BACTERIOLOGICAL QUALITY AND ANTIMICROBIAL SUSCEPTIBILITY PROFILES OF RAW, FERMENTED, AND PASTEURIZED MILK IN KADUNA METROPOLIS, NIGERIA
Keywords:
milk microbiological quality; Kirby–Bauer disc diffusion; antimicrobial resistance profiling; food-borne pathogen isolation; Kaduna dairy safetyAbstract
Background: Milk is a nutrient-rich, microbiologically permissive medium whose contamination
across production, processing, and distribution poses significant public health risks, particularly in
resource-limited settings.
Objective: To evaluate the microbiological quality of raw cow milk, traditionally fermented milk
(nono), and laboratory-pasteurized milk from Kaduna Metropolis, Nigeria, and characterize the
antimicrobial susceptibility profiles of isolated pathogens.
Methods: Twelve milk samples (n = 4 per group) were analysed for total plate count (TPC) and
coliform count by serial dilution and spread-plate method. Staphylococcus spp., Escherichia coli,
and Pseudomonas aeruginosa were selectively isolated and identified by Gram staining and
biochemical assays. Antimicrobial susceptibility testing was performed by Kirby–Bauer disc
diffusion against ceftriaxone, cefoxitin, and amoxicillin–clavulanic acid, with categorical
interpretation applied only to organisms with defined CLSI breakpoints.
Results: Mean TPC values were 1.47 × 10⁷, 6.15 × 10⁶, and 1.53 × 10⁶ CFU/mL for raw,
fermented, and pasteurized milk respectively — all exceeding the 1 × 10⁵ CFU/mL regulatory
threshold. All three pathogens were recovered from 100% of raw milk samples. Fermented milk
yielded Staphylococcus spp. and P. aeruginosa in 100% and E. coli in 75% of samples. Pasteurized
milk showed markedly reduced rates (Staphylococcus spp. and E. coli, 25% each; P. aeruginosa,
0%). Staphylococcus spp. were susceptible to amoxicillin–clavulanic acid (77.8%) but largely
resistant to ceftriaxone (66.7%). Among E. coli isolates, susceptibility was highest for ceftriaxone
(75.0%) and cefoxitin (62.5%); two isolates showed complete absence of inhibition against all
three agents, suggesting broad β-lactam non-susceptibility.
Conclusion: Microbial loads exceeded regulatory limits across all milk types. Pasteurization
reduced but did not totally eliminate pathogen burden, consistent with thermoduric organism
survival. These preliminary findings highlight the need for improved milk hygiene practices and
antimicrobial stewardship, though larger studies are required to substantiate these observations.
