Changes in the Lactobacillus community during Ricotta forte cheese natural fermentation

The loss of microbial biodiversity due to the increase in large-scale industrial processes led to the study of the natural microflora present in a typical little known dairy product. The community of lactobacilli was studied in order to understand the natural fermentation of Ricotta forte cheese. The combined use of RAPD analysis, 16S rDNA sequencing and physiological tests allowed 33 different strains belonging to 10 species of Lactobacillus to be characterized. RAPD analysis revealed the heterogeneity of both the Lact. kefiri and Lact. paracasei species. The sequence analysis of the large 16S/23S rRNA spacer region enabled Lact. plantarum to be distinguished from Lact. paraplantarum, two closely related species belonging to the Lact. plantarum group. The recovery of strains endowed with interesting physiological characteristics, such as strong stress resistance, could improve technological and/or organoleptic characteristics of Ricotta forte cheese and other fermented foods.     

Monitoring horizontal antibiotic resistance gene transfer in a colonic fermentation model

The human microbiota is suggested to be a reservoir of antibiotic resistance (ABR) genes, which are exchangeable between transient colonizers and residing bacteria. In this study, the transfer of ABR genes from Enterococcus faecalis to Listeria monocytogenes and to commensal bacteria of the human gut microbiota was demonstrated in a colonic fermentation model. In the first fermentation, an E. faecalis donor harboring the marked 50-kb conjugative plasmid pRE25(*) and a chromosomal marker was co-immobilized with L. monocytogenes and infant feces. In this complex environment, the transfer of pRE25(*) to L. monocytogenes was observed. In a second fermentation, only the E. faecalis donor and feces were co-immobilized. Enumeration of pRE25(*) and the donor strain by quantitative PCR revealed an increasing ratio of pRE25(*) to the donor throughout the 16-day fermentation, indicating the transfer of pRE25(*) . An Enterococcus avium transconjugant was isolated, demonstrating that ABR gene transfer to gut commensals occurred. Moreover, pRE25(*) was still functional in both the E. avium and the L. monocytogenes transconjugant and transmittable to other genera in filter mating experiments. Our study reveals that the transfer of a multiresistance plasmid to commensal bacteria in the presence of competing fecal microbiota occurs in a colonic model, suggesting that commensal bacteria contribute to the increasing prevalence of antibiotic-resistant bacteria.     

Static recipient cells as reservoirs of antibiotic resistance during antibiotic therapy

How does taking the full course of antibiotics prevent antibiotic resistant bacteria establishing in patients? We address this question by testing the possibility that horizontal/lateral gene transfer (HGT) is critical for the accumulation of the antibiotic-resistance phenotype while bacteria are under antibiotic stress. Most antibiotics prevent bacterial reproduction, some by preventing de novo gene expression. Nevertheless, in some cases and at some concentrations, the effects of most antibiotics on gene expression may not be irreversible. If the stress is removed before the bacteria are cleared from the patients by normal turnover, gene expression restarts, converting the residual population to phenotypic resistance. Using mathematical models we investigate how static recipients of resistance genes carried by plasmids accumulate resistance genes, and how specifically an environment cycling between presence and absence of the antibiotic uniquely favors the evolution of horizontally mobile resistance genes. We found that the presence of static recipients can substantially increase the persistence of the plasmid and that this effect is most pronounced when the cost of carriage of the plasmid decreases the cell's growth rate by as much as a half or more. In addition, plasmid persistence can be enhanced even when conjugation rates are as low as half the rate required for the plasmid to persist as a parasite on its own.     

Foam and its mitigation in fermentation systems

Key aspects of foaming and its mitigation in fermentation systems are presented. Foam properties and behavior, conditions that affect foaming, and consequences of foaming are discussed, followed by methods to detect and prevent foam, both without and with the use of antifoam, and their implications. Antifoams were catalogued according to their class (e.g., polyalkylene glycols, silicone emulsions, etc.) to facilitate recognition of antifoams possessing similar base compositions. Relatively few published studies directly comparing antifoams experimentally are available, but those reports found only partially identify clear benefits/disadvantages of any one antifoam type. Consequently, desired characteristics, trends in antifoam application, and chemical types of antifoams are evaluated on the basis of a thorough review of available literature reports describing a specific antifoam's usage. Finally, examples of specific foaming situations taken from both the literature and from actual experience in an industrial fermentation pilot plant are examined for their agreement with expected behavior.     

Non-inherited antibiotic resistance

In addition to their impressive, well-publicized and well-researched propensity to evolve and acquire genetically determined mechanisms for resistance to antibiotics, bacteria that are inherently susceptible to these drugs can also be phenotypically refractory to their action. This phenomenon of 'non-inherited resistance' to antibiotics has been known since the beginning of the antibiotic era but, relative to inherited resistance, it has been given little attention. Here, we review the in vitro and in vivo evidence for the different forms of non-inherited resistance and the mechanisms responsible. With the aid of a simple mathematical model and computer simulations, we show how non-inherited resistance could extend the duration of antibiotic treatment, cause treatment failure and promote the generation and ascent of inherited resistance in treated patients.     

Tackling antibiotic resistance

The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable but can nevertheless be controlled, and it must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of 30 scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, USA, from 16 to 18 May 2011. From these discussions there emerged a priority list of steps that need to be taken to resolve this global crisis.     

Predicting antibiotic resistance

The treatment of bacterial infections is increasingly complicated because microorganisms can develop resistance to antimicrobial agents. This article discusses the information that is required to predict when antibiotic resistance is likely to emerge in a bacterial population. Indeed, the development of the conceptual and methodological tools required for this type of prediction represents an important goal for microbiological research. To this end, we propose the establishment of methodological guidelines that will allow researchers to predict the emergence of resistance to a new antibiotic before its clinical introduction.     

Bypass of genetic constraints during mutator evolution to antibiotic resistance

Genetic constraints can block many mutational pathways to optimal genotypes in real fitness landscapes, yet the extent to which this can limit evolution remains to be determined. Interestingly, mutator bacteria elevate only specific types of mutations, and therefore could be very sensitive to genetic constraints. Testing this possibility is not only clinically relevant, but can also inform about the general impact of genetic constraints in adaptation. Here, we evolved 576 populations of two mutator and one wild-type Escherichia coli to doubling concentrations of the antibiotic cefotaxime. All strains carried TEM-1, a β-lactamase enzyme well known by its low availability of mutational pathways. Crucially, one of the mutators does not elevate any of the relevant first-step mutations known to improve cefatoximase activity. Despite this, both mutators displayed a similar ability to evolve more than 1000-fold resistance. Initial adaptation proceeded in parallel through general multi-drug resistance mechanisms. High-level resistance, in contrast, was achieved through divergent paths; with the a priori inferior mutator exploiting alternative mutational pathways in PBP3, the target of the antibiotic. These results have implications for mutator management in clinical infections and, more generally, illustrate that limits to natural selection in real organisms are alleviated by the existence of multiple loci contributing to fitness.     

Surveillance of antibiotic resistance

Surveillance involves the collection and analysis of data for the detection and monitoring of threats to public health. Surveillance should also inform as to the epidemiology of the threat and its burden in the population. A further key component of surveillance is the timely feedback of data to stakeholders with a view to generating action aimed at reducing or preventing the public health threat being monitored. Surveillance of antibiotic resistance involves the collection of antibiotic susceptibility test results undertaken by microbiology laboratories on bacteria isolated from clinical samples sent for investigation. Correlation of these data with demographic and clinical data for the patient populations from whom the pathogens were isolated gives insight into the underlying epidemiology and facilitates the formulation of rational interventions aimed at reducing the burden of resistance. This article describes a range of surveillance activities that have been undertaken in the UK over a number of years, together with current interventions being implemented. These activities are not only of national importance but form part of the international response to the global threat posed by antibiotic resistance.     

Efficiency of the cyclic batch antibiotic fermentation

For a simple mathematical model of microbial product formation, the productivities of stationary and nonstationary cultivation methods (chemostat and cyclic batch) are compared. Conditions of superiority of the cyclic batch cultivation are characterized. The model includes substrate inhibition of the product formation and the age-dependent loss of productivity of the culture.     

Evolution of antibiotic resistance

World-wide spread of bacterial resistance to antimicrobial agents may limit the future progress of medicine. A huge environmental antibiotic pressure, resulting from industrial production and marketing of these drugs, has simultaneously contributed to the increase in the diversity of resistant phenotypes, to the selection of the fittest among them, and to the dispersal of resistance genes, which is expected to result in a significant acceleration of the rate of microbial evolution. Current research is focused on the mechanisms involved in the genesis, selection and dispersal of resistance genetic determinants; strategies based on molecular epidemiology and mathematical models may contribute to control or reverse the frightening trend towards a new pre-antibiotic era.     

Characterization of self-transmissible plasmids determining lactose fermentation and multiple antibiotic resistance in clinical strains of Klebsiella pneumoniae

The lactose fermentation (Lac+) and antibiotic resistance (R+) phenotypes were conjugally transferred from Klebsiella pneumoniae strains (K166, K182, K186, K218, and K220) to Salmonella typhi, S. typhimurium, Shigella flexneri, and Vibrio cholerae. The genes for lactose fermentation and antibiotic resistance were located on the plasmids. Further analysis of plasmid DNA from these isolates indicated the presence of multiple plasmids (Mr ranged less than 2.7 to 70 X 10(6)). The Lac+R+ plasmids p166 and p182 were members of the FII incompatibility group. The fertility inhibition property of plasmids, p182, p218, and p220 was fi+ type. Furthermore, phage typing experiments showed that plasmids p166 and p218 (Lac+R+) conferred the ability to inhibit the multiplication of bacteriophages 12 and 13 in S. typhimurium. However, the plasmids p182, p186, and p220 (Lac+R+) could inhibit the visible lysis of all the 30 phages in S. typhimurium. This study describes the characterization of Lac+R+ plasmids and the medical significance of an intergeneric transfer of lactose fermentation to non-lactose-fermenting pathogens.     

抗生素抗性基因在环境中的传播扩散及抗性研究方法

抗生素在医药、畜牧和水产养殖业的大量使用造成了环境中抗性耐药菌和抗性基因日益增加,抗生素抗性基因作为一种新型环境污染物引起人们的广泛关注.本文综述了近年来国内外有关抗生素抗性基因的研究进展,其在水、土壤、空气等环境介质中和动,植物体内的传播扩散,以及开展环境中抗生素抗性基因研究的必要性,重点介绍了有关抗生素抗性（包括抗性细菌和抗性基因）的研究方法,指出抗性基因研究中存在的问题,并对未来的相关研究进行了展望.     

Hollow fiber supported gas membrane for in situ removal of ammonium during an antibiotic fermentation

To study the influence of ammonium on an antibiotic cultivation, mass transfer measurements of ammonium through microporous hydrophobic membranes using different stripping methods were carried out and compared. The higher overall mass transfer coefficients for ammonium were obtained with an acid stripping solution compared to water, vacuum, or sweeping air. A hollow fiber module for in situ removal of ammonium during cultivation was designed and operated in an external bypass to a 10-L fermentor. Compared to a control fermentation, the cell dry mass could be increased 2.6 times and the antibiotic concentration 8 times, if the in situ ammonium removal was in operation.     

Reservoirs of antibiotic resistance genes

A potential concern about the use of antibiotics in animal husbundary is that, as antibiotic resistant bacteria move from the farm into the human diet, they may pass antibiotic resistance genes to bacteria that normally reside in a the human intestinal tract and from there to bacteria that cause human disease (reservoir hypothesis). In this article various approaches to evaluating the risk of agricultural use of antibiotics are assessed critically. In addition, the potential benefits of applying new technology and using new insights from the field of microbial ecology are explained.