Detection of vancomycin-resistant enterococci before and after antimicrobial therapy: use of conventional culture and polymerase chain reaction.

Antimicrobial therapy can increase the colonization density of gastrointestinal vancomycin-resistant enterococci (VRE). Among previously VRE-colonized patients, we evaluated VRE colonization before and after initiation of antimicrobial therapy by means of polymerase chain reaction (PCR) and culture. Perianal swab samples were obtained at admission to the hospital and after receipt of antimicrobial therapy. At admission, 12 (21%) of 56 patients were culture positive, and 17 (30%) had vanA or vanB genes detected by PCR. Culture results showed that 25 (86%) of 29 culture-negative patients from whom a second swab sample was obtained remained culture negative, 2 (6.9%) had a relapse of colonization with a strain related to the previously colonizing strain type (2 and 6 days after admission), and 2 (6.9%) tested positive for a previously undetected strain type (16 and 19 days after admission). PCR at admission detected VRE in 1 of the 2 patients who later relapsed. Patients with negative results of culture of the initial swab sample and of PCR were unlikely to relapse after receipt of antimicrobial therapy.

Management of fluoroquinolone resistance in Pseudomonas aeruginosa--outcome of monitored use in a referral hospital.

We evaluated a strategy designed to improve useful activity of ciprofloxacin against Pseudomonas aeruginosa. Following changes in antimicrobial agent use made by the institutional Pharmacy and Therapeutic Drug Committee, monthly drug usage and microbial susceptibility records from June 1992 through October 1995 were reviewed. From July 1992 through October 1992 (Period 1), ciprofloxacin and ofloxacin usage represented 95 and 5% of total quinolone doses; from December 1992 to March 1993 (Period 2), ciprofloxacin represented 19%; from July 1993 to October 1993 (Period 3), ciprofloxacin usage represented 85%; from July 1994 to October 1994 (Period 4), ciprofloxacin represented 95%; and from July 1995 to October 1995 (Period 5), ciprofloxacin and ofloxacin respectively represented 98 and 2% of total quinolone doses. Comparison of the anti-pseudomonal activity of the two fluoroquinolones to ofloxacin use, ciprofloxacin use and total quinolone use during the entire observational period showed the highest (negative) correlation with ofloxacin use versus ofloxacin activity (y = -15.04x + 1367.99, r2 = 0.06, w = 0.126). Increased use of quinolones plus a change to primarily ofloxacin usage appeared to adversely affect the activity of both ofloxacin and ciprofloxacin against P. aeruginosa.

Thirteen-year evolution of azole resistance in yeast isolates and prevalence of resistant strains carried by cancer patients at a large medical center.

Drug resistance is emerging in many important microbial pathogens, including Candida albicans. We performed fungal susceptibility tests with archived isolates obtained from 1984 through 1993 and fresh clinical isolates obtained from 1994 through 1997 by testing their susceptibilities to fluconazole, ketoconazole, and miconazole and compared the results to the rate of fluconazole use. All isolates recovered prior to 1993 were susceptible to fluconazole. Within 3 years of widespread azole use, we detected resistance to all agents in this class. In order to assess the current prevalence of resistant isolates in our hematologic malignancy and transplant patients, we obtained rectal swabs from hospitalized, non-AIDS, immunocompromised patients between June 1995 and January 1996. The swabs were inoculated onto sheep's blood agar plates containing 10 microg of vancomycin and 20 microg of gentamicin/ml of agar. One hundred one yeasts were recovered from 97 patients and were tested for their susceptibilities to amphotericin B, fluconazole, flucytosine, ketoconazole, and miconazole. The susceptibility pattern was then compared to those for all clinical isolates obtained throughout the medical center. The antifungal drug histories for each patient were also assessed. The yeasts from this surveillance study were at least as susceptible as the overall hospital strains. There did not appear to be a direct linkage between prior receipt of antifungal agent therapy and carriage of a new, drug-resistant isolate. Increased resistance to newer antifungal agents has occurred at our medical center, but it is not focal to any high-risk patient population that we studied. Monitoring of susceptibility to antifungal agents appears to be necessary for optimizing clinical therapeutic decision making.

Successful treatment of persistent bacteremia due to vancomycin-resistant, ampicillin-resistant Enterococcus faecium.

Emergence of vancomycin-resistant enterococci has become an increasing problem in many medical centers. We report a liver transplant recipient with vancomycin-resistant Enterococcus faecium bacteremia who was successfully treated using very high dose continuous infusion ampicillin/sulbactam, plus gentamicin after he remained bacteremic on high dose ampicillin and gentamicin. At our institution, 83% of E. faecium isolates from 1994 were inhibited by ampicillin/sulbactam compared to 66% for ampicillin at an MIC < or = 64 micrograms/ml. None of these strains produced beta-lactamase, suggesting sulbactam may have an unexplained beneficial effect against some enterococci. Although an MIC of < or = 8 micrograms/ml is required for ampicillin to be considered active against enterococci, much higher levels of ampicillin or ampicillin/sulbactam are safely achievable. The response of our patient and the reported in vivo data have implications for future treatment of this pathogen, and may necessitate a reevaluation of susceptibility interpretation guidelines by clinical laboratories, and therapeutic drug dosing by clinicians.

Activity of twenty-one antimicrobial agents including l-ofloxacin against quinolone-sensitive and -resistant, and methicillin-sensitive and -resistant Staphylococcus aureus.

There is a need to identify alternative agents to vancomycin for the treatment of infections with methicillin-resistant Staphylococcus aureus (MRSA). One candidate is the l isomer of ofloxacin (DR-3355). We tested 520 frozen MRSA isolates, 248 fresh MRSA isolates, and 375 fresh methicillin-susceptible S. aureus (MSSA) isolates from Minnesota, and 600 clinical isolates of S. aureus (150 MRSA and 450 MSSA) from Illinois. Over 90% of the MRSA strains were resistant to 32 micrograms/ml of oxacillin. Of the 520 frozen MRSA, 24% were susceptible to < or = 2 micrograms/ml ofloxacin, and an additional 74% were susceptible to ofloxacin between 8 and 16 micrograms/ml. More than 98% of all strains were susceptible to < or = 16 micrograms/ml ofloxacin or l-ofloxacin. All the quinolones had a bimodal distribution of in vitro activity, but for only ofloxacin and l-ofloxacin was activity confined to a very narrow range.

Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance.

Bactericidal testing has been used for several decades as a guide for antimicrobial therapy of serious infections. Such testing is most frequently performed when bactericidal antimicrobial agent therapy is considered necessary (such as when treating infectious endocarditis or infection in an immunocompromised host). It has also been used to ensure that the infecting organism is killed by (not tolerant to) usually bactericidal compounds. However, few data are available to support the role of such tests in direct patient care. Several important variables affect the reproducibility of the test results; however, proposed reference methods are now available for performing the MBC test. With minor modifications, these can provide a standardized approach for laboratories that need to perform them. Currently, little evidence is available to support the routine use of such testing for the care of individual patients. However, testing of new (investigational) antimicrobial agents can be beneficial in determining their potential to provide bactericidal antimicrobial activity during clinical use. New methods to assess bactericidal activity are being developed, but as yet none have been rigorously tested in patient care settings; further, for most of these methods, little information is available as to which technical parameters affect their results. In clinical laboratories, all bactericidal tests must be performed with rigorously standardized techniques and adequate controls, bearing in mind the limitations of the currently available test procedures.

Revision of standards for adjusting the cation content of Mueller-Hinton broth for testing susceptibility of Pseudomonas aeruginosa to aminoglycosides.

A multilaboratory study was undertaken to reassess the amount of calcium and magnesium that should be added to Mueller-Hinton broth when testing Pseudomonas aeruginosa against amikacin, gentamicin, isepamicin, netilmicin, and tobramycin. To achieve parity with agar dilution tests, cation-adjusted broth should contain 20 to 25 mg of calcium and 10 to 12.5 mg of magnesium per liter rather than the 50- and 25-mg/liter supplements recommended previously. For quality control of tests with contemporary media, MIC control limits should be adjusted by lowering the current MIC limits by at least 1 doubling-dilution interval.

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.

Emergence of ciprofloxacin resistance in nosocomial methicillin-resistant Staphylococcus aureus isolates. Resistance during ciprofloxacin plus rifampin therapy for methicillin-resistant S aureus colonization.

We initiated a randomized, single-blinded trial of ciprofloxacin plus rifampin vs sulfamethoxazole and trimethoprim plus rifampin in the therapy for patients who underwent colonization with methicillin-resistant Staphylococcus aureus (MRSA). Patients who were colonized with MRSA received 2 weeks of either regimen. The study was terminated after the enrollment of 21 subjects due to the recognition of ciprofloxacin resistance in 10 of 21 new MRSA isolates during the last 2 months of the study. Five of the 10 patients with ciprofloxacin-resistant MRSA isolates had never received ciprofloxacin. Long-term (6-month) eradication had been achieved in only three of 11 ciprofloxacin plus rifampin and four of 10 sulfamethoxazole and trimethoprim plus rifampin recipients. The use of this new fluoroquinolone for the eradication of MRSA colonization is usually not effective and may risk the development of ciprofloxacin resistance in MRSA within the hospital environment.

Comparative efficacy of cefoperazone, cefoperazone plus sulbactam, ciprofloxacin, clindamycin, metronidazole, and penicillin G against anaerobic bacteria in an animal model.

Treatment efficacy of various antimicrobial regimens against anaerobes was studied in semipermeable chambers simulating a closed-space, locally neutropenic infection site in rabbits. Bacteroides fragilis, Bacteroides melaninogenicus, Clostridium perfringens, and Peptostreptococcus anaerobius were inoculated (at a mean of 5.3 log10 CFU/ml in prereduced pooled rabbit serum) into the chambers (one isolate per chamber) in triplicate. Antimicrobial therapy consisted of cefoperazone, cefoperazone plus sulbactam, ciprofloxacin, clindamycin, metronidazole (against the gram-negative anaerobes), or penicillin G (against the gram-positive anaerobes), beginning 4 hours after organism inoculation and continuing every 6 hours for 16 doses. With the use of anaerobic techniques for specimen acquisition, transport, and culture, quantitative bacterial findings were measured at the start of therapy and at various time points thereafter. Antibiotic concentrations were measured in blood and chamber fluid by liquid chromatography or bioassay methods. At the end of the study in vivo organisms were reduced by at least 3 log10 CFU/ml from drug-free growth control chambers by all the antimicrobial regimens tested except for cefoperazone against B. fragilis and ciprofloxacin against the three isolates tested. The addition of sulbactam to cefoperazone inhibited B. fragilis beta-lactamase activity and eradicated B. fragilis in vivo. In vivo results with this model confirmed in vitro susceptibilities of all tested antimicrobials except ciprofloxacin and should provide useful indications of the potential clinical efficacy of other new agents against anaerobes.

Therapy of lower extremity infections with ciprofloxacin in patients with diabetes mellitus, peripheral vascular disease, or both.

PURPOSE: Lower extremity infections in the presence vascular insufficiency are difficult and costly to treat. Few well-controlled clinical trials evaluating the management of these infections exist. We decided to investigate the ability of a new fluoroquinolone, ciprofloxacin, to reduce the morbidity associated with these infections and the amount of in-hospital time required for the administration of antibiotic therapy. PATIENTS AND METHODS: Forty-eight patients with peripheral vascular disease (46 with diabetes mellitus) who presented to the hospital for treatment of lower extremity infections were randomized in a blinded fashion to receive oral ciprofloxacin at a dosage of either 750 mg or 1,000 mg twice daily. Patients with osteomyelitis received three months of therapy and those with infections limited to soft tissues, three weeks of ciprofloxacin treatment. All subjects were followed for one year. RESULTS: One patient received an amputation 24 hours after enrollment, and two patients discontinued therapy after 20 and 34 days because of adverse effects and were not evaluable. At the one-year follow-up, 27 of the 45 (60 percent) evaluable patients had a fully successful outcome defined as not requiring either repeat antimicrobial therapy for their initial infection or amputation of the involved extremity. In the group of 18 patients in whom therapy failed, a total of only nine amputations were required. In the 15 patients whose lesion closed during therapy, 93% (14 patients) experienced a long-term successful outcome. CONCLUSION: Treatment with this new fluoroquinolone offers promise for the improved outcome of patients with the serious infectious complication of infected lower extremity ulcerations in peripheral vascular disease, diabetes mellitus, or both.

Treatment of ciprofloxacin- and ceftizoxime-induced resistant gram-negative bacilli.

Gram-negative bacilli that had been selected for resistance to either ciprofloxacin or ceftizoxime as a result of previous exposure to these agents were inoculated into semipermeable subcutaneous chambers in rabbits, modeling a locally neutropenic closed-space infection. Five resistant organisms, one Serratia marcescens (157) and four Pseudomonas aeruginosa (864, 876, 913, and 915) strains, were selected by previous therapy with ciprofloxacin, and six Pseudomonas strains (833, 845, 864, 876, 913, and 915) were selected by previous therapy with ceftizoxime. Animals were treated with either single antibiotics or combinations of antibiotics for four days, and the response was determined by quantitative bacterial count measurements. The selected (induced) resistance was stable for at least four days, both in vivo and in vitro, but was limited to the antibiotic class of the agent used for induction. Four of five isolates for which resistance had been induced by ciprofloxacin returned to preinduction susceptibility by the eight day of subculture. Organisms that were selected for resistance to ciprofloxacin were successfully treated by a combination of azlocillin and amikacin, and were as sensitive to that regimen as were the parent, uninduced strains. Organisms selected for resistance by pretreatment with ceftizoxime were successfully treated by the combination of ciprofloxacin plus azlocillin, and this regimen was also equally active against the selected strains as it was against the parental isolates. Although selection or induction of resistance is a potential problem with all new potent antimicrobial agents, it appears that infections due to these isolates can still be treated successfully through the use of appropriate combination chemotherapy.

Animal models: the in-vivo evaluation of ciprofloxacin.

Ciprofloxacin has been extensively investigated in various animal models of infection. These studies have demonstrated ciprofloxacin to possess in-vivo activity comparable to its activity previously demonstrated in vitro. The reported investigations have shown ciprofloxacin to be equal or superior to all other agents tested for Gram-negative, as well as most Gram-positive bacteria. These studies have also demonstrated that in-vitro susceptibility testing correlates well with in-vivo therapeutic outcome, in the animal models. The reported information has provided new directions for use of this agent, including the possibility for the use of ciprofloxacin as a replacement for aminoglycosides in combination therapy of serious enterococcal infections.

Comparison of azlocillin, ceftizoxime, cefoxitin, and amikacin alone and in combination against Pseudomonas aeruginosa in a neutropenic-site rabbit model.

The efficacy of beta-lactam antibiotics and amikacin alone and in various combinations against Pseudomonas aeruginosa was studied in a rabbit model simulating a closed-space infection in a locally neutropenic site. Six strains of P. aeruginosa were studied in semipermeable chambers placed subcutaneously in rabbits. Therapy was begun 4 h after inoculation of 5 X 10(4) CFU of bacteria per ml of pooled rabbit serum into the chambers. Antibiotics were administered intramuscularly every 6 h for 16 doses. Quantitative bacteriology was measured at the start of therapy and at 20, 44, and 92 h thereafter. Antibiotic concentrations were measured in blood and chamber fluid. Results were compared with in vitro tests of susceptibility and synergy. No single-agent therapy eradicated any of the six test organisms. Azlocillin (100 mg/kg per dose) plus amikacin (20 mg/kg per dose) eliminated five of six organisms by 92 h, and ceftizoxime (100 mg/kg per dose) plus amikacin (20 mg/kg per dose) eliminated three of six test strains. Azlocillin plus ceftizoxime (each 100 mg/kg per dose) failed to eliminate any of the six strains. To eliminate P. aeruginosa in this model, two drugs were required, with one being an aminoglycoside. In vitro susceptibility tests of synergy were predictive of successful therapy whenever the antibiotic concentrations (free and total) at the infection site exceeded the MBC for both the aminoglycoside alone and the beta-lactam when tested in combination with amikacin.