Assessment of bacterial contamination in buffalo milk and dairy products and associated factors along the buffalo milk chain in Noakhali district, Bangladesh

Abstract

Milk and milk products can harbor a variety of microorganisms, which might have negative impact on human health. Raw milk can be contaminated by microorganisms originating from the udder (either clinical or subclinical mastitis), by zoonotic pathogens from the environment due to poor hygienic status of the teat and udder, unhygienic handling of milk, unclean milking equipment as well as improper cooling during transportation. These are some examples of factors which influence microbial contamination and growth before the milk product reaches to the consumer through the milk chain. The present cross-sectional study was designed to investigate the level of bacterial contamination in buffalo milk and milk products and associated factors along the buffalo milk chain in Noakhali district, Bangladesh. A total of 132 milk samples and 10 milk products from households and semi-bathans (free ranging) milk and from 4 different nodes in the household and semi-bathan milk value chains (farm, middlemen, and collection centre and milk products) were collected during April, 2021. The samples were analyzed qualitatively and quantitatively for various bacterial counts and occurrence of pathogenic micro-organism. Epidemiological analyses were also performed to investigate potential risk factors associated with high bacterial counts. Quantification of bacteria as well as isolation and identification of 5 different bacteria (Non-aureus Staphylococcus, Staphylococcus aureus, Streptococcus spp., E. coli., Klebsiella spp.) were done following standard bacteriological method. Pearson’s correlation coefficient test was performed to identify correlations between bacterial counts while univariable analysis and multivariable regression analysis was performed to investigate risk factors associated with bulk milk somatic cell count (BMSCC) and total bacterial count (TBC). Farm BMSCC varied between 5.09 and 6.08 cells/ ml, whereas the mean BMSCC at the farm milk samples was 5.61 log10 cells/ ml. The mean value of TBC at the farms level was 5.54 log10 cfu/ ml, whereas TBC in milk samples at different nodes (middlemen, collection centres and milk products) were 5.81, 6.80 and 7.24 log10 cfu/ ml, respectively. The progressively increased level of TBC was found significant (p ˂0.001). However, both BMSCC and TBC have exceeded the European Union (EU) legislative standard limit of milk quality. Other bacterial counts such as total Non-aureus Staphylococcal count (TNAS) and total Enterobacteriaceae count (TEC) were also found x at significant increasing level (p˂0.001) across the milk chain except Total Staphylococcal count (TSA) which was statistically non-significant (p=0.48). The highest mean value of TSA (1.95 to 2.14 log10 cfu/ ml), TNAS (3.44 to 3.88 log10 cfu/ ml) and TEC (3.95 to 4.46 log10 cfu/ ml) were also found at the collection centre and milk product level which was also above the EU legislative standard limit of milk quality. Moreover, significant positive correlations were found between BMSCC and TNAS (r=0.35; p=0.01), TBC and TNAS(r=0.55, p<0.001) at the farm level, between TBC and TEC (r= 0.40, p =0.05) at middleman level and between TBC and TNAS (r=0.31, p =0.03), TBC and TEC (r=0.39, p= 0.02) at collection centre level. Among the prevalence of different microorganisms, Non-aureus Staphylococcus (NAS) had the highest frequency along the nodes in the value chain (71% at farm level, 69% at the middlemen level and 71% at the collection centre) followed by Streptococcus spp. (55% at farm level, 51% at the middlemen and 71% at the collection centre). S. aureus (26%) and E. coli. (29%) were highly prevalent at the collection centre where as a high amount of Klebsiella spp. (20%) was found in milk products. The univariable analysis showed different risk factors for BMSCC: “How to sell your milk” (p= 0.06) and “How do you clean your container” (p= 0.06) and for TBC: farm zones (p= 0.06), source of milk (p= 0.08), frequency of cleaning milk container/day (p =0.05) and the score of milker’s hygiene (p= 0.10) at the farm level. However, no risk factor remained in the multivariable linear regression model. The findings of this study indicate that raw milk and milk products in the milk value chain can possess high bacterial contamination that might cause serious public health hazards especially for those communities who still consume raw or improperly treated milk and milk product. So, there is a need to implement appropriate control measures to reduce microbial contamination along the milk value chain to minimize the milk-borne diseases in humans.