strong biofilm formers.
The results of in-vitro antimicrobial susceptibility against 13 antimicrobial agents revealed high resistance of staphylococcus isolates to ampicillin, amoxicillin-clavulanic, cefoxitin, cefotaxime sodium and vancomycin. Meanwhile, high susceptibilities were recorded against ciprofloxacin, levofloxacin, florophenicol, doxycycline HCl, clindamycin, gentamicin and sulfamethoxazole-trimethoprim. Streptococcus isolates revealed high resistance to gentamicin, β-lactams (penicillins and cephalosporins) and fluoroquinolones (levofloxacin and ciprofloxacin). On the other hand, high sensitivities were recorded against florophenicol, vancomycin, doxycycline HCl and clindamycin. Enterococcus isolates recorded complete or high resistances against most of the tested antimicrobial agents except vancomycin and sulfamethoxazole-trimethoprim which revealed high sensitivities. E. coli and P. aeruginosa isolates showed complete or high resistances against all the tested antimicrobial agents.
Using PCR in the current study, mecA, blaZ and tetK resistance genes were assessed in 14 MDR CNS and S. aureus isolates. The mecA, blaZ, tetK and icaD genes were detected in 78.6, 57.1, 71.4 and 42.9 % of CNS isolates as well as 100, 78.6, 71.4 and 71.4% of S. aureus isolates, respectively. Additionally, all the examined S. aureus isolates harbored nuc, coa and spa genes while, hla was detected in 64.3% of the test isolates.
All the tested E. coli isolates harbored qnrA, tetA(A) and blaTEM genes while sul1 gene was detected in 75% of the tested isolates. Meanwhile, fimH, papC and hlyA genes were detected in 100, 58.3 and 50% of the tested E. coli isolates, respectively.
The results indicated that vanC1, aac(6’)aph(2’’), tetO and vanA genes were found in all the tested streptococcus isolates. Additionally, pbpA, brpA, cfb, hyl and cylE genes were detected in 85.7, 85.7, 57.1, 42.9 and 71.4% of the tested streptococcus isolates, respectively.
The vanC1, aac(6’)aph(2’’), tetO and blaZ genes were found in all the tested enterococcus isolates. Additionally, each of vanA, hyl and asa1virulence genes were detected in 80% of the enterococcus isolates while cylE gene was detected in 60% meanwhile gelE gene was not detected in any tested isolate.
The results revealed that all the tested P. aeruginosa isolates harbored qnrA, tetA(A), blaTEM, mexR toxA, phzM and lasI genes while ecfX gene was detected in 85.7% of the tested isolates.
The results concluded that there is a strong association between the phenotypes and genotypes of AMR in different bacteria. Moreover, biofilm is a fundamental problem for dairy farms affecting the udder health and represents a risk for milk quality and consumer health. Also, biofilm formation is associated with acquiring MDR by a high proportion of bacterial pathogens recovered in this study.