Microbiological assessment of fresh, minimally processed vegetables from open air markets and supermarkets in Luzon, Philippines, for food safety

Abstract

A wide-range investigation of the microbiological quality of fresh produce from different open air markets and supermarkets in Luzon, Philippines was performed. Different vegetables which are usually consumed raw (bell pepper, carrot, lettuce, mung bean sprout, and tomato) had been screened for the presence and amount of contamination of enteric microorganisms, namely Escherichia coli, Salmonella spp., and somatic bacteriophages (or viruses). Phenotypic characterization was employed using selective and differential media such as eosin methylene blue agar and xylose lysine deoxycholate agar. Viable plate count (colony-forming units or CFU) and most probable number (MPN) methods were used to estimate the cell numbers of E. coli and Salmonella spp., respectively. Double agar assay was used to detect and quantify somatic phages as plaque-forming units (PFU). Polymerase chain reaction was also done to confirm the identity of the isolates using species-specific primers. From a total of 410 vegetable samples collected, 44 bacterial (prevalence of 5.85% E. coli and 5.12% of Salmonella spp.) and 21 (prevalence of 5.12%) viral isolates were obtained. It is alarming to note that samples contaminated with Salmonella spp. were significantly higher in counts (3.751 ± 0.60 log MPN/g) as compared to E. coli (1.472 ± 0.25 log CFU/g), while samples with coliphage (0.316 ± 0.12 log PFU/g) were the least in numbers. The degree of contamination in the samples can cause great risks on the health of individuals especially in developing countries such as the Philippines. Thus, monitoring on the handling of different produce is important to improve the country’s food quality and safety.