PubMed Health⌕ Search

Biomedical subjects

Stefan Schwarz

Publications and source records attributed to Stefan Schwarz.

At least 19 recordsLinked to original sources
PubMed2026

Genomic insights into an optrA-carrying plasmid associated with linezolid resistance in clinical Enterococcus faecalis isolates, Argentina.

The spread of the transferable optrA gene poses an increasing threat to the clinical efficacy of oxazolidinones. Here, we characterized a novel optrA-carrying plasmid, pEfa-optrA-Arg, from a linezolid-resistant Enterococcus faecalis clinical isolate from Argentina. The 68,653-bp conjugative plasmid harbored optrA together with multiple antimicrobial resistance genes and showed high similarity to a plasmid previously identified in a bovine isolate from Switzerland. pEfa-optrA-Arg, or a closely related variant, was also detected in E. faecalis isolates from several Argentinian hospitals, highlighting the role of horizontal gene transfer in the spread of antimicrobial resistance across human and animal reservoirs within the One Health continuum.

Enterococcus faecalis↗
PubMed2025

Co-existence of the oxazolidinone resistance genes cfr and optrA on a novel multiresistance plasmid from a methicillin-resistant Macrococcoides bohemicum strain.

OBJECTIVES: To identify and characterize the oxazolidinone resistance genes cfr and optrA from a methicillin-resistant Macrococcoides bohemicum strain of chicken origin. METHODS: The presence of mobile oxazolidinone resistance genes was detected by PCR. Antimicrobial susceptibility testing was conducted by broth microdilution. Transfer experiments were carried out to evaluate horizontal transferability of the plasmid. WGS was performed using a combination of Illumina NovaSeq/Oxford Nanopore PromethION platforms. RESULTS: The M. bohemicum strain HLJ23 exhibited an MDR phenotype and was positive for both cfr and optrA genes. WGS revealed that the genes cfr and optrA co-exist on the novel MDR plasmid pHLJ23-71kb. Although conjugation experiments were unsuccessful, plasmid pHLJ23-71kb could be transferred to Staphylococcus aureus RN4220 by electrotransformation. Genetic context analysis showed that the cfr and optrA together with another four antimicrobial resistance genes are located in an MDR region on plasmid pHLJ23-71kb. Sequence analysis suggested that this MDR region possibly originated from Mammaliicoccus or Staphylococcus spp. CONCLUSIONS: To the best of our knowledge, this study represents the first report of the oxazolidinone resistance genes cfr and optrA in the genus Macrococcoides. Furthermore, attention should be paid to the exchange of resistance determinants between members of the genera Staphylococcus, Mammaliicoccus and Macrococcoides.

Plasmids↗
PubMed2007

Efflux-mediated resistance to florfenicol and/or chloramphenicol in Bordetella bronchiseptica: identification of a novel chloramphenicol exporter.

OBJECTIVES: Twenty florfenicol- and/or chloramphenicol-resistant Bordetella bronchiseptica isolates of porcine and feline origin were investigated for the presence of floR and cml genes and their location on plasmids. METHODS: The B. bronchiseptica isolates were investigated for their susceptibility to antimicrobial agents by broth micro- or macrodilution and for their plasmid content. Hybridization experiments and PCR assays were conducted to identify resistance genes. Transformation and conjugation studies were performed to show their transferability. Representatives of both types of genes including their flanking regions were sequenced. Moreover, inhibitor studies with the efflux pump inhibitor Phe-Arg-beta-naphthylamide (PAbetaN) were performed. RESULTS: The gene floR was found in the chromosomal DNA of 9 of the 18 florfenicol/chloramphenicol-resistant isolates. Sequence analysis revealed that the deduced FloR protein sequence differed by a single amino acid exchange from FloR of Vibrio cholerae. A chloramphenicol-resistant, but florfenicol-susceptible isolate carried a novel plasmid-borne cml gene, designated cmlB1. The CmlB1 protein revealed only 73.8-76.5% identity to known CmlA proteins. The gene cmlB1 was not part of a gene cassette. The results of inhibitor studies with PAbetaN suggested that a so-far unidentified efflux system might play a role in phenicol resistance of the remaining florfenicol- and/or chloramphenicol-resistant isolates. CONCLUSIONS: This is to the best of our knowledge the first report of a floR gene in B. bronchiseptica isolates. The identification of the first member of a new subclass of cml genes, cmlB1 from B. bronchiseptica, extends our knowledge on specific chloramphenicol exporters.

Amino Acid Sequence↗
PubMed2006

IS21-558 insertion sequences are involved in the mobility of the multiresistance gene cfr.

During a study of florfenicol-resistant porcine staphylococci from Denmark, the genes cfr and fexA were detected in the chromosomal DNA or on plasmids of Staphylococcus hyicus, Staphylococcus warneri, and Staphylococcus simulans. A novel variant of the phenicol resistance transposon Tn558 was detected on the ca. 43-kb plasmid pSCFS6 in S. warneri and S. simulans isolates. Sequence analysis of a 22,010-bp segment revealed that the new Tn558 variant harbored an additional resistance gene region integrated into the tnpC reading frame. This resistance gene region consisted of the clindamycin exporter gene lsa(B) and the gene cfr for combined resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A antibiotics bracketed by IS21-558 insertion sequences orientated in the same direction. A 6-bp target site duplication was detected at the integration site within tnpC. Transpositionally active forms of the IS21-558 element, known as minicircles, were detected by PCR and suggest that this insertion sequence is involved in the mobility of the multiresistance gene cfr. Based on the knowledge of the transposition pathways of IS21-like insertion sequences and the sequence features detected, the resistance gene region of plasmid pSCFS6 is believed to have developed via IS21-558-mediated cointegrate formation. The data obtained in this study identified the multiresistance gene cfr not only in three novel host species but also in a novel genetic context whose further analysis suggested that insertion sequences of the type IS21-558 are likely to be involved in the dissemination of cfr.

Animals↗
PubMed2006

SPL8, a local regulator in a subset of gibberellin-mediated developmental processes in Arabidopsis.

Gibberellins (GAs) are important plant growth regulators, regulating many plant developmental processes, including seed germination, root and stem elongation, rosette expansion, floral induction and anther development. The diverse effects of GAs on plant development make it critical to maintain an appropriate endogenous GA level and a fine-tuned GA signalling. Some global regulators in GA signalling have been identified but little is known about genes specifically involved in local implementation of GA signalling. Here we report that the Arabidopsis thaliana SBP-box gene SQUAMOSA-PROMOTER-BINDING-PROTEIN-LIKE8 (SPL8) acts as a local regulator in a subset of GA-dependent developmental processes. Previous knowledge holds that SPL8 is involved in reproductive development as deduced from its loss-of-function phenotype (Unte et al. (2003) Plant Cell 15:1009-1019). We now determined that constitutive overexpression of SPL8 affects fertility due to non-dehiscent anthers, likely resulting from a constitutive GA response, suggesting a positive role of SPL8 in GA-mediated anther development. On the other hand, SPL8 gain- and loss-of-function mutants showed opposite responses to GA and its biosynthetic inhibitor paclobutrazol (PAC) with respect to seed germination and root elongation during the seedling stage. Genes involved in GA biosynthesis and signalling are transcriptionally affected by altered SPL8 expression. Our study uncovered a tissue-dependent regulatory role for SPL8 in the response to GA signalling in plant development.

Arabidopsis↗
PubMed2006

Molecular analysis of constitutively expressed erm(C) genes selected in vitro in the presence of the non-inducers pirlimycin, spiramycin and tylosin.

OBJECTIVES: As known from other lincosamides and 16-membered macrolides, the antimicrobial agents pirlimycin, spiramycin and tylosin, which are frequently used for the therapy of bovine mastitis, cannot induce the expression of the resistance gene erm(C). The aim of this study was to confirm the ability of these three non-inducers to select for constitutively expressed erm(C) mutants in Staphylococcus aureus. METHODS: A S. aureus strain carrying an inducibly expressed erm(C) gene was incubated on agar plates containing inhibitory concentrations of each of the three antimicrobial agents. The erm(C) regulatory region of mutants obtained after overnight incubation was amplified by PCR; selected amplicons were sequenced and compared with the wild-type sequence. RESULTS: Mutants developed in the presence of each of the three antimicrobial agents. Constitutive expression of erm(C) was due to variations in the erm(C) regulatory region. A total of 10 different types of deletions ranging in size between 16 and 121 bp as well as 20 different types of duplications ranging between 24 and 602 bp were detected. The frequencies by which sequence alterations occurred as well as the types of alterations detected varied with regard to the antimicrobial agents used for selection. CONCLUSIONS: All sequence alterations observed explained constitutive erm(C) gene expression by functional inactivation of translational attenuation. In order to prevent the development of constitutively resistant isolates under therapy, the results of this study support the recommendation not to use lincosamides or 16-membered macrolides for the control of staphylococcal infections caused by strains harbouring inducibly expressed erm(C) genes.

Animals↗
PubMed2006

Phenotypic and genotypic differentiation of porcine Salmonella enterica subsp. enterica serovar Derby isolates.

Sixty-two Salmonella enterica subsp. enterica serovar Derby isolates from slaughter pigs and meat products isolated in Southern Brazil were analyzed for their genomic relationships and for the presence of antimicrobial resistance genes. Twenty-four S. Derby isolates were indistinguishable by their subtracted restriction fingerprinting (SRF) pattern, XbaI- and BlnI-macrorestriction patterns, phage type, plasmid profile, and resistance pattern. In contrast to the BlnI-macrorestriction patterns, the XbaI-macrorestriction patterns were in good agreement with the results of SRF analysis and phage typing. Among the four phage types detected, PT10 and PT21 were the most common. The combination of all typing methods revealed a great diversity among the S. Derby isolates. All strains carried plasmids and the 60 resistant isolates showed at least tetracycline resistance. The resistance genes found were sul1 and/or sul2 (sulfonamide resistance), aadA2 (streptomycin/spectinomycin resistance), tet(A) (tetracycline resistance), tet(B) (tetracycline/minocycline resistance), bla(TEM) (ampicillin resistance), and dfrA14 (trimethoprim resistance). A correlation of the geno- and phenotypic characteristics with the origin of the isolates revealed a substantial temporal variation in the occurrence of specific S. Derby isolates in different independent pig production lines in Southern Brazil. The large number of resistant isolates underlined the potential risk that S. Derby isolates can pose to human health when they enter the food chain.

Animals↗
PubMed2006

Identification of the plasmid-borne quinolone resistance gene qnrS in Salmonella enterica serovar Infantis.

OBJECTIVES: A Salmonella enterica serovar Infantis isolate of avian origin was investigated for the presence of the gene qnrS, its transferability and its association with other resistance genes. METHODS: The Salmonella Infantis isolate was investigated for its susceptibility to antimicrobial agents and its plasmid content. Hybridization experiments and PCR assays were performed to identify the resistance genes while transformation and conjugation studies were conducted to show their transferability. The quinolone resistance-determining regions of the genes gyrA, gyrB, parC and parE were sequenced. Moreover, extended sequence analysis was performed to gain insight into the structure and organization of the qnrS gene area. RESULTS: The Salmonella Infantis isolate exhibited the Asp87-->Tyr87 mutation in gyrA, but no resistance-mediating mutations in the other target genes. It carried a conjugative plasmid, pINF5, on which a qnrS gene was detected in close proximity to a Tn3-like, blaTEM-1-carrying transposon. Homology to the qnrS-carrying plasmid pAH0376 of Shigella flexneri was limited to the Tn3-qnrS region. Sequence analysis of an approximately 13.4 kb region of pINF5 identified truncated insertion sequences of types IS26 and IS2 as well as an internal segment of the CS12 fimbrial gene cluster of Escherichia coli up- and downstream of the qnrS gene. CONCLUSIONS: This is to the best of our knowledge the first report of a qnrS gene in a Salmonella isolate. The analysis of the regions flanking the qnrS gene suggested that this region developed in multiple steps that included not only the integration of insertion sequences and a Tn3-like transposon, but also interplasmid recombination events.

Ampicillin↗
PubMed2006

Results of an interlaboratory test on antimicrobial susceptibility testing of bacteria from animals by broth microdilution.

A standard operating procedure for the determination of minimum inhibitory concentrations (MICs) of antimicrobial agents by the broth microdilution method was developed and evaluated for its fitness for use in an interlaboratory ring trial involving 46 routine diagnostic laboratories. All laboratories tested five strains (one reference strain and four field strains) against a total of 22 different antimicrobial agents. Gram-negative strains were tested against 16 different antimicrobial agents and Gram-positive strains against 14 different antimicrobial agents. Tests were performed once a week for three consecutive weeks. At least 80% of the results determined by 35 of the 46 participating laboratories were within the expected range (mode MIC+/-1 dilution step), with the 18 participating laboratories experienced in MIC determination showing a slightly higher mean percentage of accurate results (89.3% reproducible results) than the 28 non-experienced laboratories (86.7% reproducible results). The most accurate results were obtained for the Escherichia coli field strain, whilst the results for the Streptococcus uberis field strain showed the highest error rate. Among the 22 antimicrobial agents tested, the highest variabilities in the results (mean value for all antimicrobial agents 12.3%) were recorded for ceftiofur (27.8%), penicillin G (20.8%) and cefoperazone (20.6%).

Animals↗
PubMed2006

Plasmid-mediated florfenicol resistance in Pasteurella trehalosi.

OBJECTIVES: A florfenicol-resistant Pasteurella trehalosi isolate from a calf was investigated for the presence and the location of the gene floR. METHODS: The P. trehalosi isolate 13698 was investigated for its in vitro susceptibility to antimicrobial agents and its plasmid content. A 14.9 kb plasmid, designated pCCK13698, was identified by transformation into Pasteurella multocida to mediate resistance to florfenicol, chloramphenicol and sulphonamides. The plasmid was sequenced completely and analysed for its structure and organization. RESULTS: Plasmid pCCK13698 exhibited extended similarity to plasmid pHS-Rec from Haemophilus parasuis including the region carrying the parA, repB, rec and int genes. Moreover, it revealed similarities to plasmid RSF1010 in the parts covering the mobC and repA-repC genes and to plasmid pMVSCS1 in the parts covering the sul2-catA3-strA gene cluster. Moreover, the floR gene area corresponded to that of transposon TnfloR. In addition, two complete insertion sequences were detected that were highly similar to IS1593 from Mannheimia haemolytica and IS26 from Enterobacteriaceae. Several potential recombination sites were identified that might explain the development of plasmid pCCK13698 by recombination events. CONCLUSIONS: The results of this study showed that in the bovine pathogen P. trehalosi, floR-mediated resistance to chloramphenicol and florfenicol was associated with a plasmid, which also carried functionally active genes for resistance to sulphonamides (sul2) and chloramphenicol (catA3). This is to the best of our knowledge the first report of resistance genes in P. trehalosi and only the second report of the presence of a florfenicol-resistance gene in target bacteria of the family Pasteurellaceae.

Animals↗
PubMed2006

Genes and mutations conferring antimicrobial resistance in Salmonella: an update.

Resistance to various classes of antimicrobial agents has been encountered in many bacteria of medical and veterinary relevance. Particular attention has been paid to zoonotic bacteria such as Salmonella. Over the years, various studies have reported the presence of genes and mutations conferring resistance to antimicrobial agents in Salmonella isolates. This review is intended to provide an update on what is currently known about the genetic basis of antimicrobial resistance in Salmonella.

Anti-Infective Agents↗
PubMed2006

The clonal spread of multidrug-resistant non-typhi Salmonella serotypes.

Non-typhoid Salmonella are one of the most important organisms causing food-borne diseases worldwide. There have been significant increases in developed countries in recent years in the occurrence of resistance, in particular multidrug resistance phenotypes, in non-typhoid Salmonella spp. Such increases have been observed in many countries, not only within the European community but also the Americas and Southeast Asia. Of particular concern is the increasing detection of Salmonella isolates displaying resistance to key antimicrobials, notably fluoroquinolones and third-generation cephalosporins. An important factor associated with this increase in multidrug resistance among particular Salmonella spp. is the national and international spread of certain clonal genotypes, the most recent being the global epidemic spread of multidrug-resistant S. Typhimurium DT104, since the early 1990s. In this review, we describe examples where particular antimicrobial-resistant Salmonella serotypes emerged, persisted for periods of time, and then quickly decreased in prevalence.

Animals↗
PubMed2006

Antimicrobial resistance of coagulase-negative staphylococci from bovine subclinical mastitis with particular reference to macrolide-lincosamide resistance phenotypes and genotypes.

OBJECTIVES: The aim of this study was to analyse coagulase-negative staphylococci (CoNS) for their resistance to antimicrobial agents approved for the control of pathogens involved in bovine mastitis, with particular reference to macrolide and/or lincosamide (ML) resistance and the resistance genes involved. METHODS: A total of 298 CoNS collected between 2003 and 2005 in Germany from cases of subclinical mastitis in dairy cows were identified to the species level and investigated for their MICs by broth microdilution. ML-resistant isolates were subjected to plasmid profiling and electrotransformation experiments. The ML resistance genes were detected using PCR and hybridization. Selected PCR products were cloned and sequenced. RESULTS: The CoNS isolates used in this study showed a low level of resistance to all antimicrobial agents tested (0-7.4%) except ampicillin (18.1%). In the erythromycin-resistant and/or pirlimycin-resistant isolates, the ML resistance genes erm(B), erm(C), msr(A), mph(C) and lnu(A) were present, either alone or in different combinations. Isolates carrying erm methylase genes or the exporter gene msr(A) showed higher MICs than those harbouring only the genes mph(C) or lnu(A) coding for inactivating enzymes. Most of the ML resistance genes were found on plasmids. CONCLUSIONS: This is the first report of pirlimycin MICs for CoNS collected from cases of bovine subclinical mastitis in Germany. After 3-5 years of veterinary therapeutic use, pirlimycin resistance was rarely detected among CoNS. The finding that five different resistance genes--present in various combinations--were responsible for ML resistance underlines the heterogeneous character of this resistance trait.

Animals↗
PubMed2006

Characterization of a novel type of MLSB resistance plasmid from Staphylococcus saprophyticus carrying a constitutively expressed erm(C) gene.

An erm(C)-carrying plasmid of unusual size and restriction map, designated pSES22, was identified in a Staphylococcus saprophyticus strain and sequenced completely. Constitutive expression of the erm(C) gene from pSES22 is based on a novel 22-bp tandem duplication in the erm(C) translational attenuator. Comparative analysis of the deduced Erm(C) amino acid sequence revealed that Erm(C) from pSES22 - together with an Erm(C) methylase from S. hyicus - represented a separate branch in the homology tree of Erm(C) methylases. Structural comparisons showed that plasmid pSES22 differed distinctly from all other completely sequenced erm(C)-carrying resistance plasmids. However, pSES22 was similar to several members of a diverse group of small plasmids, all of which carried closely related plasmid backbones consisting of the genes repU and pre/mob, but differed in their resistance genes.

Amino Acid Sequence↗
PubMed2006

Old dogs that learn new tricks: modified antimicrobial agents that escape pre-existing resistance mechanisms.

Increasing numbers of resistant bacteria and decreasing numbers of efficient antimicrobial agents demand for the development of new highly potent antimicrobial agents. The two main directions for the development of new antimicrobial agents are either the development of completely novel antimicrobial agents, or the modification of already existing antimicrobial molecules. The second direction proved to be a more successful and cost-efficient way of generating new antimicrobial agents. For this, chemical modifications have been included which render the antimicrobial agents insensitive to prevalent bacterial resistance mechanisms. However, detailed knowledge of the resistance mechanisms is indispensable. Molecular analysis of resistance mechanisms provides the required data to identify critical target structures. Furthermore, modification of antimicrobial agents makes it possible to escape known resistance mechanisms. In this report, two examples for such successful developments, one from human medicine (telithromycin) and the other from veterinary medicine (florfenicol), are presented.

Animals↗
PubMed2006

The Cfr rRNA methyltransferase confers resistance to Phenicols, Lincosamides, Oxazolidinones, Pleuromutilins, and Streptogramin A antibiotics.

A novel multidrug resistance phenotype mediated by the Cfr rRNA methyltransferase is observed in Staphylococcus aureus and Escherichia coli. The cfr gene has previously been identified as a phenicol and lincosamide resistance gene on plasmids isolated from Staphylococcus spp. of animal origin and recently shown to encode a methyltransferase that modifies 23S rRNA at A2503. Antimicrobial susceptibility testing shows that S. aureus and E. coli strains expressing the cfr gene exhibit elevated MICs to a number of chemically unrelated drugs. The phenotype is named PhLOPSA for resistance to the following drug classes: Phenicols, Lincosamides, Oxazolidinones, Pleuromutilins, and Streptogramin A antibiotics. Each of these five drug classes contains important antimicrobial agents that are currently used in human and/or veterinary medicine. We find that binding of the PhLOPSA drugs, which bind to overlapping sites at the peptidyl transferase center that abut nucleotide A2503, is perturbed upon Cfr-mediated methylation. Decreased drug binding to Cfr-methylated ribosomes has been confirmed by footprinting analysis. No other rRNA methyltransferase is known to confer resistance to five chemically distinct classes of antimicrobials. In addition, the findings described in this study represent the first report of a gene conferring transferable resistance to pleuromutilins and oxazolidinones.

Anti-Bacterial Agents↗