A Retrospective National Study on Colonization Rate and Antimicrobial Susceptibility of Streptococcus agalactiae in Pregnant Korean Women, 2018–2020

Purpose@#The prevalence of Group B Streptococcus (GBS) colonization in pregnant Korean women is increasing; however, nationwide studies are lacking. Therefore, we aimed to analyze regional colonization rates and antimicrobial susceptibility for GBS in pregnant Korean women through a nationwide survey. @*Materials and Methods@#From January 2018 to December 2020, data from the Seoul Clinical Laboratories on vaginal swab cultures were retrospectively analyzed to detect maternal GBS carriers. Each swab specimen was inoculated onto a 5% blood agar plate and incubated at 35°C–37°C in a 5% CO 2 incubator for 24 h. GBS isolates were identified using a Microflex MALDI Biotyper. Antimicrobial susceptibility tests were performed using the Vitek 2 automated system. @*Results@#The overall nationwide GBS colonization rate in pregnant Korean women was found to be 10.6% (3578/33721). The maternal GBS colonization rates ranged from 10.5%–10.8% over the 3-year study period. The GBS colonization rates by province, in descending order, were as follows: Jeolla-do, 13.2%; Gangwon-do, 12.0%; Chungcheong-do, 11.8%; Gyeonggi-do, 11.3%; Seoul, 10.2%; and Gyeongsang-do, 9.6%. During the study period, the resistance rates against chloramphenicol, levofloxacin, clindamycin, erythromycin, and tetracycline were 2.6%–2.7%, 18.2%–19.6%, 33.4%–35.7%, 35.6%–36.8%, and 50.5%–53.3%, respectively. @*Conclusion@#In pregnant Korean women, GBS colonization rates were in the range of 9.6%–13.2%, with Gyeongsang-do being the lowest and Jeolla-do the highest. The resistance rate against clindamycin was high (33.4%–35.7%). GBS colonization rates during pregnancy should be studied nationwide according to the Centers for Disease Control and Prevention-recommended guidelines with periodic antimicrobial resistance monitoring.

Annual Report on the External Quality Assessment Scheme for Clinical Microbiology in Korea (2015)

Annual proficiency surveys were conducted in March, June, and September in 2015 by the Clinical Microbiology Subcommittee of the Korean Association of External Quality Assessment Service. The program covers the sections of bacteriology, advanced bacteriology and mycology, mycobacteriology, and parasitology. Each trial was composed of three sets of different combinations of five bacteria and yeasts. These sets were distributed among laboratories for Gram staining, culture, identification, and antimicrobial susceptibility tests. Five slides with fixed sputum smears were provided as part of each trial for acid-fast bacilli detection. The survey material distribution was section-based. Two survey materials were provided in each trial, while five specimens for mycobacterial culture and identification, five specimens for anti-tuberculosis susceptibility testing and two Mycobacterium tuberculosis strains for rapid detection of rifampin and isoniazid resistance were distributed in the March and June trials. Five virtual microscopy files for stool parasite examination were availed by registered participants in the June trial. Out of the 334 enrolled laboratories, 328 (98.2%), 328 (98.2%), and 329 (98.5%) submitted responses in trials I, II, and III, respectively. Identification of bacteria, namely, Escherichia coli, Klebsiella pneumoniae, Enterococcus faecalis, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Vibrio fluvialis by more than 95% of participants was acceptable. Surveillance cultures for vancomycin-resistant enterococci and carbapenem-resistant Enterobacteriaceae were determined accurately by 75.8%–85.3% and 93.1% of the respondents, respectively. Species-level identification of Candida krusei, Candida lusitanae, and Candida guilliermondii was still low at 79.8%, 55.7%, and 42.7%, respectively. Disk diffusion method revealed an unacceptably high false-positive rate of resistance to glycopeptides in E. faecalis and to trimethoprim-sulfamethoxazole in S. pneumoniae. Advanced bacteriology trials revealed unsatisfactory results for species-level identification of moulds. Mycobacterial culture, identification and susceptibility testing, and molecular detection of rifampin and isoniazid resistance were performed exceedingly well by participants. Hymenolepsis diminuta could not be identified by participants, with a correct answer rate of only 46.5% and ‘no parasite seen’ answer rate of only 31.8% for negative specimens. Species-level identification of Candida and moulds was challenging for clinical microbiology laboratories. Disk diffusion method was found to be problematic in testing the susceptibility of microorganisms to glycopeptides and trimethoprim-sulfamethoxazole. Improvement is required in result interpretation of negative specimens in parasitology.

Annual Report on External Quality Assessment Scheme for Clinical Microbiology in Korea (2014)

Annual proficiency surveys were performed in March, June and September 2014 by clinical microbiology division of The Korean Association of Quality Assurance for Clinical Laboratory. Parasitology part has been newly incorporated in this survey. For each trial, three sets which were composed of different combinations of five bacteria and yeast were distributed for gram stain, culture, identification, and antimicrobial susceptibility tests of general bacteriology and five fixed sputum smear on slides were distributed for acid fast bacilli stain. Two advanced bacteriology survey materials for culture and identification of anaerobic bacteria and mold were distributed to the voluntary participants in every trial and five mycobacterial culture and identification specimens, five anti-tuberculosis susceptibility testing specimens, and two Mycobacterium tuberculosis strains for rapid detection of rifampin and isoniazid resistance were distributed to the voluntary participants in March and June trials. Five virtual microscopic slides for stool parasite examination were open for the registered participants in June trial. A total of 340 laboratories were enrolled and 330 (97.0%), 331 (97.4%), and 331 (97.4%) returned the results on trial I, II, and III, respectively. For bacterial identification, the percent acceptable identification of Burkholderia cepacia, Klebsiella pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, Streptococcus agalactiae, Plesiomonas shigelloides, and Enterococcus faecalis were greater than 95%. Group C and group D Salmonella species challenged as the different sets of M1422 resulted in the acceptable rate lower than 95% because nine participants reported the identification of different sets. Surveillance cultures for methicillin-resistant S. aureus and vancomycin-resistant enterococci were correctly determined by 89.6% and 69.0% of the respondents, respectively. Correct identification to species level of Candida albicans, Candida auris, Candida glabrata, and Candida parapsilosis were 86.1%, 1.6%, 48.1%, and 83.8%. Vancomycin disk diffusion test in S. aureus, missing oxacillin screen or penicillin susceptibility test in S. pneumoniae and lack of reliable methods of quinolone resistance detection in Salmonella species caused unacceptable results in antimicrobial susceptibility testing. Advanced bacteriology trials revealed low performance in species identification of mold. Mycobacterial culture, identification and susceptibility test performance was kept in excellence. The performance of identification of stool parasites was acceptable >90% for detection of helminth eggs and amebic cysts but 28.6% false positive responses resulted from negative specimens. In conclusion, species-level identification of fungi of both candida species and mold were challenging to clinical microbiology laboratories. Vancomycin disk diffusion method for S. aureus and lack of proper penicillin susceptibility test for S. pneumoniae were still common cause of inaccurate results. Virtual microscopic survey has been successfully introduced in parasitology.

Annual Report on External Quality Assessment Scheme in Clinical Microbiology in Korea (2013) / 임상검사와정도관리

Annual external quality assessment was performed three times for clinical microbiology division of The Korean Association of Quality Assurance for Clinical Laboratory. For each trial, three sets composed of different combinations of four bacteria and one yeast were distributed for culture, identification, and antimicrobial susceptibility tests. A total of 340 laboratories were enrolled and 330 (97.0%), 331(97.4%), and 331(97.4%) returned the results on trial I, II, and III, respectively. For bacterial identification, the correct identification of gram-negative bacilli, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus capitis, Streptococcus agalactiae, Listeria monocytogenes, and Candida species was greater than 95%. However, correct identification of Staphylococcus lugdunensis, Corynebacterium striatum, Vibrio vulnificus, Aeromonas hydrophila, Cryptococcus neoformans, and Malassezia pachydermatis was relatively less accurate, with values of 95.4%, 89.9%, 50.7%, 91.3%, 93.6%, and 93.9%, respectively. Surveillance cultures for vancomycin-resistant enterococci and methicillin-resistant S. aureus were correctly determined by 95.4% and 93.9% of the respondents, respectively. False carbapenem-resistance due to AmpC beta-lactamase, disk diffusion testing for vancomycin in Staphylococcus species, oxacillin and penicillin susceptibility testing in S. lugdunensis and false imipenem-resistance in Proteus species were common sources of inaccurate results. The accuracy of species identification for Corynebacterium species and Vibrio species requires improvement. Consistent problems occurred with antimicrobial susceptibility testing of vancomycin for Staphylococcus species using the disk diffusion method.

Annual Report on External Quality Assessment Scheme in Clinical Microbiology in Korea (2013) / 임상검사와정도관리

Annual external quality assessment was performed three times for clinical microbiology division of The Korean Association of Quality Assurance for Clinical Laboratory. For each trial, three sets composed of different combinations of four bacteria and one yeast were distributed for culture, identification, and antimicrobial susceptibility tests. A total of 340 laboratories were enrolled and 330 (97.0%), 331(97.4%), and 331(97.4%) returned the results on trial I, II, and III, respectively. For bacterial identification, the correct identification of gram-negative bacilli, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus capitis, Streptococcus agalactiae, Listeria monocytogenes, and Candida species was greater than 95%. However, correct identification of Staphylococcus lugdunensis, Corynebacterium striatum, Vibrio vulnificus, Aeromonas hydrophila, Cryptococcus neoformans, and Malassezia pachydermatis was relatively less accurate, with values of 95.4%, 89.9%, 50.7%, 91.3%, 93.6%, and 93.9%, respectively. Surveillance cultures for vancomycin-resistant enterococci and methicillin-resistant S. aureus were correctly determined by 95.4% and 93.9% of the respondents, respectively. False carbapenem-resistance due to AmpC beta-lactamase, disk diffusion testing for vancomycin in Staphylococcus species, oxacillin and penicillin susceptibility testing in S. lugdunensis and false imipenem-resistance in Proteus species were common sources of inaccurate results. The accuracy of species identification for Corynebacterium species and Vibrio species requires improvement. Consistent problems occurred with antimicrobial susceptibility testing of vancomycin for Staphylococcus species using the disk diffusion method.

The Recent Status of Multidrug- and Extensively Drug-Resistant Tuberculosis in Korea / 결핵및호흡기질환

BACKGROUND: The increasing incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) has become a serious worldwide problem. However, there is insufficient data regarding the current status of MDR-TB and XDR-TB in Korea. This study examined the recent status of MDR- and XDR-TB using the data from 7 laboratories, in which almost all drug susceptibility tests (DST) for Mycobacterium tuberculosis were performed. METHODS: The patients' identification data and DST results were collected from all 7 laboratories from 2001 to 2006 and the number of patients with MDR-TB and XDR-TB were calculated. RESULTS: The number of DSTs was 140,638 for 6 years with an increasing incidence each year (p<0.001). The number of DST with MDR results was 18,510 and personal identifying information was obtained in 16,640 (89.9%) tests. The number of MDR-TB patients from 2001 to 2006 was 2,329, 2,496, 2,374, 2,300, 2,354, and 2,178, respectively, when counting the duplications in a year as one patient. The number of MDR-TB patients when counting the duplications in 6 years as one patient was 2,281, 1,977, 1,620, 1,446, 1,512, and 1,373, respectively. When the same method was adopted, the number of XDR-TB patients was 191, 238, 282, 260, 272, and 264, respectively, and 189, 150, 130, 90, 122, and 110 patients, respectively. CONCLUSION: Despite the national efforts to control TB, there are still a large number of MDR- and XDR-TB patients in Korea.

Evaluation of the OC-SENSOR neo System for Testing Fecal Occult Blood / 대한진단검사의학회지

BACKGROUND: Fecal occult blood tests (FOBTs) have been widely used as a means of colorectal cancer screening. Automated FOBTs using immunologic principles have the advantages such as quantitation, high specificity, and high throughput. We evaluated a newly-introduced automated FOBT analyzer, OC-SENSOR neo (OC neo) (Eiken Chemical Co., Japan). METHODS: The precision, linearity, and carry-over rate of OC neo were assessed with specimens prepared in accordance with the guidelines of CLSI. We performed a parallel test between OC neo and OC-SENSOR I (OC I) (Eiken Chemical Co.) using 300 consecutive stool specimens and 60 OC I-positive specimens. The results were analyzed with SPSS version 13.0 (SPSS Inc., USA). RESULTS: The coefficients of variation (CV) of within-run, between-run, and between-day using OCControl L (Eiken Chemical Co.) of ca. 150 ng/mL were 3.5-7.8%, 4.5-8.8% and 4.9-5.0%, respectively. The linear regression coefficient and carry-over rate with the range of 67.8-939.4 ng/mL were 0.9998 (P<0.001), and 0.1%, respectively. Correlation coefficient between OC neo and OC I was R(2)=0.954 (P<0.001) for 60 OC I-positive specimens. The positive and negative interpretations of 300 consecutive specimens by OC neo were completely consistent with those of OC I. CONCLUSIONS: Because OC neo showed an excellent performance and a good correlation with OC I, OC neo warrants to be a reliable quantitative FOBT system for high volume laboratories.

The Evaluation of Clinical Utility of ATB FUNGUS 2 for Antifungal Susceptibility Testing in Candida Species / 대한임상미생물학회지

BACKGROUND: Although the National Committee for Clinical Laboratory Standards (NCCLS) defined a standard reference broth microdilution method for testing the susceptibility of Candida species to antifungal drugs, many clinical laboratories require easier but reliable alternatives for routine antifungal susceptibility testing. We evaluated ATB FUNGUS 2 (bioMerieux, France.; ATB) compared to the method recommended by the NCCLS (NCCLS). METHODS: A total of 28 strains of Candida species consecutively isolated from blood and CSF cultures at Asan Medical Center from April to June 2004 were tested. In addition, 12 strains comprising C. krusei (3), C. glabrata (7) and C. guilliermondii (2) from the collection of Chonnam National University Hospital were included in the study. These strains were tested for minimum inhibitory concentrations (MICs) against flucytosine (FC), fluconazole (FZ), itraconazole (IZ) and amphotericin B (AB) by both of ATB and NCCLS. In NCCLS, MICs were read using a spectrophotometer after 24 and 48 hour-incubation. RESULTS: The concordance rates of MICs between ATB and NCCLS after 24 hour-incubation were 100%, 75%, 89% and 96% within two-fold dilution and 100%, 97%, 97%, 100% within four-fold dilution for FC, FZ, IZ and AB, respectively. For C. krusei, all three FC and FZ-resistant strains were either intermediate or SDD and one IZ-resistant strain was SDD in ATB, respectively. One C. tropicalis strain resulted in AB MICs of 0.5 microgram/mL in NCCLS, but 2 microgram/mL in ATB. CONCLUSIONS: ATB showed good concordance rates with NCCLS after 24 hour-incubation. ATB appears to be a useful alternatives to NCCLS for routine antifungal susceptibility tests. However, ATB needs further evaluation with more clinical strains, especially those resistant to antifungal agents.

Clinical Utility of Reticulocyte Parameters in the Early Detection of Hematopoietic Engraftment After Stem Cell Transplantation / 대한진단검사의학회지

BACKGROUND: Allogeneic or autologous bone marrow transplantation (BMT) or peripheral blood stem cell transplantation (PBSCT) has been settled a modality of treatment in hematologic malignantdisorders or solid tumors. Because engraftment or not was important for the direction of treatment and prognosis of the patients, various methods, judging it early were groped. Instead of an absoluteneutrophil count (ANC) or platelet count in PB, we used reticulocyte parameters as early predictors of hematopoietic engraftment. METHODS: We measured the ANC with reticulocyte parameters daily in 25 patients receiving allogeneic BMT or PBSCT (n=17, 30.82+/-9.97 years old) and autologous PBSCT (n=8, 30.63+/-8.55 years old) from January 2002 to February 2003 in Kyungpook National University Hospital. Wedefined erythroid engraftment as the first day of a mean corpuscular volume of reticulocyte (MCVr)>or=105 fL and immature reticulocyte fraction (IRF) >or=10% in the second rising peak and myeloid engraftment as the first day of ANC >or=500/microL. RESULTS: The erythroid engraftment occurred after a mean time of 16.24+/-4.16 days in allogeneic graft and 14.00+/-3.55 days in autologous graft and the myeloid engraftment occurred 17.94+/-3.23 days and 15.00+/-2.78 days, respectively. In the allogeneic graft, the erythroid engraftment occurred earlier than the myeloid engraftment (P=0.03). In the autologous graft, the erythroid engraftment preceded the myeloid engraftment; however, it was not statistically significant (P=0.47). Among 3 cases, wherein the erythroid engraftment occurred later than the myeloid engraftment in allogeneic graft, 2cases were ABO-incompatible PBSCT. CONCLUSIONS: Considering that the successive increase of immature reticulocytes preceded that of ANC in most cases, we concluded that as an early indicator of hematopoietic engraftment, reticulocyte parameters such as IRF and MCVr were useful especially observing them simultaneously.

Relation among the Tests and Comparison of Positivity of Tests for Multi-Drug Resistance in Newly Diagnosed Acute Leukemia / 대한진단검사의학회지

BACKGROUND: The expression of multi-drug resistance (MDR) in acute leukemia was known to decrease the outcome of chemotherapy and to increase the rate of relapse. Of the mechanism of MDR, the most well known is P-glycoprotein (P-gp) encoded by the mdr1 gene. There are MDR genes, P-gp tests and drug efflux function tests for the clinical measurement of MDR. To assess the clinical usefulness and MDR expression status in acute leukemia, MDR tests were performed. METHODS: MDR expression was assessed by MDR1 mRNA RT-PCR and flow cytometry measuring P-gp and daunorubicin (DNR) efflux in 77 patients with newly diagnosed acute leukemia (AL) including 48 acute myeloid leukemia (AML), 16 acute lymphoblastic leukemia (ALL) and 13 acute mixed-lineage leukemia (AMLL). The CD34 surface-marker study was also done by flow cytometry. The result of chemotherapy was evaluated by the percentage of remnant bone marrow (BM) blasts. RESULTS: The positivity of MDR1 mRNA was 57.1% (44/77) in AL, 61.5% (8/13) in AMLL, 60.4% (29/48) in AML, and 43.8% (7/16) in ALL. The positivity of P-gp expression was 36.5% (27/74) in AL and 100% in AML. The positivity of the DNR efflux test was 30.1% (22/73) in AL, 40.0% (18/45) in AML, 23.1% (3/13) in AMLL, and 6.7% (1/15) in ALL. There was a significant correlation between MDR1 mRNA and P-gp expression and between MDR1 mRNA and CD34 expression in AML. There was a significant correlation between the percentages of residual blast cells in BM and P-gp expression (P=0.039, r=0.312). CONCLUSIONS: It can be clinically useful to perform the mdr1 gene and P-gp test simultaneously both in newly diagnosed acute leukemia patients. The effectiveness of tests for MDR can be helpful to predict the outcome of chemotherapy.

Detection of Ureaplasma urealyticum and Mycoplasma hominis in Pregnant Women Using MYCOFAST(R) Evolution 2 and PCR / 대한임상미생물학회지

BACKGROUND: The associations between preterm labor or premature rupture of membrane (PROM) and urogenital infections of pregnant women are reported. Ureaplasma urealyticum and Mycoplasma hominis are well known as important pathogens of urogenital infections in pregnant women. In routine clinical laboratory, conventional culture for these microorganisms has not been made generally because of the requirements for strict growth condition. MYCOFAST(R) Evolution 2 is an easy and rapid liquid microculture method using metabolism of these microorganisms. Author investigated the relationship between U. urealyticum or M. hominis infections and preterm labor or PROM by MYCOFAST Evolution 2 and PCR. Also it was reviewed that the possibility of substitution of MYCOFAST Evolution 2 for conventional culture method by comparing with PCR methods. METHODS: This study was done on 91 pregnant women. They were composed of two groups; group I(n=48) had full-term delivery and group II(n=43) had preterm labor or PROM before the 37th week.Two cervical swabs were made each time. One was used for MYCOFAST(R) Evolution 2 and the other for PCR. RESULTS: The positivity of U. urealyticum was 39.6% in group Iand 58.1% in group IIby MYCOFAST Evolution 2 and 39.6% and 58.1% by PCR method, respectively. The positivity of M. hominis was 4.2% in group Iand 11.6% in group IIby MYCOFAST Evolution 2 and 4.2% and 7.0% by PCR method, respectively. The positivity of U. urealyticum and M. hominis in group IIwas higher than that in group Ibut was not significant statistically. The concordance rates between two methods were 86.8% for U. urealyticum and 97.8% for M. hominis. It showed good correlation between two methods (U. urealyticum, r=0.736; M. hominis, r=0.835). CONCLUSIONS: The infections of U. urealyticum and M. hominis were related to preterm labor or PROM. Considering vertical transmission to fetus or neonates resulting in perinatal morbidity or mortality, the detection of these microorganisms is important. MYCOFAST(R) Evolution 2 was an easy, rapid and reliable method substituting conventional culture method.

Detection of Chlamydophila pneumoniae in Acute Myocardial Infarction / 대한임상미생물학회지

BACKGROUND: There is growing evidence linking infection with Chlamydophila pneumoniae with vascular diseases, such as atherosclerosis and myocardial infarction. However, the data remain inconclusive and the clinical importance of C. pneumoniae as vasculopathic is unclear. So, we intend to detect C. pneumoniae in acute myocardial infarction patients by microimmunofluorescence (mIF) and polymerase chain reaction (PCR). METHODS: Blood and peripheral mononuclear cells (PMNCs) of 24 myocardial infarction patients and 100 normal controls were collected. Serum were used in mIF and PMNCs in PCR. PMNC sample were tested for C. pneumoniae by 'touchdown 'nested PCR. The first round PCR amplified DNA from both C. pneumoniae and Chlamydophila psittaci, while the second round specially targeted C. pneumoniae allowing the two species to be differentiated. RESULTS: Seropositivity of IgG and IgM anti-Chlamydophila pneumoniae antibody titers were 95.8% and 25% in myocardial infarction patients and 61% and 16% in control group, respectively. Positive rates of PCR of PMNCs were 8.3% in the patients and 15% in control group. CONCLUSION: The results of mIF show that mIF positive rate in myocardial infarction was much higher than control group. So an association between C. pneumoniae and myocardial infarction can be concluded. But the opposite results of PCR of PMNCs needed further studies.

Phenotypes and Interpretive Reading of Antimicrobial Susceptibility Tests for Clinical Isolates of Several Species / 대한임상미생물학회지

BACKGROUND: In recent years, knowledge of bacterial resistance to antimicobials has expanded in important ways. Availability of an increasing number of antibiotics allows more precise individualization of resistance phenotypes and recording susceptibility results as patterns or phenotypes is valuable for both surveillance and patient care. If the patterns of resistance to panels of related antimicrobials are considered the underlying mechanisms can often be inferred. And the inferred mechanisms make the clinician to be advised to use alternative treatment. Interpretation of resistance phenotypes is based on the comparison of clinical isolates with prototype susceptible bacteria belonging to the same species. But interpretative reading of antimicrobial susceptibility tests requires an immense knowledge of antibiotics. Such interpretative reading is best achieved by computerized expert systems. METHODS: The authors attempt to determine phenotypes for the clinically isolated strains for each class of drugs tested by the Vitek 2 systemTM(bioMerieux, Marcy I'Etoile, France) using the Advanced Expert SystemTM(AES, bioMerieux, Marcy I'Etoile, France). A total of 91, 107, 89, 65, 251, 113, 47, 33, 23, 122 and 110 isolates of Staphylococcus aureus, coagulase negative staphylococci, Enterococcus faecalis, Enterococcus facium, Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Enterobacter cloacae, Enterobacter aerogenes, Pseudomonas aeruginosae and Acinetobacter baumannii, were examined respectively. RESULTS: Biological correction based on the phenotype was recommended from 2.2% of E. faecalis to 46.8% of S. marcescens and therapeutic correction, from 7.3% of A. baumannii to 60.9% of E. aerogenes. A total of 25, 26, 18, 19, 22, 22, 15, 15, 17, 19, 19 phenotypes of S. aureus, coagulase negative staphylococci, E. faecalis, E. facium, E. coli, K. pneumoniae, S. marcescens, E. cloacae, E. aerogenes, P. aeruginosa and A. baumannii, were detected respectively. Association of resistance mechanism from S. aureus, coagulase negative staphylococci, E. coli, K. pneumoniae, S. marcescens, show 10, 11, 6, 4 and 3 pairs from resistant phenotypes, respectively. CONCLUSION: Vitek AES potentially provides a tool to assist the development of antimicrobial susceptibility interpretation in the clinical microbiology laboratory. The inferred mechanisms make the clinician to be advised to use alternative treatment.