Influence of different sources of contamination on the microbiological quality of lettuce in the Teresópolis region, RJ, Brazil

ABSTRACT Irrigation water and cultivated soil have been identified as possible sources of contamination in several crops. In certain vegetables that are eaten raw, such as lettuce, this contamination can lead to public health problems. Aiming to evaluate the influence of these sources on the quality of lettuce grown in the Córrego Sujo Basin, Teresópolis, RJ, an important agricultural pole whose production services the metropolitan region of Rio de Janeiro, water from different sources (spring, weir and river) was collected in this region, as well as samples of soil and lettuce irrigated with these waters, to carry out conventional microbiological analyzes (counts of total heterotrophic bacteria and thermotolerant coliforms) and molecular analyzes (PCR-DGGE). The count of fecal coliforms in lettuce suggests that there is an influence of irrigation water and the cultivated soil on the contamination of these vegetables. The grouping of bacterial communities in the different samples obtained by the PCR-DGGE technique shows that irrigation water has a greater influence on the contamination of these vegetables in relation to the soil where they are grown. These results corroborate the need to monitor water bodies used for irrigation and demonstrate that the PCR-DGGE technique is of great value for the study of microbial communities and, when associated with specific primers, can help in the detection of pathogens in food.

摘要 灌溉用水与耕作土壤已被证实为多种农作物的潜在污染源。针对生菜这类生食蔬菜而言，此类污染可能引发公共卫生安全问题。为评估上述污染源对位于里约热内卢州特雷斯波利斯市苏霍溪流域（该区域为服务里约热内卢大都会区的重要农业核心产区）生菜品质的影响，研究人员在该区域采集了不同来源（泉水、堰水及河水）的灌溉用水样本，以及使用上述水体灌溉的土壤与生菜样本，以此开展常规微生物学分析（总异养菌计数、耐热大肠菌群计数）与分子生物学分析（聚合酶链式反应-变性梯度凝胶电泳，PCR-DGGE）。生菜样本中粪大肠菌群的计数结果显示，灌溉用水与耕作土壤均会对这类蔬菜的污染水平产生影响。通过PCR-DGGE技术对不同样本的细菌群落进行聚类分析的结果表明，相较于生菜种植的耕作土壤，灌溉用水对这类蔬菜的污染影响更为显著。上述研究结果证实了开展灌溉用水体监测的必要性，同时表明PCR-DGGE技术在微生物群落研究中具备重要应用价值，若与特异性引物联用，可有效助力食品中致病菌的检测工作。