Showing papers by "Marilyn C. Roberts published in 2009"

Characterization of methicillin-resistant Staphylococcus aureus and methicillin-resistant coagulase-negative Staphylococcus spp. isolated from US West Coast public marine beaches

Abstract: Objectives: The aim of this study was to isolate and characterize methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus spp. (MRCoNS) from marine water and intertidal beach sand from public beaches in Washington State, USA. Methods: Fifty-one staphylococci from Washington State beaches were characterized using antimicrobial susceptibility testing, carriage of acquired tetracycline and/or macrolide resistance genes, staphylococcal cassette chromosome mec (SCCmec) typing, the BBL Crystal™ Gram-Positive ID System and/or 16S rRNA sequencing, coagulase test and multilocus sequence typing (MLST) for MRSA. Results: Five multidrug-resistant MRSA SCCmec type I, of which three were MLST type ST45, one ST59 and one a new MLST type, ST1405, plus one susceptible non-typeable (NT) MRSA ST30 were characterized. Thirty-three MRCoNS isolates, representing 21 strains from 9 Staphylococcus spp., carried a range of SCCmec types [I (2), II (6), III (3), V (2), I/II (1) and NT (7)] and varied in their antibiotic susceptibility to other antibiotic classes and carriage of acquired tetracycline/macrolide resistance gene(s). MRSA and MRCoNS donors co-transferred tet(M) and erm(A) genes to an Enterococcus faecalis recipient at a frequency of 10 -8 . Conclusions: This is the first report of MRSA and MRCoNS isolated from marine water and intertidal beach sand. The MLST types and antibiotic carriage of five MRSA isolates were similar to hospital MRSA isolates rather than US community-acquired MRSA isolates. Our results suggest that public marine beaches may be a reservoir for transmission of MRSA to beach visitors as well as an ecosystem for exchange of antibiotic resistance genes among staphylococci and related genera.

Xylitol Pediatric Topical Oral Syrup to Prevent Dental Caries A Double-blind Randomized Clinical Trial of Efficacy

Abstract: Objective To evaluate the effectiveness of a xylitol pediatric topical oral syrup to reduce the incidence of dental caries of very young children.

Sphingobacterium sp. strain PM2-P1-29 harbours a functional tet(X) gene encoding for the degradation of tetracycline.

Abstract: Aims: The tet(X) gene has previously been found in obligate anaerobic Bacteroides spp., which is curious because tet(X) encodes for a NADP-dependent monooxygenase that requires oxygen to degrade tetracycline. In this study, we characterized a tetracycline resistant, aerobic, Gram-negative Sphingobacterium sp. strain PM2-P1-29 that harbours a tet(X) gene. Methods and Results: Sphingobacterium sp. PM2-P1-29 demonstrated the ability to transform tetracycline compared with killed controls. The presence of the tet(X) gene was verified by PCR and nucleotide sequence analysis. Additional nucleotide sequence analysis of regions flanking the tet(X) gene revealed a mobilizable transposon-like element (Tn6031) that shared organizational features and genes with the previously described Bacteroides conjugative transposon CTnDOT. A circular transposition intermediate of the tet(X) region, characteristic of mobilizable transposons, was detected. However, we could not demonstrate the conjugal transfer of the tet(X) gene using three different recipient strains and numerous experimental conditions. Conclusions: This study suggests that Sphingobacterium sp. PM2-P1-29 or a related bacterium may be an ancestral source of the tet(X) gene. Significance and Impact of the Study: This study demonstrates the importance of environmental bacteria and lateral gene transfer in the dissemination and proliferation of antibiotic resistance among bacteria.

A conjugative macrolide resistance gene, mef(A), in environmental Clostridium perfringens carrying multiple macrolide and/or tetracycline resistance genes

Abstract: Aims: To determine if environmental Clostridium perfringens carry antibiotic resistance genes and if the genes are mobile. Methods and Results: Clostridium perfringens from water, soil and sewage (2003‐2006) were screened for the tetracycline and macrolide resistance genes previously described in animal and human C. perfringens [erm(B), erm(Q), tetA(P), tetB(P) and tet(M) genes] and the macrolide resistance mef(A) gene. Of the 160 isolates, 108 (67AE5%) carried ‡1 of the six antibiotic resistance gene(s). The tetA(P), tetB(P) and tet(M) genes were in 53%, 22% and 8%, and the erm(B), erm(Q) and mef(A) genes in 26%, 1% and 18% of the isolates, respectively. The mef(A) gene and flanking regions were sequenced. The tet(M), erm(B), erm(Q) and mef(A) genes transfer independently from C. perfringens donors to the Enterococcus faecalis recipient. Conclusions: Six resistance genes were found in the environmental C. perfringens with the most common being the tetA(P) gene and the erm(Q) gene the least common. Significance and Impact of the Study: This is the first time conjugal transfer of macrolide resistance genes and ⁄or the tet(M) gene from C. perfringens has been demonstrated. The data presented supports the hypothesis that antibioticresistant environmental C. perfringens are capable of acting as reservoirs for these antibiotic resistance genes.

Vancomycin-resistant Enterococcus spp. in marine environments from the West Coast of the USA.

Abstract: Aims: The aim of the study was to determine if vancomycin-resistant Enterococcus spp. [VRE] carrying vanA and/or vanB genes were present in public marine beaches and a fishing pier [2001–2003, 2008] from Washington and California [2008]. Methods: PCR assays for the vanA and/or vanB genes with verification by DNA–DNA hybridization of the PCR products were used. Positive isolates were speciated using the BD BBL Crystal™ Identification and/or by sequencing the 16S ribosomal region. Results: Eighteen (8%) of 227 isolates including Enterococcus faecalis, Enterococcus faecium, Enterococcus casseliflavus/gallinarum and a Staphylococcus epidermidis carrying vanA and/or vanB genes, from four of six Washington and one of two California sites, were identified. Selected VRE and the S. epidermidis were able to transfer their van genes to an E. faecalis recipient at frequencies ranging from 1·9 × 10−6 to 6·7 × 10−9. Conclusions: Vancomycin-resistant Enterococcus spp. was isolated from five of the seven sites suggesting that other North America public beaches could be the reservoirs for VRE and should be assessed. Significance & Impact of the Study: This is the first report of isolation and characterization of VRE strains (and a vanB Staphylococcus sp.) from North American environmental sources suggesting that public beaches may be a reservoir for possible transmission of VRE to beach visitors.

Tetracycline and Chloramphenicol Resistance Mechanisms

Abstract: Tetracyclines are broad-spectrum antibiotics that bind to the elongating ribosome and inhibit delivery of the ternary complex EF-Tu, GTP, and aminoacylated-tRNA to the A-site [1–3]. The primary binding site of tetracycline is located in the helix 34 (h34) of the 16S rRNA in the 30S subunit which overlaps the anticodon stem-loop of the A-site tRNA [1–3]. Over the last 60 years there has been widespread use of tetracycline in both animals and humans which has led to an increase in tetracycline resistance. Tetracycline resistance (Tcr) occurs most often as a result of the acquisition of new genes that code for energy-dependent efflux of tetracyclines (n = 29 different genes), a protein that protects bacterial ribosomes from the action of tetracyclines (n = 12 different genes) or enzymatic inactivation (n = 3 different genes) and one with unknown mechanism of action (Table 15.1). Many of these genes are associated with mobile plasmids, transposons, and conjugative transposons. Chloramphenicol resistance (Cmr) is primarily due to the presence of chloramphenicol acetyltransferases (CATs) which inactive chloramphenicol [10]. There are two different types of CAT enzymes which are genetically unrelated (Table 15.3). Cmr may also be due to the efflux of chloramphenicol via specific membrane-associated transporters [11]. Both, the genes coding for CATs and specific exporters, are often associated with mobile elements such as plasmids, transposons, or gene cassettes and are able to be transferred by conjugation, mobilization, transduction, or transformation between bacteria of different species and genera. Some chromosomal multidrug transporters have also been identified which export chloramphenicol [12]. Cmr may also occur from mutations which reduce expression of outer membrane proteins [13], mutations in the 23S rRNA [14], inactivation of chloramphenicol by 3-O-phosphotransferases [15], or target site modification by a 23S rRNA methylase.

The evolution of antibiotic-resistant microbes in foods and host ecosystems.

Abstract: In the years between the introduction of antibiotic therapy and the mid-1970s, antibiotic-resistant bacteria were generally restricted to the hospital setting and epidemic diseases which were not major issues in much of the industrialized world. In this chapter, the development of tetracycline-resistant (Tcr) fish pathogens and bacteria associated with aquaculture environments is discussed. Antibiotic residues may be found in a variety of foods produced around the world. Currently, unlabeled but high levels of cephalosporins (ceftiofur) are allowed in some foods. Rules exist which aim to minimize the level of antibiotic residues found in food products; however, not all foods are tested, nor is it clear that the standards required by farms in North America and Europe are followed when the food is produced for overseas consumption. The majority of the novel genes were mobile elements carrying antibiotic resistance and virulence genes. Enterococci are normal inhabitants of the intestinal flora of most mammals, birds, and humans, as well as from soil, surface waters, plants, vegetables, raw foods such as milk and meat, and fermented meats such as Italian salami or raw sausage. Studies have shown that fish foods, even unlabeled ones, may contain antibiotic-resistant bacteria and/or antibiotic residues. This chapter also illustrates a few examples in which specific antibiotic resistance genes, regions of DNA, and/or plasmids have been found in bacteria from very different ecosystems, from different parts of the world, and in bacteria that are host species-specific.