| dc.description.abstract | ilk is important as a valuable diet, but due to its nutritional value it serves as an ideal medium for development of various microorganisms under suitable conditions, hence it can be a potential source of zoonotic pathogens. Microbial contamination in milk comes from various sources, including: sick animals (mastitis cases), humans, environment, water, equipment used for milking and storage of milk. Antimicrobials are routinely used for treatment of dairy cattle affected with clinical mastitis. Over time, this usage has increased the number of antimicrobial-resistant bacteria. Thus, in order to identify the effective drug to use, antimicrobial susceptibility testing needs to be carried out. This study was carried out in the north-western region of Rwanda, to determine the prevalence of subclinical mastitis and associated risk factors, evaluate bacterial contamination of cow milk along the milk market chain, and establish the antimicrobial susceptibility patterns of isolated bacteria.
For subclinical mastitis (SCM), a cross-sectional study was carried out on a total of 123 crossbred milking cows from 13 dairy farms randomly selected, their milk screened for SCM using California Mastitis Test (CMT), and milk samples collected and processed for bacterial isolation and identification following the method of Black (2011). The overall SCM prevalence at cow level was 50.4%. Sixty eight (68) bacterial isolates were identified by morphological and biochemical characteristics; the most prevalent being coagulase negative staphylococci (CNS) (51.5%) followed by Staph. aureus (20.6%), while E. coli was isolated at 1.5%. Only 5.5% and 2.7% of the farmers reported using dry cow therapy and teat dips, respectively, to control mastitis.
For determination of milk contamination along the market chain, 67 raw milk samples were collected and analysed for Total Bacterial Counts (TBC) at four dominant stages of the raw milk chain: 36 dairy farmers, 15 milk hawkers, 4 milk collection centres (MCC) and 12 milk kiosks. A designed questionnaire was adapted to gather information regarding animal health management practices and milking procedures, factors and milk handling practices that influence milk quality along the milk market chain. The study revealed a TBC mean value of 1.2 x 106 cfu/ml (dairy
farmers), 2.6 x 107 cfu/ml (milk hawkers), 1.5 x 106 cfu/ml (MCC) and 6.9 x 106 cfu/ml (kiosks/restaurants). The most commonly isolated bacteria from the milk samples, along the milk market chain were: E. coli (18, 26.9%) and Salmonella spp. (11, 16.4%). Total bacterial count was significantly associated with containers used for milk transport, cleaning time for milk containers and source of water used to clean containers. It was moderately associated with production system, milking space, while there was no association found between bacterial loads and time used to supply milk to the MCC.
Agar disk diffusion method was used to evaluate antimicrobial susceptibility patterns of 83 isolates including: coagulase negative staphylococci (n=45), Staphylococcus aureus (n=19) and Escherichia coli (n=19) isolates from SCM and bulk tank milk samples, using ten (10) antimicrobials. Diameters of zones of inhibition were recorded and interpreted as susceptible, intermediate or resistant according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Coagulase negative staphylococci demonstrated high susceptibility to gentamicin (100%), ceftriaxone (100%) and ciprofloxacin (97.8%). All the isolates were resistant to ampicillin, with CNS and Staph. aureus showing resistance to penicillin at 57.8% and 73.7%, respectively and E. coli being resistant to amoxicillin/clavulanate (31.6%). However, all the isolates tested were susceptible to ciprofloxacin, ceftriaxone and gentamicin.
This study has revealed a high prevalence of subclinical mastitis predominantly caused by Staphylococcus spp. It has also revealed that milk contamination started at the farm and increased along the market chain. The results of this research also indicate that Gentamicin, Ceftriaxone and Ciprofloxacin are promising alternative agents to combat staphylococcal infections. It is, therefore, recommended that farmers in the study area implement good milking practices so as to ensure clean milk production. Other actors of the milk value chain should observe good milk handling practices to reduce contamination along the market chain. It is also recommended that regular screening of antimicrobial susceptibility for the most used drugs in the treatment of bacterial infections be encouraged. | en_US |
