Gentamicin-resistant Serratia marcescens endophthalmitis

In a case of metastatic Gram-negative endophthalmitis caused by Serratia marcescens, the bacterial isolate was resistant to gentamicin sulfate and tobramycin but sensitive to amikacin sulfate, a new semisynthetic aminoglycoside approved for systemic use. The importance of antibiotic-resistant S marcescens as a systemic and ocular pathogen is reviewed.

Microdilution aminoglycoside susceptibility testing of Pseudomonas aeruginosa and Escherichia coli with a cation-supplemented inoculum

The use of cation supplementation in aminoglycoside susceptibility testing of Pseudomonas aeruginosa by microdilution produced MIC agreement (+/- one doubling dilution) with agar dilution testing 89% of the time as compared with 35% of the time with unsupplemented controls.

Gentamicin and tobramycin resistant gram-negative bacilli in a community hospital

The incidence and spectrum of resistance to gentamicin and tobramycin among gram-negative bacilli (GNB) isolated in a community hospital over a one-year period were studied. The overall incidence of resistance was 3.7%. Pseudomonads constituted almost half of the resistant organisms. The majority of resistant GNB was isolated from the respiratory and urinary tracts. Acquisition of resistance was correlated with both the total use of gentamicin in the hospital and recent treatment of individual patients with gentamicin plus tobramycin. The overall incidence of resistant isolates (3.7%) and the incidence of resistance for the enterobacteriaceae (1.9%) were lower than rates reported by comparable studies at several university or municipal hospitals.

Distribution of genes for trimethoprim and gentamicin resistance in bacteria and their plasmids in a general hospital

The incidence of trimethoprim resistance in enterobacteria causing infection in a London hospital increased from 5.6% in 1970 to 16% in 1979. The proportion of gentamicin-resistant aerobic Gram-negative bacilli had risen to 6.5% by 1979. During a 5-month period in 1977, during which no epidemic was recognized, all isolates resistant to either trimethoprim, gentamicin, tobramycin or amikacin were studied. The proportion of enterobacteria resistant to both trimethoprim and gentamicin (3.8% of the total) was significantly higher than expected assuming no correlation between acquisition of resistance characters. The resistance was transferable in 23% of trimethoprim-resistant and 76% of gentamicin-resistant strains. Trimethoprim resistance was carried by plasmids of seven different incompatibility groups and in at least four instances was part of a transposon. Gentamicin resistance was determined by plasmids of three groups - IncC, IncFII and IncW. Transposition of gentamicin resistance was not shown, though this may have been the means of evolution of the gentamicin R plasmids of InW, which determined aminoglycoside acetyltransferase, AAC(3). Some bacterial strains with their plasmids were endemic. There was evidence for these plasmids (i) acquiring new resistance genes by transposition, (ii) losing resistance genes by deletion and (iii) being transferred between bacterial species in the hospital.

Determination of antimicrobial susceptibility of Pseudomonas aeruginosa by disk diffusion and microdilution methods

Disk diffusion susceptibility tests were performed on 180 recent clinical isolates of Pseudomonas aeruginosa. Minimal inhibitory concentration values were determined at the same time by a broth microdilution method. All isolates were sensitive to colistin (< 4 migrogram/ml), but resistant to ampicillin (greater than or equal to 16 microgram/ml), cephalothin (greater than or equal to 64 microgram/ml), and nitrofurantoin (> microgram/ml). More than 90% of the isolates were sensitive to gentamicin (median, less than or equal to 0.25 microgram/ml), tobramycin (median, less than or equal to 0.25 microgram/ml), and amikacin (median, less than or equal to 1.0 microgram/ml) and more than 70% were sensitive to carbenicillin (median, 64 microgram/ml). When the resistant and intermediate categories were combined, over 90% of the isolates were resistant to tetracycline (median 16 microgram/ml), chloramphenicol (median, > 32 microgram/ml), kanamycin (median, 16 microgram/ml), and trimethoprim-sulfonamide combiantion (median, 4 microgram/ml; 76 microgram/ml). Differences between the disk diffusion and microdilution methods in distinguishing resistant isolates of P aeruginosa from sensitive isolates were minor. Complete agreement between the two methods was obtained in 87.0% of the observations.

Immediate effects of intravenous tobramycin and gentamicin on human cochlear function

Immediate electrocochleographic changes have been studied in a series of patients following intravenous infusion of either tobramycin or gentamicin. In patients receiving tobramycin, as soon as peak serum levels of antibiotic were reached, a dramatic decrease occurred in the magnitude of the compound VIII nerve action potential (AP), and of the cochlear microphonic (CM). The shape of the AP also changed. The N1 component of the waveform became very small, and N2 increased in size; this is the dissociated pattern of basal coil cochlear damage. The speed of onset of these electrical changes and their apparent reversibility suggests a temporary metabolic block caused by tobramycin. No such changes were observed following infusion of gentamicin.

Moxalactam (LY127935), a new semisynthetic 1-oxa-beta-lactam antibiotic with remarkable antimicrobial activity: in vitro comparison with cefamandole and tobramycin

Moxalactam (LY127935) exhibited greater in vitro activity than cefamandole and tobramycin against clinical isolates of Enterobacteriaceae, Aeromonas hydrophila, and Pseudomonas maltophilia. The activities of the three drugs against other microorganisms were as follows: for staphylococci, cefamandole = tobramycin greater than moxalactam; for streptococci, cefamandole greater than moxalactam greater than tobramycin; and for Pseudomonas aeruginosa, tobramycin greater than moxalactam greater than cefamandole. Moxalactam also demonstrated significant activity against the Bacteroides fragilis group and other anaerobes. Moxalactam was comparable to cefotaxime (HR756) in its inhibition of cephalothin-resistant and aminoglycoside-resistant clinical isolates.

Activity of cefotaxime-aminoglycoside combinations against aminoglycoside-resistant Pseudomonas

The activity of cefotaxime, either alone or combined with an aminoglycoside, was determined against 50 isolates of Pseudomonas aeruginosa, of which 50, 33, and 10 were resistant to gentamicin, tobramycin, and amikacin, respectively. Cefotaxime inhibited 34 isolates at a concentration of 16 microgram/ml and all isolates at 128 microgram/ml. The combinations of cefotaxime with gentamicin, tobramycin, and amikacin were synergistic against 30, 17, and 9 isolates, respectively, and no antagonism was observed with any combination. Synergism was obtained at clinically significant antibiotic concentrations for nine isolates with cefotaxime-gentamicin, five isolates with cefotaxime-tobramycin, and nine isolates with cefotaxime-amikacin.

Comparison of in vitro activity of moxalactam (LY127935) with cefazolin, amikacin, tobramycin, carbenicillin, piperacillin, and ticarcillin against 420 blood culture isolates

To compare the in vitro activity of moxalactam (LY127935), a new broad-spectrum antimicrobial agent, with cefazolin, amikacin, tobramycin, carbenicillin, piperacillin, and ticarcillin, each drug was tested against 420 bacterial isolates from the blood of septic patients. Standard broth dilution methods were used to determine minimum inhibitory and bactericidal concentrations. LY127935 was as active as the aminoglycosides against aerobic gram-negative organisms, including Pseudomonas aeruginosa, and was at least 10-fold more active than the other beta-lactam agents against these bacteria. LY127935 was the most active agent tested against Bacteroides fragilis; its activity against all other anaerobic bacteria and Staphylococcus aureus was similar to those of the other agents tested. All streptococci, however, grew at higher concentrations of LY127935 than any other drug, and Streptococcus faecalis and Listeria monocytogenes were not inhibited at the highest concentration tested (minimum inhibitory concentration, > 64 microgram/ml). Although a greater proportion of blood culture isolates were susceptible to LY127935 than to any other drug tested, LY127935 does not have a sufficiently broad spectrum of in vitro activity to be recommended safely alone for empirical treatment of sepsis of unknown etiology.

Transduction of amikacin, gentamicin and tobramycin resistance in Pseudomonas aeruginosa

In a series of Pseudomonas aeruginosa strains resistant to gentamicin, tobramycin, amikacin and/or netilmicin (Knothe and Krcméry, 1979), wild-type phage lysates could be prepared and two of them were studied more in detail. Both lysates were shown to mediate transfer of gentamicin, amikacin and carbenicillin resistance by direct selection. In some instances also fertility function (tra) could be demonstrated in transductants by further cycles of transfer. It could be speculated that, once such wild-type phages from resistant or toxinogenic strains are liberated into the hospital environment, they could mediate these and other properties to P. aeruginosa strains in that environment.

Loss of an aminoglycoside resistance plasmid by Serratia marcescens during treatment of meningitis with amikacin

During prophylaxis with gentamicin and amoxicillin following surgical repair of a meningomyelocele in a newborn infant, a cerebrospinal fluid leak occurred and fever ensued. Cultures of ventricular fluid yielded Serratia marcescens resistant to several antibiotics, including gentamicin and tobramycin, but sensitive to amikacin. When therapy with amikacin was substituted for that with gentamicin and amoxicillin, cultures yielded an additional colony type of S. marcescens, which was antibiotic-sensitive but of the same serotype as the original isolate, that eventually replaced the original resistant organism. The resistant S. marcescens was shown to possess a 105 X 10(6)-dalton plasmid not observed in the sensitive variant. The sensitive variant may have originated by loss of the plasmid from the resistant organism, possibly by removal of the selection pressure of antibiotics, which favored the emergence of a bacterial population that did not harbor resistance plasmids during clinical therapy.

Endemic aminoglycoside resistance in gram-negative bacilli: epidemiology and mechanisms

Isolates of gentamicin-resistant gram-negative bacilli from clinical specimens peaked at nine to 10 per month in 1973-1974. Instituting barrier-type precautions during 1974-1977 was associated with a sustained 87% reduction in resistant Enterobacteriaceae. The number of resistant Pseudomonadaceae fell temporarily by 28%, paralleling gentamicin usage. During an endemic 15-month period in 1976-1977 nonenzymatically mediated resistant Pseudomonas aeruginosa often emerged after aminoglycoside therapy in patients who had prior carriage of sensitive strains of the same serotype (P = 0.002); this resistance was associated with wound or sputum isolates (P = 0.003). Resistant Enterobacteriaceae more often demonstrated the converse, that is, spread of urinary tract isolates with enzymatically mediated resistance from patients not on aminoglycoside therapy. These findings suggest that control measures to minimize occurrence of resistant bacilli include barrier-type precautions for patients with resistant Enterobacteriaceae, evaluation of transfers and readmissions as a source of resistant organisms, and reduction of aminoglycoside use to decrease the selection of nonenzymatic resistance.

Netilmicin: its in vitro activity and synergism with penicillin compounds

The in vitro efficacy of netilmicin and its synergism with penicillins were examined. Netilmicin was effective against E. coli, indole-negative and -positive Proteus, Klebsiella, Enterobacter, Salmonella, Shigella and Serratia. Netilmicin was less effective than other aminoglycosides against Citrobacter and Pseudomonas. A combination of netilmicin and piperacillin synergistically inhibited Enterococci. Netilmicin was not synergistic with either penicillin or carbenicillin against Enterococci. Netilmicin with either carbenicillin, ticarcillin or piperacillin synergistically inhibited Pseudomonas aeruginosa, but no such synergism was noted against highly resistant strains of Pseudomonas.

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.

Comparative in vitro activity of netilmicin, amikacin, tobramycin and sisomicin against gentamicin highly-resistant enterobacteriaceae

Netilmicin was compared with sisomicin, tobramycin and amikacin against 65 recent clinical enterobacterial isolates found to be highly resistant to gentamicin (MIC larger than or equal to 80 microgram/ml). Netilmicin showed a high activity against 20 out of 65 strains tested. Most of the sensitive strains (60%) to netilmicin required a concentration of gentamicin equal or lower than 160 microgram/ml for inhibition. Amikacin proved to be extremely effective in all the organisms tested. Tobramycin was consistently less active than either netilmicin or amikacin and the same was the case with sisomicin. The MIC was determined in both solid and liquid media for 24 strains. Depending upon which aminoglycoside was used, we found that 10-30% of the enterobacteriaceae exhibited a twofold diminution of MIC when tested in broth as compared to agar, while the greater proportion of strains was characterized by a higher MIC tested in broth as compared to agar.

Comparative in vitro activity of tobramycin and gentamicin on three different media

The minimal inhibitory concentration for tobramycin and gentamicin against 488 clinical isolates of Enterobacteriaceae, Staphylococcus aureus and Pseudomonas spp. were obtained on three different solid media. The results obtained on Antibiotic Sensitivity Medium AB Biodisk (PDM) were markedly different from the results obtained on Mueller-Hinton (MH) and Diagnostic Sensitivity Test Agar Oxoid (DST). It was shown that tobramycin was significantly disfavored relative to gentamicin by PDM agar compared to MH and DST agar.

Inhibition of candidacidal activity of human neutrophil leukocytes by aminoglycoside antibiotics

We have tested the effect of five aminoglycoside antibiotics (gentamicin, sisomicin, tobramycin, ribostamycin, and amikacin) on the candidacidal activity of human neutrophils in vitro; all of them are inhibitory and can be grouped into three significantly different levels of toxicity. Gentamicin in the most toxic and sisomicin is the least toxic.

Treatment of twelve burn wound infections and eight other serious infections with cefazolin and tobramycin: in vitro and in vivo evaluation

20 patients with serious infections were treated with cefazolin and tobramycin for 9--64 days. Minimal inhibitory concentration (MIC) values and minimal bactericidal concentration (MBC) values were determined for each of the 112 clinical bacterial isolates. The median cefazolin MIC/MBC was 1.56/12.5 micrograms/ml, and the median tobramycin MIC/MBC was 6.25/25.0 micrograms/ml for all organisms studied. Median cefazolin doses of 49.0 mg/kg/day gave median peak/trough serum levels of 43.0/11.0 micrograms/ml. Median tobramycin doses of 4.3 mg/kg/day gave median peak/trough serum levels of 5.0/1.4 micrograms/ml. Checkerboard studies revealed synergy with 65% of strains. Bacteriologic and clinical success was obtained in 17 of 20 patients.

Characteristics of gentamicin resistance in nosocomial infections

Characteristics of gentamicin resistance were studied in gram-negative bacilli from 50 consecutive patients with nosocomial infection, during a time when gentamicin resistance had recently become prevalent at Medical University Hospital. Burns, decubitus ulcers, and cystic fibrosis were common precipitating factors for acquisition of gentamicin-resistant organisms. Pseudomonas aeruginosa accounted for 76% and Enterobacteriaceae for 24% of isolates. There was high prevalence of cross-resistance to amikacin (61%) and tobramycin (58%). Of the P aeruginosa strains 36% possessed plasmids which were rapidly detected by agarose gel electrophoresis. None of the isolates transferred gentamicin resistance. Representative isolates failed to elaborate aminoglycoside-modifying enzymes or to take up labelled amikacin. Multiple immunotypes of P aeruginosa were identified. These data suggest that a nonplasmid mediated resistance mechanism such as impermeability was responsible for the emergence of gentamicin resistance.

In vitro activity of netilmicin, gentamicin, tobramycin and amikacin against glucose fermenting and nonfermenting bacteria

The in vitro activity of netilmicin was compared to gentamicin, tobramycin and amikacin against 461 strains of glucose fermenting and nonfermenting bacteria. The minimum inhibitory concentrations of netilmicin, gentamicin and tobramycin against the majority of Enterobacteriaceae, Staphylococcus and Streptococcus were quite similar. Gentamicin, however, was approximately fourfold more active against strains of S. marcescens. Amikacin was the most effect antibiotic against strains of fermenting and nonfermenting bacilli resistant to at least one aminoglycoside. Many gentamicin-resistant species of nonfermenting bacilli, however, remain highly resistant to all four aminoglycosides tested.

A transposon, Tn732, encoding gentamicin/tobramycin resistance

Gentamicin and tobramycin are important antibiotics in the treatment of hospital infections because of their activity against a wide range of bacterial genera. With their increasing use, bacteria resistant to these drugs have appeared, the resistance being frequently plasmid determined. The resistance genes determine various enzymes that modify and inactivate the drugs and there is association between particular gentamicin/tobramycin resistance genes and plasmids of particular groups, implying that acquisition of such a gene by any plasmid is a rare event. We now report the identification of a transposon or 'jumping gene' encoding the gentamicin/tobramycin adenylylating enzyme, ANT(2"), on a plasmid of incompatiblity group FII (IncFII).

A broth-disc technique for the assay of antibiotic synergism

A broth-disc technique has been developed to demonstrate the antibiotic synergism of some broad-spectrum penicillins plus an aminoglycoside against Pseudomonas aeruginosa and enterococci. Utilizing the zone sites obtained from Kirby-Bauer susceptibility tests, approximate minimum inhibitory concentrations of each antibiotic upon individual isolates were derived using standard regression curves. One-fourth of each value was calculated and the approximate desired concentration then prepared in Mueller-Hinton broth through use of the labelled antibiotic disc content. Tubes were inoculated with a standardized suspension of organism and incubated at 35 degrees C for 18-24 h. Subsequently, inhibitory end points were recorded. This approach to synergy testing showed good correlation with the standard checkerboard method. The broth-disc synergistic assay is also reproducible, financially feasible, and less time-consuming to execute.

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.

Global and effective synergism of amikacin, gentamicin or tobramycin when combined with carbenicillin against Pseudomonas aeruginosa

The authors describe a study to evaluate the synergistic effects of the combinations of amikacin-carbenicillin, gentamicin-carbenicillin and tobramycin-carbenicillin at the associated minimal bactericidal concentrations and at doses related to the serum levels reached by the drugs in the blood.

In vitro comparison of synergism between cefamandole and gentamicin or tobramycin by the triple layer agar method with enzymatic inactivation

A synergistic effect was shown with gentamicin and tobramycin by means of a triple layer agar technique and enzymatic inactivation of cefamandole after only four hours' incubation. When the strain is sensitive to cefamandole and aminoglycosides, synergy is observed against all the strains studied (Staphylococcus aureus, Proteus, Klebsiella, Escherichia coli, Enterobacter, and Haemophilus influenzae). No significant difference was noted between the cefamandole-tobramycin and the cefamandole-gentamicin combinations when the microbial strains were sensitive to the three antibiotics.

Synergy between carbenicillin and an aminoglycoside (gentamicin or tobramycin) against Pseudomonas aeruginosa isolated from patients with endocarditis and sensitivity of isolates to normal human serum

Isolates from the blood of 30 patients with endocarditis due to Pseudomonas aeruginosa were tested for synergy between carbenicillin and an aminoglycoside, either gentamicin or tobramycin, by in vitro checkerboard methods in modified (cation-supplemented) Mueller-Hinton broth. Twenty-five of the 30 isolates were affected synergistically. Whether given low (2.5--5 mg/kg) or high (8 mg/kg) doses of aminoglycoside along with 30 g of carbenicillin daily, all of the five patients infected with pseudomonads that were not synergistically affected were refractory to treatment with pseudomonads that were not synergistically affected were refractory to treatment with the carbenicillin-gentamicin combination, whereas the finding of synergy of carbenicillin with gentamicin (or tobramycin) did not assure a medical cure. Tests for synergy between carbenicillin and gentamicin yielded different results in Mueller-Hinton agar than in modified Mueller-Hinton broth. The majority (28) of 30 isolates of endocarditis-producing P. aeruginosa were resistant to the bactericidal effects of 50% pooled normal serum that had been freshly separated. One of the endocarditis-producing strains that was sensitive to 50% serum was resistant to 10% serum. However, sensitivity or resistance to freshly separated, pooled normal human serum did not predict the outcome of antibacterial therapy for pseudomonas endocarditis.

Comparison of serum and prostatic levels of tobramycin

Tobramycin sulfate, an aminoglycoside antibiotic, has been shown to be effective in the treatment of complicated urinary tract infections. Because of this, a study was undertaken to determine the penetrance of tobramycin into the prostate gland. It was found that the drug is concentrated at inhibitory levels in the prostate gland after the routinely recommended administration and should be useful in the treatment of bacterial prostatic infection.

Comparison of therapeutic routes in experimental Pseudomonas keratitis

We determined the efficacy of tobramycin administered by topical, intramuscular, and subconjunctival routes in guinea pigs and rabbits with experimental Pseudomonas keratitis. The topical route of administration was consistently more effective than either subconjunctival or intramuscular routes. Subconjunctival injection of antibiotic did not enhance the effectiveness of topical therapy in either guinea pigs or rabbits. Intramuscular tobramycin was more effective than saline in guinea pigs with keratitis but not in rabbits with keratitis.

[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.

Effect of time and concentration upon interaction between gentamicin, tobramycin, Netilmicin, or amikacin and carbenicillin or ticarcillin

An aminoglycoside antibiotic and carbenicillin or ticarcillin are widely used in the treatment of patients with gram-negative bacillus infections. This study evaluated the effect of time upon in vitro interaction between mixtures of four aminoglycosides at two concentrations with carbenicillin or ticarcillin at four concentrations. By linear regression analysis, the inactivation of each aminoglycoside was shown to be directly proportional to the concentration of carbenicillin (P < 0.001). Inactivation was significantly (P < 0.01) greater for gentamicin and tobramycin than for amikacin or netilmicin at all carbenicillin concentrations. At carbenicillin concentrations of 300 and 600 mug/ml, significantly (P < 0.005) less inactivation of amikacin occurred when compared to netilmicin. Ticarcillin produced a significant (P < 0.025) inactivation of gentamicin and tobramycin, with inactivation being directly proportional to ticarcillin concentration. No inactivation of amikacin or netilmicin activity occurred unless the ticarcillin concentration was 600 mug/ml. No significant change in aminoglycoside activity occurred when stored with ticarcillin or carbenicillin at concentrations ranging from 100 to 600 mug/ml at -70 degrees C for 56 days. When an aminoglycoside and carbenicillin or ticarcillin are indicated in patients with renal failure, this study supports the use of ticarcillin with either amikacin or netilmicin.

[Comparison of bactericidal effects of four aminoglycoside antibiotics: amikacin, gentamicin, kanamycin and tobramycin (author's transl)]

The authors have studied on 20 bacterial strains (5 Pseudomonas aeruginosa, 5 Escherichia coli, 5 Klebsiella and 5 Serratia) the bactericidal kinetics of 4 aminoglycoside antibiotics: amikacin, gentamicin, kanamycin and tobramycin. The antibiotic concentrations used for this work were 1.5 times the MIC for each strain previously measured in a liquid medium. The action of the aminoglycoside antibiotics shows three phases. The third phase describes a part of less susceptible bacterial population. It permits the comparison of the 4 antibiotics. Amikacin shows the best activity, followed by gentamicin, kanamycin and tobramycin.

[In-vitro antimicrobial activity of 2 aminoglycoside antibiotics: tobramycin and gentamycin]

It has been determined the in vitro antibacterial activity of two antibiotics on 409 bacterial stocks isolated from several pathologic materials and composed by E.coli,Propeus,Salmonellae,Pseudomonas,Staphylococcus aureus. The Tobramicin has shown to have activity against all stocks of E.coli(82),Pseudomonas aeruginosa (62) and Salmonellae (21) and to have a better activity in comparison with Gentamicin also against Proteus and Staphylococcus aureus.

[Antibacterial activity of amikacin towards gentamicin-resistant, Gram-negative bacilli]

Antibacterial activity of amikacin with regards to gentamicin resistant, Gram-negative bacteria was evaluated. Probable systems of enzymatic inactivation of antibiotic were postulated for amikacin and other aminoglycosides.