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.     

Tartrazine-containing drugs

Tobramycin, an aminoglycoside antibiotic, was used to treat 52 infections due to gram-negative organisms in 51 patients. Complicated urinary tract infections, bacteremia and pyelonephritis accounted for 80% of the infections. The rate of immediate satisfactory response was 79%. During therapy with tobramycin, resistant organisms emerged in four patients--two Pseudomonas aeruginosa and two Escherichia coli strains. There were four superinfections with tobramycin-resistant Providencia sp. In four seriously ill patients the serum creatinine concentration increased 1 mg/dL or more; in three the increase was transient. No auditory toxicity was noted in the 19 patients in whom serial audiograms were made. In vitro testing of isolates from these patients showed that tobramycin and gentamicin had equal activity against Enterobacteriaceae. Tobramycin was two to four times more active against susceptible P. aeruginosa.     

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.     

Semisynthetic Penicillin 6-[d(—)-α-Carboxy-3-Thienylacetamido] Penicillanic Acid Active Against Pseudomonas In Vitro

The activity of 6-[d(-)-alpha-carboxy-3-thienylacetamido] penicillanic acid, BRL2288, was determined against Pseudomonas aeruginosa and various gram-negative bacilli. The majority of Pseudomonas strains (89%) were inhibited by 100 mug of the antibiotic per ml. BRL2288 is twofold more active than carbenicillin against Pseudomonas at 100 mug/ml or less. Among Enterobacteriaceae tested, 87% Enterobacter and 87% of Proteus mirabilis strains were inhibited by 25 mug/ml or less. Indole-positive Proteus were inhibited by 10 mug/ml or less. Fifty-five per cent of ampicillin-resistant Escherichia coli were inhibited by 100 mug/ml. Klebsiella were uniformly resistant. BRL2288 is not hydrolyzed by most resistant Pseudomonas, but it is destroyed by the beta-lactamases of E. coli and P. mirabilis. The antibiotic shows synergy with gentamicin but not with penicillinase-resistant penicillins such as cloxacillin. Activity of BRL2288 against gram-positive organisms is two- to eightfold less than that of ampicillin or benzylpenicillin G.     

Optimal Combination and Concentration of Antibiotics in Media for Isolation of Pathogenic Fungi and Nocardia asteroides

Strains of Blastomyces dermatitidis, Sporothrix schenckii, Histoplasma capsulatum, Cryptococcus neoformans, Nocardia asteroides, and Coccidioides immitis were tested for in vitro susceptibility to polymyxin, gentamicin, kanamycin, chloramphenicol, and neomycin at concentrations of 1, 2, 4, 8, and 16 mug/ml. Polymyxin was the most inhibitory and gentamicin was the least inhibitory of the five antibiotics. Two Histoplasma mycelial strains were partially inhibited by 2 and 8 mug of gentamicin per ml and showed at least a 2+ growth at the higher antibiotic concentration. Kanamycin and neomycin produced significant inhibition of N. asteroides but otherwise were noninhibitory. A combination of chloramphenicol and kanamycin, each at 16 mug/ml, and gentamicin, at 4 mug/ml, was noninhibitory to the strains tested except for N. asteroides. Chloramphenicol at 16 mug/ml was not inhibitory for N. asteroides. The results suggest that the optimal antibiotic combination to use in the isolation of fungi and higher bacteria is chloramphenicol, 16 mug/ml, and gentamicin, 4 mug/ml. Addition of sheep blood (5%) had no effect on antibiotic susceptibility of the organisms studied.     

Susceptibility of Pseudomonas aeruginosa to Gentamicin Sulfate In Vitro: Lack of Correlation Between Disc Diffusion and Broth Dilution Sensitivity Data

Seventy-eight of 420 clinical isolates of Pseudomonas aeruginosa yielded zones of inhibition of less than 12 mm in diameter around 10-mug discs of gentamicin sulfate when tested by the standardized Bauer-Kirby disc diffusion method. Of 153 strains chosen from these isolates, one strain (0.65%) required 25 mug of gentamicin per ml for inhibition; the remainder (99.35%) were inhibited by 6 mug/ml or less of the antibiotic. It is recommended that those isolates of P. aeruginosa that yield zones of inhibition less than 12 mm in diameter be disc susceptibility-tested once more; those isolates that give zones of inhibition of less than 12 mm upon repeated examination should then be subjected to the broth dilution test before they are designated as sensitive or resistant to gentamicin.     

Susceptibility of antibiotic-resistant gram-negative bacteria to biocides: a perspective from the study of catheter biofilms

Bacteria resistant to both the agents deployed to prevent infections and those used to treat infections would be formidable nosocomial pathogens. The aim of this paper is to review the evidence that gram-negative bacteria resistant to antibiotics and biocides have emerged and been responsible for catheter-associated urinary tract infection. A study of patients undergoing intermittent bladder catheterization revealed that the frequent application of the antiseptic chlorhexidine to the perineal skin prior to the insertion of the catheter was effective against the normal gram-positive skin flora but not against the gram-negative organisms that subsequently colonized this site. Organisms such as Providencia stuartii, Pseudomonas aeruginosa and Proteus mirabilis were repeatedly isolated from the skin of these patients and inevitably went on to cause urinary infections. The minimum inhibitory concentration (MIC) of chlorhexidine for many of these strains proved to be 200-800 microg ml(-1) compared with the 10-50 microg ml(-1) recorded for reference strains of gram-negative species. A subsequent survey of over 800 gram-negative isolates from urinary tract infections in patients from both hospitals and the community revealed that chlorhexidine resistance was not a widespread phenomenon, but was restricted to these species and to units where the care of catheterized patients involved the extensive use of chlorhexidine. Analysis of the antibiotic resistance patterns revealed that the chlorhexidine-resistant strains were also multidrug resistant. Other clinical studies also reported catheter-associated infections with chlorhexidine- and multidrug-resistant strains of Pr. mirabilis when chlorhexidine was being used extensively. This species poses particular problems to the catheterized patient. Chlorhexidine thus proved counterproductive in the care of catheters and its use in this context has been largely abandoned. Suggestions of reintroducing this agent in the form of biocide-impregnated catheters should be resisted.     

Time-kill study and synergistic activity of cell-wall inhibitor antibiotics in combination with gentamicin against Enterococcus faecalis and Enterococcus faecium

The synergy between gentamicin and vancomycin, teicoplanin, ampicillin and linezolid was studied by time-kill method. Two clinical vancomycin resistant enterococci (VRE) and two vancomycin susceptible enterococci (VSE) isolates were used. Different concentrations of antibiotics were combined. Two VSE strains and the control strain exhibited synergism with the combination of gentamicin, vancomycin, teicoplanin, ampicillin and linezolid. Two VRE strains exhibited synergism with the combination of gentamicin and ampicillin. Synergy between gentamicin and vancomycin, teicoplanin and linezolid was not observed against these isolates. The VRE isolates were positive for vanA, aac (6')-Ie aph (2") and aph (3')-IIIa genes and their vancomycin, teicoplanin and gentamicin MICs were 512 μg/ml, 512 μg/ml and >4000 μg/ml, respectively. In order to treat serious enterococcal infections, further clinical evaluation is needed to examine the in vitro combined effects of gentamicin and vancomycin, teicoplanin and linezolid.     

In vitro activity of cefamandole, cefoxitin, cefuroxime, and carbenicillin, alone and in combination with aminoglycosides against Serratia marcescens.

Synergistic antibiotic studies were undertaken to compare the effectiveness of two new beta-lactamase resistant cephalosporins, cefamandole, and carbenicillin, with four aminoglycosides against clinical strains of Serratia marcescens. The strains demonstrated various combinations of resistance and/or susceptibility to the antibiotics tested. Tobramycin was the most effective aminoglycoside when used in combination with beta-lactam antibiotics. Carbenicillin and cefamandole demonstrated similar activity with aminoglycosides in synergy experiments. Tobramycin-carbenicillin was found to be the superior pairs as indicated by the total number of strains inhibited. This combination was the only one effective against certain high drug resistant strains and the strain resistant to all four aminoglycosides. Carbenicillin or cefamandole with tobramycin exhibited comparable activity against multiple drug resistant organisms. However, mutants significantly more resistant to cefamandole developed during susceptibility testing. The findings of this study have clinical relevance for treating infections by this formidable pathogen.     

Gentamycin activity in combination with etonium in relation to Pseudomonas aeruginosa]

Gentamicin is one of the most effective drugs for treatment of infections caused by Ps. aeruginosa. However, isolation of the strains resistant to the antibiotics was not infrequent. It was shown in the experiments with 40 cultures that the activity of gentamicin against Ps. aeruginosa increased approximately 20 times when it was used in combination with ethonium, a derivative of bis-quaternary ammonium compounds.     

Antibiotic sensitivity of Proteus, Pseudomonas pyocyanea and staphyloccoci isolated from scleroma and ozena patients]

Antibiotic sensitivity of 292 strains of Proteus, 60 strains of Ps, aeruginosa, 309 strains of S. aureus and 88 strains of S. epidermidis isolated from the upper respiratory tract of patients with scleroma and ozena was studied. The cultures of Pr. mirabilis were sensitive to aminoglucosides (54.9-96.2 per cent) and Pr. morganii were sensitive to levomycetin (81.5 per cent) and neomycin (92.6 per cnet). Sensitivity of Pr. vulgaris and Pr. morganii was reliably higher (p less than 0.001) than that of Pr. mirabilis. The strains of Pr. morganii were less sensitive to monomycin (P less than 0.001) and streptomycin (p less than 0.01) as compared to the cultures of other Proteus species tested. The strains of Ps. aeruginosa were sensitive only to gentamicin (90 per cent) and neomycin (81.1 per cent). Most of the strains of S. aureus (85.4-100 per cent) were sensitive to oleadomycin, erythromycin, olemorphocycline, tetraolean, oxacillin, methicillin ceporin, lincomycin, ristomycin, kanamycin, monomycin and gentamicin. Benzylpenicillin (90.8 per cent of the sensitive strains), ampicillin (67.1 per cent), tetracycline (66.7 per cent), levomycetin (68.6 per cent) and streptomycin (38.1 per cent) were less effective. Antibacterial therapy in cases with scleroma and ozena should be directed not only against causative agents of the diseases but also against the microbes developing due to disbacteriosis. Combination of parenteral and local use of the antibiotics in the treatment of chronic clebsiellesis decreased the isolation rate of Proteus and Ps. aeruginosa in the patients.     

Resistance of Pseudomonas to Quaternary Ammonium Compounds: II. Cross-Resistance Characteristics of a Mutant of Pseudomonas aeruginosa

Tube dilution experiments showed that benzalkonium chloride (BC)-resistant mutants of Pseudomonas aeruginosa grown in the presence of 1,000 mug of BC per ml were at least 20 times more sensitive to polymyxin B and colistin sulfate than the BC-sensitive (BCS) parent strain. BCS cells selected for resistance to 500 mug of polymyxin B per ml remained sensitive to BC. There was little difference in the amount of carbenicillin, gentamicin sulfate, or rifampin needed to prevent growth of either the BCS or BC-resistant (BCR) strains. Growth of BCR cells was inhibited by ethylenediaminetetraacetate at a concentration of 400 mug/ml or less, whereas the BCS strain grew at ethylenediaminetetraacetate levels of 10,000 mug/ml. Phenylmercuric acetate and thimerosal inhibited growth of BCR and BCS cells at concentrations of 10 mug/ml or less. BCR cells were cross-resistant to >1,000 mug/ml concentrations of five other quaternary ammonium compounds, including three with C(16) alkyls and two with alkyl groups of shorter length. The BCS strain was also resistant to >1,000 mug/ml concentrations of the three quaternary ammonium compounds with C(16) alkyl groups but, in addition to BC, was inhibited by 200 mug/ml levels or less of the two quaternary ammonium compounds containing alkyl groups of less than 16 carbon atoms.     

Antibiotic sensitivity of the causative agents of suppurative surgical infection]

Sensitivity of 1492 strains of the causative agents of the surgical purulent infections, i. e. pathogenic Staphylococcus, Proteus, Ps. aeruginosa and E. coli to benzylpenicillin, streptomycin, levomycetin, tetracycline, erythromycin, oleandomycin, monomycin, kanamycin, novobiocin, ampicillin, oxacillin, ceporin, gentamicin and rifampicin was studied. Gentamicin was most active against all the bacterial species tested. The staphylococci were in addition sensitive in a high percentage of the cases to rifampicin, novobiocin, ceporin, monomycin and kanamycin. The isolates of E. coli were in addition sensitive to ceporin, monomycin and kanamycin. Sensitivity of the strains of Ps. aeruginosa and Proteus was low to all of the antibiotics except gentamycin. Most of the strains of the causative agents of the surgical purulent infections were multiresistant to 4 antibiotics. The number of the staphylococcal strains sensitive to benzylpenicillin, streptomycin and levomycetin increased in 1976 as compared to 1975 on the background of a limited use of these antibiotics in clinics.     

Comparative study of the antibacterial activity of a number of new antibiotics and their combinations in relation to Pseudomonas aeruginosa]

Tobramycin and sisomycin proved to have the highest antibacterial activity against 156 clinical strains of Ps. aeruginosa and were 4--8 times more effective than monomycin, kanamycin, neomycin and to a lesser extent gentamicin. The combination of mecillinam and sisomycin had a synergistic effect with respect to 26 out of 50 strains of Ps. aeruginosa and the combination of mecillinam and tobramycin had a synergistic effect on 18 strains. An antagonistic effect was observed with the use of the above combinations in 3 cases. The effect of the combinations depended on sensitivity of Ps. aeruginosa cultures to the aminoglycoside antibiotic included into the compositions.     

Synthetic peptide vaccine and antibody therapeutic development: prevention and treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa and Pseudomonas maltophilia account for 80% of opportunistic infections by pseudomonads. Pseudomonas aeruginosa is an opportunistic pathogen that causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, and a variety of systemic infections, particularly in patients with severe burns, and in cancer and AIDS patients who are immunosuppressed. Pseudomonas aeruginosa is notable for its resistance to antibiotics, and is therefore a particularly dangerous pathogen. Only a few antibiotics are effective against Pseudomonas, including fluoroquinolones, gentamicin, and imipenem, and even these antibiotics are not effective against all strains. The difficulty treating Pseudomonas infections with antibiotics is most dramatically illustrated in cystic fibrosis patients, virtually all of whom eventually become infected with a strain that is so resistant that it cannot be treated. Since antibiotic therapy has proved so ineffective as a treatment, we embarked on a research program to investigate the development of a synthetic peptide consensus sequence vaccine for this pathogen. In this review article we will describe our work over the last 15 years to develop a synthetic peptide consensus sequence anti-adhesin vaccine and a related therapeutic monoclonal antibody (cross-reactive to multiple strains) to be used in the prevention and treatment of P. aeruginosa infections. Further, we describe the identification and isolation of a small peptide structural element found in P. aeruginosa strain K (PAK) bacterial pili, which has been proven to function as a host epithelial cell-surface receptor binding domain. Heterologous peptides are found in the pili of all strains of P. aeruginosa that have been sequenced to date. Several of these peptide sequences have been used in the development of an consensus sequence anti-adhesin vaccine targeted at the prevention of host cell attachment and further for the generation of a monoclonal antibody capable of prevention and treatment of existing infections.     

In Vitro Susceptibility of Pseudomonas aeruginosa to Carbenicillin and the Combination of Carbenicillin and Gentamicin

One hundred and eleven strains of Pseudomonas aeruginosa isolated from clinical material were studied for susceptibility to carbenicillin. Of the strains, 80% were inhibited by 125 mug/ml or more. The combination of carbenicillin and gentamicin was shown to have inhibitory and bactericidal synergistic effect on 15 of 16 strains of P. aeruginosa tested. There was poor correlation between the single-disc sensitivity method and the tube dilution method.     

Antibiotic utilization and Pseudomonas aeruginosa resistance in intensive care units

Pseudomonas aeruginosa is one of the most frequent and dangerous pathogens involved in the etiology of severe nosocomial infections. A retrospective observational study was conducted at all intensive care units of the University Hospital in Olomouc, Czech Republic (155 ICU beds). Complete antibiotic utilization data of the ICUs in the period of 1999 to 2008 were processed according to ATC/DDD system and expressed in defined daily doses per 100 bed-days (DBD). Utilization of meropenem, imipenem, ciprofloxacin, ofloxacin, pefloxacin, gentamicin, amikacin, ceftazidime, cefoperazone, cefoperazone/sulbactam and piperacillin/tazobactam was measured. Pseudomonas aeruginosa strains were isolated from clinical material obtained from patients hospitalized in ICUs. During the ten-year period, utilization of the entire group of antibiotics monitored grew. It increased from 23.52 DBD in 1999 to 27.48 DBD in 2008 with a peak of 33.04 DBD in 2007. P. aeruginosa accounted for as much as 42% of pneumonias and 23% of surgical wound infections. Our results show that P. aeruginosa strains became gradually resistant to all antibiotics used in the treatment of the infections caused by them, with the exception of amikacin and piperacillin/tazobactam.     

Drug susceptibility of Pseudomonas aeruginosa strains isolated from patients of a hospital and specialistic outpatients clinics of the SP ZOZ in Nidzica

The aim of this study was to evaluate a frequency of isolation and antimicrobial susceptibility testing (AST) of Pseudomonas aeruginosa strains cultured from clinical specimens collected from patients hospitalized in wards and specialistic outpatients clinics of a hospital in Nidzica (01. 09. 2000 -31. 12. 2003). During over three years 392 Pseudomonas aeruginosa strains were cultured from 16346 clinical samples provided to bacteriological laboratory. P. aeruginosa strains were isolated from 2.5% of examined specimens. Susceptibility of Pseudomonas aeruginosa strains to antimicrobial agents was tested. The highest in vitro activity against clinical P. aeruginosa strains demonstrated imipenem. One strain was resistant to imipenem. This strain was isolated from a patient of a surgical department. Metalo-beta-lactamase was not detected (MBL-negative strain).Twenty nine strains were ESBL producer (7.4% of all strains). The contribution of Pseudomonas aeruginosa strains to the etiology of nosoconial and ambulatory infections increases. In vitro activity of antibacterial agents against P. aeruginosa strains should be monitored during therapy of infections. Resistance to antibiotics/chemothe-rapeutics may be acquired during treatment with antibacterial agent to which P. aeruginosa strain was susceptible according to the antibiogram.     

Sensitivity of the wound microflora of oncological patients to some new antibiotics]

Sensitivity of the microflora of the oncological patients' wounds to the new antibiotics, such as gentamicin, kanamycin, oxacillin, ampicillin and lincomycin was studied with the help of the disc method. The discs with the above antibiotics were prepared under laboratory conditions in accordance with the respective instructions in the WHO. Sensitivity of 429 bacterial cultures, including 98 cultures of pathogenic staphylocci, 45 cultures of Enterococci, 43 hemolytic streptococci, 143 cultures of Escherichia, 50 cultures of Ps. aeruginosa and 50 cultures of Proteus was determined. The studies showed that gentamicin was the most active antibiotic aganist all the microbial species isolated from the surgical and other wounds of oncological patients. It may be used in treatment of the infections caused by association of the microbes belonging to different species, as well as in treatment of purulent processes before elucidating their etiology, 16.7 per cent of the Enterococcal isolates were resistant to gentamicin. Monomycin, kanamycin, oxacillin, lincomycin and macrolide antibiotics at present are sufficiently active against pathogenic staphylococci and hemolytic streptococci.     

Aminoglycoside resistance rates, phenotypes, and mechanisms of Gram-negative bacteria from infected patients in upper Egypt

With the re-emergence of older antibiotics as valuable choices for treatment of serious infections, we studied the aminoglycoside resistance of Gram-negative bacteria isolated from patients with ear, urinary tract, skin, and gastrointestinal tract infections at Minia university hospital in Egypt. Escherichia coli (mainly from urinary tract and gastrointestinal tract infections) was the most prevalent isolate (28.57%), followed by Pseudomonas aeruginosa (25.7%) (mainly from ear discharge and skin infections). Isolates exhibited maximal resistance against streptomycin (83.4%), and minimal resistance against amikacin (17.7%) and intermediate degrees of resistance against neomycin, kanamycin, gentamicin, and tobramycin. Resistance to older aminoglycosides was higher than newer aminoglycosides. The most common aminoglycoside resistance phenotype was that of streptomycin resistance, present as a single phenotype or in combination, followed by kanamycin-neomycin as determined by interpretative reading. The resistant Pseudomonas aeruginosa strains were capable of producing aminoglycoside-modifying enzymes and using efflux as mechanisms of resistance. Using checkerboard titration method, the most frequently-observed outcome in combinations of aminoglycosides with β-lactams or quinolones was synergism. The most effective combination was amikacin with ciprofloxacin (100% Synergism), whereas the least effective combination was gentamicin with amoxicillin (53.3% Synergistic, 26.7% additive, and 20% indifferent FIC indices). Whereas the studied combinations were additive and indifferent against few of the tested strains, antagonism was never observed. The high resistance rates to aminoglycosides exhibited by Gram-negative bacteria in this study could be attributed to the selective pressure of aminoglycoside usage which could be controlled by successful implementation of infection control measures.