Evolution of Ciprofloxacin Resistance-Encoding Genetic Elements in Salmonella

Comprehensive genomic and plasmid characterization of multidrug-resistant bacterial strains by R10.4.1 nanopore sequencing

The escalating prevalence of multidrug-resistant (MDR) bacteria pose a significant public health threat. Understanding the genomic features and deciphering the antibiotic resistance profiles of these pathogens is crucial for development of effective surveillance and treatment strategies. In this study, we employed the R10.4.1 nanopore sequencing technology, specifically through the use of the MinION platform, to analyze eight MDR bacterial strains originating from clinical, ecological and food sources. A single 72-hour sequencing run could yield approximately 12 million reads which covered a total of 34 gigabases (Gbp). The nanopore R10.4.1 data was processed using the Flye assembler, successfully assembling the genomes of eight bacterial strains and their 18 plasmids. Notably, the assemblies generated solely from R10.4.1 nanopore data closely matched those from next-generation sequencing data. Diverse antibiotic resistance patterns and specific resistance genes in the test strains were identified. Hospital strains that exhibited multidrug resistance were found to harbor various resistance genes that encode efflux pumps and extended-spectrum β-lactamases. Environmental and food sources were found to display resistance profiles in a species-specific manner. The composition of structurally complex plasmids in the test strains could also be revealed by analysis of nanopore long reads, which also suggested evidence of horizontal transfer of plasmids between different bacterial species. These findings provide valuable insights into the genetic characteristics of MDR bacteria and demonstrating the practicality of nanopore sequencing technology for detecting of resistance elements in bacterial pathogens.

Characterization of quinolone resistance in Salmonella enterica serovar Typhimurium and its monophasic variants from food and patients in China

OBJECTIVES

The study aimed to characterize the quinolone resistance of Salmonella enterica serovar Typhimurium and its monophasic variant (Salmonella enterica serovar 1,4,[5],12:i:-) isolated from food and patients in China.

METHODS

All of the isolates were assessed for quinolone susceptibility via the broth microdilution method. Then, the isolates were checked for mutations within quinolone resistance-determining regions of gyrA, gyrB, parC, and parE and were examined for plasmid-mediated quinolone resistance genes.

RESULTS

High rates of resistance to nalidixic acid in the S. Typhimurium (70.7%) and S. 1,4,[5],12:i:- (41.9%) isolates were observed, and a considerable proportion of isolates with reduced susceptibility to ciprofloxacin and levofloxacin were also detected. The high frequency of mutations in GyrA (60.8%) and a variety of genes (aac[6']-Ib-cr [23.2%], oqxAB [19.2%], qnrS [13.6%], and qnrA [3.2%]) conferring quinolone resistance in these Salmonella isolates were noteworthy. Lastly, the isolates carrying qnrS for transferability and transmission of the quinolone resistance were analysed by conjugation. Multiple locus variable-number tandem repeat analysis profiles indicated that some qnrS-positive isolates were clonally related, whilst the other isolates were genetically divergent. This suggested that both clonal spread of resistant strains and horizontal transmission of the plasmid-mediated resistance genes contributed to the dissemination of qnrS-positive Salmonella isolates.

CONCLUSION

This study highlights the prevalence of quinolone-resistant S. Typhimurium and S. 1,4,[5],12:i:- in China, posing a threat to public health.

Potentiation and Mechanism of Berberine as an Antibiotic Adjuvant Against Multidrug-Resistant Bacteria

The growing global apprehension towards multi-drug resistant (MDR) bacteria necessitates the development of innovative strategies to combat these infections. Berberine (BER), an isoquinoline quaternary alkaloid derived from various medicinal plants, has surfaced as a promising antibiotic adjuvant due to its ability to enhance the effectiveness of conventional antibiotics against drug-resistant bacterial strains. Here, we overview the augmenting properties and mechanisms of BER as an adjunctive antibiotic against MDR bacteria. BER has been observed to exhibit synergistic effects when co-administered with a range of antibiotics, including β-lactams, quinolones, aminoglycosides, tetracyclines, macrolides, lincosamides and fusidic acid. The adjunctive properties of BER led to an increase in antimicrobial effectiveness for these antibiotics against the corresponding bacteria, a decrease in minimal inhibitory concentrations, and even the reversal from resistance to susceptibility sometimes. The potential mechanisms responsible for these effects included the inhibition of antibiotic efflux, the disruption of biofilm formation, the modulation of host immune responses, and the restoration of gut microbiota homeostasis. In brief, BER demonstrated significant potential as an antibiotic adjuvant against MDR bacteria and is a promising candidate for combination therapy. Further research is necessary to fully elucidate its mechanism of action and address the challenges associated with its clinical application.

Identification and genetic characterization of two conjugative plasmids that confer azithromycin resistance in Salmonella

With the development of multidrug resistance in Salmonella spp. in recent years, ciprofloxacin, ceftriaxone, and azithromycin have become the principal antimicrobial agents used for the treatment of Salmonella infections. The underlying mechanisms of plasmid-mediated ciprofloxacin and ceftriaxone resistance have attracted extensive research interest, but not much is focused on azithromycin resistance in Salmonella. In this study, we investigated the genetic features of two conjugative plasmids and a non-transferable virulence plasmid that encode azithromycin resistance in food-borne Salmonella strains. We showed that the azithromycin resistance phenotype of these strains was conferred by erm(B) gene and/or the complete genetic structure IS26-mph(A)-mrx-mphR-IS6100. Comparative genetic analysis showed that these conjugative plasmids might originate from Escherichia coli and play a role in the rapid dissemination of azithromycin resistance in Salmonella. These conjugative plasmids may also serve as a reservoir of antimicrobial resistance (AMR) genes in Salmonella in which these AMR genes may be acquired by the virulence plasmids of Salmonella via genetic transposition events. Importantly, the formation of a novel macrolide-resistance and virulence-encoding plasmid, namely pS1380-118 kb, was observed in this study. This plasmid was found to exhibit transmission potential and pose a serious health threat as the extensive transmission of azithromycin resistant and virulent Salmonella strains would further compromise the effectiveness of treatment for salmonellosis. Further surveillance and research on the dissemination and evolution routes of pS1380-118kb-like plasmids in potential human pathogens of the family of Enterobacteriaceae are necessary.

Genetic context of blaCTX–M–55 and qnrS1 genes in a foodborne Salmonella enterica serotype Saintpaul isolate from China

Salmonella enterica resistant to fluoroquinolones (FQs) and extended-spectrum cephalosporins (ESCs) has been deemed a high-priority pathogen by the WHO. Salmonella enterica serovar Saintpaul (S. Saintpaul) co-resistant to ESCs and FQs and harboring corresponding resistance genes (bla_CTX–M–55 and qnrS1) have been previously reported. However, they have not been reported in China. Moreover, the genetic context and transferability of ESCs and FQs resistance genes in S. Saintpaul remain obscure. This study is the first study to characterize a multidrug-resistant (MDR) S. Saintpaul isolate (16Sal016) harboring plasmid-mediated bla_CTX–M–55 and qnrS1 genes recovered from weever fish in China. The whole genome short- and long-read sequencing results identified the presence of 15 acquired antibiotic resistance genes encoding resistance to nine classes of antibiotics, as well as abundant mobile genetic elements residing on a 259,529 bp IncHI2 plasmid. The bla_CTX–M–55 and qnrS1 genes were located in a 12,865 bp region, IS26-orf-orf-ISKpn19-qnrS1-IS3-Tn3-orf-bla_CTX–M–55-ISEc9-orf-IS26. Similar structures have been identified in various bacterial species, indicating a high transferability of bla_CTX–M–55 and qnrS1 genes within this gene cluster. The plasmid was found to be transferable to Escherichia coli (E. coli) J53 by conjugation and resulted in the acquisition of multiple resistances by the transconjugants. Genome sequence comparisons by core genome multilocus sequence typing (cgMLST) based on global 2,947 S. Saintpaul isolates indicated that strain 16Sal016 was epidemiologically linked with an isolate from the United Kingdom (UK). Our findings suggest that plasmids and IS26-mediated mobile genetic elements are carriers of bla_CTX–M–55 and qnrS1 genes in S. Saintpaul, and highlight their potential transmission, which needs continuous investigations.

Dynamics of Antimicrobial Resistance and Genomic Epidemiology of Multidrug-Resistant Salmonella enterica Serovar Indiana ST17 from 2006 to 2017 in China

The genetic features of foodborne Salmonella have changed in recent years as multidrug-resistant (MDR) strains have become prevalent among various serovars. The recent expansion of MDR Salmonella enterica serovar Indiana sequence type 17 (ST17) poses an increasing threat to global public health, as 24.3% (61/251) of S. Indiana isolates in this study exhibited resistance to three clinically important antimicrobial agents: fluoroquinolones (ciprofloxacin), extended-spectrum β-lactams (cephalosporin), and macrolides (azithromycin). Both the evolutionary histories and antimicrobial resistance (AMR) profiles of this serovar remain to be described. Bioinformatic analysis revealed multiple lineages have coexisted and spread throughout China. Specifically, emergence of a predominant lineage appears to be associated with accumulated various substitutions in the chromosomal quinolone resistance-determining regions (GyrA S83F D87N and ParC T57S S80R) (141 [56.2%]), as well as acquisition of an extended-spectrum β-lactamase (ESBL)-producing IncHI2 plasmid that has subsequently undergone extensive rearrangement and an IncX1 plasmid that contains mph(A), conferring resistance to azithromycin. Several other evolutionary events influencing the trajectory of this drug-resistant serovar were also identified, including sporadic acquisitions of bla_CTX-M-carrying plasmids, along with chromosomal integration of bla_CTX-M within subclusters. Most human isolates reside in clusters containing isolates from animals, mainly from chickens, indicating the close relationship of human isolates with those from food animals. These data demonstrate that MDR S. Indiana ST17 is already widespread and capable of acquiring resistance traits against the clinical important antimicrobial agents, suggesting it should be considered a high-risk global MDR pathogen. The complexity of its evolutionary history has implications for AMR surveillance, epidemiological analysis, and control of emerging clinical lineages.

IMPORTANCE The emergence and worldwide spread of AMR Salmonella constitute great public health concerns. S. enterica serovar Indiana is a typical MDR serovar characterized by sporadic reports. However, comprehensive population genomics studies have not been performed on this serovar. This study provides a detailed and comprehensive insight into the rapid evolution of AMR in this important Salmonella serovar in the past 15 years in eight provinces of China. We documented diverse contributory genetic processes, including stable chromosomal integrations of resistance genes, the persistence and evolution of mobile resistance elements within sublineages, and sporadic acquisition of different resistance determinants that occur at all genetic levels (genes, genetic contexts, plasmids, and host strains). There are different mechanisms of antimicrobial resistance in S. enterica serovar Indiana from those of other serovars. This study sheds light on the formation of MDR S. enterica serovar Indiana with chickens as its potential reservoirs and paves the way to curb its further expansion among food animals.

Plasmid-Mediated Quinolone Resistance (PMQR) in Two Clinical Strains of Salmonella enterica Serovar Corvallis

Non-typhoid serovars of Salmonella enterica are one of the main causes of bacterial food-borne infections worldwide. For the treatment of severe cases of salmonellosis in adults, fluoroquinolones are amongst the drugs of choice. They are categorized by the World Health Organization (WHO) as “critically important with highest priority in human medicine”. In the present study, two clinical S. enterica serovar Corvallis isolates (HUA 5/18 and HUA 6/18) from a Spanish hospital, selected on the basis of fluoroquinolone resistance, were characterized. The MICs of ciprofloxacin, determined by E-test, were 0.5 and 0.75 µg/mL for HUA 5/18 and HUA 6/18, respectively, and both were also resistant to pefloxacin but susceptible to nalidixic acid. Whole genome sequencing (WGS) of the isolates was performed with Illumina platform, and different bioinformatics tools were used for sequence analysis. The two isolates belonged to ST1541, and had the Thr57Ser substitution in the ParC protein which is also found in ciprofloxacin susceptible isolates. However, they harbored identical ColE plasmids of 10 kb carrying the qnrS1 gene. In these plasmids, the gene was flanked by defective versions of IS2-like and ISKra4-like insertion sequences. HUA 5/18 and HUA 6/18 were also phenotypically resistant to streptomycin, sulfonamides and tetracycline, with the responsible genes: strA, strB, sul2 and tet(A) genes, being located on a IncQ1 plasmid. ColE plasmids with the qnrS1 gene are widely spread among multiple serovars of S. enterica from different samples and countries. These mobilizable plasmids are playing an important role in the worldwide spread of qnrS1. Thus, their detection in hospitals is a cause of concern which deserves further attention.

Genotypic Diversity of Ciprofloxacin Nonsusceptibility and Its Relationship with Minimum Inhibitory Concentrations in Nontyphoidal Salmonella Clinical Isolates in Taiwan

This study analyzed the genetic diversity of ciprofloxacin (CIP) nonsusceptibility and the relationship between two major mechanisms and minimum inhibitory concentrations (MICs) of CIP in nontyphoidal Salmonella (NTS). Chromosomal mutations in quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes were searched from ResFinder, ARG-ANNOT, and PubMed for designing the sequencing regions in gyrA, gyrB, parC, and parE, and the 13 polymerase chain reactions for PMQR genes. We found that QRDR mutations were detected in gyrA (82.1%), parC (59.0%), and parE (20.5%) but not in gyrB among the 39 isolates. Five of the 13 PMQR genes were identified, including oqxA (28.2%), oqxB (28.2%), qnrS (18.0%), aac(6′)-Ib-cr (10.3%), and qnrB (5.1%), which correlated with the MICs of CIP within 0.25–2 μg/mL, and it was found that oxqAB contributed more than qnr genes to increase the MICs. All the isolates contained either QRDR mutations (53.8%), PMQR genes (15.4%), or both (30.8%). QRDR mutations (84.6%) were more commonly detected than PMQR genes (46.2%). QRDR mutation numbers were significantly associated with MICs (p < 0.001). Double mutations in gyrA and parC determined high CIP resistance (MICs ≥ 4 μg/mL). PMQR genes contributed to intermediate to low CIP resistance (MICs 0.25–2 μg/mL), thus providing insights into mechanisms underlying CIP resistance.

Antibiotyping and genotyping of extensively drug-resistant (XDR) Salmonella sp. isolated from clinical samples of Lahore, Pakistan

AIMS

Antibiotic resistance is a major problem in Salmonella enterica serovar Typhi. The objective of this study was to evaluate the prevalence of XDR Salmonella among local population of Lahore and genotyping of isolates for antibiotic-resistant genes.

METHODS AND RESULTS

A total of 200 blood samples from suspected typhoid fever patients were collected. One hundred and fifty-seven bacterial samples were confirmed as Salmonella Typhi and 23 samples were confirmed as Salmonella Paratyphi after biochemical, serological and PCR based molecular characterization. Antibiogram analysis classified 121 (67·2%) Salmonella isolates as MDR and 62 isolates (34·4%) as XDR. The predominant resistance gene was ampC with 47·7% prevalence, followed by gyrA, catA1, tet(A), aac (3)-la, qnrS, bla_NDM-1 and bla_CTX-M-15 genes in 45·5, 40, 21·6, 18·3, 11·6, 2·2 and 0·5% isolates respectively. Sequence analysis showed the presence of sul1 and dfrA7 gene cassette arrays in 12 class 1 integron integrase positive isolates.

CONCLUSION

Large number of clinical XDR S. Typhi-resistant against third generation cephalosporins have been reported.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current study highlights the possible emergence of clinical XDR S. Typhi cases in Lahore, Pakistan. Potential attribution of phenotypic and genotypic XDR cases may help to contribute targeted therapy.