Amostragem de águas superficiais sob impacto agropecuário na Paraíba: efeitos do uso de suabe de moore modificado em triplicata sobre a frequência e diversidade de sorovares de Salmonella enterica

Abstract

The increasing number of studies reporting the occurrence of Salmonella enterica in non recycled surface water warrants further investigations into their real role as potential sources of contamination. Considering the low concentration of Salmonella in water, the use of modified Moore swabs (MMS) has established itself as a viable technique for the recovery of Salmonella enterica for this type of sample, enabling the sampling of larger volumes of water and reducing logistical costs and problems. Here we report the unprecedented effects of the use of replicates of MMS on the recovery and diversity of Salmonella enterica serovars. A total of 270 water samples were collected in triplicate by MMS, totaling 810 swabs. The MMS were cultured using conventional microbiological procedures for isolation of Salmonella enterica. In addition, we also tested the accuracy of enrichment broth-PCR as a screening method for the recovery of Salmonella enterica. Furthermore, the serovars of Salmonella enterica from a sample of 84 isolates were determined in silico after whole genome sequencing. The overall frequency of Salmonella enterica in water samples was 77.8% (210/270), while the frequencies observed in each individual replicate were 63.7, 62.6, and 61.1%. The use of triplicates resulted in higher (P<0.05) frequencies of isolation of Salmonella enterica. Among the 210 samples containing Salmonella enterica, 123 (58.6%) were positive in all triplicates. However, 50 (23.8%) samples were positive in two of three replicates, while 32 (17.6%) samples were positive only in one of three replicates. Enrichment broth-PCR cultivation showed high sensitivity (98.37%) in detecting viable Salmonella compared with conventional water culture, although no significant differences were observed between Tetrathionate and Rappaport-Vassiliadis broths. Furthermore, the use of triplicates significantly increased the diversity of Salmonella serovars recovered from each sample. Our results indicated that the use of 10L-SMM triplicates could significantly improve the recovery and diversity of Salmonella enterica serovars in water samples. However, other aspects involving technical and cost limitations associated with the use of triplicates should be considered.