Evaluation of the Bacteriological Quality of Milk Sold in Nnewi, Nigeria

Introduction: Contamination of milk products can result to severe intestinal and extra-intestinal diseases in man. This study was aimed at evaluating the bacteriological quality of various milk products sold in Nnewi.

Materials and Methods: Using the Cluster sampling technique, 30 milk samples (5 pasteurized skimmed milk, 5 powdered infant milk formulas, 5 powdered milk, 5 unsweetened evaporated milk, 5 branded soya milk and 5 unbranded soya milk) were purchased randomly from different shops and hawkers around Nnewi. Sample processing was done by serially diluting samples in sterile 1% peptone water before plating onto Mannitol Salt Agar, Violet Red Bile Glucose Agar, Blood Agar, MacConkey and Cysteine Lactose Electrolyte Deficient (CLED) agar using the Pour-plate technique. Bacterial count and identification were done using standard bacteriological as well as molecular techniques. The molecular techniques used were Polymerase Chain Reaction, Sanger Sequencing and BLAST analysis on the NCBI BLAST online.

Results: This showed that 15 (50%) out of 30 milk samples were contaminated to varying degrees with bacteria. Nine (9) samples showed the presence of Escherichia coli with 32.14% of all the milk samples tested. E. coli was present in skimmed milk (20%), evaporated milk (20%), branded soyamilk (40%) and unbranded soyamilk (100%) but was not isolated from Infant formula and Powder milk. Klebsiella spp. showed the second highest prevalence (28.57%) and was present in evaporated milk (20%), branded soyamilk (40%), unbranded soyamilk (100%). Salmonella spp. (3.57%) was isolated from unbranded soyamilk,Enterobacter spp. (14.29%) was isolated from powder milk and in unbranded soyamilk samples, Staphylococcus aureus(3.57%) and Staphylococcus epidermidis (3.57%) were isolated only in unbranded soyamilk, Macrococcus caseolyticus (3.57%) was isolated from unbranded soyamilk. Novel species such as Aquitalea magnusonii (3.57%), Alishewanella fetalis (3.57%) and Lysinibacillus macroides (3.57%) were identified by molecular analysis to be present in infant formula, evaporated milk and unbranded soyamilk respectively.

Conclusion: This research revealed that the bacteriological quality of some milk and milk products sold in Nnewi is not acceptable especially the unbranded soyamilk samples that showed gross contamination.