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：灌溉水与耕作土壤已被证实为多种作物的潜在污染源。对于生菜这类生食蔬菜而言，此类污染可引发公共卫生问题。为评估位于里约热内卢州（RJ）特雷斯波利斯市（Teresópolis）的苏苏溪流域（Córrego Sujo Basin）——这一服务于里约热内卢大都会区的重要农业产区——的生菜种植质量受上述污染源的影响，研究人员在该区域采集了不同来源的水体样本（泉水、堰坝取水及河水），同时采集了经上述水体灌溉的土壤与生菜样本，以开展常规微生物分析（总异养菌计数与耐热大肠菌群计数）及分子分析（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表明，灌溉水与耕作土壤均对该类蔬菜的污染存在影响。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显示，相较于生菜的种植土壤，灌溉水对该类蔬菜的污染影响更为显著。上述研究结果印证了开展灌溉用水体监测的必要性，同时证实PCR-DGGE技术在微生物群落研究中具有重要应用价值；当与特异性引物联用时，该技术可辅助检测食品中的病原体。