Comparative study of the antibacterial activity of aminoglycoside antibiotics and their combinations with carbenicillin against Pseudomonas aeruginosa

Antibacterial activity of 7 aminoglycoside antibiotics and combinations of tobramycin or gentamicin with carbenicillin was studied with respect to 33 clinical strains of Ps. aeruginosa. Tobramycin, sisomicin, gentamicin and amicacin showed high levels of antibacterial activity. Tobramycin and sisomicin were 3-4 and 2 times more effective than gentamicin. 100 per cent of the Ps. aeruginosa isolates was sensitive to tobramycin and amicacin. The number of the isolates sensitive to sisomicin and gentamicin amounted to 97 and 94 per cent respectively. The respective numbers for streptomycin and kanamycin were 32 and 11 per cent. No monomycin sensitive isolates were detected. Combination of tobramycin or gentamicin with carbenicillin increased the antibacterial activity of the aminoglycoside antibiotics by 2-16 times and that of carbenicillin by 2-32 times. The synergistic effect of gentamicin or tobramycin with carbenicilin was observed with respect to 50 and 58 per cent of the isolates respectively. No antagonistic effect was detected on the combined use of the antibiotics. The majority of the isolates (96 per cent) were sensitive to combinations of carbenicillin in a concentration of 50 micrograms/ml with tobramycin or gentamicin in concentrations of 0.15 or 0.3 micrograms/ml respectively.     

Incidence of antimicrobial resistance among Enterobacteriaceae isolated in Riyadh

The antimicrobial resistance of 1,018 isolates of Enterobacteriaceae isolated from fecal specimens of the urban population of Riyadh, Saudi Arabia, was studied. Resistance to 1 or more of 10 antimicrobial agents was encountered in 50.2% of the isolates. Of the isolates tested,Escherichia coli (0.8%) andKlebsiella species (1.6%) were found resistant to seven antimicrobial agents simultaneously: ampicillin, chloramphenicol, kanamycin, colistin, streptomycin, tetracycline, and carbenicillin. Resistance to nalidixic acid was encountered in only 0.68% of theE. coli isolates. No isolate was found to be resistant to gentamicin. Eighty-six of the resistant strains were tested for their ability to transfer their resistance. Forty percent were able to do so withE. coli K-12.     

The patterns and transmissibility of antibiotic resistance among clinical strains of Pseudomonas aeruginosa.

Four hundred and ninety-eight predominantly pyocin-type 10 clinical strains of Pseudomonas aeruginosa were analyzed for resistance to carbenicillin, cefoperazone, cefotaxime, ceftazidime, gentamicin, amikacin and netilmicin. Based on NCCLS-recommended MIC breakpoints, 245 strains were found to be resistant, of which 41.6% were resistant to carbenicillin, 38% to gentamicin, 37.8% to netilmicin, 26.3% to cefoperazone, 17.9% to cefotaxime, 0.6% to amikacin and none to ceftazidime. Quadruple resistance to carbenicillin, cefoperazone, gentamicin and netilmicin was the most frequent pattern observed. Resistance to older antibiotics (kanamycin, streptomycin and tetracycline) and to mercuric chloride were also common. Conjugation experiments suggested that self-transmissible and non-transmissible plasmids occurred in at least 66 strains.     

Characterization of glycopeptides, aminoglycosides and macrolide resistance among Enterococcus faecalis and Enterococcus faecium isolates from hospitals in Tehran

The prevalence of glycopeptides, aminoglycosides and erythromycin resistance among Enterococcus faecalis and Enterococcus faecium was investigated. The susceptibility of 326 enterococcal hospital isolates to amikacin, kanamycin, netilmicin and tobramycin were determined using disk diffusion method. The minimum inhibitory concentration (MIC) of vancomycin, teicoplanin, gentamicin, streptomycin, and erythromycin were determined by microbroth dilution method. The genes encoding aminoglycoside modifying enzymes described as AMEs genes, erythromycin-resistant methylase (erm) and vancomycin-resistant were targeted by multiplex-PCR reaction. High level resistance (HLR) to gentamicin and streptomycin among enterococci isolates were 52% and 72% respectively. The most prevalent of AMEs genes were aac (6')-Ie aph (2") (63%) followed by aph (3')-IIIa (37%). The erythromycin resistance was 45% and 41% of isolates were positive for ermB gene. The ermA gene was found in 5% of isolates whereas the ermC gene was not detected in any isolates. The prevalence of vancomycin resistant enterococci (VRE) was 12% consisting of E. faecalis (6%) and E. faecium (22%) and all of them were VanA Phenotype. The results demonstrated that AMEs, erm and van genes are common in enterococci isolated in Tehran. Furthermore our results show an increase in the rate of vancomycin resistance among enterococci isolates in Iran.     

Amikacin resistance of clinical strains of Enterobacteriaceae and Pseudomonas]

Amikacin resistance was studied in 380 bacterial strains of Enterobacter, Klebsiella, Serratia, Pseudomonas and E. coli isolated in clinics of the Moscow Region. It was shown that 69 isolates were resistant to amikacin. Plasmid DNA was detected in 10 amikacin resistant isolates. Three of them belonging to Klebsiella and 3 belonging to E. coli contained plasmids controlling resistance to amikacin. The plasmids isolated from the strains of Klebsiella determined as well resistance to kanamycin and streptomycin but did not control resistance to sisomicin, tobramycin and gentamicin while the plasmids isolated from the strains of E. coli determined resistance to amikacin, kanamycin, gentamicin, tobramycin and sisomicin.     

Comparison of the sensitivity of Pseudomonas aeruginosa cultures that synthesize melanin and other pigments to 12 antibiotics and 5-nitro-8-quinolinol]

Sensitivity of 80 Pseudomonas aeruginosa cultures forming melanin and 80 cultures synthesizing other pigments to amikacin, gentamicin, kanamycin, carbenicillin, levomycetin, monomycin, 5-NOK, polymyxin M, rifampicin, streptomycin, tetracycline, tobramycin and erythromycin was determined. It was found that the cultures of Ps. aeruginosa synthesizing melanin were less resistant to most of the antibiotics that the other representatives of this species.     

Evaluation of the In Vitro Activity of Tobramycin as Compared with That of Gentamicin Sulfate

The in vitro activity of tobramycin was quantitatively compared with that of gentamicin sulfate against 195 bacterial isolates from clinical material. Tobramycin was found to be twice as active as gentamicin against isolates of Pseudomonas aeruginosa. Conversely, gentamicin proved fourfold more active than tobramycin against isolates of Serratia marcescens. Both drugs were of comparable activity against isolates of Staphylococcus aureus and the majority of the enterobacterial isolates other than S. marcescens. On the basis of the obtained data, the following criteria are proposed for the interpretation of diffusion susceptibility tests with 10-μg discs of gentamicin and tobramycin. Enterobacteriaceae and isolates of S. aureus are designated as susceptible to gentamicin and tobramycin if the zones of inhibition measure 15 mm or more in diameter; zones of 14 mm or less are indicative of resistance. Pseudomonadaceae are interpreted as sensitive to tobramycin and gentamicin if the inhibition zones measure at least 15 and 12 mm in diameter, respectively.     

Sensitivity of Shigella to antibiotics]

Three hundred and twenty two Shigella cultures isolated from dysentery patients within 1986-1989 were tested with the use of standard paper disks for their sensitivity to levomycetin, streptomycin, tetracycline, monomycin, neomycin, kanamycin, erythromycin, gentamicin, carbenicillin, ampicillin, oxacillin, methicillin and doxycycline. The number of the cultures belonging to Shigella sonnei amounted to 85.1 per cent of the total number of the strains studied. 91.9, 89.5, 87.3, 87.3, 80.1 and 80.1 per cent of the cultures were sensitive to gentamicin, kanamycin, carbenicillin, neomycin, levomycetin and ampicillin, respectively. 99.4 per cent of the isolates were resistant to streptomycin and 97.2 per cent were resistant to tetracycline. The sensitivity to erythromycin remained rather high (70.2 per cent). The overwhelming majority of the Shigella sonnei isolates had multiple resistance.     

Occurrence and antibiotic sensitivity of Enterobacteriaceae isolated from a group of Jordanian patients with community acquired urinary tract infections

The type and antibiotic sensitivity of urinary tract pathogens may differ in various communities. Of 207 isolates recovered from midstream urine specimens collected from a group of patients with community acquired urinary tract infections (UTI), 86% were species of Enterobacteriaceae. The most frequently recovered pathogens were Escherichia coli (82%), Klebsiella spp. (7.3%), Proteus spp. (6.2%), Enterobacter spp. (3.4%) and Citrobacter spp. (1.1%). High rates of resistance were found against ampicillin (95%), tetracycline (86%), carbenicillin (84%), trimethoprim/sulphamethoxazole (48%), and amoxycillin/clavulanic acid (45%). For the antibiotics tobramycin, aztreonam, ceftriaxone and gentamicin 7% of the isolates were resistant, while resistance varied from 9-18% for amikacin, ciprofloxacin, norfloxacin, nalidixic acid and cefuroxime. The incidence of UTI caused by Enterobacteriaceae was three times higher in females than in males, particularly in young and middle age groups (< or = 19 and 20-39 years).     

Effect of mucoid property on antibiotic susceptibility ofPseudomonas aeruginosa

Clinical isolates ofPseudomonas aeruginosa from patients with cystic fibrosis (CF) were examined for susceptibility to the antibiotics carbenicillin, ticarcillin, tobramycin, gentamicin, and tetracycline. Minimal inhibitory concentrations of the antibiotics were determined for mucoid and nonmucoid isolates from the same patient by a single-colony replica plating method. This method allows the rapid determination of antibiotic susceptibility of a single cell’s progeny and the individual screening of each colony against all antibiotics. Twenty of 34 (58%) cystic fibrosis patients had a mucoid isolate which was more susceptible to antibiotics than their nonmucoid isolate of the same serotype. Nonmucoid revertant segregants of mucoid strains isolated from 50% of the patients demonstrated greater resistance to at least one antibiotic than the original mucoid strain. Multiple isolates from 25 patients were serotyped by Difco (Liu) or Homma antiserum; only 2 patients harbored multiple strains with no common serotyping antigens. Serotypes of the nonmucoid revertants were the same as the original mucoid isolate even if the susceptibilities of the two strains were not similar.     

In vitro antibacterial activity of a new 1-oxa cephalosporin compound

The in vitro activity of a unique new 1-oxa cephalosporin beta-lactam antibiotic (LY 127935) was tested against clinical isolates of gram-positive and gram-negative bacteria and compared with the activities of cefoxitin, cefamandole, cephalothin, clindamycin, amikacin, tobramycin, gentamicin, ticarcillin, and carbenicillin. The new compound was observed to have a broad spectrum of antibacterial activity which far exceeded the activity of older cephalosporins against aerobic gram-negative enteric bacilli. This new compound was the most active drug tested against Klebsiella, Serratia, Enterobacter, indole-negative and positive Proteus species, and E. coli. Against clinical isolates of Pseudomonas species the new compound was more active than cefoxitin, cefamandole, cephalothin, and clindamycin, comparable to ticarcillin and carbenicillin, and less active than gentamicin, tobramycin, and amikacin. Yet, most of the Pseudomonas isolates were inhibited by 16 micrograms/ml of the new compound. Against both beta-lactamase and non beta-lactamase producing Staphylococcus aureus isolates, the new 1-oxa compound was less active than the older cephalosporins of which cephalothin and cefamandole were the most effective. The 1-oxa compound had no appreciable activity against isolates of Streptococcus faecalis. Activity of all four cephalosporins studied was decreased in the presence of an increased inoculum of Enterobacteriaceae in trypticase soy and Mueller-Hinton broth. The activity of the new compound against Pseudomonas species was also decreased by an increased inoculum in Mueller-Hinton but not in trypticase soy broth. These results indicate that this new 1-oxa compound may have great promise as a broad spectrum antibiotic and may warrant controlled clinical trials in man.     

Biochemical determinants of aminoglycoside resistance in Gr- microorganisms isolated from urocultures

The investigation was focused on 60 strains of Gr- microorganisms isolated from urocultures and resistant to gentamicin and/or amikacin. Resistance evaluation by the method of Bauer--Kirby with respect to 7 aminoglycoside aminocyclitols (streptomycin, spectinomycin, kanamycin, gentamicin, tobramycin, sisomicin, netilmicin and amikacin) as well as determination of minimal inhibitory concentrations revealed that the most frequently occurring resistance phenotype was streptomycin kanamycin gentamicin sisomicin tobramycin (91.66% tested microorganisms). Approximately 50% of all tested organisms were found to be susceptible to netilmicin. Assays for aminoglycoside-modifying enzymes using 32P ATP and 14C ATP confirmed APH(3')(5")--I and AAD(2") as resistance determinants regarding 4,6-substituted deoxystreptamines. Acetyltransferase determination by the method of Shannon and Phillips and that by van de Klundert et al. most frequently assumes for the formation of AAC(3)-II and AAC(3)-I. Assays utilizing radioactive labels in amikacin-resistant strains determine the enzymes APH(3') and AAD(2")-II.     

Prevalence of multidrug-resistant Staphylococcus aureus in diabetics clinical samples

Antibiotic resistance in 40 Staphylococcus aureus clinical isolates from 110 diabetic patients (36%) was evaluated. Of these, 32 (80%) of the isolates showed multidrug-resistance to more than eight antibiotics and 35% isolates were found to be methicillin resistant S. aureus (MRSA). All 40 S. aureus strains (100%) screened from diabetic clinical specimens were resistant to penicillin, 63% to ampicillin, 55% to streptomycin, 50% to tetracycline and 50% to gentamicin. Where as low resistance rate was observed to ciprofloxacin (20%) and rifampicin (8%). In contrast, all (100%) S. aureus strains recorded susceptibility to teicoplanin, which was followed by vancomycin (95%). Genotypical examination revealed that 80% of the aminoglycoside resistant S. aureus (ARSA) have aminoglycoside modifying enzyme (AME) coding genes; however, 20% of ARSA which showed non-AME mediated (adaptive) aminoglycoside resistance lacked these genes in their genome. In contrast all MRSA isolates possessed mecA, femA genetic determinants in their genome.

     

Resistance to gentamicin and related aminoglycosides in Staphylococcus aureus isolated in Brazil

Isolates of Staphylococcus aureus obtained from a Brazilian university hospital were characterized in relation to resistance to gentamicin and related aminoglycosides. Thirty-six isolates were susceptible to methicillin (MSSA) and 14 were resistant (MRSA). All isolates were sensitive to nucleic acid-binding compounds. All MRSA isolates and one MSSA isolate were demonstrated to be resistant to gentamicin and were coincidentally resistant to amikacin, kanamycin, neomycin and tobramycin. Among the gentamicin sensitive MSSA isolates, five isolates were found to be resistant only to kanamycin/neomycin. The resistance to gentamicin (and related aminoglycosides: kanamycin and tobramycin) must be due to AAC(6')-APH(2") activity. As these isolates also showed resistance to neomycin, they must carry an additional genetic element, probably the one responsible for APH(3')III activity, which accounts for the high level of resistance to kanamycin and to amikacin. The resistance to kanamycin/neomycin in the gentamicin sensitive isolates could not be attributed to the AAD(4')(4") activity because of the tobramycin sensitivity, and so could be ascribed to the APH(3')III activity. Curing and transfer experiments, as well as electrophoresis procedures, indicate that gentamicin resistance in Staph. aureus strains here studied has, characteristically, chromosomal localization.     

Antibiotic sensitivity of Shigella isolated from patients from 1974-1985

Antibiotic sensitivity of 3524 Shigella cultures isolated from patients in 1974-1982 and 414 cultures isolated in 1983-1985 was assayed with standard paper disks. The isolates of 1974-1982 were mostly responsive to ampicillin, carbenicillin, kanamycin, gentamicin, monomycin, neomycin and chloramphenicol. Certain differences in the level of the antibiotic resistance were observed in the Shigella isolates belonging to diverse species. Polyresistant cultures of Shigella amounted to 96.5% and ranged from 88.5 to 99.4% in different years. The number of the cultures with multiple resistance among Shigella sonnei was somewhat higher than that among the Flexneri and Newcastle bacilli. The Shigella isolates of 1983-1985 were mostly responsive to gentamicin, carbenicillin, neomycin, kanamycin and monomycin. 55.5% of the Shigella isolates were responsive to chloramphenicol and only 3.1% to tetracycline. Almost all the causative agents of dysentery isolated within that period were polyresistant. Phenotypic characteristics of multiple resistance in the Shigella cultures were studied.     

Tobramycin (Nebramycin Factor 6): In Vitro Activity Against Pseudomonas aeruginosa

Tobramycin (factor 6 of the nebramycin complex) is a new aminoglycoside antibiotic isolated from Streptomyces tenebrarius which is active against S. aureus, Enterobacteriaceae, and Pseudomonas aeruginosa. Susceptibility to tobramycin of 96 strains of P. aeruginosa, including 45 recent isolates from blood, was studied by using agar and broth dilution methods. The minimum inhibitory concentration (MIC) for 83 of 96 strains was 3.12 mug/ml or lower in Mueller Hinton agar; MIC values were two to eight times lower in Mueller Hinton broth tests. Agar dilution MIC values were generally lower than those obtained in parallel tests with gentamicin. Killing curves obtained from serial sampling of broth cultures showed a 100- to 10,000-fold decline in viability of log-phase organisms within 30 min of exposure to the drug. Two-dimensional agar dilution tests with carbenicillin and tobramycin with 79 strains showed additive or synergistic effects; no antagonism was documented. Seventy-eight of 79 strains were inhibited by a combination of 50 mug of carbenicillin per ml and 1.56 mug of tobramycin per ml, blood levels which seem attainable in man. Tobramycin appears to be a potent, rapidly bactericidal antibiotic against P. aeruginosa and merits clinical evaluation.     

Nosocomial infection caused by vancomycin‐susceptible multidrug‐resistant Enterococcus faecalis over a long period in a university hospital in Japan

Compared with other developed countries, vancomycin‐resistant enterococci (VRE) are not widespread in clinical environments in Japan. There have been no VRE outbreaks and only a few VRE strains have sporadically been isolated in our university hospital in Gunma, Japan. To examine the drug susceptibility of Enterococcus faecalis and nosocomial infection caused by non‐VRE strains, a retrospective surveillance was conducted in our university hospital. Molecular epidemiological analyses were performed on 1711 E. faecalis clinical isolates collected in our hospital over a 6‐year period [1998–2003]. Of these isolates, 1241 (72.5%) were antibiotic resistant and 881 (51.5%) were resistant to two or more drugs. The incidence of multidrug resistant E. faecalis (MDR‐Ef) isolates in the intensive care unit increased after enlargement and restructuring of the hospital. The major group of MDR‐Ef strains consisted of 209 isolates (12.2%) resistant to the five drug combination tetracycline/erythromycin/kanamycin/streptomycin/gentamicin. Pulsed‐field gel electrophoresis analysis of the major MDR‐Ef isolates showed that nosocomial infections have been caused by MDR‐Ef over a long period (more than 3 years). Multilocus sequence typing showed that these strains were mainly grouped into ST16 (CC58) or ST64 (CC8). Mating experiments suggested that the drug resistances were encoded on two conjugative transposons (integrative conjugative elements), one encoded tetracycline‐resistance and the other erythromycin/kanamycin/streptomycin/gentamicin‐resistance. To our knowledge, this is the first report of nosocomial infection caused by vancomycin‐susceptible MDR‐Ef strains over a long period in Japan.     

Resistance to aminoglycoside antibiotics of gram-negative bacilli isolated in Canadian hospitals.

A survey was made of the frequency of resistance to amikacin, gentamicin and tobramycin among aerobic gram-negative bacilli isolated over a 4-week period in 1979 at six large, geographically separated Canadian hospitals. In the entire series of 4407 isolates the frequency of resistance was 2.5% to amikacin, 8.1% to gentamicin, 5.9% to tobramycin and 1.7% to all three. Most (81%) of the resistant bacteria were acquired by the patients after admission to hospital. The frequency of resistance to the three aminoglycoside antibiotics in each hospital largely reflected the local rate of cross-infection by endemic strains of resistant bacteria.     

Conjugation transfer of plasmid resistance to gentamycin and other antibiotics in clinical strains of Ps. aeruginosa]

A possibility of conjugation transfer of the markers of the plasmid resistance to gentamicin and other antibiotics from 10 clinical strains of Ps. aeruginosa, isolated from burn patients to the recipient strain of Ps. aeruginosa PTO 629 Rfr was shown. The marker of gentamicin resistance was transferred to 100 out of 110 of the exconjugants, i.e. 86.2 per cent. The rate of the conjugation transfer in the crosses between the clincal strains of Ps. aeruginosa and the recipient strain PTO 629 Rfr with respect to the gentamicin marker was about 10--7. The plasmid resistance markers in the clincal strains Ps. aeruginosa were transferred in various combinations. Transfer of the markers of resistance to streptomycin, carbenicillin, neomycin and combinations Sm, Nm and Sm, Nm, Cm was not achieved.     

Characteristics ofPseudomonas aeruginosa strains isolated from urinary tract infections

Thirty-three uropathogenic strains ofPseudomonas aeruginosa were investigated for hemolytic activity in both bacterial broth culture filtrates and isolate lyzates, resistance to bactericidal activity of fresh human serum, resistance to six antibiotics and plasmid DNA profile. Twenty-four of the 33 (73%) bacterial filtrates showed lysis of rabbit erythrocytes, as did the three after guinea-pig erythrocyte treatment. Twelve of 33 isolate lysates showed in parallel lysis of both types of erythrocytes used. Serum resistance was found in 17 (52%) isolates, intermediate resistance in 15 (45%) isolates and only one isolate showed serum sensitivity. Resistance to antibiotics was detected as follows (in %): tetracycline 94, kanamycin 79, chloramphenicol 76, septrin 73, ampicillin 64, streptomycin 45, gentamicin 18. None of the isolates investigated showed resistance to colistine. With the exception of one isolate, plasmid DNA was detected in allP. aeruginosa strains.