Mine tailings contain high concentrations of heavy metals such as As, Pb, Cu, Mn, and Fe, which are detrimental to the health of humans and the environment. In tailings at the El Fraile mine in Guerrero, Mexico, some plant species are apparently tolerant of heavy metals and can be found growing in the tailings. These plants could be associating with heavy metal-tolerant bacteria that promote plant growth and improve biomass production, and these bacteria could be a useful alternative for bacteria-assisted phytoremediation. The objective of this study was to isolate bacteria detected in the mine tailings at El Fraile-Taxco, focusing on those in the soil from the rhizosphere, the inner tissue of the root, leachate, and water, which have the potential to promote plant growth. The ability of the isolated bacteria to promote plant growth was evaluated in vitro. Of the 151 morphotypes isolated, 51% fix nitrogen, 12% dissolve phosphates, and 12%, 39.7%, and 48.3% produce indole acetic acid, gibberellins, and siderophores, respectively. In addition, 66.7% were observed to produce lytic enzymes, such as proteases, celluloses, lipases, esterases, and amylases, which exhibited activity against Fusarium, Aspergillus, and Colletotrichum. The use of 16S rRNA analysis led to the identification of the bacterial genera Chryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium, Enterobacter, Agrobacterium, Ochrobactrum, Serratia, Stenotrophomonas, and Acinetobacter. The bacteria isolated from the rhizosphere exhibited the greatest ability to fix nitrogen and produced indole acetic acid, gibberellins, siderophore, and lytic enzymes. In addition, the isolates collected from the soil samples demonstrated ability to solubilize phosphate.

Background: Bacillus cereus is associated with milk, dairy product, and dairy farm contamination. The aim of this study was to characterize strains of B. cereus in the small-scale artisanal cheese production chain in southwestern Mexico. Methods: 130 samples were collected. B. cereus isolation was performed on Mannitol Egg Yolk Polymyxin (MYP) agar. Genotyping, enterotoxigenic profile, and determination of genes involved in the formation of B. cereus biofilm were performed by PCR. An antimicrobial susceptibility test was made by broth microdilution assay. The phylogenetic analysis was performed by amplification and sequencing of 16s rRNA. Results: B. cereus sensu lato was isolated and molecularly identified in 16 samples and B. cereus sensu stricto (B. cereus) was the most frequently isolated and identified species (81.25%). Of all the isolated B. cereus sensu lato strains, 93.75% presented at least one gene for some diarrheagenic toxins, 87.5% formed biofilms, and 18.75% were amylolytic. All B. cereus sensu lato strains were resistant to beta-lactams and folate inhibitors. A close phylogenetic relationship between isolates was found between the cheese isolates and the air isolates. Conclusions: Strains of B. cereus sensu lato were found in small-scale artisanal cheeses on a farm in southwestern Mexico.

The mining activity has left mine tailings with high quantities of heavy metals and metalloids. Due their extreme toxicity, they represent a hostile environment for microbial colonization; however, there are metalotolerant bacteria in these mining wastes, and this is attributed to mechanisms of bioaccumulation and biotransformation of metals. The native bacteria from El Fraile mine tailings have developed adaptation mechanisms that allow them to persist in a toxic environment, thus, the objective of this study was to isolate and identify bacteria with the ability to tolerate, bioaccumulate or biotransform heavy metals. Our study was based on descriptive observations, we isolated 141 strains from water, leachate, soil, and rhizosphere and stems of plants from El Fraile mine tailings, Guerrero, Mexico. Bacterial tolerance was determined by the minimum inhibitory concentration in different metallic salts, the capacity of bioaccumulation of Ag, Pb, Cr, and Cd, and by the biotransformation of As (III) and Cr6+; in addition, representative bacteria were identified using 16S rRNA gene sequences. The results of the 141 strains analyzed showed ascending tolerance to Cd2+ 2 mM, Cu2+ 5 mM, Pb2+ 9 mM, Zn2+ 9 mM, Ag2+ 10 mM, As3+ 30 mM, and As5+ 45 mM. Only 9.24 and 39% of the strains bioaccumulated Zn2+, Pb2+ and Ag2+. In regard to biotransformation, 9% oxidized As3+ to As5+, and 7 and 24% reduced As5+ to As3+ and Cr6+ to Cr3+, respectively. The genera that prevailed were Chryseobacterium sp., Staphyloccoccus sp., Stenotrophomonas sp., Acinetobacter sp., Bacillus sp., Serratia sp., and Enterobacter sp. These results showed that in El Fraile mine tailings, there are bacterial strains capable of bioaccumulating and biotransforming heavy metals and metalloids; therefore, further studies must be conducted to know their potential in the processes of bioremediation of areas polluted with metals.

Water pollution is a serious environmental problem. We analyzed the presence of total fecal coliforms and Escherichia coli, the prevalence of diarrheal pathotypes, and the profiles of antibiotic resistance at different stages. Three composite samples from a wastewater treatment plant (WWTP) in Mexico were analyzed for the presence E. coli with the physical and chemical parameters established in the Mexican Official Standard NOM-001-SEMARNAT-1996. Fifty seven strains were selected from the different stages of the process, and the following pathotypes were determined by multiplex polymerase chain reaction: enteropathogenic (EPEC), enterotoxigenic (ETEC), enteroinvasive (EIEC), enteroaggregative (EAEC). enterohemorrhagic (EHEC), and diffuse adherence (DAEC). Their resistance was assessed by the Kirby Bauer method. The results showed a removal efficiency of 95.4% based on the chemical oxygen demand (BOD5). Coliforms and E. coli were found to be higher in the influent. The total frequency of pathotypes was 39 % (22/57) for EIEC, 30 % (17/57) for ETEC, and 15.5 % (9/57) for DAEC and EPEC. Regarding the distribution, 39% of ETEC was detected in the influent, 50% of EIEC before disinfection, 100% of ELEC after disinfection and 43% of ETEC in the effluent.

Mammillaria mystax, commonly called “Biznaga de la Mixteca” is a Cactaceae endemic to the state Puebla in Mexico. It is an ornamental plant of great economic and environmental value. During August ...

Staphylococcus aureus es un patógeno reconocido como causa de mastitis en bovinos a nivel mundial, por lo cual el objetivo de este trabajo fue determinar la presencia de Staphylococcus aureus en la piel de pezón de la ubre bovina y relacionarlo a la presencia de mastitis, así como determinar los factores de virulencia y la diversidad genética de las cepas. En tres establos se tomaron muestras de 250 vacas de ordeña en dos temporadas del año, estiaje y lluvias. Además, se realizó la prueba de California. Staphylococcus aureus fue aislado en agar sal y manitol e identificado bioquímicamente y confirmado con la amplificación del gen femA. Para la identificación de los factores de virulencia se usaron los genes hlB, mec, saK, pvL, tsst-1, seA, seB, seC, seD y seE por PCR en punto final. Para la tipificación de S. aureus, se realizó la amplificación y restricción del gen coag. La frecuencia de S. aureus fue 13.4 %. No se encontró una relación estadística entre la presencia de S. aureus en la piel de la ubre bovina y el desarrollo de mastitis subclínica. El gen de la enterotoxina más frecuente en las cepas fue el de la enterotoxina A. Aunque el porcentaje de tipificación es bajo, se lograron identificar dos restrictotipos que agrupan cepas aisladas de diferentes vacas, lo cual evidencia la capacidad infectocontagiosa del microorganismo.