Showing papers by "Marilyn C. Roberts published in 2004"

Resistance to Macrolide, Lincosamide, Streptogramin, Ketolide, and Oxazolidinone Antibiotics

Abstract: Macrolides have enjoyed a resurgence as new derivatives and related compounds have come to market. These newer compounds have become important in the treatment of community-acquired pneumoniae and nontuberculosis-Mycobacterium diseases. In this review, the bacterial mechanisms of resistance to the macrolide, lincosamide, streptogramin, ketolide, and oxazolidinone antibiotics, the distribution of the various acquired genes that confer resistance, as well as mutations that have been identified in clinical and laboratory strains are examined.

Distribution of macrolide, lincosamide, streptogramin, ketolide and oxazolidinone (MLSKO) resistance genes in Gram-negative bacteria.

Abstract: A number of different mechanisms of macrolide resistance have been described in Gram-negative bacteria. These include 16 acquired genes (esterases, phosphorylases, rRNA methylases, and effluxes) and include those thought to be unique to Gram-negative bacteria (both esterases and two of the phosphorylases) and those shared with Gram-positive bacteria (one phosphorylase) and those primarily of Gram-positive origin (rRNA methylases and efflux genes). In addition, mutations, which modify the 23S rRNA, ribosomal proteins L4 and/or L22, and/or changes in expression of innate efflux systems which occur by missense, deletion and/or insertion events have been described in five Gram-negative groups, while an innate transferase conferring resistance to streptogramin A has been identified in a sixth genus. However, the amount of information on both acquisition and mutations leading to macrolide, lincosamides, streptogramins, ketolides and oxazolidinones (MLSKO) resistance is limited. As a consequence this review likely underestimates the true distribution of acquired genes and mutations in Gram-negative bacteria. As use of these drugs increases, it is likely that interaction between members of the MLSKO antibiotic family and Gram-negative bacteria will continue to change resistance to these antibiotics; by mutations of existing genes as well as by acquisition and perhaps mutations of acquired resistant genes in these organisms and more work needs to be done to get a clearer picture of what is in the Gram-negative population now, such that changes can be monitored.

Antibiotic Resistance and Distribution of Tetracycline Resistance Genes in Escherichia coli O157:H7 Isolates from Humans and Bovines

Abstract: Escherichia coli O157:H7 is rare yet widely distributed within bovine populations, where it is a benign commensal of the gastrointestinal tract (3) Most E coli O157:H7-related human illness has been the result of contamination of meat, other foodstuffs, and/or drinking water with bovine wastes containing this organism (Division of Bacterial and Mycotic Diseases, Centers for Disease Control and Prevention, Escherichia coli O157:H7 [http://wwwcdcgov/ncidod/dbmd/diseaseinfo/escherichiacoli_ghtm]) In humans, E coli O157:H7 may cause no symptoms, mild to severe diarrhea, hemorrhagic colitis, or hemolytic-uremic syndrome (11; http://wwwcdcgov/ncidod/dbmd/diseaseinfo/escherichiacoli_ghtm) As previously reported, an increase in antibiotic resistance has been noted within E coli O157:H7 populations over the last 20 years (3, 4, 10) Testing of susceptibility to 12 different antibiotics and antibiotic combinations was performed on 901 randomly selected E coli O157:H7 isolates collected between 1997 and 2000 from our collection This included 663 bovine isolates from feedlots in the midwestern United States and 238 human isolates, which represented both outbreaks and sporadic cases, from public health departments of Washington, Oregon, Nevada, Wisconsin, Georgia, and Illinois Isolates were verified as E coli O157:H7 by being plated on sorbitol MacConkey agar (Becton Dickinson, Sparks, Md), followed by a latex agglutination test (Oxoid, Basingstoke, Hampshire, United Kingdom) Disk diffusion assays were done using the National Committee for Laboratory Standards protocol and the control E coli strain ATCC 25922 (7) The following antibiotic disks were used: ampicillin (10 μg), ampicillin-sulbactam (10 and 10 μg, respectively), ceftriaxone (30 μg), nalidixic acid (30 μg), ciprofloxacin (5 μg), kanamycin (30 μg), gentamicin (10 μg), amikacin (30 μg), streptomycin (10 μg), tetracycline (30 μg), and trimethoprim-sulfamethoxazole (125 and 2375 μg, respectively) Antibiotic disks were supplied by Becton Dickinson Microbiology Systems (Franklin Lakes, NJ) Forty-four (66%) bovine isolates and 29 (122%) human isolates were resistant to one or more antibiotics Tetracycline resistance (Tcr) was the most common resistance found, with 43 of 44 (98%) resistant bovine isolates and 15 of 29 (52%) resistant human isolates being tetracycline resistant Streptomycin resistance was found in 29 (66%) resistant bovine isolates and 13 (45%) resistant human isolates Ampicillin was the third most common resistance phenotype with four (9%) of the resistant bovine isolates and eight (27%) of the resistant human isolates being ampicillin resistant Thirty (68%) of the resistant bovine isolates and 15 (52%) of the resistant human isolates were multidrug resistant, defined as resistance to two or more different classes of antibiotics such as tetracycline and ampicillin These results are similar to those of Kim et al (4), who reported 13 of 176 (74%) isolates collected between 1989 and 1991 to be resistant to streptomycin, sulfisoxazole, and tetracycline Schroeder et al (10) also found similar results with 5% of 85 human isolates being ampicillin resistant and 11% of 93 cow isolates being tetracycline resistant among isolates collected between 1985 and 2002 In contrast, Galland et al (3) found 10 (385%) isolates resistant to tetracycline and 2 (77%) resistant to ampicillin from 26 cattle isolates of E coli O157:H7 However, this group tested very few isolates, which may account for the differences found The level of antibiotic resistance within E coli O157:H7 from humans and bovines between 1997 and 2000 was lower than that traditionally found with other E coli isolates; however the level of resistance appears stable compared to those found in other studies of resistance within O157:H7 (3, 4, 10) Previously the tet(A), tet(B), tet(C), tet(D), tet(E), and tet(G) genes have been identified in tetracycline-resistant E coli strains (1, 2, 3, 4, 5, 6, 9) However, little is known about distribution among E coli O157:H7 isolates from either humans or animals Whole-bacterium dot blots were used to screen for the presence of the six genes as previously described (6, 8) The oligonucleotide sequence for each probe and the number of isolates carrying each gene are listed in Table ​Table11 TABLE 1 Primers used for DNA-DNA hybridization of tetracycline resistance determinants and distribution of tetracycline genes by host Sixty percent of the Tcr strains carried the tet(B) gene, which was the most prevalent tet gene found (Table ​(Table1)1) In a previous study, of non-O157 E coli strains, tet(B) was also the dominant gene and found in 80% of Tcr E coli isolates (1) The tet(A) gene was found in four (10%) of the Tcr bovine isolates and three (20%) of the Tcr human isolates The tet(C) gene was found in three (7%) of the Tcr bovine isolates and no human isolates The tet(G) gene was found in one (2%) Tcr bovine isolate and three (20%) Tcr human isolates The tet(D) and tet(E) genes were not found in any of the isolates One Tcr bovine isolates and four Tcr human isolates carried two different tetracycline resistance genes, and one Tcr bovine isolate carried three different tet genes Thirteen (31%) Tcr bovine isolates and three (20%) Tcr human isolates did not hybridize with any of the known genes examined In preliminary analysis, none of the 16 isolates hybridized with the recently identified tet(Y) gene (9), suggesting that these strains either may carry one of the other known tet genes not previously identified in E coli or may have a novel gene To distinguish between these hypotheses, the other known efflux tet genes, the only type currently identified in E coli, will need to be screened The finding that 31% of the Tcr bovine isolates carried unidentified tetracycline resistance genes, in this study, is very similar to a recent report that 40% of the Tcr isolates from Chilean salmon farms (6) carried unidentified tetracycline resistance genes The data from these two studies suggest that Tcr gram-negative bacteria taken from nonhuman animals and/or the environment carry a more diverse group of tetracycline resistance genes than are usually found when characterizing Tcr gram-negative bacteria from humans

The mef(A) Gene Predominates among Seven Macrolide Resistance Genes Identified in Gram-Negative Strains Representing 13 Genera, Isolated from Healthy Portuguese Children

Abstract: Of the 176 randomly selected, commensal, gram-negative bacteria isolated from healthy children with low exposure to antibiotics, 138 (78%) carried one or more of the seven macrolide resistance genes tested in this study. These isolates included 79 (91%) isolates from the oral cavity and 59 (66%) isolates from urine samples. The mef(A) gene, coding for an efflux protein, was found in 73 isolates (41%) and was the most frequently carried gene. The mef(A) gene could be transferred from the donors into a gram-positive E. faecalis recipient and a gram-negative Escherichia coli recipient. The erm(B) gene transferred and was maintained in the E. coli transconjugants but was found in 0 to 100% of the E. faecalis transconjugants tested, while the other five genes could be transferred only into the E. coli recipient. The individual macrolide resistance genes were identified in 3 to 12 new genera. Eight (10%) of the oral isolates and 30 (34%) of the urine isolates for which the MICs were 2 to >500 microg of erythromycin per ml did not hybridize with any of the seven genes and may carry novel macrolide resistance genes.

Effect of povidone-iodine on Streptococcus mutans in children with extensive dental caries.

Abstract: Purpose: The purpose of this pilot project was to determine the effect of a 10% povidone-iodine solution on plaque Streptococcus mutans and on incidence of new caries in young children following dental rehabilitation under general anesthesia. Methods: Twenty-five children ages 2 to 7 years, scheduled for dental treatment under general anesthesia, were enrolled. Children in the experimental group (N=13) had povidone-iodine applied 3 times at 2-month intervals. Control children (N=12) had no treatment. Plaque samples were taken from all children at baseline, 6 months and cultured for total bacteria and S mutans. Dental examinations were conducted at baseline, 6 months, and 1 year. Results: Experimental and control children had similar dietary habits, caries experience, and S mutans levels at baseline. All children’s S mutans counts decreased significantly at 6 months (P=.003). The difference between the 2 groups was not significant (P=.58). At 1 year, 5 of 8 children in the control group had new caries compared to 2 of 11 children in the experimental group (P=.06). Povidone-iodine was well accepted by participating families. Conclusions: Extensive one-time restorative dental treatment resulted in a significant suppression S mutans levels at 6 months. Further exploration of the role of povidoneiodine in caries management is indicated. (Pediatr Dent. 2004;26:5-10)

Distribution and molecular analysis of mef(A)-containing elements in tetracycline-susceptible and -resistant Streptococcus pyogenes clinical isolates with efflux-mediated erythromycin resistance

Abstract: Objectives To analyse the distribution and molecular features of mef(A)-containing elements in a large collection of different Streptococcus pyogenes clinical isolates with efflux-mediated erythromycin resistance. To further characterize a tet(O)-mef(A) element. Methods Gene detection was carried out by PCR using primers designed from established sequences or from sequences in this study. From a tet(O)-mef(A) element (approximately 60 kb), an 11 972 bp region including the tet(O) and mef(A) genes was sequenced. Results In the tetracycline-susceptible isolates (n =28), the mef(A) gene was contained in a regular Tn1207.1 transposon (7.2 kb), which was inserted into one of two previously described elements, Tn1207.3 (approximately 52 kb) or a 58.8 kb chimeric element, both flanked by the comEC gene. In the tetracycline-resistant isolates (n =61), all of which carried the tet(O) gene, the mef(A) gene was part of a variable Tn1207.1-related transposon inserted into unique elements which contained the tet(O) gene approximately 2.3 to 5.5 kb upstream of the mef(A) gene and were not flanked by the comEC gene. In the Tn1207.1-like transposon of these tet(O)-mef(A) elements, only msr(D) (orf5) and a modified orf6, in addition to mef(A), were detected by PCR in all isolates tested; while orf1 and orf2 were always undetectable, orf3, orf7 and orf8 were found in variable percentages. In an orf3-positive element, sequencing identified four new open reading frames downstream of the tet(O) gene, followed by three short sequences with homology to sequences of the pneumococcal mega element. Conclusions The mef(A) gene is carried on different chromosomal genetic elements depending on whether the isolates are susceptible or resistant to tetracycline.

Gram-positive merA gene in gram-negative oral and urine bacteria

Abstract: Clinical mercury resistant (Hg r ) Gram-negative bacteria carrying Gram-positive mercury reductase (merA)-like genes were characterized using DNA–DNA hybridization, PCR and sequencing. A PCR assay was developed which discriminated between the merA genes related to Staphylococcus and those related to the Bacillus/Streptococcus merA genes by the difference in size of the PCR product. DNA sequence analysis correlated with the PCR assay. The merA genes from Acinetobacter junii, Enterobacter cloacae and Escherichia coli were sequenced and shared 98–99% identical nucleotide (nt) and 99.6–100% amino acid identity with the Staphylococcus aureus MerA protein. A fourth merA gene, from Pantoeae agglomerans, was partially sequenced (60%) and had 99% identical nt and 100% amino acid identity with the Streptococcus oralis MerA protein. All the Hg r Gram-negative bacteria transferred their Gram-positive merA genes to a Gram-positive Enterococcus faecalis recipient with the resulting transconjugants expressing mercury resistance. These Gram-positive merA genes join Gram-positive tetracycline resistance and Gram-positive macrolide resistance genes in their association with mobile elements which are able to transfer and express in Gram-negative bacteria.