Decreased incidences of resistance to antimicrobial agents among Escherichia coli and Klebsiella-enterobacter. Observations in a university hospital over a 10-year period

Review of epidemic aminoglycoside resistance worldwide

Epidemic aminoglycoside resistance may be caused by the spread of a species with distinctive chromosomal genes (e.g., Pseudomonas aeruginosa), or it may be due to the dissemination of plasmids or transposons between genera. Although strains of P. aeruginosa resistant to aminoglycosides because of impermeability may cause nosocomial outbreaks, most of the acute increases in aminoglycoside resistance are due to the spread of inactivating enzymes by plasmids. The index species for intergeneric outbreaks is usually Klebsiella pneumoniae carrying the ANT(2") or AAC(3) gene; however, the distribution of resistance varies greatly by location and species. The AAC(6')-I gene is most common in Serratia marcescens and in East Asian isolates of other species, whereas the AAC(3) gene is common in Chile. In the United States, the ANT(2") and AAC(3) genes are particularly common among Enterobacteriaceae, except for Proteus and Providencia, which often carry the AAC(2') gene. The most common patterns of epidemic resistance lead to the inactivation of gentamicin and, less frequently, tobramycin, but only rarely affect amikacin.

Resistance of Escherichia coli in faeces and the use of antimicrobial agents in the treatment of hospital patients

Resistance of faecal Escherichia coli to ampicillin, tetracycline, sulphamethoxazole and gentamicin was studied in patients admitted to seven different departments in two hospitals. The resistance of ampicillin, tetracycline and sulphamethoxazole in the seven patient groups was 27-57%, 26-56% and 35-63%, respectively. Resistance to gentamicin was found in only one department. An E. coli flora predominantly resistant to ampicillin, tetracycline or sulphamethoxazole (greater than 50% of the E. coli strains in a faecal sample resistant) was found in 10-38%, 4-30% and 21-35% of the samples. A cross-sectional study focusing on the influence of the use of antimicrobial agents on the occurrence of resistant strains revealed a positive correlation between the annual turnover of broad-spectrum penicillins in various departments and the occurrence of predominantly ampicillin-resistant E. coli strains in these departments.

Resistance of gram-negative bacilli as related to hospital use of antimicrobial agents

The development of resistance of gram-negative bacilli, which are common nosocomial pathogens, is an increasing problem. It is generally accepted that this resistance may directly reflect the frequency of use of various antimicrobial agents. Because our institution experienced in 1976 a dramatic change in the pattern of antimicrobial use, primarily a marked decrease in prescribing cephalosporins, we attempted to evaluate retrospectively the effects of this change upon the resistance of gram-negative bacilli that are common nosocomial pathogens. Susceptibilities of Klebsiella and Providencia spp., Pseudomonas aeruginosa, and Serratia marcescens were determined for the years 1975 to 1979. Not unexpectedly, we observed a substantial decrease in cephalosporin resistance. An unexpected finding was a decrease in aminoglycoside resistance, despite increased use of these agents. The possibility that decreased cephalosporin use may lead to decreased aminoglycoside resistance is an intriguing and provocative thesis which can only be speculative at this time but which would seem worthy of additional formal investigation.

Surveying antibiotic use in a general teaching hospital

Four antibiotic surveys were carried out in a teaching hospital within the framework of an intensive drug monitoring system during 1976-1978. The proportion of inpatients receiving antibiotic therapy at any one time varied from 25% to 32%. Penicillin, ampicillin and co-trimoxazole were the most frequently used antibiotics. The use of cloxacillin increased over the survey period. Approximately 85% of presumed infections were treated before the results of microbiological tests became available. Between 29% and 39% of all courses of antibiotics were given for prophylaxis of infection. Between 13% and 30% of patients received more than one antibiotic concurrently; indication for such combined use appeared inadequate in 31% to 80% of courses.

The emergence of gentamicin-resistant klebsiellae in a large general hospital

Between March and December, 1975, an outbreak of infection with gentamicin-resistant Klebsiella pneumoniae (klebsiella (Gmr)) occurred at the Royal Melbourne Hospital. The klebsiellae were considered to be causing significant infection in 24 of 42 patients harbouring the microorganism. Commonest culture sources were urine and sputum, all but one of the significant urinary infections being associated with indwelling bladder catheters. Antibiotic therapy had been given to 40 patients before the isolation of klebsiella (Gmr), and of these 22 had received gentamicin. Cross infection was a major factor in the outbreak, and control measures (to limit this aspect and curtail the usage of gentamicin) have prevented wider spread within the hospital; at the time of writing the microorganism had been eradicated from all but one of the infected patients. It was shown that klebsiella (Gmr) carry an R-factor capable of transferring gentamicin resistance. Of 22 isolates tested quantitatively, 20 were resistant to 10 mug/ml of gentamicin.

Microbial development of drug resistance: mechanisms and clinical significance

Bacteria have demonstrated a disconcerting ability to develop resistance to antimicrobial agents nearly as quickly as new compounds become available. During the past two decades the molecular bases of several types of resistance have been elucidated. Mechanisms of resistance include the transference of genetic material either through conjugation (involving direct contact between microorganisms), or indirectly through transduction (involving bacteriophages). In addition to this "infectious" drug resistance, genetic mutations which permit the utilization of new metabolic pathways, and the production of enzymes which can inactivate the antimicrobic have been described. One particularly complex problem has been the ability of many Enterobacteriaceae to develop resistance to multiple antimicrobials simultaneously. The possible effect of such an occurrence is illustrated by the recent epidemic of multiply resistant Salmonella typhi in Mexico. Because the typhoid bacilli shared an identical resistance pattern to an epidemic Shigella dysenteriae type 1 the in vivo interspecies transmission of resistance has been postulated. Understanding the various mechanisms of resistance development should allow more rational use of antimicrobial agents.

Drug resistance of coliform bacteria in hospital and city sewage

The number and properties of drug-resistant coliform bacteria in hospital and city sewage were compared. There was little difference in the counts of organisms with nontransferable resistance to one or more of 13 commonly used drugs. An average of 26% of coliforms in hospital waste water had transferable resistance to at least one of the drugs ampicillin, chloramphenicol, streptomycin, sulfonamide, or tetracycline as compared to an average of 4% in city sewage. R(+) bacteria in the hospital discharge were also resistant to a broader spectrum of drugs than those in city sewage. In both effluents, the occurrence of fecal Escherichia coli among R(+) coliforms was twice as high as among coliforms with nontransferable resistance. Resistance was transferable to Salmonella typhi, and such drug-resistant pathogens in the water environment could be of particular concern. The significance of the results with regard to environmental pollution with R(+) bacteria and the dissemination of these organisms is discussed.