BACKGROUND: At antimicrobial susceptibility testing (AST), clinical isolates may appear susceptible sometimes to the antibiotics that are clinically ineffective or due to technical errors in the testing. So an interpretive reading of AST should be done, but most hospitals do not perform it routinely. Here, we developed and evaluated a computerized expert system to interpret AST of Enterobacteriaceae to beta-lactam antibiotics. METHODS: We made a rule-based expert system according to the natural resistance of the members of Enterobacteriaceae and the common phenotypes of resistance mechanisms for Enterobacteriacae. Antimicrobial suceptibility testings were performed using the disk diffusion method with 12 beta-lactam antibiotics for a total of 1, 016 clinical isolates. Then we compared the raw and expert results of AST. RESULTS: An overall discrepancy rate due to natural resistance was 5.9%; 10.4% for Klebsiella spp. and Citrobacter diversus, 15.0% for Enterobacter spp., 2.6% for Serratia marcescens, 31.6% for Morganella morganii and Providencia stuartti. Accoriding to acquired antimicrobial resistant mechanisms, overall resistant discrepancy was 21.8%; 18.8% for Escherichia coli, Proteus mirabilis, Salmonella and Shigella spp., 25.9% for Citrobacter diversus and Klebsiella spp., 21.6% for Citrobacter freundii and Enterobacter spp., 45.6% for Morganella morganii, 10.0% for Proteus vulgaris, 12.2% for Serratia spp.. CONCLUSIONS: These results indicate that the application of the expert system for interpretation of antimicrobial susceptibility test may provide more reliable data for the treating physician. Additional information should be applied on the software for new resistant mechanisms or some misinterpretive readings.
Anti-Bacterial Agents ; beta-Lactams* ; Citrobacter freundii ; Citrobacter koseri ; Diffusion ; Enterobacter ; Enterobacteriaceae* ; Escherichia coli ; Expert Systems* ; Immunity, Innate ; Klebsiella ; Morganella morganii ; Phenotype ; Proteus mirabilis ; Proteus vulgaris ; Providencia ; Reading ; Salmonella ; Serratia ; Serratia marcescens ; Shigella

BACKGROUND: In 2010, the Clinical and Laboratory Standards Institute (CLSI) revised breakpoints for cephalosporins and carbapenems and indicated that extended-spectrum beta-lactamase (ESBL) testing is no longer necessary for Enterobacteriaceae. We compared the results of the CLSI 2010 and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) MIC breakpoints for Enterobacteriaceae producing ESBL and/or plasmid-mediated AmpC beta-lactamase (PABL). METHODS: A total of 94 well-characterized clinical isolates of Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Proteus mirabilis, Salmonella spp., Shigella spp., Citrobacter freundii, Enterobacter aerogenes, Enterobacter cloacae, and Serratia marcescens were analyzed. Of them, 57 were ESBL producers, 24 were PABL producers, and 13 were ESBL plus PABL co-producers. Broth microdilution MIC tests were performed for cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem. RESULTS: Among the 94 isolates containing ESBL and/or PABL, the number of isolates that were susceptible to cefotaxime, ceftazidime, aztreonam, cefepime, and imipenem according to the CLSI 2010 vs. the EUCAST breakpoints were 4 (4.3%) vs. 4 (4.3%); 26 (27.7%) vs. 8 (8.5%); 37 (39.4%) vs. 14 (14.9%); 71 (75.5%) vs. 31 (33.0%); and 76 (80.9%) vs. 90 (95.7%), respectively. Of the 18 isolates that were not susceptible to imipenem according to the CLSI 2010 breakpoints, 13 isolates (72.2%) were P. mirabilis. CONCLUSION: The CLSI 2010 MIC breakpoints without tests to detect ESBL and/or PABL for Enterobacteriaceae could be unreliable. Thus, special tests for ESBLs and AmpC beta-lactamases are required to detect the resistance mechanisms involved.
Aztreonam ; Bacterial Proteins ; beta-Lactamases ; beta-Lactams ; Carbapenems ; Cefotaxime ; Ceftazidime ; Cephalosporins ; Citrobacter freundii ; Enterobacter aerogenes ; Enterobacter cloacae ; Enterobacteriaceae ; Escherichia coli ; Imipenem ; Klebsiella oxytoca ; Klebsiella pneumoniae ; Proteus mirabilis ; Salmonella ; Serratia marcescens ; Shigella

BACKGROUND: In clinical microbiology the accurate and rapid identification of members of the family Enterobacteriaceae is essential for diagnostic and therapeutic purposes and for epidemiologic studies. Accuracy of identification system depends mainly on data base such as positive rate of biochemical reactions, relative frequency of occurrence of biotype, and isolation frequency of microorganisms. The purpose of this study was to analyze the isolation rate and biotype frequency of the family Enterobacteriaceae isolated from tertiary care hospital in Korea. METHODS: Isolation frequency of the family Enterobacteriaceae isolated from clinical specimens during the period of January 1998 to June 1998 were analyzed. And biochemical phenotypes of 2,022 isolates tested by 10 tube system consisting of 14 conventional biochemical tests were also analyzed. RESULTS: Isolation rate of the family Enterobacteriaceae to the genus level in order of decreasing frequency were Escherichia (37.0%), Serratia (15.9%), Klebsiella (14.9%), Enterobacter (11.1%), Providencia (8.1%), Citrobacter (2.8%), Proteus (2.5%), Morganella (2.4%), Salmonella (2.4%), and Cedecea (0.7%). Among the genus of the family Enterobacteriaceae, Budvicia, Edwardsiella, Ewingella, Hafnia, Kluyvera, Leminorella, Moellerella, Shigella, Tatumella, Xenorhabdus, Yersinia, and Yokenella were not isolated. The number of species and genus of the family Enterobacteriaceae by this study were 48 and 12, respectively. Over 95% of all clinical isolates belonged to only 25 species. CONCLUSIONS: Although these data about frequency of relative isolation rate and biotype patterns of the family Enterobacteriaceae is inadequate according to species and genus, yet these data will be utilized for the application and development of identification method of the family Enterobacteriaceae.
Citrobacter ; Edwardsiella ; Enterobacter ; Enterobacteriaceae* ; Escherichia ; Hafnia ; Humans ; Klebsiella ; Kluyvera ; Korea ; Morganella ; Phenotype ; Proteus ; Providencia ; Salmonella ; Serratia ; Shigella ; Tertiary Healthcare ; Xenorhabdus ; Yersinia

BACKGROUND: Recent clinical isolates of bacteria often produce various beta-lactamases, for example, extended spectrum beta-lactamase (ESBL) by some species of Enterobacteriaceae, TEM beta-lactamase by Haemophilus influenzae, and penicillinase by methicillin-susceptible Staphylococcus aureus (MSSA). Cefminox, a commonly used cephamycin, is stable to various beta-lactamases, but its activity against recent clinical isolates has not been evaluated. The aim of this study was to determine the activities of cefminox against recent clinical isolates of Enterobacteriaceae, H. influenzae, and MSSA. METHODS: The organisms, isolated from Severance Hospital patients during 1997 to 1998, were kept frozen until the test. Antimicrobial susceptibility was determined by the NCCLS agar dilution method. RESULTS: All 30 isolates of Escherichia coli and 90% of 30 Klebsiella pneumoniae isolates were susceptible to cefminox, cefotetan and amikacin. All of the Enterobacter cloacae and Serratia marcescens, and 86% of Citrobacter freundii isolates were susceptible to amikacin. All of the 15 isolates each of Proteus mirabilis, P. vulgaris and Morganella morganii were susceptible to cefminox, cefotetan, cefotaxime, ceftazidime, and aztreonam, while all of the Providencia spp. were susceptible to ceftazidime and aztreonam. All of the 29 H. influenzae isolates were susceptible to cefminox, cefotaxime, and levofloxacin, while all MSSA isolates were susceptible to cefoxitin and cotrimoxazole. CONCLUSION: Cefminox is more active than the other beta-lactams against Enterobacteriaceae including, ESBL- producing E. coli, and K. pneumoniae.
Agar ; Amikacin ; Aztreonam ; Bacteria ; beta-Lactamases ; beta-Lactams ; Cefotaxime ; Cefotetan ; Cefoxitin ; Ceftazidime ; Citrobacter freundii ; Enterobacter cloacae ; Enterobacteriaceae* ; Escherichia coli ; Haemophilus influenzae* ; Haemophilus* ; Humans ; Influenza, Human ; Klebsiella pneumoniae ; Levofloxacin ; Morganella morganii ; Penicillinase ; Pneumonia ; Proteus mirabilis ; Providencia ; Serratia marcescens ; Staphylococcus aureus* ; Staphylococcus* ; Trimethoprim, Sulfamethoxazole Drug Combination

BACKGROUND: Cefroxadine is an oral first-generation cephalosporin, which has been used for several years. But, the susceptibility data of cefroxadine were rarely reported in Korea. The current study attempted to determine the antibacterial activity of cefroxadine against the major clinical isolates. METHODS: According to the NCCLS recommendations, antibacterial activities of cefroxadine were measured against total 500 major clinical isolates. MICs were determined by the agar dilution method, a series of doubling dilutions from 128 to 0.03 /mL, on Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, Proteus mirabilis, and Staphylococcus spp. In case of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis, broth microdilution method, a series of doubling dilutions from 16 to 0.015 /mL, was performed. RESULTS: Cefroxadine had variable activity against Enterobacteriaceae. MIC cumulative curves showed that cefroxadine had relatively low MIC distributions against E. coli, K. pneumoniae and P. mirabilis, showing MIC50 were 4, 4, and 8 /mL, respectively. Against E. cloacae, C. freundii, and S. marcescens, cefroxadine 's MIC50 values ranged from 128 to >128 /mL. For clinical isolates of methicillin-susceptible Staphylococcus aureus and methicillin-susceptible Staphylococcus epidermidis, cefroxadine had MIC90 values were 4 /mL and 8 /mL, respectively. Cefroxadine had MIC50 values of 1 /mL and >16 /mL for penicillin-susceptible and penicillin-not-susceptible strains of S. pneumoniae, respectively. Cefroxadine had MIC50 values of 8 /mL and 4 /mL against H. influenzae and M. catarrhalis, respectively. CONCLUSION: Cefroxadine had good activity against gram-positive bacteria, except penicillin-resistant S. pneumoniae, and showed moderate antimicrobial activity against M. catarrhalis, E. coli, P. mirabilis, and K. pneumonaie. Cefroxadine had variable activity against Enterobacteriaceae other than the above-mentioned species.
Agar ; Citrobacter freundii ; Cloaca ; Enterobacter cloacae ; Enterobacteriaceae ; Escherichia coli ; Gram-Positive Bacteria ; Haemophilus influenzae ; Influenza, Human ; Klebsiella pneumoniae ; Korea ; Mirabilis ; Moraxella (Branhamella) catarrhalis ; Pneumonia ; Proteus mirabilis ; Serratia marcescens ; Staphylococcus ; Staphylococcus aureus ; Staphylococcus epidermidis ; Streptococcus pneumoniae

BACKGROUND: The aim of this study was to evaluate the Vitek system and the disk diffusion method for susceptibility testing of Enterobacteriaceaeagainst piperacillin-tazobactam (TZP) and methicillin-resistant Staphylococcus aureus (MRSA) against trimethoprim-sulfamethoxazole (SXT)using the broth microdilution method as the reference. METHODS: Using the Vitek system and the disk diffusion method, we tested 96 isolates of Enterobacteriaceae (48 Escherichia coli, 26 Klebsiella pneumoniae, 8 Serratia marcescens, 6 Enterobacter cloacae, 2 E. aerogenes, 2 K. oxytoca, 2 Citrobacter freundii, 2 Pantoea agglomerans) and 61 isolates of MRSA for susceptibity against TZP and SXT, respectively; the broth microdilution of National Committee for Clinical Laboratory Standards was used as the reference method. RESULTS: In the susceptibility testing of Enterobacteriaceae against TZP, Vitek system yielded 10 (10%) minor errors, and the disk diffusion method one (1%) very major and 13 (14%) minor errors. For the MRSA against SXT, the rate of categorical agreement between the reference method and the Vitek or the disk diffusion method was both 100%. The rates of agreement between the reference method and the Vitek system in term of MICs (within +/-1 dilution) were 93% and 98% in the susceptibility testing of Enterobacteriaceae against TZP and MRSA against SXT, respectively. CONCLUSION: Both Vitek system and disk diffusion method showed an acceptable level of accuracy for the susceptibility test of Enterobacteriaceaeagainst TZP and MRSA against SXT.
Citrobacter freundii ; Diffusion* ; Enterobacter cloacae ; Enterobacteriaceae* ; Escherichia coli ; Klebsiella pneumoniae ; Methicillin Resistance* ; Methicillin-Resistant Staphylococcus aureus* ; Pantoea ; Serratia marcescens ; Trimethoprim, Sulfamethoxazole Drug Combination*

BACKGROUND: There have been few studies about the kinds of species causing surgical site infections and their resistance pattern in Korea. An increase of extended-spectrum beta-lactamase (ESBL) producing strains is a worldwide problem. However, there is not enough data on the prevalence of ESBL-producing strains in Korea and the true extent of this problem seems to be under-recognized. METHODS: Minimal inhibitory concentrations of gram-negative bacilli isolated from surgical site infections were tested using the standard agar dilution method according to the National Committee for Clinical Laboratory Standards. To identify and characterize beta-lactamases, we performed conjugation test, isoelectric focusing, Southern hybridization, and polymerase chain reaction. RESULTS: A total of 54 strains of gram-negative enteric bacilli were identified:two strains of Acinetobacter spp., one of Citrobacter freundii, nine of Enterobacter cloacae, one of Enterobacter sakazakii, one of Escherichia coli, two of Klebsiella pneumoniae, one of Morganella morganii, one of Proteus vulgaris, 23 of Pseudomonas aeruginosa, four of Xanthomonas maltophila, and nine of Serratia marcescens. Three strains produced ESBL. CONCLUSION: Various species of gram-negative organisms isolated from surgical site infections showed complex antibiograms to various beta-lactams, even to the new generation of antibiotics. A large proportion of these strains showed conjugally transferable, plasmid-mediated, beta-lactam resistance. Some strains were ESBL-producing. This evidence suggests that there has been a molecular evolution of beta-lactamase genes to a great extent in Korea, possibly due to indiscriminate use of antibiotics.
Acinetobacter ; Agar ; Anti-Bacterial Agents ; beta-Lactam Resistance* ; beta-Lactamases ; beta-Lactams ; Citrobacter freundii ; Cronobacter sakazakii ; Drug Resistance ; Enterobacter cloacae ; Escherichia coli ; Evolution, Molecular ; Isoelectric Focusing ; Klebsiella pneumoniae ; Korea ; Microbial Sensitivity Tests ; Morganella morganii ; Polymerase Chain Reaction ; Prevalence ; Proteus vulgaris ; Pseudomonas aeruginosa ; Serratia marcescens ; Xanthomonas

BACKGROUND: There have been few studies about the kinds of species causing surgical site infections and their resistance pattern in Korea. An increase of extended-spectrum beta-lactamase (ESBL) producing strains is a worldwide problem. However, there is not enough data on the prevalence of ESBL-producing strains in Korea and the true extent of this problem seems to be under-recognized. METHODS: Minimal inhibitory concentrations of gram-negative bacilli isolated from surgical site infections were tested using the standard agar dilution method according to the National Committee for Clinical Laboratory Standards. To identify and characterize beta-lactamases, we performed conjugation test, isoelectric focusing, Southern hybridization, and polymerase chain reaction. RESULTS: A total of 54 strains of gram-negative enteric bacilli were identified:two strains of Acinetobacter spp., one of Citrobacter freundii, nine of Enterobacter cloacae, one of Enterobacter sakazakii, one of Escherichia coli, two of Klebsiella pneumoniae, one of Morganella morganii, one of Proteus vulgaris, 23 of Pseudomonas aeruginosa, four of Xanthomonas maltophila, and nine of Serratia marcescens. Three strains produced ESBL. CONCLUSION: Various species of gram-negative organisms isolated from surgical site infections showed complex antibiograms to various beta-lactams, even to the new generation of antibiotics. A large proportion of these strains showed conjugally transferable, plasmid-mediated, beta-lactam resistance. Some strains were ESBL-producing. This evidence suggests that there has been a molecular evolution of beta-lactamase genes to a great extent in Korea, possibly due to indiscriminate use of antibiotics.
Acinetobacter ; Agar ; Anti-Bacterial Agents ; beta-Lactam Resistance* ; beta-Lactamases ; beta-Lactams ; Citrobacter freundii ; Cronobacter sakazakii ; Drug Resistance ; Enterobacter cloacae ; Escherichia coli ; Evolution, Molecular ; Isoelectric Focusing ; Klebsiella pneumoniae ; Korea ; Microbial Sensitivity Tests ; Morganella morganii ; Polymerase Chain Reaction ; Prevalence ; Proteus vulgaris ; Pseudomonas aeruginosa ; Serratia marcescens ; Xanthomonas

BACKGROUND: The occurrence of extended-spectrum beta-lactamases (ESBLs) in enterobacteria that possess inducible Bush group 1 chromosomal beta-lactamases is being increasingly reported worldwide. The current National Committee for Clinical Laboratory Standards documents do not indicate the tests that should be used for the detection of ESBLs in Enterobacteriaceae except Klebsiella spp. and Escherichia coli. We determined the occurrence and detection of ESBL-producing Enterobacteriaceae isolates. METHODS: One hundred fifty-six consecutive, non-repeated isolates of Citrobacter freundii, Enterobacter spp., Proteus spp., and Serratia marcescens were collected. These isolates were performed broth microdilution antimicrobial susceptibility test, Vitek ESBL detection test, and double disk synergy (DDS) test. All the DDS-positive strains were tested PCR amplification of the blaTEM and blaSHV alleles. RESULTS: S. marcescens (27.3%) was the most frequently isolated ESBL producers followed by E. cloacae (23.8%), E. aerogenes (18.2%), C. freundii (13.3%), and P. mirabilis (8.3%). Among the total of 30 isolates that were considered ESBL producers, the Vitek ESBL detection test was positive for 26 (86.7%) strains. The genotypes of ESBLs were predominently SHV type (10 isolates) followed by others (8 isolates), SHV and TEM (7 isolates), and TEM type (5 isolates). CONCLUSIONS: Our findings indicate that 19.2% of all Enterobacteriaceae except E. coli and Klebsiella spp. tested produced ESBLs. The Vitek ESBL detection test seems to be a useful test to identify ESBL-producing strains of C. freundii, Enterobacter spp., Proteus spp., and S. marcescens isolates.
Alleles ; beta-Lactamases ; Citrobacter freundii* ; Citrobacter* ; Cloaca ; Enterobacter* ; Enterobacteriaceae ; Escherichia coli ; Genotype ; Klebsiella ; Mirabilis ; Polymerase Chain Reaction ; Proteus* ; Serratia marcescens* ; Serratia*

BACKGROUND: No significant information on the prevalence of extended-spectrum beta-Lactamase (ESBL)-producing Enterobacteriaceae in Korea has been available, because a few studies conducted to date in Korea have involved only discontinuous isolates of Klebsiella pneumoniae and Escherichia coli. In this study, a survey of clinical isolates of Enterobacteriaceae was carried out to assess the prevalence of ESBL-producing Enterobacteriaceae and to investigate the ESBL derivatives for phenotypical and genotypical characteristics. METHODS: A total of 500 consecutive clinical isolates of Enterobacteriaceae were screened for the presence of ESBL according to the new guidelines of the National Committee for Clinical Laboratory Standards. A double-disk synergy test, as a confirmatory test, was performed in screening positive strains. The presence of the ESBL gene was determined using polymerase chain reaction (PCR). The types of the beta-Lactamase gene were determined by isoelectric focusing and nucleotide sequence analysis. RESULTS: Among the collected strains, 21 of 293 E. coli (7.2%), 46 of 108 K. pneumoniae (42.6%), 10 of 20 Enterobacter cloacae (50.0%), 1 of 12 E. aerogenes (8.3%), 12 of 16 Citrobacter freundii (75.5%), and 1 of 14 Serratia marcescens (7.2%) were ESBL-producing strains. DNA sequencing and deduced amino acid sequence analysis revealed TEM-52 specific mutations in five strains (1 E. coli, 3 K. pneumoniae, and 1 E. cloacae) expressing pI 6.0 beta-Lactamases, SHV-2a in two K. pneumoniae of pI 7.6, and SHV-12 in four strains (1 E. coli of pI 8.2, 1 K. pneumoniae of pI 7.8, and 2 K. pneumoniae of pI 8.4). CONCLUSION: ESBLs were present in other genera of the family Enterobacteriaceae, such as Enterobacter, Citrobacter, and Serratia in Korea. ESBL types in E. coli isolates were TEM-52, SHV-12, and SHV-2a in decreasing order, and in K. pneumoniae isolates were TEM-52, SHV-2a and SHV-12 in decreasing order. The pIs of SHV-12 were 8.4 and 7.8 as well as 8.2, and a TEM-52 producing E. cloacae was first found.
Base Sequence ; beta-Lactamases ; Citrobacter ; Citrobacter freundii ; Cloaca ; Enterobacter ; Enterobacter cloacae ; Enterobacteriaceae* ; Escherichia coli ; Humans ; Isoelectric Focusing ; Klebsiella pneumoniae ; Korea ; Mass Screening ; Pneumonia ; Polymerase Chain Reaction ; Prevalence ; Sequence Analysis, DNA ; Sequence Analysis, Protein ; Serratia ; Serratia marcescens