Impact of Organic Practices on the Microbiological Quality and Safety of Lettuce in São Paulo, Brazil

Introduction: The consumption of organic products has increased worldwide in consequence of the demand for healthy food, without chemical residues. However, organic farming practices, such as the use of animal manure, can increase the risk of contamination by pathogenic microorganisms. Little is known about the microbiological characteristics of organic vegetables produced and retailed in the city of Sao Paulo, Brazil.

Purpose: As part of a large project on microbiological risks associated with organic vegetables produced and retailed in Sao Paulo, Brazil, the aim of this work was to report results on the quality and safety of organic lettuce samples (Lactuca sativa L.) collected from three certified farms located in the vicinity of the Sao Paulo, where chicken manure was regularly used as fertilizer.

Methods: Thirty samples of different lettuce varieties (looseleaf, red looseleaf, butterhead, and romaine lettuce), collected at three organic farms, were submitted for enumeration of total coliforms and Escherichia coli using the standard MPN method. Samples were also tested for Salmonella spp. using ISO 6579:2002 method.

Results: All samples were positive for total coliforms (average 2.6±0.7 log MPN/g) and E.coli was detected in 14 (47%) samples (average 1.0±0.6 log MPN/g). None of the samples was positive for Salmonella spp. in 25 g.

Significance: Results indicated that the samples presented good microbiological quality and were in accordance with the current limits established by the Brazilian Surveillance Agency for fresh vegetables (<2 log MPN/g for thermotolerant coliforms and absence of Salmonella spp./25 g). These preliminary results suggested that chicken manure used as fertilizer had little, if any, impact on the safety of organic lettuce produced on the tested farms.