ABSTRACT
This study investigated the antimicrobial susceptibility and molecular characterization of
Staphylococcus aureus in mastitic cows in southern part of Kano State of Nigeria. A total of two hundred and thirty four (234) milk and swab samples were collected from six (6) local government areas of Kano State in northern part of Nigeria. Staphylococcus aureus was isolated from samples and identified using standard microbiological procedures. The antimicrobial susceptibility of the isolates was determined using Kirby- Bauer disc diffusion technique as described by the Clinical and Laboratory standards institute (CLSI). Resistant isolates were tested for Beta-lactamase production. A total of 200 (85.5%) have staphylococcal isolates, of which 141 (70.5%) were Staphylococcus aureus (coagulase positive staphylococci, CPS), 59 (29.5%) were coagulase negative staphylococci (CoNS) and 6 (2.9%) were non- Staphylococcal (rods) isolates. The antibiotic susceptibilities of the Staphylococcus aureus isolates were in the following order: ofloxacin (99.3%) > ciprofloxacin (98.6%) > gentamicin (91.5%) > cephalexine (56%) > sulphamethoxazole/trimethoprim (46.1%) > tetracycline (43.3%) > cefuroxime (33.3%) > cefoxitin (2.1%) > amoxicillin (1.4%) > ampicillin (1.4%). Resistance to three or more antimicrobials was presented in 98.6% of the Staphylococcus aureus isolates. Of the 141
Staphylococcus aureus isolates tested for β-lactamase production, 31 (22.5%) were β lactamase producers. However, of the 31 β-lactamase producers, only 13 (41.9%) were multidrug resistant to cefoxitin, Ampicillin and cephalexine. PCR assay was used to detect mecA and blaZ genes in multi-drug resistant Staphylococcus aureus isolates that were β-lactamase producers. The MDR-
Staphylococcus aureus was also tested by latex agglutination for presence of PBP2a. PCR results indicated none of the isolates showed any amplification to both mecA gene and blaZ gene. All the Beta-lactamase producing MDR- Staphylococcus aureus isolates tested showed negative reaction to latex agglutination test which was also an indication of absence of Pinicillin binding protein (PBP2a). In conclusion, high isolation of Staphylococcus aureus (70.5%) causing bovine mastitis was observed in this study in which both mecA and blaZ genes were absent.
CHAPTER ONE
1.0: INTRODUCTION
Mastitis is the inflammation of the parenchyma of the mammary gland regardless of the cause. It is characterized by a range of physical and chemical changes in the milk and pathological changes in the glandular tissue. The most important changes in the milk include discoloration, the presence of clots and the presence of large number of leukocytes. There is swelling, heat, pains and indurations in the mammary gland in many clinical cases (Roberson et al., 1994).
Bovine mastitis is a multifactorial disease that results in reduced milk production, changes in milk composition and milk discard. It imposes serious economic losses to the farmers and the dairy industry (Ribeiro et al., 2003; Pitkala et al., 2004). Mastitis can be moderate or severe, and can be caused by many different bacterial species but more commonly by Staphylococcus and
Streptococcus strains (Pyorala, 2002). Coagulase-negative staphylococci (CoNS) are of great interest in veterinary medicine because they are currently being considered emerging pathogens of bovine mastitis. Although CoNS are not as pathogenic as the other principal mastitis pathogens and infection mostly remains subclinical. They can however result in persistent infections, which result in increased milk somatic cell count (SCC) and decreased milk quality (Pyorala, 2002). Prevalent CoNS species vary according to the geographical region under scrutiny (Huxley et al., 2002). Antibiotic resistance is the most puzzling question of public health concern in the earlier decade of this 21st century. Mastitis is the single most common reason for the use of antimicrobials in dairy cattle husbandry. Use of antimicrobial treatment is required for clinical mastitis, persistent infections and in heifers before calving (Taponen et al.,
2006). Therefore, antimicrobial resistance of mastitis pathogens has received much interest over.....
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