Clearance from a hospital of gram-negative bacilli that transfer carbenicillin-resistance to Pseudomonas aeruginosa

Nosocomial Infection Caused by Antibiotic-Resistant Organisms in the Intensive-Care Unit

Resistance to antimicrobial agents is an evolving process, driven by the selective pressure of heavy antibiotic use in individuals living in close proximity to others. The intensive care unit (ICU), crowded with debilitated patients who are receiving broad-spectrum antibiotics and being cared for by busy physicians, nurses, and technicians, serves as an ideal environment for the emergence of antibiotic resistance. Problem pathogens presently include multiply resistant gram-negative bacilli, methicillin-resistantStaphylococcus aureus, and the recently emerged vancomycin-resistant enterococci. The prevention of antimicrobial resistance in ICUs should focus on recognition via routine unit-based sur veillance, improved compliance with handwashing and barrier precautions, and antibiotic-use policies tailored to individual units within hospitals.

Pilot study of antibiotic cycling in a pediatric intensive care unit

OBJECTIVE

This pilot study was performed to determine the safety and size of effect of antibiotic cycling to reduce colonization and infection with antibiotic-resistant bacteria.

DESIGN

Open, observational study.

SETTING

The study was performed in a 16-bed pediatric medical-surgical intensive care unit.

PATIENTS

Critically ill children requiring antibiotic therapy.

INTERVENTIONS

Three antibiotic classes were systematically cycled for 3-month intervals over 18 months. Antibiotic regimens were used for all empirical therapy and continued if the bacterial isolate was susceptible.

MEASUREMENTS

The primary outcome was colonization with antibiotic-resistant bacteria, determined by surveillance cultures obtained twice monthly from all patients in the unit. Rates of antibiotic-resistant, nosocomial blood stream infections, and risks of colonization over calendar time in the intensive care unit were also evaluated.

MAIN RESULTS

The cycling of broad-spectrum, empirical antibiotics was safe and did not generate increased antibiotic resistance nor select for new organisms. Over the study period, the trend in prevalence of children colonized with antibiotic-resistant bacteria was from 29% to 24% (p =.41). The effect on prevalence of resistant blood stream infections was similar (p =.29). Changes in individual risks of colonization with resistant bacteria over calendar time were consistent with the ecologic effect in size and direction.

CONCLUSIONS

Results of this pilot intervention suggest that cycling antibiotics may be a safe and viable strategy to minimize the emergence of antibiotic resistance in intensive care units. A definitive study will require a randomized and controlled trial of only four pediatric intensive care units over an 18-month period.

Association between intensity of chlorhexidine use and micro-organisms of reduced susceptibility in a hospital environment

The potential for emergence of resistance to biocides has been a concern in recent years. This study tested whether an association exists between the intensity of chlorhexidine use and chlorhexidine susceptibility of micro-organisms isolated from patients in different clinical areas in an acute-care general hospital. Organisms frequently involved in nosocomial infections in the hospital were chosen for study over a six week period: Staphylococcus aureus (60 isolates), coagulase-negative staphylococci (48), Klebsiella pneumoniae (32), Pseudomonas aeruginosa (60), Acinetobacter baumannii (16) and Candida albicans (35). An index of chlorhexidine exposure for each clinical unit was derived for the year preceding organism collection. Chlorhexidine susceptibility was evaluated using agar incorporation minimum inhibitory concentrations (MICs) and disk diffusion. A statistically significant inverse correlation was shown between intensity of chlorhexidine use and the overall susceptibility of all study organisms taken together. There was no association when individual taxa were considered. These findings must be interpreted with caution considering that greater use of chlorhexidine is likely to occur in difficult clinical disciplines where antibiotic use, invasive procedures and other intensive care-related procedures, cross-infection and immunosuppression are all potential confounding factors. There was an excellent correlation between MICs and disk testing, suggesting that disk diffusion might be useful in studies involving more than one biocide.

Epidemiologic aspects on antibiotic resistance

The increasing usage of antibiotics has selected for resistant bacteria. Spread of such bacteria may follow mathematical models of infectious diseases, taking into consideration the number of infectious individuals, the number of susceptible individuals, and the effective contact rate between individuals from these two groups. According to calculations of the theoretical epidemic curves, the highest incidence of individuals infected with a resistant bacterial strain is present when the prevalence of patients and carriers is approximately 20-80%. Moreover, the rapidity of the spread of an epidemic increases drastically if the total number of individuals in the exposed group increases and also if the contact rate increases. This means that precautions to stop an epidemic spread of a resistant bacterial strain in a given group of individuals should be undertaken early when the prevalence is below 20%. Efficient precautions consist of cohort isolation, decrease of the number of individuals in exposed groups by subdivision into several smaller groups, and decrease of contact rates by hygienic precautions. Examples are given where such precautions have proven efficient.

The potential for clinical guidelines to impact appropriate antimicrobial agent use

Practice guidelines can help clinicians and microbiologists improve the quality and efficiency of health care. Numerous areas are in need of guideline development and development of quality improvement programs. These areas include antibiotic control, duration of antibiotic administration, use of narrowest spectrum, least toxic, lowest cost-effective antibiotic, use of rapid diagnostic tests, management of outpatient intravenous antibiotics, antibiotic prophylaxis for surgery, switching from intravenous to oral antibiotics, antibiotic selection for special situations, diagnosis of Lyme disease, and several other topics. IDSA, SHEA, CDC, NIH, and other organizations are cooperating to develop these guidelines.

Formulary control of antimicrobial usage. What price freedom?

Formulary controls are the most common and probably the most effective method for controlling abuse of antimicrobial agents in hospitalized patients. Such programs may include restriction of both the number of agents available and the way these agents may be used. These programs have been demonstrated to control pharmacy expenditures. Other potential advantages include reductions in the incidence of adverse drug reactions and the antimicrobial resistance among the hospital flora, and improvements in the overall quality of prescribing of antimicrobials. There are few data to document such benefits, however. Potential disadvantages are also poorly documented but include inconvenience for prescribing physicians, increased administrative costs, prescribing errors, and increased antimicrobial resistance. Antimicrobial control programs will likely remain common, but the availability of new information technologies should enable a transition to systems based on concurrent assessment of antimicrobial appropriateness with immediate feedback to the prescribing physician.

Detection and interspecies-transformation of a beta-lactamase-encoding plasmid from Pasteurella haemolytica

Pasteurella haemolytica-cultures, isolated from cattle with respiratory diseases, were investigated for their biotype, serotype, antimicrobial resistance and plasmid content. A plasmid encoding a beta-lactamase could be demonstrated in 9 of 19 Pasteurella haemolytica-cultures. These 9 cultures, all belonging to biotype A and serotype 1, were resistant to ampicillin, carbenicillin, penicillin G and ticarcillin. The plasmid of the respective cultures proved to be identical upon Southern blot hybridization. It could be transformed into Escherichia coli 490 A where it expressed again a beta-lactamase-activity.

Transferable enzymatic resistance to third-generation cephalosporins during nosocomial outbreak of multiresistant Klebsiella pneumoniae

Klebsiella pneumoniae strains that were resistant to third-generation cephalosporins and amikacin were recovered from 62 of 395 patients (15.7%) during 1986. 25 isolates (40%) caused urinary tract infections. The outbreak involved three intensive care units (54 isolates), and spread from one unit to another and then to four wards (8 isolates). K pneumoniae of various serotypes and strains of different Enterobacteriaceae demonstrating the same antibiotic resistance pattern were isolated, which suggests dissemination of an R-factor. The isolates had low-level resistance to third-generation cephalosporins (mode minimum inhibitory concentration of cefotaxime, 2 mg/l) but remained sensitive to cephamycins. Cefotaxime was effective in cases of uncomplicated urinary tract infection, but failed in major infections at other sites. 1-5 mg/l of the beta-lactamase inhibitors clavulanic acid or sulbactam restored normal activity to cefotaxime against the multiresistant strains. Resistance to third-generation cephalosporins was mediated by a new broad-spectrum enzyme of isoelectric point 6.3. Resistance to beta-lactams and aminoglycosides was transferable to Escherichia coli. The emergence of transferable enzymatic resistance to newer beta-lactams in K pneumoniae strains indicates a major risk of spread of such resistance to otherwise sensitive strains.

Effect of UV light disinfection on antibiotic-resistant coliforms in wastewater effluents

Total coliforms and total coliforms resistant to streptomycin, tetracycline, or chloramphenicol were isolated from filtered activated sludge effluents before and after UV light irradiation. Although the UV irradiation effectively disinfected the wastewater effluent, the percentage of the total surviving coliform population resistant to tetracycline or chloramphenicol was significantly higher than the percentage of the total coliform population resistant to those antibiotics before UV irradiation. This finding was attributed to the mechanism of R-factor-mediated resistance to tetracycline. No significant difference was noted for the percentage of the surviving total coliform population resistant to streptomycin before or after UV irradiation. Multiple drug resistance patterns of 300 total coliform isolates revealed that 82% were resistant to two or more antibiotics. Furthermore, 46% of these isolates were capable of transferring antibiotic resistance to a sensitive strain of Escherichia coli.

Parameters controlling interbacterial plasmid spreading in a gnotoxenic chicken gut system: influence of plasmid and bacterial mutations

Conjugative transfer of R plasmids R64 and R64drd-11 has been compared in vitro and in vivo without selective pressure by antibiotics in a simplified experimental system; the ecosystem was the bowel of germfree chickens, with the host bacteria almost isogenic, and the plasmids differing only in their conjugative transfer frequency. The spread of repressed and derepressed (drd) R plasmids in recipient bacterial populations was very extensive. The repressed phenotype had only a transient effect during the first 4 h. The level of implantation of the donor bacterial population seems to be of minor importance. Only with a poor recipient (con strain) could the spread of R plasmids be reduced and a steady state with a predominantly sensitive bacterial population be established. It is suggested that this steady state results from an equilibrium between the frequencies of R plasmid transfer and loss.

Partial characterization of R-plasmids from Pasteurella multocida isolated from turkeys

Pasteurella multocida, isolated from turkeys during an outbreak of septicemic disease ("fowl cholera"), was found to be resistant to tetracycline, streptomycin, and sulfonamides. Agarose gel electrophoretic analysis of DNA from these isolates indicated the presence of extrachromosomal elements. Plasmid DNA was isolated by cesium chloride-ethidium bromide density centrifugation. Escherichia coli was transformed to antimicrobic resistance with this DNA. Two plasmids were isolated. One of these plasmids had a buoyant density of 1.7158 g/cm(3) (56.9 mol% guanine plus cytosine) and a molecular weight of 4.4 x 10(6) and conferred resistance to tetracycline, streptomycin, and sulfonamides. The other, having a buoyant density of 1.7198 g/cm(3) (61 mol% guanine plus cytosine) and a molecular weight of 3.44 x 10(6), conferred resistance to streptomycin and sulfonamides. Streptomycin resistance was mediated by streptomycin phosphotransferase. Compatibility group testing indicated that neither plasmid belonged to any of 13 compatibility groups (of conjugal plasmids). Both plasmids were also found to be compatible with three small, nonconjugative resistance plasmids.

Antibiotic resistance patterns of gram-negative bacteria isolated from environmental sources

A total of 2,445 gram-negative bacteria belonging to fecal coliform, Pseudomonas, Moraxella, Acinetobacter, and Flavobacterium-Cytophaga groups were isolated from the rivers and bay of Tillamook, Oregon, and their resistances to chloramphenicol (25 microgram/ml), streptomycin (10 microgram/ml), ampicillin (10 microgram/ml), tetracycline (25 microgram/ml), chlortetracycline (25 microgram/ml), oxytetracycline (25 microgram/ml), neomycin (50 microgram/ml), nitrofurazone (12.5 microgram/ml), nalidixic acid (25 microgram/ml), kanamycin (25 microgram/ml), and penicillin G (10 IU/ml) were determined. Among fecal coliforms the bay isolates showed greater resistance to antibiotics than those from tributaries or surface runoff. No such well-defined difference was found among other bacterial groups. The antibiotic resistance patterns of gram-negative bacteria from different sources correlated well, perhaps indicating their common origin. The antibiotic resistance patterns of gram-negative bacteria of different general also correlated well, perhaps indicating that bacteria which share a common environment also share a common mode for developing antibiotic resistance.

The spectrum of infection and sensitivity of organisms isolated from African and Indian children in a Durban hospital

A prospective study was undertaken over a period of six months to determine the spectrum of infection, sensitivity of organisms isolated, and suitability of antibiotics chosen in 520 consecutive patients admitted to a paediatric unit. Culture and sensitivity of stool, urine and blood yielded 752 isolates; in 147 cases, more than one pathogen was isolated from the same or different sites. High rates of resistance to chloramphenicol, ampicillin, and kanamycin were seen in salmonellae other than Salmonella typhi, which differed in retaining its original sensitive susceptibility profile. Most Enterobacteria were sensitive to gentamicin. Penicillin-resistance was seen in 9% of meningococci, and several Haemophilus influenzae strains (20%) were resistant to ampicillin. Methicillin-resistance was encountered in 13% of Staphylococcus aureus strains and 17% of pneumococci were resistant to penicillin G. The sensitivity pattern of organisms isolated was probably directly related to widespread use of antibiotics.

Infectious complications of burns casualties during the Yom-Kippur War

During the October 1973 military conflict, 41 burned patients hospitalized at the Sheba Medical Center were closely followed up. All the patients who had burns occupying 20% or more of the body surface developed wound infections. Pseudomonas aeruginosa was the major pathogen isolated. Most infections occurred during the second week following the injury. Serial cultures revealed that only the isolation of Proteus species and P. aeruginosa from wounds could predict an infection caused by those microorganisms. During treatment with gentamicin and carbenicillin a marked increase in carbenicillin-resistant P. aeruginosa and gentamicin-resistant Klebsiella strains was noted. Cross-infections with carbenicillin-resistant P. aeruginosa was not a major cause in the development of resistant strains.

Drug resistance in relation to use of silver sulphadiazine cream in a burns unit

Topical chemoprophylaxis of extensive burns with silver sulphadiazine cream led to a large increase in the proportion of sulphadiazine-resistant Gram-negative bacilli in a burns unit. When all sulphonamide treatment in the ward was stopped; the incidence of sulphonamide-resistant strains fell back to levels similar to those recorded when silver sulphadiazine treatment was introduced. This was associated with a large reduction in the incidence of resistance of certain Gram-negative bacilli (especially Klebstella sp) to several antibiotics. Transferable resistance to sulphadiazine, shown by conjugation experiments with Escherichia coli K12, was found in a majority of the strains of Klebsiella sp tested, and in other species. A pattern of transferable resistance to tetracycline, cephaloridine, chloramphenicol, ampicillin, carbenicillin, and sulphadiazine (T Ce Cl A Ca S) was found in four of the 22 strains of Klebsiella tested, and closely related patterns were transferred by five other strains. These patterns of resistance were commonly found in Klebsiella sp isolated from burns in the period before the withdrawal of sulphonamides from the ward but were found in none of the Klebsiella strains isolated in the first six months after that period. Strains of Acinetobacter and Proteus, in which transferable resistance was not found, showed no appreciable fall or rise in sulphadiazine resistance; there was no fall in resistance of these organisms to tetracycline, cephaloridine, chloramphenicol, ampicillin or carbenicillin on withdrawal of sulphonamides from the ward, but there were substantial falls in resistance of Acinetobacter to kanamycin, gentamicin, trimethoprim, and tetracycline which were probably not caused by the withdrawal of sulphonamides.

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.

Antibiotic-resistant Staphylococcus aureus in dermatology and burn wards

Staphylococcus aureus isolated between 1967 and 1975 from the nose and skin lesions of patients in dermatology wards and from the burns of patients in a burns unit in Birmingham showed a high incidence of multiple antibiotic-resistant strains in both environments. Over 20% of the strains isolated from patients on admission to the dermatology wards were multiresistant. Resistance to benzylpenicillin, tetracycline, erythromycin, and fusidic acid was common in the dermatology wards; a smaller proportion of strains were resistant to lincomycin, and few (since 1972 none) were resistant to methicillin; resistance to novobiocin and chloramphenicol was uncommon. In the burns unit, fusidic acid resistance was uncommon, but resistance to benzylpenicillin, tetracycline, erythromycin, novobiocin, neomycin, methicilin, and lincomycin was common. Several of the antibiotics to which resistance was common in the burns unit were rarely if ever used there; strains resistant to these antibiotics probably remained common in the ward through the frequent use of other antibiotics, especially erythromycin, to which these strains were also resistant.

Comparison of the epidemiology of bacterial resistance to mecillinam and ampicillin

Mecillinam is a new type of beta-lactam antibiotic (an amidinopenicillanic acid) that is particularly active against Enterobacteriaceae and is taken orally as in the form of an ester, pivmecillinam. Assessment of any new antibiotic should include a survey of levels of bacterial resistance and investigation of its capacity to select resistant organisms or harm the commensal flora. Antibiotic resistance patterns of 2,000 Enterobacteriaceae isolated from the urine of patients with significant urinary tract infections were therefore determined. Mecillinam-resistant Enterobacteriaceae were found to be much less common than ampicillin-amoxycillin-resistant organisms both in the community and in hospital patients. Most ampicillin-resistant Enterobacteriaceae from infected urines were susceptible to mecillinam, but the relatively rare mecillinam-resistant organisms were usually resistant to ampicillin and cephaloridine. The fecal flora of 26 healthy volunteers who served as controls or were given repeated courses of therapeutic doses of either ampicillin or pivmecillinam was studied. Pivmecillinam had only a transient effect on the aerobic fecal flora and in contrast to ampicillin did not increase populations of resistant Enterobacteriaceae, which would be a potential hazard to the patient and contaminate the environment.

R-plasmid transfer in vivo in the absence of antibiotic selection pressure

The persistence of an O18 Escherichia coli strain resistant to tetracycline, streptomycin, and sulfonamide has been followed in the fecal flora of a single individual over a period of 9 months. The strain in question carrying an R plasmid was detectable from the beginning of the survey, but it was only after a 10-day period of tetracycline therapy that it reached an all but permanent dominance in the fecal flora. No transfer of the R plasmid carried by the strain to any other coliform could be detected for 202 days after the end of tetracycline treatment. At this point, however, an O88 E. coli carrying the same plasmid as the O18 strain appeared briefly as a predominant component of the flora. The two plasmids isolated from the O18 and the O88 E. coli strains have been characterized in molecular terms and found to be similar. This suggests that R-plasmid transfer between two E. coli strains occurred in an individual who was living a normal daily life and who was not receiving antibiotics.

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.

A quarter-century of the antibiotic era

A series of 1,500 strains of Pseudomonas aeruginosa was collected from a variety of sources to provide a group of strains which would truly represent the species. All of them were pyocine typed, and a wide range of types was included among the isolates from each source. The gentamicin, carbenicillin, colistin, and polymyxin minimal inhibitory concentration of each strain was measured by the agar dilution method employing the Steers inocula replicator. Over 99% of strains were inhibited by 8 μg of gentamicin per ml, by 256 μg of carbenicillin per ml, and by 4 μg of colistin per ml. The small number of strains more resistant to each antibiotic comprised a variety of different pyocine types. Few strains were found to be susceptible to tetracycline, chloramphenicol, kanamycin, or streptomycin at the single concentration tested.