In vitro activities of doripenem and other carbapenems against clinically important bacteria isolated in intensive care units: nationwide data from the SMART Programme.

This nationwide surveillance of clinically important bacteria from the intensive care units (ICUs) of major teaching hospitals throughout Taiwan investigated the susceptibilities to doripenem and other comparator carbapenems from September through November 2005. Minimum inhibitory concentrations (MICs) were determined for 1,311 clinical isolates using the broth microdilution method according to Clinical and Laboratory Standards Institute (CLSI) 2005 guidelines. Doripenem showed similar (within four-fold difference of MICs) in vitro activity to meropenem for Enterobacteriaceae and probably comparable activity to meropenem against important nosocomial non-fermentative Gram-negative bacilli (NFGNBs), including Pseudomonas aeruginosa, Acinetobacter baumannii and Burkholderia cepacia. Among the four carbapenems analysed, doripenem and meropenem exhibited better in vitro activity than imipenem or ertapenem against extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae and Escherichia coli isolates. However, the meropenem MIC(90) against ESBL-producing K. pneumoniae isolates was 2 microg/ml. Besides, doripenem with the MIC(90) of 0.5 microg/ml to Streptococcus pneumoniae possibly suggested its potential therapeutic effect regarding community-acquired pneumonia. Because of the heavy resistance burden in Taiwan, closely monitoring the evolutionary trend of carbapenem susceptibilities against clinically important pathogens is crucial in the future.

Nationwide surveillance of antimicrobial resistance among Enterobacteriaceae in intensive care units in Taiwan.

To determine the antimicrobial resistance profiles among clinical isolates of Enterobacteriaceae in Taiwanese intensive care units (ICUs), a national surveillance of antibiotic resistance among important Enterobacteriaceae was conducted from September 2005 through November 2005 at the ICUs of ten major teaching hospitals in Taiwan. A total of 574 Enterobacteriaceae isolates recovered from various clinical samples of our ICU patients were submitted for in vitro test. Minimum inhibitory concentrations (MICs) of these isolates to 18 antimicrobial agents were determined by the broth microdilution method. The prevalences of Enterobacteriaceae isolates with phenotypic extended-spectrum beta-lactamase (ESBL) production were 26% in Klebsiella pneumoniae, 16% in Serratia marcescens, 14% in Escherichia coli, and 13% in Proteus mirabilis, in which a significantly rising prevalence of ESBL production among K. pneumoniae was noted (p = 0.002) when compared with a previous Taiwanese survey in 2000. Heterogeneous resistance to various fluoroquinolones was found among our Enterobacteriaceae isolates, except for Enterobacter cloacae. Emergence of ertapenem-resistant isolates of E. coli, K. pneumoniae, E. cloacae, and S. marcescens was noted. Gradually increasing rates of drug-resistant Enterobacteriaceae were noted in Taiwanese ICUs. Periodic surveillance of the evolutionary trend of antimicrobial resistance among ICU isolates is crucial for starting appropriately empirical antimicrobial therapy in the future.

Nationwide surveillance of antimicrobial resistance among Haemophilus influenzae and Streptococcus pneumoniae in intensive care units in Taiwan.

A nationwide susceptibility surveillance of Streptococcus pneumoniae and Haemophilus influenzae isolates collected from patients treated at the intensive care units (ICUs) of ten Taiwanese major teaching hospitals was conducted from September 2005 through November 2005. High rates of resistance (intermediate/resistant) of S. pneumoniae to penicillin (85% resistance), ceftriaxone (46%/20%), and cefepime (43%/15%) by meningitis criteria, and in contrast, non-susceptibilities (intermediate/resistant) to penicillin (0%/0%), ceftriaxone (20%/0%) and cefepime (15%/0%) by non-meningitis criteria were noted (p values < 0.05) by the Clinical and Laboratory Standards Institute 2008. Resistant rate of S. pneumoniae to azithromycin was also high (63%). S. pneumoniae isolates were significantly more susceptible to ertapenem (87%) than to imipenem (39%) and meropenem (44%) (p values < 0.05). Rates of non-susceptibilities of H. influenzae isolates to ampicillin and cefaclor were high (55% and 45%, respectively). No beta-lactamase-negative ampicillin-resistant (BLNAR) H. influenzae isolates were found. Imipenem has a notably higher MIC(90) value (8 microg/ml) for H. influenzae than that of the other two carbapenems. Tigecycline showed good in vitro activities against these two respiratory pathogens. High rates of resistance among isolates of S. pneumoniae and H. influenzae continue to exist in the ICUs of Taiwan.

Toluidine blue O photodynamic inactivation on multidrug-resistant Pseudomonas aeruginosa.

BACKGROUND AND OBJECTIVES: Multidrug-resistant (MDR) Pseudomonas aeruginosa infection is becoming a critical problem worldwide. Currently, only limited therapeutic options are available for the treatment of infections caused by MDR P. aeruginosa, therefore, the development of new alternative treatments is needed. Toluidine blue O (TBO) is an effective antibacterial photosensitizing agent against various bacteria. However, reports on antibacterial photosensitization of MDR bacteria are limited. This study aims to determine the in vitro photobactericidal activity of TBO against MDR P. aeruginosa. STUDY DESIGN/MATERIALS AND METHODS: The efficacy of antibacterial photodynamic inactivation, DNA fragmentation and protein carbonylation of three MDR P. aeruginosa strains and one susceptible strain was compared using TBO as the photosensitizer followed by red light irradiation (630 nm, 90 J/cm(2)) from a light-emitting diode light source. Subsequently, the efficacy of TBO photodynamic inactivation (TBO-PDI) on 60 MDR strains, including 11 with the efflux pump phenotype and 49 with no pump activity, was tested using the minimum lethal drug concentration (MLC) assay. RESULTS: TBO-PDI caused similar bactericidal effect (6-7 logs of killing effect), DNA fragmentation and protein carbonylation in three MDR and one susceptible P. aeruginosa strains. Although the TBO accumulation assay indicated that TBO is a substrate for the efflux pump, TBO-PDI produce similar photobactericidal activity against 60 MDR P. aeruginosa strains, either with or without efflux-pump phenotype, and 19 susceptible strains. CONCLUSION: MDR did not affect the susceptibility of P. aeruginosa strains to TBO-PDI. The efflux pump played an insignificant role in TBO-PDI of MDR P. aeruginosa.

Comparative bactericidal activities of daptomycin, glycopeptides, linezolid and tigecycline against blood isolates of Gram-positive bacteria in Taiwan.

In-vitro MICs and minimum bactericidal concentrations (MBCs) of daptomycin, linezolid, tigecycline, vancomycin and teicoplanin against Gram-positive bacteria were determined using the broth microdilution method for ten blood isolates each of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), including two vancomycin-intermediate S. aureus (VISA), vancomycin-resistant Enterococcus faecium and Enterococcus faecalis. One strain of VISA was tested in a time-kill synergism assay of daptomycin combined with oxacillin, imipenem, rifampicin and isepamicin. Daptomycin showed excellent in-vitro bactericidal activity against all the isolates tested, with no tolerance or synergism effects when combined with other agents, except with rifampicin against VISA. Vancomycin had better bactericidal activity against MRSA and MSSA than did teicoplanin. Linezolid had the poorest bactericidal activity against the isolates tested, with 100% tolerance by the MSSA and VRE isolates, and 80% tolerance by the MRSA isolates. Tolerance towards tigecycline was exhibited by 40% of the MRSA isolates, 100% of the MSSA and vancomycin-resistant E. faecalis isolates, and 90% of the vancomycin-resistant E. faecium isolates.

Fatal case of ST8/SCCmecIVl community-associated methicillin-resistant Staphylococcus aureus infection in Japan.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) with ST8/SCCmecIV threatens human health. However, its pathogenesis remains unclear. ST8 CA-MRSA (CA-MRSA/J) with SCCmecIVl, which carries the large LPXTG-motif-containing putative adhesin gene, spj, has emerged in Japan. We present the first reported case of death from CA-MRSA/J. The patient was a 64-year-old woman with iliopsoas abscesses complicated by septic pulmonary embolism and multiorgan abscesses. Vancomycin, arbekacin, daptomycin and rifampicin were ineffective. CA-MRSA/J was resistant to erythromycin, clindamycin and antiseptics and was invasive in a HEp-2 cell assay, in contrast to skin-derived villous-adherent CA-MRSA/J. This suggests the strongly invasive pathotype of CA-MRSA/J.

Clonal spread of SCCmec type IV methicillin-resistant Staphylococcus aureus between community and hospital.

The staphylococcal chromosome cassette (SCC)mec types of 382 hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates in Taiwan were analysed over a 7-year period (1999-2005). There was an abrupt increase in SCCmec type IV in HA-MRSA during 2005. The molecular epidemiology of a subset (n = 69) of HA-MRSA isolates with SCCmec types III, IV or V was characterised and compared with that of community-acquired MRSA (CA-MRSA) (n = 26, collected during 2005). Pulsed-field gel electrophoresis revealed three major pulsotypes (A, B and C) and 15 minor clones. Pulsotypes B and C, which contained isolates carrying SCCmec types IV and V, respectively, included both CA-MRSA and HA-MRSA isolates. Among 24 toxin genes analysed, five genes had significant differential distribution between CA-MRSA and SCCmec type III HA-MRSA. Furthermore, among SCCmec type IV isolates, the seb gene was detected more commonly in HA-MRSA. Analysis of representative members of the three major pulsotypes by multilocus sequence typing revealed two sequence types (STs), namely ST239 (SCCmecIII) and ST59 (SCCmecIV or SCCmecV). This suggests that ST59:SCCmecIV, which is usually community-acquired, has become an important nosocomial pathogen in the hospital studied.

Emerging ST121/agr4 community-associated methicillin-resistant Staphylococcus aureus (MRSA) with strong adhesin and cytolytic activities: trigger for MRSA pneumonia and fatal aspiration pneumonia in an influenza-infected elderly.

The pathogenesis of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) pneumonia in influenza-infected elderly individuals has not yet been elucidated in detail. In the present study, a 92-year-old man infected with influenza developed CA-MRSA pneumonia. His CA-MRSA was an emerging type, originated in ST121/agr4 S. aureus, with diversities of Panton-Valentine leucocidin (PVL)(-)/spat5110/SCCmecV(+) versus PVL(+)/spat159((etc.))/SCCmec (-), but with common virulence potentials of strong adhesin and cytolytic activities. Resistance to erythromycin/clindamycin (inducible-type) and gentamicin was detected. Pneumonia improved with the administration of levofloxacin, but with the subsequent development of fatal aspiration pneumonia. Hence, characteristic CA-MRSA with strong adhesin and cytolytic activities triggered influenza-related sequential complications.

Pan-drug-resistant Pseudomonas aeruginosa causing nosocomial infection at a university hospital in Taiwan.

This study evaluated the clinical and microbiological characteristics of 16 patients who were colonised or infected with 26 isolates of pan-drug-resistant Pseudomonas aeruginosa (PDRPA; intermediately-resistant or resistant to all cephalosporins, piperacillin-tazobactam, aztreonam, carbapenems, ciprofloxacin and aminoglycosides) in a university hospital during 1999-2002. All the isolates had colistin MICs < or = 4 mg/L, 19 (73%) isolates had bla(VIM-3), and 25 (96%) isolates had class I integrons (intI). Time-kill studies for two PDRPA blood isolates demonstrated synergism for cefepime-amikacin after 24 h. Pulsed-field gel electrophoresis analysis of the isolates revealed a polyclonal nature (12 pulsotypes), although clonal dissemination of PDRPA isolates among these patients was also present.

Emergence of vancomycin-resistant enterococci at a university hospital in Taiwan: persistence of multiple species and multiple clones.

OBJECTIVES: To describe the epidemiology of vancomycin-resistant enterococci (VRE) in a university hospital in Taipei, Taiwan. DESIGN: Retrospective review over a 27-month period, from March 1996 to May 1998. SETTING: A tertiary-care teaching hospital in Taiwan. PARTICIPANTS: Patients with VRE isolated from any body site. METHODS: Patients were identified through hospital microbiology and infection control records. Patient charts were reviewed for clinical and epidemiology data, including age, gender, previous hospital admissions, underlying diseases, types of infection, and recent antibiotic use. VRE isolates were characterized by their typical biochemical reactions, cellular fatty acid profiles, and the presence of van genes. Antibiotypes using the E-test and randomly amplified polymorphic DNA (RAPD) patterns of these isolates were used to determine the clonality. RESULTS: Twenty-five isolates of VRE recovered from 12 patients were identified. One patient with a perianal abscess had 12 isolates of VRE (4 Enterococcus faecalis, 7 Enterococcus faecium, and 1 Enterococcus casseliflavus) recovered from perianal lesions. Among 3 patients who were hospitalized in the same room, 1 had a community-acquired cellulitis over the left leg caused by E. faecalis, and the other 2 patients both had anal colonization with 2 isolates of E. faecalis. The other 8 patients had 1 E. faecalis isolate each from various clinical specimens. All isolates possessed vanA resistance phenotype and vanA genes. Different antibiotypes and RAPD patterns of the isolates from different patients excluded the possibility of nosocomial spread at the hospital. CONCLUSIONS: Multiple species of VRE (E. faecalis, E. faecium, and E. casseliflavus) and multiple clones of E. faecium could colonize or infect hospitalized patients. In addition, clones of VRE can persist long-term in patients' lower gastrointestinal tracts. These results extend our knowledge of the coexistence and the persistence of multiple species and multiple clones of VRE in hospitalized patients.

Outbreak of scarlet fever at a hospital day care centre: analysis of strain relatedness with phenotypic and genotypic characteristics.

An outbreak of scarlet fever involving 12 children occurred at a hospital day care centre from February to March 1996. Twenty-five throat isolates of Streptococcus pyogenes (GAS, group A streptococcus) available from 24 children, including 10 children with scarlet fever and 14 asymptomatic carriers, and one asymptomatic staff member were studied for the presence of genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), and C (speC) and for protease activity. Antimicrobial susceptibilities using the E-test, cluster analysis by cellular fatty acid composition and random amplified polymorphic DNA (RAPD) patterns by means of arbitrarily-primed polymerase chain reaction (APPCR) of the isolates were performed to investigate the outbreak. Only one isolate from an asymptomatic child possessed the speA gene. All isolates possessed the speB gene and 24 (96%) isolates were positive for the speC gene. There was no difference in protease activity between isolates from children with scarlet fever and from asymptomatic carriers. Thirteen isolates (10 recovered from children with scarlet fever, two from asymptomatic children, and one from the staff member) were considered to be the same strain according to the identical antimicrobial susceptibility profile and RAPD patterns and were also considered to be similar by cluster analysis of fatty acid composition. These findings suggest that the outbreak was caused by a unique clone of GAS. We conclude that RAPD typing and cluster analysis by cellular fatty acids composition both provide a powerful tool for epidemiological investigation of GAS infections.

Persistent bacteraemia caused by a single clone of Burkholderia cepacia with unusual phenotype.

We report a case of persistent bacteraemia caused by a single clone of Burkholderia cepacia with unusual characteristics. Six isolates of B. cepacia were recovered from a patient with acute myeloid leukaemia and chemotherapy-induced neutropenia within a 3-week period. All six isolates were initially incompletely identified as B. cepacia with the API 20NE system. The further use of cellular fatty acid analysis and PCR-restriction fragment length polymorphism of the 16S rDNA confirmed the identification. These isolates also displayed an identical but unusual antibiotype. The identical cellular fatty acid profiles and genomic typing generated by random amplified polymorphic DNA identified these isolates as derivatives of a single strain.

Comparison of preservation mixtures for Helicobacter pylori.

Long-term preservation of 40 isolates of Helicobacter pylori was investigated with five storage media (brucella broth with 17% glycerol, brucella broth with 17% glycerol and 2% fetal calf serum [FCS], brucella broth with 17% glycerol and 10% FCS, brucella broth with 17% glycerol and 2% horse blood, and 10% mucin) at -70 degrees C for 4, 6 and 9 months. In addition to glycerol, FCS or horse blood in the storage media is necessary for survival of H. pylori. Storage of H. pylori isolates at -70 degrees C in 10% mucin is a simple and effective preservation procedure.

High protease activity of Chryseobacterium indologenes isolates associated with invasive infection.

In order to understand virulence factors of Chryseobacterium indologenes isolates associated with invasive infection, enzymatic activities and cellular fatty acid profiles of 42 isolates recovered at National Taiwan University Hospital from January 1994 to December 1996 were studied. Among them, 12 blood isolates were considered as invasive and 30 (recovered from urine, sputa, infected burn wounds, and catheter tips) were noninvasive. All isolates showed strong activities of alkaline phosphatase, acid phosphatase, naphthol-AS-BI-phosphohydrolase, and N-acetyl-beta-glucosaminidase, and had no activities for alpha-galactosidase, beta-galactosidase, beta-glucuronidase, alpha-mannosidase, and alpha-fucosidase. The activities of other enzymes were variable. Thirty-two isolates (76%) had varying degrees of protease activity. Two profiles (profiles I and II) of cellular fatty acids of the isolates were found and profile I predominated. There was no significant difference of distribution of cellular fatty acid profiles and activities of enzymes between invasive and noninvasive isolates, except protease activity which was significantly higher in invasive isolates than that in noninvasive isolates. Protease activity may play an important role in virulence on invasive infections caused by C. indologenes.

Use of polymerase chain reaction to detect Proteus mirabilis and Ureaplasma urealyticum in urinary calculi.

In this study, we evaluated the efficacy of the polymerase chain reaction (PCR) in detecting urea-splitting microorganisms in desiccated urinary tract infection stones. Seventy-eight urinary tract stones were tested for the presence of Proteus mirabilis and Ureaplasma urealyticum by means of PCR with species-specific primers. Twenty-seven stone samples were composed of struvite and/or carbonate apatite (infection stone); 40 were calcium oxalate and/or calcium phosphate; seven were mixed, with struvite/carbonate apatite and calcium oxalate; and four were uric acid stones. PCR was performed with DNA extracted from pulverized stone pieces. Initial assays using the pulverized stone specimens spiked with microorganisms showed that PCR could not detect U. urealyticum at densities below 10(3) color changing units (CCU), or P. mirabilis at densities below 10(4) colony-forming units (CFU). PCR was negative for U. urealyticum and P. mirabilis in all metabolic stones from patients. P. mirabilis was detected by PCR in 10 of 34 patients with infection stones. Preoperative urine cultures grew P. mirabilis in three of these 10 patients, and were negative for P. mirabilis in the other seven. U. urealyticum was detected by PCR in stone samples from four patients, two of which were also PCR-positive for P. mirabilis. All four of these patients had infection stones: two had residual stones, and the other two had recurrence of urinary stones after their operations. These results demonstrate that microorganisms in urinary stones can be detected by PCR even when the voided urine culture is negative. Investigations into the role of bacterial infection in stone formation will require further improvements in the sensitivity of PCR assays for pathogen detection.

In vitro activities of 36 antimicrobial agents against clinically isolated Bacteroides fragilis.

Thirty-six antimicrobial agents were evaluated for in vitro activities against 100 clinical isolates of Bacteroides fragilis. The minimal inhibitory concentration (MIC) of each agent for each isolate was determined by the agar dilution method. Among 25 beta-lactam antibiotics, the most active agent was imipenem with an MIC90 and a geometric mean of 1 and 0.15 micrograms/ml, respectively; followed by ticarcillin-clavulanic acid, and amoxicillin-clavulanic acid. Ampicillin-sulbactam, piperacillin-tazobactam, moxalactam, and flomoxef were the next most active agents. Piperacillin, ticarcillin, ceftizoxime, cefotaxime, cefuzonam, cefoxitin, and cefmetazole were equally active with the MIC50s ranging from 4 to 16 micrograms/ml, and MIC90s ranging from 32 to greater than or equal to 256 micrograms/ml. The remaining 10 beta-lactam antibiotics, ampicillin, amoxicillin, cefazolin, cefuroxime, cefoperazone, cefmenoxime, ceftazidime, cefpirome, aztreonam, and carumonam were less active. All isolates were resistant to cefotiam at a low breakpoint. Among 6 quinolones, ciprofloxacin was the most active agent with an MIC50 and an MIC90 of 4 and 16 micrograms/ml, respectively. All isolates were resistant to nalidixic acid, pipemidic acid, cinoxacin, enoxacin, and norfloxacin. Among 5 frequently used agents, chloramphenicol, ornidazole, and metronidazole were the most effective agents which inhibited 100% of the isolates at 8, 2, and 2 micrograms/ml, respectively; while clindamycin and minocycline had less activity.

Antimicrobial susceptibilities of clinical isolates of vancomycin-resistant enterococci in Taiwan.

To understand the antimicrobial resistance patterns of vancomycin-resistant enterococci in Taiwan, we tested the in vitro activities of 10 antimicrobial agents against 71 clinical isolates (39 of Enterococcus faecalis and 32 of Enterococcus faecium) by means of the agar dilution method. Resistance was determined on the basis of the minimum inhibitory concentration (MIC) of each antimicrobial agent--MIC50 and MIC90 (minimum concentrations required to inhibit growth of 50% and 90% of isolates, respectively) were determined. No beta-lactamase producers were identified with the cefinase test. All E. faecalis isolates were susceptible to penicillin and ampicillin, and 97% of these isolates were resistant to teicoplanin (vanA phenotype). Of the E. faecium isolates, 75% were susceptible to teicoplanin (vanB phenotype) and most were resistant to penicillin (94%) and ampicillin (94%). Quinupristin/dalfopristin was markedly less active against E. faecalis than E. faecium isolates (MIC50, 64 vs 2 micrograms/mL; MIC90, 128 vs 8 micrograms/mL; susceptibility rates, 3% vs 81%). Five of the eight vanA phenotype E. faecium isolates and one of the 24 vanB phenotype E. faecium isolates were resistant to quinupristin/dalfopristin. The activity of rifampin was also species-specific, with E. faecium being markedly less susceptible to this agent than E. faecalis (MIC50, 16 vs 1 microgram/mL; MIC90, 64 vs 4 micrograms/mL). Our data suggest the potential of teicoplanin and quinupristin/dalfopristin as appropriate antimicrobial agents in the treatment of infections caused by vanB phenotype E. faecium. Penicillin, ampicillin, and rifampin alone, or preferably in combination with other agents, appear to be the most appropriate agents for the treatment of vancomycin-resistant E. faecalis infections in Taiwan.

Antimicrobial susceptibility testing for Klebsiella pneumoniae isolates resistant to extended-spectrum beta-lactam antibiotics.

Detection of Klebsiella pneumoniae strains with extended-spectrum beta-lactamase (ESBL)-related resistance phenotypes is becoming important in clinical microbiology laboratories. In this study, we investigated the usefulness of three screening methods, the Etest ESBL screen, the double-disk synergy test, and the ceftazidime disk test, for identifying ESBL-producing K. pneumoniae strains. The agar dilution method was used as the standard. We also determined the in vitro activity of several new antimicrobial agents against these organisms. Strains that exhibited an increase in the minimum inhibitory concentration (MIC) to the third-generation cephalosporins or aztreonam of 2 micrograms/mL or more, but were susceptible to the three cephamycins tested, were considered to have ESBL-related resistance phenotypes. The frequency of ESBL-producing K. pneumoniae isolates (according to the disk-diffusion method) has increased markedly in recent years, from 3.4% in 1993 to 10.3% in 1997. A total of 93 preserved isolates of K. pneumoniae collected from December 1995 through March 1997 were found to be resistant to at least one of the third-generation cephalosporins (cefotaxime and ceftazidime) or aztreonam using the routine disk diffusion method. Among these isolates, 35 were classified as having an ESBL phenotype using the agar dilution method. The remaining 58 isolates were classified as cephamycin resistant, which indicated resistance to both cephamycins and third-generation cephalosporins or aztreonam. The susceptibility rates of the ESBL-producing isolates were 11% for cefotaxime, 14% for ceftazidime, and 6% for aztreonam. The susceptibility rates of these 35 isolates to imipenem, ciprofloxacin, and ofloxacin were 100%, 80%, and 86%, respectively. Both the MIC50 and MIC90 of meropenem were 0.06 microgram/mL, while the MIC50 and MIC90 of BAY 12-8039 were 0.125 and 2 micrograms/mL, respectively. Thirty-two (91%) of the 35 isolates of K. pneumoniae with the ESBL-related resistance phenotype were detected by the Etest ESBL screen, while the ceftazidime disk screen test detected 77% of these isolates, and the double-disk synergy test detected 74%. The Etest ESBL screen appears to be an acceptable, convenient, and sensitive method for the detection of ESBL-producing isolates in the clinical microbiology laboratory.

Heterogeneity of resistance elements in clinical isolates of enterococci with high-level gentamicin resistance.

High-level resistance (minimum inhibitory concentration, MIC > 1,000 micrograms/ml) to gentamicin (HLGR) in enterococci is common in Taiwan. In this study, we investigated the distribution of gentamicin resistance elements in enterococci isolated at National Taiwan University Hospital in a 1-year period, and also examined the transfer and the genetic variability of the resistance elements of different isolates. Among 109 isolates tested, 43 (39%) HLGR isolates were identified. HLGR was most common in Enterococcus faecium isolates (7/15, 47%), followed by Enterococcus faecalis (34/80, 43%), Enterococcus avium (1/5, 20%), and Enterococcus casseliflavus (1/9, 11%). To understand the mechanism of resistance transfer, four isolates of E. faecalis and five isolates of E. faecium showing HLGR were studied. Transfer of resistance markers to a plasmid-free recipient strain of E. faecalis JH2-7 was observed, with transfer frequencies ranging from 10(-2) to 10(-8). All of the transconjugants contained plasmids, with sizes ranging from 45 kb to larger than 70 kb. At least three plasmid patterns were observed on digestion with HaeIII. Hybridization with a probe specific for the aac6'aph2" gentamicin resistance gene confirmed that all of these HLGR isolates carried a Gm(r) determinant, though the hybridization patterns of the plasmids from E. faecalis and E. faecium were different. Although many similarities exist among enterococcal Gm(r) determinants, the results suggest heterogeneity may occur in the flanking regions of resistance elements.

Constitutive fatty acid and enzyme profiles of Mycobacterium species.

Sixty-one strains of Mycobacterium tuberculosis complex and 47 strains of nontuberculous mycobacteria were analyzed for fatty acids and enzyme profiles. Cellular fatty acids were extracted from bacteria, methylated and analyzed by gas liquid chromatography operated either manually (Perkin-Elmer) or by the automatic Microbial Identification System. The major cellular fatty acids in all mycobacterial species were C16:0 and C18:1. Tuberculostearic acid was found in all species with the exception of Mycobacterium gordonae. The fatty acids with a carbon-length longer than 20 could be detected only by conventional gas chromatography. Strains of M. tuberculosis had a high ratio of C26:0 to C24:0, and a relatively low ratio of C14:0 to C15:0. For determination of branched-chain fatty acids, the MIS provided more definitive results. The data indicated that the fatty acid profiles could provide rapid species identification. The results of the enzyme profile analysis using API-ZYM strips showed 39 different patterns from 59 strains of M. tuberculosis, and 41 different patterns from 46 nontuberculous mycobacteria strains, suggesting that enzyme profiles can also be used for strain characterization within the same species.