Biomedical subjects
R N Jones
Publications and source records attributed to R N Jones.
Clinical use of beta-lactamase inhibitors in combination with extended-spectrum penicillins.
The in vitro antimicrobial spectrum of piperacillin-tazobactam is described and the results of clinical trials are summarized. Injectable products combining a beta-lactam antibiotic with a beta-lactamase inhibitor have a broad spectrum of activity, principally influenced by the potency of the beta-lactam. Piperacillin-tazobactam can be used for the treatment of infections caused by gram-negative, gram-positive, aerobic, and anaerobic bacteria. Appropriate indications include infections caused by mixed flora, such as gynecologic, intra-abdominal, and surgical wound infections. Other infections that appear responsive include those associated with human and animal bites, ischemic or diabetic foot infections, infected ischemic or pressure ulcers, and lower-respiratory-tract infections. Piperacillin-tazobactam has been reported to be superior to ticarcillin-clavulanate in community-acquired lower-respiratory-tract infections and superior to imipenem-cilastatin (at 1.5 g/day of imipenem) in intra-abdominal infection.
Modifications for disk diffusion susceptibility testing criteria of clinafloxacin (CI-960, AM-1091, PD127371) and fleroxacin (Ro 23-6240, AM-833) following studies with a challenge panel of ciprofloxacin-resistant clinical isolates.
A collection of ciprofloxacin-resistant organisms (200 strains) was developed among 300 total test strains to "challenge" the initial interpretive criteria developed for clinafloxacin (formerly CI-960), fleroxacin (formerly Ro 23-6240, AM-833), and ciprofloxacin. Generated results indicate the necessity for modified criteria for disk diffusion tests (5-micrograms disks) as follows: for clinafloxacin, susceptible at > or = 21 mm ( < or = 1 microgram/ml) and resistant at < or = 17 mm ( > or = 4 micrograms/ml), or susceptible at > or = 19 mm ( < or = 2 micrograms/liter) and resistant at < or = 15 mm ( > or = 8 micrograms/ml); for fleroxacin, susceptible at > or = 16 mm ( < or = 2 micrograms/ml) and resistant at < or = 11 mm ( > or = 8 micrograms/ml); and for ciprofloxacin, resistant at < or = 17 mm > or = 4 micrograms/ml). These modifications maximize total absolute interpretive accuracy between the standardized test methods, especially minimizing the potential for false susceptibility (very major errors) when testing truly resistant isolates. The clinafloxacin spectrum was widest against these resistant isolates, and the other two tested fluoroquinolones (ciprofloxacin, fleroxacin) possessed comparable overall spectrums of activity, although ciprofloxacin was generally more active on a weight basis. We urge the rapid acceptance of these criteria to improve the accuracy of the widely used National Committee for Clinical Laboratory Standards method for disk diffusion tests.
Interpretive errors using an automated system for the susceptibility testing of imipenem and aztreonam.
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Development, characterization, and initial evaluations of S1. A new chromogenic cephalosporin for beta-lactamase detection.
A novel, chromogenic cephalosporin reagent (S1) for beta-lactamase testing was produced that shares physicochemical characteristics with nitrocefin (formerly 87/312). S1 and nitrocefin in a disk-testing format for beta-lactamase performed at 100% agreement for detecting enzyme-producing isolates of Bacteroides fragilis group, Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Staphylococcus aureus, and selected Enterobacteriaceae. The time required to achieve an initial color change or a strong positive reaction was comparable for both chromogenic reagents for all organisms except the Gram-positive species. S1 reaction times were approximately 50% faster than nitrocefin for beta-lactamase-positive enterococci and S. aureus. These results from the developmental studies and a commercially prepared disk lot indicate that S1 is a promising beta-lactamase disk test reagent with the ability to detect all significant enzyme-producing species strains, some significantly earlier than the nitrocefin disk method.
Cross-resistance analysis for DU-6859a, a new fluoroquinolone, compared to six structurally similar compounds (ciprofloxacin, clinafloxacin, fleroxacin, levofloxacin, ofloxacin, and sparfloxacin).
Emerging resistance to the current fluoroquinolones has encouraged synthesis of new compounds in this class. We have evaluated the activity of DU-6859a, a novel halogenated quinolone, against a panel of 300 bacteria, relative to the activity of ciprofloxacin, clinafloxacin, fleroxacin, levofloxacin, ofloxacin, and sparfloxacin. DU-6859a was the most active of the fluoroquinolones studied and retains potentially useful activity against 80% of isolates resistant (minimum inhibitory concentration, > or = 4 micrograms/ml) to ciprofloxacin. Continued clinical investigation of DU-6859a and similar new quinolones is urged.
Emerging multiply resistant enterococci among clinical isolates. II. Validation of the etest to recognize glycopeptide-resistant strains.
Accurate, quantitative susceptibility testing of the enterococci for glycopeptide (vancomycin and teicoplanin) activity has become very important to guide chemotherapy as a result of emerging resistance. Reference dilution tests using broth and agar are generally difficult to perform, or in some commercial forms have demonstrated interpretive error. An alternative method, the Etest has promise as a system with qualitative and quantitative accuracy. Nearly 2000 enterococci from 97 laboratories in the United States were tested using broth microdilution, disk diffusion, and Etest methods. The Etest quantitative accuracy (+/- 1 log2 dilution) compared to the broth microdilution minimum inhibitory concentration was 90.1% (teicoplanin) to 94.1% (vancomycin). The qualitative interpretive accuracy of the Etest ranged from 98.7% for vancomycin to 99.9% for teicoplanin (no false-susceptible errors). All three tests were in remarkable agreement, with < or = 0.8% maximal discord by interpretive category. The Etest appears to be an excellent alternative to reference and standardized methods for producing quantitative activity measurements of glycopeptide susceptibility or resistance.
Emerging multiply resistant enterococci among clinical isolates. I. Prevalence data from 97 medical center surveillance study in the United States. Enterococcus Study Group.
To assess the evolving problem of therapeutic drug resistances among enterococci, we organized a comprehensive national (United States) surveillance trial using 99 recruited microbiology laboratories in 48 of the 49 contiguous states or districts. All but two sites completed the protocol that generated information from nearly 2000 enterococci, usually isolated from blood cultures. All strains were speciated by the same method (API 20S) and were susceptibility tested by three methods (broth microdilution, disk diffusion, and Etest) against ampicillin, penicillin, vancomycin, teicoplanin, gentamicin, and streptomycin. Strains resistant to a glycopeptide or penicillin, or possessing high-level aminoglycoside resistance were referred to the monitor's laboratory for validation and additional susceptibility testing against other alternative antimicrobial agents. The most common species were Enterococcus faecalis and Enterococcus faecium. However, antimicrobial resistance occurred most often among the E. faecium isolates. Twenty-three percent of participant centers (22 sites) reported 87 vancomycin-resistant isolates, which accounts for 4.4% of the isolates evaluated. A recent audit (March 1994) of the laboratories not reporting vancomycin resistance during the study interval (October-December 1992) revealed that 61% of sites have now recognized these strains, a threefold increase in 12-15 months. Teicoplanin remained active against 28% (Van B phenotype) of vancomycin-resistant enterococci (10 E. faecalis, 13 E. faecium, and one Enterococcus spp.). Ampicillin-resistant beta-lactamase-positive strains were found only at one medical center (two strains, 0.2% of referred or validated strains); however, ampicillin-resistant strains represented 12% of all enterococcal, but nearly 60% of E. faecium strains.(ABSTRACT TRUNCATED AT 250 WORDS)
Antimicrobial activity of 11 newer and investigational drugs tested against aerobic isolates from spontaneous bacterial peritonitis.
The in vitro susceptibility of 124 aerobic bacterial pathogens isolated from patients with spontaneous bacterial peritonitis (SBP) were tested against 11 antimicrobial agents, including parenteral or oral cephalosporins and fluoroquinolones. Most SBP isolates were Gram-negative organisms, and Escherichia coli and Klebsiella pneumoniae were responsible for 63% of the episodes evaluated. The fluoroquinolones (ciprofloxacin and ofloxacin) and the "fourth-generation" cephalosporin cefpirome were the most active agents against the Gram-negative bacteria. Commonly used cefotaxime and cefotaxime-desacetylcefotaxime (DES-CTX) combinations were also very active against Gram-negative bacteria with only few Enterobacter cloacae isolates being resistant (minimum inhibitory concentrations > 32 micrograms/ml). All streptococci were susceptible to cefotaxime, cefpirome, and cefdaloxime and to the cefotaxime-DES-CTX combinations, whereas only ofloxacin demonstrated acceptable activity against the enterococci. The widest spectrum of activity versus SBP isolates was found for ofloxacin (98% susceptibility) among the fluoroquinolones. For the beta-lactams, the widest spectrum of activity was demonstrated by cefpirome and the 2:1 cefotaxime-DES-CTX combination (93% susceptibility). These results indicate that the role of ofloxacin and newer parenteral or orally administered cephalosporins in the treatment of prophylaxis of SBP should be further evaluated.
National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers.
Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacillin-tazobactam was the most active beta-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95-97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii. In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting > 90% of all isolates tested.
Comparative antimicrobial activity of piperacillin-tazobactam tested against more than 5000 recent clinical isolates from five medical centers. A reevaluation after five years.
Piperacillin combined with tazobactam at a fixed concentration (4 micrograms/ml) and a ratio (8:1) was tested against 5,029 aerobic isolates and 447 fastidious organisms, including anaerobes. Among the Enterobacteriaceae, > 95% inhibition was shared only by imipenem (99.1% at < or = 4 micrograms/ml), and some newer cephalosporins (95.1% - 99.8% at < or = 8 micrograms/ml), and piperacillin-tazobactam (95.8% at < or = 16/4 micrograms/ml). Piperacillin-tazobactam was the most active agent tested against nonenteric Gram-negative bacilli (93.5% at < or = 8 micrograms/ml). Ampicillin-sulbactam was the most active agent against staphylococci (95.0% at < or = 8 micrograms/ml), followed by imipenem (91.8%), piperacillin-tazobactam (89.3% at < or = 8/4 micrograms/ml), and cefepime (86.2% at < or = 8 micrograms/ml). Against the enterococci, only ampicillin (93.0% at < or = 8 micrograms/ml) with or without sulbactam, piperacillin (91.0% at < or = 16 micrograms/ml) with or without tazobactam, and imipenem (91.0%) had acceptable activity. Piperacillin-tazobactam and imipenem were the most active drugs tested against all aerobic isolates, inhibiting 93.5% of isolates each. Piperacillin-tazobactam inhibited all fastidious isolates tested, including Haemophilus influenzae (MIC90, 0.094/4 micrograms/ml), Moraxella catarrhalis (MIC90, 0.064/4 micrograms/ml), Neisseira gonorrhoeae (MIC90, < or = 0.016/4 micrograms/ml), and Streptococcus pneumoniae (all MICs, < or = 4/4 micrograms/ml). Against the anaerobic isolates, the most broad-spectrum antimicrobial agents tested were imipenem (100.0%), piperacillin-tazobactam (99.5% at < or = 32/4 micrograms/ml), metronidazole (98.4% at < or = 8 micrograms/ml), and ticarcillin-clavulanic acid (95.1% at < or = 32/2 micrograms/ml). These results are nearly identical to a previous study involving the same five medical centers in 1989. Piperacillin-tazobactam appears to remain a highly effective beta-lactamase inhibitor combination with a wide empiric spectrum and potency in teaching hospitals.
Automation of polymerase chain reaction tests. Reduction of human errors leading to contamination.
We compared the performance over 21 months of manually performed polymerase chain reaction (PCR)-based DNA analysis experiments with 25 months of automated PCR performed by a Zymark robotic system. Automation of the PCR technique resulted in a sixfold reduction in the number of experiments reporting carryover contamination and decreased the overall rate of contamination among total reactions 68-fold. Whereas contamination occurrences among manual experiments were evenly dispersed over the study interval and correlated with the lack of experience of laboratory personnel, the contamination that occurred with the robotic system was confined to the first 10 months of operation. In manual experiments, many of the 81 no-target false positives were sufficiently strong to result in the invalidation of 151 samples and positive controls. The seven no-target control false positives in the automated system were weak bands that were easily subtracted as background. Because none of the negative samples had DNA bands, no sample on the automated system has ever been invalidated as a result of contamination. Automation of PCR tests appears to offer great promise in reducing contamination to acceptable levels (e.g., < or = 0.1%).
Reevaluations of disk diffusion susceptibility testing interpretive criteria for lomefloxacin and norfloxacin using fluoroquinolone-resistant isolates.
The current National Committee for Clinical Laboratory Standards interpretive criteria for disk diffusion susceptibility testing of lomefloxacin and norfloxacin were reevaluated using a test panel of 298 bacteria (200 with ciprofloxacin minimum inhibitory concentrations (MICs) at > or = 4 micrograms/ml). MICs were correlated with the diameter of zones of inhibition by regression statistics and error-rate bounding methods. Modifications of the interpretive criteria for lomefloxacin disk susceptibility testing are proposed as follows: susceptible at > or = 20 mm and resistant at < or = 16 mm, a 2-mm decrease of existing break-point zones. These criteria result in an absolute interpretive agreement of 95.3% with a very major (false susceptible) error rate of only 0.7%. The currently used criteria for norfloxacin (susceptible at > or = 16 mm and resistant at < or = 13 mm) were validated, and these break-points had an absolute interpretive correlation between methods of 91.9%. The change proposed for lomefloxacin disk interpretations would minimize minor and major errors most often reported for Staphylococcus saprophyticus isolates.
Evaluation of the Etest for determinations of antimicrobial spectrum and potency against anaerobes associated with bacterial vaginosis and peritonitis.
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Evaluation of the in-vitro activity of furopenem (SY5555 or SUN5555) against respiratory tract pathogens and beta-lactamase producing bacteria.
Furopenem is a novel orally active penem. In this study, furopenem was highly active in vitro against Streptococcus pneumoniae (MIC90 0.03 mg/L), Haemophilus influenzae (MIC90, 2 mg/L), and Moraxella catarrhalls (MIC90, 0.5 mg/L). Its activity was not reduced by a variety of beta-lactamase enzymes, however beta -lactam resistance by other mechanisms was associated with higher MICs.
In vitro evaluation of DV-7751a, a new fluoroquinolone with an enhanced spectrum of activity against gram-positive aerobic organisms and anaerobes.
DV-7751a is an investigational fluoroquinolone with improved spectrum and potency against gram-positive bacteria. We studied the in vitro activity of this compound against 771 recent clinical isolates by the reference agar and broth microdilution methods. Its activity was compared with those of ciprofloxacin, levofloxacin, and ofloxacin and with those of ceftazidime, oxacillin, and gentamicin where relevant. DV-7751a was four- to eightfold more active than the comparison fluoroquinolones against Enterococcus spp. (including vancomycin-resistant strains), Staphylococcus spp. (including oxacillin-resistant Staphylococcus aureus), Streptococcus spp., other gram-positive pathogens, and some anaerobes. The DV-7751a activity against most gram-negative species was similar to that of ofloxacin and ciprofloxacin. DV-7751a appears to be a candidate for the therapy of some mixed-flora infections and the treatment of bacteria resistant to the current fluoroquinolones.
Suggested modifications for disk diffusion susceptibility testing criteria for levofloxacin and sparfloxacin following tests with a predictor panel of ciprofloxacin-resistant clinical isolates.
A predictor panel of 300 clinical bacterial isolates (200 resistant to ciprofloxacin) was used to compare 5-micrograms disk diffusion test results with the MICs of ofloxacin (control), levofloxacin, and sparfloxacin. Regression analysis demonstrated high correlations between the methods for all three fluoroquinolones (r > or = 0.95). In order to minimize disk diffusion testing errors among the fluoroquinolone-resistant strains, the following modifications to previously proposed or published interpretive criteria were suggested: for levofloxacin, susceptible at > or = 17 mm (< or = 2 micrograms/ml) and resistant at < or = 13 mm (> or = 8 micrograms/ml); for sparfloxacin, susceptible at > or = 20 mm (< or = 1 microgram/ml) and resistant at < or = 16 mm (> or = 4 micrograms/ml). The study control drug, ofloxacin, did not appear to possess a significant error rate (5% minor error) when fluoroquinolone-resistant strains were tested, and no modifications were proposed. Under these proposed interpretive criteria, the absolute categorical agreements between standardized susceptibility testing methods for levofloxacin and sparfloxacin results were 91.3 and 94.0%, respectively (< or = 0.3% major errors and nil very major errors).
Susceptibility to levofloxacin predicted from in vitro susceptibility testing results obtained with ciprofloxacin and with ofloxacin.
A test battery of bacterial strains with a high incidence of resistance to fluoroquinolones was studied to determine the extent to which susceptibility to levofloxacin could be predicted from susceptibility tests performed with ciprofloxacin or ofloxacin as reagents. Isolates susceptible or intermediately susceptible to ofloxacin (MICs < or = 4 micrograms/ml) may be regarded as susceptible to levofloxacin, with the exception of Enterococcus faecium. Ciprofloxacin-susceptible isolates (MICs < or = 1 micrograms/ml) were also completely susceptible to levofloxacin. Clinical laboratories could use either of the currently used fluoroquinolones (ciprofloxacin or ofloxacin) to predict levofloxacin activity and spectrum with little risk of false-susceptible errors (0.0 to 1.3%). Results obtained with ofloxacin are superior in maximizing recognition of levofloxacin-susceptible clinical isolates.