I-Wen Huang

Emergence of extensively drug-resistant Acinetobacter baumannii complex over 10 years: Nationwide data from the Taiwan Surveillance of Antimicrobial Resistance (TSAR) program

BackgroundAcinetobacter baumannii complex (ABC) has emerged as an important pathogen causing a variety of infections. Longitudinal multicenter surveillance data on ABC from different sources in Taiwan have not been published. Using data from the Taiwan Surveillance of Antimicrobial Resistance (TSAR) conducted biennially, we investigated the secular change in resistance of 1640 ABC from 2002 to 2010 (TSAR period III to VII) to different antimicrobial agents and identified factors associated with imipenem-resistant and extensively drug-resistant ABC (IRABC and XDRABC).MethodsIsolates were collected by TSAR from the same 26 hospitals located in all 4 regions of Taiwan. Minimum inhibitory concentrations (MIC) were determined by reference broth microdilution method. Isolates nonsusceptible to all tested aminoglycosides, fluoroquinolones, β-lactam, β-lactam/β-lactam inhibitors, and carbapenems were defined as extensively drug-resistant (XDR). Multivariate logistic regression analysis was performed to assess the relationship between predictor variables among patients with resistant ABC and patients with non-resistant ABC.ResultsThe prevalence of IRABC increased from 3.4% in 2002 to 58.7% in 2010 (P < 0.001; odds ratio [OR], 2.138; 95% confidence interval [CI], 1.947 to 2.347) and that of XDRABC increased from 1.3% in 2002 to 41.0% in 2010 (P < 0.001; OR, 1.970; 95% CI, 1.773-2.189). The rates of non-susceptibility to other antimicrobial agents remained high (>55%) over the years with some fluctuations before and after TSAR V (2006) on some agents. Multivariate analysis revealed that recovery from elderly patients, origins other than blood, from ICU settings, or geographic regions are independent factors associated with IRABC and XDRABC. Although the prevalence of XDRABC increased in all four regions of Taiwan over the years, central Taiwan had higher prevalence of XDRABC starting in 2008. Susceptibility to polymyxin remained high (99.8%).ConclusionsThis longitudinal multicenter surveillance program revealed significant increase and nationwide emergence of IRABC and XDRABC in Taiwan over the years. This study also identified factors associated with IRABC and XDRABC to help guide empirical therapy and at-risk groups requiring more intense interventional infection control measures with focused surveillance efforts.

Carriage rates of methicillin-resistant Staphylococcus aureus (MRSA) depend on anatomic location, the number of sites cultured, culture methods, and the distribution of clonotypes

The present study was carried out to determine how active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) could be improved by the use of enrichment broth and the inclusion of extra-nasal sites with nares cultures. Molecular typing was also performed to identify colonization by single or multiple strains. Surveillance cultures for MRSA were obtained from 650 patients on admission to a medical and surgical intensive care unit (ICU) in Taiwan. MRSA was detected on directly plated vs. broth-enrichment cultures in any site at 10.0% vs. 24.2%, nares 8.2% vs. 17.5%, throat 4.8% vs. 13.4%, axilla 1.2% vs. 9.1%, and perineum 1.8% vs. 9.5%, respectively. Nares cultures alone detected only 81.5% and 72.5% of all colonized patients by direct and broth-enriched cultures, respectively. The molecular typing of 68 isolates from 17 patients revealed that multisite isolates were largely indistinguishable within each patient, but four patients had multiple subtypes and another three patients had different clonotypes. The detection of MRSA carriers was considerably enhanced by broth-enrichment cultures at multiple anatomic sites and simultaneous colonization by multiple strains at different sites can occur. Epidemiological studies are needed to determine the likelihood of subsequent nosocomial infection among colonized patients detected via direct nasal versus broth-enriched cultures from multiple sites.

Methicillin-resistant Staphylococcus aureus in Taiwan

We found a virulent closely related clone (Panton-Valentine leukocidin–positive, SCCmec V:ST59) of methicillin-resistant Staphylococcus aureus in inpatients and outpatients in Taiwan. The isolates were found mostly in wounds but were also detected in blood, ear, respiratory, and other specimens; all were susceptible to ciprofloxacin, gentamicin, and trimethoprim-sulfamethoxazole.

mecA-Positive Staphylococcus aureus with Low-Level Oxacillin MIC in Taiwan

ABSTRACT Although the presence of mecA is the genotypic determinant of methicillin-resistant Staphylococcus aureus (MRSA), certain MRSA strains, especially community-associated MRSA (C-MRSA), can display an oxacillin MIC in the Clinical and Laboratory Standards Institute susceptible breakpoint range (≤2 μg/ml). Among 91 and 180 isolates thought to be methicillin-susceptible S. aureus (MSSA) with oxacillin MICs of 2 and 1 μg/ml as determined by the Sensititre broth microdilution test initially, 52 (57.1%) and 6 (3.3%), respectively, were mecA positive. These mecA-positive low-oxacillin-MIC isolates belong to the dominant Taiwan C-MRSA clone (clonal complex [CC] 59), 56 of which carried SCCmec type V and were pvl positive, and 43 of which belonged to spa CC t437. All 271 isolates were retested by Sensititre, as well as by Vitek II and disk diffusion (DD). Based on the oxacillin results, the sensitivities of the Sensititre, Vitek II, and DD methods were 48.3% (28/58), 46.6% (27/58), and 89.6% (52/58), respectively. Although cefoxitin was better at detecting these isolates, 12.1, 10.4, and 5.2% of these isolates were still misidentified as MSSA by Sensititre, Vitek II, and DD, respectively. These results highlight the difficulty in the accurate identification of MRSA with borderline oxacillin MICs in the CC59:SCCmec V clone, which likely has contributed to its spread in the health care and community settings. Since this clone has now been detected in other countries, and since other C-MRSA lineages have also been found to have low-level β-lactam resistance, the findings of the present study may be relevant to other regions. Further studies are warranted to determine the extent and clinical impact of such misidentification.

Complete Genome Sequence of Staphylococcus aureus M013, a pvl-Positive, ST59-SCCmec Type V Strain Isolated in Taiwan

We report the complete genome sequence of M013, a representative strain of a pvl-positive, sequence type 59-staphylococcal cassette chromosome mec type V (ST59-SCCmec type V) community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) clone in Taiwan. Comparison of M013 with the genomes of two CA-MRSA strains in the United States revealed major differences in the regions covering several genomic islands and prophages.

Panton-Valentine leukocidin (PVL)-positive methicillin-susceptible and resistant Staphylococcus aureus in Taiwan: identification of oxacillin-susceptible mecA-positive methicillin-resistant S. aureus

Methicillin-resistant Staphylococcus aureus (MRSA) arises when methicillin-susceptible S. aureus (MSSA) acquires the staphylococcal cassette chromosome mec (SCCmec). Most pvl-positive MRSA in Taiwan belong to ST59 lineage and carry SCCmec V. The genetic profiles of 51 MSSA were compared with those of 80 MRSA from the same hospitals. Nine pvl-positive MSSA (oxacillin MIC < or = 2 microg/mL) shared >80% similarity in pulsed field gel electrophoresis pattern with 17 pvl-positive SCCmec V MRSA. Further investigation found that 5 of these 9 isolates were MRSA by cefoxitin and carried SCCmec V. All 26 pvl-positive isolates had very similar genetic profile (ST59, protein A clonal complex [spa-CC] c2:441/437, and agr group I). The success of the ST59:SCCmec V MRSA may be due in part to its heterogeneous and borderline resistance to methicillin, which may be missed by testing only oxacillin, with subsequent exposure to beta-lactams causing the emergence of more resistant subpopulations.

Epidemiology and Molecular Characterization of Macrolide-Resistant Streptococcus pyogenes in Taiwan

ABSTRACT Our multicenter nationwide surveillance data indicated that erythromycin (ERY) resistance among group A Streptococcus (GAS) isolates in Taiwan declined from 53.1% in 1998 and 2000 to 14.6% in 2002 and 2004 and 10.7% in 2006 to 2010 (P < 0.01). The present study aimed to assess the epidemiology of GAS in Taiwan and identify factors associated with ERY resistance. All 127 ERY-resistant (ERYr) isolates and 128 randomly selected ERY-susceptible (ERYs) isolates recovered from 1998 to 2010 were emm typed. ERYr isolates were also characterized by ERY resistance phenotype and mechanisms and pulsed-field gel electrophoresis (PFGE). Multilocus sequence typing was performed on selected ERYr isolates. The predominant emm types in ERYr isolates were emm22 (n = 33, 26.0%), emm12 (n = 24, 18.9%), emm4 (n = 21, 16.5%), and emm106 (n = 15, 11.8%). In ERYs isolates, emm12 (n = 27, 21.9%), emm1 (n = 18, 14.1%), emm106 (n = 16, 12.5%), and emm11 (n = 9, 7.1%) predominated. The most common ERY resistance phenotype was the M phenotype (resistant to macrolides) (70.9%), with all but one isolate carrying mef(A), followed by the constitutive macrolide-lincosamide-streptogramin B resistance (cMLSB) phenotype (26.8%), with isolates carrying erm(B) or erm(TR). ERYr isolates of the emm12-sequence type 36 (ST36) lineage with the cMLSB phenotype were mostly present before 2004, while those of the emm22-ST46 lineage with the M phenotype predominated in later years. Recovery from respiratory (throat swab) specimens was an independent factor associated with ERY resistance. emm1 and emm11 GAS isolates were significantly associated with ERYs, while emm22 was detected only in ERYr GAS. In addition, emm106 isolates were prevalent among the abscess/pus isolates, whereas emm12 isolates were strongly associated with a respiratory (throat) origin. In addition to identifying factors associated with ERY resistance in GAS, our study provides helpful information on the changing GAS epidemiology in Taiwan.

Development of Daptomycin Nonsusceptibility with Heterogeneous Vancomycin-Intermediate Resistance and Oxacillin Susceptibility in Methicillin-Resistant Staphylococcus aureus during High-Dose Daptomycin Treatment

The use of daptomycin has increased in recent years, especially in patients with persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia following vancomycin treatment failure (10). We report a case of persistent MRSA bacteremia in a patient who received a dosage of daptomycin (12 mg/kg body weight/day) that was higher than that of the recommended standard therapy (6 mg/kg/day) (2, 10). The patient received 4 weeks of teicoplanin followed by 5 months of oral linezolid prior to daptomycin. In addition to daptomycin nonsusceptibility, the causative strain also developed heterogeneous and intermediate resistance to vancomycin, and an inverse or “seesaw” effect of daptomycin nonsusceptibility and oxacillin susceptibility was noted. A 59-year-old man with stage IV non-Hodgkins lymphoma was admitted for chemotherapy. Six days later, he developed catheter-associated septic phlebitis. Two sets of blood cultures (BCs) yielded MRSA (CGK1). Transesophageal ultrasound revealed no vegetation. Teicoplanin (800 mg/day) was initiated, and the patients fever subsided. However, the hip magnetic resonance image (MRI) indicated left sacroiliac joint septic arthritis, and repeat BCs yielded MRSA (CGK2) after 4 weeks of teicoplanin. The patient chose to receive therapy at home. After 3 months of oral linezolid (1,200 mg/day), fever and MRSA bacteremia (CGK3) reoccurred on the second day after linezolid was discontinued, but the fever subsided immediately after restarting linezolid. MRSA bacteremia (CGK4) reoccurred after another 2 months. After the patient was readmitted, linezolid was replaced by parenteral daptomycin (700 mg/day; 12 mg/kg), but fever developed 12 days later. Peripheral vein and Port-A-Cath BCs both yielded MRSA (CGK5). The Port-A-Cath was removed, but fever and MRSA bacteremia persisted (CGK6). Transesophageal echocardiography performed on hospital day 26 revealed no vegetation, but MRI indicated infective spondylitis of the thoracic spine that was associated with a progressive infectious process on the left hip joint. On hospital day 35, daptomycin was replaced by parenteral linezolid (1,200 mg/day) and cefpirome (2 g every 12 h) because of persistent fever and refractory MRSA bacteremia (CGK7). BCs obtained 3 days after linezolid and cefpirome were started still grew MRSA (CGK8). Profound septic shock occurred thereafter, and the patient died on hospital day 45. All 8 isolates had indistinguishable pulsed-field gel electrophoresis patterns (data not shown) and shared the same genetic profile (sequence type 59 [ST59], staphylococcal cassette chromosome mec type IV [SCCmec IV], pvl negative, agr group I), indicating that the persistent bacteremia was due to the same strain of MRSA or its progeny. The MICs of daptomycin increased from ≤0.75 μg/ml in CGK1 through CGK5 to 4 μg/ml in CGK6 through CGK8. Concurrent with the increase in daptomycin MICs, oxacillin MICs decreased from 32 to >256 μg/ml to 1 to 3 μg/ml (Table ​(Table1).1). Vancomycin nonsusceptibility also developed in CGK7, with a MIC of 3 μg/ml, which fit the vancomycin-intermediate S. aureus (VISA) category (4). Population analysis profiles showed a distinct increased population of CGK6 through CGK8 able to grow at daptomycin concentrations of ≥2 μg/ml (Fig. ​(Fig.11 A), and only CGK7 met the heterogeneous VISA (hVISA) criteria (Fig. ​(Fig.1B)1B) (17). Sequencing of the mprF gene for all 8 isolates revealed an L431F amino acid substitution in CGK6 through CGK8, but no mutation was found in the sites (S295, P314, T345, I420) previously reported in other daptomycin-nonsusceptible strains (6-9, 11, 18). FIG. 1. Population analysis profiles (PAP) of daptomycin (A) and vancomycin (B) on 6 of 8 sequential methicillin-resistant Staphylococcus aureus (MRSA) isolates from a fatal, persistent bacteremia case. CGK1, CGK3, and CGK5 isolates were daptomycin susceptible, ... TABLE 1. MICs of daptomycin, linezolid, oxacillin, teicoplanin, and vancomycin for 8 MRSA isolates from a fatal, persistent bacteremia case prior to, during, and after high-dose daptomycin therapy Much remains to be elucidated on the mechanisms involved in daptomycin and associated vancomycin nonsusceptibility (1-3, 5-9, 12, 14, 18) and the inversed oxacillin susceptibility (13, 15, 16). Previous reports have emphasized the importance of draining infection foci for successful treatment outcomes (2, 10), but surgical intervention was not possible in our patient due to coagulopathy secondary to his non-Hodgkins lymphoma. The causative strain, with initial vancomycin MICs (2 μg/ml) at the upper susceptible limit, and priming by glycopeptide exposure (in this case, teicoplanin) likely contributed to the development of daptomycin and vancomycin nonsusceptibility (2, 10). Until practical laboratory methods for timely detection of strains with heteroresistance or attenuated susceptibility are developed, close monitoring for the emergence of daptomycin nonsusceptibility during treatment is needed.

Genomic diversity of citrate fermentation in Klebsiella pneumoniae

BackgroundIt has long been recognized that Klebsiella pneumoniae can grow anaerobically on citrate. Genes responsible for citrate fermentation of K. pneumoniae were known to be located in a 13-kb gene cluster on the chromosome. By whole genome comparison of the available K. pneumoniae sequences (MGH 78578, 342, and NTUH-K2044), however, we discovered that the fermentation gene cluster was present in MGH 78578 and 342, but absent in NTUH-K2044. In the present study, the previously unknown genome diversity of citrate fermentation among K. pneumoniae clinical isolates was investigated.ResultsUsing a genomic microarray containing probe sequences from multiple K. pneumoniae strains, we investigated genetic diversity among K. pneumoniae clinical isolates and found that a genomic region containing the citrate fermentation genes was not universally present in all strains. We confirmed by PCR analysis that the gene cluster was detectable in about half of the strains tested. To demonstrate the metabolic function of the genomic region, anaerobic growth of K. pneumoniae in artificial urine medium (AUM) was examined for ten strains with different clinical histories and genomic backgrounds, and the citrate fermentation potential was found correlated with the genomic region. PCR detection of the genomic region yielded high positive rates among a variety of clinical isolates collected from urine, blood, wound infection, and pneumonia. Conserved genetic organizations in the vicinity of the citrate fermentation gene clusters among K. pneumoniae, Salmonella enterica, and Escherichia coli suggest that the13-kb genomic region were not independently acquired.ConclusionNot all, but nearly half of the K. pneumoniae clinical isolates carry the genes responsible for anaerobic growth on citrate. Genomic variation of citrate fermentation genes in K. pneumoniae may contribute to metabolic diversity and adaptation to variable nutrient conditions in different environments.

Complete Genome Sequence of Staphylococcus aureus Z172, a Vancomycin-Intermediate and Daptomycin-Nonsusceptible Methicillin-Resistant Strain Isolated in Taiwan

ABSTRACT We report the complete genome sequence of Z172, a representative strain of sequence type 239-staphylococcal cassette chromosome mec type III (ST239-SCCmec type III) hospital-associated methicillin-resistant Staphylococcus aureus in Taiwan. Strain Z172 also exhibits a vancomycin-intermediate and daptomycin-nonsusceptible phenotype.