Five subgroups of sulfate-reducing bacteria (SRB) were detected by PCR in three macrophyte rhizospheres (Polygonum densiflorum, Hymenachne donacifolia, and Ludwigia helminthorriza) and three subgroups in Eichhornia crassipes from La Granja, a floodplain lake from the upper Madeira basin. The SRB community varied according to the macrophyte species but with different degrees of association with their roots. The rhizosphere of the C 4 plant Polygonum densiflorum had higher frequencies of SRB subgroups as well as higher mercury methylation potentials (27.5 to 36.1%) and carbon (16.06 ؎ 5.40%), nitrogen (2.03 ؎ 0.64%), Hg (94.50 ؎ 6.86 ng Hg g ؊1 ), and methylmercury (8.25 ؎ 1.45 ng Hg g ؊1 ) contents than the rhizosphere of the C 3 plant Eichhornia crassipes. Mercury methylation in Polygonum densiflorum and Eichhornia crassipes was reduced when SRB metabolism was inhibited by sodium molybdate.

Salmonella is a major foodborne pathogen causing important zoonosis worldwide. Pigs asymptomatically infected in mesenteric lymph nodes (MLN) can be intermittent shedders of the pathogen through faeces, being considered a major source of human infections. European baseline studies of fattening pig salmonellosis are based on Salmonella detection in MLN. This work studies the relationship between Salmonella infection in MLN and intestinal content (IC) shedding at slaughter and the relationship between the presence of the pathogen and the serologic status at farm level. Mean Salmonella prevalence in the selected pigs (vertically integrated production system of Navarra, Spain) was 7.2% in MLN, 8.4% in IC and 9.6% in serum samples. In this low-moderate prevalence context, poor concordance was found between MLN infection and shedding at slaughter and between bacteriology and serology. In fact, most of shedders were found uninfected in MLN (83%) or carrying different Salmonella strains in MLN and in IC (90%). The most prevalent Salmonellae were Typhimurium resistant to ACSSuT ± Nx or ASSuT antibiotic families, more frequently found invading the MLN (70%) than in IC (33.9%). Multivariable analysis revealed that risk factors associated with the presence of Salmonella in MLN or in IC were different, mainly related either to good hygiene practices or to water and feed control, respectively. Overall, in this prevalence context, detection of Salmonella in MLN is an unreliable predictor of faecal shedding at abattoir, indicating that subclinical infections in fattening pigs MLN could have limited relevance in the IC shedding.

bEnterotoxigenic Escherichia coli (ETEC) is an important cause of childhood diarrhea. This study aimed to characterize ETEC strains isolated from Bolivian children aged <5 years according to enterotoxin profile, colonization factors (CFs), suggested virulence genes, and severity of disease. A total of 299 ETEC isolates recovered from children with diarrhea and 55 ETEC isolates from children without diarrhea (controls) were isolated over a period of 4 years. Strains expressing heat-labile toxin (LT) or heat-stable toxin (ST) alone were about equally common and twice as common as ETEC producing both toxins (20%). ETEC strains expressing human ST (STh) were more common in children aged <2 years, while ETEC strains expressing LT plus STh (LT/STh) were more frequent in 2-to 5-year-old children. Severity of disease was not related to the toxin profile of the strains. CF-positive isolates were more frequently identified in diarrheal samples than in control samples (P ‫؍‬ 0.02). The most common CFs were CFA/I and CS14. CFA/I ETEC strains were more frequent in children aged <2 years than CS1؉CS3 isolates and CS14 isolates, which were more prevalent in 2-to 5-year-old children. The presence of suggested ETEC virulence genes (clyA, eatA, tia, tibC, leoA, and east-1) was not associated with disease. However, east-1 was associated with LT/STh strains (P < 0.001), eatA with STh strains (P < 0.001), and tia with LT/STh strains (P < 0.001). A minor seasonal peak of ETEC infections was identified in May during the cold-dry season and coincided with the peak of rotavirus infections; this pattern is unusual for ETEC and may be important for vaccination strategies in Bolivia.

BackgroundSalmonellosis is a major worldwide zoonosis, and Salmonella-infected finishing pigs are considered one of the major sources of human infections in developed countries. Baseline studies on salmonellosis prevalence in fattening pigs in Europe are based on direct pathogen isolation from mesenteric lymph nodes (MLN). This procedure is considered the most reliable for diagnosing salmonellosis in apparently healthy pigs. The presence of simultaneous infections by different Salmonella strains in the same animal has never been reported and could have important epidemiological implications.ResultsFourteen finishing pigs belonging to 14 farms that showed high salmonellosis prevalence and a variety of circulating Salmonella strains, were found infected by Salmonella spp, and 7 of them were simultaneously infected with strains of 2 or 3 different serotypes. Typhimurium isolates showing resistance to several antimicrobials and carrying mobile integrons were the most frequently identified in the colonized MLN. Four animals were found infected by Salmonella spp. of a single serotype (Rissen or Derby) but showing 2 or 3 different antimicrobial resistance profiles, without evidence of mobile genetic element exchange in vivo.ConclusionThis is the first report clearly demonstrating that pigs naturally infected by Salmonella may harbour different Salmonella strains simultaneously. This may have implications in the interpretation of results from baseline studies, and also help to better understand human salmonellosis outbreaks and the horizontal transmission of antimicrobial resistance genes.