High-level aminoglycoside resistance and virulence characteristics among Enterococci isolated from recreational beaches in Malaysia

Towards the standardization of Enterococcus culture methods for waterborne antibiotic resistance monitoring: A critical review of trends across studies

Antibiotic resistance is a major 21^st century One Health (humans, animals, environment) challenge whose spread limits options to treat bacterial infections. There is growing interest in monitoring water environments, including surface water and wastewater, which have been identified as key recipients, pathways, and sources of antibiotic resistant bacteria (ARB). Aquatic environments also facilitate the transmission and amplification of ARB. Enterococcus spp. often carry clinically-important antibiotic resistance genes and are of interest as environmental monitoring targets. Enterococcus spp. are Gram-positive bacteria that are typically of fecal origin; however, they are also found in relevant environmental niches, with various species and strains that are opportunistic human pathogens. Although the value of environmental monitoring of antibiotic-resistant Enterococcus has been recognized by both national and international organizations, lack of procedural standardization has hindered generation of comparable data needed to implement integrated surveillance programs. Here we provide a comprehensive methodological review to assess the techniques used for the culturing and characterization of antibiotic-resistant Enterococcus across water matrices for the purpose of environmental monitoring. We analyzed 117 peer-reviewed articles from 33 countries across six continents. The goal of this review is to provide a critical analysis of (i) the various methods applied globally for isolation, confirmation, and speciation of Enterococcus isolates, (ii) the different methods for profiling antibiotic resistance among enterococci, and (iii) the current prevalence of resistance to clinically-relevant antibiotics among Enterococcus spp. isolated from various environments. Finally, we provide advice regarding a path forward for standardizing culturing of Enterococcus spp. for the purpose of antibiotic resistance monitoring in wastewater and wastewater-influenced waters within a global surveillance framework.

Phenotype-Genotype Correlations and Distribution of Key Virulence Factors in Enterococcus faecalis Isolated from Patients with Urinary Tract Infections

Background and Objective

Enterococcus faecalis can cause different nosocomial infections, especially urinary tract infection (UTI). Pathogenicity of E. faecalis is driven by various virulence factors; however, no specific genetic pattern is restricted to a particular type of infection. The current study aimed to investigate the correlation between different virulence factors in E. faecalis clinical isolates causing UTIs.

Methods

We phenotypically analyzed 60 urinary isolates, identified as E. faecalis, for biofilm formation, gelatinase, protease and hemolytic activities by Crystal Violet assay, gelatin hydrolysis, casein hydrolysis and blood agar hemolysis assays, respectively. Additionally, we detected different genes associated with species identification, virulence phenotypes, adherence and quorum sensing by the polymerase chain reaction (PCR). The detected genes included D-alanine-D-alanine ligase (ddl), cytolysin (cyl), gelatinase (gelE), serine protease (sprE), faecal streptococci regulator locus genes (fsrA, fsrB, fsrC), pili (pil), adhesin to collagen of E. faecalis (ace) and aggregation substance (agg).

Results

All isolates formed biofilms, mostly with strong to moderate ability. Although gelE was detected in 87% of the isolates, only 22% of the isolates had gelatinase activity. Similar phenotype-genotype incongruities were observed with hemolysis and casein hydrolysis activities, as the isolates that expressed these two phenotypes were fewer than those carrying the genes encoding them.

Conclusion

A clear variability in virulence gene distribution among the isolates was observed, and no particular pattern was associated with UTI. Whereas all isolates carried at least ace and pil, whose products are involved in adherence, which is a virulence phenotype that is required for urinary colonization, six isolates carried the entire set of investigated genes. Statistical analysis of the results suggests cyl as a biomarker for hemolytic activity, fsrB as a diagnostic biomarker for the gelatinase activity, and gelE-sprE as predictors for biofilm formation strength in E. faecalis.

Natural transformation of the filamentous cyanobacterium Phormidium lacuna

Research for biotechnological applications of cyanobacteria focuses on synthetic pathways and bioreactor design, while little effort is devoted to introduce new, promising organisms in the field. Applications are most often based on recombinant work, and the establishment of transformation can be a risky, time-consuming procedure. In this work we demonstrate the natural transformation of the filamentous cyanobacterium Phormidium lacuna and insertion of a selection marker into the genome by homologous recombination. This is the first example for natural transformation filamentous non-heterocystous cyanobacterium. We found that Phormidium lacuna is polyploid, each cell has about 20-90 chromosomes. Transformed filaments were resistant against up to 14 mg/ml of kanamycin. Formerly, natural transformation in cyanobacteria has been considered a rare and exclusive feature of a few unicellular species. Our finding suggests that natural competence is more distributed among cyanobacteria than previously thought. This is supported by bioinformatic analyses which show that all protein factors for natural transformation are present in the majority of the analyzed cyanobacteria.

Biofilm synthesis and other virulence factors in multidrug-resistant uropathogenic enterococci isolated in Northern India

Purpose

Enterococci express high degree of resistance towards wide range of antibiotics. Production of biofilm and many virulence factors along with drug resistance makes it difficult to eradicate the infection from urinary tract. The present study detected the expression of such factors including biofilm production by multidrug-resistant (MDR) enterococci.

Materials and Methods

Drug susceptibility of 103 uropathogenic enterococci was performed followed by estimation of minimum inhibitory concentration of high-level gentamicin and vancomycin by microbroth dilution method. Vancomycin-resistant genes were detected by multiplex polymerase chain reaction. Production of virulence factors such as haemagglutination, caseinase, lipase, gelatinase, haemolysin and β-lactamase was detected by phenotypic methods in MDR strains. Biofilm production was detected by calcofluor-white fluorescence staining and semi-quantitative adherence assay.

Results

45% and 18.4% of the isolates were high-level gentamicin-resistant and vancomycin-resistant enterococci (VRE), respectively. vanA gene was detected in 14 and vanB gene in 5 strains. Biofilm, caseinase and gelatinase were the most expressed virulence factor. Expression of caseinase, gelatinase and lipase was significantly higher in Enterococcus faecalis (P < 0.05). Expression of haemagglutination, gelatinase and haemolysin among the vancomycin-resistant isolates was significantly higher (P < 0.05).

Conclusion

VanA and vanB are the prevalent genotypes responsible for vancomycin resistance. The high prevalence of MDR enterococcal strains producing biofilm and virulence determinants raises concern. asa1, hyl, esp, gelE, cyl and other genes are known to express these factors and contribute to biofilm formation. Most uropathogenic enterococci expressed biofilm at moderate level and can be detected effectively by calcofluor-white staining. No correlation was noted between vancomycin resistance and biofilm production.

Efflux pumps genes of clinical origin are related to those from fluconazole-resistant Candida albicans isolates from environmental water

Efflux pumps coded for by CDR1, CDR2, FLU1 and MDR1 genes could be responsible for the observed resistant phenotypes in azole-resistant Candida albicans from environmental water. This was demonstrated for clinical isolates. The aim of this study was to determine the presence and genetic similarity between efflux pump genes from clinical and environmental C. albicans isolates. Yeasts were isolated and identified using 26S rRNA gene sequencing. Disk diffusion tests were conducted. PCR was used to detect the presence of efflux genes. The fragments were sequenced and subjected to BLAST and subsequent phylogenetic analysis. Thirty seven C. albicans were identified from five selected rivers; Mooi River (19 isolates), Harts River (9 isolates), Marico River (5 isolates), Crocodile River (3 isolates) and Schoonspruit River (1 isolate). All the isolates were completely resistant to azoles. Efflux pump genes were detected in most (≥60%) of the isolates. Phylogenetic analysis showed high sequence similarity between sequences from environmental isolates and clinical isolates. Resistance to the azoles and the detection of efflux pump genes renders these antifungal agents ineffective. This is a major problem, particularly for the immune-compromised sector of the community of the North West Province and warrants further investigation.

Molecular assessment of virulence determinants, hospital associated marker (IS16gene) and prevalence of antibiotic resistance in soil borne Enterococcus species

Enterococci, no more regarded as GRAS (Generally Recognized As Safe) organism, are emerging as an important source of nosocomial infections worldwide. The main contributors in pathogenesis of enterococci are the presence of various virulent factors and antibiotic resistance genes. We aimed to examine the prevalence, dissemination, antibiotic resistance and virulent factors associated with enterococci from bulk soil (BS). A total of 372 enterococci were isolated from 500 soil samples. PCR was used to identify the isolates up to species level and for carriage of 16 virulence genes including hospital associated marker (i.e. IS16). E. faecium (77%), E. faecalis (10%), E. hirae (4%) and E. casseliflavus (1%) were the major species isolated. The efaAfs was the most dominant gene (100%), followed by gelE (78.9%), sprE (76.3%) and esp (13%) in E. faecalis isolates. The E. faecium carried largely efaAfm (86.8%) and acm (50.3%) genes. Presence of entP (10%), entA (8.3%) and entB (6.9%) genes was detected mostly in E. faecium, while enlA (18%) and ef1097 (2.6%) was only detected in E. faecalis isolates. 50% E. faecalis and 2% E. faecium isolates harbored IS16, while five E. faecalis harbored both IS16 and espTIM genes providing strong evidence about the presence of espTIM gene on 64 Kb pathogenicity island. BOX and RAPD PCR analysis revealed high degree of genetic variation within the species. Degree of resistance against 12 major antibiotics showed chloramphenicol as the most effective and meropenom as the least effective antibiotic. Presence of multiple antibiotic resistant, virulent and hospital associated enterococci in bulk soil represents a potential source for further dissemination to humans and animals and poses potential impact on public health.

Antibiotic resistance, efflux pump genes and virulence determinants in Enterococcus spp. from surface water systems

The aim of this study was to report on antibiotic susceptibility patterns as well as highlight the presence of efflux pump genes and virulence genetic determinants in Enterococcus spp. isolated from South African surface water systems. One hundred and twenty-four Enterococcus isolates consisting of seven species were identified. Antimicrobial susceptibility testing revealed a high percentage of isolates was resistant to β-lactams and vancomycin. Many were also resistant to other antibiotic groups. These isolates were screened by PCR, for the presence of four efflux pump genes (mefA, tetK, tetL and msrC). Efflux genes mefA and tetK were not detected in any of the Enterococcus spp. However, tetL and msrC were detected in 17 % of the Enterococcus spp. The presence of virulence factors in the Enterococcus spp. harbouring efflux pump genes was determined. Virulence determinants were detected in 86 % of the Enterococcus spp. harbouring efflux pump genes. Four (asa1, cylA, gel and hyl) of the five virulence factors were detected. The findings of this study have demonstrated that Enterococcus from South African surface water systems are resistant to multiple antibiotics, some of which are frequently used for therapy. Furthermore, these isolates harbour efflux pump genes coding for resistance to antibiotics and virulence factors which enhance their pathogenic potential.

The prevalence of aminoglycoside-modifying enzyme and virulence genes among enterococci with high-level aminoglycoside resistance in Inner Mongolia, China

This study highlights the prevalence of aminoglycoside-modifying enzyme genes and virulence determinants among clinical enterococci with high-level aminoglycoside resistance in Inner Mongolia, China. Screening for high-level aminoglycoside resistance against 117 enterococcal clinical isolates was performed using the agar-screening method. Out of the 117 enterococcal isolates, 46 were selected for further detection and determination of the distribution of aminoglycoside-modifying enzyme-encoding genes and virulence determinants using polymerase chain reaction -based methods. Enterococcus faecium and Enterococcus faecalis were identified as the species of greatest clinical importance. The aac(6′)-Ie-aph(2″)-Ia and ant(6′)-Ia genes were found to be the most common aminoglycoside-modifying enzyme genes among high-level gentamicin resistance and high-level streptomycin resistance isolates, respectively. Moreover, gelE was the most common virulence gene among high-level aminoglycoside resistance isolates. Compared to Enterococcus faecium, Enterococcus faecalis harbored multiple virulence determinants. The results further indicated no correlation between aminoglycoside-modifying enzyme gene profiles and the distribution of virulence genes among the enterococcal isolates with high-level gentamicin resistance or high-level streptomycin resistance evaluated in our study.