Antimicrobial agents and microbial ecology

<abstract> <p>Antimicrobials are therapeutic substances used to prevent or treat infections. Disinfectants are antimicrobial agents applied to non-living surfaces. Every year, several thousand tonnes of antimicrobials and their by-products are released into the environment and in particular into the aquatic environment. This type of xenobiotic has ecological consequences in the natural environment but also in technological environments such as wastewater treatment plants and methane fermentation sewage sludge treatment plants. The constant exposure of microbial communities not only to high concentrations but also to sub-inhibitory concentrations of antibiotics is a key element in the development of antibiotic resistance in aquatic environments and in soils. The future of antimicrobials lies in the development of biosourced or bioinspired molecules. The observation and deciphering of interactions between living organisms is the key to this development.</p> </abstract>

Interruption of the tricarboxylic acid cycle in Staphylococcus aureus leads to increased tolerance to innate immunity

<abstract> <p><italic>Staphylococcus aureus</italic> is widely known for its resistance and virulence causing public health concerns. However, antibiotic tolerance is also a contributor to chronic and relapsing infections. Previously, it has been demonstrated that persister formation is dependent on reduced tricarboxylic acid (TCA) cycle activity. Persisters have been extensively examined in terms of antibiotic tolerance but tolerance to antimicrobial peptides (AMPs) remains largely unexplored. AMPs are a key component of both the human and <italic>Drosophila</italic> innate immune response. TCA cycle mutants were tested to determine both antibiotic and AMP tolerance. Challenging with multiple classes of antibiotics led to increased persister formation (100- to 1,000-fold). Similarly, TCA mutants exhibited AMP tolerance with a 100- to 1,000-fold increase in persister formation when challenged with LL-37 or human β-defensin 3 (hβD3). The ability of TCA cycle mutants to tolerate the innate immune system was further examined with a <italic>D. melanogaster</italic> model. Both males and females infected with TCA cycle mutants exhibited increased mortality and had higher bacterial burdens (1.5 log) during the course of the infection. These results suggest increasing the percentage of persister cells leads to increased tolerance to components of the innate immune system.</p> </abstract>

Isolation, identification and potential probiotic characterization of lactic acid bacteria from Thai traditional fermented food

<abstract> <p>The probiotic potential of lactic acid bacteria (LAB) isolated from Thai traditional fermented food was investigated. Forty-two samples were collected from four markets in Phra Nakhon Si Ayutthaya Province. Out of 50 isolated LAB, 6 (a3, f4, f8, K1, K4 and K9) obtained from pla-ra and bamboo shoot pickle samples showed high tolerance to gastrointestinal tract conditions. These isolates were selected to identify and characterize their probiotic properties. Isolate a3 was identified as <italic>Weissella thailandensis</italic>, isolates f4 and f8 were identified as belonging to <italic>Enterococcus thailandicus</italic> and isolates K1, K4 and K9 were determined as <italic>Limosilactobacillus fermentum</italic>. All six LAB exhibited high autoaggregation ability (93.40–95.01%), while <italic>W. thailandensis</italic> isolate a3 showed potential for coaggregation in almost all the pathogenic bacteria tested. Cell-free supernatant (CFS) obtained from all isolates did not inhibit <italic>Staphylococcus aureus</italic>. CFS derived from <italic>L. fermentum</italic> isolate K4 showed the most efficient antimicrobial activity, in particular against Gram-negative bacteria, while <italic>L. fermentum</italic> isolate K4 presented high surface hydrophobicity in the presence of xylene and n-hexane. All LAB isolates were found to be resistant to clindamycin and nalidixic acid, whereas <italic>E. thailandicus</italic> isolate f8 exhibited resistance to most of the antibiotics tested. <italic>L. fermentum</italic> isolate K4 showed promise as a suitable probiotic candidate for future applications in the food industry due to tolerance to gastrointestinal tract conditions with high surface hydrophobicity and inhibited most of the pathogens tested.</p> </abstract>

Substrate preferences, phylogenetic and biochemical properties of proteolytic bacteria present in the digestive tract of Nile tilapia (Oreochromis niloticus)

<abstract> <p>Vertebrate intestine appears to be an excellent source of proteolytic bacteria for industrial and probiotic use. We therefore aimed at obtaining the gut-associated proteolytic species of Nile tilapia (<italic>Oreochromis niloticus</italic>). We have isolated twenty six bacterial strains from its intestinal tract, seven of which showed exoprotease activity with the formation of clear halos on skim milk. Their depolymerization ability was further assessed on three distinct proteins including casein, gelatin, and albumin. All the isolates could successfully hydrolyze the three substrates indicating relatively broad specificity of their secreted proteases. Molecular taxonomy and phylogeny of the proteolytic isolates were determined based on their 16S rRNA gene barcoding, which suggested that the seven strains belong to three phyla viz. Firmicutes, Proteobacteria, and Actinobacteria, distributed across the genera <italic>Priestia</italic>, <italic>Citrobacter</italic>, <italic>Pseudomonas</italic>, <italic>Stenotrophomonas</italic>, <italic>Burkholderia</italic>, <italic>Providencia</italic>, and <italic>Micrococcus</italic>. The isolates were further characterized by a comprehensive study of their morphological, cultural, cellular and biochemical properties which were consistent with the phylogenetic annotations. To reveal their proteolytic capacity alongside substrate preferences, enzyme-production was determined by the diffusion assay. The <italic>Pseudomonas</italic>, <italic>Stenotrophomonas</italic> and <italic>Micrococcus</italic> isolates appeared to be most promising with maximum protease production on casein, gelatin, and albumin media respectively. Our findings present valuable insights into the phylogenetic and biochemical properties of gut-associated proteolytic strains of Nile tilapia.</p> </abstract>

A comparison of different DNA extraction methods and molecular techniques for the detection and identification of foodborne pathogens

<abstract> <p>Foodborne infections continue to plague Europe. Food safety monitoring is in crisis as the existing techniques for detecting pathogens do not keep up with the global rising of food production and consumption. Thus, the development of innovative techniques for detecting and identifying pathogenic bacteria has become critical. The aim of the present study was firstly to develop an innovative simple and low cost method of extracting bacterial DNA from contaminated food and water samples with <italic>Salmonella enteric</italic> subsp. <italic>enteric</italic> serovar Typhimurium and <italic>Listeria monocytogenes</italic> and its comparison with two commercial DNA extraction kits (Qiagen, Macherey-Nagel). Finally, pathogens' detection using two molecular techniques (PCR-electrophoresis, LAMP), in order to evaluate the best combination of DNA extraction and identification based on their sensitivity, cost, rapidity and simplicity. Considering the above criteria, among them, best was proved an in-house bacterial DNA extraction method, based on the chloroform-isoamyl alcohol protocol, with certain modifications. This technique showed statistically similar results in terms of sensitivity, compared to the commercial kits, while at the same time maintained high rapidity and much lower cost. Lastly, between the molecular techniques, LAMP was found more promising considering its simplicity, high rapidity and sensitivity. Conclusively, the in-house DNA extraction method along with the LAMP technique, was proven to be the best among the presented combinations.</p> </abstract>

Antimicrobial activities encountered by sulfur nanoparticles combating Staphylococcal species harboring sccmecA recovered from acne vulgaris

<abstract> <p>Over decades, sulfur has been employed for treatment of many dermatological diseases, several skin and soft tissue, and <italic>Staphylococcus</italic> infections. Because of its abuse, resistant bacterial strains have emerged. Nanotechnology has presented a new horizon to overcome abundant problems including drug resistance. Nano-sized sulfur has proven to retain bactericidal activity. Consequently, the specific aims of this study are exclusively directed to produce various sulfur nanoparticles formulations with control of particle size and morphology and investigate the antibacterial activity response specifically classified by the category of responses of different formulations, for the treatment of acne vulgaris resistant to conventional antibiotics. In this study, we produced uncoated sulfur nanoparticles (SNPs), sulfur nano-composite with chitosan (CS-SNPs), and sulfur nanoparticles coated with polyethylene glycol (PEG-SNPs) and evaluate their bactericidal impact against <italic>Staphylococcus aureus</italic> and <italic>Staphylococcus epidermidis</italic> isolated from 173 patients clinically diagnosed acne vulgaris. Accompanied with molecular investigations of <italic>erm</italic>B and <italic>mec</italic>A resistance genes distribution among the isolates. Sulfur nanoparticles were synthesized using acid precipitation method and were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), energy dispersed x-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). Moreover, agar diffusion and broth micro-dilution methods were applied to determine their antibacterial activity and their minimum inhibitory concentration. PCR analysis for virulence factors detection. Results: TEM analysis showed particle size of SNPs (11.7 nm), PEG-SNPs (27 nm) and CS-SNPs (33 nm). Significant antibacterial activity from nanoparticles formulations in 100% dimethyl sulfoxide (DMSO) with inhibition zone 30 mm and MIC at 5.5 µg/mL. Furthermore, the prevalence of <italic>mecA</italic> gene was the most abundant among the isolates while <italic>ermB</italic> gene was infrequent. Conclusions: sulfur nanoparticles preparations are an effective treatment for most <italic>Staphylococcus</italic> bacteria causing acne vulgaris harboring multi-drug resistance virulence factors.</p> </abstract>

Lignocelluloytic activities and composition of bacterial community in the camel rumen

<abstract> <p>The camel is well-adapted to utilize the poor-quality forages in the harsh desert conditions as the camel rumen sustains fibrolytic microorganisms, mainly bacteria that are capable of breaking down the lignocellulosic biomass efficiently. Exploring the composition of the bacterial community in the rumen of the camel and quantifying their cellulolytic and xylanolytic activities could lead to understanding and improving fiber fermentation and discovering novel sources of cellulases and xylanases. In this study, Illumina MiSeq sequencing of the V4 region on 16S rRNA was applied to identify the bacterial and archaeal communities in the rumen of three camels fed wheat straw and broom corn. Furthermore, rumen samples were inoculated into bacterial media enriched with xylan and different cellulose sources, including filter paper (FP), wheat straw (WS), and alfalfa hay (AH) to assess the ability of rumen bacteria to produce endo-cellulase and endo-xylanase at different fermentation intervals. The results revealed that the phylum Bacteroidetes dominated the bacterial community and <italic>Candidatus Methanomethylophilus</italic> dominated the archaeal community. Also, most of the bacterial community has fibrolytic potential and the dominant bacterial genera were <italic>Prevotella</italic>, <italic>RC9_gut_group</italic>, <italic>Butyrivibrio</italic>, <italic>Ruminococcus</italic>, <italic>Fibrobacteres</italic>, and <italic>Treponema</italic>. The highest xylanase production (884.8 mU/mL) was observed at 7 days. The highest cellulase production (1049.5 mU/mL) was observed when rumen samples were incubated with Alfalfa hay for 7 days.</p> </abstract>