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

Prophylactic Antibiofilm Activity of Antibiotic-Loaded Bone Cements against Gram-Negative Bacteria

Gram-negative bacilli can be responsible for prosthetic joint infection (PJI) even if staphylococci are the main involved pathogens. Gram-negative PJIs (GN-PJI) are considered difficult-to-treat infections due to the increase in antimicrobial resistance and biofilm formation. To minimize the risk of infection in cases of arthroplasties with cemented prosthesis, bone cement can be loaded with antibiotics, especially gentamicin. In this study, we aimed to compare the prophylactic antibiofilm activity of ready-to-use antibiotic-loaded bone cements (ALBC), already commercialized or new prototypes. We compared ALBCs containing gentamicin alone, gentamicin plus vancomycin, gentamicin plus clindamycin, gentamicin plus Fosfomycin, and fosfomycin alone, to plain cement (no antibiotic); these comparisons were conducted to investigate the biofilm formation of three strains of Escherichia coli, three strains of Pseudomonas aeruginosa and two strains of Klebsiella pneumoniae, with or without specific resistance to gentamicin or fosfomycin. We reported that ALBC containing gentamicin and clindamycin (COPAL G+C) seems to be the most interesting ALBC of our tested panel for the prevention of biofilm formation by gentamicin-susceptible strains, even if clindamycin is not effective against Gram-negative bacteria. However, gentamicin-resistant strains are still a problem, and further studies are needed to identify an antibiotic to associate with gentamicin for an efficient dual ALBC against Gram-negative bacteria.

Longitudinal Analysis of Endemic Gentamicin- and Tobramycin-Resistant Gram-Negative Bacilli in a Community Hospital

The epidemiology of endemic gentamicin- and tobramycin-resistant gram-negative bacilli at a community hospital was analyzed over a one-year period three years following an original analysis at the same hospital. The frequency and distribution of resistant organisms remained stable over the time spanning the two studies. Only 2.8% of all gram-negative bacilli were resistant to gentamicin or tobramycin, and the majority of resistant isolates were non-Enterobacteriaceae. The respiratory and urinary tracts remained the body sites most prone to harbor resistant organisms. Risk analysis using a matched comparison group again revealed prior treatment with an aminoglycoside to be the only significant factor pre-disposing to acquisition of resistant gram-negative bacilli. This analysis indicates that community hospitals may not be important reservoirs of endemic aminoglycoside-resistant gram-negative bacilli, and reconfirms the observation that each hospital must define its own pattern of aminoglycoside resistance and unique risk factors.

Aminoglycoside resistance and aminoglycoside usage: ten years of experience in one hospital

For 10 years the 700-bed Minneapolis Veterans Affairs Medical Center has conducted a policy of carefully controlled aminoglycoside usage and monitoring of resistance of over 25,000 aerobic and facultative gram-negative bacillary isolates to the aminoglycosides. On two occasions during the 1980s, our experience of introducing amikacin at a high level of usage was associated with a significant reduction in resistance to gentamicin and tobramycin among gram-negative bacilli. Rapid reintroduction of gentamicin usage in 1982 after the first amikacin period was associated with a significant and rapid increase in gentamicin and tobramycin resistance. However, in 1986, gentamicin was again reintroduced to this institution at an initially modest level, and the percentage of usage of gentamicin was gradually increased over a 15-month period without a significant change in resistance to gentamicin, tobramycin, or amikacin while maintaining an overall 68% gentamicin usage and 30% amikacin usage. Aminoglycoside usage (measured as patient days) rose steadily from under 2,000 patient days per quarter in 1980 and 1981 to over 3,000 days per quarter in 1985. Since 1985, usage has declined to under 2,500 patient days per quarter in 1990. This usage rise and fall occurred during a steadily declining daily patient census that was 590 in 1980 and 465 in 1989. A move to a new hospital building in June 1988 was associated with an additional significant decline in resistance to all aminoglycosides (P less than 0.05), continuing a trend that was evident for the year preceding the move. Resistance to aminoglycoside antibiotics is now at the lowest level in 10 years at this institution, with only one gram-negative organism, Pseudomonas aeruginosa, that exhibits more than 5% resistance to gentamicin and no gram-negative species that are more than 5% resistant to amikacin and tobramycin.

Mechanism of aminoglycoside resistance among beta-lactam-resistant Escherichia coli in the United States

We examined aminoglycoside (AG) resistance in ampicillin-resistant Escherichia coli obtained from nine hospitals participating in the National Nosocomial Infections Study. The isolates were tested to 25 antimicrobials using broth microdilution methods. If the organism was intermediate or resistant to gentamicin, tobramycin, netilmicin, or amikacin, we determined the class of aminoglycoside-modifying enzyme (AME) using the phosphocellulose paper binding assay. Of 423 E. coli, 21 (5%) were intermediate or resistant to one or more of the AGs. All but two of these E. coli isolates had at least one AME. Twelve isolates had phosphotransferase (APH) enzymes; seven had adenyltransferase (ANT) enzymes (all ANT[2"]); and four had acetyltransferase (AAC) enzymes. The seven ANT[2"]-producing isolates were more likely to be acquired in the community than in the hospital (4/7 ANT[2"]-producing E. coli versus one of 14 of the other AG-resistant E. coli, p = 0.03, Fisher's exact test). These findings suggest that for E. coli resistant to both ampicillin and an AG, APH enzymes are the predominant AME class. Additionally, isolates with certain AMEs may be acquired both in the community and in the hospital.

Aminoglycoside antibiotics in infectious diseases. An overview

This article presents an overview of the aminoglycoside antibiotics used in clinical practice. Facts concerning the discovery and properties of the aminoglycosides are followed by information about spectrums of activity and mechanisms of action and resistance. Individual compounds are compared and proposals on the possibilities for their clinical use, both as single drugs and in combination with beta-lactam antibiotics, are made. The importance placed on measuring the serum concentrations of aminoglycoside antibiotics should serve as a remainder that this procedure is important, on one hand, to increase clinical efficacy and, on the other, to reduce the side effects of these antibiotics. Finally, the aminoglycosides are compared briefly with other antibacterial compounds, some of which are very new. There is no doubt that in the future the aminoglycosides will continue to occupy an important place in the treatment of severe infections, although newly developed agents appear to be effective complements.

Role of amikacin in the management of intra-abdominal sepsis

Controversy has developed regarding the antibiotic management of intra-abdominal sepsis because of the recent availability of the third-generation cephalosporins and ureidopenicillins as alternatives to traditional combination therapy (aminoglycosides plus clindamycin). Most observers now acknowledge the need to provide anti-anaerobic as well as anti-aerobic gram-negative drug coverage. Although most of the newer agents do provide such broad-spectrum coverage, doubt remains regarding their efficacy because of flaws in comparative study design and the observation that resistance to the newer agents, which may even extend to the aminoglycosides, can emerge in individual patients during single courses of antibiotic therapy. Indeed, such resistance is most likely to occur during the treatment of seriously ill, immunodepressed patients who have undergone multiple reoperation for persistent or recurrent intra-abdominal sepsis--the precise group for which the new drugs were most desired as less toxic alternatives to the aminoglycosides. On the basis of such observations, combination therapy with the aminoglycosides, appears to remain the most logical choice. In the setting of nosocomial sepsis and pathogen resistance to other aminoglycosides, amikacin may be especially effective. Recent surveillance data indicate that the use of amikacin under such circumstances not only may provide effective antibiotic therapy, but also may actually reduce the level of microbial resistance to the other aminoglycosides. Past concern regarding the development of resistance to amikacin has probably been excessive and should not deter the use of this agent under appropriate clinical circumstances.

Aminoglycoside resistance in gram-negative bacilli during increased amikacin use. Comparison of experience in 14 United States hospitals with experience in the Minneapolis Veterans Administration Medical Center

Resistance to amikacin, gentamicin, and tobramycin was surveyed prospectively during controlled aminoglycoside usage in 14 hospitals. Following an initial baseline period (minimum, three months) during which gentamicin use predominated, gentamicin and tobramycin were placed on restrictive control, establishing amikacin as the aminoglycoside of general use (86 percent of total aminoglycoside usage). During an average of 35 months' restriction of gentamicin and tobramycin, significant reductions in gram-negative resistance to gentamicin (8.4 to 7.0 percent, p less than 0.001) and tobramycin (6.0 to 5.3 percent, p less than 0.01) were observed. The most significant decreases in resistance to gentamicin and tobramycin (p less than 0.001) were found for Pseudomonas aeruginosa, Klebsiella species, Serratia species, and Proteus species. Amikacin resistance among gram-negative bacilli was observed to increase marginally from 1.4 to 1.7 percent (p less than 0.05) during the surveillance period, primarily due to a significant increase in resistance among P. aeruginosa (3.0 to 3.9 percent, p = 0.05). These data were compared with data from a similar surveillance program at the 700-bed Minneapolis Veterans Administration Medical Center. Over a period of 54 months, both gentamicin and tobramycin resistance decreased significantly when amikacin was used (p less than 0.001), then increased with reintroduction of gentamicin (p less than 0.05), and decreased significantly with reintroduction of amikacin (p less than 0.001). Despite predominant amikacin use for a total of 38 months, amikacin resistance did not increase and actually decreased significantly (p less than 0.05) in the last 12 months.

Antimicrobial agent susceptibility patterns of bacteria in hospitals from 1971 to 1982

Bacterial susceptibility to 16 commonly used antibiotics was analyzed for a 12-year period (from 1971 to 1982, inclusive). Susceptibilities of 5,828,243 strains isolated from a mean of 242 hospitals nationwide and of 194,575 strains isolated at the Massachusetts General Hospital, Boston, Mass., and the Bronx Lebanon Hospital Center, New York, N.Y., were compared. Strains of Escherichia coli, Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa showed virtually the same susceptibilities to antibiotics throughout the 12-year period, whereas Streptococcus faecalis and Staphylococcus epidermidis showed significant increases in resistance to most antibiotics. The close similarity between antibiotic susceptibilities shown at both the 242 hospitals and the 2 individual hospitals suggests that this analysis accurately reflects trends of bacterial resistance to antibiotics in U.S. hospitals. Since most of the species analyzed produce serious disease and high mortality, their susceptibility to antibiotics is relevant both to physicians treating infectious diseases and to epidemiologists.

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.

Plasmid-determined tobramycin and gentamicin resistance in strains of Pseudomonas aeruginosa from two Sydney hospitals

Strains of Pseudomonas aeruginosa resistant to gentamicin, tobramycin, streptomycin, and sulphonamide have been isolated from patients at two Sydney hospitals. The multiple resistance of all these strains was due to a transmissible plasmid. The significance of the identification of this plasmid, in this variety of strains and at two hospitals, for the treatment of Ps. aeruginosa infections is discussed.

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.

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.