Influence of PhoPQ and PmrAB two component system alternations on colistin resistance from non-mcr colistin resistant clinical E. Coli strains

BACKGROUND

The current understanding of acquired chromosomal colistin resistance mechanisms in Enterobacterales primarily involves the disruption of the upstream PmrAB and PhoPQ two-component system (TCS) control caused by mutations in the regulatory genes. Interestingly, previous studies have yielded conflicting results regarding the interaction of regulatory genes related to colistin resistance in Escherichia coli, specifically those surrounding PhoPQ and PmrAB TCS.

RESULTS

In our study, we focused on two clinical non-mcr colistin-resistant strains of E. coli, TSAREC02 and TSAREC03, to gain a better understanding of their resistance mechanisms. Upon analysis, we discovered that TSAREC02 had a deletion (Δ27-45) in MgrB, as well as substitutions (G206R, Y222H) in PmrB. On the other hand, TSAREC03 exhibited a long deletion (Δ84-224) in PhoP, along with substitutions (M1I, L14P, P178S, T235N) in PmrB. We employed recombinant DNA techniques to explore the interaction between the PhoPQ and PmrAB two-component systems (TCSs) and examine the impact of the mutated phoPQ and pmrB genes on the minimum inhibitory concentrations (MICs) of colistin. We observed significant changes in the expression of the pmrD gene, which encodes a connector protein regulated by the PhoPQ TCS, in the TSAREC02 wild-type (WT)-mgrB replacement mutant and the TSAREC03 WT-phoP replacement mutant, compared to their respective parental strains. However, the expressions of pmrB/pmrA, which reflect PmrAB TCS activity, and the colistin MICs remained unchanged. In contrast, the colistin MICs and pmrB/pmrA expression levels were significantly reduced in the pmrB deletion mutants from both TSAREC02 and TSAREC03, compared to their parental strains. Moreover, we were able to restore colistin resistance and the expressions of pmrB/pmrA by transforming a plasmid containing the parental mutated pmrB back into the TSAREC02 and TSAREC03 mutants, respectively.

CONCLUSION

While additional data from clinical E. coli isolates are necessary to validate whether our findings could be broadly applied to the E. coli population, our study illuminates distinct regulatory pathway interactions involving colistin resistance in E. coli compared to other species of Enterobacterales. The added information provided by our study contribute to a deeper understanding of the complex pathway interactions within Enterobacterales.

Molecular drivers of resistance to sulbactam-durlobactam in contemporary clinical isolates of Acinetobacter baumannii

Acinetobacter baumannii-calcoaceticus complex (ABC) causes severe infections that are difficult to treat due to pre-existing antibiotic resistance. Sulbactam-durlobactam (SUL-DUR) is a targeted β-lactam/β-lactamase inhibitor combination antibiotic designed to treat serious infections caused by Acinetobacter, including multidrug- and carbapenem-resistant strains. In a recent global surveillance study of 5,032 ABC clinical isolates collected from 2016 to 2021, less than 2% of ABC isolates had SUL-DUR MIC values >4 µg/mL. Molecular characterization of these isolates confirmed the primary drivers of resistance are metallo-β-lactamases or penicillin-binding protein 3 (PBP3) mutations, as previously described. In addition, this study shows that certain common PBP3 variants, such as A515V, are insufficient to confer sulbactam resistance and that the efflux of durlobactam by AdeIJK is likely to play a role in a subset of strains.

A 20-Year Study of Capsular Polysaccharide Seroepidemiology, Susceptibility Profiles, and Virulence Determinants of Klebsiella pneumoniae from Bacteremia Patients in Taiwan

In this study, we selected bacteremic Klebsiella pneumoniae isolates from the Taiwan Surveillance of Antimicrobial Resistance program. A total of 521 isolates were collected over a period of 2 decades, including 121 from 1998, 197 from 2008, and 203 from 2018. Seroepidemiology showed that the top five capsular polysaccharide types were serotypes K1, K2, K20, K54, and K62, constituting 48.5% of the total isolates, and the respective ratios at each time point have remained similar over the past 2 decades. The antibacterial susceptibility tests showed that K1, K2, K20, and K54 were susceptible to most antibiotics, while K62 was relatively resistant compared to other typeable and nontypeable strains. In addition, six virulence-associated genes, clbA, entB, iroN, rmpA, iutA, and iucA, were predominant in K1 and K2 isolates of K. pneumoniae. In conclusion, serotypes K1, K2, K20, K54, and K62 of K. pneumoniae are the most prevalent serotypes and carry more virulence determinants in bacteremia patients, which may indicate their invasiveness. If further serotype-specific vaccine development is performed, these five serotypes should be included. Since the antibiotic susceptibility profiles were stable over a long duration, empirical treatment may be predicted according to serotype if rapid diagnosis from direct clinical specimens is available, such as PCR or antigen serotyping for serotype K1 and K2. IMPORTANCE This is the first nationwide study to examine the seroepidemiology of Klebsiella pneumoniae using blood culture isolates collected over a period of 20 years. The study found that the prevalence of serotypes remained consistent over the 20-year period, with high-prevalence serotypes associated with invasive types. Nontypeable isolates had fewer virulence determinants than other serotypes. With the exception of serotype K62, the other high-prevalence serotypes were highly susceptible to antibiotics. If rapid diagnosis using direct clinical specimens, such as PCR or antigen serotyping, is available, empirical treatment can be predicted based on serotype, particularly for K1 and K2. The results of this seroepidemiology study could also help the development of future capsule polysaccharide vaccines.

Appropriate antibiotic therapy is a predictor of outcome in patients with Stenotrophomonas maltophilia blood stream infection in the intensive care unit

BACKGROUND/PURPOSE

The study was to assess the relationship between antibiotic therapy and the outcome in intensive care unit (ICU) patients with Stenotrophomonas maltophilia bloodstream infection (BSI).

METHODS

ICU patients with monomicrobial S. maltophilia BSI from January 2004 to December 2019 were included and divided into two groups-those with- and without appropriate antibiotic therapy after BSI-for comparison. The primary outcome was the relationship between appropriate antibiotic therapy and 14-day mortality. The secondary outcome was the influence of different antibiotic therapies: levofloxacin- and trimethoprim-sulfamethoxazole (TMP/SMX)-containing regimens, on 14-day mortality.

RESULTS

A total of 214 ICU patients were included. Patients received appropriate antibiotic therapy (n = 133) after BSI had a lower 14-day mortality than those (n = 81) without appropriate antibiotic therapy (10.5% vs. 46.9%, p < 0.001). No difference on 14-day mortality between groups of patients by time of appropriate antibiotic therapy was observed (p > 0.05). After a propensity score matching, the results is consistent that 14-day mortality were lower in patients with appropriate antibiotic therapy than those without appropriate antibiotic therapy (11.5% vs. 39.3%, p < 0.001). Among patients with S. maltophilia BSI receiving appropriate antibiotic therapy, there was a trend levofloxacin-containing regimens is associated with lower mortality than TMP/SMX-containing regimens (HR 0.233, 95% CI 0.050-1.084, p = 0.063).

CONCLUSION

Appropriate antibiotic therapy was associated with decreased 14-day mortality in ICU patients with S. maltophilia BSI regardless of time. Levofloxacin-containing regimens may be better choice than TMP/SMX -containing regimens in treating ICU patients with S. maltophilia BSI.

Placental mesenchymal stem cells boost M2 alveolar over M1 bone marrow macrophages via IL-1β in Klebsiella-mediated acute respiratory distress syndrome

RATIONALE

Acute respiratory distress syndrome (ARDS) is a lethal complication of severe bacterial pneumonia due to the inability to dampen overexuberant immune responses without compromising pathogen clearance. Both of these processes involve tissue-resident and bone marrow (BM)-recruited macrophage (MΦ) populations which can be polarised to have divergent functions. Surprisingly, despite the known immunomodulatory properties of mesenchymal stem cells (MSCs), simultaneous interactions with tissue-resident and recruited BMMΦ populations are largely unexplored.

OBJECTIVES

We assessed the therapeutic use of human placental MSCs (PMSCs) in severe bacterial pneumonia with elucidation of the roles of resident alveolar MΦs (AMΦs) and BMMΦs.

METHODS

We developed a lethal, murine pneumonia model using intratracheal infection of a clinically relevant Klebsiella pneumoniae (KP) strain with subsequent intravenous human PMSC treatment. Pulmonary AMΦ and recruited BMMΦ analyses, histological evaluation, bacterial clearance and mice survival were assessed. To elucidate the role of resident AMΦs in improving outcome, we performed AMΦ depletion in the KP-pneumonia model with intratracheal clodronate pretreatment.

MEASUREMENTS AND MAIN RESULTS

Human PMSC treatment decreased tissue injury and improved survival of severe KP-pneumonia mice by decreasing the presence and function of recruited M1 BMMΦ while preserving M2 AMΦs and enhancing their antibacterial functions. Interestingly, PMSC therapy failed to rescue AMΦ-depleted mice with KP pneumonia, and PMSC-secreted IL-1β was identified as critical in increasing AMΦ antibacterial activities to significantly improve pathogen clearance-especially bacteraemia-and survival.

CONCLUSIONS

Human PMSC treatment preferentially rescued resident M2 AMΦs over recruited M1 BMMΦs with overall M2 polarisation to improve KP-related ARDS survival.

Protocol for human placental mesenchymal stem cell therapy in a murine model of intra-abdominal infection of hypervirulent Klebsiella

Hypervirulent Klebsiella pneumoniae (hvKP) strains cause extra-pulmonary infections such as intra-abdominal infection (IAI) even in healthy individuals due to its resistance to polymorphonuclear neutrophil (PMN) killing and a high incidence of multidrug resistance. To assess whether human placental mesenchymal stem cell (PMSC) therapy can be an effective treatment option, we established a murine model of hvKP-IAI to evaluate immune cell modulation and bacterial clearance for this highly lethal infection. This protocol can rapidly assess potential therapies for severe bacterial IAIs.

For complete details on the use and execution of this protocol, please refer to Wang et al. (2020).

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PMSC treatment in a mouse model of hvKP-induced intra-abdominal infection

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Isolation of mouse peritoneal immune cells without affixing mice to a dissecting board

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Analysis of PMN, T, and NK cells in peritoneal washings

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Determination of bacterial CFUs in hvKP-infected peritoneal fluid

Does Antimicrobial Therapy Affect Mortality of Patients with Carbapenem-Resistant Klebsiella pneumoniae Bacteriuria? A Nationwide Multicenter Study in Taiwan

Few clinical studies have previously discussed patients with carbapenem-resistant Klebsiella pneumoniae (CRKP) bacteriuria. This study aimed to assess the effect of antimicrobial therapy on the mortality of patients with CRKP bacteriuria. Hospitalized adults with CRKP bacteriuria were enrolled retrospectively from 16 hospitals in Taiwan during 2013 and 2014. Critically ill patients were defined as those with an Acute Physiology and Chronic Health Evaluation (APACHE) II score ≥ 20. Multivariate Cox regression analysis was used to determine independent risk factors for 14- and 28-day mortality. Of 107 patients with CRKP bacteriuria, the 14-day and 28-day mortality was 14.0% and 25.2%, respectively. Thirty-three patients received appropriate antimicrobial therapy. In the multivariate Cox regression analysis, the APACHE II score ≥ 20 was the only independent risk factor for 14-day mortality (hazard ratio [HR]: 6.15, p = 0.024). APACHE II score ≥ 20 (HR: 3.05, p = 0.018) and male sex (HR: 2.57, p = 0.037) were associated with 28-day mortality. Among critically ill patients with CRKP bacteriuria, appropriate antimicrobial therapy was not associated with 14-day or 28-day survival. In conclusion, in patients with CRKP bacteriuria, the use of appropriate antimicrobial therapy was not an independent factor associated with reduced mortality. Our findings may inform future antibiotic stewardship interventions for bacteriuria caused by multidrug resistant pathogens.

Human Placental MSC-Secreted IL-1β Enhances Neutrophil Bactericidal Functions during Hypervirulent Klebsiella Infection

Hypervirulent Klebsiella pneumoniae (hvKP) causes severe infections even in healthy individuals by escaping surveillance and killing from polymorphonuclear neutrophils (PMNs), the first-line leukocytes in bacterial infections; moreover, the emergence of multidrug-resistant strains further limits treatment options. We therefore assess whether multilineage mesenchymal stem cells (MSCs), best known for immunomodulation toward T cells, could be therapeutic for highly virulent bacterial infections via modulation of PMNs. We find that both bone marrow MSCs and placental MSCs (PMSCs) preserve in vitro PMN survival, but only PMSCs significantly enhance multiple PMN bactericidal functions, including phagocytosis, through secretion of interleukin-1β (IL-1β). PMSC treatment of hvKP-infected mice suppresses T and natural killer (NK) cell responses as expected but can preferentially recruit PMNs and enhance antibacterial functions to allow for disease survival; IL-1β knockdown in PMSCs significantly decreases hvKP clearance, worsening survival and resulting in 100% lethality. Our data strongly implicate the possible use of PMSCs for infections of PMN-resistant hvKP strains.

Effects of different resistance mechanisms on antimicrobial resistance in Acinetobacter baumannii: a strategic system for screening and activity testing of new antibiotics

A total of 50 engineered strains with various antimicrobial resistance mechanisms were constructed by in-frame deletion, site-directed mutagenesis and plasmid transformation from two fully-susceptible strains (Acinetobacter baumannii KAB1544 and ATCC 17978), including 31 strains with chromosomally-mediated resistance and 19 with plasmid-mediated resistance. Each of the 50 resistance mechanisms showed similar effects on the minimum inhibitory concentrations (MICs) of KAB1544 and ATCC 17978. Compared with the parental strains, the engineered strains related to some efflux pumps showed a significant (≥4-fold) difference in the MICs of β-lactams, quinolones, aminoglycosides, tetracyclines, folate pathway inhibitors and/or phenicols, whereas no significant effects on the MICs were found for the engineered strains lacking OmpA, CarO, Omp25, Omp33, OmpW or OprD. Mechanisms due to GyrA/ParC mutations, β-lactamases, aminoglycoside-modifying enzymes, 16S rRNA methylases and tet resistance genes contributed their corresponding resistance, as previously published. In conclusion, strains constructed in this study have clear resistance mechanisms and can be used to screen and assess compounds against specific resistance mechanisms for treating Acinetobacter. In addition to our previously published system for Enterobacteriaceae, the combination of these two systems could increase the coverage of bacterial types for drug assessment and facilitate the selection process of new candidates in drug development against drug-resistant superbugs.

Resistance mechanisms and molecular epidemiology of carbapenem-nonsusceptible Escherichia coli in Taiwan, 2012-2015

Purpose

This study aimed to investigate the resistance mechanisms and molecular epidemiology of carbapenem-nonsusceptible Escherichia coli (CnsEC) in Taiwan.

Patients and methods

From 2012 to 2015, 237 E. coli isolates with minimum inhibitory concentrations of imipenem or meropenem >1 μg/mL were collected in a nationwide surveillance and subjected to polymerase chain reaction (PCR) for carbapenemase, AmpC-type β-lactamase, and extended spectrum β-lactamase (ESBL) genes. We evaluated outer membrane proteins (OmpF and OmpC) loss and conducted multilocus sequence typing and pulsed-field gel electrophoresis (PFGE). Isolates that were resistant to all carbapenems were designated as pan-carbapenem-resistant E. coli (pCREC) in this study.

Results

The predominant resistance mechanism of CnsEC in Taiwan was the CMY-2 β-lactamase in combination with OmpF and OmpC loss. Sequence type 131 was the most prevalent type (29.2%). Among 237 CnsEC isolates, 106 (44.7%) isolates were pCREC and 18 (7.59%) produced carbapenemase. The prevalence of carbapenemases increased from 6% in 2012 to 11.36% in 2015. Various carbapenemases including KPC-2, IMP-8, NDM-1, NDM-5, VIM-1, OXA-48, and OXA-181 were identified, with NDM-1 being the most common (38.9%) carbapenemase. Comparison between pCREC and non-pCREC among the non-carbapenemase-producing CnsEC isolates revealed SHV, CMY, co-carriage of SHV and CTX-M and concurrent loss of both OmpF and OmpC were more commonly detected in the pCREC group. PFGE revealed no nationwide clonal spread of carbapenemase-producing E. coli.

Conclusion

NDM-1 was the most common carbapenemase and combination of CMY-2 and concurrent OmpF and OmpC porin loss was the most prevalent resistance mechanism in CnsEC in Taiwan.

Appropriate Treatment for Bloodstream Infections Due to Carbapenem-Resistant Klebsiella pneumoniae and Escherichia coli: A Nationwide Multicenter Study in Taiwan

Background

In a multicenter study from Taiwan, we aimed to investigate the outcome of patients who received different antimicrobial therapy in carbapenem-resistant Enterobacteriaceae bloodstream infections and proposed a new definition for tigecycline use.

Methods

Patients from 16 hospitals in Taiwan who received appropriate therapy for bloodstream infections due to carbapenem-resistant Klebsiella pneumoniae and Escherichia coli were enrolled in the study between January 2012 and June 2015. We used a cox proportional regression model for multivariate analysis to identify independent risk factors of 14-day mortality. Tigecycline was defined as appropriate when the isolates had a minimum inhibitory concentration (MIC) ≤0.5 mg/L, and we investigated whether tigecycline was associated with mortality among patients with monotherapy.

Results

Sixty-four cases with carbapenem-resistant K pneumoniae (n = 50) and E coli (n = 14) bloodstream infections were analyzed. Of the 64 isolates, 17 (26.6%) had genes that encoded carbapenemases. The 14-day mortality of these cases was 31.3%. In the multivariate analysis, Charlson Comorbidity Index (hazard ratio [HR], 1.21; 95% confidence interval [CI], 1.03–1.42; P = .022) and colistin monotherapy (HR, 5.57; 95% CI, 2.13–14.61; P < .001) were independently associated with 14-day mortality. Among the 55 patients with monotherapy, the 14-day mortality was 30.9% (n = 17). Tigecycline use was not associated with mortality in the multivariate analysis.

Conclusions

Tigecycline monotherapy was a choice if the strains exhibited MIC ≤0.5 mg/L, and colistin monotherapy was not suitable. Our findings can initiate additional clinical studies regarding the efficacy of tigecycline in carbapenem-resistant Enterobacteriaceae infections.

Klebsiella pneumoniae disassembles host microtubules in lung epithelial cells

Klebsiella pneumoniae raises significant concerns to the health care industry as these microbes are the source of widespread contamination of medical equipment, cause pneumonia as well as other multiorgan metastatic infections and have gained multidrug resistance. Despite soaring mortality rates, the host cell alterations occurring during these infections remain poorly understood. Here, we show that during in vitro and in vivo K. pneumoniae infections of lung epithelia, microtubules are severed and then eliminated. This destruction does not require direct association of K. pneumoniae with the host cells, as microtubules are disassembled in cells that are distant from the infecting bacteria. This microtubule dismantling is dependent on the K. pneumoniae (Kp) gene ytfL as non-pathogenic Escherichia coli expressing Kp ytfL disassemble microtubules in the absence of K. pneumoniae itself. Our data points to the host katanin catalytic subunit A like 1 protein (KATNAL1) and the katanin regulatory subunit B1 protein (KATNB1) as the gatekeepers to the microtubule severing event as both proteins localise specifically to microtubule cut sites. Infected cells that had either of these proteins knocked out maintained intact microtubules. Taken together, we have identified a novel mechanism that a bacterial pathogen has exploited to cause microtubule destruction within the host epithelia.

Effects of different resistance mechanisms on susceptibility to different classes of antibiotics in Klebsiella pneumoniae strains: a strategic system for the screening and activity testing of new antibiotics

Objectives

A strategic system for the screening and testing of new antibiotics was created to facilitate the development of antibiotics that are robustly effective against MDR bacteria.

Methods

In-frame deletion, site-directed mutagenesis and plasmid transformation were used to generate genetically engineered strains with various resistance mechanisms from a fully susceptible clinical isolate of Klebsiella pneumoniae. Antimicrobial susceptibility testing and a mouse infection model were used to test antibiotics against these strains in vitro and in vivo, respectively.

Results

A total of 193 strains, including 29 strains with chromosome-mediated resistance, 33 strains with plasmid-mediated resistance and 131 strains with a combination of both resistance mechanisms were constructed; these strains covered resistance to β-lactams, quinolones, aminoglycosides, tetracyclines, folate pathway inhibitors and other antibiotics. MICs for all strains were tested, and the effects of genetic modifications on increasing the MICs were assessed. Ceftazidime and cefotaxime were used to assess the correlation between antibacterial activities in vitro and in vivo. Against a K. pneumoniae strain with blaOXA-48, ceftazidime had a lower MIC (0.5 mg/L) than cefotaxime (2 mg/L). Ceftazidime had an ED50 of 30 mg/kg, and no mice survived treatment with the same dose of cefotaxime. A positive correlation was observed between these in vitro and in vivo results.

Conclusions

The system developed here could reduce the considerable time required to evaluate the effectiveness of new antibiotics against MDR bacteria, particularly in the early stages of drug development. This system could also be expanded as new resistance mechanisms emerge.

Treatment outcome of non-carbapenemase-producing carbapenem-resistant Klebsiella pneumoniae infections: a multicenter study in Taiwan

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are associated with high mortality, and experiences with its treatment are usually based on carbapenemase-producing strains. Non-carbapenemase-producing CRKP is of clinical significance, but relevant studies are lacking. This nationwide study aimed to evaluate the outcome of antimicrobial therapy in patients with non-carbapenemase-producing CRKP infections. Patients with non-carbapenemase-producing CRKP infections were enrolled from 16 hospitals during January 2013 to December 2014 in Taiwan. Carbapenem resistance was defined as reduced susceptibility with a minimum inhibitory concentration of ≥2 mg/L for imipenem or meropenem. The resistance mechanisms of CRKP isolates were analyzed, and the clinical data of these patients were collected retrospectively. Independent risk factors of 14-day morality were determined by Cox regression analysis. A total of 99 patients with non-carbapenemase-producing CRKP infections were enrolled, and 14-day mortality was 27.3%. Among 67 patients treated with appropriate antimicrobial therapy, most (n = 61) patients received monotherapy. The 14-day mortality was lower in patients treated with appropriate monotherapy (21.3%) than in those with inappropriate therapy (37.5%). The multivariate regression model identified monotherapy (hazard ratio [HR], 0.30; 95% confidence interval [CI], 0.13-0.71; P = 0.005) as protective factor, and APACHE II scores (HR, 1.09; 95% CI, 1.01-1.18; P = 0.022) as risk factor associated with 14-day mortality. Tigecycline, colistin, and carbapenem were the most commonly used drugs in monotherapy. This study provides evidence supporting the efficacy of monotherapy in the treatment of non-carbapenemase-producing CRKP infections, and provides a future target for antibiotics stewardship for CRKP infection.

Outbreak of imipenem-resistant Acinetobacter baumannii in different wards at a regional hospital related to untrained bedside caregivers

BACKGROUND

This study describes an outbreak caused by imipenem-resistant Acinetobacter baumannii (IRAB) involving 2 general wards at the Penghu branch of Tri-Service General Hospital.

METHODS

Clinical data obtained from the patients with IRAB during an outbreak from May 2014-October 2014 were reviewed. Microbiologic sampling from the environment and the hands of health care workers (HCWs) was performed. Clinical isolates from case patients were genotyped using pulsed-field gel electrophoresis (PFGE).

RESULTS

During the outbreak period, 12 patients were colonized or infected with IRAB. The hospital room environments of the case patients were contaminated with IRAB. Hands of nurses and physicians were not colonized with IRAB, but the hands of 2 bedside caregivers of case patients were colonized with IRAB. The PFGE analysis revealed that at least 2 major genetically distinct strains disseminated between 2 different wards. After implementation of infection control measures with a cohort of nursing patients, hand hygiene education for caregivers who had not received instructions before the outbreak, and a critical value alert system to notify case patients, the outbreak was controlled successfully.

CONCLUSIONS

This outbreak study highlights the importance of adherence to hand hygiene by all HCWs to prevent the dissemination of multidrug-resistant organisms.

The plasmid-mediated fosfomycin resistance determinants and synergy of fosfomycin and meropenem in carbapenem-resistant Klebsiella pneumoniae isolates in Taiwan

BACKGROUND

Epidemiology of fosfomycin susceptibility and the plasmid-mediated fosfomycinase genes of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates in Taiwan remain unclear.

METHODS

642 CRKP clinical isolates were collected from a nation-wide surveillance study (16 hospitals) in Taiwan in 2012-2013. Antimicrobial susceptibilities were determined. PFGE and MLST determined the clonal relatedness. Carbapenemases and fosfomycinases genes were detected by PCR, and their flanking regions were determined by PCR and sequencing. Synergistic activity of meropenem with fosfomycin was examined by the checkerboard method.

RESULTS

In total, 36.4% (234/642) of CRKP isolates in Taiwan were resistant to fosfomycin. Among 234 fosfomycin-resistant CRKP isolates, PFGE analysis revealed 81 pulsotypes. Pulsotype XXIII (n = 63) was predominant and belonged to ST11. 71 had carbapnemases (65 bla_KPC-2-positive, 1 bla_VIM-1-positive and 5 bla_IMP-8-positive) and 62 had fosfomycinases (35 fosA3-positive and 27 foskp96-positive). Only 18.5% (5/27) of foskp96-positive isolates carried foskp96 and bla_KPC-2, while 71.4% (25/35) of fosA3-positive isolates contained fosA3 and bla_KPC-2. There were five types of flanking sequences for fosA3, and 85.7% (30/35) of fosA3 genes were flanked by IS26, suggesting possible horizontal gene transfer. Synergistic effect of fosfomycin and meropenem was observed in all 25 randomly selected pulsotype XXIII strains (100%; 25/25), even those containing fosfomycinase (48%, 12/25) or carbapnemase (96%, 24/25).

CONCLUSIONS

A clone (pulsotype XXIII, ST11) has been found to be prevailing among fosfomycin-resistant CRKP in Taiwan. According to the in vitro data, the combination of fosfomycin and meropenem is a potentially alternative choice.

Tigecycline resistance among carbapenem-resistant Klebsiella Pneumoniae: Clinical characteristics and expression levels of efflux pump genes

Objectives

Tigecycline is a treatment option for infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). Emerging tigecycline resistance in CRKP represents a growing threat. Knowledge of the clinical, microbiological, and molecular characteristics of tigecycline- and carbapenem-resistant Klebsiella pneumoniae (TCRKP) is limited.

Methods

Patients infected with TCRKP were identified from a Taiwanese national surveillance study. Clinical data were collected from medical records. We performed susceptibility tests, carbapenemase gene detection, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Furthermore, we performed quantitative real-time polymerase chain reaction (qRT-PCR) analyses to assess the expression levels of the efflux pump genes acrB and oqxB.

Results

We identified 16 patients infected with TCRKP, with urinary tract infection (UTI) being the most common type of infection (63%). The all-cause 30-day mortality rate was 44% in patients with TCRKP infection. Patients with a site of infection other than the urinary tract had a significantly higher mortality rate than patients with UTIs (83% vs. 20%, p = 0.035). PFGE and MLST revealed no dominant clone or sequence type. Using qRT-PCR, overexpression of both the acrB and oqxB genes was identified in seven isolates, and overexpression of the oqxB gene was observed in another seven. There was poor correlation between acrB or oqxB expression and tigecycline MICs (r = -0.038 and -0.166, respectively).

Conclusions

The mortality rate in patients infected with TCRKP in this study was 44% and this is an important subset of patients. The absence of a linear relationship between efflux pump genes expression and MICs indicates that tigecycline resistance may be mediated by other factors. Continuous monitoring of tigecycline resistance among CRKP isolates and resistance mechanisms are necessary.

High minimum inhibitory concentration of imipenem as a predictor of fatal outcome in patients with carbapenem non-susceptible Klebsiella pneumoniae

Carbapenem resistance in Klebsiella pneumoniae is important because of its increasing prevalence and limited therapeutic options. To investigate the clinical and microbiological characteristics of patients infected or colonized with carbapenem non-susceptible K. pneumoniae (CnsKP) in Taiwan, we conducted a retrospective study at Taipei Veterans General Hospital from January 2012 to November 2013. Carbapenem non-susceptibility was defined as a minimum inhibitory concentration (MIC) of ≥2 mg/L for imipenem or meropenem. A total of 105 cases with CnsKP were identified: 49 patients with infection and 56 patients with colonization. Thirty-one isolates had genes that encoded carbapenemases (29.5%), including K. pneumoniae carbapenemase (KPC)-2 (n = 27), KPC-3 (n = 1), VIM-1 (n = 1) and IMP-8 (n = 2). The in-hospital mortality among patients with CnsKP was 43.8%. A MIC for imipenem ≥16 μg/mL, nasogastric intubation and Acute Physiology and Chronic Health Evaluation II score were independent risk factors for in-hospital mortality for all patients with CnsKP. A MIC for imipenem ≥16 μg/mL was also an independent risk factor for 14-day mortality in patients with CnsKP. In conclusion, a positive culture for CnsKP was associated with high in-hospital mortality. A high imipenem MIC of CnsKP can predispose a patient to a poor prognosis.

Effect in virulence of switching conserved homologous capsular polysaccharide genes from Klebsiella pneumoniae serotype K1 into K20

The capsular polysaccharides in different serotypes of Klebsiella pneumoniae (KP) coded by the (CPS) gene cluster are characterized by a conserved and a hyper-variable region. We performed a virulence study by switching genes in the highly conserved region of the CPS cluster between strains. Six genes in the CPS conserved region in serotype K20, including galF, acidPPc, wzi, wza, wzb and wzc, were knocked out and replaced by the homologous genes from serotype K1. Compared to the parental K20 strain, the mutants showed a decline in lethality (LD₅₀) in mice from 10-fold to > 10⁵-fold and were categorized in terms of the effect on virulence as low (L) for galF and acidPPC, moderate (M) for wzi, and high (H) for wza, wzb and wzc. Although substituting the acidPPC gene from K1 for acidPPC in the K20 strain fully restored virulence, substitution with the wzi, wza, wzb or wzc homologs from K1 did not. The restoration with wzi from K1 led to a partial restoration of virulence, with the LD₅₀ in mice changing from 10⁴ to 10³ CFU_. For the wza, wzb and wzc genes, Complementation of K20 wza, wzb and wzc from K1 resulted in varied degrees of lethality in mice. Variable improvement in serum killing and phagocytosis was observed when the knockout mutants were compared with the gene-switched strains. In conclusion, homologous genes for capsule synthesis failed to exhibit the same functionality when switched between serotypes and virulence was decreased in different degree in according to the genes' homology.

Characterization of Extended-Spectrum β-Lactamase-Carrying Plasmids in Clinical Isolates of Klebsiella pneumoniae from Taiwan

We analyzed the replicon types, sizes, and restriction fragment length polymorphism (RFLP) typing of plasmids carrying extended-spectrum β-lactamase (ESBL) genes in Klebsiella pneumoniae isolates from Taiwan. Fifty-one Escherichia coli transconjugant strains with plasmids from ESBL-producing K. pneumoniae from the Taiwan Surveillance of Antimicrobial Resistance III Program in 2002 were included. All the 51 plasmids carried a bla_CTX-M gene, the majority of which were bla_CTX-M-3 (28/51 [54.9%]). Plasmids ranged in size from 126 to 241 kb by S1 nuclease digestion and subsequent pulsed-field gel electrophoresis, and the most common plasmid size (37.3%) was 161-170 kb. The most common replicon type of plasmids was incompatibility group (Inc)A/C (60.8%). The IncA/C plasmids all carried bla_CTX-M (bla_{CTX-M-3, -14, -15}), and some also carried bla_SHV (bla_{SHV-5, -12}) genes. All 51 plasmids could be typed with PstI, and 27 (52.9%) belonged to 10 clusters. Thirty-eight of the 51 plasmids were typable with BamHI, and 21 plasmids (55.3%) fell into 7 clusters. Plasmids in the same cluster belonged to the same incompatibility group, with the exception of cluster C6. In conclusion, IncA/C plasmids are the main plasmid type responsible for the dissemination of ESBL genes of K. pneumoniae from Taiwan. RFLP with PstI possessed better discriminatory power than that with BamHI and PCR-based replicon typing for ESBL-carrying plasmids in K. pneumoniae in this study. Greater than 50% of plasmids fell into clusters, and >60% of cluster-classified plasmids were present in clonally unrelated isolates, indicating that horizontal transfer of plasmids plays an important role in the spread of ESBL genes.

Influence of ethanol concentration in the phagocytic function of neutrophils against Klebsiella pneumoniae isolates in an experimental model

BACKGROUND/PURPOSE

Although the prevalence of pneumonia or other extrapulmonary infections is higher in people with alcoholism or acute alcohol intoxication, the possible relationship of acute alcohol intoxication to phagocytic function has not been investigated. Our aim was to determine whether acute alcohol intoxication suppresses phagocytic function in human neutrophils.

METHODS

Twenty healthy individuals were enrolled for isolating neutrophils to evaluate the neutrophil phagocytic function at different alcohol concentrations. Klebsiella pneumoniae was isolated from clinical specimens of liver abscesses. The rate of K. pneumonia phagocytosis (K2 and non-K1/K2 isolates) by neutrophils was determined using flow cytometry and compared among the nine groups with different alcohol concentrations.

RESULTS

The rate of phagocytic uptake decreased significantly with increasing alcohol concentration in both the K2 and non-K1/K2 K. pneumonia groups (r = -0.866, p = 0.03 vs. r = -0.975, p < 0.001). Moreover, the percentage of K. pneumoniae ingested by neutrophils decreased with age.

CONCLUSION

The ability of neutrophils to phagocytose virulent K2 K. pneumoniae was suppressed by ethanol at high concentrations. This finding may account for the higher prevalence of pneumonia or other extrapulmonary infection in people with acute alcohol intoxication.

Emergence of OXA-48-Producing Klebsiella pneumoniae in Taiwan

The isolation of OXA-48-producing Enterobacteriaceae has increased dramatically in Mediterranean countries in the past 10 years, and has recently emerged in Asia. Between January 2012 and May 2014, a total of 760 carbapenem non-susceptible Klebsiella pneumoniae (CnSKP) isolates were collected during a Taiwan national surveillance. Carbapenemases were detected in 210 CnSKP isolates (27.6%), including 162 KPC-2 (n = 1), KPC-3, KPC-17, and NDM-1 (n = 1 each), OXA-48 (n = 4), IMP-8 (n = 18), and VIM-1 (n = 24). The four blaOXA-48 CnSKP isolates were detected in late 2013. Herein we report the emergence OXA-48-producing K. pneumoniae isolates in Taiwan. PFGE analysis revealed that the four isolates belonged to three different pulsotypes. Three isolates harboured blaCTX-M genes and belonged to MLST type ST11. In addition, the plasmids belonged to the incompatibility group, IncA/C. One isolate belonged to ST116 and the plasmid incompatibility group was non-typeable. The sequence upstream of the blaOXA-48 gene in all four isolates was identical to pKPOXA-48N1, a blaOXA-48-carrying plasmid. This is the first report of OXA-48-producing Enterobacteriaceae in Taiwan and the second report to identify blaOXA-48 on an IncA/C plasmid in K. pneumoniae. Given that three isolates belong to the same pandemic clone (ST11) and possess the IncA/C plasmid and similar plasmid digestion profile that indicated the role of clonal spread or plasmid for dissemination of blaOXA-48 gene, the emergence of OXA-48-producing K. pneumoniae in Taiwan is of great concern.

Quantification and comparison of virulence and characteristics of different variants of carbapenemase-producing Klebsiella pneumoniae clinical isolates from Taiwan and the United States

BACKGROUND/PURPOSE

The emergence of Klebsiella pneumoniae carbapenemase (KPC)-producing strains is a challenge for clinicians. The characteristics and virulence of variants of KPC-producing K. pneumoniae isolates were evaluated.

METHODS

Five clinical isolates-three KPC subtypes from Taiwan (KPC2-TW, KPC3-TW, and KPC17-TW) and two clinical strains from the United States (US; KPC2-US, KPC3-US)-were included. Virulent traits and capsular serotypes were analyzed by Polymerase Chain Reaction (PCR). Serum killing, neutrophil phagocytosis, and mice lethargy studies were performed to evaluate virulence.

RESULTS

Multilocus sequence typing (MLST) demonstrated that KPC2-TW and KPC17-TW belonged to sequence type (ST)11, and KPC2-US, KPC3-US, and KPC3-TW to ST258. KPC3-TW expressed capsular serotype K1, whereas the others were non-K1/K2/K5 isolates. MLST analysis indicated that ST11 strains were serum resistant, whereas ST258 isolates were serum sensitive. ST11 isolates exhibited significantly higher 15-minute phagocytic rates than ST258 isolates (70.28 ± 16.68% vs. 34.88 ± 10.52%, p < 0.001). The capsular serotype K1 strain was more resistant to neutrophil phagocytosis than non-K1/K2/K5 isolates (27.1 ± 10.23% vs. 54.46 ± 20.94%, p = 0.050). All KPC-producing strain variants from Taiwan and the US demonstrated less virulence in a mouse lethality study, where the LD50 ranged from approximately 10(6) colony-forming units (CFU) to >10(7) CFU. Immunological responses were not significantly correlated with KPC subtype; however, responses were associated with MLST and capsular serotype.

CONCLUSION

Production of KPC itself was not associated with increased virulence despite different variants of KPC. The ST11 KPC-producing strain was resistant to serum killing, whereas capsular ss K1 was associated with resistance to neutrophil phagocytosis.

A Common Flanking Region in Promiscuous Plasmids Encoding blaNDM-1 in Klebsiella pneumoniae Isolated in Singapore

Bacteria encoding the New Delhi metallo-β-lactamase gene (blaNDM-1) are regarded as superbugs for their resistance to multiple antibiotics. Plasmids encoding blaNDM-1 have been observed to be spreading among gram-negative bacteria around the world. Previous studies have demonstrated that multiple modifications of blaNDM-1-harboring plasmids might contribute to the spread of the gene. In this study, we analyzed blaNDM-1-encoding plasmids from two Klebsiella pneumoniae isolates, DU7433 and DU1301, found to be unrelated by pulsed field gel electrophoresis and multilocus sequencing typing (DU7433: ST14 and DU1301: ST11), and compared them with previously published plasmids. Although strains DU1301, DU7433, and previously published strain DU43320 carried unrelated plasmids, their transconjugants exhibited similar antimicrobial resistance profiles. Transconjugants lacked the resistance to aztreonam, ciprofloxacin, gentamicin, tetracycline, and trimethoprim/sulfamethoxazole when compared with the corresponding clinical isolates. Plasmids pTR1 from DU1301 and pTR2 from DU7433 had completely different plasmid backbones except a short conserved region of blaNDM-1 and ble flanked with truncated or nontruncated ISAba125 and trpF. The presence of this common region among known blaNDM-1-carrying plasmids implies that the dissemination of blaNDM-1 may be facilitated by mobilization of this conserved immediate region among different plasmids. Control measures should be strictly enforced whenever increasing incidences of epidemiological unrelated strains were identified.

Efficacy of Appropriate Antimicrobial Therapy on the Survival of Patients With Carbapenem Nonsusceptible Klebsiella Pneumoniae Infection: A Multicenter Study in Taiwan

The impact of antimicrobial treatment on the outcome of carbapenem nonsusceptible Klebsiella pneumoniae (CnsKP) infections needs to be elucidated. This nationwide, multicenter study was conducted to evaluate the impact of appropriate antimicrobial therapy on 14-day mortality among patients with CnsKP infection in Taiwan.Patients with CnsKP infections from 11 medical centers and 4 regional hospitals in Taiwan were enrolled in 2013. Carbapenem nonsusceptibility was defined as a minimum inhibitory concentration of ≥2 mg/L for imipenem or meropenem. Predictors of 14-day mortality were determined using the Cox proportional regression model. The influence of infection severity on the impact of appropriate use of antimicrobials on 14-day mortality was determined using the Acute Physiology and Chronic Health Evaluation (APACHE) II score.Overall 14-day mortality was 31.8% (49/154). Unadjusted mortality for appropriate antimicrobial therapy was 23.1% (18/78 patients). Appropriate therapy was independently associated with reduced mortality (hazard ratio [HR], 0.44; 95% confidence interval [CI], 0.24-0.80; P = 0.007). A subgroup analysis revealed that the benefit of appropriate therapy was limited to patients with higher APACHE II scores (HR for patients with scores >15 and ≤35, 0.46; 95% CI 0.23-0.92; and for those with scores >35, 0.14; 95% CI, 0.02-0.99).In conclusion, appropriate antimicrobial therapy significantly reduces 14-day mortality for CnsKP infections. Survival benefit is more notable among more severely ill patients.

A suitable streptomycin-resistant mutant for constructing unmarked in-frame gene deletions using rpsL as a counter-selection marker

The streptomycin counter-selection system is a useful tool for constructing unmarked in-frame gene deletions, which is a fundamental approach to study bacteria and their pathogenicity at the molecular level. A prerequisite for this system is acquiring a streptomycin-resistant strain due to rpsL mutations, which encodes the ribosomal protein S12. However, in this study no streptomycin resistance was found to be caused by rpsL mutations in all 127 clinical strains of Klebsiella pneumoniae isolated from liver abscess patients. By screening 107 spontaneous mutants of streptomycin resistance from a clinical strain of K. pneumoniae, nucleotide substitution or insertion located within the rpsL was detected in each of these strains. Thirteen different mutants with varied S12 proteins were obtained, including nine streptomycin-dependent mutants. The virulence of all four streptomycin-resistant mutants was further evaluated. Compared with the parental strain, the K42N, K42T and K87R mutants showed a reduction in growth rate, and the K42N and K42T mutants became susceptible to normal human serum. In the mice LD50 (the bacterial dose that caused 50% death) assay, the K42N and K42T mutants were ∼ 1,000-fold less lethal (∼ 2 × 10(5) CFU) and the K87R mutant was ∼ 50-fold less lethal (∼ 1 × 10(4) CFU) than the parental strain (∼ 2 × 10(2) CFU). A K42R mutant showed non-observable effects on the above assays, while this mutant exhibited a small cost (P < 0.01) in an in vitro growth competition experiment. In summary, most of the K. pneumoniae strains with streptomycin resistance caused by rpsL mutations are less virulent than their parental strain in the absence of streptomycin. The K42R mutant showed similar pathogenicity to its parental strain and should be one of the best choices when using rpsL as a counter-selection marker.

Identification of the first imported KPC-3 Klebsiella pneumoniae from the USA to Taiwan

Establishment of KPC-associated genes into a new region usually requires travellers with hospital admission and their carriage into the communities. In this report, a worldwide spreading clone carrying KPC-3 was isolated from the sputum of a hospitalised patient with a serious infection who had just come from the USA and had been admitted to a New York hospital. By genetic comparison with a strain isolated from New Jersey (NJ-KPC-21), this isolate from the traveller was genetically related. The blaKPC-3 gene was harboured on a large plasmid with a complex structure of a Tn3-based transposon, Tn4401a. The KPC-3-carrying plasmid was very similar (>99.9% identity) to the 113 637-bp blaKPC-3-encoding plasmid pKpQIL that originated from the 2006 epidemic carbapenem-resistant Klebsiella pneumoniae outbreak in Israel. With the first recognition of KPC-2 in 2011 and continuing spread, physicians should be aware of the coming of KPC-3 K. pneumoniae in Taiwan.

Genotypes and virulence in serotype K2 Klebsiella pneumoniae from liver abscess and non-infectious carriers in Hong Kong, Singapore and Taiwan

In Klebsiella pneumoniae liver abscess (KP-LA), K. pneumoniae K2 is the most frequently isolated serotype after K1, but this serotype has been much less studied. In the present study, the molecular types sequences type (MLST) of serotype K2 isolates from three different regions in Asia were identified and the virulence of these isolates was investigated. Eight different MLSTs were found among 26 isolates (ST 65, 66, 86, 373, 374, 375, 380, and 434). There were two major MLST groups, ST-65-like (42%) and ST86-like (46%). No isolates contained allS while all isolates contained rmpA. The prevalence of aerobactin gene and kfu were 25/26 (96%) and 3/26 (11.5%) respectively. Although liver abscess isolates were generally more resistant (11/15 isolates) to serum killing, there was no specific distribution of serum killing resistant or susceptible ST types between stool carriage and liver abscess isolates. Neutrophil phagocytosis showed that the liver abscess and carriage isolates varied in their susceptibility to phagocytosis. Strains with resistance to both neutrophil phagocytosis and serum killing were generally hypervirulent with lethality at LD₅₀ < 10³ colony forming units by intraperitoneal injection. In conclusion, Anti-phagocytosis and resistance to serum killing are two parameters that most predict hyperviurlence in serotype K2 isolates. Unlike serotype K1 KP-LA that mainly belong to ST-23, ST-65-like and −86-like are the two major MLST types among serotype K2 isolates from Singapore, Hong Kong and Taiwan.

Updated molecular epidemiology of carbapenem-non-susceptible Escherichia coli in Taiwan: first identification of KPC-2 or NDM-1-producing E. coli in Taiwan

BACKGROUND

The global spread and increasing incidence of carbapenem-resistant Enterobacteriaceae have resulted in treatment and public health concerns. Here, we present an investigation of the molecular mechanisms and clonality of carbapenem-non-susceptible Escherichia coli (CnSEC) based on a nationwide survey in Taiwan.

METHODS

We collected 32 and 43 carbapenem-non-susceptible E. coli isolates in 2010 and 2012, respectively. The genes encoding cabapenemases and plasmidic AmpC-type and extended-spectrum β-lactamases (EBSLs) were analyzed by polymerase chain reaction (PCR). The major porin channels OmpF and OmpC were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Molecular typing was performed with pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST).

RESULTS

The resistance rates of CnSEC isolates to cefazolin, cefotaxime, cefoxitin, ceftazidime, and ertapenem were all 100%, and most (94.7%) isolates were CMY producers. The main mechanism of CnSEC in Taiwan is via plasmidic AmpC β-lactamase CMY-2 and DHA-1 in combination with the loss of OmpC/F. In 2010, one isolate was confirmed to harbor blaIMP-8; a KPC-2 producer and an NDM-1 producer were detected in 2012. No isolate had VIM- or OXA-carbapenemases. ST131 was the predominant ST type (33.3%). PFGE revealed no large cluster in CnSEC isolates in Taiwan.

CONCLUSIONS

The co-existence of plasmidic AmpC β-lactamase and outer membrane protein loss is the main mechanism for CnSEC in Taiwan. The emergence of KPC-2 and NDM-1 in 2012 and the predominance of ST131 warrant close monitoring and infection control.

Single or in combination antimicrobial resistance mechanisms of Klebsiella pneumoniae contribute to varied susceptibility to different carbapenems

Resistance to carbapenems has been documented by the production of carbapenemase or the loss of porins combined with extended-spectrum β-lactamases or AmpC β-lactamases. However, no complete comparisons have been made regarding the contributions of each resistance mechanism towards carbapenem resistance. In this study, we genetically engineered mutants of Klebsiella pneumoniae with individual and combined resistance mechanisms, and then compared each resistance mechanism in response to ertapenem, imipenem, meropenem, doripenem and other antibiotics. Among the four studied carbapenems, ertapenem was the least active against the loss of porins, cephalosporinases and carbapenemases. In addition to the production of KPC-2 or NDM-1 alone, resistance to all four carbapenems could also be conferred by the loss of two major porins, OmpK35 and OmpK36, combined with CTX-M-15 or DHA-1 with its regulator AmpR. Because the loss of OmpK35/36 alone or the loss of a single porin combined with bla CTX-M-15 or bla DHA-1-ampR expression was only sufficient for ertapenem resistance, our results suggest that carbapenems other than ertapenem should still be effective against these strains and laboratory testing for non-susceptibility to other carbapenems should improve the accurate identification of these isolates.

KPC-2-encoding plasmids from Escherichia coli and Klebsiella pneumoniae in Taiwan

OBJECTIVES

Two plasmids carrying bla(KPC-2) isolated from carbapenem-resistant Escherichia coli (CR-EC) and carbapenem-resistant Klebsiella pneumoniae (CR-KP), respectively, were completely sequenced. The CR-KP strain was selected from an outbreak in 2012, and the CR-EC strain was the first blaKPC-2-carrying E. coli identified in the same carbapenem resistance monitoring programme in Taiwan.

METHODS

Antimicrobial susceptibility tests, multilocus sequence typing (MLST) and the conjugal transfer of plasmids were performed. Complete sequencing of the plasmids was performed using a shotgun approach.

RESULTS

The CR-EC and CR-KP strains in this study were determined to be ST410 and ST11, respectively, by MLST. From CR-EC, we identified a 145 kb conjugative plasmid that carries bla(KPC-2), bla(CMY-2), bla(CTX-M-3) and bla(TEM-1). The plasmid is a chimera composed of three regions related to IncI, IncN and RepFIC replicons. From CR-KP, we identified an 86.5 kb plasmid, pKPC-LK30, which carries bla(KPC-2) and bla(SHV-11). The plasmid is very similar to two bla(KPC-2)-carrying IncFII(K) plasmids, but lacks one of the replication origins and cannot conjugate.

CONCLUSIONS

The differences in cross-species transferability of the two plasmids can be explained by genetic differences between their backbones and could have resulted in the confined bla(KPC-2)-carrying CR-KP outbreak in Taiwan. Plasmid pKPC-LKEc is the first bla(KPC-2)-carrying plasmid identified from CR-EC in Taiwan. With relatively high transferability it should be closely monitored.

National surveillance study on carbapenem non-susceptible Klebsiella pneumoniae in Taiwan: the emergence and rapid dissemination of KPC-2 carbapenemase

Objectives

The global spread and increasing incidence of carbapenem non-susceptible Klebsiella pneumoniae (CnSKP) has made its treatment difficult, increasing the mortality. To establish nationwide data on CnSKP spread and carbapenem-resistance mechanisms, we conducted a national surveillance study in Taiwanese hospitals.

Methods

We collected 100 and 247 CnSKP isolates in 2010 and 2012, respectively. The tests performed included antibiotic susceptibility tests; detection of carbapenemase, extended-spectrum β-lactamases (ESBL), and AmpC β-lactamases genes; outer membrane porin profiles; and genetic relationship with pulsed-field gel electrophoresis and multilocus sequence type.

Results

The resistance rate of CnSKP isolates to cefazolin, cefotaxime, cefoxitin, ceftazidime, and ciprofloxacin was over 90%. Susceptibility rate to tigecycline and colistin in 2010 was 91.0% and 83.0%, respectively; in 2012, it was 91.9% and 87.9%, respectively. In 2010, carbapenemase genes were detected in only 6.0% of isolates (4 bla_IMP-8 and 2 bla_VIM-1). In 2012, carbapenemase genes were detected in 22.3% of isolates (41 bla_KPC-2, 7 bla_VIM-1, 6 bla_IMP-8, and 1 bla_NDM-1). More than 95% of isolates exhibited either OmpK35 or OmpK36 porin loss or both. Impermeability due to porin mutation coupled with AmpC β-lactamases or ESBLs were major carbapenem-resistance mechanisms. Among 41 KPC-2-producing K. pneumoniae isolates, all were ST11 with 1 major pulsotype.

Conclusions

In 2010 and 2012, the major mechanisms of CnSKP in Taiwan were the concomitance of AmpC with OmpK35/36 loss. KPC-2-KP dissemination with the same ST11 were observed in 2012. The emergence and rapid spread of KPC-2-KP is becoming an endemic problem in Taiwan. The identification of NDM-1 K. pneumoniae case is alarming.

Clinical features and risk factors of mortality for bacteremia due to community-onset healthcare-associated methicillin-resistant S. aureus

Studies comparing adult community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and community-onset healthcare-associated MRSA (COHCA MRSA bacteremia have not been available. From 1 January 2010 through 30 October 2010, a prospective observational program was conducted among all patients aged >16 years with positive Staphylococcus aureus blood cultures within 48 h after their arrival at the emergency department of our hospital. Clinical course of infection and infection foci of bacteremia were evaluated. Resistance to oxacillin was confirmed with the presence of mecA gene examined by polymerase chain reaction. Presence of TSST-1, PVL gene, SCCmec elements (I-V), mecA gene, and multilocus sequence typing were identified through methods described elsewhere. Univariate and multivariate analysis revealed that chronic renal failure was significantly more common in COHCA-MRSA than in CA-MRSA. In addition, APACHE III score was significantly higher in COHCA-MRSA than in CA-MRSA. Both the 7-day and 30-day mortality rates in COHCA-MRSA, 14.6% (7/48) and 29.2% (14/48), respectively, were higher than those in CA-MRSA without a significant difference. SCCmec II was more common in COHCA-MRSA, but SCCmecVT was more common in CA-MRSA. The majority of MRSA isolates belonged to ST59, ST239, and ST5. ST59 was significantly more common in CA-MRSA, while ST239 was nearly equally common in both CA-MRSA and COHCA-MRSA. SCCmec III and II isolates were the first and second most resistant to the antibiotics commonly used for S. aureus, whereas SCCmecVT isolates were the most susceptible to these antibiotics. We conclude that, although both CA-MRSA and COHCA-MRSA bacteremia had community onset, these 2 MRSA infections were different in underlying diseases, risk of mortality, SCCmec types, sequence types, and antimicrobial susceptibility. It is more appropriate to understand the MRSA pathogen and clinical features based on etiology and ST types than based on the location of disease onset. CA-MRSA and HCA-MRSA should be differentiated also based on etiology and ST types, in addition to location of acquisition.

Klebsiella pneumoniae liver abscess: a new invasive syndrome

Klebsiella pneumoniae is a well known human nosocomial pathogen. Most community-acquired K pneumoniae infections cause pneumonia or urinary tract infections. During the past two decades, however, a distinct invasive syndrome that causes liver abscesses has been increasingly reported in Asia, and this syndrome is emerging as a global disease. In this Review, we summarise the clinical presentation and management as well the microbiological aspects of this invasive disease. Diabetes mellitus and two specific capsular types in the bacterium predispose a patient to the development of liver abscesses and the following metastatic complications: bacteraemia, meningitis, endophthalmitis, and necrotising fasciitis. For patients with this invasive syndrome, appropriate antimicrobial treatment combined with percutaneous drainage of liver abscesses increases their chances of survival. Rapid detection of the hypervirulent strain that causes this syndrome allows earlier diagnosis and treatment, thus minimising the occurrence of sequelae and improving clinical outcomes.

Klebsiella pneumoniae in gastrointestinal tract and pyogenic liver abscess

To determine the role of gastrointestinal carriage in Klebsiella pneumoniae liver abscess, we studied 43 patients. Bacterial isolates from liver and fecal samples from 10 patients with this condition and 7 healthy carriers showed identical serotypes and genotypes with the same virulence. This finding indicated that gastrointestinal carriage is a predisposing factor for liver abscess.

Sequence of closely related plasmids encoding bla(NDM-1) in two unrelated Klebsiella pneumoniae isolates in Singapore

Background

Spread of the bla_NDM-1 gene that encodes the New Delhi metallo-β-lactamase (NDM-1) in Enterobacteriaceae is a major global health problem. Plasmids carrying bla_NDM-1 from two different multi-drug resistant Klebsiella pneumonia isolates collected in Singapore were completely sequenced and compared to known plasmids carrying bla_NDM-1.

Methodology/Principal Findings

The two plasmids, pTR3 and pTR4, were transferred to Escherichia coli recipient strain J53 and completely sequenced by a shotgun approach using 3-kb paired-end libraries on 454. Although the K. pneumoniae strains were unrelated by molecular typing using PFGE and MLST, complete sequencing revealed that pTR3 and pTR4 are identical. The plasmid sequence is similar to the E. coli NDM-1-encoding plasmid p271A, which was isolated in Australia from a patient returning from Bangladesh. The immediate regions of the bla_NDM-1 gene in pTR3/4 are identical to that of p271A, but the backbone of our plasmid is much more similar to another IncN2 plasmid reported recently, pJIE137, which contained an additional 5.2-kb CUP (conserved upstream repeat) regulon region in comparison to p271A. A 257-bp element bounded by imperfect 39-bp inverted repeats (IR) and an incomplete version of this element flanking the 3.6-kb NDM-1-encoding region were identified in these plasmids and are likely to be the vestiges of an unknown IS.

Conclusions

Although the hosts are not epidemiologically linked, we found that the plasmids bearing the bla_NDM-1 gene are identical. Comparative analyses of the conserved NDM-1-encoding region among different plasmids from K. pneumoniae and E. coli suggested that the transposable elements and the two unknown IR-associated elements flanking the NDM-1-encoding region might have aided the spreading of this worrisome resistance determinant.

Molecular typing and resistance mechanisms of imipenem-non-susceptible Klebsiella pneumoniae in Taiwan: results from the Taiwan surveillance of antibiotic resistance (TSAR) study, 2002-2009

We investigated the molecular mechanisms and clonality of imipenem-non-susceptible Klebsiella pneumoniae isolates collected during a Taiwan national surveillance programme, between 2002 and 2009. Genes for carbapenemases, plasmid-borne ampC-type genes and extended-spectrum β-lactamase (ESBL) genes were analysed by PCR. The major porin channels OmpK35 and OmpK36 were studied by SDS-PAGE. Molecular typing was performed with pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). Our study revealed that all 29 of the isolates tested were ESBL producers. Of the K. pneumoniae isolates collected in Taiwan from 2002 to 2009, most (84.6 %, 11/13) imipenem-resistant (MIC >2 mg l(-1)) isolates carried the bla(IMP-8) gene. Isolates with an imipenem MIC of 2 mg l(-1) produced ESBLs with or without DHA-1 in combination with OmpK35/36 loss. PFGE analysis revealed that six small clusters of isolates were clonally related. The MLST grouping results were in concordance with the PFGE results. The predominant sequence types (ST) were ST11, ST48 and ST101. Two novel STs, ST1033 and ST1034, were found. The dominant clone in Taiwan, ST11, has been reported worldwide to be associated with various resistance mechanisms.

Virulence and plasmid transferability of KPC Klebsiella pneumoniae at the Veterans Affairs Healthcare System of New Jersey

Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae infections are associated with high mortality; however, little is known about the virulence determinants of KPC-producing K. pneumoniae. At the Veterans Affairs New Jersey Healthcare System (VA NJHCS), we investigated the virulence and plasmid transferability of 60 clinically unique KPC-containing K. pneumoniae isolates. All 60 isolates were negative for known virulence factors K1, K2, and K5 capsular antigens; rmpA; and the aerobactin gene by polymerase chain reaction. Isolates varied in their susceptibility to neutrophil phagocytosis, but were less resistant than the virulent serotype K1 isolate. Additionally, no deaths were seen on murine lethality studies. Conjugation results of this study showed that the bla(KPC) gene can be transferred into an Escherichia coli J-53 strain but not to E. coli JP-995. However, the stability is very limited as E. coli J-53 does not retain bla(KPC)-containing plasmids for any period of time. The lack of virulence factors in the set of KPC-producing K. pneumoniae studied suggests that morbidity and mortality may be due to detection issues or lack of effective antibiotics.

Increasing opsonizing and killing effect of serum from patients with recurrent K1 Klebsiella pneumoniae liver abscess

BACKGROUND

Klebsiella pneumoniae liver abscess (KLA) is an emerging infectious disease caused by the virulent K pneumoniae strains of capsular serotype K1 and commonly associated with diabetes mellitus. Recurrent KLA is rarely reported and the mechanism of recurrence is uncertain. In this study we evaluated both phagocytosis by neutrophils and serum killing ability of serum from recurrent K1 KLA patients compared to normal healthy subjects (NHS).

METHODS

This prospective study included six cases of recurrent K1 KLA consisting of three male and three female patients with a mean age of 67.2 years (range, 56-88 years). The different serotypes of K pneumoniae were reacted with serum from patients with recurrent KLA and NHS. Subsequent phagocytosis by neutrophils was determined using flow cytometry and serum killing assays were performed.

RESULTS

The most common underlying disease in patients with recurrent KLA was diabetes mellitus, occurring in about 83.3% (5/6) of patients. The antibiogram of the strains associated with recurrent KLA remained uniquely resistant to ampicillin. The average percentage derived from the serum killing assays showed serotype K1 and K2 resistance to serum from NHS (1281% and 621%, respectively); however, serum susceptibly was observed in the serum of patients with recurrent K1 KLA (0.3% and 1.1%, respectively). A significant increase in neutrophil phagocytosis of serotype K1 was observed following opsonisation with serum from patients with recurrent KLA compared with serum from NHS (p = 0.008). No significant difference in the phagocytic rate of non-K1/K2 or K2 serotypes was observed between NHS and patients with recurrent KLA (p = 0.76 and p = 0.132, respectively).

CONCLUSION

These preliminary results showed possible immunologic protection in patients with recurrent KLA due to increasing opsonization and serum killing.

Seroepidemiology of Klebsiella pneumoniae colonizing the intestinal tract of healthy Chinese and overseas Chinese adults in Asian countries

Background

Capsular serotypes K1 and K2 of Klebsiella pneumoniae are thought to the major virulence determinants responsible for liver abscess. The intestine is one of the major reservoirs of K. pneumoniae, and epidemiological studies have suggested that the majority of K. pneumoniae infections are preceded by colonization of the gastrointestinal tract. The possibility of fecal-oral transmission in liver abscess has been raised on the basis of molecular typing of isolates. Data on the serotype distribution of K. pneumoniae in stool samples from healthy individuals has not been previously reported. This study investigated the seroepidemiology of K. pneumoniae isolates from the intestinal tract of healthy Chinese in Asian countries. Stool specimens from healthy adult Chinese residents of Taiwan, Japan, Hong Kong, China, Thailand, Malaysia, Singapore, and Vietnam were collected from August 2004 to August 2010 for analysis.

Results

Serotypes K1/K2 accounted for 9.8% of all K. pneumoniae isolates from stools in all countries. There was no significant difference in the prevalence of K1/K2 isolates among the countries excluding Thailand and Vietnam. The antimicrobial susceptibility pattern was nearly the same in K. pneumoniae isolates. The result of pulsed-field gel electrophoresis revealed no major clonal cluster of serotype K1 isolates.

Conclusions

The result showed that Chinese ethnicity itself might be a major factor predisposing to intestinal colonization by serotype K1/K2 K. pneumoniae isolates. The prevalent serotype K1/K2 isolates may partially correspond to the prevalence of K. pneumoniae liver abscess in Asian countries.

Clinical and bacteriological characteristics of Klebsiella pneumoniae causing liver abscess with less frequently observed multi-locus sequences type, ST163, from Singapore and Missouri, US

BACKGROUND

Klebsiella pneumoniae is the major cause of liver abscesses in several Asian countries. Differences in the type of circulating Klebsiella strains and/or the genetic make up of the host seem to be plausible explanations for this.

METHODS

Two recent K. pneumoniae strains isolated from patients with liver abscess, one from Missouri in the US, and a second one from Singapore, were fully characterized by molecular typing, association of virulent genes, neutrophil phagocytosis, susceptibility to serum killing, and lethality in mice.

RESULTS

Both strains had mucoid colony morphology and were similar in multilocus sequence type (ST-163), drug-susceptibility profile, resistance to phagocytosis and susceptibility to serum killing. Although ST-163 is a single nucleotide variant (SNV) to the major ST-23, which is specific to serotype K1 K. pneumoniae that causes liver abscess in Taiwan, these two isolates differ in capsular serotype. One was serotype K1 and the other K29. Since a serotype K35 with ST163 was reported previously to cause peritonitis, serotype K29 with SNV to ST-23 was not impossible. Pulsed field gel electrophoresis by XbaI digestion showed different restriction patterns. The virulence-associated genes rmpA and aerobactin were only present in the serotype K1 isolate from Singapore and not in the serotype K29 isolate from Missouri. The serotype K1 isolate was also more virulent to mice.

CONCLUSION

The reasons underlying the high prevalence of ST-23 or its SNV in K. pueumonaie liver abscesses is worth further investigation.

Appearance of Klebsiella pneumoniae liver abscess syndrome in Argentina: case report and review of molecular mechanisms of pathogenesis

Klebsiella pneumoniae liver abscess syndrome (KLAS) is an emerging invasive infection caused by highly virulent community-acquired strains of K. pneumoniae displaying hypermucoviscosity. The salient features of this syndrome include the presence of bacteremia, primary monomicrobial liver abscess, and metastatic complications. A previously healthy Argentinean man presented with fever and found to have liver abscess caused by K. pneumoniae with metastatic seeding of gastric wall. Cultures from blood and liver abscess grew hypermucoviscous K1 K. pneumoniae with sequence type (ST) 23 by multilocus sequence typing (MLST), positive for rmpA (regulator of mucoid phenotype A), wzy_KpK1 (capsular polymerase) and aerobactin genes. The hypermucoviscous phenotype of this K. pneumoniae isolate was readily identified by the "string test" (colonies formed a long string when touched with a loop). The patient responded favourably to percutaneous drainage of the abscess and antibiotics. This is the first documented report of KLAS described in Argentina, and may signal the emergence of this syndrome in South America.