Physical and chemical quality, biodiversity, and thermodynamic prediction of adhesion of bacterial isolates from a water purification system: a case study

The objective of this study was to evaluate the quality of water purification system and identify the bacteria this system, predict bacterial adherence according to the hydrophobicity of these microorganisms and of the polypropylene distribution loop for purified water. The assessment of drinking water that supplies the purification system allowed good-quality physical, chemical, and microbiological specifications. The physicochemical specifications of the distributed purified water were approved, but the heterotrophic bacteria count was higher than allowed (>;2 log CFU mL-1).The sanitation of the storage tank with chlorine decreased the number of bacteria adhered to the surface (4.34 cycles log). By sequencing of the 16SrDNA genes, six species of bacteria were identified. The contact angle was determined and polypropylene surface and all bacteria were considered to be hydrophilic, and adhesion was thermodynamically unfavorable. This case study showed the importance of monitoring the water quality in the purified water systems and the importance of sanitization with chemical agents. The count of heterotrophic bacteria on the polypropylene surface was consistent with the predicted thermodynamics results because the number of adhered cells reached approximate values of 5 log CFU cm-2

The adhesion control of Listeria monocytogenes on food-processing surfaces by silver ion implantation

Bacterial adhesion to a solid surface is a crucial step in the biofilm process. Listeria monocytogenes can adhere to food-processing surfaces, survive and grow over a wide range of environmental conditions such as refrigeration temperatures and consequently cause severe disease. Several strategies have been developed with the aim to decrease the adherence of bacteria to surfaces, namely the silver ion implantation on surfaces. Thus, the aim of this work was to determine the Listeria monocytogenes CECT 4031 T adhesion ability onto four types of AISI 304 and AISI 430 surfaces usually used in food industry, restaurant, and kitchens, and simultaneously to evaluate the influence of the thermodynamics aspects on bacteria adhesion on these different surfaces.Coupons (1 cm-2) were cut from a 1 mm layer of AISI 304 and AISI 430 surfaces (N° 2B, 4 , 6 and 8). The silver ions (Ag+1) were implanted at 200 keV, 1.0 μA.cm-2 and a dose of 2.0×1016 ions.cm-2. All coupons were cleaned by immersion in 0.2% solution of a commercial detergent for 5 min, followed by immersion in ethanol for 15 min. The coupons were twice rising with ultrapure water and dried at 60 °C. Each strain was subcultured in trypticase soy broth (TSB) at 37 ºC in an orbital shaker (120 rpm), overnight. The cells were then harvested by centrifugation at 9000 rpm for 5 min and washed twice with phosphate buffered saline (PBS 0.1M pH 7). The pellets were resuspended in PBS to an inoculum level of 109 CFU.ml-1, determined by optical density. Adhesion assays were performed in sterile 24-well microtiter plates and each well was filled with 970 μl of TSB supplemented with 0.6% (w/v) of yeast extract, 30 μl of cell suspension and the respective coupon. The plates were incubated at 4 ºC for 2 h, with constant agitation at 120 rpm. After incubation, the coupons were washed once with 1.0 ml of minimal medium (MM) to remove non-adherent cells and replaced to a new well and the adhered cells were removed by scrapping on 1.0 ml of MM carefully. The number of viable cells was quantified by colony forming units (CFUs) on trypticase soy agar (TSA). The materials and Listeria cells hydrophobicity properties were evaluated through contact angle measurements and using the approach of van Oss and coworkers. The results showed that the strain used was able to adhere to all materials. It was not found significant differences (p > 0.05) between the means of the L. monocytogenes adhered cells on the twelve surfaces studied. However, the highest mean value of adherence cells occurred to AISI 304 N° 4 (4.78 ± 0.32 log CFU.cm-2) without silver ion implantation (wi) surface. Moreover, it was possible to observe that AISI 430 N° 8 with silver ion implantation (i) (4.29 ± 0.37 log CFU.cm-2) and AISI 430 N° 4 wi (3.60 ± 0.31 log CFU.cm-2) surfaces presentes the lowest means (p < 0.05). Concerning hydrophobicity, silver ion implantation increase the hydrophilicity of the surfaces, except in case of AISI 304 N° 6 (p.> 0.05). Furthermore, the results showed that L. monocytogenes cells are hydrophilic. Moreover, no correlation was observed between the number of adhered cells and substrate surface hydrophobicity, despite of the highest number of bacteria cells adhered mainly occured on surfaces with highest water contact angle value. The contact time between microorganism and silver implantated stainless steel surfaces seems not to be enough to confer antimicrobial activity. So, we consider that more studies are necessary to evaluate the effective effect of silver as antimicrobial agent to control the adhesion of L. monocytogenes cells and biofilms formation. As future work, we will study the effect of silver ion as antimicrobial different time periods

Evaluation of different cut-off points for IgG avidity and IgM in the diagnosis of acute toxoplasmosis in pregnant women participating in a congenital toxoplasmosis screening program

The main social impact of toxoplasmosis stems from its ability to be vertically transmitted. Postnatally acquired infection is generally asymptomatic in approximately 70–90% of cases, making diagnosis often dependent on laboratory tests using serological methods to search for anti-T. gondii antibodies. This study aimed to investigate the ability of the VIDAS TOXO IgG avidity and VIDAS TOXO IgM assays to confirm recent toxoplasmosis. In total, 341 pregnant women with suspected acute toxoplasmosis were systematically monitored in the Program for Control of Congenital Toxoplasmosis in Minas Gerais State, Brazil. We conducted an observational analytical-descriptive cross-sectional study and grouped according to clinical and laboratory criteria as having acute or chronic toxoplasmosis. The VIDAS TOXO IgG avidity and VIDAS TOXO IgM assays were evaluated to investigate the capacity to identify acute infection. IgG avidity showed good performance in identifying acute toxoplasmosis when the IgG avidity index was lower than or equal to 0.1. Values greater than or equal to 3.16 according to the TOXO IgM kit were associated with a greater chance of acute infection. These results may contribute to a more adequate diagnosis of acute gestational toxoplasmosis and, consequently, the avoidance of inadequate or unnecessary treatments

Aspectos coloidais da adesão de micro-organismos

The ability of bacteria to attach to surface and develop into a biofilm has been of considerable interest to food industry. Electrostatic, Lifhistz-van der Waals and Lewis acid-base forces are usually considered responsible for the interactions at the interface of the bacterial adhesion. The study of microbial adhesion thermodynamic is important because it represents the reflection of microbial surface and food processing surface physicochemical characteristics. This review examines the most important aspects involved in bacterial attachment to a surface with emphases in thermodynamics of adhesion process

Resistência de bactérias lácticas, isoladas de fezes de suínos e sua capacidade antagônica frente a microrganismos indicadores

Lactic acid bacteria (LAB) were isolated from the faeces of nearly 40 healthy pigs, with different ages. The isolates were selected previously, based on the coloration in All Purpose Tween (APT) agar modified by the addition of 0,004% of purple bromocresol and 0,5% of calcium carbonate, on their morphology and on the coloration in gram and catalase activity. Approximately 50% of the isolated colonies presented morphology of Gram-positive cocos/bastonetes, negative catalase and yellow colonies when cultivated in modified APT agar, being classified as LAB. These isolates of pig faeces were compared by their ability to resist the pH 3.0, to grow in the presence of bile salts for 3 hours and by their antagonistic capacity against the indicative microrganisms (Salmonella typhi ATCC 6539, Campylobacter jejuni ATCC 29428, Escherichia coli ATCC 11229, Staphylococcus aureus ATCC 6538 and Enterococcus faecalis ATCC 19433). Only 18% of the isolates presented less than 1 Decimal Reduction (DR) when cultivated in the presence of pH 3.0. Nearly 36.5% reduced from 1 to 2 DR and 45.5% had more than 2 DR. No isolate had the capacity to grow in specific means with the adjusted pH for 3.0. About 36.5% of the isolates grew in cultivation medim modified with the addition of 0.3% of bile salts, 59% of isolates had decimal reduction smaller or equal to 2 and 4.5% presented decimal reduction larger than 2 DR. The 12 isolates that presented larger resistance to the pH 3.0 and resisted in cultivation medium added of bile salts were selected for the antagonism analysis. No inhibition halo was detected among the isolates, indicating a possible simultaneous growth to produce a probiotic. All the evaluated isolates produced an inhibition halo on at least two of the tested indicative microrganisms.Bactérias do ácido lático (BAL) foram isoladas das fezes de aproximadamente 40 suínos sadios e em diferentes idades. Os isolados foram previamente selecionados com base na coloração das colônias em ágar All Purpose Tween (APT) modificado pelo acréscimo de 0,004% de púrpura de bromocresol e 0,5% de carbonato de cálcio, morfologia, coloração em Gram e atividade de catalase. Das bactérias lácticas isoladas, aproximadamente 50% das colônias apresentaram morfologia de cocos/bastonetes Grampositivo, catalase negativa e colônias amareladas quando cultivadas em ágar APT modificado, sendo, portanto, classificadas como BAL. Estes isolados foram comparados pela sua habilidade em resistirem a pH 3,0, crescerem na presença de sais biliares por 3 horas e pela sua capacidade antagônica frente a microrganismos indicadores (Salmonella typhi ATCC 6539, Campylobacter jejuni ATCC 29428, Escherichia coli ATCC 11229, Staphylococcus aureus ATCC 6538 e Enterococcus faecalis ATCC 19433). Apenas 18% dos isolados obtiveram menos que 1 Redução Decimal (RD) quando cultivados na presença de pH 3,0. Cerca de 36,5% reduziram entre 1 e 2 RD e 45,5% tiveram mais que 2 RD. Nenhuma das cepas avaliadas teve capacidade de crescer em meios específicos com o pH ajustado para 3,0. Cerca de 36,5% dos isolados cresceram em meio de cultivo adicionado de 0,3% de sais biliares, 59% tiveram redução decimal menor ou igual a 2 e 4,5% maior que 2 RD. Os 12 isolados que apresentaram maior resistência ao pH 3,0 e que responderam melhor em meio de cultivo acrescido de sais biliares foram selecionados para análise de antagonismo. Nos teste de antagonismo entre os próprios lactobacilos isolados nenhum halo de inibição foi detectado, indicando a possibilidade de serem cultivados simultaneamente para produção de um probiótico. Todas as cepas avaliadas levaram a formação de halo de inibição sobre pelo menos dois dos microrganismos indicadores testados