Carbapenemases of Chryseobacterium (Flavobacterium) meningosepticum: distribution of blaB and characterization of a novel metallo-beta-lactamase gene, blaB3, in the type strain, NCTC 10016

Rarely Encountered Gram-Negative Rods and Lung Transplant Recipients: A Narrative Review

The respiratory tract of lung transplant recipients (LTR) is likely to be colonized with non-fermentative Gram-negative rods. As a consequence of the improvements in molecular sequencing and taxonomy, an increasing number of bacterial species have been described. We performed a review of the literature of bacterial infections in LTR involving non-fermentative Gram-negative rods with exclusion of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Achromobacter spp. and Burkholderia spp. Overall, non-fermenting GNR were recovered from 17 LTR involving the following genera: Acetobacter, Bordetella, Chryseobacterium, Elizabethkinga, Inquilinus, and Pandoraea. We then discuss the issues raised by these bacteria, including detection and identification, antimicrobial resistance, pathogenesis, and cross-transmission.

A Rare Case of Elizabethkingia meningoseptica Bacteremia After Liver Transplantation

BACKGROUND Elizabethkingia meningoseptica is an emerging pathogen in hospital environments. Immunocompromised individuals have a high risk of infections caused by E. meningoseptica, especially after transplantation. E. meningoseptica is associated with prolonged hospital stays and high mortality. In addition, E. meningoseptica is commonly resistant to many antibiotics used for gram-negative bacterial infections. We introduce the first case of E. meningoseptica bacteremia in a recipient of a liver transplant in Vietnam. CASE REPORT A 55-year-old woman with end-stage liver disease due to biliary cirrhosis underwent living donor liver transplantation at the 108 Military Central Hospital. On day 3 after transplantation, the patient had an acute cellular rejection, and corticosteroid pulse therapy was used. On day 7 after transplantation, the patient had a fever and an increased white blood cell count and C-reactive protein level. Blood cultures were positive for E. meningoseptica. Intravenous levofloxacin was administered for 10 days. The patient showed an excellent treatment response to the antibiotic therapy and was discharged. CONCLUSIONS E. meningoseptica, a multidrug-resistant gram-negative bacteria, can be considered an emerging pathogen in the hospital environment, especially in patients receiving organ transplants. Early recognition helps physicians to improve patient outcomes.

Clinically relevant antibiotic-resistant bacteria in aquatic environments - An optimized culture-based approach

The emergence of antibiotic-resistant clinically relevant facultative pathogenic bacteria in the environment has become one of the most important global health challenges. Antibiotic-resistant bacteria (ARB) have been found in surface waters and wastewater treatment plants. Drinking water guidelines and the EU bathing water directive 2006/7/EC include the surveillance of defined microbiological parameters on species level, while the monitoring of ARB is missing in all existing guidelines. However, standardized methods for the detection of ARB exist for clinical investigations of human materials only. They are based on cultivation on selective agar plates. These methods cannot be used directly for environmental samples, because of the high amount and diversity of bacterial background flora which interferes with the detection of human-relevant ARB. The aim of this study was to introduce a proposal for future normative standard operation procedures, with international relevance, for the culture-based detection of clinically-relevant antibiotic resistant bacteria in aquatic environmental samples like wastewater and surface water: gram-negative bacteria resistant against 3rd generation cephalosporins (ESBL) and against carbapenems (CARBA), gram-positive vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA). The final adaptation of standardized cultivation methods included increasing the standard incubation temperature from 36 °C to 42 °C, which effectively inhibits the environmental background flora on agar plates while the desired target species survive. This enables the detection of target species in suitable sample volumes. Putative target colonies which belong to the remaining background flora had to be excluded by morphological and physiological differentiation. Therefore, a time and cost optimized testing scheme with good performance was developed, which allows an effective exclusion of non-target isolates in samples. Depending on the target species and sample type, sensitivity of up to 100% is achieved, and specificity ranges from 91.1% to 99.7%, while the positive predictive value, negative predicted value and accuracy rate are always >90%.

Molecular diversity of chromosomal metallo-β-lactamase genes in Elizabethkingia genus

Elizabethkingia genus is an opportunistic life-threatening pathogen with an intrinsic multidrug-resistant phenotype. It is the only known microorganism with multi-chromosome-borne metallo-β-lactamase (MBL) genes. To determine the diversity and distribution of MBLs Bla_BlaB and Bla_GOB in this genus, comprehensive bioinformatic screening was applied in 109 available Elizabethkingia genomes. A total of 23 and 32 novel Bla_BlaB and Bla_GOB variants were found in Elizabethkingia spp., respectively; 12 and 15 clusters were assigned in these Bla_BlaB and Bla_GOB based on the amino acid identities and phylogenetic studies. Clustering of some variants did not conform to species-specific clades, which indicated potential inter-species dissemination of MBL genes among Elizabethkingia species. Cloning of representative bla_BlaB and bla_GOB into E. coli DH5α resulted in increased and diverse minimum inhibitory concentrations (MICs) to most β-lactams, including cephalosporins, carbapenems, and β-lactams-inhibitors. This study extends the database of class B carbapenemases, emphasizing the diversity of different MBL genes in the genus Elizabethkingia, which may represent potential reservoirs of acquired MBLs.

Molecular Characteristics and Antimicrobial Susceptibility Profiles of Elizabethkingia Clinical Isolates in Shanghai, China

Purpose

To investigate molecular characteristics and antimicrobial susceptibility profiles of clinical isolates of Elizabethkingia in Shanghai, China.

Methods

Elizabethkingia isolates were collected in a university-affiliated hospital in 2012–2015 and 2017–2018. They were re-identified to species level by 16S rRNA gene and species-specific gene sequencing. Antimicrobial susceptibility testing, screening for metallo-beta-lactamase production, identification of antimicrobial resistance genes and pulsed-field gel electrophoresis (PFGE) were performed.

Results

Among 52 Elizabethkingia isolates, E. anophelis was the most prevalent species (67.3%), followed by E. meningoseptica (26.9%). High carriage rates of bla_CME, bla_BlaB and bla_GOB genes were consistent with the poor in vitro activity of most β-lactams including carbapenems. Nevertheless, β-lactamase inhibitors increased susceptibility rates significantly for cefoperazone and piperacillin. Susceptibility rates for minocycline, tigecycline, rifampin and levofloxacin were 100%, 78.8%, 76.9% and 71.2%, respectively. Ser83Ile or Ser83Arg substitution in the DNA gyrase A unit was associated with resistance to fluoroquinolones. MIC₅₀/MIC₉₀ values of vancomycin and linezolid were 16/16 mg/L and 16/32 mg/L, respectively. Molecular typing showed twenty-one different types of PFGE and more than one indistinguishable isolates were observed in each of the eight subtypes.

Conclusion

Tetracyclines, tigecycline, β-lactam/β-lactamase inhibitor combinations, rifampin and fluoroquinolones demonstrated high rates of in vitro activity against clinical isolates of Elizabethkingia. Both genetic diversity and clonality were observed from this health-care facility. Our report provides potential alternative treatment options for Elizabethkingia infections.

Bacteremia due to Elizabethkingia meningoseptica

Elizabethkingia meningoseptica is a nonfermentative gram-negative bacillus that is ubiquitously found in hospital environments and as such, it has been associated with various nosocomial infections. Immunocompromised individuals are particularly at increased risk for developing severe infections due to E. meningoseptica, including bacteremia. E. meningoseptica is resistant to multiple antimicrobials commonly used for gram-negative bacteria and conventional empirical antimicrobials targeting those organisms may result in unfavorable outcome. We report a case of bacteremia due to E. meningoseptica in a patient who necessitated chronic hemodialysis therapy to heighten awareness of this emerging pathogen among patients on hemodialysis.

Whole-genome sequence of Chryseobacterium oranimense, a colistin-resistant bacterium isolated from a cystic fibrosis patient in France

For the first time, we report the whole-genome sequence analysis of Chryseobacterium oranimense G311, a multidrug-resistant bacterium, from a cystic fibrosis patient in France, including resistance to colistin. Whole-genome sequencing of C. oranimense G311 was performed using Ion Torrent PGM, and RAST, the EMBL-EBI server, and the Antibiotic Resistance Gene-ANNOTation (ARG-ANNOT) database were used for annotation of all genes, including antibiotic resistance (AR) genes. General features of the C. oranimense G311 draft genome were compared to the other available genomes of Chryseobacterium gleum and Chryseobacterium sp. strain CF314. C. oranimense G311 was found to be resistant to all β-lactams, including imipenem, and to colistin. The genome size of C. oranimense G311 is 4,457,049 bp in length, with 37.70% GC content. We found 27 AR genes in the genome, including β-lactamase genes which showed little similarity to the known β-lactamase genes and could likely be novel. We found the type I polyketide synthase operon followed by a zeaxanthin glycosyltransferase gene in the genome, which could impart the yellow pigmentation of the isolate. We located the O-antigen biosynthesis cluster, and we also discovered a novel capsular polysaccharide biosynthesis cluster. We also found known mutations in the orthologs of the pmrA (E8D), pmrB (L208F and P360Q), and lpxA (G68D) genes. We speculate that the presence of the capsular cluster and mutations in these genes could explain the resistance of this bacterium to colistin. We demonstrate that whole-genome sequencing was successfully applied to decipher the resistome of a multidrug resistance bacterium associated with cystic fibrosis patients.

Draft Genome Sequences of Elizabethkingia meningoseptica

Elizabethkingia meningoseptica is ubiquitous in nature, exhibits a multiple-antibiotic resistance phenotype, and causes rare opportunistic infections. We now report two draft genome sequences of E. meningoseptica type strains that were sequenced independently in two laboratories.

Activity of MK-7655 combined with imipenem against Enterobacteriaceae and Pseudomonas aeruginosa

OBJECTIVES

MK-7655 is a novel inhibitor of class A and C β-lactamases. We investigated its potential to protect imipenem.

METHODS

Chequerboard MICs were determined by CLSI agar dilution: (i) for Enterobacteriaceae with carbapenemases; (ii) for Enterobacteriaceae with carbapenem resistance contingent on combinations of impermeability together with an extended-spectrum β-lactamase or AmpC enzyme; and (iii) for Pseudomonas aeruginosa and other non-fermenters.

RESULTS

At a concentration of 4 mg/L, MK-7655 reduced imipenem MICs for Enterobacteriaceae with KPC carbapenemases from 16-64 mg/L to 0.12-1 mg/L. Synergy also was seen for Enterobacteriaceae with impermeability-mediated carbapenem resistance, with weaker synergy seen for isolates with the OXA-48 enzyme. On the other hand, MK-7655 failed to potentiate imipenem against Enterobacteriaceae with metallo-carbapenemases. In the case of P. aeruginosa, where endogenous AmpC confers slight protection versus imipenem, 4 mg/L MK-7655 reduced the MIC of imipenem for all isolates, except those with metallo-carbapenemases: the MICs of imipenem fell from 1-2 mg/L to 0.25-0.5 mg/L for imipenem-susceptible P. aeruginosa and from 16-64 mg/L to 1-4 mg/L for OprD-deficient strains. No potentiation was seen for chryseobacteria or for Stenotrophomonas maltophilia.

CONCLUSIONS

MK-7655 potentiated imipenem against Enterobacteriaceae with KPC carbapenemases or combinations of β-lactamase and impermeability, but not those with metallo-carbapenemases. It augmented the activity of imipenem against P. aeruginosa in general and OprD mutants in particular.

Carbapenem resistance in Elizabethkingia meningoseptica is mediated by metallo-β-lactamase BlaB

Elizabethkingia meningoseptica, a Gram-negative rod widely distributed in the environment, is resistant to most β-lactam antibiotics. Three bla genes have been identified in E. meningoseptica, coding for the extended-spectrum serine-β-lactamase CME (class D) and two unrelated wide-spectrum metallo-β-lactamases, BlaB (subclass B1) and GOB (subclass B3). E. meningoseptica is singular in being the only reported microorganism possessing two chromosomally encoded MBL genes. Real-time PCR and biochemical analysis demonstrate that the three bla genes are actively expressed in vivo as functional β-lactamases. However, while CME elicits cephalosporin resistance, BlaB is the only β-lactamase responsible for E. meningoseptica resistance to imipenem, as GOB activity is masked by higher cellular levels of BlaB. On the other hand, we demonstrate that bla(BlaB) expression is higher in the stationary phase or under conditions that mimic the nutrient-limiting cerebrospinal fluid colonized by E. meningoseptica in human meningitis.

Genetic diversity of chromosomal metallo-beta-lactamase genes in clinical isolates of Elizabethkingia meningoseptica from Korea

This study was performed to characterize the chromosomal metallo-beta-lactamases (MBLs) of Elizabethkingia meningoseptica isolated from Korea and to propose a clustering method of BlaB and GOB MBLs based on their amino acid similarities. Chromosomal MBL genes were amplified by PCR from 31 clinical isolates of E. meningoseptica. These PCR products were then cloned into a vector and electrotransformed into E. coli DH5 alpha. Nucleotide sequencing was performed by the dideoxy chain termination method using PCR products or cloned DNA fragments. Antimicrobial susceptibilities were determined by the agar dilution method. PCR experiments showed that all 31 E. meningoseptica isolates contained both the blaB and the bla (GOB) genes. DNA sequence analysis revealed that E. meningoseptica isolates possessed seven types of blaB gene, including five novel variants (blaB-9 to blaB-13) and 11 types of bla (GOB) gene, including 10 novel variants (bla (GOB-8) to bla (GOB-17)). The most common combination of MBL was BlaB-12 plus GOB-17 (n=19). Minimum inhibitory concentrations of imipenem and meropenem for the electrotransformants harboring novel BlaB and GOB MBLs were two- or four-fold higher than those for the recipient E. coli DH5 alpha. BlaB and GOB MBLs were grouped in three and six clusters including fifteen novel variants, respectively, based on amino acid similarities.

Differences in carbapenem resistance genes among Acinetobacterbaumannii, Acinetobacter genospecies 3 and Acinetobacter genospecies 13TU in Taiwan

A total of 81 clinical isolates of the three clinically important Acinetobacter spp., namely Acinetobacterbaumannii, Acinetobacter genospecies 3 and Acinetobacter genospecies 13TU, were analysed for differences in carbapenem resistance genes. Of the 81 isolates, 40 (49%) were resistant to carbapenems. Most A. baumannii isolates (47/53, 88.7%) contained the ISAba1-bla(OXA-51)-like gene and exhibited a higher minimum inhibitory concentration to imipenem than A. baumannii without the ISAba1 element. All four carbapenem-resistant A. genospecies 3 isolates contained bla(IMP-1) and an ISAba3-bla(OXA-58)-like gene. Three A. genospecies 13TU isolates contained an ISAba3-bla(OXA-58)-like and either a bla(IMP-1) or a bla(VIM-11) gene. The five bla(IMP-1)-containing strains were resistant to imipenem and were positive for metallo-beta-lactamase (MBL) activity by the Etest, and the two bla(VIM-11)-containing strains were susceptible to imipenem and were MBL-negative by Etest. Imipenem hydrolysis tests showed that the bla(IMP-1)-containing strains exhibited much higher imipenem-hydrolysing activity than the two bla(VIM-11)-containing strains. No transcripts of bla(VIM-11) or bla(OXA-58)-like genes were detected. Analysis of outer membrane proteins showed that OprD was absent in the only bla(IMP-1)-containing A. genospecies 13TU strain owing to the presence of a premature stop codon in the oprD gene. In summary, several differences were detected between the carbapenem resistance genes of clinical Acinetobacter spp. in Taiwan, and loss of OprD may be associated with imipenem resistance in A. genospecies 13TU.

Diversity of carbapenem resistance mechanisms in Acinetobacter baumannii from a Taiwan hospital: spread of plasmid-borne OXA-72 carbapenemase

OBJECTIVES

We investigated the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii from a Taiwanese hospital and determined the mechanisms responsible for resistance.

METHODS

Ninety-two consecutive meropenem-resistant A. baumannii isolates collected between January 2005 and June 2007 were screened for genes encoding OXA carbapenemases, metallo-beta-lactamases and for the carO gene encoding an outer membrane protein. PFGE was used to define clonal relatedness. PCR mapping was used to examine the linkage of insertion sequences and bla(OXA) genes. Southern hybridization of plasmid extracts and I-CeuI-restricted chromosomal DNA was used to locate bla(OXA-24-like) genes. Sequences of selected bla(OXA-24-like) and carO genes were determined and loss of CarO expression was confirmed by SDS-PAGE.

RESULTS

Most (70/92, 76%) isolates belonged to one of three PFGE pulsotypes, indicating clonal spread. Fifty-nine isolates, including the majority of those of pulsotypes I and III, produced OXA-72 carbapenemase. The bla(OXA-72) gene was located on a 54 kb plasmid in selected isolates. Thirty-three (36%) isolates, including all 16 of pulsotype II, had ISAba1 preceding the bla(OXA-51-like) gene, promoting its expression. In addition to OXA-72 carbapenemase, two pulsotype I and three pulsotype III isolates did not produce CarO protein as the carO gene was disrupted by insertion of an ISAba1 element. Two isolates of a minor pulsotype had a bla(OXA-58-like) gene and a single PFGE-unique isolate had a bla(OXA-23-like) gene.

CONCLUSIONS

Although diverse mechanisms were identified, production of OXA-72 carbapenemase was the most common mechanism of carbapenem resistance in A. baumannii from this Taiwanese hospital. The plasmidic location of the gene had facilitated its spread to multiple strains.

Carbapenemases: molecular diversity and clinical consequences

Carbapenemases are beta-lactamases that hydrolyze most beta-lactams including carbapenems. Carbapenemases are classified in four molecular classes; those belonging to class A are the chromosomally-encoded and clavulanic acid-inhibited IMI, NMC-A and SME, identified in Enterobacter cloacae and Serratia marcescens; the plasmid-encoded KPC enzymes identified in Enterobacteriaceae (and rarely in Pseudomonas aeruginosa); and the GES-type enzymes identified in Enterobacteriaceae and P. aeruginosa. The class B enzymes are the most clinically-significant carbapenemases; they are metallo-beta-lactamases, mostly of the IMP and the VIM series. They have been reported worldwide and their genes are plasmid- and integron-located, hydrolyzing all beta-lactams with the exception of aztreonam. One single plasmid-mediated AmpC beta-lactamase, CMY-10, identified in an Enterobacter aerogenes isolate, has been shown to be a cephaslosporinase with some carbapenemase properties. Finally, the class D carbapenemases are being increasingly reported, mostly in Acinetobacter baumannii, and they compromise the efficacy of imipenem and meropenem significantly.

Heterogeneity of metallo-beta-lactamases in clinical isolates of Chryseobacterium meningosepticum from Hangzhou, China

OBJECTIVES

To determine the distribution and heterogeneity of metallo-beta-lactamases (MBLs) responsible for imipenem resistance in Chryseobacterium meningosepticum.

METHODS

Clinical C. meningosepticum isolates (n = 170) were collected from hospitals in Hangzhou, China. Production of MBLs was investigated by determination of imipenem MICs, and by using both a three-dimensional test and a 2-mercaptopropionic acid inhibitory test. Genes encoding BlaB and GOB MBLs were amplified by PCR, sequenced and compared with genes in GenBank.

RESULTS

More than 95% of the 170 isolates showed high (MIC > 16 mg/L) or intermediate resistance to imipenem, but only 94 isolates (55%) were shown phenotypically to produce MBLs (imipenem MIC range, 8-256 mg/L), with MBL genes detected in 93 of these. Among them, 83 isolates had blaB alleles and 65 isolates had bla(GOB) alleles; 38 isolates possessed one MBL gene and 55 isolates contained two genes. The major blaB alleles encoded BlaB-2, -3 and -11, while the major bla(GOB) alleles encoded GOB-2, -4, -8 and -10. MBLs or their genes were not detected in 76 (45%) isolates, including many that were highly resistant to imipenem.

CONCLUSIONS

High levels and rates of imipenem resistance in C. meningosepticum from Hangzhou often result from the presence of heterogeneous BlaB and/or GOB MBLs, although undefined carbapenem resistance mechanisms also exist. Susceptibility testing and screening for MBLs should be conducted in order to inform effective treatment for C. meningosepticum infections.

Resistance pattern and assessment of phenicol agents' minimum inhibitory concentration in multiple drug resistant Chryseobacterium isolates from fish and aquatic habitats

AIMS

To assess the susceptibility of Chryseobacterium isolates of fish and aquatic habitats to antimicrobial compounds. Special attention was paid to the resistance to chloramphenicol and florfenicol, a phenicol derivative recently licensed for use in veterinary medicine and fish farming.

METHODS AND RESULTS

Sixty-seven Chryseobacterium spp. isolates and reference strains, originating mainly from different aquatic habitats, were tested using the disk-diffusion method. In addition, agar dilution was used for assessing minimum inhibitory concentration of chloramphenicol and florfenicol. In spite of (i) conditions that hampered properly standardized experiments and (ii) the heterogeneity of the isolates resulting in some aberrant values in diffusion, correlation between the two methods was confirmed. Most of the isolates exhibited considerable multiresistance to most antimicrobial drug families, and many were clearly resistant to phenicols. Molecular investigations conducted on 10 strains selected for high resistance to florfenicol did not establish the existence of floR or cmlA genes currently reported in the literature as responsible for florfenicol resistance. Nevertheless, when an efflux pump inhibitor, phenyl-arginin-beta-naphthylamide, was combined with diffusion tests, drug susceptibility to florfenicol was restored, suggesting that Chryseobacterium's resistance to this molecule is under the control of efflux mechanisms.

CONCLUSIONS

Constitutive multiresistance to antibiotics is common in chryseobacteria isolated from the aquatic environment. Although no gene related to the floR family could be detected, efflux mechanisms could partly support the resistance to phenicols.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results explain the difficulty of treatment and clearly reflect the properties previously reported in Chryseobacterium isolates of human origin. Because several species have been involved in opportunistic infections in humans, the possible role of aquatic organisms as a source of infection should be considered.

Metallo-beta-lactamases: the quiet before the storm?

The ascendancy of metallo-beta-lactamases within the clinical sector, while not ubiquitous, has nonetheless been dramatic; some reports indicate that nearly 30% of imipenem-resistant Pseudomonas aeruginosa strains possess a metallo-beta-lactamase. Acquisition of a metallo-beta-lactamase gene will invariably mediate broad-spectrum beta-lactam resistance in P. aeruginosa, but the level of in vitro resistance in Acinetobacter spp. and Enterobacteriaceae is less dependable. Their clinical significance is further embellished by their ability to hydrolyze all beta-lactams and by the fact that there is currently no clinical inhibitor, nor is there likely to be for the foreseeable future. The genes encoding metallo-beta-lactamases are often procured by class 1 (sometimes class 3) integrons, which, in turn, are embedded in transposons, resulting in a highly transmissible genetic apparatus. Moreover, other gene cassettes within the integrons often confer resistance to aminoglycosides, precluding their use as an alternative treatment. Thus far, the metallo-beta-lactamases encoded on transferable genes include IMP, VIM, SPM, and GIM and have been reported from 28 countries. Their rapid dissemination is worrisome and necessitates the implementation of not just surveillance studies but also metallo-beta-lactamase inhibitor studies securing the longevity of important anti-infectives.

Outbreak of Klebsiella pneumoniae producing a new carbapenem-hydrolyzing class A beta-lactamase, KPC-3, in a New York Medical Center

From April 2000 to April 2001, 24 patients in intensive care units at Tisch Hospital, New York, N.Y., were infected or colonized by carbapenem-resistant Klebsiella pneumoniae. Pulsed-field gel electrophoresis identified a predominant outbreak strain, but other resistant strains were also recovered. Three representatives of the outbreak strain from separate patients were studied in detail. All were resistant or had reduced susceptibility to imipenem, meropenem, ceftazidime, piperacillin-tazobactam, and gentamicin but remained fully susceptible to tetracycline. PCR amplified a blaKPC allele encoding a novel variant, KPC-3, with a His(272)-->Tyr substitution not found in KPC-2; other carbapenemase genes were absent. In the outbreak strain, KPC-3 was encoded by a 75-kb plasmid, which was transferred in vitro by electroporation and conjugation. The isolates lacked the OmpK35 porin but expressed OmpK36, implying reduced permeability as a cofactor in resistance. This is the third KPC carbapenem-hydrolyzing beta-lactamase variant to have been reported in members of the Enterobacteriaceae, with others reported from the East Coast of the United States. Although producers of these enzymes remain rare, the progress of this enzyme group merits monitoring.

Clinical and microbiological analysis of bloodstream infections caused by Chryseobacterium meningosepticum in nonneonatal patients

Chryseobacterium meningosepticum bloodstream infections in 11 nonneonatal patients were reported. More than half of the infections were community acquired. PCR assays indicated that the organisms produced extended-spectrum beta-lactamases as well as metallo-beta-lactamases. Genotyping showed diverse fingerprints among the isolates. Six patients survived without appropriate antibiotic treatment. Host factors are the major determinant of the outcomes of C. meningosepticum infections.

Pseudomonas infections in the thermally injured patient

Pseudomonas aeruginosa, remains a serious cause of infection and septic mortality in burn patients, particularly when nosocomially acquired. A prototypic burn patient who developed serious nosocomially acquired Pseudomonas infection is described as an index case which initiated investigations and measures taken to identify the source of the infection. The effect of changes in wound care to avoid further nosocomial infections was measured to provide data on outcome and cost of care. The bacteriology of Pseudomonas is reviewed to increase the burn care providers understanding of the behaviour of this very common and serious pathogen in the burn care setting, before reviewing the approach to detection of the organism and treatment both medically and surgically. After controlling the nosocomial spread of Pseudomonas in our burn unit, we investigated the morbidity and mortality associated with nosocomial infection with an aminoglycoside resistant Pseudomonas and the associated costs compared to a group of case-matched control patients with similar severity of burn injury, that did not acquire resistant Pseudomonas during hospitalization at our institution. We found a significant increase in the mortality rate in the Pseudomonas group compared to controls. The morbidity in terms of length of stay, ventilator days, number of surgical procedures, and the amount of blood products used were all significantly higher in the Pseudomonas group compared to controls. Costs associated with antibiotic requirements were also significantly higher in the Pseudomonas group. Despite this increased resource consumption necessary to treat Pseudomonas infections, these efforts did not prevent significantly higher mortality rates when compared to control patients who avoided infection with the resistant organism. Thus, in addition to the specific measures required to identify and treat nosocomial Pseudomonas infections in burn patients, prevention of infection through modification of treatment protocols together with continuous infection control measures to afford early identification and eradication of nosocomial Pseudomonas infection are critical for cost-effective, successful burn care.

Epidemiology of Nosocomial Pneumonia in Infants After Cardiac Surgery

BACKGROUND

The pattern of nosocomial pneumonia (NP) in infants in a pediatric surgical ICU after cardiac surgery may differ from that seen in adult ICUs.

STUDY OBJECTIVES

The primary aim of this study was to describe the epidemiology of NP in infants after cardiac surgery and, secondarily, to describe the changes of the distribution and antibiotic resistance of the pathogen during the last 3 years.

METHODS

Data were collected between June 1999 and June 2002 from 311 consecutive infants who underwent open-heart surgery in our hospital. We retrospectively analyzed the distribution and antibiotic resistance pattern of all the pathogenic microbial isolates cultured from lower respiratory tract aspirations.

RESULTS

Of 311 infants, 67 patients (21.5%) acquired NP after cardiac surgery. The incidence of NP was more frequently associated with complex congenital heart defect (CHD) compared to simple CHD (43% vs 15.9%, chi(2) = 22.47, p < 0.0001). The proportion of late-onset NP was higher in patients with complex CHD (chi(2) = 6.02, p = 0.014). A total of 79 pathogenic microbial strains were isolated. Gram-negative bacilli (GNB) were the most frequent isolates (68 isolates, 86.1%), followed by fungi (6 isolates, 7.6%) and Gram-positive cocci (5 isolates, 6.3%). The main GNB were Acinetobacter baumanii (11 isolates, 13.9%), Pseudomonas aeruginosa (10 isolates, 12.7%); other commonly seen GNB were Flavobacterium meningosepticum (7 isolates, 8.9%), Klebsiella pneumoniae (7 isolates, 8.9%), Escherichia coli (6 isolates, 7.6%), and Xanthomonas maltophilia (5 isolates, 6.2%). The most commonly seen Gram-positive cocci were Staphylococcus aureus (2 isolates, 2.5%) and Staphylococcus epidermidis (2 isolates, 2.5%). The frequent fungi were Candida albicans (5 isolates, 6.3%). Most GNB were sensitive to cefoperazone-sulbactum, piperacillin-tazobactam, imipenem, ciprofloxacin, amikacin. The bacteria producing extended spectrum beta-lactamases were mainly from K pneumoniae and E coli; the susceptibility of ESBL-producing strains to imipenem was 100%. There were one case of methicillin-resistant S aureus (MRSA) and 1 case of methicillin-resistant S epidermidis; their susceptibility to vancomycin, gentamycin, and ciprofloxacin were 100%. From 1999 to 2002 in infants with NP after open-heart surgery, there was a trend of increasing frequency of multiresistant GNB such as A baumanii, P aeruginosa, and K pneumoniae. However, no remarkable changes of distribution were found in Gram-positive cocci and fungi in the 3-year period. Early onset episodes of NP were frequently caused by Haemophilus influenzae, methicillin-sensitive S aureus, and other susceptible Enterobacteriaceae. Conversely, in patients who acquired late-onset NP, P aeruginosa, A baumannii, other multiresistant GNB, MRSA, and fungi were the predominant organisms.

CONCLUSIONS

The pattern of pathogens and their antibiotic-resistance patterns in NP in infants after cardiac surgery had not shown an increasing prevalence of Gram-positive pathogens as reported by several adult ICUs. GNB still remained the most common pathogens during the last 3 years in our hospital. There was a trend of increasing antibiotic resistance in these isolates.

The 1.5-A structure of Chryseobacterium meningosepticum zinc beta-lactamase in complex with the inhibitor, D-captopril

The crystal structure of the class-B beta-lactamase, BlaB, from the pathogenic bacterium, Chryseobacterium meningosepticum, in complex with the inhibitor, d-captopril, has been solved at 1.5-A resolution. The enzyme has the typical alphabeta/betaalpha metallo-beta-lactamase fold and the characteristic two metal binding sites of members of the subclass B1, in which two Zn2+ ions were identified. d-Captopril, a diastereoisomer of the commercial drug, captopril, acts as an inhibitor by displacing the catalytic hydroxyl ion required for antibiotic hydrolysis and intercalating its sulfhydryl group between the two Zn2+ ions. Interestingly, d-captopril is located on one side of the active site cleft. The x-ray structure of the complex of the closely related enzyme, IMP-1, with a mercaptocarboxylate inhibitor, which also contains a sulfhydryl group bound to the two Zn2+ ions, shows the ligand to be located on the opposite side of the active site cleft. A molecule generated by fusion of these two inhibitors would cover the entire cleft, suggesting an interesting approach to the design of highly specific inhibitors.

Biochemical characterization of the acquired metallo-beta-lactamase SPM-1 from Pseudomonas aeruginosa

SPM-1 is a new metallo-beta-lactamase recently identified in Pseudomonas aeruginosa strain 48-1997A, isolated in Sao Paulo, Brazil. Kinetic analysis demonstrated that SPM-1 has a broad hydrolytic profile across a wide range of beta-lactam antibiotics. Considerable variation was observed within the penicillin, cephalosporin, and carbapenem subfamilies; however, on the whole, SPM-1 appears to preferentially hydrolyze cephalosporins. The highest k(cat/)K(m) ratios (in micromolar per second) overall were observed for this subgroup. The hydrolytic profile of SPM-1 bears the most similarity to that of the metallo-beta-lactamase IMP-1, yet for the most part, SPM-1 has k(cat)/K(m) values higher than those of IMP-1. Zinc chelator studies established that progressive inhibition of SPM-1 by EDTA, dipicolinic acid, and 1-10-o-phenanthroline demonstrated a biexponential pattern in which none of the chelators completely inhibited SPM-1. A homology model of SPM-1 was developed on the basis of the IMP-1 crystal structure, which showed the protein folding and active-site structure characteristic of metallo-beta-lactamases and which provides an explanation for the kinetic profiles observed.

Emerging carbapenemases in Gram-negative aerobes

Carbapenemases may be defined as beta-lactamases that significantly hydrolyze at least imipenem or/and meropenem. Carbapenemases involved in acquired resistance are of Ambler molecular classes A, B, and D. Class A, clavulanic acid-inhibited carbapenemases are rare. They are either chromosomally encoded (NMC-A, Sme-1 to Sme-3, IMI-1) in Enterobacter cloacae and Serratia marcescens, or plasmid encoded, such as KPC-1 in Klebsiella pneumoniae and GES-2 in Pseudomonas aeruginosa, the latter being a point-mutant of the clavulanic acid-inhibited extended-spectrum beta-lactamase GES-1. The class B enzymes are the most clinically significant carbapenemases. They are metalloenzymes of the IMP or VIM series. They have been reported worldwide but mostly from South East Asia and Europe. Metalloenzymes, whose genes are plasmid and integron located, hydrolyze virtually all beta-lactams except aztreonam. Finally, the class D carbapenemases are increasingly reported in Acinetobacter baumannii but compromise imipenem and meropenem susceptibility only marginally. The sources of the acquired carbapenemase genes remain unknown, as does the relative importance of the spread of epidemic strains as opposed to the spread of plasmid- or integron-borne genes. Because most of these carbapenemases confer only reduced susceptibility to carbapenems in Enterobacteriaceae, they may remain underestimated as a consequence of the lack of their detection.

Nosocomial outbreak of carbapenem-resistant Pseudomonas aeruginosa with a new bla(IMP) allele, bla(IMP-7)

Pseudomonas aeruginosa isolates from an outbreak in Canada were highly resistant to carbapenems and ceftazidime but not piperacillin. They produced a novel integron-associated metallo-beta-lactamase, designated IMP-7, with 91% identity to IMP-1. bla(IMP-7) was not detected with standard bla(IMP)-specific primers, owing to mismatches in the forward primer.

Characterization of OXA-25, OXA-26, and OXA-27, molecular class D beta-lactamases associated with carbapenem resistance in clinical isolates of Acinetobacter baumannii

Carbapenem resistance in Acinetobacter spp. is increasingly being associated with OXA-type beta-lactamases with weak hydrolytic activity against imipenem and meropenem. Such enzymes were characterized from Acinetobacter isolates collected in Belgium, Kuwait, Singapore, and Spain. The isolates from Spain and Belgium had novel class D beta-lactamases that were active against carbapenems. These were designated OXA-25 and OXA-26, respectively, and had >98% amino acid homology with each other and with the OXA-24 enzyme recently described by others from an Acinetobacter isolate collected elsewhere in Spain. The isolate from Singapore had OXA-27 beta-lactamase, another novel class D type with only 60% homology to OXA-24, -25, and -26, but with 99% homology to OXA-23 (ARI-1), described previously from an Acinetobacter baumannii isolate collected in Scotland. Sequence data were not obtained for the carbapenem-hydrolyzing OXA enzyme from the isolate from Kuwait; nevertheless, the enzyme was phenotypically similar to OXA-25 and -26. The enzymes OXA-23, -24, -25, -26, and -27 retained the STFK and SXV motifs typical of class D beta-lactamases, but the YGN motif was altered to FGN. The KTG motif was retained by OXA-27 and -23 but was replaced by KSG in OXA-24, -25, and -26. OXA-25 and -26 enzymes were strongly active against oxacillin, but unusually for an OXA-type beta-lactamase, OXA-27 had apparently weak activity, although measurement was complicated by biphasic kinetics. None of the new enzymes was transmissible to Escherichia coli recipients. Many Acinetobacter isolates are multiresistant to other antibiotics, and the emergence of class D enzymes with carbapenem-hydrolyzing activity is a disturbing development for antimicrobial chemotherapy.

Characterization of a divergent vanD-type resistance element from the first glycopeptide-resistant strain of Enterococcus faecium isolated in Brazil

Enterococcus faecium 10/96A from Brazil was resistant to vancomycin (MIC, 256 microg/ml) but gave no amplification products with primers specific for known van genotypes. A 2,368-bp fragment of a van cluster contained one open reading frame encoding a peptide with 83% amino acid identity to VanH(D), and a second encoding a D-alanine-D-lactate ligase with 83 to 85% identity to VanD. The divergent glycopeptide resistance phenotype was designated VanD4.

Carbapenemases: a problem in waiting?

Carbapenems are stable to most prevalent beta-lactamases, and chromosomal carbapenemases are restricted to Stenotrophomonas maltophilia, to a few Bacteroides fragilis, and to rare pathogens. Nevertheless, an acquired metallo-beta-lactamase called IMP-1 is beginning to emerge in Pseudomonas aeruginosa and Enterobacteriaceae isolates in Japan, and has also been found in isolates from Singapore. Furthermore, IMP-producing Acinetobacter spp. have been identified in Italy and Hong Kong. Recently a second group of acquired metallo-carbapenemases, the VIM types, has been recorded from P. aeruginosa isolates in five Eurasian countries. Weak carbapenemases belonging to molecular class D are emerging in A. baumannii world-wide, with two sub-groups apparent. A few acquired carbapenemases belonging to molecular class A also have been reported. Finally it has also been shown that enzymes with feeble carbapenemase activity (e.g. AmpC types and some SHV enzymes) may confer resistance in exceptionally impermeable strains; counterwise, even potent carbapenemases, such as IMP-1, may only give a small reduction in susceptibility in Enterobacteriaceae that lack permeability lesions. Is the emergence of carbapenemase a problem waiting to happen?