Automated antimicrobial susceptibility testing: what the infectious diseases subspecialist need to know.
Explore the source record for details and available documents.
Drug Resistance, Microbial↗
Biomedical subjects
M J Ferraro
Publications and source records attributed to M J Ferraro.
Effect of pH variation on the susceptibility of Helicobacter pylori to three macrolide antimicrobial agents and temafloxacin.
The in vitro susceptibility of 27 clinical isolates of Helicobacter pylori to erythromycin, clarithromycin, azithromycin and temafloxacin under various pH conditions was evaluated. Clarithromycin (MIC90 0.03 micrograms/ml) was found to be significantly more active than either erythromycin (MIC90 0.125 micrograms/ml) or azithromycin (MIC90 0.25 micrograms/ml) at a neutral pH. Lowering the pH to 5.75 resulted in a loss in efficacy from 8- to 32-fold for all three macrolides studied. The MIC90 of clarithromycin (0.5 micrograms/ml) remained lower than those of azithromycin (2 micrograms/ml) and erythromycin (4 micrograms/ml). No synergism or antagonism was observed with combinations of clarithromycin and temafloxacin at either the neutral or lower pH values.
Anti-Bacterial Agents↗
Comparison of four methods in the diagnosis of Clostridium difficile disease.
Nine hundred forty-five stool specimens from patients suspected of having Clostridium difficile disease were examined using a cell culture cytotoxicity assay (CTA), two enzyme immunoassay (EIA) kits (Cytoclone for toxins A and B; VIDAS for toxin A) and a latex agglutination assay (CDT). One hundred nineteen specimens had positive titers (> or = 90) in the CTA; clinical review of 16 discordant samples and 49 controls supported the significance of 90 as the positive cut-off titer. The performance of the two EIAs and the latex assay was assessed relative to CTA titers of the samples. Sensitivity was < or = 50% for all three assays for the 24 specimens with CTA titers of 90, but it reached 97-100% for the two EIAs and 84% for the latex assay at titers of > or = 2,250. The Cytoclone EIA exhibited higher sensitivity at the lower positive titers. Overall, specificity of the methods ranged from 96.7% (CDT latex assay) to 99.1% (Cytoclone EIA).
Bacterial Proteins↗
In vitro activity of CP-99,219, a new fluoroquinolone, against clinical isolates of gram-positive bacteria.
The in vitro activity of the fluoroquinolone CP-99,219 against gram-positive bacteria was compared with those of five other antimicrobial agents. Against ciprofloxacin-susceptible staphylococci and against streptococci, MICs were < or = 0.12 and < or = 0.5 microgram/ml, respectively. CP-99,219 was also more active than ciprofloxacin against ciprofloxacin-resistant staphylococci, most enterococci, Leuconostoc spp., and lactobacilli.
Anti-Bacterial Agents↗
In vitro activity of RP59500, an injectable streptogramin antibiotic, against vancomycin-resistant gram-positive organisms.
The in vitro activity of RP59500, a streptogramin antibiotic, against 146 clinical isolates of vancomycin-resistant gram-positive bacteria was examined. Five strains of the species Enterococcus casseliflavus and Enterococcus gallinarum, for which the MIC of vancomycin was 8 micrograms/ml, were also studied. Twenty-eight vancomycin-susceptible strains of Enterococcus faecalis and Enterococcus faecium were included for comparison. The drug was highly active against Leuconostoc spp., Lactobacillus spp., and Pediococcus spp. (MICs, < or = 2 micrograms/ml). RP59500 was more active against vancomycin-susceptible strains of E. faecium than E. faecalis (MICs for 90% of the strains [MIC90s], 1.0 versus 32 micrograms/ml). Vancomycin-resistant strains of E. faecalis were as resistant to RP59500 as vancomycin-susceptible strains (MIC90, 32 micrograms/ml), but some vancomycin-resistant E. faecium strains were relatively more resistant to the new agent (MIC90, 16; MIC range, 0.5 to 32 micrograms/ml) than were vancomycin-susceptible organisms of this species.
Drug Resistance, Microbial↗
In vitro activity of ramoplanin against vancomycin-resistant gram-positive organisms.
In vitro activity of ramoplanin, a cyclic lipoglycopeptide, against 92 vancomycin-resistant gram-positive organisms was evaluated. Ramoplanin demonstrated potent activity against many highly vancomycin-resistant organisms including enterococci (MICs for 90% of strains tested of 0.5 micrograms/ml) and against Lactobacillus spp., Leuconostoc spp., and Pediococcus spp., all of which were inhibited at concentrations of < or = 0.25 micrograms/ml. This drug or a derivative compound merits further investigation as a potential therapeutic agent for infections due to vancomycin-resistant enterococci.
Anti-Bacterial Agents↗
Cytomegalovirus antigenemia: clinical correlations in transplant recipients and in persons with AIDS.
We evaluated a rapid immunoperoxidase technique for the detection of cytomegalovirus (CMV) antigenemia in peripheral blood neutrophils of 56 transplant recipients (117 specimens) and 36 persons with AIDS (59 specimens). Antigenemia was 92% sensitive and 98% specific for the detection of clinical CMV infection in transplant recipients and 100% sensitive and 86% specific in persons with AIDS. Overall, CMV antigenemia was a more rapid and sensitive method for the detection of clinical CMV infection than either shell vial culture or conventional tube culture of blood.
Acquired Immunodeficiency Syndrome↗
Cefuroxime screening test for pneumococci.
Explore the source record for details and available documents.
Cefuroxime↗
Understanding and diagnosing infectious complications in the immunocompromised host. Current issues and trends.
The number of patients who are at an increased risk of life-threatening infection has expanded greatly during the past decade. This expansion is because of two events, one terrible in its consequences, the other very positive. The first is the unprecedented epidemic of opportunistic infection that follows infection with the human immunodeficiency virus or the acquired immunodeficiency syndrome. The second is a direct consequence of the successes of the transplant surgeon, the cancer chemotherapist, the hematologist, and the rheumatologist. The authors review the current issues and trends in understanding and diagnosing infectious complications in the immunocompromised host.
Acquired Immunodeficiency Syndrome↗
Lack of activity of zidovudine against Ureaplasma urealyticum and Mycoplasma hominis.
Explore the source record for details and available documents.
Drug Evaluation, Preclinical↗
New vancomycin disk diffusion breakpoints for enterococci. The National Committee for Clinical Laboratory Standards Working Group on Enterococci.
Since 1988, when the first vancomycin-resistant enterococcus was described, several descriptions of failures of disk diffusion breakpoints to detect low-level vancomycin resistance (MICs, 8 to 32 micrograms/ml) have been published. A four-laboratory collaborative study was undertaken to establish more accurate breakpoints for the disk test. Mueller-Hinton agar was used to perform dilution testing (in three laboratories) and disk diffusion testing (in all laboratories). Results were determined at 18, 24, and 48 h, and zones of inhibition were read using both transmitted and reflected light. One hundred organisms (35 Enterococcus faecalis, 55 E. faecium, and 10 E. gallinarum or E. casseliflavus isolates) were selected to represent vancomycin-susceptible and -resistant phenotypes. Interlaboratory agreement of agar dilution MICs was better at 24 h (91 to 94% within +/- 1 dilution) than at 18 h (76% within +/- 1 dilution). Therefore, 24-h agar dilution MIC results were used as the reference. For disk diffusion, it was critical to note the presence of a haze or colonies inside the zone when interpreting the test, since this correlated better with the results of the agar dilution test. The presence of a haze or inner colonies was best detected by reading the zones with transmitted light and incubating the plates for a full 24 h. When plotted against 24-h agar dilution MICs, breakpoints of </= 14 mm (resistant), 15 to 16 mm (intermediate), and >/= 17 mm (susceptible) resulted in 58 minor errors (14.5% of total values) and 5 very major errors (2.2% of resistant values or 1.3% of total values). No major errors were seen. Results of repeat testing using a common lot of Mueller-Hinton agar showed 52 minor errors (13.3%) and 4 major errors (4.2% of susceptible values of 1.0% pf total values) but no very major errors. It is recommended that any haze or colonies within the zone be taken into account when determining zones of inhibition and that an MIC test be performed for strains with intermediate zones if vancomycin is being considered for treatment.
Agar↗
Multicenter evaluation of the use of Haemophilus test medium for broth microdilution antimicrobial susceptibility testing of Streptococcus pneumoniae and development of quality control limits.
A five-laboratory collaborative study was undertaken to determine the precision and accuracy of broth microdilution susceptibility tests of Streptococcus pneumoniae isolates performed with Haemophilus test medium (HTM) compared with tests performed with lysed horse blood-supplemented Mueller-Hinton broth (LHB). The intra-and interlaboratory reproducibilities of MICs of 10 antimicrobial agents determined with the two media were found to be quite similar and highly reproducible in both media. On the basis of favorable performance in this study, S. pneumoniae ATCC 49619 is recommended as a quality control strain to assess the performance of HTM when this medium is used for testing of pneumococci. Testing of 293 unique clinical isolates of S. pneumoniae with both media in the respective participant laboratories allowed a direct comparison of MIC results and a calculation of interpretive error rates. Although there were some slight differences between MICs determined with HTM and MICs determined with LHB, few very major or major errors resulted from testing the clinical isolates against the 10 antimicrobial agents. However, MIC-interpretive criteria specific for S. pneumoniae should be developed and promulgated through a national consensus mechanism.
Culture Media↗
Development of revised quality control limits for disk diffusion susceptibility tests of selected cephem antibiotics with Haemophilus influenzae and description of a new control strain.
Inconsistent quality control results in disk diffusion testing of cefaclor, cefamandole, cefonicid, and cefuroxime with Haemophilus influenzae ATCC 49247 and Haemophilus test medium (HTM) prompted a search for an alternative control strain that would provide more reliable results. A five-laboratory study was conducted to evaluate two candidate H. influenzae strains as possible alternatives to the aforementioned strain. Repetitive testing of the candidate strains and H. influenzae ATCC 49247 over several days with a total of six different lots of HTM documented consistent performance of the two candidate strains and confirmed inconsistent results for some of the antibiotics with H. influenzae ATCC 49247. In particular, certain lots of HTM failed to yield cefaclor and cefamandole zone sizes within the quality control range advocated by the National Committee for Clinical Laboratory Standards. Because of the greater consistency offered by the new strains, one was selected (now designated H. influenzae ATCC 49766) to be recommended for routine quality control testing of cefaclor, cefamandole, cefonicid, cefuroxime, and the related carbacephem loracarbef. The new control strain and zone size ranges proposed here have been approved by the National Committee for Clinical Laboratory Standards in place of the previously recommended strain and zone size limits for testing of these five cephem antibiotics.
Ampicillin↗
Increasing resistance to beta-lactam antibiotics among clinical isolates of Enterococcus faecium: a 22-year review at one institution.
To identify any change in the antibiotic resistance of Enterococcus faecium, we examined the antibiotic susceptibilities of clinical strains (n = 84) isolated at one institution during the 22 years since 1968. A significant increase in resistance to penicillin was observed during the study period: the MICs of penicillin for 50 and 90% of isolates tested were 16 and 64 micrograms/ml, respectively, from 1969 to 1988 (n = 48; geometric mean MIC, 14 micrograms/ml) , whereas they were 256 and 512 micrograms/ml, respectively, from 1989 to 1990 (n = 36; geometric mean MIC, 123 micrograms/ml) (P less than 0.001). A comparable increase in resistance to ampicillin was also noted (P less than 0.001). No strains produced detectable beta-lactamase. In contrast, susceptibilities to vancomycin, teicoplanin, and ciprofloxacin remained stable. High-level resistance to gentamicin was observed in none of 48 isolates from 1969 to 1988, but was present in 22 of 36 strains (61%) from 1989 to 1990 (P less than 0.001) and was significantly associated with resistance (MIC, greater than or equal to 128 micrograms/ml) to penicillin (P less than 0.001). To assess the potential evolution of antibiotic resistance in this species, clinical isolates (n = 24) were compared with strains isolated in 1968 from a human population in the Solomon Islands that was never exposed to antibiotics. Solomon Island isolates were significantly more susceptible than all clinical strains to penicillin, ampicillin, and vancomycin (P less than 0.001 for each), but they exhibited no differences in susceptibility to teicoplanin or ciprofloxacin. The penicillin-binding affinity of penicillin-binding protein 5 (PBP 5) in penicillin-resistant clinical strains (MIC, 512 micrograms/ml) was notably lower than that in strains with more typical susceptibilities, suggesting an alteration in this PBP as a possible mechanism for increased penicillin resistance. Solomon Island strains most susceptible to penicillin demonstrated a prominent PBP 5* and the absence of PBP 5. These changes in the antibiotic resistance of E. faecium emphasize the importance of identifying this species in patients with serious enterococcal infections and the necessity of assessing its susceptibility to both beta-lactams and aminoglycosides if effective therapy is to be identified.
Anti-Bacterial Agents↗
Detection of enterococcal high-level aminoglycoside resistance with MicroScan freeze-dried panels containing newly modified medium and Vitek Gram-Positive Susceptibility cards.
Both conventional and modified MicroScan Type 5 panels and Vitek Gram-Positive Susceptibility cards were compared with agar dilution screen plates for their abilities to detect high-level resistance to gentamicin and streptomycin in 235 enterococcal isolates, including 167 Enterococcus faecalis and 63 E. faecium isolates. The modified Type 5 panels contained dextrose-phosphate broth instead of Mueller-Hinton broth in their high-level-resistance screen wells. The sensitivities for detection of gentamicin and streptomycin high-level resistance were 100 and 100% (E. faecalis) and 100 and 94% (E. faecium) for the modified MicroScan panels, 100 and 89% (E. faecalis) and 100 and 98% (E. faecium) for the conventional MicroScan panels, and 81 and 86% (E. faecalis) and 85 and 94% (E. faecium) for the Vitek cards. All specificities were 100% except for the Vitek cards with streptomycin, where it was 96%. Isolates that showed resistance on the streptomycin agar screen plates were rescreened on plates containing 32,000 micrograms/ml to detect ribosomally mediated resistance. For all three systems, every failure to detect streptomycin high-level resistance occurred in isolates with enzymatic, not ribosomal, resistance. The modified MicroScan Type 5 panels are a suitable method for detecting enterococcal high-level resistance to gentamicin and streptomycin. The Vitek cards are too insensitive for this purpose.
Aminoglycosides↗
Association of Helicobacter pylori infection with dyspeptic symptoms in patients undergoing gastroduodenoscopy.
PURPOSE: To determine the prevalence of Helicobacter pylori in patients with non-ulcer dyspepsia and ulcer disease as well as in a control population undergoing endoscopic retrograde cholangiopancreatography (ERCP) for suspected pancreatic or biliary disease. PATIENTS AND METHODS: Forty-six eligible patients undergoing upper endoscopy at Massachusetts General Hospital were studied over a period of 18 months, as well as 24 patients undergoing ERCP for presumed pancreatic or biliary disease. Two biopsy specimens from the fundus and two from the antrum were taken for microbiologic and histopathologic analysis. Sera were examined by enzyme-linked immunoabsorbent assay. All specimens were processed in a blind fashion. Chi-square test with Yates' correction was used for statistical analysis. RESULTS: H. pylori was found in 31 of 46 (67%) study patients and in six of 24 (25%) control patients (by microbiologic or histologic techniques) (p less than 0.01). H. pylori was found in all patients with peptic ulcer disease and in 60% of patients without ulcers. No association between H. pylori and any specific gastrointestinal symptom was observed. H. pylori was identified in the fundus as often as in the antrum, although in the antrum the organism was more often associated with histologic gastritis. Compared with histology, serologic assays for IgG and IgA antibodies to H. pylori had sensitivities of 100% and 94%, and specificities of 86% and 76%, respectively. Reexamination of selected specimens without knowledge of their identity revealed that the specificity of serology exceeded 94% while the sensitivity of histologic and microbiologic studies may have been closer to 80%. CONCLUSIONS: H. pylori was more common in dyspeptic patients than in our control subjects undergoing ERCP. Multiple biopsy sites from fundus and antrum are required to exclude infection. Serologies of IgG and IgA were sensitive and specific for H. pylori, suggesting a possible role for non-endoscopic diagnosis of this infection. The frequent association of H. pylori with active inflammation rather than with quiescent gastritis is consistent with a pathologic role of this organism.
Adult↗
Comparative in vitro activity of WIN 57273, a new fluoroquinolone antimicrobial agent.
The in vitro activity of WIN 57273, a new fluoroquinolone antimicrobial agent, was evaluated against approximately 600 bacterial isolates. The new drug was 4- to 128-fold more active than ciprofloxacin against a broad range of gram-positive organisms, with the new drug inhibiting 90% of strains of each species except Enterococcus faecium at concentrations of less than or equal to 0.25 microgram/ml. WIN 57273 was four- to eightfold less active than ciprofloxacin against many members of the family Enterobacteriaceae, but the MICs of the new drug for 90% of strains tested (MIC90s) were less than or equal to 8 micrograms/ml (range, 0.25 to 8 micrograms/ml) for all species. Branhamella catarrhalis, Haemophilus influenzae, Neisseria gonorrhoeae, and Legionella spp. were highly susceptible (MIC90s, less than or equal to 0.06 microgram/ml). WIN 57273 demonstrated excellent activity against anaerobes (MIC90s, less than or equal to 0.25 microgram/ml), and the drug was also more active than ciprofloxacin against 30 strains of Mycobacterium avium-M. intracellulare (MIC, 0.1 to 1.0 microgram/ml). The activity of WIN 57273 against gram-positive organisms was minimally affected by pH and increased at low pH (5.4) against gram-negative organisms. The bactericidal activity of WIN 57273 was demonstrated by time-kill techniques against selected organisms. The frequencies of spontaneous resistance to the new agent were low, but resistant colonies could be selected after serial passage of initially susceptible organisms through incremental concentrations of the drug.
4-Quinolones↗
Evaluation of two single-plate incubation systems and the anaerobic chamber for the cultivation of anaerobic bacteria.
Three systems that are available for the incubation of anaerobic organisms were evaluated to assess their ability to support the growth of 25 anaerobic stock strains and to successfully recover anaerobic bacteria from clinical specimens. These were the anaerobic chamber, the Anaerobic Pouch System Catalyst-Free (Difco Laboratories, Detroit, Mich.), and the Bio-Bag Environmental Chamber Type A (Marion Scientific, Div. Marion Laboratories, Inc., Kansas City, Mo.). Three study centers were involved, the Wadsworth Anaerobe Laboratory (Los Angeles, Calif.), the Good Samaritan Hospital (San Jose, Calif.), and the Massachusetts General Hospital (Boston). A total of 171 anaerobic organisms were isolated from 49 clinical specimens that were cultured at the three test centers. Of these, 169 (99%) were recovered from media that were incubated in the anaerobic chamber, 163 (95%) were recovered from the Anaerobic Pouch, and 147 (86%) were recovered from the Bio-Bag. A similar trend was seen with the stock strains, in which the anaerobic chamber often supported better growth of the organisms than did either of the bag systems.
Anaerobiosis↗