Evolution of Ciprofloxacin Resistance-Encoding Genetic Elements in Salmonella

ABSTRACTThe incidence of ciprofloxacin resistance in Salmonella has increased dramatically in the past decade. To track the evolutionary trend of ciprofloxacin resistance-encoding genetic elements during this period, we surveyed the prevalence of Salmonella in food products in Shenzhen, China, during the period of 2012 to 2017 and performed whole-genome sequencing and genetic analysis of 566 ciprofloxacin-resistant clinical Salmonella strains collected during this survey. We observed that target gene mutations have become much less common, with single gyrA mutation currently detectable in Salmonella enterica serovar Typhimurium only. Multiple plasmid-mediated quinolone resistance (PMQR) genes located in the chromosome and plasmids are now frequently detectable in ciprofloxacin-resistant Salmonella strains of various serotypes. Among them, the qnrS1 gene was often harbored by multiple plasmids, with p10k-like plasmids being the most dominant. Importantly, p10k-like plasmids initially were not conjugative but became transmissible with the help of a helper plasmid. Ciprofloxacin resistance due to combined effect of carriage of the qnrS1 gene and other resistance mechanisms is common. In S. Typhimurium, carriage of qnrS1 is often associated with a single gyrA mutation; in other serotypes, combination of qnrS1 and other PMQR genes located in the chromosomal fragment or plasmid is observed. Another major mechanism of ciprofloxacin resistance, mainly observable in S. Derby, involves a chromosomal fragment harboring the qnrS2–aac(6′)lb-cr–oqxAB elements. Intriguingly, this chromosomal fragment, flanked by IS26, could form a circular intermediate and became transferrable. To conclude, the increase in the incidence of various PMQR mobile genetic elements and their interactions with other resistance mechanism contribute to a sharp increase in the prevalence of ciprofloxacin-resistant clinical Salmonella strains in recent years.IMPORTANCE Resistance of nontyphoidal Salmonella to fluoroquinolones such as ciprofloxacin is known to be mediated by target mutations. This study surveyed the prevalence of Salmonella strains recovered from 2,989 food products in Shenzhen, China, during the period 2012 to 2017 and characterized the genetic features of several PMQR gene-bearing plasmids and ciprofloxacin resistance-encoding DNA fragments. The emergence of such genetic elements has caused a shift in the genetic location of ciprofloxacin resistance determinants from the chromosomal mutations to various mobile genetic elements. The distribution of these PMQR plasmids showed that they exhibited high serotype specificity, except for the p10k-like plasmids, which can be widely detected and efficiently transmitted among Salmonella strains of various serotypes by fusing to a new conjugative helper plasmid. The sharp increase in the prevalence of ciprofloxacin resistance in recent years may cause a predisposition to the emergence of multidrug-resistant Salmonella strains and pose huge challenges to public health and infection control efforts.

PENERAPAN EFEK INTERAKSI RADIASI DENGAN SISTEM BIOLOGI SEBAGAI DOSIMETER BIOLOGI

AbstrakInteraksi radiasi pengion dengan sistem biologi dapat menyebabkan berbagai macam efek biologik yang akan dimanifestasikan baik pada tingkat seluler, sitogenetik maupun tingkat molekuler. Berbagai macam metode biologik yang dimaksudkan untuk memperkirakan dosis radiasi telah dikembangkan oleh banyak peneliti menggunakan efek tersebut terutama dalam hal teIjadinya peristiwa kecelakaan radiasi. Hal ini dipertegas lagi dengan kenyataan bahwa dosimetri fisik tidak dapat diandalkan secara sendirian. Dengan kelebihan dan kekurangannya masing-masing, ulasan ulang ini memberikan gambaran yang meluas akan pentingnya uji atau biomarker dalam dosimetri biologi seperti kromosom disentrik, mikronuklei, fragmen kromosom,biokimia darah dan spermatogenesis. Adapun sampel biologik yang dapat dipergunakanuntuk pengkajian dosis radiasi yang diterima oleh pekeIja maupun korban kecelakaanantara lain darah, sperma, rambut, dan urin.Kata kunci : Interaksi radiasi pengion, sistem biologiAbstractInteraction between ionizing radiation with biological system could results in various types of biological effects which will be manifested either in cellular, cytogenetics or molecular levels. Various types of biological methods with the aim for predicting radiation dose have been developed by many researchers by using these effects mainly in the case of radiation accident. This case is supported by the fact that physical dosimetry could not available as alone. With their own advantages and disadvantages, this review provides a broader figure about the importance of assays or markers in biological dosimetry such as dicentric chromosome, micronuclei, chromosomal fragment, biochemistry of blood and spermatogenesis. Whereas the biological samples that can be used for assessing the radiation dose received by workers or accidental victims are blood, sperm, hair, and urine.Keywords: Interaction between ionizing radiation, biological system

Mechanism of Intrinsic Resistance to Vancomycin in Clostridium innocuum NCIB 10674

ABSTRACT We have studied the basis for intrinsic resistance to low levels of vancomycin in Clostridium innocuum NCIB 10674 (MIC = 8 μg/ml). Analysis by high-pressure liquid chromatography (HPLC) and mass spectrometry of peptidoglycan nucleotide precursors pools revealed the presence of two types of UDP-MurNac-pentapeptide precursors constitutively produced, an UDP-MurNAc-pentapeptide with a serine at the C terminus which represented 93% of the pool and an UDP-MurNAc-pentapeptide with an alanine at the C terminus which represented the rest of the pool. C. innocuum cell wall muropeptides containing pentapeptide[Ser], either dialanine substituted on the epsilon amino group of lysine or not, were identified and represented about 10% of the monomers while only 1% of pentapeptide[d-Ala] monomers were found. The sequence of a 2,465-bp chromosomal fragment from C. innocuum was determined and revealed the presence of ddlc. innocuum and C. innocuum racemase genes putatively encoding homologues of d-Ala:d-X ligases and amino acid racemases, respectively. Analysis of the pool of precursors of Enterococcus faecalis JH2-2, containing cloned ddlc. innocuum and C. innocuum racemase genes showed in addition to the UDP-MurNAc-pentapeptide[d-Ala], the presence of an UDP-MurNAc-pentapeptide[d-Ser] precursor. However, the expression of low-level resistance to vancomycin was observed only when both genes were cloned in E. faecalis JH2-2 together with the vanXYc gene from Enterococcus gallinarum BM4174 which encodes a d,d-peptidase which eliminates preferentially the high affinity vancomycin UDP-MurNAc-pentapeptide [d-Ala] precursors produced by the host. We conclude that resistance to vancomycin in C. innocuum NCIB 10674 was related to the presence of the two chromosomal ddlc. innocuum and C. innocuum racemase genes allowing the synthesis of a peptidoglycan precursor terminating in serine with low affinity for vancomycin.