Pathogenic Bacteria and Crabmeat Contamination in Mangrove Habitats

The aim of this paper was to establish a relation between the abundance of some pathogenic bacteria in water and sediment of mangrove habitats and the level of contamination of the meat obtained from crabs collected in the mangrove forest. Samples of water, sediment and crabs were collected monthly during both rainy and dry season at two areas of mangroves that differ in influence of tide and sewage discharge in the "Paraiba do Norte" estuary (Northeastern Brazil), a river that receive domestic, municipal and industrial sewage containing diverse pollutants such as viral and bacterial pathogens, toxic chemicals and a variety of organic and inorganic wastes.

The results showed that the two mangrove sites noticeably differ in physical, chemical and microbiological characteristics of the water and sediment. The sampling site "Camboa Grande" (CG), closer to the waste discharge and more distant from the river estuary, showed lower salinity, less dissolved oxygen and an higher incidence of total heterotrophic, coliforms and pathogenic bacteria in both water and sediment samples if compared to the control site "Ilha do Stuart" (IS), situated in the river course, at about 3.5 km distance from the waste discharge. This latter showed, during the dry season, lower salinity and higher values of BOD than CG, while temperature and pH did not differ significantly between the two sites. The organic matter content in the sediment of both the sites was similar, but total nitrogen content was much lower in IS site than CG. S. aureus was more abundant at CG, especially during the dry season and Salmonella spp. was detected only at this site. E. coli was found in all the water and sediment samples of CG, while its incidence was much lower at the site IS, where no coliforms and less total heterotrophic bacteria were observed in the dry season. Among other identified bacterial strains (92 in total), the most frequent were Enterobacter, Proteus and Pseudomonas. The average numbers of heterotrophic bacteria in the water of CG were 3.3 log CFU 100 mL-1, while their counts were lower at site IS (0.2 log CFU 100 mL-1), especially in the dry season. The counts of heterotrophic bacteria in the sediment were similar at both the locations (5.5 – 6.3 log CFU g-1) and their population size did not differ significantly between sampling sites and seasons. The authors also found a decrease of contaminant microorganisms in the river, downstream the discharge point, probably caused by the lower influence of sewage, as well as by the increase of salinity, which is known to affect the bacterial community and the microbial responses in the wastewater discharge.

The mangrove crab Ucides cordatus is the most harvested and has the highest commercial and subsistence importance to the local coastal population. These crabs are hand-picked and then transported to markets alive or already cooked. The quality of environment may affect the quantity and diversity of the microorganisms present on their surface, as well as the mode of collection and processing of products may cause increase of microbial contamination. In Brazil, pathogenic bacteria from genera Salmonella, Staphylococcus and Vibrio, are frequently found in crabmeat because crabs are usually processed in inadequate hygienic conditions, resulting in bacterial contamination. Moreover when crabs are collected, they are usually covered with mud, and then washed with mangrove water, that does not eliminate the contamination by saprophytic and pathogenic bacteria. However, in this study, no crabmeat sample showed the presence of coliforms and the counts of heterotrophic bacteria (mostly Enterobacter spp. and Pseudomonas spp.) has been always below 5 log CFU g-1. Moreover, in contrast to what has been obtained in other studies and in spite of differences between the bacterial abundance in the water and sediment, the contamination level of crabmeat did not differ significantly between the two stations and did not reflect the distribution pattern of bacteria in the environment. However, the influence of season on the number of total heterotrophic bacteria was significant and the meat of crabs captured in the dry season showed higher quantity of bacteria than the crabs collected in the rainy season. In addition, crabs must be cooked before obtaining the meat and the numbers of heterotrophic bacteria in crabmeat cooked for 60 minutes were slightly lower than in samples cooked for 30 minutes. Thus, the way of crabmeat processing and handling is more important in determining an increase in the contamination level of crabs than water or sediment pollution level. Anyhow, brazilian mangrove ecosystems are the first to suffer with urbanization and industrialization at coastal regions, and extensive mangrove ecosystems are already disappeared, putting an end to many of their important ecological functions. Therefore, the anthropogenic influence must be constantly monitored and every effort must be done to reduce human impact on these precious ecosystems.

Reference:

Grisi, T.C.S.D. and Gorlach-Lira, K. (2010) The abundance of some pathogenic bacteria in mangrove habitats of Paraiba do Norte Estuary and crabmeat contamination of mangrove crab Ucides cordatus. Braz Arch Biol Technol 53: 227–234.