Papers by Marilyn Roberts
Journal of Clinical Periodontology, 2002
Only limited information exists about the prevalence in children of pathogens associated with per... more Only limited information exists about the prevalence in children of pathogens associated with periodontitis. The aim of the present study was to determine by culture whether 8-11-year-old children carry Porphyromonas gingivalis, Prevotella intermedia, and/or P. nigrescens in samples from the gingiva and/or the buccal mucosa taken before, and after caries treatment and oral hygiene instruction. A second aim was to assess the proportion of subjects who had gram-negative anaerobes carrying the tet(Q) and erm(F) genes, suggesting antibiotic resistance to tetracycline or erythromycin. A total of 150 children provided gingival and buccal swab bacterial samples that were cultured for P. gingivalis, P. intermedia, and P. nigrescens. The species was verified using DNA-DNA hybridization with species-specific probes made from the variable region of the 16S rRNA sequences. Antibiotic-resistant genes, tet(Q) and erm(F), were identified using specific DNA-DNA hybridization with specific DNA probes. A total of 116 isolates of black-pigmented bacteria were cultured from 47 (31%) of 150 children. Five isolates were identified as P. gingivalis, 29 as P. intermedia, 33 as P. nigrescens, and 49 as other species. In general, the bacteria were not culturable at more than one time period. We found that 55% of these 47 children harbored black pigmented bacteria that carried either one or both of the two antibiotic-resistant genes studied (tet(Q), and erm(F)). The present study demonstrated that children not exposed to regular dental treatment carry bacteria outside the gingival sulcus that have been associated with periodontitis, and that standard treatment procedures may not clear the presence of the putative pathogens. In addition, antibiotic-resistant genes are common in identifiable gram-negative anaerobes, including putative pathogens.
Antimicrobial Agents and Chemotherapy, 2002
We screened 615 gram-positive isolates from 150 healthy children for the presence of the erm (A),... more We screened 615 gram-positive isolates from 150 healthy children for the presence of the erm (A), erm (B), erm (C), erm (F), and mef (A) genes. The mef (A) genes were found in 20 (9%) of the macrolide-resistant isolates, including Enterococcus spp., Staphylococcus spp., and Streptococcus spp. Sixteen of the 19 gram-positive isolates tested carried the other seven open reading frames (ORFs) described in Tn 1207.1 , a genetic element carrying mef (A) recently described in Streptococcus pneumoniae . The three Staphylococcus spp. did not carry orf1 to orf3 . A gram-negative Acinetobacter junii isolate also carried the other seven ORFs described in Tn 1207.1. A Staphylococcus aureus isolate, a Streptococcus intermedius isolate, a Streptococcus sp. isolate, and an Enterococcus sp. isolate had their mef (A) genes completely sequenced and showed 100% identity at the DNA and amino acid levels with the mef (A) gene from S. pneumoniae .
Water SA, 2012
The objective of this study was to determine antibiotic resistance patterns and specific resistan... more The objective of this study was to determine antibiotic resistance patterns and specific resistance genes in Gram-negative enteric bacteria recovered from 42 different drinking water sources servicing 2 rural villages in southwestern Uganda. These water sites were prone to contamination by both human and cattle activity. Of the 52 isolates examined, 26 carried antibiotic resistance genes with 25 being ampicillin resistant, 21 carrying the bla TEM gene, and no isolate carrying genes coding for extended-spectrum β−lactamases. Twelve isolates were tetracycline resistant and these bacteria carried between 1 and 3 different tet genes, with the tet(A) gene the most common. Six isolates carried the macrolide resistance mef(A) and/ or the macrolide-lincosamide-streptogramin B resistance erm(B) genes. Four isolates carried the sul1 gene, and 4 isolates carried the sul1 and int1 genes indicating the presence of Class 1 integrons. The Ugandan isolates in this study had lower than expected carriage rates of antibiotic and multi-drug resistance genes, carriage of Class 1 integrons and lacked genes coding for extended-spectrum β−lactamases as compared to antibiotic resistance carriage in clinical African isolates.
Oral Microbiology and Immunology, 2002
Little is known about carriage of Candida albicans, the predominant pathogenic yeast in oral infe... more Little is known about carriage of Candida albicans, the predominant pathogenic yeast in oral infection, in children. We cultured buccal mucosal and gingival swabs from 150 Portuguese children to investigate the prevalence of C. albicans at baseline (before dental treatment), post-treatment, and 12, 24, and 36 months post-baseline. The children, aged 8 to 11 years at baseline, had no systemic disease or clinical symptoms of oral candidiasis. At each successive visit, respectively, 47, 32, 21, 27, and 28% of children were C. albicans positive, resulting in an almost 50% reduction in prevalence from baseline to post-treatment (P < 0.0005). Children who carried C. albicans at one visit had 3 to 20 times greater odds of carrying C. albicans at another visit. C. albicans was cultured from 12 children at all time-points and from 10 children at four time-points. Children with oral C. albicans frequently maintained carriage over time, even with regular dental care.
FEMS Microbiology Letters, 2005
This mini-review summarizes the changes in the field of bacterial acquired tetracycline resistanc... more This mini-review summarizes the changes in the field of bacterial acquired tetracycline resistance (tet) and oxytetracycline (otr) genes identified since the last major review in 2001. Thirty-eight acquired tetracycline resistant (Tc r) genes are known of which nine are new and include five genes coding for energy-dependent efflux proteins, two genes coding for ribosomal protection proteins, and two genes coding for tetracycline inactivating enzymes. The number of inactivating enzymes has increased from one to three, suggesting that work needs to be done to determine the role these enzymes play in bacterial resistance to tetracycline. In the same time period, 66 new genera have been identified which carry one or more of the previously described 29 Tc r genes. Included in the new genera is, for the first time, an obligate intracellular pathogen suggesting that this sheltered group of bacteria is capable of DNA exchange with non-obligate intracellular bacteria. The number of genera carrying ribosomal protection genes increased dramatically with the tet(M) gene now identified in 42 genera as compared with 24 and the tet(W) gene found in 17 new genera as compared to two genera in the last major review. New conjugative transposons, carrying different ribosomal protection tet genes, have been identified and an increase in the number of antibiotic resistance genes linked to tet genes has been found. Whether these new elements may help to spread the tet genes they carry to a wider bacterial host range is discussed.
FEMS Microbiology Letters, 2008
This Minireview summarizes the changes in the field of bacterial resistance to macrolide, lincosa... more This Minireview summarizes the changes in the field of bacterial resistance to macrolide, lincosamide, streptogramin, ketolide, and oxazolidinone (MLSKO) antibiotics since the nomenclature review in 1999. A total of 66 genes conferring resistance to this group of antibiotics has now been identified and includes 13 new rRNA methylase genes, four ATP-binding transporter genes coding for efflux proteins, and five new inactivating enzymes. During this same time period, 73 new genera carrying known rRNA methylase genes and 87 new genera carrying known efflux and/or inactivating genes have been recognized. The number of bacteria with mutations in the genes for 23S rRNA, L4 and L22 ribosomal proteins, resulting in reduced susceptibility to some members of the group of MLSKO antibiotics has also increased and now includes nine different Gram-positive and 10 different Gram-negative genera. New conjugative transposons carrying different MLSKO genes along with an increased number of antibiotics and/or heavy metal resistance genes have been identified. These mobile elements may play a role in the continued spread of the MLSKO resistance genes into new species, genera, and ecosystems.
Background: Vancomycin resistant enterococci [VRE] outside the health-care setting were first ide... more Background: Vancomycin resistant enterococci [VRE] outside the health-care setting were first identified in the EU in 1993, while VRE had not been identified outside healthcare settings in North America until two recent reports of two vanA Enterococcus faecalis from hospital impacted sewage and 11 uncharacterized VRE from water impacted by a concentrated swine feeding operation were reported recently. The current study examined 213 presumptive enterococci from recreational marine waters, associated beaches, and from wastewater effluent collected in the Seattle WA metropolitan area, between 2001 and 2008, for the presence of high-level vancomycin resistance. Methods: The isolates were identified by standard biochemical methods and 16S RNA sequencing and included 212 enterococci and one Staphylococcus epidermidis. The vanA and vanB genes were determined using PCR assays, hybridization of the PCR products with specific labeled probes and/or sequencing. Strains were differentiated using...
Journal of Dental Research, 2008
Mercury emitted from dental amalgam may select for increased numbers of antibiotic- or mercury-re... more Mercury emitted from dental amalgam may select for increased numbers of antibiotic- or mercury-resistant commensal bacteria in patients and increase their risk for bacterial diseases that are resistant to common therapies. We hypothesized that the presence of dental amalgams would increase the level of mercury-, tetracycline-, ampicillin-, erythromycin-, or chloramphenicol-resistant oral and urinary bacteria as compared with levels in children receiving composite fillings. Samples were collected at baseline, 3–6 months after the initial dental treatment, and annually for 7 years of follow-up. There were no statistically significant differences between treatment groups in the numbers of bacteria growing on antibiotic- or mercury-supplemented plates. This study provided no evidence that amalgam fillings on posterior teeth influenced the level of antibiotic- or mercury-resistant oral or urinary bacteria as detected by culture.
Journal of Antimicrobial Chemotherapy, Mar 1, 1994
By using dot blot hybridization, 69 of 102 Clostridium difficile isolates (68%) from the United S... more By using dot blot hybridization, 69 of 102 Clostridium difficile isolates (68%) from the United States and other countries hybridized with at least one of nine DNA probes for erythromycin (Erm), tetracycline (Tet) or chloramphenicol (Cat) resistance determinants. The distribution of individual determinants in descending order of frequency was: Tet M, 32%; Erm Q, 25%; Erm FS, 18%; Tet P, 15%; Tet K, 15%; Cat P, 15%; Cat Q, 12%; Erm BP, 11%; Tet L, 7%. This is the first report of Tet P being carried by C. difficile and hitherto Erm FS has only been found within the genus Bacteriodes, while neither Tet K nor Tet L have been previously identified among the genus Clostridia. Eighteen percent of the hybridizing isolates carried multiple determinants coding for the same phenotype. A higher frequency of resistance genes was associated with prior exposure to antimicrobial agents, cytotoxin production and diarrhoea. Isolates recovered from bone marrow transplant patients carried significantly fewer antibiotic resistance genes than did those from immunocompetent general medicine patients. However, this may be due to the fact that each was located at a different site. Antibiotic resistance determinants may play a role in the virulence associated with C. difficile.
Journal of Environmental Health, May 1, 2010
Comment on MRSA Studies in High School Wrestling and Athletic Training Facilities/The Authors Res... more Comment on MRSA Studies in High School Wrestling and Athletic Training Facilities/The Authors Respond. Marilyn C Roberts, John Scott Meschke, Olusegun O Soge, Kelly A Reynolds, Timothy J Ryan Journal of Environmental ...
Fems Microbiology Ecology, Feb 1, 2012
The aim of the study was to determine the spatial distribution of methicillin-resistant Staphyloc... more The aim of the study was to determine the spatial distribution of methicillin-resistant Staphylococcus aureus [MRSA] at two marine and one fresh water recreational beaches in the Seattle area. Fifty-six marine water, 144 fresh water, and 96 sand samples were collected from June through August 2010. Isolates were biochemically verified as MRSA. Staphylococcal cassette chromosome mec (SCCmec) typing, multilocus sequence typing [MLST], pulse field gel electrophoresis [PFGE] and the presence of other antibiotic resistance genes were determined. Twenty-two fresh water [15.3%; n = 144], one dry sand [1.9%; n = 53], six wet sand [14%; n = 43], and 2 marine water samples [3.6%; n = 56] were MRSA positive. Of the 27 fresh water stream sites sampled multiple times, 37% of the sites were positive for MRSA and/or S. aureus ≥ 2 times. Twenty-one (67.7%) of 31 MRSA were SCCmec type IV, fifteen (48.4%) of the isolates had MLST types not previously associated with humans, and 29 (93.5%) of the isolates carried other antibiotic resistance genes. This study is the first to report and characterize repeated MRSA positive samples from fresh water drainages and creeks surrounding popular recreational beaches.
Journal of Antimicrobial Chemotherapy, 2009
... Correspondence Marilyn C. Roberts, Department of Environmental and Occupational Health Scienc... more ... Correspondence Marilyn C. Roberts, Department of Environmental and Occupational Health Sciences, 357234, School of Public Health, University of Washington, Seattle, WA ... in cen-tral London and cultured MSSA from 8% of the sites but did not find MRSA (Otter and French ...
Journal of Antimicrobial Chemotherapy, 2015
The objective of this study was to identify the molecular mechanism of macrolide resistance in th... more The objective of this study was to identify the molecular mechanism of macrolide resistance in the actinomycete Rhodococcus equi, a major equine pathogen and zoonotic agent causing opportunistic infections in people. Macrolide-resistant (n = 62) and macrolide-susceptible (n = 62) clinical isolates of R. equi from foals in the USA were studied. WGS of 18 macrolide-resistant and 6 macrolide-susceptible R. equi was performed. Representative sequences of all known macrolide resistance genes identified to date were used to search the genome assemblies for putative homologues. PCR was used to screen for the presence of the identified resistance determinant in the rest of the isolates. Mating experiments were performed to verify mobility of the gene. A novel erm gene, erm(46), was identified in all sequenced resistant isolates, but not in susceptible isolates. There was complete association between macrolide resistance and the presence of erm(46) as detected by PCR screening of all 124 clinical isolates of R. equi. Expression of erm(46) in a macrolide-susceptible strain of R. equi induced high-level resistance to macrolides, lincosamides and streptogramins B, but not to other classes of antimicrobial agents. Transfer of erm(46) to macrolide-susceptible R. equi was confirmed. The transfer frequency ranged from 3 × 10(-3) to 1 × 10(-2). This is the first molecular characterization of resistance to macrolides, lincosamides and streptogramins B in R. equi. Resistance was due to the presence of a novel erm(46) gene mobilizable likely by conjugation, which has spread among equine isolates of R. equi in the USA.
Frontiers in microbiology, 2012
Objectives: In this study, extended-spectrum b-lactamases (ESBLs) were characterized from 30 sele... more Objectives: In this study, extended-spectrum b-lactamases (ESBLs) were characterized from 30 selected multidrug-resistant Klebsiella pneumoniae strains isolated from patients with community-acquired urinary tract infections from Southwest Nigeria. Methods: The b-lactamases were phenotypically characterized using isoelectric focusing, genotypically characterized using PCR assays and hybridization of the PCR products. Two of the blaCTX-M genes were completely sequenced. The location of the CTX-M-type
Frontiers in Microbiology, 2013
[MRSA] has emerged as a major cause of disease in the general population with no health care expo... more [MRSA] has emerged as a major cause of disease in the general population with no health care exposure or known classical risk factors for MRSA infections. The potential community reservoirs have not been well defined though certain strains such as ST398 and USA300 have been well studied in some settings. MRSA has been isolated from recreational beaches, hightouch surfaces in homes, universities and other community environmental surfaces. However, in most cases the strains were not characterized to determine if they are related to communityacquired or hospital-acquired clinical strains. We compared 55 environmental MRSA from 805 samples including sand, fresh and marine water samples from local marine and fresh water recreational beaches (n=296), high touch surfaces on the University of Washington campus (n=294), surfaces in UW undergraduate housing (n=85), and the local community (n=130).
Background: Xylitol is a naturally occurring sugar substitute that has been shown to reduce the l... more Background: Xylitol is a naturally occurring sugar substitute that has been shown to reduce the level of mutans streptococci in plaque and saliva and to reduce tooth decay. It has been suggested that the degree of reduction is dependent on both the amount and the frequency of xylitol consumption. For xylitol to be successfully and cost-effectively used in public health prevention strategies dosing and frequency guidelines should be established. This study determined the reduction in mutans streptococci levels in plaque and unstimulated saliva to increasing frequency of xylitol gum use at a fixed total daily dose of 10.32 g over five weeks.
Letters in Applied Microbiology, 2006
Aims: In this study, multidrug-resistant bacteria previously recovered from the indoor air of a l... more Aims: In this study, multidrug-resistant bacteria previously recovered from the indoor air of a large-scale swine-feeding operation were tested for the presence of five macrolide, lincosamide and streptogramin (MLS) resistance genes and five tetracycline (tet) resistance genes. Methods and Results: Enterococcus spp. (n ¼ 16) and Streptococcus spp. (n ¼ 16) were analysed using DNA-DNA hybridization, polymerase chain reaction (PCR) and oligoprobing of PCR products. All isolates carried multiple MLS resistance genes, while 50% of the Enterococcus spp. and 44% of the Streptococcus spp. also carried multiple tet resistance genes. All Enterococcus spp. carried erm(A) and erm(B), 69% carried erm(F), 44% carried mef(A), 75% carried tet(M), 69% carried tet(L) and 19% carried tet(K). All Streptococcus spp. carried erm(B), 94% carried erm(F), 75% carried erm(A), 38% carried mef(A), 50% carried tet(M), 81% carried tet(L) and 13% carried tet(K). Conclusions: Multidrug resistance among airborne bacteria recovered from a swine operation is encoded by multiple MLS and tet resistance genes. These are the first data regarding resistance gene carriage among airborne bacteria from swine-feeding operations.
Letters in Applied Microbiology, 2005
To compare antibiotic resistance and ribotyping patterns ability to identify triplicate isolates ... more To compare antibiotic resistance and ribotyping patterns ability to identify triplicate isolates sent from a group of 40 Escherichia coli taken from seven host sources. Of the 120 isolates, 22 isolates were resistant to ampicillin, streptomycin, tetracycline and trimethoprim and 98 isolates were susceptible. Antibiotic patterns identified 33 of the triplicates and three of the six groups had isolates from multiple hosts. Ribotyping divided the isolates into 27 ribotype groups with all triplicates grouped into the same ribotype group with one host per group. Antibiotic susceptibility pattern placed 98 of the isolates in a single group with 50% of the antibiotic susceptibility pattern groups containing multiple host species. Ribotyping groups were host specific with each host having one to seven ribotype groups. Antibiotic susceptibility pattern groups have been used for environmental source identification and faecal pollution tracking, however these groups do not always distinguish between host species. Stability of the markers is a potential concern and this system can only be used if antibiotic resistance levels are high in the isolates studied. All isolates have a ribotype group which was stable and like other molecular methods has advantages over antibiotic susceptibility pattern groups which uses a phenotypic method.
Journal of Dental Research, 2006
Xylitol is promoted in caries-preventive strategies, yet its effective dose range is unclear. Thi... more Xylitol is promoted in caries-preventive strategies, yet its effective dose range is unclear. This study determined the dose-response of mutans streptococci in plaque and unstimulated saliva to xylitol gum. Participants (n = 132) were randomized: controls (G1) (sorbitol/maltitol), or combinations giving xylitol 3.44 g/day (G2), 6.88 g/day (G3), or 10.32 g/day (G4). Groups chewed 3 pellets/4 times/d. Samples were taken at baseline, 5 wks, and 6 mos, and were cultured on modified Mitis Salivarius agar for mutans streptococci and on blood agar for total culturable flora. At 5 wks, mutans streptococci levels in plaque were 10x lower than baseline in G3 and G4 (P = 0.007/0.003). There were no differences in saliva. At 6 mos, mutans streptococci in plaque for G3 and G4 remained 10x lower than baseline (P = 0.007/0.04). Saliva for G3 and G4 was lower than baseline by 8 to 9x (P = 0.011/0.038). Xylitol at 6.44 g/day and 10.32 g/day reduces mutans streptococci in plaque at 5 wks, and in plaque and unstimulated saliva at 6 mos. A plateau effect is suggested between 6.44 g and 10.32 g xylitol/day.
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Papers by Marilyn Roberts