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PubMed2005

Susceptibility testing accuracy of a CTX-M-type extended-spectrum beta-lactamase organism-producing population of Enterobacteriaceae: intermethod analysis for 9 beta-lactams.

To assess the wide geographical applicability of the current and proposed susceptibility breakpoint criteria for 9 beta-lactam antimicrobials, the performance characteristics of 2 standardized methods were analyzed by testing a contemporary collection of 354 isolates of Enterobacteriaceae, enriched (76; 21.5%) for extended-spectrum beta-lactamase (ESBL)-producing strains. Molecular characterization of 57 ESBL strains revealed that majority of the strains (94.7%) were CTX-M type, with a predominance (85.2%) of CTX-M-14 and -3 types, those types prevalent in China. Bloodstream isolates constituted 68.6% of the entire collection. The 9 beta-lactam antimicrobials analyzed were aztreonam, cefepime, cefotaxime, cefotetan, cefoxitin, ceftazidime, ceftriaxone, ceftizoxime, and cefuroxime. Reference broth microdilution minimal inhibitory concentration (MIC) results were compared to those zone diameters obtained by disk diffusion testing. The regression coefficient was acceptable for most antimicrobials, ranging from r = 0.84 (cefotetan) to r = 0.98 (cefotaxime, cefuroxime, and ceftriaxone). Using the current breakpoint criteria, the absolute intermethod categorical agreement was acceptable for 8 of the 9 antimicrobials (not cefoxitin, 85.1%) ranging from 92.6% (cefotaxime) to 97.8% (ceftazidime). Very major (false-susceptible) and major (false-resistant) errors were nil (0.0%) for 5 of the beta-lactams and minor errors ranged from 0.8% (cefotetan) to 14.1% (cefoxitin). The proposed (generally lower) MIC breakpoint criteria also had acceptable intermethod concordance ranging from 91.6% (cefoxitin) to 99.2% (cefotaxime and ceftriaxone). Furthermore, an improvement in the intermethod absolute categorical agreement ranging from +0.8% (ceftazidime) to +6.6% (cefotaxime) was observed for 7 of 9 antimicrobials tested, including the ESBL screening test compounds (aztreonam, ceftazidime, cefotaxime, and ceftriaxone). No modification of the susceptible breakpoint criteria, with removal of the intermediate category, was proposed for cefoxitin and cefuroxime, resulted in a shift of error type from minor to major or very major, but the categorical agreement improved (+ >or=1.2%) for both cephems. In conclusion, our results confirm that both the current and the proposed MIC breakpoint criteria with appropriately selected zone diameter correlates have acceptable intermethod error rates even when tested against an Enterobacteriaceae collection enriched with CTX-M-type ESBL-producing strains that are endemic in locations (China) outside the United States.

Anti-Bacterial Agents↗

PubMed1979

A rapid (4--6-hour) urine-culture system for direct identification and direct antimicrobial susceptibility testing.

This study evaluates a new direct rapid system for urine cultures, including detection and quantitation of positive specimens by Gram stain, direct identification by 4--6-hour incubation of sediment with reagent strips, and antibiotic susceptibility testing by direct (3--4-hour) disk-elution methods. Of 987 routine urine specimens, 121 had significant (less than or equal to 10(5) colony-forming units/ml) gram-negative bacilluria, of which 89% were detected by the Gram stain. Direct rapid identification was correct in 94%. Results of direct disk-elution antimicrobial tests showed overall agreement with results of standard disk diffusion of 93% of tests, and major discrepancies in 4%. For urine specimens with gram-negative bacilluria, this system permitted detection, quantitation, identification, and antimicrobial susceptibility testing in four to six hours with reasonable, though not complete, accuracy.

Anti-Bacterial Agents↗

PubMed1980

In vitro susceptibility of Haemophilus equigenitalis, the causative organism of contagious equine metritis 1977, to antimicrobial agents.

The in vitro susceptibility of recent clinical isolates of Haemophilus equigenitalis to various antimicrobial agents was determined by the disk diffusion test and the World Health Organization-International Collaborative Study agar dilution procedure. Ampicillin and tetracycline were the most active drugs. All strains were susceptible to beta-lactam antibiotics, chloramphenicol, trimethoprim-sulfamethoxazole, nalidixic acid, nitrofurantoin (Furadantin), and bacitracin. All but two strains were resistant to streptomycin, whereas all strains were susceptible to the other aminocyclitol antibodies. All strains were resistant to clindamycin, lincomycin, and metronidazole.

Animals↗

PubMed1999

Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: potential human-to-animal transmission.

During a 13-month period, 11 equine patients visiting a veterinary teaching hospital for various diagnostic and surgical procedures developed postprocedural infections from which methicillin (oxacillin)-resistant Staphylococcus aureus (MRSA) strains were isolated. The S. aureus isolates were identified by conventional methods that included Gram staining, tests for colonial morphology, tests for clumping factor, and tests for coagulase and urease activities and were also tested with the API STAPH IDENT system. Antimicrobial susceptibility tests were performed by the disk diffusion method. The biochemical profile and antibiogram of each isolate suggested that the isolates may have come from a common source. Because MRSA strains are very uncommon animal isolates but are rather common human isolates, a nasal swab specimen for culture was collected voluntarily from five persons associated with equine surgery and recovery in an attempt to identify a possible source of the organisms. MRSA strains were isolated from three of the five people, with one person found to be colonized with two biotypes of MRSA. The MRSA isolates from the people appeared to be identical to the isolates from horses. Further study of the isolates included SmaI and EagI macrorestriction analysis by pulsed-field gel electrophoresis conducted in two different laboratories. The results indicated that both the equine and human isolates were members of a very closely related group which appear to have originated from a common source. On the basis of the pattern associated with the infection, it is speculated that the members of the Veterinary Teaching Hospital staff were the primary source of the infection, although the specific mode of transmission is unclear.

Animals↗

PubMedDate not supplied

Fecal shedding and antimicrobial susceptibility of selected bacterial pathogens and a survey of intestinal parasites in free-living waterfowl.

Free-living waterfowl residing in metropolitan parks in central Ohio were surveyed for the fecal shedding and antimicrobial susceptibility patterns of Campylobacter jejuni, Escherichia coli, Salmonella spp., and Pasteurella multocida. In addition, a survey for intestinal parasites was also conducted in these same waterfowl to determine parasite burdens in free-living waterfowl. Prevalences of 67%, 50%, and 0.2% of E. coli, C. jejuni, and Salmonella spp., respectively, were observed for all waterfowl species. Pasteurella multocida was not isolated from the sampled population. Salmonella java was isolated from one mallard duck. Statistically, there was a significantly higher E. coli isolation rate for mallard ducks than for Canada geese, but no difference was observed for C. jejuni isolation rates between waterfowl species. Antimicrobial susceptibility testing was conducted via the disk diffusion method and multidrug resistance was exhibited for penicillin G, lincomycin, vancomycin, erythromycin, and bacitracin. In addition, the prevalence of endoparasites in these sampled waterfowl ranged from 5% to 66%. Protozoan oocysts were most prevalent followed by nematode ova. No trematode or cestode ovum was recovered from this sampled population.

Animals↗

PubMed1985

Biological activity of 4-hydroxyisophthalic acid derivatives. III. Variously substituted anilides with antimicrobial activity.

A series of 1,3-bis-anilides of 4-hydroxyisophthalic acid was prepared and investigated for antibacterial and antifungal activities. The prepared compounds (I-XIV), of the general formula (A), where Xn = 2-NO2 (I); 2,4-(NO2)2 (II); 2,4-NO2, Cl (III); 2,4-NO2,CF3 (IV); 3,4-NO2,Cl (V); 2,4-Cl,NO2 (VI); 2,5-Cl,NO2 (VII); 2,4,6-Cl,NO2,Cl (VIII); 2,4-Br, NO2 (IX); 2-CF3 (X); 3-CF3 (XI); 2,5-Cl,CF3 (XII); 2,5-CH3,Cl (XIII); 3,4-Cl,CH3 (XIV), were obtained in satisfactory yield by reacting 4-hydroxyisophthalic acid with the appropriate substituted aniline. (Formula: see text). The prepared compounds were tested for antimicrobial activity by a disk-diffusion assay (Kirby-Bauer modified). The organisms used were the following: S. aureus, B. subtilis, B. anthracis, M. paratuberculosis 607, E. coli Bb, S. typhi, S. typhimurium, S. paratyphi B, Pr. vulgaris, K1. pneumoniae, Ps. aeruginosa, C. albicans, and A. niger. The results of the antimicrobial screening showed that a number of substituted anilides exhibited varying degrees of activity against Gram-positive and Gram-negative bacteria, and fungi, nitro-halogen-derivatives being the most interesting members of the series.

Anilides↗

PubMed1985

[The search for Yersinia enterocolitica in vegetables treated by a cold line in school cafeterias in Montpellier].

From 134 samples of raw or cooked vegetables taken in two points of a cold line we isolated 19 strains of Yersinia enterocolitica, 3 of Y. intermedia 3 of Y. kristensenii. None of them belongs to serotypes usually pathogenic for man. The raw vegetables are most contaminated. Y. kristensenii and Y. intermedia were isolated especially from samples of green salad. The used method was a cold enrichment at 4 degrees C followed by a potassium hydroxyde treatment. The activity of 16 antimicrobial drugs was studied by the disk diffusion test at 28 degrees C. All strains were sensitive to aminoglycosides, minocycline, colistine and cotrimoxazole. The results obtained with chloramphenicol and beta-lactam antibiotics vary in terms of species and/or biotypes.

Anti-Bacterial Agents↗

PubMed2003

Prevalence of antimicrobial resistance of Streptococcus pneumoniae in Chinese children: four hospitals surveillance.

OBJECTIVE: To investigate the nasal carriage of antibiotic-resistant pneumococci in children of < 5 years old in the following four cities, Beijing, Shanghai, Guangzhou and Xi'an. METHODS: A total of 647 pneumococci strains were isolated and detected. Minimal inhibition concentrations (MICs) of antibiotics were determined by E-test. Disk diffusion test was used for the measurement of antimicrobial susceptibility. RESULTS: Prevalence of penicillin non-susceptible Streptococcus pneumoniae in the four cities was 41%, with Guangzhou (60.8%) ranking first, followed by Xi'an (45%), Shanghai (37%) and Beijing (25.9%). The majority of penicillin non-susceptibility isolates (23.9% - 53.8%) had a low level of resistance (MIC 0.64 - 1.5 microg/ml). The most sensitive antimicrobials in terms of percentage of susceptible organisms were amoxicillin-clavulanic acid (99.4%), followed by ceftriaxone (92.1%); cefurxime and cefaclor were slightly more sensitive than penicillin with susceptibility of 74.8% and 77.9%. Erythromycin, tetracycline and TMP-SMZ were highly resistant (83.6%, 82.1% and 76.2% respectively). Among erythromycin resistant isolates, 100% were resistant to azithromycin, 98.6% to clarithromycin, 97.2% to roxithromycin and spiramycin, and 96.6% to clindamycin. 97.2% (141/145) were typical of the macrolides-lincosamides-streptogramons B (MLSB) resistance phenotype, and 2.8% (4/145) were M phenotype. The group of PRSP was with significantly higher rates of non-susceptibility for ceftriaxone (18.4%), cefurxime (58.6%), cefaclor (53.4%), compared with the group of PEN-S (0.5%, 1.8% and 0.2%, respectively) and the rate of multi-drug resistance in the isolates of PRSP group (92.9%) was significantly higher than that of PEN-S group (59.2%). CONCLUSION: The rates of penicillin and multi-drug resistance among isolates of pneumococci carried nasally in are high children and the high prevalence of multi-drug resistance in the Chinese population may be becoming one of the most serious problems in this century.

Anti-Bacterial Agents↗

PubMedDate not supplied

Antibiotic susceptibility testing (agar disk diffusion and agar dilution) of clinical isolates of Corynebacterium jeikeium.

Thirty-three clinical isolates of Corynebacterium jeikeium were examined for susceptibility to 27 antimicrobial drugs with the agar dilution test. Sheep-blood-supplemented Mueller-Hinton agar performed better than Wilkins-Chalgren agar. Disk susceptibility (Bauer-Kirby) tests were carried out in parallel with 24 of the chemotherapeutic agents. All isolates were susceptible to teicoplanin and vancomycin. All isolates resisted fosfomycin, mupirocin, and trimethoprim-sulfamethoxazole. The isolates varied in susceptibility to ciprofloxacin, doxycycline, fusidic acid, ofloxacin, and tetracycline; most were susceptible to rifampin. Surprisingly few discrepancies between agar dilution and disk diffusion tests were encountered when utilizing NCCLS interpretive criteria currently valid for enterococcal isolates.

Agar↗

PubMed2006

Susceptibility testing practices for Streptococcus pneumoniae: results of a proficiency testing survey of clinical laboratories.

In June 2003, a test sample was sent to 355 laboratories enrolled in a proficiency testing program to assess their ability to detect low-level penicillin resistance in a strain of Streptococcus pneumoniae. One hundred fifty participants reported results for antimicrobial susceptibility testing. Of the 62 respondents using disk diffusion, 34 (55%) failed to report a result that was acceptable for detecting penicillin resistance and 30 (48%) reported a result for one or more drugs not approved for testing S. pneumoniae. Moreover, 12 (14%) of the 88 respondents using minimum inhibitory concentration methods reported results for at least one unapproved drug. These findings support the conclusions of other studies that antimicrobial susceptibility testing practices are suboptimal in many laboratories. Resolution of this problem will require continued educational initiatives, studies to discover the reasons why laboratories fail to follow published standards, and enforcement of the use of standards by regulatory and credentialing agencies.

Bacteriological Techniques↗

PubMed1988

Disk diffusion susceptibility testing for LY163892 (KT-3777), a new orally administered 1-carbacephem.

LY163892, a new orally administered 1-carbacephem, was found to have a spectrum of antimicrobial activity very similar to that of cefaclor. Diffusion tests with 30-micrograms LY163892 disks produced acceptable interpretive error rates with greater than or equal to 22 mm as the susceptibility zone diameter. This was required to reduce potential false-susceptibility results, particularly among Enterobacter spp. and Providencia stuartii: both species included strains that produce beta-lactamases capable of hydrolyzing Ly163892. Preliminary recommendations for LY163892 disk tests are presented, but the continued use of the 30-micrograms cephalothin "class representative" disk might be the best procedure to minimize LY163892 interpretive errors for clinical trials. A separate LY163892 disk for testing Haemophilus influenzae strains should be seriously considered.

Bacteria↗

PubMed2002

Extended spectrum beta-lactamase mediated resistance in urinary tract isolates of family Enterobacteriaceae.

BACKGROUND & OBJECTIVES: Extended spectrum beta-lactamases (ESBL) hydrolyse expanded spectrum cephalosporins like ceftazidime, cefotaxime and monobactam aztreonam. ESBL producing bacteria may not be detectable in the routine disk diffusion susceptibility tests leading to inappropriate use of antibiotics and treatment failures. As information on ESBL producers causing urinary tract infection (UTI) is not available from our country, the occurrence of ESBL producing strains causing UTI was studied as also the differences between the antimicrobial susceptibility patterns of ESBL and non-ESBL producers. METHODS: Urinary isolates (233) were tested for antimicrobial susceptibility by Stoke's method and ESBL production by double disk diffusion method (ceftazidime and clavulanic acid). The clinical and demographic profile of the patients was noted. RESULTS: Sixty two of the 233 isolates tested (26.6%) were ESBL producers. Approximately 38.5 per cent of Klebsiellae, 24.7 per cent of Escherichia coli, 24 per cent of Enterobacter aerogenes, 33.3 per cent of Proteus sp. and the only Citrobacter strain produced ESBL. Recent surgery was found to be a significant (P < 0.01) risk factor for acquisition of ESBLs. Approximately 30 per cent of the ESBL producers appeared falsely sensitive or moderately sensitive to cefotaxime/ceftazidime in routine susceptibility testing. There was no difference between the ESBL producers and non-producers in the susceptibility to non-beta lactam agents except for gentamicin. INTERPRETATION & CONCLUSION: A high percentage of urinary tract isolates produced ESBL. Since they are likely to be missed in routine disk diffusion susceptibility tests, all microbiology laboratories should look for ESBL production routinely to avoid treatment failures.

Cephalosporins↗

PubMed1975

Laboratory evaluation of a rapid, automatic susceptibility testing system: report of a collaborative study.

Seven laboratories participated in a collaborative study to evaluate the Autobac 1 system. Results obtained with this assay system were compared to those obtained by the standardized Bauer-Kirby disk diffusion test, and each of these two methods was compared to the agar dilution technique. Comparison of the Autobac 1 and the disk diffusion results from the seven laboratories showed an overall average of 91.5% interpretive agreement with the 17 antimicrobial agents tested. The distribution in the levels of Autobac 1/disk diffusion agreement was such that with 13 antimicrobial drugs agreement was 90% or higher; with three, between 85 and 90%; and with one, 77% (nitrofurantoin). Comparison of the Autobac 1 and disk diffusion tests with the International Collaborative Study agar dilution test showed that both methods gave levels of agreement with the International Collaborative Study agar dilution technique that were generally high and equivalent. The average overall agreement between the agar dilution test and each of the other two methods was approximately 90%. Disagreements that did occur tended to involve organisms that were drug susceptible by the Autobac 1 system but intermediate or resistant by the other two methods. This was in part due to the narrow intermediate interpretive zone of the Autobac 1 test. In reproducibility studies with the Autobac 1 and disk diffusion methods, no significant differences were observed between the interpretive reproducibility of the two methods.

Anti-Bacterial Agents↗

PubMed1979

Antimicrobial susceptibility testing of Mycobacterium fortuitum complex.

A total of 24 strains of the Mycobacterium fortuitum complex were tested for susceptibility to antimicrobial agents by the disk diffusion and agar dilution techniques. By comparing zones of inhibition obtained with the disk diffusion technique with results of minimal inhibitory concentration determinations, it was shown that disk diffusion results could predict in vitro susceptibility to selected antimicrobial agents. All of 17 strains of M. fortuitum were susceptible to </=1 mug of amikacin per ml. The corresponding average zone of inhibition around a 10-mug amikacin disk was 37 mm. Seven M. chelonei strains were more resistant to amikacin, with minimal inhibitory concentrations ranging from 1 to 32 mug/ml, and the corresponding average zone size was 21 mm. Susceptibility of both M. fortuitum and M. chelonei to tetracycline was variable and none of the M. chelonei strains was inhibited by polymyxin B, whereas M. fortuitum strains consistently had zones of inhibition around the polymyxin disk. It appears that identification to species of the M. fortuitum complex may be of importance with regard to antibiotic susceptibility. Separation of M. fortuitum and M. chelonei was readily accomplished in the present study by the nitrate reduction and 3-day arylsulfatase tests.

Aminoglycosides↗

PubMed1990

Disk diffusion susceptibility testing of Haemophilus influenzae using haemophilus test medium.

A three-center collaborative study was performed with the aim of determining the reproducibility of disk diffusion and broth microdilution susceptibility tests of Haemophilus influenzae with 19 different antimicrobial agents using a newly described medium, Haemophilus Test Medium. The results of both methods were found to be highly reproducible. Using Haemophilus Test Medium, inhibitory zone diameters and MICs were then determined for 150 test strains of Haemophilus influenzae, selected with an emphasis on known mechanisms of resistance. Regression analysis of zone diameter-MIC comparisons was used to define zone diameter interpretive criteria and MIC correlates for Haemophilus Test Medium disk diffusion tests performed with Haemophilus spp. for the following antimicrobial agents: ampicillin, amoxicillin/clavulanate, ampicillin/sulbactam, cefaclor, cefuroxime, cefamandole, ceftriaxone, cefotaxime, ceftizoxime, ceftazidime, cefixime, trimethoprim/sulfamethoxazole, rifampin, chloramphenicol, tetracycline, imipenem, aztreonam and ciprofloxacin.

Anti-Bacterial Agents↗

PubMedDate not supplied

Interactions of antimicrobials in milk and their detection by the disk diffusion method and Delvotest SP.

The combination of more than 2 different microbials might show interactions with various effects (synergistic, additive, antagonistic, or indifferent) on target microorgnisms. An objective of this paper was to evaluate the possible interactions of several antimicrobials--those used most frequently in the treatment of mastitis in clinical veterinary practice (beta-lactam antibiotics, aminoglycosides, peptides, other antibiotics, and sulfonamides)--and their consequences on detection limits. In the model experiment with milk artificially altered by means of Delvotest SP and the disk diffusion method with Bacillus stearothermophilus var. calidolactis C 953, we observed the synergistic effect between all the antimicrobials tested. The results show that Delvotest SP is more sensitive (approximately 7.5- to 40-fold) than the disk diffusion method in estimating the detection limits of cephalosporin antibiotics.

Animals↗

PubMedDate not supplied

Antibiotic susceptibility of Serratia marcescens and Serratia liquefaciens.

BACKGROUND: Over a period of 20 years, a total of 1,603 Serratia isolates were recovered from clinical specimens and examined for susceptibility to 29 antimicrobial drugs using the Bauer-Kirby agar disk diffusion test. Serratia marcescens was recovered most frequently (n = 1,409), followed by S. liquefaciens (n = 172); other Serratia species were scarce. During the 2-decade observation period there occurred 35 putative episodes/clusters of nosocomial cross-infection and 1 pseudo-outbreak due to S. marcescens, but none due to S. liquefaciens. METHODS: The antimicrobial susceptibility data for S. marcescens and S. liquefaciens were subdivided into two observation periods: I = 1980-1993, and II = 1993-1999. The crude data (series A) obtained for S. marcescens were corrected in two ways: by the omission of repetitive patient isolates (series B) and the additional removal of outbreak isolates except for index case isolates (series C). RESULTS AND CONCLUSIONS: Comparison of data obtained in series IC and IIC disclosed an increase in the susceptibility of S. marcescens to ampicillin + sulbactam, cefotaxime, chloramphenicol, doxycycline, fosfomycin, gentamicin, piperacillin, piperacillin + tazobactam, timentin and tobramycin during observation period II. Conversely, there was a decrease in susceptibility to ciprofloxacin, nalidixic acid and trovafloxacin, and slightly diminished susceptibility to norfloxacin and ofloxacin during observation period II as compared with the previous period. The crude data obtained for S. liquefaciens required no correction, as there were only a few repeat isolates. There was an increase in susceptibility to ampicillin, ampicillin + sulbactam, cefuroxime, doxycycline, fosfomycin, nitrofurantoin and polymyxin B (clear inhibition zones). However, there was an inexplicable decrease in susceptibility to piperacillin + tazobactam. Cocarde growth around polymyxin B disks was noted with 55.8% of the S. marcescens isolates as compared with 6.8% of the S. liquefaciens isolates. Slime around fluoroquinolone inhibition zones was produced by 83.4% of the S. marcescens isolates. Slime production around carbapenem inhibition zones was noted with 52% of the S. liquefaciens isolates, but with only a single isolate of S. marcescens.

Anti-Bacterial Agents↗

PubMed2002

Antimicrobial resistance pattern of Escherichia coli causing urinary tract infections, and that of human fecal flora, in the southeast of Iran.

Sensitivity of 500 Escherichia coli isolates from urinary tract infections (UTIs, 311 isolate) and fecal samples (189 isolates) was tested against 12 antimicrobial agents using the standard disk diffusion method. Although the rate of resistance to antimicrobial agents was higher in the UTIs, in comparison with the fecal samples, the only significant difference was found in cases of tetracycline (p = 0.008), nalidixic acid (p = 0.038), and trimethoprim-sulfamethoxazole (Sxt,p = 0.05). The pattern of sensitivity to antimicrobial agents with respect to statistically significant difference in the number of sensitive isolates (p < or = 0.01) was: ceftizoxime (99.4%) and ceftriaxone (99.2%) > gentamicin (97.8%), ciprofloxacin (93%) and nitrofurantoin (92%) > cefazoline (85.2%) and nalidixic acid (84.6%) > chloramphenicol (71.6%), cephradine (69.6%) and tetracycline (63.2%) > Sxt (41.6%) > ampicillin (23.2%). Sensitivity of the isolates in respect to sex and age was also determined and compared during this study. Resistance to three or more antimicrobial agents (multidrug resistance, MDR) was found in 209 (41.8%) of the isolates. The high rate of resistance to Sxt and the presence of a high rate of MDR isolates in this area suggest that a reevaluation of the first-line therapeutic may be necessary for the treatment of UTIs in this area.

Adolescent↗