Multidrug-resistant phenotype and isolation of a novel SHV- beta-Lactamase variant in a clinical isolate of Enterobacter cloacae

Characterization of a Salmonella enterica serovar Typhimurium lineage with rough colony morphology and multidrug resistance

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a major cause of salmonellosis, and the emergence of multidrug-resistant pathovariants has become a growing concern. Here, we investigate a distinct rough colony variant exhibiting a strong biofilm-forming ability isolated in China. Whole-genome sequencing on 2,212 Chinese isolates and 1,739 publicly available genomes reveals the population structure and evolutionary history of the rough colony variants. Characterized by macro, red, dry, and rough (mrdar) colonies, these variants demonstrate enhanced biofilm formation at 28 °C and 37 °C compared to typical rdar colonies. The mrdar variants exhibit extensive multidrug resistance, with significantly higher resistance to at least five classes of antimicrobial agents compared to non-mrdar variants. This resistance is primarily conferred by an IncHI2 plasmid harboring 19 antimicrobial resistance genes. Phylogenomic analysis divides the global collections into six lineages. The majority of mrdar variants belong to sublineage L6.5, which originated from Chinese smooth colony strains and possibly emerged circa 1977. Among the mrdar variants, upregulation of the csgDEFG operons is observed, probably due to a distinct point mutation (-44G > T) in the csgD gene promoter. Pangenome and genome-wide association analyses identify 87 specific accessory genes and 72 distinct single nucleotide polymorphisms associated with the mrdar morphotype.

Genomic Characteristics and Molecular Epidemiology of Multidrug-Resistant Klebsiella pneumoniae Strains Carried by Wild Birds

This study aimed to explore the relationship between wild birds and the transmission of multidrug-resistant strains. Klebsiella pneumoniae was isolated from fresh feces of captured wild birds and assessed by the broth microdilution method and comparative genomics. Four Klebsiella pneumoniae isolates showed different resistance phenotypes; S90-2 and S141 were both resistant to ampicillin, cefuroxime, and cefazolin, while M911-1 and S130-1 were sensitive to most of the 14 antibiotics tested. S90-2 belongs to sequence type 629 (ST629), and its genome includes 30 resistance genes, including blaCTX-M-14 and blaSHV-11, while its plasmid pS90-2.3 (IncR) carries qacEdelta1, sul1, and aph(3')-Ib. S141 belongs to ST1662, and its genome includes a total of 27 resistance genes, including blaSHV-217. M911-1 is a new ST, carrying blaSHV-1 and fosA6, and its plasmid pM911-1.1 (novel) carries qnrS1, blaLAP-2, and tet(A). S130-1 belongs to ST3753, carrying blaSHV-11 and fosA6, and its plasmid pS130-1 [IncFIB(K)] carries only one resistance gene, tet(A). pM911-1.1 and pS90-2.3 do not have conjugative transfer ability, but their resistance gene fragments are derived from multiple homologous Enterobacteriaceae strain chromosomes or plasmids, and the formation of resistance gene fragments (multidrug resistance region) involves interactions between multiple mobile element genes, resulting in a complex and diverse resistance plasmid structure. The homologous plasmids related to pM911-1.1 and pS90-2.3 were mainly from isolated human-infecting bacteria in China, namely, K. pneumoniae and Escherichia coli. The multidrug-resistant K. pneumoniae isolates carried by wild birds in this study had drug resistance phenotypes conferred primarily by multidrug resistance plasmids that were closely related to human-infecting bacteria. IMPORTANCE Little is known about the pathogenic microorganisms carried by wild animals. This study found that the multidrug resistance phenotype of Klebsiella pneumoniae isolates carried by wild birds was mainly attributed to multidrug resistance plasmids, and these multidrug resistance plasmids from wild birds were closely related to human-infecting bacteria. Wild bird habitats overlap to a great extent with human and livestock habitats, which further increases the potential for horizontal transfer of multidrug-resistant bacteria among humans, animals, and the environment. Therefore, wild birds, as potential transmission hosts of multidrug-resistant bacteria, should be given attention and monitored.

Genetic basis of molecular mechanisms in β-lactam resistant gram-negative bacteria

Antibiotic-resistant bacteria are considered one of the major global threats to human and animal health. The most harmful among the resistant bacteria are β-lactamase producing Gram-negative species (β-lactamases). β-lactamases constitute a paradigm shift in the evolution of antibiotic resistance. Therefore, it is imperative to present a comprehensive review of the mechanisms responsible for developing antimicrobial resistance. Resistance due to β-lactamases develops through a variety of mechanisms, and the number of resistant genes are involved that can be transferred between bacteria, mostly via plasmids. Over time, these new molecular-based resistance mechanisms have been progressively disclosed. The present review article provides information on the recent findings regarding the molecular mechanisms of resistance to β-lactams in Gram-negative bacteria, including CTX-M-type ESBLs with methylase activity, plasmids harbouring phages with β-lactam resistance genes, the co-presence of β-lactam resistant genes of unique combinations and the presence of β-lactam and non-β-lactam antibiotic-resistant genes in the same bacteria. Keeping in view, the molecular level resistance development, multifactorial and coordinated measures may be taken to counter the challenge of rapidly increasing β-lactam resistance.

Carbapenem-Resistant Enterobacter hormaechei ST1103 with IMP-26 Carbapenemase and ESBL Gene bla SHV-178

Purpose

To investigate the occurrence and genetic characteristics of the bla_IMP-26-positive plasmid from a multidrug-resistant clinical isolate, Enterobacter hormaechei L51.

Methods

Species identification was determined by MALDI-TOF MS and Sanger sequencing. Antimicrobial susceptibility testing was performed by the agar dilution and broth microdilution. Whole-genome sequencing was conducted using Illumina HiSeq 4000-PE150 and PacBio Sequel platforms, and the genome was annotated by the RAST annotation server. The ANI analysis of genomes was performed using OAT. Phylogenetic reconstruction and analyses were performed using the Harvest suite based on the core-genome SNPs of 61 publicly available E. hormaechei genomes.

Results

The E. hormaechei L51 genome consists of a 5,018,729 bp circular chromosome and a 343,918 bp conjugative IncHI2/2A plasmid pEHZJ1 encoding bla_IMP-26 which surrounding genetic context was intI1-bla_IMP-26-ltrA-qacE∆1-sul1. A new sequence type (ST1103) was assigned for the isolate L51 which was resistant to cephalosporins, carbapenems, but sensitive to piperacillin-tazobactam, amikacin, tigecycline, trimethoprim-sulfamethoxazole and colistin. Phylogenetic analysis demonstrated that E. hormaechei L51 belonged to the same subspecies as the reference strain E. hormaechei SCEH020042, however 18,248 divergent SNP were identified. Resistance genes in pEHZJ1 including aac(3)-IIc, aac(6ʹ)-IIc, bla_SHV-178, bla_DHA-1, bla_TEM-1, bla_IMP-26, ereA2, catII, fosA5, qnrB4, tet(D), sul1 and dfrA19.

Conclusion

In our study, we identified a conjugative IncHI2/2A plasmid carrying bla_IMP-26 and bla_SHV-178 in E. hormaechei ST1103, a novel multidrug-resistant strain isolated from China, and describe the underlying resistance mechanisms of the strain and detailed genetic context of mega plasmid pEHZJ1.

Antimicrobial resistance of 3 types of gram-negative bacteria isolated from hospital surfaces and the hands of health care workers

BACKGROUND

There has been an increased focus in recent years on antimicrobial resistance of bacteria isolated from clinical samples. However, resistance of bacteria from hospital environments has been less frequently investigated.

METHODS

According to hygienic standard for disinfection in hospitals, samples were collected from hospital inanimate surfaces and the hands of health care workers after daily cleaning. An automatic microorganism analyzer was used to identify bacteria and test for antimicrobial susceptibility. Polymerase chain reaction was used to detect antimicrobial resistance genes.

RESULTS

The detection rate of bacteria in general wards was significantly higher than that in intensive care units. The isolates were predominantly gram-negative (GN) bacteria, with Pseudomonas aeruginosa, Enterobacter cloacae, and Klebsiella pneumoniae being the most common. P aeruginosa isolates from other surfaces were much higher than those from medical instruments. E cloacae was isolated more frequently from the hands of other staff than medical staff. Most P aeruginosa and K pneumoniae were resistant to sulfonamides and β-lactam antimicrobials. Only 1 strain of P aeruginosa and 1 strain of K pneumoniae showed multiple antimicrobials resistance.

CONCLUSIONS

The GN bacteria isolated from hospital environments demonstrate variable resistance to antimicrobials.

A Review of SHV Extended-Spectrum β-Lactamases: Neglected Yet Ubiquitous

β-lactamases are the primary cause of resistance to β-lactams among members of the family Enterobacteriaceae. SHV enzymes have emerged in Enterobacteriaceae causing infections in health care in the last decades of the Twentieth century, and they are now observed in isolates in different epidemiological settings both in human, animal and the environment. Likely originated from a chromosomal penicillinase of Klebsiella pneumoniae, SHV β-lactamases currently encompass a large number of allelic variants including extended-spectrum β-lactamases (ESBL), non-ESBL and several not classified variants. SHV enzymes have evolved from a narrow- to an extended-spectrum of hydrolyzing activity, including monobactams and carbapenems, as a result of amino acid changes that altered the configuration around the active site of the β -lactamases. SHV-ESBLs are usually encoded by self-transmissible plasmids that frequently carry resistance genes to other drug classes and have become widespread throughout the world in several Enterobacteriaceae, emphasizing their clinical significance.