To Trimethoprim Research Articles

Interpretive criteria and quality control parameters for testing of susceptibilities of Haemophilus influenzae and Streptococcus pneumoniae to trimethoprim and trimethoprim-sulfamethoxazole. The Antimicrobial Susceptibility Testing OC Group.

Two hundred twenty-eight strains of Haemophilus influenzae and 234 strains of Streptococcus pneumoniae were tested by broth microdilution and disk diffusion methods for susceptibility to trimethoprim (TMP) and TMP-sulfamethoxazole (SMX) to evaluate proposed criteria. Data are presented to support the proposed TMP MIC breakpoints of < or = 2.0 micrograms/ml for susceptibility and > or = 4.0 micrograms/ml for resistance for both species and TMP-SMX MIC breakpoints of < or = 2.0-38 micrograms/ml for susceptibility and > or = 4.0-76 micrograms/ml for resistance. Corresponding zone diameter breakpoints for H. influenzae for both drugs are proposed: < or = 10 mm = resistant; > or = 16 mm = susceptible. A 10-laboratory study documented reproducibility of such tests with standard control strains. The following control limits are proposed for tests of H. influenzae ATCC 49247 against TMP; MIC, 0.12 to 0.5 microgram/ml; zone diameter, 27 to 33 mm. The current limits for TMP-SMX were confirmed. For tests of S. pneumoniae ATCC 49619, MICs of TMP were 1.0 to 4.0 micrograms/ml and the current TMP-SMX MIC range was confirmed. Disk susceptibility tests of either drug against pneumococci were not reproducible, and consequently neither quality control limits nor interpretive criteria could be established. Endpoint interpretation and lot-to-lot variability in Mueller-Hinton agars were significant factors leading to interlaboratory variability.

Transferable high-level trimethoprim resistance among isolates of Escherichia coli from urinary tract infections in Ontario, Canada.

Of 1171 isolates of Escherichia coli isolated from urine samples at the Public Health Laboratory, Toronto, Ontario, Canada, between May 1990 and December 1991, 120 (10.3%) were resistant to trimethoprim (TMP), cotrimoxazole (TMP/SMX), sulfamethoxazole (SMX) and other antimicrobial agents; 110 of the 120 isolates (91.7%) were resistant to four or more agents. The majority of resistant isolates (91.7%) exhibited high-level resistance (MIC > 1000 mg/L) to TMP. The MIC of TMP/SMX for all 120 isolates was > 2.0/38.0 mg/L and for SMX > 1024 mg/L. High-level resistances were also present among the beta-lactam antimicrobials with MICs ranging from 16- > 256 mg/L. Forty-three of 120 TMP-resistant (35.8%) isolates conjugally transferred TMP-resistance to E. coli K-12. Co-transfer of several other resistances was observed. SMX cotransferred from 86% of the 43 donors and beta-lactams together with SMX cotransferred from 70%. Nalidixic acid resistance was present among 22 (18.3%) of the 120 resistant isolates, however, nalidixic acid resistance was not transferred to E. coli K-12.

Lack of homology of enterococci which have high-level resistance to trimethoprim with the dfrA gene of Staphylococcus aureus

Multiresistant enterococci were tested for susceptibility to trimethoprim (TMP). Although most enterococci are inhibited by less than or equal to 1.0 microgram/ml, the MICs for 7 of 29 selected multiresistant isolates were greater than or equal to 8 micrograms/ml, including for two beta-lactamase positive (Bla+) strains, for which the MICs of TMP were greater than 1,000 micrograms/ml, and for another Bla+ strain, for which the MIC was 128 micrograms/ml. None of five isolates tested transferred TMP resistance and none of the resistant isolates hybridized to the dfrA gene of Staphylococcus aureus. Whether TMP resistance in enterococci is due to a mutation(s) or to acquisition of a new gene is not known. Acquisition of resistance to TMP is another example of the multiple antimicrobial resistance typically displayed by enterococci.

Bacterial resistance to trimethoprim in geriatric medical wards.

Urinary tract infections (UTI) caused by organisms resistant to trimethoprim (TMP), as well as their faecal carriage were studied in two geriatric wards. TMP-resistant UTI was common (26 and 50% of admission and ward-acquired infections, respectively) and was associated with male sex, recurrent and transferred admissions and length of stay. There was a strong relationship between faecal carriage and isolation of TMP-resistant organisms from urine. Antimicrobial exposure was the major determinant of TMP-resistant faecal carriage.

Some pharmacokinetic data of aditoprim and trimethoprim in healthy and tick-borne fever infected dwarf goats.

Aditoprim (AP) is a new dihydrofolate reductase inhibitor, which is structurally related to trimethoprim (TMP). The pharmacokinetics of AP (10 mg/kg) and TMP (20 mg/kg) were assessed in healthy dwarf goats. Therapeutic efficacy against rickettsial infections was tested in tick-borne fever (TBF) infected goats. The animals were given TMP (n = 5) or AP (n = 5) by i.v. injection, and subsequently the drugs were administered orally (same groups, similar doses). Finally, both groups were infected with TBF and the i.v. experiment was repeated. Plasma concentration-time curves for both drugs followed first-order two-compartment decay. For TMP, mean t1/2 beta +/- SEM (h) was 0.84 +/- 0.06 (i.v. control) and 0.90 +/- 0.06 (i.v. infected), respectively, whereas for AP values of 8.00 +/- 0.31 (i.v. control) and 10.28 +/- 0.67 (i.v. infected) were obtained (P less than 0.05). Mean Vd beta +/- SEM values (l/kg) were 3.84 +/- 0.27 (i.v. control) and 4.07 +/- 0.85 (i.v. infected) for TMP (NS) and 7.02 +/- 0.63 vs 9.29 +/- 0.21 (P less than 0.05) for AP. After i.v. injection, rumen fluid concentrations of AP were significantly (P less than 0.05) higher and more persistent than those of TMP. For AP, the plasma and rumen fluid concentrations at 3 h were 1.20 +/- 0.06 micrograms/ml and 0.85 +/- 0.17 microgram/ml, respectively. After oral administration of TMP, Cmax in plasma was 0.12 +/- 0.01 microgram/ml and the maximum was reached after 1.2 +/- 0.16 h; systemic bioavailability (F) was 10.3% (relative to AUC i.v.). Oral treatment with AP resulted in a Cmax value of 0.21 +/- 0.02 microgram/ml with Tmax of 22.5 +/- 1.65 h and a F value of 71%. Based on WBC, serum ALP and rectal temperature responses, it was concluded that both TMP and AP were inactive against Ehrlichia phagocytophila.

Trimethoprim-resistant Shigella and enterotoxigenic Escherichia coli strains in children in Thailand.

The percentage of Shigella and enterotoxigenic Escherichia coli (ETEC) strains resistant to trimethoprim (TMP)-sulfamethoxazole isolated from children with diarrhea at the outpatient department of the Children's Hospital in Bangkok increased from 3 and 0%, respectively, in 1982 to 29% and 25% in 1986. One hundred thirty-nine Shigella and 22 ETEC strains resistant to greater than 1024 micrograms/ml of trimethoprim (TMPr) isolated from children with diarrhea in Bangkok in 1984 and 1985 were analyzed for the presence of type I, II and III plasmid-specific dihydrofolate reductase (DHFR) genes. Thirty-two percent (45 of 139) of TMPR Shigella had genes encoding type II and 9% (13 of 139) had genes encoding type I DHFR genes. Fifty percent (11 of 22) of TMPR ETEC had type II and 14% (3 of 22) had type I DHFR genes. Plasmids encoding DHFR were identified by the Southern technique in 24% (14 of 58) of Shigella and 1 of 14 ETEC that contained genes encoding DHFR. Plasmids coding for type II DHFR were transferred to E. coli K12 by conjugation from 13 of 14 Shigella and a plasmid coding for type I DHFR was transferred from the single ETEC containing a plasmid coding for type I DHFR. Genes coding for DHFR were presumably situated on the chromosome in 76% (44 of 58) of Shigella and 93% (13 of 14) of ETEC that contained genes encoding DHFR. Since 58% (81 of 139) of TMPR Shigella and 36% (8 of 22) of TMPR ETEC strains examined did not contain genes encoding type I, II or III DHFR, high level TMP resistance was presumably caused by other types of DHFR genes.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro and in vivo efficacy of the combination trimethoprim-sulfamethoxazole against clinical isolates of methicillin-resistant Staphylococcus aureus.

The in vitro susceptibilities of 16 independent, geographically distinct clinical isolates of methicillin-resistant Staphylococcus aureus to trimethoprim (TMP) in combination with sulfamethoxazole (SMX) were evaluated. Although methicillin-resistant S. aureus strains appear to be universally resistant to SMX, the combination TMP-SMX was found to be synergistic in vitro (in combination, the MICs of both drugs decreased 6- to 25-fold) as well as in vivo (5- to 6-fold reduction in TMP at 50% effective doses).

Increasing resistance to trimethoprim-sulfamethoxazole among isolates of Escherichia coli in developing countries.

Resistance of Escherichia coli to trimethoprim (TMP)-sulfamethoxazole remains at 3%-8% at many medical centers within the United States. In this study a 44% resistance rate was observed among E. coli isolated at a pediatric hospital in Santiago, Chile, and a 40% resistance rate at a general teaching hospital in Bangkok, Thailand. Most isolates were from urinary tract infections and showed high-level resistance (minimal inhibitory concentration of TMP greater than 1,000 micrograms/ml). Nineteen of 35 isolates tested transferred resistance to TMP; most cotransferred resistance to streptomycin and sulfonamides. Dihydrofolate reductase type I was detected by gene probing in 14 of 35 strains. Subsequent investigations in Brazil, Honduras, and Costa Rica revealed that this high rate of resistance was not an isolated phenomenon.

Reversal of the in vitro susceptibility of enterococci to trimethoprim-sulfamethoxazole by folinic acid.

The in vitro susceptibilities of 21 clinical isolates of Streptococcus faecalis to trimethoprim (TMP) in combination with sulfamethoxazole (SMX) was evaluated in Mueller-Hinton broth (MHB) in the presence and absence of folinic acid as well as in urine. The mean MIC and MBC in MHB, expressed as the TMP concentration, was 0.13 and 0.32 micrograms of TMP-SMX per ml, respectively. In MHB supplemented with folinic acid, the mean MIC and MBC was 3.3 and 5.5 micrograms of TMP-SMX per ml, respectively. In urine the mean MIC of TMP-SMX for these isolates was 8.1 micrograms/ml (range, 1.6 to 50 micrograms/ml). All isolates were inhibited by less than 0.01 micrograms of TMP-SMX per ml when methotrexate was added to the urine.

Trimethoprim resistance in multiple genera of Enterobacteriaceae at a U.S. hospital: spread of the type II dihydrofolate reductase gene by a single plasmid.

The percentage of clinical isolates of several species of Enterobacteriaceae, particularly Escherichia coli and Klebsiella pneumoniae, resistant to trimethoprim (TMPR) has increased gradually at the Brigham and Women's Hospital (Boston) in recent years. Thirty-seven of 42 TMPR isolates from six species of gram-negative bacilli conjugally transferred TMP resistance to K12 E. coli. beta-Lactam resistance cotransferred from 21 of the 37 donors, and sulfamethoxazole (SMZ) resistance cotransferred from five of the 37 donors. Plasmids that encoded TMP resistance either alone or with SMZ resistance had a molecular size of approximately 52.5 kilobases, with identical restriction endonuclease-generated "fingerprints." Plasmids encoding beta-lactam-mediated resistance (beta R) were approximately four kilobases larger and had fragment patterns that were identical for all of the TMPR/beta R plasmids tested and had many restriction endonuclease-generated bands in common with TMPR plasmids. Radiolabeled dihydrofolate reductase (DHFR) probes identified the type II DHFR as the determinant of TMP resistance. In contrast with reports from Europe, TMP resistance in multiple species of Enterobacteriaceae was found to be spread in one hospital by a single, stable conjugative plasmid that has a wide host range and encodes the type II DHFR gene.

Synergistic Action of Trimethoprim and Sulfamethoxazole for Nocardia Asteroides: Efficacious Therapy in Five Patients

Eighteen isolates of Nocardia asteroides were tested for in vitro susceptibility to trimethoprim (TMP) and sulfamethoxazole (SMZ) alone and in various combinations using disc and paper strip diffusion tests. TMP-SMZ showed synergistic action for two-thirds of the Nocardia isolates tested. Five patients with Nocardia pneumonia were treated with TMP-SMZ and all were cured. Four of the patients’ isolates were tested and all showed synergistic patterns of inhibition with the spaced disc and paper strip methods. The agar diffusion disc and synergy tests of TMP-SMZ appear to correlate with clinical usefulness when the Nocardia are susceptible with large zones of inhibition around the combination TMP-SMZ disc.

Antimicrobial susceptibility, growth kinetic and pathogenicity of thymidine-requiring Streptococcus species.

18 strains of thymidine-requiring streptococcal mutants (thy-) were isolated from urines of patients with urinary tract infection treated with trimethoprim-sulfameth-oxazole (TMP-SMZ) or trimethoprim-sulfadiazine (TMP-SDZ). All thy- mutants were catalase- and beta-lactamase-negative, grew in the presence of bile and esculin, and required from 0.3 to greater than 1280 micrograms/ml of thymidine for normal growth. The antibiotic susceptibility of wild-type and thy- mutants to 21 antimicrobial agents tested were comparable except to trimethoprim (TMP), TMP-SMZ and TMP-SDZ. Ampicillin, penicillin G, erythromycin and rifampin were among the most active compounds tested. Growth kinetic studies with a Streptococcus faecalis thy- mutant in a synthetic basal medium without thymidine resulted in a decrease of 2-3 logarithmic units in viable cells after 24 h of incubation. The addition of thymidine to this thymidine-deprived culture prevented the thymineless death of the cells. In vivo, this thy- mutant was less virulent than the wild-type strain in producing kidney infection in mice.

Resistance to trimethoprim among urinary tract isolates in the United Kingdom.

Sequential surveys of resistance to trimethoprim (TMP) were made from 1978 to 1980 among urinary tract isolates of enterobacteria from the Nottingham area of the United Kingdom. These surveys revealed an increasing trend toward levels of resistance to TMP, both in hospitals and in the general environment. Because of this trend, the chances of initial infection with an organism resistant to TMP are increased. Much of this increased resistance can be accounted for by the accelerated spread of TMP resistance plasmids and transposons. The appearance of chromosomally located resistance to TMP mediated by a transposon in the absence of a plasmid is unfortunate because of the potential stability of this form of resistance. The clinical isolation of organisms resistant to TMP but sensitive to sulfonamides, coupled with the increasing use of TMP by itself in the United Kingdom, emphasizes the need for continued monitoring of the relationship between resistance to TMP and to sulfonamides in urinary tract pathogens.

Incidence and Mechanisms of Resistance to Trimethoprim in Clinically Isolated Gram-Negative Bacteria

Over an 18-month period (October 1973 to April 1975), 133 strains of gram-negative bacteria with acquired resistance to trimethoprim (TM) were isolated from infected urines cultured at the Royal Free Hospital. The overall frequency of resistance was 3.2%. A disproportionately high number of resistant strains (63.1%) were Kebsiella aerogenes. Resistance to TM mediated by R plasmids occurs infrequently (9% of all resistant strains); the majority of TMR plasmids isolated belonged to one incompatability group (W). Chromosomally mediated resistance to TM in most Escherichia coli and K. aerogenes strains appears to be due mainly to production of a dihydrofolate reductase with a reduced susceptibility to TM. In some strains, increased activity of the DHFR was also a contributing factor. Increase in enzyme level alone was only great enough to account for the level of resistance to TM in a small number of cases.

Combined Action of Sulphamethoxazole and Trimethoprim Against Clinically-Isolated Sulphonamide–Resistant Bacteria

42 strains of gram-negative bacteria, isolated from clinical material, resistant to trimethoprim (TM), sulphamethoxazole (SMZ) or both, have been tested for synergistic sensitivity to TM + SMZ. The combination showed no synergy against strains 'highly resistant' to SMZ (MIC greater than 1 mg/ml). Indifference was invariably observed. However, synergy was seen with strains 'moderately resistant' to SMZ (MIC 100--1,000 microgram/ml). Our results indicate that present techniques for the testing of urinary tract isolates for sensitivity to co-trimoxazole need revision.

Transposition of a deoxyribonucleic acid sequence encoding trimethoprim and streptomycin resistances from R483 to other replicons.

R483, a plasmid of the Ialpha incompatibility group, contained a deoxyribonucleic acid (DNA) sequence encoding resistance to trimethoprim (TpR) and streptomycin (SmR) that could be transposed to other replicons, i.e., to the Escherichia coli chromosome and to related and unrelated plasmids. Each transposition resulted in the acquisition by the recipient replicon of a segment of DNA of about 9 X 10(6) daltons, both resistance genes, but never the colicin Ia or pilus genes of R483. Transposition took place at a single chromosomal site between dnaA and ilv and did not suppress the DnaA phenotype, in contrast to integration of the whole R483 plasmid. The chromosome, having received the transposition, could secondarily act as a transposition donor to another plasmid. Such a plasmid was indistinguishable from one having received a direct transposition from R483. TpR SmR transposition was very site specific and did not require a functional recA+ gene. We postulate that the TpR SmR segment of R483 is a transposon (TnC) with specific boundary sequences.

In Vitro Sensitivity of 33 Strains of Pseudomonas pseudomollei to Trimethoprim and Sulfamethoxazole

The tube dilution method was used to test 33 strains of Pseudomonas pseudomallei for in vitro sensitivity to trimethoprim (TMP), sulfamethoxazole (SMZ), and a combination of the drugs maintaining a ratio of 20 parts SMZ to one part TMP. Results disclosed no activity by TMP alone except at extremely high levels. Twelve of 33 strains were sensitive to SMZ, and 75% of the strains were inhibited by the combination at therapeutically achievable levels. In no instance did TMP fail to potentiate the action of SMZ against the organism. In vitro susceptibility of the organism indicates that a combination of TMP and SMZ could be useful in the treatment of melioidosis.

The susceptibility of Serratia marcescens to sulfamethoxazole, trimethoprim, and trimethoprim-sulfamethoxazole.

The sensitivities of strains of Serratia marcescens isolated from clinical specimens, to trimethoprim (TMP), sulfamethoxazole (SMZ), and to a combination of the two drugs (trimethoprim-sulfamethoxazole) were examined. All strains were sensitive to TMP (MICs, 0.1-1 ELg/ml) with varying degrees of sensitivity to SMZ (MICs, 1.0 tg/ml). Potentiation of antibacterial activity of the two drugs together was indicated by the larger clear zones of inhibition around the combination disk and by results of checkerboard titrations of combinations of the two drugs. Small colonies were present in many of the zones around the TMP and SMZ disks on Mueller-Hinton agar and sensitivity test agar (Wellcome), with and without 5% lysed horse blood.

Susceptibility of recently isolated pathogenic bacteria to trimethoprim and sulfamethoxazole separately and combined.

A number of media and modifications were used in preliminary tests of susceptibility of common pathogenic aerobic bacteria to trimethoprim (TMP) and sulfamethoxazole (SMZ) separately and combined. The effect of varying the density of the lawn for the disk-susceptibility test was also investigated. Various serial dilution tests in liquid and on solid media were also compared, and the effect of varying the size of the inoculum for these tests was investigated. As a result of these tests, done largely on laboratory-maintained strains, a lawn of overnight cultures diluted 10-3 was considered most useful and practical for the disk tests, but the standard dilution specified in the Kirby-Bauer method was generally included for comparison. In the serial dilution tests, the one using the inocula replicator and 10-3 dilution of culture for inoculum on a modified (thymidinefree) Mueller-Hinton agar was selected as optimal, but similar tests with undiluted cultures and other modifications of various media were also used for some species. By use of these methods groups of recently isolated common pathogenic bacteria were tested by the disk and inocula replicator methods for susceptibility to TMP and SMZ separately and combined in ratio of 1:20 in the former and 1:16 in the latter method. Against nearly all strains of almost all species tested TMP alone and combined with the sulfonamide was found to be active in clinically useful concentrations, and against a large proportion of the organisms the two agents were clearly synergistic even for strains that were moderately or highly resistant to SMZ.