Molecular characteristics of carbapenemase-producing Enterobacteriaceae in China from 2008 to 2011: predominance of KPC-2 enzyme

Clinical characteristics and risk factors for neonatal bloodstream infection due to carbapenem-resistant Enterobacteriaceae: A single-centre Chinese retrospective study

OBJECTIVES

To analyse the clinical characteristics and risk factors for bloodstream infections (BSIs) caused by carbapenem-resistant Enterobacteriaceae (CRE) in neonates.

METHODS

This single-centre, retrospective study included all patients with BSIs admitted to a neonatal intensive care unit between 1 January 2015 and 30 April 2022. The clinical and microbiological data of patients were collected; predictors of 30-day mortality in patients with CRE BSIs were also identified in this study.

RESULTS

Among the 224 neonates with Enterobacteriaceae BSIs, 39.29% (88/224) of the patients developed CRE BSIs. The 30-day mortality rate reached up to 21.59% (19/88). The Quick Sequential Organ Failure Assessment score > 2 (odds ratio [OR] and 95% credibility interval [CI]: 3.852 [1.111-13.356], P < 0.05), prior to more than two kinds of antibiotics use (OR and 95% CI: 9.433 [1.562-56.973], P < 0.05), pneumonia (OR and 95% CI: 3.847 [1.133-13.061], P < 0.05), and caesarean section (OR and 95% CI: 2.678 [1.225-5.857], P < 0.05) were independent risk factors associated with CRE BSIs. Moreover, the risk factors for mortality in neonates with CRE BSIs were significantly associated with neonatal Sequential Organ Failure Assessment score > 6 (OR and 95% CI: 16.335 [1.446-184.517], P < 0.05).

CONCLUSION

Prior to more than two kinds of antibiotics use, Quick Sequential Organ Failure Assessment score > 2, pneumonia and caesarean section were independent risk factors for CRE BSIs. The Neonatal Sequential Organ Failure Assessment score > 6 was a risk factor for mortality associated with CRE BSIs.

Mechanism for transmission and pathogenesis of carbapenem-resistant Enterobacterales harboring the carbapenemase IMP and clinical countermeasures

Carbapenem-resistant Enterobacterales (CRE) are some of the most important pathogens causing infections, which can be challenging to treat. We identified four blaIMP-carrying CRE isolates and collected clinical data. The transferability and stability of the plasmid were verified by conjugation, successive passaging, and plasmid elimination assays. The IncC blaIMP-4-carrying pIMP4-ECL42 plasmid was successfully transferred into the recipient strain, and the high expression of traD may have facilitated the conjugation transfer of the plasmid. Interestingly, the plasmid showed strong stability in clinical isolates. Whole-genome sequencing was performed on all isolates. We assessed the sequence similarity of blaIMP -harboring plasmid from our institution and compared it to plasmids for which sequence data are publicly available. We found that four blaIMP-carrying CRE belonged to four different sequence types. The checkerboard technique and time-kill assays were used to investigate the best antimicrobial therapies for blaIMP-carrying CRE. The time-kill assay showed that the imipenem of 1× minimum inhibitory concentration (MIC) alone had the bactericidal or bacteriostatic effect against IMP-producing strains at 4-12 h in vitro. Moreover, the combination of tigecycline (0.5/1/2 × MIC) and imipenem (0.5/1 × MIC) showed a bactericidal effect against the blaIMP-26-carrying CRECL60 strain.IMPORTANCECarbapenem-resistant Enterobacterales (CRE) are an urgent public health threat, and infections caused by these microorganisms are often associated with high mortality and limited treatment options. This study aimed to determine the clinical features, molecular characteristics, and plasmid transmissible mechanisms of blaIMP carriage as well as to provide a potential treatment option. Here, we demonstrated that conjugated transfer of the IncC blaIMP-4-carrying plasmid promotes plasmid stability, so inhibition of conjugated transfer and enhanced plasmid loss may be potential ways to suppress the persistence of this plasmid. The imipenem alone or tigecycline-imipenem combination showed a good bactericidal effect against IMP-producing strains. In particular, our study revealed that imipenem alone or tigecycline-imipenem combination may be a potential therapeutic option for patients who are infected with IMP-producing strains. Our study supports further trials of appropriate antibiotics to determine optimal treatment and emphasizes the importance of continued monitoring of IMP-producing strains in the future.

Molecular Characterization and Epidemiology of Carbapenem-Resistant Enterobacteriaceae Isolated from Pediatric Patients in Guangzhou, Southern China

Background

Carbapenem-resistant Enterobacteriaceae (CRE) are spreading worldwide, posing a serious public health concern. However, the data on CRE strains that cause infections in children in Guangzhou remain limited. Therefore, this study aimed to investigate the epidemiology of CRE, drug resistance, and resistance mechanisms in children in Guangzhou, Southern China.

Methods

In total, 54 nonrepetitive CRE strains were collected in pediatric patients at three centers in Guangzhou, Southern China, from January 2016 to August 2018. CRE isolates were used for further studies on antimicrobial susceptibility, the modified Hodge test (MHT), the modified carbapenem inactivation method (mCIM), and drug resistance genes. Multilocus sequence typing (MLST) was used to elucidate the molecular epidemiology of K. pneumoniae.

Results

The isolated CRE strains include 34 K. pneumoniae (63.0%), 10 E. coli (18.5%), 4 Enterobacter cloacae (7.4%), and 6 Proteus mirabilis (11.1%) strains. The strains were isolated mainly from the blood (31.5%, n = 17), sputum (31.5%, n = 17), and urine (16.7%, n = 9). All CRE isolates were highly resistant to the third- or fourth-generation cephalosporins, carbapenems, and β-lactam + β-lactamase inhibitors (94.4%-96.3%). In addition, the resistance rates to amikacin, ciprofloxacin, levofloxacin, tigecycline, and colistin were 5.6%, 14.8%, 16.7%, 9.3%, and 0%, respectively. Carbapenemase was detected in 35 (64.8%) of the CRE isolates. The most dominant carbapenemase gene was bla _NDM (n = 17, 48.6%), followed by bla _IMP (n = 13, 37.1%) and bla _OXA-23 (n = 4, 11.4%). Other carbapenemase genes (bla _KPC, bla _sim, bla _Aim, bla _GES, bla _Gim, bla _OXA-2 , and bla _OXA-48 ) and the mcr-1 gene were not detected. MLST analysis showed high diversity among the K. pneumoniae, and ST45 (11.7%, 4/34) was the dominant sequence type.

Conclusion

This study revealed bla _NDM was the most dominant carbapenemase gene in children in Guangzhou. Infection control measures need to be taken for the prevention and treatment of CRE infections.

Pyogenic liver abscess-caused Klebsiella pneumoniae in a tertiary hospital in China in 2017: implication of hypervirulent carbapenem-resistant strains

Background

To investigate the epidemiology of Klebsiella pneumoniae (K. pneumoniae) inducing pyogenic liver abscess (PLA) in east China and the role of hypervirulent carbapenem-resistant K. pneumoniae (Hv-CRKP).

Methods

Forty-three K. pneumoniae strains were collected from 43 patients with PLA at Hangzhou, China in 2017. Antimicrobial susceptibility tests, string test, multilocus sequence typing, pulsed-field gel electrophoresis, mobile genetic elements typing, regular PCR and sequencing, and Galleria mellonella (G. mellonella) lethality test were used to elucidate the epidemiology. Clinical data were collected.

Results

K. pneumoniae strains with serotypes K1 and K2 accounted for 69.8%, which shared 46.5% and 23.3% respectively. K. pneumoniae strains with clonal group 23 were predominant with a rate of 34.9%. Such antimicrobials showed susceptible rates over 80.0%: cefuroxime, cefotaxime, gentamycin, ticarcillin/clavulanate, ceftazidime, cefoperazone/tazobactam, cefepime, aztreonam, imipenem, meropenem, amikacin, tobramycin, ciprofloxacin, levofloxacin, doxycycline, minocycline, tigecycline, chloramphenicol, and trimethoprim-sulfamethoxazole. PFGE dendrogram showed 29 clusters for the 43 K. pneumoniae strains. Three Hv-CRKP strains were confirmed by G. mellonella lethality test, showing a constituent ratio of 7.0% (3/43). Totally three deaths were found, presenting a rate of 7.0% (3/43). The three died patients were all infected with Hv-CRKP.

Conclusions

K1 and K2 are the leading serotypes of K. pneumoniae causing PLA, which show highly divergent genetic backgrounds. Aminoglycosides, Generation 2^nd to 4^th cephalosporins, β-lactamase/β-lactamase inhibitors, carbapenems, fluoroquinolones are empirical choices. Hv-CRKP may confer an urgent challenge in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07648-0.

Clinical Outcomes and Microbiological Characteristics of Sequence Type 11 Klebsiella pneumoniae Infection

Background

Sequence type 11 (ST11) Klebsiella pneumoniae (Kp) is highly prevalent in China and is a typical sequence type among KPC-producing isolates. This study aimed to evaluate the clinical outcomes and microbiological features of ST11 Kp infections.

Methods

A retrospective cohort study was conducted at Peking University Third Hospital from January 2017 to March 2021. Clinical data were collected from medical records. Antimicrobial susceptibility testing and string tests were performed. Whole-genome sequencing was used to analyze the capsular serotypes, detect virulence-associated genes, and perform multilocus sequence typing. The risk of all-cause mortality in ST11 Kp-infected patients was compared to that in non-ST11 Kp-infected patients.

Results

From 139 patients infected with Kp, 49 ST11 Kp (35.3%) strains were isolated. The Charlson comorbidity index in the ST11 group was higher than that in the non-ST11 group (3.94 ± 1.59 vs. 2.41 ± 1.54, P = 0.001). A greater number of ST11 Kp-infected patients required ICU admission (46.9 vs. 16.7%, P < 0.001) and mechanical ventilation (28.6 vs. 10.0%, P = 0.005). All ST11 isolates presented a multidrug-resistant (MDR) phenotype, and twenty-nine (59.2%) hypervirulent Kp (hvKp) were identified. Twenty-four ST11 strains presented with hypermucoviscosity. The presence of capsular types K47 and K64 was frequent in the ST11 Kp strains (P < 0.001). The key virulence-associated genes rmpA, rmpA2, iucA, iroB, and peg344 were present in 26.5, 42.9, 59.2, 0, and 26.5% of the isolates, respectively, in the ST11 group. Twenty-one ST11 isolates harbored the combination of iucA+rmpA2. The 30-day mortality rate and sequential organ failure assessment (SOFA) score were significantly higher in ST11 Kp-infected patients than in non-ST11 Kp-infected patients (P < 0.01). ST11 Kp infection appeared to be an independent risk factor for mortality in ST11 Kp-infected patients.

Conclusions

A high prevalence of the ST11 clone was found in the hospital, which accounted for elevated antimicrobial resistance and exhibited great molecularly inferred virulence. Patients with ST11 Kp infection had a tendency toward increased 30-day mortality and SOFA scores. ST11 Kp infection was an independent risk factor for mortality, suggesting that enhanced surveillance and management are essential.

Using Whole Genome Sequencing to Trace, Control and Characterize a Hospital Infection of IMP-4-Producing Klebsiella pneumoniae ST2253 in a Neonatal Unit in a Tertiary Hospital, China

Background: The purpose of this study is to use whole genome sequencing (WGS) combined with epidemiological data to track a hospital infection of the carbapenem-resistant Klebsiella pneumoniae (CRKP), which affected 3 neonatal patients in the neonatal intensive care unit (NICU). Methods: The minimum inhibitory concentrations for the antimicrobial agents were determined according to the guidelines of the Clinical and Laboratory Standards Institute. Beta-lactamases were investigated using the polymerase chain reaction and DNA sequencing. The transferability of the plasmid was investigated by a conjugation experiment. The clonal relationships were evaluated using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). WGS and single nucleotide polymorphisms (SNPs) analysis were performed on the CRKP isolates to investigate how the infection might progress. Results: Nine CRKP isolates were obtained from the NICU, seven from three patients, one from a duster cloth and one from the hand of a nurse, they all harbored blaIMP-4. Other resistance genes including blaKPC-2, blaIMP-4, blaSHV-1, blaTEM-1, blaCTX-M-15, and blaDHA-1 were also detected. PFGE analysis showed that IMP-4-producing K. pneumoniae were clonally related, and MLST assigned them to a new sequence type 2253. The SNP variations throughout the genome divided the 9 strains into three clades. Clade 1 comprised 7 strains (K1- K2 and K4-K8), whereas clade 2 and 3 consisted of only one strain each: K3 and K9, respectively.The sputum isolate K3 from patient 3 was the most distinct one differing from the other eight isolates by 239-275 SNPs. Conclusions: This is a report of using WGS to track a hospital infecion of IMP-4-producing K. pneumoniae ST2253 among neonates. Nosocomial surveillance systems are needed to limit the spread of the infection caused by these pathogens resulting from the environmental exposure in NICUs.

Resistance Trends of Klebsiella pneumoniae Causing Urinary Tract Infections in Chongqing, 2011-2019

Purpose

To analyze the characteristics and trends of drug resistance for Klebsiella pneumoniae (K. pneumoniae), isolated from urinary tract infections (UTIs), to common antibiotics used in clinics.

Methods

This retrospective study was conducted in a teaching hospital in Chongqing from 2011 to 2019. Laboratory data of isolated bacteria were collected and analyzed.

Results

Among the 17,966 non-repetitive strains isolated from the urine sample, a total of 1543 K. pneumoniae isolates were identified, with an isolation frequency secondary only to Escherichia coli (E. coli) and there was a peak in the K. pneumoniae isolates in the year 2013. During the period, the rate of extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae fell from 48.4% in 2011 to 32.9% in 2019, and a marked jump of resistance was seen in carbapenems from 2.2% to 18.0%. The peak of carbapenem resistance rate (22.6%) to K. pneumoniae was observed in 2017 along with a low ESBL-producing rate (30.9%). Piperacillin/tazobactam and cefepime resistance levels went up from 4.4% to 25.7% and from 18.2% to 30.5%, respectively. Moreover, the K. pneumoniae isolates resistance rate to carbapenems and amikacin gradually grew up, showing their peaks in 2017, and then dropped year by year. However, ceftazidime and aztreonam resistance levels were relatively stable, fluctuating between 21.8% and 35.6%, 32.2% and 39.4%, respectively.

Conclusion

There is a significant upward tendency in carbapenem resistance rate and a downward tendency in ESBL-production rate in K. pneumoniae isolates from UTIs, and continuous surveillance is necessary in the future.

Analysis of Pathogen Distribution and Its Antimicrobial Resistance in Bloodstream Infections in Hospitalized Children in East China, 2015-2018

This study analyzed the pathogen distribution in bloodstream-infected (BSI) children hospitalized in Shandong Province from 2015 to 2018, to identify prevention strategies and select empiric antimicrobial therapy for BSI in children. Blood sample data from 14 107 children from 162 hospitals of Shandong Province were obtained from the China Antimicrobial Resistance Surveillance System and analyzed with WHONET 5.6 software. The results of the blood culture test showed the growth of 70.6% Gram-positive and 29.4% Gram-negative bacteria. Of the 14 107 blood isolates, 59.3% were collected from males and 40.7% were from females. Coagulase-negative staphylococci (47.1%) were the most commonly distributed pathogens. The distribution of pathogens varied according to age group and season. All Staphylococcus isolates were susceptible to vancomycin, teicoplanin and linezolid. Clinically, significant declines in penicillin-resistant Streptococcus pneumonia and carbapenem-resistant Escherichia coli were observed during the study period; however, detection rates of carbapenem-resistant Klebsiella pneumoniae increased over time (p < 0.05). Empiric antimicrobial therapy should be prescribed according to corresponding regional pediatric antimicrobial-resistant data.

Hypervirulent Klebsiella pneumoniae is emerging as an increasingly prevalent K. pneumoniae pathotype responsible for nosocomial and healthcare-associated infections in Beijing, China

OBJECTIVES

Hypervirulent Klebsiella pneumoniae(hvKp) is an increasingly important pathogen. Tracking its epidemiology and evolving antimicrobial resistance will facilitate care.

METHODS

A retrospective study was conducted in two hospitals. We collected the clinical data. Antimicrobial and virulence-associated phenotype and genotype, sequence type, and whole genome sequencing of selected strains were performed. HvKp was defined by the presence of some combination of prmpA, prmpA2, iucA, iroB, and peg-344, genes shown to accurately identify hvKp.

RESULTS

Of 158 Kp clinical isolates, 79 (50%) were hvKp. Interestingly, 53/79 (67.1%) of hvKp strains were isolated from patients with nosocomial infection and 19/79 (24.1%) from patients with healthcare-associated infection, but only 7/79 (8.8%) from patients with community-acquired infections. Importantly, 27/53 (50.9%) and 4/19 (21.1%) of hvKp nosocomial and healthcare-associated isolates, respectively, were multi-drug-resistant (MDR); 25/53 (47.2%) and 5/19 (26.3%) expressed ESBLs and 14/53 (26.4%) and 2/19 (10.5%) were carbapenem-resistant. Of the hvKp isolates from community-acquired infection, 0/7 (0%) were MDR and 0/7 (0%) were carbapenem-resistant. Additionally, unique characteristics of nosocomial, healthcare-associated, and community-acquired hvKp infection were identified. In summary, 50% of K. pneumoniae infections were caused by hvKp. A concerning, novel finding from this report is a major shift in hvKp epidemiology. Ninety-one percent of hvKp infections were nosocomial or healthcare-associated, and 43.1% of these isolates were MDR.

CONCLUSIONS

These data suggest that hvKp may be replacing classical K. pneumoniae as the dominant nosocomial and healthcare-associated pathotype. Ongoing surveillance is needed to determine if this trend is occurring elsewhere.

Emergence of NDM-5-Producing Carbapenem-Resistant Klebsiella pneumoniae and SIM-Producing Hypervirulent Klebsiella pneumoniae Isolated from Aseptic Body Fluid in a Large Tertiary Hospital, 2017-2018: Genetic Traits of blaNDM-Like and blaSIM-Like Genes as Determined by NGS

Purpose

To characterize the clinical, resistance, and virulence features of carbapenem-resistant Klebsiella pneumonaie (CRKP) and hypervirulent Klebsiella pneumoniae (hvKP) and also provide an effective selection of drug in CRKP and hvKP treatment.

Materials and Methods

Twelve strains were collected and investigated these isolates for their antimicrobial susceptibility and molecular features. Resistance mechanisms, virulence-associated genes, multilocus sequence typing (MLST), and serotypes were detected by PCR and sequencing. Next general sequencing (NGS) was carried out to determine the features of carbapenem resistance and virulence. The synergistic activity of tigecycline–imipenem (TGC+IPM), tigecycline–meropenem (TGC+MEM), and tigecycline–aztreonam (TGC+ATM) combinations were performed by microdilution checkerboard method.

Results

Eleven CRKP and one hvKP strains were collected. All strains showed highly sensitive rates to tigecycline (TGC) and amikacin (AMK). NDM (33.3%, 4/12) was the main resistance mechanism and MLST assigned 3 of them to ST11. CTX-M-producing (n = 1) and KPC-2-producing (n = 1) isolates belonged to ST147 and ST11, respectively. The MICs of ATM and quinolones in NDM-1 CRKP and NDM-5 CRKP strains were different. The serotype of the majority strains was KL22KL137 (58.3%, 7/12), hvKP stain belonged to K64. CRKP strains harbored plasmid-mediated quinolone resistance genes (oqxA, oqxB, qnrS, qnrB), β-lactams (bla_CTX-M-3), aminoglycosides, type I and type III fimbriae genes, siderophore genes, and transporter and pumps. SIM-producing ST1764 K64 showed typical features of hvKP, showing hypermucoviscosity phenotype. The virulence genes, including rmpA2, alls and aerobactin genes, linked to hvKP, were found in ST1764 hvKP. hvKP was sensitive to quinolone; also, oqxA gene was detected. All TGC combinations showed highly synergistic effects and TGC+IPM was more effective treatment.

Conclusion

We first identified the NDM-5-producing ST690 CRKP and SIM-producing ST1764 hvKP strains in Shanxi province. Tigecycline-carbapenem combinations were available treatments for CRKP.

Long-Term Continuous Antimicrobial Resistance Surveillance Among Nosocomial Gram-Negative Bacilli in China from 2010 to 2018 (CMSS)

Purpose

The Chinese Meropenem Surveillance Study (CMSS) was conducted every 2 years from 2010 to 2018 to monitor the antimicrobial activity of commonly used antimicrobial agents against nosocomial gram-negative bacilli in China.

Methods

From 2010 to 2018, 6,537 gram-negative bacilli were collected from 14 teaching hospitals. The minimum inhibitory concentrations (MICs) of meropenem and other antimicrobial agents were determined using the agar dilution and broth microdilution methods.

Results

Continuous surveillance indicated that, except for Klebsiella pneumoniae, the susceptibility of Enterobacterales to carbapenems was relatively stable over time. Carbapenems had the highest activity against the tested isolates, with MIC₉₀ values (MIC for 90% of organisms) ranging from 0.032 mg/L to 8 mg/L. More than 90% of bacteria were susceptible to either meropenem or imipenem; more than 80% were susceptible to ertapenem. The prevalence of extended-spectrum beta-lactamase (ESBL)-producing E. coli, K. pneumoniae, and P. mirabilis each year was 50.4–64.3%, 18–41.2%, and 1.9–33.8%, respectively. The prevalence of carbapenem-resistant K. pneumoniae (CRKP) and carbapenem-resistant Acinetobacter baumannii (CRAB) continued to increase significantly over time, from 7.6% to 21.2% and 64.6% to 69.3%, respectively. The prevalence of CRKP was higher from urinary tract infections (25.4%) than from bloodstream infections (14.2%), intra-abdominal infections (14.5%), and respiratory infections (14.4%). In total, 129 CRKP isolates were evaluated by PCR; of these, 92 (71.3%) carried the bla_KPC-2 gene. Colistin maintained very high in vitro antimicrobial activity against P. aeruginosa and A. baumannii (more than 95% of isolates exhibited susceptibility at all timepoints).

Conclusion

The results indicate an increase in K. pneumoniae resistance to carbapenems over time, mainly owing to KPC-type carbapenemase production. A. baumannii was severely resistant to carbapenems in China. Ongoing MIC-based resistance surveillance, like CMSS, provides additional data for clinical anti-infective treatment.

Phenotypic and Genomic Characterization of Virulence Heterogeneity in Multidrug-Resistant ST11 Klebsiella pneumoniae During Inter-Host Transmission and Evolution

Background

Multidrug-resistant (MDR) ST11 hypervirulent Klebsiella pneumoniae (hvKp) is emerging in China.

Purpose

The aim of this study was to track the transmission and evolution of hvKp.

Materials and Methods

A retrospective study focused on Kp infection was conducted. Clinical data were collected from electronic medical records. Whole-genome sequencing of Kp strains was performed. Single-nucleotide polymorphisms (SNPs) were analyzed and a transmission map was constructed. Sequence type, and antimicrobial and virulence-associated genes were characterized. Strains with some combination of the virulence genes, _prmpA, _prmpA2, iucA, iroB, and peg-344, were defined as hvKp. Kp virulence phenotypes were evaluated using the Galleria mellonella model.

Results

All 33 Kp strains were MDR-Kp and 13 (39.4%) were hvKp. Most hvKp strains (84.6%, 11/13) were hospital-acquired infections (HAIs). Two unique combinations of virulence-associated genes were detected among hvKp strains. Eleven cases were associated with _prmpA2+iucA and two strains presented with peg-344+_prmpA+_prmpA2+iucA. Surprisingly, two community-acquired MDR-hvKp infection cases were identified. Eight hvKp strains (61.5%, 8/13) exhibited a hypervirulent phenotype in the G. mellonella model. Five MDR-hvKp strains with the hypervirulence phenotype originated from a single cluster. Additionally, nine clones were identified among the two clades, six of which were hvKp. Moreover, the hvKp in clade 1 carried the IncHI1B plasmid replicon, whereas none of the hvKp strains in clade 2 harbored IncHI1B. These data, showing that different hvKp clones distributed into separate clades, indicate that transmission and evolution occurred within the hospital.

Conclusion

During inter-host evolution and transmission, various virulence clusters of the epidemic clone, MDR-ST11, converged, conferring phenotypic virulence heterogeneity and spread within the hospital and possibly the community. Mobile/conjugative genetic elements associated with virulence-encoding gene clusters might emerge and have been transmitted within the hospital, suggesting that enhanced ongoing surveillance is essential.

Dynamic Epidemiology and Virulence Characteristics of Carbapenem-Resistant Klebsiella pneumoniae in Wenzhou, China from 2003 to 2016

Purpose

To investigate transitions in resistance mechanisms, virulence characteristics and molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) during 2003–2016 in a major Eastern Chinese medical center.

Patients and Methods

From a total of 2299 K. pneumoniae clinical strains collected from 2003 to 2016, 214 were found to be CRKP isolates and were selected for further study. Characterization of these was conducted by molecular detection of antibiotic resistance markers and virulence determinants, modified carbapenem inactivation method and multilocus sequence typing (MLST).

Results

In this study, the prevalence of CRKP was increasing over the 14-year period, mirroring a national trend. These CRKP strains were resistant to most of the tested, clinically relevant drugs. The majority of these CRKP strains were positive for carbapenemases, with the Klebsiella pneumoniae carbapenemase (KPC) found to be the dominant type (207/210, 98.6%). The carrier rates of virulence genes uge, entB, fimH, mrkD and ureA increased in 2016, while the ybtA, iucA and irp2 showed a relatively constant trend. From MLST data, ST11 (88.8%, 190/214) was the preponderant sequence type (ST), followed by ST15 (1.9%, 4/214) and ST656 (1.4%, 3/214). Several strains with less common STs (ST690, ST895, ST1823 and ST1384) were also detected, and these too showed high levels of antimicrobial resistance.

Conclusion

The average national rise in CRKP across China is mirrored in this in-depth analysis of a single hospital, while the prevalence of hypervirulent CRKP (such as ST15) was relatively low as of 2016. Continuous monitoring is necessary to keep track of CRKP and should include the prospect of newly emerging strains with less common STs and the prospect of detecting carbapenem-resistant, carbapenemase-negative Klebsiella pneumoniae.

Clonal dissemination of KPC-2-producing Klebsiella pneumoniae ST11 and ST48 clone among multiple departments in a tertiary teaching hospital in Jiangsu Province, China

Background

The world-wide prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a threat to the public health. The objective of this study was to determine the epidemiological and molecular patterns of KPC-producing Klebsiella pneumoniae (K. pneumoniae) clinical isolates.

Methods

In this study, a total of 82 non-duplicated CRKP isolates were analyzed for the prevalence of resistant determinants including carbapenemase, extended spectrum β-lactamase (ESBLs), and AmpC as well as integrons and cassette regions by polymerase chain reaction (PCR) and DNA sequencing. The genetic relatedness was investigated by pulsed field gel electrophoresis (PFGE) and multi-locus sequencing typing (MLST).

Results

Overall, bla _KPC-2 (n=75) was the predominant carbapenemase gene, followed by high prevalence of bla _SHV (92.7%) and bla _CTX-M (90.2%). PFGE and MLST analysis revealed that 65 out of 68 KPC-2-producing CRKP belonged to the ST11 clone and were distributed mainly in the department of neurology ICU. Moreover, first report on clonal dissemination of KPC-2-producing CRKP ST48 clone and NDM-5-producing CRKP ST337 clone was also identified. Class I integron were detected in 17 (20.7%) of 82 isolates with aadA2 being the most common cassette. And a novel cassette array of integron, aac(6')-II-bla _CARB/PSE-1 was identified.

Conclusions

All in all, KPC-2-producing CRKP ST11 and ST48 clone were widely disseminated in multiple departments of our hospital, which triggers the need for active surveillance and implementation of infection control measures.

Phenotypic and Genotypic Characterization of Carbapenem-resistant Enterobacteriaceae: Data From a Longitudinal Large-scale CRE Study in China (2012-2016)

Background

Carbapenem-resistant Enterobacteriaceae (CRE) strains are a major threat to global health. The development of effective control measures requires more detailed phenotypic and genotypic characterization of CRE.

Methods

CRE isolates were collected from 65 hospitals in 25 provinces across China between January 1, 2012, and December 31, 2016. The isolates were characterized by antimicrobial susceptibility testing and multilocus sequence typing. Genes encoding carbapenemases, mobilized colistin resistance (mcr-1), and β-lactamases were detected by polymerase chain reaction and DNA sequencing.

Results

A total of 1801 independent CRE isolates (1201 Klebsiella pneumoniae, 282 Escherichia coli, and 179 Enterobacter cloacae) were collected during the study period. Overall, 96.9%, 89.7%, 54.5%, 49.9%, and 40% of CRE strains were susceptible to colistin, tigecycline, amikacin, minocycline, and fosfomycin, respectively. Notably, 1091/1201 (91%) K. pneumoniae, 225/282 (80%) E. coli, and 129/179 (72%) E. cloacae harbored carbapenemase gene. K. pneumoniae carbapenemase (KPC) was predominant in K. pneumoniae (77%), whereas New Delhi metallo-β-lactamase (NDM) was predominant in E. coli (75%) and E. cloacae (53%). The mcr-1 gene was detected in 13 NDM-carrying E. coli isolates (4.6%). Sequence type (ST)11 and ST167 were predominant among the 100 K. pneumoniae and 47 E. coli STs, respectively. KPC-ST11, which accounted for 64% of K. pneumoniae isolates, had higher levels of resistance than non-ST11 strains to aztreonam, fosfomycin, and amikacin (P < .001). The proportions of KPC and NDM enzymes in CRE increased from 2012 to 2016 (54%-59% and 12%-28%, respectively).

Conclusions

The number of CRE strains harboring carbapenemase is increasing. KPC-ST11 K. pneumoniae, the predominant strain, shows a reduced susceptibility to most available antibiotics.

Characterize carbapenem-resistant Klebsiella pneumoniae isolates for nosocomial pneumonia and their Gram-negative bacteria neighbors in the respiratory tract

This study was conducted to perform an epidemiological survey of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates for nosocomial pneumonia (NP) and visit their Gram-negative bacteria neighbors (GNNs) from the respiratory tracts. Pulsed-field gel electrophoresis and multi locus sequence typing were performed to evaluate the clonal relationships of these isolates. Statistical methods were then used to understand their possible relationship between CRKP and their GNNs. Among the 63 CRKP isolates, 84.1% produced a KPC-2 carbapenemase gene, followed by blaNDM-1 and blaIMP-38 like. 13 different STs and 29 clones were identified. Less heterogeneous clone backgrounds were observed in 53 KPC-2 K. pneumoniae isolates, and 6 STs have been found to contain KPC-2, of which the predominant ST11 harbored 47 KPC-2-producing K. pneumoniae isolates. Particularly, the two infrequent isolates co-possessing blaKPC-2 and blaIMP-38 like shared a different clonal relationship. 87 GNNs isolates of CRKP were established, the analysis present that different strains showed significant or no difference with CRKP upon antibiotics susceptibility. Conclusion, ST11 harboring KPC-2-producing K. pneumoniae isolates were dominant for NP, and both clonal spread and horizontal transfer contributed to the dissemination of CRKP. However, additional studies are needed to explore the biological relationship with their GNNs.

Molecular Characterization of Extended Spectrum β-lactamase and Carbapenemase Producing Klebsiella pneumoniae from a Tertiary Care Hospital

Objective

The extended-spectrum beta-lactamase (ESBL) and carbapenemase producing gram-negative bacteria among the members of Enterobacteriaceae are of major health concern globally. The present study was carried out to determine proportion and genetic characterization of ESBL and carbapenemase producing Klebsiella pneumoniae strains isolated from intensive care units of a tertiary care hospital.

Materials and methods

A total of 250 non-duplicate K. pneumoniae isolates were recovered from various clinical specimens from our intensive care units from May 2014 to May 2015. Antibiotic susceptibility testing was performed as recommended by Clinical and Laboratory Standard Institute. Phenotypic identification of ESBL and carbapenemase producing isolates were confirmed by the double-disk synergy test, modified Hodge test, imipenem and imipenem-EDTA combined test, respectively. Molecular characterization of β-lactamase genes were performed by polymerase chain reaction.

Results

Out of 250 Klebsiella pneumonaie, 84% isolates were ESBL producers, 66% were carbapenem resistant based on their reduced susceptibility to imipenem, meropenem and ertapenem. Among these 165 carbapenem resistant isolates, 9.7% were positive for bla_NDM-1 and these isolates were also found to be positive for one or more bla genes. Co-carriage of AmpC in ESBL and carbapenem resistant isolates were 7.8% and 3.6%, respectively and were negative for bla_KPC genes.

Conclusion

The study indicated the prevalence of ESBLs and bla_NDM-1, with additional bla genes and AmpC among the K. pneumoniae isolates in our intensive care units. NDM-1 producing Enterobacteriaceae is a growing health care problem. Detection of the prevalence of antibacterial resistance pattern helps towards improved antibiotic policy and empirical antibiotic treatment.

How to cite this article

Beena HB, Shenoy SM, et al. Molecular Characterization of Extended Spectrum β-lactamase and Carbapenemase Producing Klebsiella pneumoniae from a Tertiary Care Hospital. Indian J of Crit Care Med 2019;23(2):61-66.

Characterization of the population structure, drug resistance mechanisms and plasmids of the community-associated Enterobacter cloacae complex in China

Objectives

To investigate the population structure, drug resistance mechanisms and plasmids of community-associated Enterobacter cloacae complex (CA-ECC) isolates in China.

Methods

Sixty-two CA-ECC isolates collected from 31 hospitals across China were typed by hsp60 typing and MLST. ESBL and AmpC-overexpression phenotype was determined by double-disc synergy test. Replicon typing and conjugation were performed for plasmid analysis. All ESBL-positive isolates and representative conjugants were subjected to detailed characterization by WGS.

Results

Enterobacter hormaechei and Enterobacter kobei were predominant in our collections. MLST distinguished 46 STs with a polyclonal structure. ST591 was the most prevalent clone detected in northern China. Twenty-two isolates (35.5%) were ESBL positive and half of them were E. kobei. ESBL positivity was related to ESBL production (15/22) and to AmpC overexpression (18/22). Core-genome phylogenetic analysis identified intra- and inter-regional dissemination of ESBL-producing E. kobei clones. ESBL producers were exclusively classified as E. hormaechei and E. kobei, and blaCTX-M-3 was the most prevalent ESBL genotype (10/15) detected in four different environments. In the ESBL-positive population, the ESBL producers encoded more drug resistance genes (8-24 genes) by carrying more plasmids (1-3 plasmids) than the non-ESBL-producing isolates, resulting in an inter-group difference in drug susceptibilities. IncHI-type plasmids were prevalent in the ESBL producers (12/15). All IncHI2-type plasmids (n = 11) carried ESBL genes and shared a similar backbone to p09-036813-1A_261 recovered from Salmonella enterica in Canada.

Conclusions

The species-specific distribution, species-dependent ESBL mechanism and endemic plasmids identified in our study highlight the necessity for tailored surveillance of CA-ECC in the future.

Comparative Evaluation of Four Phenotypic Methods for Detection of Class A and B Carbapenemase-Producing Enterobacteriaceae in China

The objective of this study was to evaluate the performance of four phenotypic methods in the detection of carbapenemase-producing Enterobacteriaceae (CPE) in China. We evaluated the performance of four carbapenemase detection methods, the modified Hodge test (MHT), the Carba NP test, the meropenem hydrolysis assay (MHA) with 1- and 2-h incubation, and the modified carbapenem inactivation method (mCIM) with meropenem, imipenem, and ertapenem, on 342 carbapenem-resistant Enterobacteriaceae isolates (CRE) in China. PCR was used as the gold standard. The 2-h-incubation MHA performed the best in carbapenemase detection (overall sensitivity, specificity, positive predictive value, and negative predictive value all 100%). Second was the Carba NP test, with a sensitivity of 99.6%. The 1-h-incubation MHA performed poorly in Klebsiella pneumoniae carbapenemase (KPC) detection (sensitivity, 71.3%). For mCIM, the best performance was observed with the meropenem disk. The MHT exhibited the worst performance, with a specificity of 88.8%. All assays except 1-h-incubation MHA, which failed to identify 68 KPC-2s, had a sensitivity of >98% in the detection of 172 KPCs. Likewise, all assays had a sensitivity of >95% in the detection of 70 class B carbapenemases, except for MHT (82.9%). The 2-h-incubation MHA significantly improved the accuracy in CPE detection compared with that for 1-h incubation and performed the best in the detection of class A and B carbapenemases. Our findings suggest that the MHA is the most practical assay for carbapenemase detection. For those who cannot afford the associated equipment, both the Carba NP test and mCIM are good alternatives with regard to the practical requirements of time and cost.

Carbapenem Nonsusceptible Klebsiella pneumoniae in Taiwan: Dissemination and Increasing Resistance of Carbapenemase Producers During 2012-2015

Before 2011, the prevalence rates of carbapenemase-producing Klebsiella pneumoniae (CPKP) among carbapenem nonsusceptible K. pneumoniae (CnSKP) isolates were below 10% in Taiwan. The study presents the dissemination and increased antimicrobial resistance of CPKP from January 2012 to August 2015, as shown by Taiwanese multicenter surveillance. Isolates with minimum inhibitory concentrations (MICs) of >1 μg/mL for imipenem or meropenem were collected, screened for various carbapenemase genes by PCR, and tested for antimicrobial susceptibility. Among 1,457 CnSKP isolates, 1,250 were collected from medical centers. The CnSKP prevalence in medical centers increased by 1.7-fold during the study. Among all CnSKP isolates, 457 were CPKP. The CPKP rate among CnSKP increased by 1.5-fold and reached 36.8% in 2015. The CPKP nonsusceptibility rate to aztreonam, fluoroquinolones, and aminoglycosides increased yearly. Six CPKP isolates carried dual carbapenemase genes. Three Ambler classes were identified in 451 isolates with a single carbapenemase: classes A (315 blaKPC-2, 2 blaKPC-3, 28 blaKPC-17, 2 blaKPC-34), B (26 blaIMP-8, 2 blaNDM-1, 36 blaVIM-1), and D (40 blaOXA-48). The blaOXA-48 rate among CPKP increased by 6-fold over three years. Most KPC and OXA-48 producers were ST11. CnSKP was increasingly prevalent, owing to CPKP dissemination. Additionally, CPKP became more resistant during the study period.

Multi-level analysis of bacteria isolated from inpatients in respiratory departments in China

Background

With the different situation for clinical antibiotic usage and its management in different regions and medical institutions, the antimicrobial resistance varied in different level. However, the epidemiological data of multi-drug resistant (MDR) strains from the department of respiration is limited. Thus, this study aims to investigate the epidemiology of bacteria isolated from inpatients of respiratory departments, and analyze the distribution variation of major multi-drug resistant bacteria in China.

Methods

Based on data from China Antimicrobial Resistance Surveillance System (CARSS) in 2015, 50,417 non-duplicate isolates obtained from inpatients of respiratory departments from 91 general hospitals in seven regions of China were enrolled in the study. The distribution of methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Escherichia coli (CREC) and Klebsiella pneumoniae (CRKP), carbapenem-resistant Pseudomonas aeruginosa (CRPA) and Acinetobacter baumannii (CRAB), extended-spectrum β-lactamases-producing E. coli (ESBL-EC) and K. pneumoniae (ESBL-KP), were further analyzed by geographic regions, age groups, wards and specimen types.

Results

The major specimens type were sputum (81.6%, 41,131/50,417), followed by blood (5.3%, 2,649/50,417), urine (4.5%, 2,249/50,417) and bronchoalveolar lavage fluid (BALF) (3.2%, 1,620/50,417). The top four bacteria species isolated from sputum and BALF were similar: K. pneumonia (18.9% and 14.8%, respectively), P. aeruginosa (13.6% and 22.2%, respectively), A. baumannii (11.3% and 11.9%, respectively) and S. pneumonia (11.1% and 9.6%, respectively). The four most common bacteria species were K. pneumonia (17.2%), P. aeruginosa (12.1%), A. baumannii (10.4%) and S. pneumonia (10.1%) in tertiary hospitals but K. pneumonia (20.8%), P. aeruginosa (16.3%), E. coli (11.3%) and A. baumannii (6.9%) in secondary hospitals. The top four bacteria species in respiratory intensive care unit (RICU) were A. baumannii (25.8%), P. aeruginosa (13.1%), K. pneumonia (12.2%) and S. aureus (9.2%). The prevalence of CRKP, CRPA and CRAB in tertiary hospitals was significantly higher than that in secondary hospitals (5.2% vs. 2.5%, 23.8% vs. 12.8% and 53.5% vs. 33.9%, respectively) (all P<0.05). However, the prevalence of ESBL-EC in secondary hospitals was higher than in tertiary ones (63.9% vs. 55.0%, P=0.011). The prevalence of MRSA, CRKP, CRAB, CRPA, ESBL-EC, ESBL-KP in RICU were higher than that in non-ICU respiratory departments (76.5% vs. 35.7%, 20.1% vs. 4.1%, 90.6% vs. 45.5%, 64.2% vs. 19.3%, 47.2% vs. 28.3% and 43.0% vs. 11.2%, respectively) (all P<0.01). Among seven regions in China, central area had the highest detection rates of MRSA (70.3%, 237/337), CRPA (30.9%, 376/1,218), CRAB (71.8%, 487/678) and ESBL-KP (38.8%, 241/621). The prevalence of ESBL-EC and ESBL-KP in pediatric group (68.2% and 55.3%, respectively) was higher than that in geriatric group (54.2% and 27.1%, respectively) and adult group (51.1% and 15.1%, respectively) (all P<0.001).

Conclusions

In China, the predominant bacterial pathogens in the respiratory ward were Enterobacteriaceae and non-fermentative bacteria. High prevalence of ESBL-EC and ESBL-KP isolated from lower respiratory tract (LRT) was revealed in primary hospitals and pediatric patients.

Emergence and mechanism of carbapenem-resistant Escherichia coli in Henan, China, 2014

The emergence and dissemination of carbapenem-resistant Escherichia coli (E. coli) strains is a main risk for global public health, but little is known of carbapenemase producing E. coli in Henan, China. The study was undertaken to investigate the prevalence and mechanism of carbapenem-resistant E. coli strains in a hospital in Xinxiang, Henan, China, 2014. A total of 5 carbapenemase-producing E. coli strains were screened from 1014 isolates. We found that they were all resistant to meropenem and imipenem. Amikacin showed the best sensitivity, with gentamicin coming up next. The positive rate of blaNDM was 80% (4/5). The sequencing results showed that two isolates belonged to blaNDM-1 whereas other 2 isolates carried the blaNDM-5. Other carbapenemase genes including blaIMP,blaVIM, blaKPC and blaOXA-48 were not detected. The blaCTX-M-15,blaTEM-1,sul2, aad, and aac(6")-Ib-cr were also detected. MLST analysis showed that NDM-producing E. coli were sporadic. Conjugation test indicated blaNDM could be transferred. In conclusion, the blaNDM was the principal resistance mechanism of carbapenem-resistant E. coli in the hospital, Henan, China.

Antimicrobial Resistance of Hypervirulent Klebsiella pneumoniae: Epidemiology, Hypervirulence-Associated Determinants, and Resistance Mechanisms

Klebsiella pneumoniae is one of the most clinically relevant species in immunocompromised individuals responsible for community-acquired and nosocomial infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Since the mid-1980s, hypervirulent K. pneumoniae, generally associated with the hypermucoviscosity phenotype, has emerged as a clinically significant pathogen responsible for serious disseminated infections, such as pyogenic liver abscesses, osteomyelitis, and endophthalmitis, in a generally younger and healthier population. Hypervirulent K. pneumoniae infections were primarily found in East Asia and now are increasingly being reported worldwide. Although most hypervirulent K. pneumoniae isolates are antibiotic-susceptible, some isolates with combined virulence and resistance, such as the carbapenem-resistant hypervirulent K. pneumoniae isolates, are increasingly being detected. The combination of multidrug resistance and enhanced virulence has the potential to cause the next clinical crisis. To better understand the basic biology of hypervirulent K. pneumoniae, this review will provide a summarization and discussion focused on epidemiology, hypervirulence-associated factors, and antibiotic resistance mechanisms of such hypervirulent strains. Epidemiological analysis of recent clinical isolates in China warns the global dissemination of hypervirulent K. pneumoniae strains with extensive antibiotic resistance in the near future. Therefore, an immediate response to recognize the global dissemination of this hypervirulent strain with resistance determinants is an urgent priority.

Characterization of OXA-48-like-producing Enterobacteriaceae isolated from river water in Algeria

The spread of carbapenemase-producing Enterobacteriaceae (CPE) is a significant problem for healthcare worldwide. The prevalence of carbapenem-resistant Enterobacteriaceae (CPE) in water environments in Algeria are unknown. The aim of this study was to screen for the presence of CPE isolates in the Soummam River in Bejaia, Algeria. Isolates of Enterobacteriaceae recovered from twelve samples of river water and showing reduced susceptibility to carbapenems were included in this study. The isolates were identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Isolates were subjected to antimicrobial susceptibility testing and the modified Carba NP test. Carbapenemase and extended-spectrum β-lactamase (ESBL) determinants were studied by PCR amplification and sequencing. The clonal relatedness between isolates was studied by Multilocus Sequence Typing (MLST) method. A total of 20 carbapenem-resistant Enterobacteriaceae strains were included in this study, identified as Escherichia coli (n = 12), Klebsiella pneumoniae (n = 3), Raoultella ornithinolytica (n = 3), Citrobacter freundii (n = 1) and Citrobacter braakii (n = 1). Carbapenemase genes identified in this study included bla_OXA-48, observed in 17 isolates (9 E. coli, 3 K. pneumoniae, 3 R. ornithinolytica, 1 C. freundii and 1 C. braakii), and bla_OXA-244, a variant of bla_OXA-48, was found in three E. coli isolates. MLST showed that 12 E. coli strains belonged to six different sequence types (ST559, ST38, ST212, ST3541, 1972 and ST2142), and we identified three different STs in K. pneumoniae isolates, including ST133, ST2055, and a new sequence type: ST2192. This study showed the presence of OXA-48-like-producing Enterobacteriaceae in water environments and highlighted the potential role of aquatic environments as reservoirs of clinically relevant antimicrobial-resistant bacteria, with the potential to spread throughout the community.

Molecular characterization of clinical IMP-producing Klebsiella pneumoniae isolates from a Chinese Tertiary Hospital

BACKGROUND

IMP-producing Klebsiella pneumoniae (IMPKpn) exhibits sporadic prevalence in China. The mechanisms related to the spread of IMPKpn remain unclear.

METHODS

Carbapenem non-susceptible K. pneumoniae isolates were collected from our hospital. The genetic relatedness, antimicrobial susceptibility, as well as sequence types (ST) were analyzed by pulsed-field gel electrophoresis (PFGE), VITEK 2 AST test Kit, and multilocus sequence typing (MLST), respectively. S1-PFGE, Southern blot analysis and multiple PCR amplification were used for plasmid profiling.

RESULTS

Between October 2009 and June 2016, 25 non-repetitive IMPKpn isolates were identified. PFGE results showed that these isolates belonged to 20 genetically unrelated IMPKpn strains. Diverse STs were identified by MLST. Most strains carried bla IMP-4, followed by bla IMP-1. Four incompatibility types of bla IMP-carrying plasmids were identified, which included A/C (n = 2), B/O (n = 2), L/M (n = 1) and N (n = 14), while type of other one plasmid failed to be determined.

CONCLUSIONS

The IMPKpn isolates exhibited sporadic prevalence in our hospital. IncN types of plasmids with various sizes have emerged as the main platform mediating the spread of the bla IMP genes in our hospital.

Epidemiology of Carbapenem-Resistant Klebsiella pneumoniae Bloodstream Infections in a Chinese Children's Hospital: Predominance of New Delhi Metallo-β-Lactamase-1

The spread of carbapenem-resistant Klebsiella pneumoniae (CRKp) has become a significant problem worldwide; however, relevant data in children are limited. We performed a retrospective study to better understand the epidemiology of CRKp bloodstream infections at Beijing Children's Hospital. A total of 164 K. pneumoniae strains were collected from blood cultures between January 2011 and September 2014, of which 52 (31.7%) were CRKp strains. All 52 CRKp strains were multidrug resistant; 46 (88.5%) and 49 (94.2%) isolates were resistant to meropenem and imipenem, respectively. Low rates of resistance to amikacin (5.8%), levofloxacin (7.7%), and ciprofloxacin (15.4%) were observed. All isolates were susceptible to colistin. Among the tested carbapenem resistance genes, the predominant gene was bla_NDM-1, detected in 28 (53.8%) isolates, followed by bla_IMP-4 (19, 36.5%) and bla_KPC-2 (4, 7.7%). Multilocus sequence typing identified 31 sequence types (STs), the most predominant of which was ST782 (9, 29.0%). All ST782 strains were New Delhi metallo-β-lactamase-1 (NDM-1) producing. Four novel STs (ST2010, ST2011, ST2012, and ST2013) and two novel alleles (phoE243 and tonB324) were also detected. Hematologic disease was the most common underlying disease (73.1%). All children received initial empirical therapy. A total of 59.6% (31/52) patients received inappropriate empirical therapy, and 45.2% (14/31) changed antimicrobial therapy after blood culture results were obtained. The overall mortality rate was 11.5%. In conclusion, we observed a high rate of CRKp isolates collected from blood cultures and the predominance of NDM-1-producing K. pneumoniae among children from 2011 to 2014.

Outbreak by Hypermucoviscous Klebsiella pneumoniae ST11 Isolates with Carbapenem Resistance in a Tertiary Hospital in China

Hypervirulent and multidrug resistant Klebsiella pneumoniae strains pose a significant threat to the public health. In the present study, 21 carbapenem-resistant K. pneumoniae isolates (CRKP) were determined by the string test as hypermucoviscous K. pneumoniae (HMKP), with the prevalence of 15.0% (21/140) among CRKP, and 1.1% (21/1838) among all K. pneumoniae isolates. Among them, 7 (33.3%), and 1 (4.76%) isolate belonged to capsular serotype K20 and K2 respectively, while 13 (61.9%, 13/21) weren't successfully typed by capsular serotyping. All the 21 isolates were carbapenemase-producers and were positive for bla_KPC-2. In addition to bla_KPC-2, all the 21 isolates except one harbor bla_SHV-11, and 15 carry extended-spectrum β-lactamase gene bla_CTX-M-65. The virulence-associated genes with more than 90% of positive rates among 21 isolates included ureA (100%, 21/21), wabG (100%, 21/21), fimH (95.2%, 20/21), entB (95.2%, 20/21), ycf (95.2%, 20/21), ybtS (95.2%, 20/21), and iutA (90.5%, 19/21). rmpA and aerobactin were found in 57.1% (12/21) isolates. Five sequence types (STs) were identified by multilocus sequence typing (MLST), including ST11 (11 K-non capsule typable and 5 K20 isolates), ST268 (1 K20 isolate and 1 K-non capsule typable isolate), ST65 (1 K2 isolate), ST692 (1 K-non capsule typable isolate), and ST595, a novel sequence type (1 K-non capsule typable isolate). Pulsed-field gel electrophoresis (PFGE) results showed two major PFGE clusters, of which cluster A accounts for 6 ST11 isolates (28.6%) and cluster B includes 8 ST11 isolates (38.1%, 8/21). Ten and six ST11 isolates were isolated from 2014 and 2015, respectively, while 8 were isolated from the same month of December in 2014. Ten isolates were collected from the intensive care unit (ICU), and all except one belonged to ST11. Additional 4 ST11 isolates were collected from patients in non-ICU wards, who had more than 10 days of ICU stay history in 2014 prior to transfer to their current wards where the isolates were recovered. Taken together, the present study showed a hospital outbreak and dissemination of ST11 HMKP with carbapenem resistance caused by KPC-2. Effective surveillance and strict infection control strategies should be implemented to prevent outbreak by HMKP with carbapenem resistance in hospitals.

Genome sequencing and comparative analysis of an NDM-1-producing Klebsiella pneumoniae ST15 isolated from a refugee patient

The escalating problem of antibiotic resistance, specifically cabarpenemase and extended-spectrum β-lacatamase (ESBL) producing K. pneumoniae strains, is directly correlated with increased patient morbidity and mortality and prolonged hospitalization and costs. In this study, a comprehensive genomic analysis encompassing the resistomics, virulence repertoire and mobile genetic elements of an NDM-1 positive ESBL-producing K. pneumoniae EA-MEH ST15 isolated from a urine sample collected from a Syrian refugee was conducted. Illumina paired-end libraries were prepared and sequenced resulting in 892,300 high-quality reads. The initial assembly produced 329 contigs with a combined 5,954,825 bp and a 56.5% G+C content. Resistome analysis revealed the presence of several β-lactamases including NDM-1, SHV-28, CTX-M-15 and OXA-1 in addition to 18 other genes encoding for resistance, among which are aph(3')-Ia, aac(6')Ib-cr, armA, strB, strA and aadA2 genes. Additionally, five plasmids IncFIB(Mar), IncHI1B, IncFIB(pKPHS1), IncFIB(K) and IncFII(K) and four integrated phages were detected. In silico MLST analysis revealed that the isolate was of sequence type ST15. To our knowledge this is the first in-depth genomic analysis of a NDM-1 positive K. pneumoniae ST15 in Lebanon associated with the recent population migration. The potential dissemination of such MDR strains is an important public health concern.

Implications of direct amplification for measuring antimicrobial resistance using point-of-care devices

Antimicrobial resistance (AMR) is recognized as a global threat to human health. Rapid detection and characterization of AMR is a critical component of most antibiotic stewardship programs. Methods based on amplification of nucleic acids for detection of AMR are generally faster than culture-based approaches but they still require several hours to more than a day due to the need for transporting the sample to a centralized laboratory, processing of sample, and sometimes DNA purification and concentration. Nucleic acids-based point-of-care (POC) devices are capable of rapidly diagnosing antibiotic-resistant infections which may help in making timely and correct treatment decisions. However, for most POC platforms, sample processing for nucleic acids extraction and purification is also generally required prior to amplification. Direct amplification, an emerging possibility for a number of polymerases, has the potential to eliminate these steps without significantly impacting diagnostic performance. This review summarizes direct amplification methods and their implication for rapid measurement of AMR. Future research directions that may further strengthen the possibility of integrating direct amplification methods with POC devices are also summarized.

Molecular Characteristics of Carbapenem-Resistant Enterobacter cloacae in Ningxia Province, China

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has become a major public health concern worldwide and a new challenge in the treatment of infectious diseases. The molecular characteristics of Enterobacter cloacae in Ningxia China are unknown. In this study, we reported 10 carbapenem-resistant E. cloacae isolates from the General Hospital of Ningxia Medical University, the largest university hospital in Ningxia between January 2012 and December 2013. Bacteria isolates were identified by Vitek2 compact and the identity of non-duplicate E. cloacae isolates was further confirmed by PCR and sequencing. The drug susceptibility and phenotype identification of these isolates were analyzed by agar dilution method, modified Hodge test (MHT), and EDTA synergy test. Beta-lactamase (bla) genes bla_NDM−1 was found in 8 out of 10 isolates. Most isolates harbored multiple resistance genes including bla_ESBL, bla_AmpC, quinolones, aminoglycosides, and disinfectant resistance genes. Pulsed field gel electrophoresis (PFGE) showed that these E. cloacae isolates were grouped into 6 clusters based on a cutoff of 80% genetic similarity. In conjugative assay, 9 out of 10 isolates transferred carbapenem-resistant genes to Escherichia coli. Our study has revealed that NDM-1-producing isolates are the most prevalent carbapenem-resistant E. cloacae in Ningxia. These isolates also carry several other carbapenem-resistant genes and can transfer these genes to other bacteria through conjugation. These findings highlight an urgent need to monitor these isolates to prevent their further spread in this region.

Outbreak of nosocomial NDM-1-producing Klebsiella pneumoniae ST1419 in a neonatal unit

OBJECTIVES

The aim of this study was to characterise carbapenem-resistant Klebsiella pneumoniae isolates recovered from neonatal clinical specimens over a 4-month period.

METHODS

Seven carbapenem-resistant K. pneumoniae isolates were analysed. Antibiotic susceptibilities of the isolates were determined by the agar dilution method, and the drug resistance genes were evaluated by PCR. Clonal relatedness of the isolates was assessed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Conjugation experiments and Southern blot hybridisation were performed to determine the transferability of the plasmids.

RESULTS

All of the K. pneumoniae isolates carried the bla_NDM-1 gene but were negative for all other carbapenemases tested. All of the isolates harboured bla_SHV-12, and five isolates also carried bla_CTX-M-15 and/or bla_TEM-1. All of the isolates exhibited multidrug resistance. The isolates belonged to sequence types ST1419 and ST101 and formed three different PFGE patterns. Plasmids carrying bla_NDM-1 were successfully transferred from six of the seven isolates to the Escherichia coli recipient. These six NDM-1-producing K. pneumoniae were clonal and carried bla_NDM-1 on the same plasmid, but one isolate possibly carried chromosomal bla_NDM-1.

CONCLUSIONS

This is the first report of NDM-1-positive K. pneumoniae ST1419 from neonates in China. Closer attention should be paid to monitoring bla_NDM-1 gene dissemination because it is potentially transferred horizontally.

Performance evaluation of three automated identification systems in detecting carbapenem-resistant Enterobacteriaceae

Background

Carbapenem-resistant Enterobacteriaceae (CRE) is prevalent around the world. Rapid and accurate detection of CRE is urgently needed to provide effective treatment. Automated identification systems have been widely used in clinical microbiology laboratories for rapid and high-efficient identification of pathogenic bacteria. However, critical evaluation and comparison are needed to determine the specificity and accuracy of different systems. The aim of this study was to evaluate the performance of three commonly used automated identification systems on the detection of CRE.

Methods

A total of 81 non-repetitive clinical CRE isolates were collected from August 2011 to August 2012 in a Chinese university hospital, and all the isolates were confirmed to be resistant to carbapenems by the agar dilution method. The potential presence of carbapenemase genotypes of the 81 isolates was detected by PCR and sequencing. Using 81 clinical CRE isolates, we evaluated and compared the performance of three automated identification systems, MicroScan WalkAway 96 Plus, Phoenix 100, and Vitek 2 Compact, which are commonly used in China. To identify CRE, the comparator methodology was agar dilution method, while the PCR and sequencing was the comparator one to identify CPE.

Results

PCR and sequencing analysis showed that 48 of the 81 CRE isolates carried carbapenemase genes, including 23 (28.4 %) IMP-4, 14 (17.3 %) IMP-8, 5 (6.2 %) NDM-1, and 8 (9.9 %) KPC-2. Notably, one Klebsiella pneumoniae isolate produced both IMP-4 and NDM-1. One Klebsiellaoxytoca isolate produced both KPC-2 and IMP-8. Of the 81 clinical CRE isolates, 56 (69.1 %), 33 (40.7 %) and 77 (95.1 %) were identified as CRE by MicroScan WalkAway 96 Plus, Phoenix 100, and Vitek 2 Compact, respectively. The sensitivities/specificities of MicroScan WalkAway, Phoenix 100 and Vitek 2 were 93.8/42.4 %, 54.2/66.7 %, and 75.0/36.4 %, respectively.

Conclusions

The MicroScan WalkAway and Viteck2 systems are more reliable in clinical identification of CRE, whereas additional tests are required for the Pheonix 100 system. Our study provides a useful guideline for using automated identification systems for CRE identification.

Emergence and characterization of tigecycline resistance in multidrug-resistant Klebsiella pneumoniae isolates from blood samples of patients in intensive care units in northern China

Serious infections in intensive care unit patients caused by multidrug-resistant (MDR) Klebsiella pneumoniae represent a major threat worldwide owing to increased mortality and limited treatment options. With the application of tigecycline for MDR pathogens, tigecycline-non-susceptible K. pneumoniae isolates have recently emerged in China. To identify the susceptibility profile of MDR K. pneumoniae to tigecycline and evaluate the molecular characterization of tigecycline resistance, 214 MDR K. pneumoniae isolates were collected from blood samples of patients in intensive care units. MICs and clonal relatedness were determined by standard broth microdilution and multilocus sequence typing, respectively. Expression levels of efflux pumps and their global regulators were examined using real-time PCR. Mutations of local repressor were identified by PCR and sequencing. Our results show that the tigecycline resistance rate of 214 MDR K. pneumoniae isolates was 6.07 %. ST11 was the predominant clone type of tigecycline-non-susceptible K. pneumoniae isolates. Expression of efflux pump AcrB and global regulator RamA correlated with tigecycline MICs (AcrB: x2=8.91, P=0.03; RamA: x2=13.91, P<0.01), and mean expression levels of AcrB for the MICs ≥4 mg l-1 were significantly higher than MICs ≤2 mg l-1 (t=2.48, P=0.029). In addition, one tigecycline-resistant isolate harboured a deletion mutation in the ramR gene. These data indicated a linear correlative trend for overexpression of the AcrB and the tigecycline MICs resulting from the upregulation of RamA. The emergence of molecular type ST11 of MDR K. pneumoniae isolates should be monitored to identify factors that contribute to tigecycline resistance in intensive care units.

Global Dissemination of Carbapenemase-Producing Klebsiella pneumoniae: Epidemiology, Genetic Context, Treatment Options, and Detection Methods

The emergence of carbapenem-resistant Gram-negative pathogens poses a serious threat to public health worldwide. In particular, the increasing prevalence of carbapenem-resistant Klebsiella pneumoniae is a major source of concern. K. pneumoniae carbapenemases (KPCs) and carbapenemases of the oxacillinase-48 (OXA-48) type have been reported worldwide. New Delhi metallo-β-lactamase (NDM) carbapenemases were originally identified in Sweden in 2008 and have spread worldwide rapidly. In this review, we summarize the epidemiology of K. pneumoniae producing three carbapenemases (KPCs, NDMs, and OXA-48-like). Although the prevalence of each resistant strain varies geographically, K. pneumoniae producing KPCs, NDMs, and OXA-48-like carbapenemases have become rapidly disseminated. In addition, we used recently published molecular and genetic studies to analyze the mechanisms by which these three carbapenemases, and major K. pneumoniae clones, such as ST258 and ST11, have become globally prevalent. Because carbapenemase-producing K. pneumoniae are often resistant to most β-lactam antibiotics and many other non-β-lactam molecules, the therapeutic options available to treat infection with these strains are limited to colistin, polymyxin B, fosfomycin, tigecycline, and selected aminoglycosides. Although, combination therapy has been recommended for the treatment of severe carbapenemase-producing K. pneumoniae infections, the clinical evidence for this strategy is currently limited, and more accurate randomized controlled trials will be required to establish the most effective treatment regimen. Moreover, because rapid and accurate identification of the carbapenemase type found in K. pneumoniae may be difficult to achieve through phenotypic antibiotic susceptibility tests, novel molecular detection techniques are currently being developed.

Treatment options for infections caused by carbapenem-resistant Enterobacteriaceae: can we apply "precision medicine" to antimicrobial chemotherapy?

INTRODUCTION

For the past three decades, carbapenems played a central role in our antibiotic armamentarium, trusted to effectively treat infections caused by drug-resistant bacteria. The utility of this class of antibiotics has been compromised by the emergence of resistance especially among Enterobacteriaceae.

AREAS COVERED

We review the current mainstays of pharmacotherapy against infections caused by carbapenem-resistant Enterobacteriaceae (CRE) including tigecycline, aminoglycosides, and rediscovered 'old' antibiotics such as fosfomycin and polymyxins, and discuss their efficacy and potential toxicity. We also summarize the contemporary clinical experience treating CRE infections with antibiotic combination therapy. Finally, we discuss ceftazidime/avibactam and imipenem/relebactam, containing a new generation of beta-lactamase inhibitors, which may offer alternatives to treat CRE infections. We critically evaluate the published literature, identify relevant clinical trials and review documents submitted to the United States Food and Drug Administration.

EXPERT OPINION

Defining the molecular mechanisms of resistance and applying insights about pharmacodynamic and pharmacokinetic properties of antibiotics, in order to maximize the impact of old and new therapeutic approaches should be the new paradigm in treating infections caused by CRE. A concerted effort is needed to carry out high-quality clinical trials that: i) establish the superiority of combination therapy vs. monotherapy; ii) confirm the role of novel beta-lactam/beta-lactamase inhibitor combinations as therapy against KPC- and OXA-48 producing Enterobacteriaceae; and, iii) evaluate new antibiotics active against CRE as they are introduced into the clinic.

Outbreak of plasmid-mediated NDM-1-producing Klebsiella pneumoniae ST105 among neonatal patients in Yunnan, China

Background

In the past decade, the carbapenemase-producing Enterobacteriaceae (CPE) have been reported worldwide. Emergence of carbapenemase-producing strains among Enterobacteriaceae has been a challenge for treatment of clinical infection. The present study was undertaken to investigate the characteristics of carbapenem-resistant Klebsiella pneumoniae recovered from an outbreak that affected 17 neonatal patients in neonatal intensive care unit (NICU) of Kunming City Maternal and Child health Hospital, which is located in the Kunming city in far southwest of China.

Methods

Minimum inhibitory concentrations (MICs) for antimicrobial agents were determined according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI); Modified Hodge test and Carba-NP test were preformed to identified the phenotypes of carbapenemases producing; To determine whether carbapenem resistance was transferable, a conjugation experiment was carried out in mixed broth cultures; Resistant genes were detected by using PCR and sequencing; Plasmids were typed by PCR-based replicon typing method; Clone relationships were analyzed by using multilocus-sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).

Results

Eighteen highly carbapenem-resistant Klebsiella pneumoniae were isolated from patients in NICU and one carbapenem-resistant K. pneumoniae isolate was detected in incubator water. All these isolates harbored bla_NDM-1. Moreover, other resistance genes, viz., bla_IMP-4, bla_SHV-1, bla_TEM-1, bla_CTX-M-15, qnrS1, qnrB4, and aacA4 were detected. The bla_NDM-1 gene was located on a ca. 50 kb IncFI type plasmid. PFGE analysis showed that NDM-1-producing K. pneumoniae were clonally related and MLST assigned them to sequence type 105.

Conclusions

NDM-1 producing strains present in the hospital environment pose a potential risk and the incubator water may act as a diffusion reservoir of NDM-1- producing bacteria. Nosocomial surveillance system should play a more important role in the infection control to limit the spread of these pathogens.

Clonal dissemination of KPC-2 producing Klebsiella pneumoniae ST11 clone with high prevalence of oqxAB and rmtB in a tertiary hospital in China: results from a 3-year period

Background

Carbapenemase-producing Klebsiella pneumoniae (CPKP) strains have emerged as a major problem for healthcare systems. The aim of this study was to determine the circulating clones and analyze the clinical and molecular characteristics of CPKP in our hospital.

Methods

A total of 74 carbapenemase producers collected from our hospital from 2012 to 2014 were analyzed for the prevalence of extended-spectrum β-lactamase (ESBLs), plasmid-mediated quinolone resistance genes (PMQRs), exogenously acquired 16S rRNA methyltransferase (16S-RMTase), and plasmid-mediated AmpC enzyme (pAmpCs) by PCR and DNA sequencing. The sequence types (STs) of the carbapenemase producers were analyzed by multi-locus sequence typing (MLST). And Pulsed-field gel electrophoresis (PFGE) was performed to investigate the genetic relationship of KPC-2 producing strains. Clinical data were retrieved from the medical records.

Results

KPC-2 (n = 72) was the predominant enzyme followed by NDM-1 (n = 2); The genes blaCTX-M, blaSHV, blaTEM-1, blaDHA-1, rmtB, armA, oqxA, oqxB, and qnrB were present in 29 (39.2 %), 27 (36.5 %), 46 (62.2 %), 2 (2.7 %), 25 (33.8 %), 1 (1.4 %), 60 (81.1 %) and 56 (75.7 %), 6 (8.1 %) isolates, respectively. MLST analysis revealed 10 different STs. The most dominant ST was ST11 (78.4 %, 58/74), followed by ST15 (8.1 %, 6/74). PFGE patterns of the KPC-2 producing K. pneumoniae isolates exhibited clonal dissemination of ST11 and ST15 clones as well as a genetic diversity of the remaining strains.

Conclusion

The intra- and inter-hospital cross-transmission of KPC-2-producing K. pneumoniae ST11 co-carrying oqxAB and rmtB in our hospital strongly suggested that rapid identification of colonized or infected patients and screening of carriers is quite necessary to prevent a scenario of endemicity.

Emergence of tigecycline- and carbapenem-nonsusceptible Klebsiella pneumoniae ST11 clone in patients without exposure to tigecycline

BACKGROUND/PURPOSE

Currently, tigecycline-nonsusceptible Klebsiella pneumoniae (TNSKP) is mainly reported to emerge following clinical use of tigecycline and is usually polyclonal. This study aimed to characterize TNSKP isolated from patients without prior tigecycline use.

METHODS

Twenty-six TNSKP clinical isolates were collected, and carbapenemase and 16S rRNA methylase genes were identified by polymerase chain reaction and sequencing. Molecular typing was conducted by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Clinical data of patients in the carbapenem-susceptible TNSKP group and the tigecycline- and carbapenem-nonsusceptible K. pneumoniae (TCNSKP) group were compared.

RESULTS

Of the 26 TNSKP isolates, eight contained both bla_KPC-2 and 16S rRNA methylase genes. In the remaining 18 TNSKP isolates, no carbapenemase gene was detected, and only three had the 16S rRNA methylase gene. Among the 26 isolates, 24 distinct pulsotypes and 19 sequence types (STs) were identified by PFGE and MLST, respectively. Six of the eight TCNSKP were ST11, whereas the remaining 18 TNSKP isolates were assigned to 17 different STs. No patient received tigecycline prior to the isolation of TNSKP. By comparison, intensive care unit exposure, mechanical ventilation, prior β-lactam/β-lactamase use, and longer hospitalization were more common for the TCNSKP group than for the carbapenem-susceptible TNSKP group.

CONCLUSION

TNSKP can occur without tigecycline use, and TCNSKP ST11 is predominant among them. Further, this report proposes potential risk factors for the occurrence of carbapenem-nonsusceptibility in TNSKP.

Emergence of KPC-2-producing Escherichia coli isolates in an urban river in Harbin, China

Three KPC-2-producing Escherichia coli (E1, E2, and E3) were recovered from water samples of an urban river in the city of Harbin, China. Antimicrobial susceptibility was determined by broth microdilution. Molecular characterization and genetic relatedness of the isolates were determined by polymerase chain reaction (PCR), pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST) and PCR-directed phylotyping. Plasmids were analyzed by conjugation, S1-PFGE, Southern blotting and PCR-based replicon typing (PBRT). The genetic environment of the bla KPC-2 gene was determined using PCR and sequencing. PCR analyses revealed that the E1 isolate carried the bla KPC-2, bla CMY-2, bla TEM-1, bla CTX-M-14, and qnrB2 genes and belonged to sequence type ST410, phylogenetic type A; the E2 isolate was assigned to ST131-B2 and carried the bla KPC-2, bla TEM-1, bla CTX-M-3, bla DHA-1, aac(6')-Ib-cr, and qnrS1 genes; while the E3 isolate was of ST648-D and possessed bla KPC-2, bla TEM-1, bla OXA-1, bla CTX-M-15, armA, and aac(6')-Ib-cr genes. PFGE demonstrated that each of the three KPC-2-producing E. coli isolates exhibited an individual XbaI patterns. The bla KPC-2 gene was located on plasmids of 60-140 kb with IncA/C, IncN, or non-typeable replicon types. The genetic environment of bla KPC-2 of the three strains was consistent with the genetic structure of bla KPC-2 on the plasmid pKP048.

Comparative evaluation of tigecycline susceptibility testing methods for Acinetobacter baumannii and Enterobacteriaceae

The objectives of this study were to recommend suitable susceptibility testing methods for tigecycline for clinical laboratory use and to evaluate differences in tigecycline susceptibility between carbapenem-susceptible and carbapenem-non-susceptible isolates. Broth microdilution (BMD) was used as the reference method to evaluate MIC Test Strip (MTS), agar dilution, VITEK^® 2 and disk diffusion testing methods for tigecycline against Acinetobacter baumannii and Enterobacteriaceae. MIC_50/90 values (minimum inhibitory concentrations for 50% and 90% of the isolates, respectively) of A. baumannii and Enterobacteriaceae were, respectively, 2/4μg/mL and 0.5/4μg/mL by BMD, 1.5/3μg/mL and 0.5/3μg/mL by MTS, 2/4μg/mL and 1/8μg/mL by agar dilution and 2/4μg/mL and 2/8μg/mL by VITEK^® 2. Essential agreement for A. baumannii/Enterobacteriaceae detected by MTS, agar dilution and VITEK^® 2 methods was 96.0/97.3%, 98.0/97.3% and 94.0/63.9%, respectively. Categorical agreement for A. baumannii/Enterobacteriaceae detected by MTS, agar dilution, VITEK^® 2 and disk diffusion methods was 90.0/91.8%, 72.0/93.7%, 62.0/86.5% and 72.0/81.2%, respectively. No very major errors were found for all isolates by the four methods evaluated. Major error rates were produced by VITEK^® 2 (for Enterobacteriaceae) and by disk diffusion (for A. baumannii and Enterobacteriaceae). Tigecycline susceptibility of carbapenem-susceptible and carbapenem-non-susceptible isolates was 85.2% and 83.6% (χ²=0.15, P>0.05) using the reference method. In conclusion, in this study MTS showed the best correlation with BMD for tigecycline MICs. Based on in vitro testing, tigecycline can be considered an equally useful choice for infections caused by carbapenem-susceptible and carbapenem-non-susceptible isolates.

In Vitro Analysis of Activities of 16 Antimicrobial Agents against Gram-Negative Bacteria from Six Teaching Hospitals in China

To evaluate the in vitro antimicrobial activities of biapenem, arbekacin, and cefminox against different gram-negative bacterial isolates in China, a total of 100 non-duplicated Escherichia coli, 100 Acinetobacter baumannii, 100 Pseudomonas aeruginosa, and 99 Klebsiella pneumoniae isolates were collected from 6 teaching hospitals in China in 2012. The minimal inhibitory concentrations (MICs) of biapenem, arbekacin, cefminox and 13 other antibiotics were determined by the broth microdilution method. The carbapenems (biapenem, meropenem, and imipenem) exhibited high antimicrobial activity against E. coli (98%) and K. pneumoniae (≥95%), followed by colistin and amikacin. The MIC50 and MIC90 of biapenem against E. coli were ≤0.06 mg/L and 0.25 mg/L, respectively. For K. pneumoniae, the MIC50 and MIC90 of biapenem were 0.25 mg/L and 1.0 mg/L, respectively. The MIC50 and MIC90 of cefminox against E. coli were 1.0 mg/L and 4.0 mg/L, respectively. The resistance rates of A. baumannii to most of the antibiotics were more than 50%, except for colistin. Amikacin was the most active antibiotic against P. aeruginosa (97%), followed by colistin (93%). The MIC50 and MIC90 of arbekacin against P. aeruginosa were 2.0 mg/L and 8.0 mg/L, respectively. In conclusion, carbapenems, colistin, amikacin, and arbekacin exhibited high antimicrobial activities against gram-negative bacteria, except A. baumannii.