["In vitro" determination of bacterial sensitivity to tobramycin (author's transl)]

The authors report the tobramycin minimal inhibitory concentration (MIC) of 264 strains (dilution in Mueller-Hinton agar). Staphylococcus aureus (96 strains) have a MIC of 0.02 mcg/ml, 80 % being inhibited by 0.07 mcg/ml. Most Enterobacteriaceae (70 strains) are sensitive to 0.7 mcg/ml ; Providencia are the most resistant (MIC 11.88 mcg/ml). Among Pseudomonas aeruginosa (98 strains, MIC : 11.57 mcg/ml) 50 % are inhibited by 0.30 mcg/ml, 80 % by 18.8 mcg/ml. Relationships of MIC to zone diameters with the use of 10 mcg (D 10) and 30 mcg (D 30) tobramycin discs allow to draw the regression line which is respectively : y = -- 0,331 x + 6,64 and y = -- 0.263 x + 7,68. The strains are sensitive with an inhibition diameter greater than or equal to 16 mm (D 10) or greater than or equal to 18.5 mm (D 30).

Tobramycin: a review of its antibacterial and pharmacokinetic properties and therapeutic use

SYNOPSIS

Tobramycin is a new aminoglycoside antibiotic with a broad antibacterial spectrum in vitro, and pharmacokinetic properties similar to those for gentamicin. Tobramycin is more active than gentamicin against Pseudomonas aeruginosa and active against many gentamicin resistant strains, but is not active against enterobacteriaceae resistant to gentamicin. Theoretically, tobramycin has an advantage over gentamicin against infections caused by P. aeruginosa, but any advantage in clinical practice has yet to be adequately demonstrated. Clinical experience with tobramycin is considerably less than with gentamicin. Whilst tobramycin appears to offer no clear advantages over gentamicin against sensitive organisms it is indicated in infection caused by strains of P. aeruginosa which are resistant to gentamicin, but sensitive to tobramycin. Like gentamicin, tobramycin acts synergistically with corbenicillin and the cephalosporins. The efficacy of the tobramycin-carbenicillin combination has been shown in endocarditis caused by P. aeruginosa which was unresponsive to gentamicin plus carbenicillin. Ototoxicity and nephrotoxicity similar to that seen with other animoglycosides have been encountered in therapeutic trials with tobramycin and wider clinical experience is necessary to determine the relative incidence of these side-effects with gentamicin and tobramycin used under similar conditions. Antimicrobial activity: In comparative studies, in vitro, tobramycin is more active than gentamicin against clinical isolates of Pseudomonas aeruginosa. Similarly, the inhibitory index, which is the ratio between the serum concentration attained at usual therapuetic doses and the minimum inhibitory concentration, for Pseudomonas aeruginosa is higher for tobramycin than for gentamicin. Against Gram-negative bacteria other than Pseudomonas spp. the spectrum of activity of tobramycin is similar to that of gentamicin. For most species the activity of tobramycin is slightly less than that of gentamicin. Gentamicin is consistently more active than tobramycin against Serratia marcescens. Like other aminoglycoside antibiotics, tobramycin is active in vitro in low concentrations against Staphylococcus aureus. Tobramycin is essentially inactive against Streptococcus pyogenes, Streptococcus faecalis and Streptococcus pneumoniae (pneumococci). Maner aminoglycosides and of other antibiotics against various bacteria in vitro, but comparisons between studies cannot always be interpreted literally because the activity of many antibiotics in vitro, including tobramycin, is influenced by the nature of the culture media and the presence of certain salts. The sensitivity of P. aeruginosa to tobramycin is influenced by the magnesium, and calcium content of the culture media whilst that of all species is reduced by sodium ions. Wide variations in the concentration of these ions may result in divergent MIC values and an inappropriate choice of antibacterial agent to treat pseudomonas infection...

Characterization of a nosocomially significant, multiple drug-resistant strain of Serratia marcescens

A multiple drug-resistant strain of Serratia marcescens (bacteriocin type 18) was isolated from three clinical patients. The isolates were found to carry a conjugally nontransferable, nonmobilizeable resistance plasmid (R-plasmid) with resistance-(r)-determinants against ten antimicrobial drugs: ampicillin, carbenicillin, chloramphenicol, gentamicin, kanamycin, neomycin, streptomycin, tobramycin, triple sulfonamides, cotrimoxazole, and--possibly--nalidixic acid, as determined with exposure to 'curing' agents (ethidium bromide, acridine orange, and sodium dodecyl sulfate) and by the high rate of spontaneous loss of r-determinants. Dyebuoyant density centrifugation allowed recovery of R-plasmid DNA that measured roughly 24 mum in contour length; after 'curing' with concomitant loss of 9 r-determinants, the contour length of the R-plasmid DNA of one isolate (No. SE 154) had decreased to roughly 15 mum, and none was detected in the sole variant of the isolate that spontaneously had lost 11 r-determinants.

Nebcin in the treatment of experimental Pseudomonas keratitis

When the ocular toxicity and the in vivo and in vitro effects of gentamicin, Nebcin, and saline solution were compared in experimentally induced Pseudomonas keratitis in rabbits, both antibiotics showed the same toxicity for the rabbits' conjunctival tissues. But Nebcin showed better in vitro and in vivo results than gentamicin, and the clinical effect was confirmed by culture study: significant numbers of organisms were recovered from the corneas of the gentamicin-treated rabbits but none from the corneas of the Nebcin-treated rabbits.

Neuromuscular blocking properties of some antibiotics in man

Neuromuscular blocking properties of ribostamycin (1 gm), dibecacin (100 mg) and tobramycin (60 mg) were studied in a man during anesthesia and surgery by observing the effects of these antibiotics on muscle twitch tension. These drugs alone did not show any neuromuscular blocking action in those therapeutic doses. However, during the recovery phase of d-tubocurarine block the intravenous administration of 1 gm of ribostamycin caused a fairly rapid decrease in twitch tension. Tobramycin 60 mg did not show any remarkable effect, but dibecacin 100 mg produced a slight potentiating effect on the action of d-tubocurarine. The enhancement of the action of d-tubocurarine was antagonized promptly by edrophonium and more slowly by calcium.

[Some data from studying and using aminoglycoside antibiotics in reconstructive surgery]

Effectiveness of antibacterial drugs from the group of aminoglycoside antibiotics,i.e. kanamycin, gentamycin and tobramycin with respect to the main causative agents of surgical infections, i.e. Staphylococcus, Coli bacteria, Proteus and Ps. aeruginosa was shown. The highest activity against Ps. aeruginosa was registered to tobramycin. The aminoglycoside antibiotics were satisfactorily absorbed after their intramuscular administration providing therapeutic levels of the antibiotics in the blood. For instance, administration of gentamycin in a dose of 80 mg and tobramycin in a dose of 50 mg 1-2 times a day provided the blood levels higher than the minimun inhibitory concentrations for most strains of gramnegative flora including Ps. aeruginosa. The use of the above drugs in theraphy and prophylaxis of infections caused by Ps. aeruginosa is expedient.

[Bacteriological studies on the therapy of bacillus pyocyaneus infections]

The effect of combined antibiotics was studied in 25 strains of Pseudomonas aeruginosa by serial diluting tests. A synergistic effect was stated in 15 strains with oxacillin plus ampicillin, and in 7 strains with carbenicillin plus ampicillin. In these examinations, the quantities of antibiotics needed each time were within the highest admissible level of therapuetic concentrations. A constant rate of the optimum single concentrations could not be observed. On principle, the inhibitory tobramycin concentrations (0.06 - 1 gamma/ml) were lower than the corresponding concentrations of gentamycin (0.25 - 2gamma/ml); tobramycin was more effective than gentamycin also in 6 strains resistant to carbenicillin, tobramycin only had a synergistic effect - in five of these six strains - when very high ampicillin concentrations (i.e. 250-500 gamma/ml) were used.

Susceptibility of Pseudomonas aeruginosa to tobramycin or gentamicin alone and combined with carbenicillin

To explore more effective therapy for Pseudomonas aeruginosa, 264 recent clinical isolates were tested by agar dilution using gentamicin and tobramycin alone and combined with carbenicillin to seek synergistic effects. Synergism was defined as a fourfold or greater decrease in the minimal inhibitory concentration of each drug in a pair. At a concentration of 3.12 mug/ml, gentamicin inhibited 73% of the strains and tobramycin inhibited 98%. The gentamicin-carbenicillin combination was synergistically active against 57% of the strains, and tobramycin-carbenicillin was active against 46%. The effect did not correlate with either susceptibility or resistance to gentamicin or tobramycin alone. The data suggest that tobramycin or tobramycin plus carbenicillin may provide alternate therapy where susceptibility to gentamicin or synergism between gentamicin and carbenicillin cannot be demonstrated; however, the degree of susceptibility to either aminoglycoside antibiotic alone cannot be used to predict a synergistic effect.

[Comparison of the antibacterial activity of amikacin (BB-K8) with other aminoglycosides against pathogens recently isolated from clinical materials (author's transl) ]

We determined the antibacterial activity of amikacin against 1,277 strains of pathogenic bacteria isolated from clinical materials during 1974, including beta hemolytic streptococci, pneumococci, enterococci, Staphylococcus aureus, Staph. epidermidis, Escherichia coli, Klebsiella, Enterobacter, Citrobacter, Serratia, Proteus morganii and Pseudomonas aeruginosa, and compared the minimum inhibitory concentration (MIC) of this drug with gentamicin, dibekacin, tobramycin and kanamycin. 1)Antibacterial activity of amikacin against beta hemolytic streptococci, pneumococci and enterococci was as weak as the other four aminoglycosides, but against Staph. aureus, Staph. epidermidis, various groups of Enterobacteriaceae and Pseudomonas aeruginosa showed amikacin the good antibacterial activity as gentamicin, dibedacin and tobramycin, and also showed the good activity against kanamycin resistant strains. 2) Amikacin has the similar antibacterial spectrum as gentamicin, dibekacin or tobramycin, but its antibacterial activity is generally weakest among these four drugs. 3) On many strains tested the cross resistance is observed between amikacin and one of gentamicin, dibekacin and tobramycin, but several strains of Proteus morganii and Pseudomonas aeruginosa which have rather large MIC against gentamicin, dibekacin or tobramycin showed rather small MIC against amikacin.

Comparative activity of tobramycin and gentamicin against Pseudomonas, Proteus and Providencia species

Tobramycin is a new antibiotic resembling gentamicin. We measured the minimal inhibitory concentrations of these two antibiotics against five bacterial species that cause hospital-acquired infections and are resistant to many presently available antibiotics. The organisms tested were 500 strains of Pseudomones aeruginosa, 100 strains of each of Proteus rettgeri and Pr. morganii, 50 strains of Pr. vulgaris and 250 strains of Providencia stuartii. Tobramycin was 2 to 4 times more active than gentamicin against Ps. aeruginosa; all except 6 of 70 strains resistant to 4 mug/ml of gentamicin were sensitive to 4 mug/ml of tobramycin. The two antibiotics showed a similar degree of activity against the other four species. Tobramycin promises to be of particular value in the treatment of Pseudomonas infections.

Therapy of Pseudomonas aeruginosa infections with tobramycin

The efficacy of tobramycin in doses of 2.7 to 5.6 mg/kg per day in 29 courses of therapy in 25 hospitalized patients with serious Pseudomonas aeruginosa infections was studied. Eighty-three percent of the P. aeruginosa strains showed zones of inhibition of 16 mm or more around a 10-mug tobramycin disk in the Bauer-Kirby disk method. Tobramycin minimal inhibitory concentration ranged from <0.05 to 1.5 mug/ml (microtiter twofold dilution method); for gentamicin they ranged from 0.05 to 6.2 mug/ml; corresponding geometric means were 0.19 and 0.49 mug/ml. Therapy was given for a median of 10 days (mean 19, range 1 to 83). The clinically satisfactory response rate for the 29 courses of therapy was 52%: critically ill, 44%; seriously ill, 50%; moderately ill, 80%. The response rates for various sites of infection were bone and cartilage, 100%; urinary tract infection, 56%; wound, 50%; respiratory tract, 67%; septicemia, 40%; abscess, 0%; burns, 44%. No adverse reactions were seen. Serum concentration (mug/ml +/- standard deviation) of tobramycin determined by an agar-well plate method, were 4.81 +/- 2.17 (1 h); 3.24 +/- 1.43 (2 h); 2.35 +/- 1.30 (4 h); and 1.40 +/- 1.09 (8 h). Tobramycin appears to be as effacacious as gentamicin in the treatment of serious P. aeruginosa infections and has a theoretical advantage of lower minimal inhibitory concentration for P. aeruginosa. The data suggest that, for life-threatening infections, dosages of tobramycin may need to be increased over those used in this study.

Infection caused by Proteus mirabilis strains with transferrable gentamicin-resistance factors

During a period of 10 weeks, four patients in one hospital became infected with gentamicin-resistant Proteus mirabilis. In two of them septicaemia associated with indwelling catheters developed, one had urinary tract and wound infections, and in the fourth patient the organism was isolated from a superficial wound. The P. mirabilis strains showed multiple drug resistance. Strains form the first three patients were apparently identical and were sensitive to tobramycin. Their gentamicin resistance was not transferable to Escherichia coli K12, but could be transferred to another strain of P. mirablilis (PM13-3). The fourth strain was resistant to tobramycin; its gentamicin/tobramycin resistance was transferable to E. coli K12.

The diagnostic value of enzymuria, cell excretion, and proteinuria in experimental renal diseases

Enzymuria, urinary cell excretion and proteinuria were simultaneously determined in renal diseases of female Wistar rats in order to investigate the diagnostic value of urinary enzymes. Investigations were carried out on rats with E. coli-pyelonephritis facilitated by oestradiolundecylate, aminonucleoside nephrosis, aminoglycoside induced renal lesions and pyelonephritic animals treated with therapeutic and toxic doses of tobramycin. --From the results of these studies it was concluded that the main diagnostic value of urinary enzymes is detection of drug induced tubular lesions in individuals with preexisting renal diseases.

Treatment of surgical infections with tobramcin

A survey of the safety and effectiveness of tobramycin, a newly developed aminoglycoside antibiotic, was assessed in 116 septic surgical patients. For comparison, the final 52 cases were randomized with 51 similarly infected patients who were treated with gentamicin. The two antibiotics gave equally good results when evaluated bacteriologically and clinically. Nevertheless, gram-negative infections appeared more likely to be susceptible to tobramycin than to gentamicin. No toxicity to the liver or bone marrow was observed. Although there were 13 cases of nephrotoxicity and 4 of ototoxicity, only one instance of such an adverse drug reaction could be attributed to parenterally administered aminoglycoside alone. In fact, topical neomycin and established renal damage caused by prior episodes of shock or dehydration appeared to be significantly more responsible for such adverse effects.

Effectiveness of carbenicillin - aminoglycoside and of cephalothin-aminoglycoside combinations against enterococci in vitro

Combination of carbenicillin and cephalothin with various aminoglycosides (gentamicin, sisomicin, tobramycin, kanamycin and amikacin) were studied in vitro using 20 strains of enterococci isolated from clinical material. The addition of the aminoglycosides to carbenicillin increased the rate of bactericidal action of carbenicillin on most strains. Little benefit was obtained by adding the aminoglycosides to cephalothin and antagonistic action has been observed on some strains.

Antibiotic sensitivity of two Aeromonas and nine Pseudomonas species

An agar dilution method was used to determine the in vitro sensitivity of different Pseudomonas and Aeromonas species to sulphonamide, tetracycline, colistin, gentamicin, tobramycin, amplicillin, carbenicillin, and cephalothin. P. aeruginosa was generally sensitive to carbenicillin, colistin, tobramycin, and gentamicin. P. putida and P. fluorescens were generally resistant to beta-lactam antibodies but sensitive to gentamicin and tobramycin. P. cepacia and P. maltophilia were mostly resistant to colistin, gentamicin and tobramycin. Other Pseudomonas species were usually more sensitive to the antibodies tested. Strains of Aeromonas hydrophila were mostly resistant to beta-lactam antibiotics but sensitive to other antibiotics, while strains of A. shigelloides were very sensitive to all antibiotics tested.

Apparent antagonism by a resident R plasmid for entry of related gentamicin-tobramycin resistance plasmids in Pseudomonas aeruginosa

From altogether 17 strains of Pseudomonas aeruginosa resistant to gentamicin, isolated in January 1975, 4 have been found to transfer their resistance to gentamicin and tobramycin, along with the resistance to other aminoglycosides, to rifampicin-resistant recipient strains of the same species. In some instances the transfer was strain-specific and therefore it was advisable to use more divergent recipient strains. It was found that a variant of a recipient strain (ML-4258) which already carries an R plasmid (found in the same area in 1972), accepted the Gm-R To-R plasmids with much lower frequencies than the original plasmid-free recipient. From this it may be concluded that R plasmids in P. aeruginosa from the Frankfurt area did not undergo significant genetic alterations within 3 years and thus they might be regarded as phylogenetically related.

In vitro bacteriological study of a new antibiotic substance: sisomicin

Effects of a new antimicrobial agent sisomicin on microorganisms isolated from pathologic material (Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Klebsiella pneumoniae, Salmonella spp., Streptococcus pyogenes-B, Citrobacter Freundii) were studied. The results obtained were compared with another two aminoglycoside antibiotics - gentamicin and tobramycin. All three antibiotics were found to be very effective in vitro; their effect was enhanced by addition of an antibiotic of the penicillin group (carbenicillin, suncillin) or an antibiotic of the tetracyklin series (oxytetracyklin, doxycyklin). All three preparations were tested on 26 Mycobacterium tuberculosis strains. Tobramycin inhibited growth of 22 strains and thus presented the highest level of efficiency among these deoxystreptamin preparations.

Antibacterial activity of tobramycin against gram-negative bacteria and the combination of ampicillin/tobramycin against E. coli

The antibacterial activity of tobramycin, gentamicin, erythromycin, cloxacillin, kanamycin, cephalexin, penicillin, carbenicillin and polymyxin were compared against 303 clinical bacterial isolates from a pediatric hospital patient population. Standard disk diffusion and agar-dilution methods were employed. Significant activity was demonstrated for tobramycin against pseudomonas, Klebsiella, Escherichia coli and both Staphylococcus aureus and albus; Tobramycin was significantly more active against Pseudomonas than gentamicin or the other antibiotics testedmcomparable activity to gentamicin was present for the other types of bacteria; Cross-resistance was not encountered between tobramycin and gentamicin. 30 isolates of E. coli were tested against the combination of tobramycin and ampicillin by the growth-curve method. Synergism was demonstrated in 4 isolates, antagonism in 1 and an additive effect in 25. A bactericidal effect was present at 24h against 17 isolates with tobramycin alone and against 25 isolates when combined with ampicillin. These results provide in vitro rationale for the consideration of tobramycin for clinical use in patients with Psuedomonas infections for the combination of ampicillin and tobramycin for the treatment of selected E.coli infections.

Transferrable resistance to tobramycin in Klebsiella pneumoniae and Enterobacter cloacae associated with enzymatic acetylation of tobramycin

Among gram-negative bacilli isolated from burn wound cultures, some strains of Enterobacteriaceae were resistant to tobramycin (minimal inhibitory concentration [MIC]>/= 20 mug/ml) but susceptible to gentamicin (MIC </= 5 mug/ml). One Klebsiella pneumoniae and two Enterobacter cloacae strains were selected for studies on their mechanisms of resistance to aminoglycoside antibiotics. Resistance to high concentrations of tobramycin (MICs of 25 to 50 mug/ml) was conjugally transferred to a susceptible Escherichia coli strain at rates of 1.2 x 10(-4) to 2.8 to 10(-4) per donor cell, suggesting that resistance is controlled by R factors. Resistances to tobramycin, kanamycin, and neomycin were cotransferred. Enzymatic activities were present that acetylated tobramycin, gentamicin, and kanamycin in osmotic lysates from the donor and transcipient strains. Enzymatic adenylylation of these aminoglycosides was not observed. The aminoglycoside-acetylating activities from K. pneumoniae and E. cloacae resembled kanamycin acetyltransferase (KAT) in their specificity for aminoglycoside substrates. Not all isolates of bacteria that produce KAT are resistant to tobramycin, but the factors that determine susceptibility or resistance to tobramycin in KAT-producing bacteria have not yet been established.

Comparative activity of tobramycin, amikacin, and gentamicin alone and with carbenicillin against Pseudomonas aeruginosa

The effect of gentamicin against 130 clinical isolates of Pseudomonas aeruginosa was compared with that of two investigational aminoglycoside antibiotics, tobramycin and amikacin. Minimal inhibitory concentration data indicated that, on a weight basis, tobramycin was two to four times as active as gentamicin against most isolates. However, 14 of 18 organisms highly resistant to gentamicin (>/=80 mug/ml) were also highly resistant to tobramycin. Amikacin was the least active aminoglycoside on a weight basis, but none of the isolates were highly resistant to this antibiotic. When therapeutically achievable concentrations were used, adding carbenicillin to gentamicin or to tobramycin enhanced inhibitory activity against those isolates susceptible (</=5 mug/ml) or moderately resistant (10 to 40 mug/ml) to the aminoglycoside. Such synergy was seldom demonstrated for isolates highly resistant to gentamicin or tobramycin. The combination of carbenicillin and amikacin enhanced inhibition against all but two of the isolates. Both tobramycin and amikacin offer in vitro advantages over gentamicin against P. aeruginosa.

Antagonistic effect of calcium in serum on the activity of tobramycin against Pseudomonas

Physiological concentrations of calcium in serum antagonize the activities of colistin, polymyxin B, and gentamicin against Pseudomonas aeruginosa. Studies were carried out to determine whether tobramycin, a new aminoglycoside antibiotic, is also antagonized by calcium. The activity of tobramycin in vitro was shown to be antagonized by human serum and by physiological concentrations of calcium. The addition of human serum in broth-dilution tests produced a fourfold rise in the minimal inhibitory concentrations of tobramycin for five strains of Pseudomonas. In disc diffusion tests, the addition of calcium to the agar significantly decreased the size of inhibition zones, and the addition of a chelating agent to the agar increased the zone sizes. In a limited comparative study, tobramycin and gentamicin were tested against both light and heavy bacterial inocula of two strains of Pseudomonas. Tobramycin appeared to be antagonized less by serum than was gentamicin at equal antibiotic concentrations.