Tobramycin, amikacin, sissomicin, and gentamicin resistant Gram-negative rods

A comparison of intravenous cefoxitin and a combination of gentamicin and metronidazole as prophylaxis in colorectal surgery

In a prospective randomized clinical trial, 103 patients undergoing elective colorectal surgery received either cefoxitin or a combination of metronidazole and gentamicin. Six of 52 patients in the cefoxitin group (11.5 per cent) and six of 48 patients in the metronidazole/gentamicin group (12.5 per cent) developed serious wound infections. Two patients (3.8 per cent) in the cefoxitin group and one patient (2.1 per cent) in the metronidazole/gentamicin group developed deep sepsis. These results suggest that cefoxitin is as effective as the combination of metronidazole and gentamicin for prophylaxis against serious postoperative septic complications.

Endemic resistance to amikacin among hospital isolates of gram-negative bacilli: implications for therapy

We reviewed the records of the microbiology laboratory of the Veterans Administration Medical Center, Bronx, New York in order to determine the prevalence, epidemiology and complete antibiotic susceptibility profile of amikacin-resistant aerobic and facultative gram-negative bacilli isolated from clinical specimens submitted for culture between January 1, 1980 and May 1, 1981. Of more than 5000 gram-negative rods isolated during this 16-month period, 2.8% were determined to be resistant to amikacin by the disc diffusion method. Eighty-eight of the amikacin-resistant organisms were unique isolates derived from cultures on 74 patients located throughout the hospital. Urine (51%) and sputum (27%) were the predominant sources of specimens yielding resistant strains. These organisms represented seven different genera of Enterobacteriaceae (58%) or Pseudomonas aeruginosa (31%) and other glucose non-fermenting species (11%). Resistance to amikacin was usually associated with resistance to gentamicin, tobramycin and most of the other antimicrobials tested. Twenty percent of isolates were susceptible to only a single antimicrobial, and another 5% were resistant to every agent routinely tested. Although geographic clustering of a small number of amikacin-resistant organisms occurred twice (a strain of Proteus mirabilis on the spinal cord injury service and a strain of P. aeruginosa on one medical ward), the vast majority of isolations were consistent with a pattern of endemic resistance.

Aspects of the plasmid-mediated antibiotic resistance and epidemiology of Klebsiella species

In an international collection of 108 epidemiologically distinct strains of gentamicin-resistant Klebsiellae, extensive plasmid-mediated multiple antibiotic resistance was found in 80.6 percent of strains. In vivo conjugation was recognized in eight patients within two years in one hospital, and identical plasmids were found in different serotypes from hospitals in West Germany, the United Kingdom, Italy and Australia. Of 45 patients who were infected or colonized with gentamicin-resistant Klebsiellae, 26 had positive skin sites and of these, six had negative clinical specimens and served as a "hidden" reservoir of strains which provide a source for the contamination of nurses' hands and sustain nosocomial outbreaks. It is suggested that the few agents effective against gentamicin-resistant Klebsiellae, such as amikacin and cefuroxime, should be reserved; that gentamicin-resistant strains are selectively favored by the use of agents other than gentamicin which are more widely prescribed; and that more careful identification of skin carriers and attention to staff handwashing will control the spread of such strains and their plasmids.

Evaluation of amikacin dosage regimes in the low and very low birthweight newborn

The recommended neonatal dosage regime for amikacin of 15 mg/kg/day was found to be unsatisfactory in four neonates and a loading dose of 10 mg/kg did not improve levels in two further newborns with normal renal function. Fourteen neonates on 20 mg/kg/day regime achieved satisfactory levels; peak values were 21.5 +/- 4.5 microgram/ml and trough levels 3.34 +/- 2.05 microgram/ml. Peak time ranged from 17 to 60 minutes and varied with the dose given. The half-life was related to plasma creatinine, urea, post-natal age and weight. Thirteen neonates with pre-existing renal impairment were managed by alteration of dosage interval or quantity given. Side-effects were confined to eosinophilia in six infants, and no definite nephrotoxicity or gross eighth nerve damage was demonstrated.

Colonization of an amputation site by Flavobacterium odoratum after gentamicin therapy

Flavobacterium odoratum was isolated from the stumps of the amputated toes of a debilitated patient. Gentamicin therapy and the poor state of health of the patient provided suitable conditions for this gentamicin-resistant species to multiply. When the gentamicin therapy was stopped, and as the patient's heal improved, F. odoratum gradually disappeared to be replaced by Staphylococcus aureus. This appears to be the first report of the isolation of F. odoratum in Australia, and it indicates the potential of this resistant species to act as a source of infection for groups at risk.

The sensitivity of gentamicin-resistant gram-negative bacilli to cefotaxime, other cephalosporins and aminoglycosides

The sensitivities of 80 gentamicin-resistant gram-negative bacilli to cefotaxime, cefuroxime, cefoxitin, cefamandole, cefazolin, tobramycin, netilmicin and amikacin were determined. Amikacin was the most active amino-glycoside. However, the percentage sensitivity to cefotaxime of most of the species was higher than, or equal to any of the other antibiotics tested. Cefotaxime was particulary active against Providencia spp., Serratia spp., Klebsiella spp., and Pseudomonas maltophilia, being 16 to 256 times more active than the next best cephalosporin or cephamycin. Clinical trials of cefotaxime are now required.

Preliminary experience with parenteral mecillinam

Case reports are reviewed of 26 patients, mainly with severe Gram-negative infections, treatment with parenteral mecillinam. Twenty-three patients received other antibiotics in addition to mecillinam. In 19 patients, potentially synergistic antimicrobial therapy was given. Overall, a beneficial clinical effect was recorded in 17 (68%) of the 25 patients assessed. A better response was observed in those patients who had not received other antibiotics before treatment with mecillinam was instituted. It is concluded that parenteral mecillinam may have an important role in the treatment of severe Gram-negative infections.

Flavobacterium odoratum: a species resistant to a wide range of antimicrobial agents

During the period 1966-77, 24 strains of Flavobacterium odoratum were identified from among strains of Gram-negative, non-fermentative bacteria submitted to the National Collection of Type Cultures for computer-assisted identification. The F. odoratum strains showed resistance to therapeutic levels of gentamicin, tobramycin, amikacin, and carbenicillin as well as to several other antimicrobial agents generally useful in the treatment of infections caused by Gram-negative, non-fermentative bacteria. Two strains isolated from amputation stumps and another three strains isolated in significant numbers from urine specimens were possibly opportunist pathogens. The biochemical characteristics of the 24 strains, the proposed neotype strain of F. odoratum, and three strains representative of a group, referred to at the Center for Disease Control, Atlanta as group M-4f, were compared with those of biochemically similar species which may be isolated from clinical material.

Surveillance of gentamicin-resistant gram-negative bacilli in a general hospital

Aerobic gram-negative bacilli isolated from clinical specimens from 1 January to 31 December 1976 were tested for gentamicin and tobramycin resistance by standardized disk testing. For Pseudomonas isolates, gentamicin resistance was 17.1% and tobramycin resistance was 2.8%. For other gram-negative bacilli, gentamicin resistance was 5.5% and tobramycin resistance was 5.4%. Seventy-four patients from whom gentamicin-resistant organisms were isolated from 1 January to 30 June 1976 were studied prospectively. These patients were elderly, had serious underlying diseases, and had received prior antibiotic therapy. Eleven patients carried gentamicin-resistant organisms at the time of transfer to our hospital from community hospitals or nursing homes. Of the 82 isolates from these 74 patients, 52 were from the urine. Pseudomonas was found most frequently (32 isolates), followed by Klebsiella (15 isolates), Enterobacter (10 isolates), Serratia (10 isolates), and Proteus (9 isolates). Only 3 of 32 Pseudomonas isolates caused symptomatic infection, while 16 of 50 other gram-negative bacilli were responsible for symptomatic infection. Although amikacin was the most active drug against gentamicin-resistant gram-negative bacilli and had not been used in our hospital at the time of this study, 25% of Pseudomonas and 18% of all gram-negative bacilli showed resistance to this aminoglycoside.

In vitro susceptibility of gentamicin and/or tobramycin resistant gram-negative bacilli to seven aminoglycosides

The in vitro activity of gentamicin, tobramycin, sisomicin, netilmicin, amikacin, kanamycin and streptomycin was tested simultaneously by the agar dilution method against 584 clinical isolates of gram-negative bacilli that were resistant to gentamicin and/or tobramycin. About half of the gentamicin-resistant Pseudomonas were susceptible to tobramycin but cross-resistance was virtually complete between gentamicin and tobramycin for Enterobacteriaceae. Sisomicin was much more active than gentamicin against Klebsiella, Escherichia and Citrobacter species. Only 18.9%, 27.4% and 27.9% of Klebsiella, Enterobacter and Serratia respectively were resistant to netilmicin. Amikacin was the most effective aminoglycoside with an overall resistance of 15.6%. Kanamycin was effective against 40% of Proteus and Providencia species. Surprisingly, more than half of Klebsiella and Enterobacter species and 85.3% of Serratia species were susceptible to streptomycin.

Emergence in a burn center of populations of bacteria resistant to gentamicin, tobramycin, and amikacin: evidence for the need for changes in zone diameter interpretative standards

From July 1974 through June 1976, a number of isolates of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa from the Burn Center exhibited a shift to smaller zone diameters with gentamicin than did isolates from the general hospital population. Although many had zone diameters >/=13 mm and would have been considered susceptible by this breakpoint, they were found to have minimal inhibitory concentrations (MICs) of >/=8 mug of gentamicin per ml by agar dilution testing. Zone diameters and MICs of gentamicin, tobramycin, and amikacin were subsequently compared for 168 isolates from both the Burn Center and general hospital. The results revealed many isolates that fell into presently used gentamicin- and tobramycin-"susceptible" categories by disk diffusion tests but were resistant by MIC. The data indicated that criteria for gentamicin disk diffusion testing should include an intermediate or indeterminate category, and that the limits of the intermediate category for tobramycin and amikacin should be expanded.