Emerging resistance of van genotype in enterococci: A potential menace for therapeutic failure

Objectives:

Emerging cases of vancomycin-resistant enterococci (VRE) are detrimental for the patients. The current study aimed to ascertain the occurrence of VRE, their antibiogram and the van genotype responsible for vancomycin resistance.

Methods:

A total number of 2,958 clinical specimens were processed at Microbiology Department of the Alrazi Health Care, Lahore during the one year (2016-2017) using microbiological culture media, biochemical and serology. Antibiogram of enterococcal strains was performed using disc diffusion and E-test. ATCC Enterococcus faecalis 29212 was used as a quality control strain. The detection of van genotypes was accomplished by multiplex PCR assay.

Results:

Out of the 147 enterococci, 139 (94.6%) were E. faecalis, and 8 (5.4%) were E. faecium. Statistically significant associations of urine (p < 0.001), pus (p < 0.001) and wound swabs (p = 0.001) were observed with E. faecalis. A significant correlation of enterococcal infections (p = 0.05) was seen with female patients. Four (2.9%) strains of E. faecalis found to be VRE with vanB (75%) and vanA (25%) genotypes.

Conclusion:

The emerging strains of VRE (vanB and vanA genotype) in the current study are a potential menace for therapeutic failure, which left the physicians with only linezolid as a therapeutic option.

Regulation of teicoplanin biosynthesis: refining the roles of tei cluster-situated regulatory genes

Teicoplanin is a frontline glycopeptide antibiotic produced by Actinoplanes teichomyceticus. It is used to treat complicated cases of infection, including pediatric ones, caused by Gram-positive pathogens. There is a steady interest in elucidating the genetic mechanisms determining teicoplanin production, as they would help overproduce known teicoplanins and discover novel glycopeptides. Herein, we investigate the transcriptional organization of the tei biosynthetic gene cluster and the roles of the cluster-situated regulatory genes in controlling teicoplanin production and self-resistance in A. teichomyceticus. We demonstrate that the tei cluster is organized into nine polygenic and nine monogenic transcriptional units. Most of tei biosynthetic genes are subjected to StrR-like Tei15* control, which, in turn, appears to be regulated by LuxR-type Tei16*. Expression of the genes conferring teicoplanin self-resistance in A. teichomyceticus is not co-regulated with antibiotic production. The gene tei31*, coding for a putative DNA binding protein, is not expressed under teicoplanin producing conditions and is dispensable for antibiotic production. Finally, phylogenesis reconstruction of the glycopeptide cluster-encoded regulators reveals two main clades of StrR-like regulators. Tei15* and close orthologues form one of these clades; the second clade is composed by orthologues of Bbr and Dbv4, governing the biosynthesis of balhimycin and teicoplanin-like A40926, respectively. In addition, the LuxR-type Tei16* appears unrelated to the LuxR-like Dbv3, which is controlling A40926 biosynthesis. Our results shed new light on teicoplanin biosynthesis regulation and on the evolution of novel and old glycopeptide biosynthetic gene clusters.

Characteristics of clinical and environmental vanM-carrying vancomycin-resistant enterococci isolates from an infected patient

vanM, an uncommon glycopeptide resistance gene, was first identified in an Enterococcus faecium isolate (Efm-HS0661) from Shanghai, China, in 2006 and has been predominant in this city since 2011. A vanM-carrying E. faecium was isolated from the bloodstream of a patient in an intensive care unit (ICU) in Hangzhou, China, in 2014. Further surveillance screening of a rectal swab and environmental surfaces of the patient yielded a large number of vanM-positive E. faecium. These isolates (including 1 from the bloodstream, 1 from the rectal swab and 43 representative isolates from environmental samples) were classified into four pulsed-field gel electrophoresis (PFGE) patterns and two sequence types (ST78 and ST564). PCR amplification and sequence analysis indicated that the genetic structure surrounding the vanM gene of these isolates was similar to that of the original vanM-carrying isolate Efm-HS0661. This study highlights the emergence of infections and environmental contamination caused by vanM-carrying E. faecium in an ICU of another Chinese city outside of Shanghai.

Emergence of dalbavancin non-susceptible, vancomycin-intermediate Staphylococcus aureus (VISA) after treatment of MRSA central line-associated bloodstream infection with a dalbavancin- and vancomycin-containing regimen

OBJECTIVES

Dalbavancin is a long-acting lipoglycopeptide with activity against gram-positives, including methicillin-resistant Staphylococcus aureus (MRSA). The potential for lipoglycopeptides, with half-lives greater than 1 week, to select for resistance is unknown. Here we explore a case of MRSA central line-associated bloodstream infection in which dalbavancin and vancomycin non-susceptibility emerged in a urine isolate collected after the patient was treated with vancomycin and dalbavancin sequentially.

METHODS

Isolates from blood and urine underwent susceptibility testing, and whole genome sequencing (WGS). The blood isolate was subjected to successive passage in vitro in the presence of escalating dalbavancin concentrations and the emergent isolate was subjected to repeat susceptibility testing and WGS.

RESULTS

The blood isolate was fully susceptible to vancomycin; however, MICs of the urine isolate to dalbavancin, vancomycin, telavancin, and daptomycin were at least fourfold higher than the blood-derived strain. Both strains were indistinguishable by spa and variable number tandem repeat (VNTR) typing, and WGS revealed only seven variants, indicating clonality. Four variants affected genes, including a 3bp in-frame deletion in yvqF, a gene which has been implicated in glycopeptide resistance. Vancomycin and dalbavancin non-susceptibility emerged in the blood isolate after successive passage in vitro in the presence of dalbavancin, and WGS identified a single non-synonymous variant in yvqF.

CONCLUSIONS

This is the first case in which VISA has emerged in the context of a dalbavancin-containing regimen. The selection for cross-resistance to vancomycin in vitro by dalbavancin exposure alone is troubling. Clinicians should be aware of the possibility for emergence of dalbavancin non-susceptibility and glycopeptide cross-resistance arising following therapy.

vanA Gene Harboring Enterococcal and Non-enterococcal Isolates Expressing High Level Vancomycin and Teicoplanin Resistance Reservoired in Surface Waters

Untreated wastewaters and treated effluents even after final disinfection contain antibiotic resistant bacteria and resistance genes before they are released into surface waters. A correlation between resistant bacteria and antibiotics in surface waters has been found, as have antibiotic resistance genes. Of particular interest are vancomycin-resistant enterococci harboring vanA gene that confers high level of resistance to glycopeptide antibiotics including teicoplanin. Therefore, in this study, river water samples were analysed to investigate vancomycin- and teicoplanin-resistant bacterial isolates harboring vanA gene. Out of 290, 15 surface water isolates displayed resistance to both antibiotics. These glycopeptide resistant enterococcal and non-enterococcal isolates, identified by 16S rRNA sequencing, were found to harbor vanA gene with sequence similarities of 50 % to 100 %. The presence of D-alanine-D-lactate ligase encoded by vanA gene was also shown for all vancomycin- and teicoplanin-resistant isolates through western blot analysis. Due to reuse of treated wastewater and release of untreated wastewaters to water bodies, antibiotic resistant bacteria and resistance genes are being introduced into surface waters and present human health risks. Therefore, surface waters are not only hot spots for vanA harboring enterococcal isolates but also non-enterococcal isolates due to gene dissemination and require special scientific consideration.

vanA-targeted oligonucleotide DNA probe designed to monitor vancomycin- and teicoplanin-resistant bacteria in surface waters

The glycopeptide antibiotics teicoplanin and vancomycin are common to treat severe Gram-positive bacterial infections. The gene vanA confers high-level resistance to these antibiotics, and these phenomena have been shown to be transferable. Release of vancomycin- and teicoplanin-resistant bacteria to surface waters is, therefore, of particular concern since they might proliferate and spread in different environments. Monitoring of the fate of vanA gene in these waters provides information on the exposure and potential threats of those bacteria for the environment and public health. Therefore, this study aimed at preparing a 25-mer-oligonucleotide DNA probe based on the 909 bp BamHI-ClaI fragment from Enterococcus faecium plasmids pVEF1 and pVEF2 through the use of Vector NTI Express Software. The newly designed vanA probe displayed highly specific hybridization with vanA-positive Enterococcus faecalis tested at 46 °C, 55 % formamide, and 0.020 M NaCl stringency conditions. In situ fluorescein hybridizations under the same stringency conditions were also used to monitor river water samples by using fluorescein microscopy. The results showed that the vanA-targeted oligonucleotide DNA probe prepared was not only highly specific but also quantitative tool for monitoring vancomycin- and teicoplanin-resistant bacteria in surface waters.

Emergence of multidrug resistant enterococci at a tertiary care centre

BACKGROUND

Enterococci have assumed great clinical importance because of their increasing resistance to various antimicrobial agents. Thus, knowledge about the antibiogram of these multidrug resistant isolates is of utmost importance in formulating an effective antibiotic policy to treat these infections and reducing the morbidity and mortality. Aim of this study was to assess the antimicrobial resistance pattern of enterococci and determine the prevalence of multidrug resistance among them.

METHODS

This cross sectional study was carried out from August 2011 to February 2014, in which 200 non-repetitive clinical isolates of enterococci were included. Antimicrobial susceptibility testing was done by disc diffusion method. Minimum inhibitory concentration (MIC) of gentamicin, streptomycin, vancomycin, teicoplanin and linezolid was determined by E-test method.

RESULTS

The prevalence of multidrug resistance among enterococcal isolates was found to be 63%. Varying levels of resistance was seen to various antibiotics. Most of the isolates were resistant to penicillin (95%), ampicillin (95%) and cotrimoxazole (90%). High level aminoglycoside resistance (HLAR) and glycopeptide resistance was seen in 39% and 14% isolates respectively. Only 4 isolates (2%) were found to be resistant to linezolid.

CONCLUSION

The prevalence of multidrug resistance among enterococci was found to be 63%, the resistance being more common in Enterococcus faecium as compared to Enterococcus faecalis. The study highlights the emergence and increased prevalence of multidrug resistant enterococci which pose a serious therapeutic challenge.