Multicellular behavior of environmental Escherichia coli isolates grown under nutrient-poor and low-temperature conditions

Genomic Features of E. ruysiae Associated with the Ecological Origin: Implications for the Environmental Hypothesis

Escherichia cryptic clades represent a relatively unexplored taxonomic cluster believed to exhibit characteristics associated with a free-living lifestyle, which is known as the environmental hypothesis. This hypothesis suggests that certain Escherichia strains harbour traits that favour their environmental persistence, thus expanding the ecological commensal niche of the genus. While surveying Escherichia diversity in an urban South American stream we isolated the first environmental cryptic clade IV strain in South America (339_SF). Here we report the genomic characterization of 339_SF strain in the context of existing genomic information for E. ruysiae (cryptic clades III and IV). A comparative analysis of genomes within the same species stemming from diverse ecological sources and geographical locations reveals close phylogenetic proximity between our isolate and strains of environmental origin. Based on genetic content, we observed two clusters associated with the environmental source within E. ruysiae. In addition, we identified genes relatively more represented in the environmental strains: genes associated with carbohydrate metabolism (ydjG), stress response and DNA damage repair (such as umuD, higA and yddM). On the other hand, the gene rrrQ, associated with defense against other microorganisms, was significatively enriched in genomes of commensal origin. Our findings suggest that genomic features within E. ruysiae favoring its persistence in open environments may have arisen more than once, with these events being associated with the use of alternative energy sources and the resistance to various stressors specific to these environments.

Morphological variability of Escherichia coli colonizing human wounds: a case report

BACKGROUND

Escherichia coli, known for its adaptability, can cause diverse infections. Morphological variants, such as smooth and mucoid forms, correspond to different infection capabilities and antibiotic resistance profiles. This report presents the isolation of two distinct E. coli strains, a smooth strain and a mucoid strain, from a single patient.

CASE PRESENTATION

A 70-year-old woman with a leg wound and lung infection was found to have two E. coli strains: a mucoid strain from her wound and sputum and a smooth strain from her rectal swab. Whole-genome sequencing confirmed genetic similarity between the strains with minor SNPs linked to their morphological differences. Both strains were resistant to β-lactam and quinolone antibiotics, complicating treatment. The patient recovered following treatment with Piperacillin/Tazobactam and regular wound care.

CONCLUSION

This case highlights E. coli's phenotypic plasticity within a single host, impacting infection management and antibiotic response. Understanding the genetic basis of such morphological changes could inform more effective treatment strategies.

Effect of the initial pH of the culture medium on the nutrient consumption pattern of Bifidobacterium animalis subsp. lactis Bb12 and the improvement of acid resistance by purine and pyrimidine compounds

AIMS

During fermentation, the accumulation of acidic products can induce media acidification, which restrains the growth of Bifidobacterium animalis subsp. lactis Bb12 (Bb12). This study investigated the nutrient consumption patterns of Bb12 under acid stress and effects of specific nutrients on the acid resistance of Bb12.

METHODS AND RESULTS

Bb12 was cultured in chemically defined medium (CDM) at different initial pH values. Nutrient consumption patterns were analyzed in CDM at pH 5.3, 5.7, and 6.7. The patterns varied with pH: Asp + Asn had the highest consumption rate at pH 5.3 and 5.7, while Ala was predominant at pH 6.7. Regardless of the pH levels (5.3, 5.7, or 6.7), ascorbic acid, adenine, and Fe2+ were vitamins, nucleobases, and metal ions with the highest consumption rates, respectively. Nutrients whose consumption rates exceeded 50% were added individually in CDM at pH 5.3, 5.7, and 6.7. It was demonstrated that only some of them could promote the growth of Bb12. Mixed nutrients that could promote the growth of Bb12 were added to three different CDM. In CDM at pH 5.3, 5.7, and 6.7, it was found that the viable cell count of Bb12 was the highest after adding mixed nutrients, which were 8.87, 9.02, and 9.10 log CFU ml-1, respectively.

CONCLUSIONS

The findings suggest that the initial pH of the culture medium affects the nutrient consumption patterns of Bb12. Specific nutrients can enhance the growth of Bb12 under acidic conditions and increase its acid resistance.

Emergence of novel non-aggregative variants under negative frequency-dependent selection in Klebsiella variicola

Klebsiella variicola is an emergent human pathogen causing diverse infections, some of which in the urinary tract. However, little is known about the evolution and maintenance of genetic diversity in this species, the molecular mechanisms and their population dynamics. Here, we characterized the emergence of a novel rdar-like (rough and dry) morphotype which is contingent both on the genetic background and the environment. We show that mutations in either the nitrogen assimilation control gene (nac) or the type III fimbriae regulator, mrkH, suffice to generate rdar-like colonies. These morphotypes are primarily selected for the reduced inter-cellular aggregation as a result of MrkH loss-of-function which reduces type 3 fimbriae expression. Additionally, these clones also display increased growth rate and reduced biofilm formation. Direct competitions between rdar and wild type clones show that mutations in mrkH provide large fitness advantages. In artificial urine, the morphotype is under strong negative frequency-dependent selection and can socially exploit wild type strains. An exhaustive search for mrkH mutants in public databases revealed that ca 8% of natural isolates analysed had a truncated mrkH gene many of which were due to insertions of IS elements, including a reported clinical isolate with rdar morphology. These strains were rarely hypermucoid and often isolated from human, mostly from urine and blood. The decreased aggregation of these mutants could have important clinical implications as we hypothesize that such clones could better disperse within the host allowing colonisation of other body sites and potentially leading to systemic infections.

Fecal indicator bacteria from environmental sources; strategies for identification to improve water quality monitoring

In tropical to temperate environments, fecal indicator bacteria (FIB), such as enterococci and Escherichia coli, can persist and potentially multiply, far removed from their natural reservoir of the animal gut. FIB isolated from environmental reservoirs such as stream sediments, beach sand and vegetation have been termed "naturalized" FIB. In addition, recent research suggests that the intestines of poikilothermic animals such as fish may be colonized by enterococci and E. coli, and therefore, these animals may contribute to FIB concentrations in the aquatic environment. Naturalized FIB that are derived from fecal inputs into the environment, and subsequently adapted to maintain their population within the non-host environment are termed "naturalized enteric FIB". In contrast, an additional theory suggests that some "naturalized" FIB diverged from enteric FIB many millions of years ago and are now normal inhabitants of the environment where they are referred to as "naturalized non-enteric FIB". In the case of the Escherichia genus, the naturalized non-enteric members are identified as E. coli during routine water quality monitoring. An over-estimation of the health risk could result when these naturalized, non-enteric FIB, (that is, not derived from avian or mammalian fecal contamination), contribute to water quality monitoring results. It has been postulated that these environmental FIB belonging to the genera Escherichia and Enterococcus can be differentiated from enteric FIB by genetic methods because they lack some of the genes required for colonization of the host intestine, and have acquired genes that aid survival in the environment. Advances in molecular tools such as next generation sequencing will aid the identification of genes peculiar or "enriched" in particular habitats to discriminate between enteric and environmental FIB. In this appraisal, we have reviewed the research studying "naturalized" FIB, and discussed the techniques for their differentiation from enteric FIB. This differentiation includes the important distinction between enteric FIB derived from fresh and non-recent fecal inputs, and those truly non-enteric environmental microbes, which are currently identified as FIB during routine water quality monitoring. The inclusion of tools for the identification of naturalized FIB (enteric or environmental) would be a valuable resource for future studies assessing water quality.