Detection in two hospitals of transferable ceftazidime-avibactam resistance in Klebsiella pneumoniae due to a novel VEB β-lactamase variant with a Lys234Arg substitution, Greece, 2019

Two ceftazidime-avibactam (CAZ-AVI)-resistant Klebsiella pneumoniae carbapenemase (KPC)-positive K. pneumoniae strains, including one pandrug resistant, were isolated in 2019 from two Greek hospitals. The strains were sequence types (ST)s 258 and 147 and both harboured similar self-transmissible IncA/C2 plasmids encoding a novel Lys234Arg variant of the Vietnamese extended-spectrum β-lactamase (VEB)-1, not inhibited by AVI (VEB-25). Conjugal transfer of VEB-25-encoding plasmids to Escherichia coli yielded CAZ-AVI-resistant clones, supporting that VEB-25 is directly linked to the derived phenotype.

Emergence and maintenance of multidrug-resistant Escherichia coli of canine origin harbouring a blaCMY-2-IncI1/ST65 plasmid and topoisomerase mutations

OBJECTIVES

To characterize the mechanisms implicated in fluoroquinolone (FQ) and expanded-spectrum cephalosporin (ESC) resistance in three clinical and seven faecal multidrug-resistant (MDR; resistant to at least three antimicrobial classes) Escherichia coli isolates from a dog with atopic dermatitis, also suffering from recurrent otitis, that had already been exposed to prolonged antimicrobial treatment and colonized for a long period.

METHODS

MICs of FQs, ESCs and other antimicrobials were determined by the broth microdilution method. Phenotypic tests (efflux pump inhibition and combination disc tests) and isoelectric focusing were combined with genotypic analyses [PCRs, sequencing, conjugation, S1 nuclease PFGE, PCR-based replicon typing, plasmid multilocus sequence typing (pMLST) and PCR mapping] to characterize the molecular basis of FQ and ESC resistance. Isolates were further characterized by MLST and PFGE.

RESULTS

Three otitis and five faecal isolates with enrofloxacin MICs of 32 to >128 mg/L displayed the GyrA:S83L+D87N/ParC:E62K/ParE:G545D pattern harbouring novel ParC and ParE substitutions, whereas the two remaining faecal isolates were susceptible or borderline resistant single-step mutants (GyrA:S83L pattern) and carried qnrS1. Efflux pump overexpression also contributed to FQ resistance and the MDR phenotype. The three otitis and five faecal isolates also exhibited cefoxitin/ceftazidime MICs of 32-64 mg/L and harboured blaCMY-2, adjusted to ISEcp1, on an IncI1/ST65 conjugative plasmid, previously described in Salmonella Heidelberg from poultry. Interestingly, all isolates shared an identical MLST type (ST212), with the otitis isolates showing indistinguishable patterns with the high-level resistant faecal E. coli isolates.

CONCLUSIONS

The long-term maintenance of FQ- and ESC-resistant clones harbouring topoisomerase mutations and a blaCMY-2-IncI1/ST65 plasmid in canine commensal flora after prolonged antimicrobial use may contribute to the dissemination of multidrug resistance.

Characterization of pKP1780, a novel IncR plasmid from the emerging Klebsiella pneumoniae ST147, encoding the VIM-1 metallo-β-lactamase

OBJECTIVES

To determine the complete nucleotide sequence of the VIM-1-encoding plasmid pKP1780 from Klebsiella pneumoniae ST147 representing a distinct group of IncR replicons.

METHODS

The plasmid pKP1780 was from a K. pneumoniae clinical strain (KP-1780) isolated in Greece in 2009. Plasmid DNA was extracted from an Escherichia coli DH5α transformant and sequenced using the 454 Genome Sequencer GS FLX procedure on a standard fragment DNA library. Contig gaps were filled by sequencing of PCR-produced fragments. Annotation and comparative analysis were performed using software available on the Internet.

RESULTS

Plasmid pKP1780 (49 770 bp) consisted of an IncR-related sequence (12 083 bp) including replication and stability systems, and a multidrug resistance (MDR) mosaic region (37 687 bp). blaVIM-1 along with the aacA7, dfrA1 and aadA1 cassettes comprised the variable region of an integron similar to In-e541 from pNL194. The mosaic structure also included the strA, strB, aphA1 and mphA resistance genes as well as intact (n = 10) or defective (n = 3) insertion sequences and fragments of various transposons.

CONCLUSIONS

The mosaic structure of pKP1780 exhibited high similarity with the acquired region of the IncN plasmid pNL194, indicating the acquisition of the VIM-1-encoding MDR region from pNL194 by an IncR-type plasmid.

Combined disc methods for the detection of KPC- and/or VIM-positive Klebsiella pneumoniae: improving reliability for the double carbapenemase producers

Klebsiella pneumoniae strains co-producing klebsiella pneumoniae carbapenemase (KPC) and verona integron-encoded metallo-beta-lactamase (VIM) are frequently isolated in Greece and have also occurred in other European countries. Conventional combined disc tests exhibit low sensitivity against these emerging pathogens. We have evaluated modifications of the KPC/Metallo-β-Lactamase Confirmation kit (ROSCO) exhibiting high diagnostic value against KPC, VIM and KPC + VIM producers. The key changes were the inclusion of additional combined tablets containing meropenem plus two inhibitors (dipicolinic acid (1000 μg per tablet) for metallo-β-lactamases and a boronic acid derivative for KPCs) and the replacement of aminophenylboronic acid by phenylboronic acid (400 μg per tablet).

Rapid evolution and spread of carbapenemases among Enterobacteriaceae in Europe

Plasmid-acquired carbapenemases in Enterobacteriaceae, which were first discovered in Europe in the 1990s, are now increasingly being identified at an alarming rate. Although their hydrolysis spectrum may vary, they hydrolyse most β-lactams, including carbapenems. They are mostly of the KPC, VIM, NDM and OXA-48 types. Their prevalence in Europe as reported in 2011 varies significantly from high (Greece and Italy) to low (Nordic countries). The types of carbapenemase vary among countries, partially depending on the cultural/population exchange relationship between the European countries and the possible reservoirs of each carbapenemase. Carbapenemase producers are mainly identified among Klebsiella pneumoniae and Escherichia coli, and still mostly in hospital settings and rarely in the community. Although important nosocomial outbreaks with carbapenemase-producing Enterobacteriaceae have been extensively reported, many new cases are still related to importation from a foreign country. Rapid identification of colonized or infected patients and screening of carriers is possible, and will probably be effective for prevention of a scenario of endemicity, as now reported for extended-spectrum β-lactamase (mainly CTX-M) producers in all European countries.

Identification and screening of carbapenemase-producing Enterobacteriaceae

Carbapenem-hydrolysing β-lactamases are the most powerful β-lactamases, being able to hydrolyse almost all β-lactams. They are mostly of the KPC, VIM, IMP, NDM and OXA-48 types. Their current extensive spread worldwide in Enterobacteriaceae is an important source of concern, as these carbapenemase producers are multidrug-resistant. Detection of infected patients and of carriers are the two main approaches for prevention of their spread. Phenotypic and molecular-based techniques are able to identify these carbapenemase producers, although with variable efficiencies. The detection of carriers still relies mostly on the use of screening culture media.

Identification of OXA-23-producing Acinetobacter baumannii in Greece, 2010 to 2011

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Identification of OXA-23-producing Acinetobacter baumannii in Greece, 2010 to 2011

We report on the sequence type and beta-lactamase content of 174 carbapenem-resistant Acinetobacter baumannii isolates recovered from clinical specimens during 2010 and 2011 in a tertiary care hospital in central Greece. Carbapenem resistance was associated mainly with carriage of the bla(OXA-23) gene (in 72.4% of the isolates). To our knowledge, this is the first description of A. baumannii strains producing OXA-23 in Greece. During 2011, in our hospital they rapidly ‘replaced’ the previously predominant OXA-58- positive A. baumannii strains.

Detection of Citrobacter koseri carrying beta-lactamase KPC-2 in a hospitalised patient, Greece, July 2011

This report describes the detection of Citrobacter koseri carrying K. pneumoniae carbapenemase (KPC-2) isolated in July 2011 from a Greek patient, who was also colonised by a Klebsiella pneumoniae strain coproducing KPC-2 and Verona integron-encoded metallo-beta-lactamase (VIM)-1.

Detection of Citrobacter koseri carrying beta-lactamase KPC-2 in a hospitalised patient, Greece, July 2011

This report describes the detection of Citrobacter koseri carrying K. pneumoniae carbapenemase (KPC-2) isolated in July 2011 from a Greek patient, who was also colonised by a Klebsiella pneumoniae strain co-producing KPC-2 and Verona integron-encoded metallo-beta-lactamase (VIM)-1.

Acquired carbapenemases in Gram-negative bacterial pathogens: detection and surveillance issues

Acquired carbapenemases are emerging resistance determinants in Gram-negative pathogens, including Enterobacteriaceae, Pseudomonas aeruginosa and other Gram-negative non-fermenters. A consistent number of acquired carbapenemases have been identified during the past few years, belonging to either molecular class B (metallo-beta-lactamases) or molecular classes A and D (serine carbapenemases), and genes encoding these enzymes are associated with mobile genetic elements that allow their rapid dissemination in the clinical setting. Therefore, detection and surveillance of carbapenemase-producing organisms have become matters of major importance for the selection of appropriate therapeutic schemes and the implementation of infection control measures. As carbapenemase production cannot be simply inferred from the resistance profile, criteria must be established for which isolates should be suspected and screened for carbapenemase production, and for which tests (phenotypic and/or genotypic) should be adopted for confirmation of the resistance mechanism. Moreover, strategies should be devised for surveillance of carbapenemase producers in order to enable the implementation of effective surveillance programmes. The above issues are addressed in this article, as a follow-up to an expert meeting on acquired carbapenemases that was recently organized by the ESCMID Study Group for Antibiotic Resistance Surveillance.

SCO-1, a novel plasmid-mediated class A beta-lactamase with carbenicillinase characteristics from Escherichia coli

A novel class A beta-lactamase (SCO-1) encoded by an 80-kb self-transferable plasmid from Escherichia coli is described. The interaction of SCO-1 with beta-lactams was similar to that of the CARB-type enzymes. Also, SCO-1 exhibited a 51% amino acid sequence identity with the RTG subgroup of chromosomal carbenicillinases (RTG-1, CARB-5, and CARB-8).

Activity of imipenem against VIM-1 metallo-β-lactamase-producing Klebsiella pneumoniae in the murine thigh infection model

The in-vivo activity of imipenem against VIM-1-producing Klebsiella pneumoniae (VPKP) was assessed in a thigh infection model in neutropenic mice. Animals were infected with three VPKP isolates (imipenem MICs 2, 4 and 32 mg/L, respectively) and a susceptible clinical isolate (MIC 0.125 mg/L) that did not produce any beta-lactamase with broad-spectrum activity. Bacterial density at the site of infection was determined after imipenem treatment (30 and 60 mg/kg every 2 h for 24 h). The log(10) reduction in CFU/thigh was greatest for the wild-type isolate, intermediate for the two imipenem-susceptible VPKP isolates, and lowest for the imipenem-resistant VPKP isolate. Whilst in-vivo imipenem activity appeared reduced against in-vitro susceptible VIM-1 producers compared with a VIM-1-negative control, an increased drug dosage could moderate this reduction.

Sources of diversity of carbapenem resistance levels in Klebsiella pneumoniae carrying blaVIM-1

OBJECTIVES

To elucidate the mechanisms responsible for the diversity of beta-lactam resistance phenotypes among isolates of a VIM-1-producing Klebsiella pneumoniae (VPKP) strain that is endemic in Greek hospitals.

METHODS

Five VPKP clinical isolates were studied. MICs of beta-lactams were determined by agar dilution. PFGE of XbaI-digested genomic DNA was used for typing. Profiles of outer membrane proteins (OMPs) were determined by SDS-PAGE. Selected isolates were transformed with a plasmid encoding the Omp36K porin. beta-Lactamase activities were analysed by IEF and imipenem hydrolysis was assessed by spectrophotometry. VIM-1-encoding, self-transmissible plasmids were characterized by replicon typing, RFLP and hybridization with bla(VIM)- and IS26-specific probes. Characterization of integrons was performed by PCR, cloning and sequencing.

RESULTS

Isolates exhibited highly similar PFGE patterns. Imipenem MICs were 2, 4, 16, 32 and 64 mg/L. The isolate with the highest imipenem MIC (Vipm-64) lacked a 36 kDa OMP. Expression of a cloned OmpK36 in this isolate reduced the imipenem MIC to susceptibility levels. Imipenem-hydrolysing activity was significantly higher in Vipm-16 as compared with the other isolates that expressed similar amounts of VIM-1. All isolates transferred beta-lactam resistance to Escherichia coli through conjugative, IncN plasmids that exhibited differences in the RFLP and hybridization patterns with bla(VIM)- and IS26-specific probes. The Vipm-16 plasmid, mediating the higher imipenem MICs among transconjugants, carried two copies of bla(VIM-1). Cloning and sequencing showed In-e541-like integrons truncated at the 5'CS by insertion of IS26 elements at two different positions.

CONCLUSIONS

A VIM-1-producing strain of K. pneumoniae has evolved through OMP alterations and rearrangements in the bla(VIM-1)-carrying plasmid probably mediated by IS26, generating isolates with imipenem MICs ranging from susceptibility to resistance.

Discrepancies and interpretation problems in susceptibility testing of VIM-1-producing Klebsiella pneumoniae isolates

Susceptibilities to beta-lactam antibiotics of five VIM-1-producing Klebsiella pneumoniae isolates were determined by broth microdilution, Etest, disk diffusion, and the automated systems Vitek 2, Phoenix, and MicroScan. Significant discrepancies were observed in the determination of susceptibility to imipenem and meropenem. Interpretation problems by the automated systems were also noted.

Emergence of CTX-M-15-producing enterobacteria in Cameroon and characterization of a blaCTX-M-15-carrying element

CTX-M-15-producing Klebsiella pneumoniae and Escherichia coli emerged recently in Cameroon. CTX-M-15 was encoded by two different multiresistance plasmids, of which one carried an ISEcp1-bla(CTX-M-15) element flanked by a 5-bp target site duplication and inserted within a Tn2-derived sequence. A truncated form of this element in the second plasmid was identified.

CMY-13, a novel inducible cephalosporinase encoded by an Escherichia coli plasmid

An IncN plasmid (p541) from Escherichia coli carried a Citrobacter freundii-derived sequence of 4,252 bp which included an ampC-ampR region and was bound by two directly repeated IS26 elements. ampC encoded a novel cephalosporinase (CMY-13) with activity similar to that of CMY-2. AmpR was likely functional as indicated in induction experiments.

Expanded-spectrum cephalosporin resistance in non-typhoid Salmonella

Expanded-spectrum cephalosporins (ESCs) such as ceftriaxone, together with fluorinated quinolones, are the choice antibiotics in the treatment of invasive salmonella infections. Resistance to ESCs among non-typhoid salmonella has been recognised since the late 1980s. Currently, ESC-resistant salmonella strains are reported world-wide and in some areas their incidence is significant. Resistance is mainly due to acquisition of multi-resistant plasmids encoding a variety of extended-spectrum and AmpC-type beta-lactamases. The origins of ESC-resistant salmonellae are diverse. Exchange of resistance determinants between salmonellae and nosocomial enterobacteria seems to be frequent, at least in developing countries. Also, the use of newer beta-lactams in animal husbandry and veterinary medicine may have facilitated the spread of ESC-resistant salmonella strains in livestock.

Characterization of In111, a class 1 integron that carries the extended-spectrum beta-lactamase gene blaIBC-1

A class 1 integron, In111, carried by a self-transferable plasmid from an Escherichia coli clinical strain was characterized. The variable region of In111 constituted an array of gene cassettes encoding the extended-spectrum beta-lactamase IBC-1, the aminoglycoside-modifying enzymes AAC(6')-Ib and ANT(3")-Ia, dihydrofolate reductase I and a putative polypeptide (SMR-2) sharing similarity with the Qac transporters. Transcription of the gene cassettes was driven by a hybrid-type P1 promoter located in a typical 5' conserved segment (CS). The 3'CS included sulI, qacEDelta1, orf5 and orf6. In111 was bounded on the right by an inversely oriented IRt. The 5'CS was preceded by an intact IS26 element followed by an aphA1 gene.

VIM-1 Metallo-beta-lactamase-producing Klebsiella pneumoniae strains in Greek hospitals

Seventeen Klebsiella pneumoniae clinical isolates carrying the bla(VIM-1) metallo-beta-lactamase gene were collected in the intensive care units of three hospitals in Athens, Greece, in 2002. They exhibited various carbapenem resistance levels (Etest MICs of imipenem ranged from 4 to 32 microg/ml). All isolates gave positive results by the imipenem-EDTA synergy Etest. The isolates were classified into four main types by pulsed-field gel electrophoresis; the majority of the isolates (5 and 10 isolates) belonged to two types. The bla(VIM-1) gene cassette was part of the variable region of a class 1 integron that also included aac6, dhfrI, and aadA. This structure was carried by transferable plasmids.

Expression of immunoreactive forms of the hepatitis C NS5A protein in E. coli and their use for diagnostic assays

In this study different forms of the hepatitis C virus (HCV) NS5A protein, including a nearly full-length, an amino-terminal and a carboxy-terminal truncated form were produced in E. coli as fusion proteins with the MBP or the GST protein. The chimeric proteins were tested for their reactivity with sera from HCV infected patients by immunoblot and ELISA assays. A panel of 110 sera specimens, including 39 HCV-positive sera, 27 sera from patients with non-HCV-associated liver disease and 44 healthy individuals were analyzed for the presence of antibodies to NS5A. Twenty four (61 %) out of the 39 HCV positive sera, showed reactivity against the nearly full length NS5A, 21 (54 %) against the amino-terminal part of NS5A and 20 (51 %) against the carboxy-terminal part of the NS5A protein in immunoblot assays, suggesting that immunoreactive epitopes are present both at the carboxy- and the amino- terminal part of the protein. None of the 71 HCV-negative serum samples showed any reactivity against the NS5A antigens. With the exception of one patient, similar data were obtained with an ELISA assay based on the use of the nearly full-length NS5A antigen. The data indicate that new forms of NS5A may be potentially valuable antigens for the development of serological assays for HCV.

CTX-m-3 beta-lactamase-producing Escherichia coli from Greece

An Escherichia coli clinical strain resistant to all beta-lactams except carbapenems was isolated in a Greek hospital. Analysis of beta-lactamase content by isoelectric focusing, PCR assays specific for various bla genes, and DNA sequencing showed that the strain produced TEM-1, a Citrobacter freundii AmpC-related cephalosporinase, and CTX-M-3. The blaCTX.M-3 gene was carried by a 120-kb plasmid that was readily transferable to a susceptible E. coli host.

Evaluation of an anti-PBP 2a slide latex agglutination test in coagulase-negative staphylococci isolated in Greek hospitals

Oxacillin resistance was examined in 258 coagulase-negative staphylococci from Greek hospitals. mecA DNA was detected in 168 isolates, which were also resistant to oxacillin by agar dilution and disk diffusion, according to the current NCCLS breakpoints. Both methods exhibited a relatively low specificity misclassifying 21 and 19 of the 90 mecA-negative isolates respectively as oxacillin resistant. In contrast, an anti-PBP 2a latex agglutination test, applied after induction by oxacillin, correctly classified 163 mecA-positive (sensitivity 97%) and 88 mecA-negative isolates (specificity 97.7%).

Survey of methicillin-resistant coagulase-negative staphylococci in the hospitals of central Greece

A sample of 450 consecutive, non-replicated coagulase-negative staphylococci (CoNS), collected from clinical specimens during the period 2000-2001 from the five major hospitals of Thessaly district (Central Greece) were investigated for resistance to methicillin. Most of the isolates had been collected in a sporadic fashion from the intensive care units and the surgical wards of the participating hospitals. The majority of the isolates (76%) were Staphylococcus epidermidis (50%), Staphylococcus haemolyticus (14.8%) and Staphylococcus hominis (11.1%). All 316 isolates (70%) were classified as resistant according to NCCLS breakpoints (MIC > or =0.5 mg/l); 268 (59.5%) of them were mecA-positive in a PCR-based assay. All isolates with MIC > or =8 mg/l carried the gene, while, only 23.8% of isolates with MIC, 0.5-4 mg/l were carriers. Only 9% of the mecA-positive isolates were found to be sensitive to various non-beta-lactams, while 41.8% of the isolates were resistant to more than three antimicrobial groups apart from beta-lactams. Molecular typing by PFGE showed apparent heterogeneity among isolates of each species and the absence of predominant clones.

An integron-associated beta-lactamase (IBC-2) from Pseudomonas aeruginosa is a variant of the extended-spectrum beta-lactamase IBC-1

An extended-spectrum beta-lactamase, IBC-2, produced by a clinical strain of Pseudomonas aeruginosa, was characterized. bla(IBC-2) was found, as a gene cassette, to be the sole gene within the variable region of a class 1 integron probably located in the chromosome. IBC-2 is a variant of IBC-1 and GES-1, differing by one amino acid from each of these beta-lactamases. When expressed in Escherichia coli, IBC-2 was observed to confer resistance to ceftazidime and decreased susceptibility to other oxyimino-beta-lactams.

Substitution of Thr for Ala-237 in TEM-17, TEM-12 and TEM-26: alterations in beta-lactam resistance conferred on Escherichia coli

Non-naturally occurring mutants of TEM-17 (E104K), TEM-12 (R164S) and TEM-26 (E104K:R164S) extended-spectrum (ES) beta-lactamases bearing threonine at position 237 were constructed by site-specific mutagenesis and expressed under isogenic conditions in Escherichia coli. Quantification of beta-lactamase activities and immunoblotting indicated that Ala-237-->Thr did not significantly affect expression levels of these ES enzymes. Minimum inhibitory concentrations of beta-lactam antibiotics showed that the presence of threonine at position 237 exerted a dominant effect increasing the enzymes' preference for various early generation cephalosporins over penicillins. Activity against broad-spectrum oxyimino-beta-lactams was also changed. The effect of Ala-237-->Thr on the activity against ceftazidime, aztreonam, cefepime and cefpirome of all three ES TEM enzymes was detrimental. Introduction of Thr-237 improved activity against cefotaxime and ceftriaxone in TEM-12 and TEM-26, but not in TEM-17.

Methicillin-resistant Staphylococcus aureus in the hospitals of central Greece

A total of 250 consecutive Staphylococcus aureus clinical isolates were collected during the period 1999-2000 from the five major hospitals of the district of Thessaly (Central Greece). Thirty seven (14.8%) of the isolates were mecA-positive (MRSA) in a PCR-based assay; all exhibited resistance to oxacillin (agar dilution MICs > or =4 mg/L) and were also resistant to multiple antibiotics. Most of the MRSA isolates had been collected in the intensive care units and the surgical wards of the participating hospitals in a sporadic fashion. The MRSA incidence found here was significantly lower than reported in previous studies from Greece. Molecular typing by PFGE showed that the MRSA isolates were distributed between three pulsotypes. Evaluation of various conventional methods for assessing methicillin resistance showed that oxacillin agar dilution and immunological detection of PBP2a with the Slidex MRSA Detection kit were the most reliable in this setting. Misclassifications of isolates exhibiting low-level resistance (oxacillin MIC 2-4 mg/L) occurred with the salt agar screen, the oxacillin disk diffusion and the ATB Staph System methods.

Diversity of beta-lactam resistance levels among related Klebsiella pneumoniae strains isolated in an intensive care unit

Seven multiresistant Klebsiella pneumoniae strains isolated in an intensive care unit were studied. Susceptibility to beta-lactams was determined with the E test. Molecular-typing of the isolates was performed by a PCR-based technique (ERIC2-PCR). Sonic cell-extracts were used as beta-lactamase preparations. Beta-lactamase quantities were evaluated measuring nitrocefin hydrolysis. The similarity of the ERIC2-PCR patterns indicated that the seven isolates constituted a single clone. The levels of resistance to oximino-beta-lactams, however, were different. There were indications that the differences in susceptibilities were due, at least partly, to differences in the levels of expression of an extended-spectrum beta-lactamase (most likely SHV-5). Related K. pneumoniae isolates may exhibit different levels of resistance to beta-lactams. Therefore, comparison of resistance phenotypes is of limited usefulness in epidemiological investigations of nosocomial infections caused by resistant K. pneumoniae.

The C-terminal cytoplasmic tail of herpes simplex virus type 1 gE protein is phosphorylated in vivo and in vitro by cellular enzymes in the absence of other viral proteins

Herpes simplex virus 1 glycoprotein E (gE-1) is highly phosphorylated in culture cells during infection. In this report, it is shown that phosphorylation is mediated by host enzymes in human cells stably transfected with gE, in the absence of other herpesvirus products. In contrast, a tailless gE product (C terminus deletion mutant) is not phosphorylated. By using an in vitro kinase assay combined with linker-insertion mutagenesis, it is shown that casein kinase II catalyses the phosphorylation of the C-terminal domain of the protein. Also, it is demonstrated that the serine residues at positions 476 and/or 477 in the cytoplasmic portion of the protein are the major acceptors for the phosphate groups.

Properties of mutant SHV-5 beta-lactamases constructed by substitution of isoleucine or valine for methionine at position 69

The effect of replacement of Met-69 by Ile or Val on the properties of the extended-spectrum beta-lactamase SHV-5 was studied. Mutant enzymes were constructed by site-specific mutagenesis and expressed under isogenic conditions in Escherichia coli DH5alpha cells. Compared with SHV-5, the mutant beta-lactamases conferred lower levels of beta-lactam resistance and were less efficient in hydrolyzing ampicillin, cephalothin, and cefotaxime. The substitutions rendered SHV-5 less susceptible to inhibition by clavulanate, sulbactam, and tazobactam; however, the MICs of penicillin-inhibitor combinations remained similar, suggesting an attenuation of penicillinase activity.

Emergence of an inhibitor-resistant beta-lactamase (SHV-10) derived from an SHV-5 variant

An inhibitor-resistant beta-lactamase (SHV-10), derived from an SHV-5 variant (SHV-9), was found in an Escherichia coli clinical isolate. In SHV-10, Ser-130 was replaced by Gly. The enzyme partially retained its ability to hydrolyze penicillins, but its activity against cephalosporins was drastically reduced. A Ser-130-->Gly mutant of the prototype SHV-5, obtained by site-directed mutagenesis, had properties similar to those of SHV-10.

In vitro activity of cefetamet against enterobacteria expressing an SHV-5-type beta-lactamase

The in vitro activity of cefetamet against Escherichia coli, Klebsiella pneumoniae and Serratia marcescens strains expressing an SHV-5-type beta-lactamase was evaluated. Most of the examined strains were susceptible to the antibiotic. Cefetamet was found to be considerably more active than ceftazidime and aztreonam. Its activity was comparable to that of cefotaxime. Cefetamet MIC values were related to the quantity of the enzyme expressed. The SHV-5-type enzyme hydrolysed cefetamet with an efficiency (Vmax/Km) similar to that of ceftazidime.

Transferable cefoxitin resistance in enterobacteria from Greek hospitals and characterization of a plasmid-mediated group 1 beta-lactamase (LAT-2)

Cefoxitin resistance in Klebsiella pneumoniae from Escherichia coli strains isolated in Greek hospitals was found to be due to the acquisition of similar plasmids coding for group 1 beta-lactamases. The plasmids were not self-transferable but were mobilized by conjugative plasmids. These elements have also been spread to Enterobacter aerogenes. The most common enzyme was a Citrobacter freundii-derived cephalosporinase (LAT-2) which differed from LAT-1 by three amino acids.

Characterization of the US8.5 protein of herpes simplex virus

In a previous study a novel gene designated as US8.5 was identified in the unique short component of the herpes simplex virus type 1 (HSV1) genome. Epitope tagging experiments suggested the existence of a protein encoded by this gene in HSV1 infected cells. To further analyze the US8.5 gene product and function, a rabbit polyclonal antiserum was raised against a recombinant beta-galactosidase-US8.5 fusion protein expressed in E. coli. This antiserum reacted specifically with a 19 kDa protein in HSV1(F) infected cells as shown by immunoblotting and immunoprecipitation experiments. In addition, using the same antiserum a 21 kDa protein was detected in lysates from cells infected with HSV2(G), which was most likely the HSV2 homolog of US8.5. Kinetic studies indicated that US8.5 is expressed as gamma 1 gene. In addition, the US8.5 protein was immunoprecipitated with the anti-US8.5 serum from 32P-labeled lysates of Vero cells infected with HSV1, demonstrating that the protein is phosphorylated. Immunofluorescence studies localized the US8.5 protein to the nucleoli of HSV1 infected cells.

Expression of the herpes simplex virus type 1 glycoprotein E in human cells and in Escherichia coli: protection studies against lethal viral infection in mice

The objective of this study was to examine the protective efficacy of purified recombinant herpes simplex virus type 1 (HSV-1) glycoprotein E (gE-1) in the mouse lethal challenge model. A secreted form of gE-1 (hgE-1s) protein, containing amino acids 1-406, was produced in human cells by using the episomal replicating pRP-RSV expression vector. In addition, a portion of the gE-1 (bgE-1t) protein corresponding to amino acids 90-406, was expressed in Escherichia coli as a fusion protein with maltose binding protein using the pMAL-c2 expression vector. Mice vaccinated with hgE-1s developed high serum titres of HSV-1-neutralizing antibodies and were significantly protected from intraperitoneal lethal HSV-1 challenge, whereas mice vaccinated with bgE-1t exhibited only moderate levels of protective immunity. These results demonstrate that the expression of gE-1 in human cells has a strong impact on its protective efficacy and that most importantly the hgE-1s protein could be of values as a component of an HSV multi-subunit vaccine.

Escherichia coli expressed herpes simplex virus gG1 and gG2 proteins in ELISA and immunoblotting assays

The type 1 and type 2 glycoprotein G (gG1 and gG2) of herpes simplex virus (HSV) were expressed in Escherichia coli as fusion proteins with the maltose binding protein (MBP) using the pMAL-c2 expression vector. The MBP-gG1 fusion protein contains all but the four amino acids from the amino-terminus of gG1, whereas the MBP-gG2 fusion protein was missing the first 30 amino acids that comprise the signal peptide of the protein. The diagnostic value of these antigens was examined by two methods: (1) immunoblot assay based on MBP-gG1 and MBP-gG2 fusion proteins present in crude E. coli cell extracts and (2) enzyme-linked immunosorbent assay (ELISA) of immunoaffinity-purified recombinant MBP-gG1 and MBP-gG2 fusion proteins. Of 28 serum samples known to have antibody to HSV-1 (10 specimens positive for HSV-1 alone and 18 specimens positive for mixed antibody to HSV-1/HSV-2), 27 were reactive to the MBP-gG1 recombinant protein both in ELISA and in immunoblotting. In addition, of 20 serum samples known to have antibody to HSV-2 (2 specimens positive for HSV-2 alone and 18 samples positive for mixed antibody to HSV-1/HSV-2), 15 were found to be reactive to the MBP-gG2 recombinant protein by ELISA and 16 by immunoblotting. None of the 13 HSV-antibody-negative serum samples showed reactivity to the MBP-gG1 or MBP-gG2 antigens by either assay. Moreover, none of the serum samples known to have antibody to HSV-1 alone showed reactivity to the MBP-gG2 recombinant antigen. This study verified the potential application of the E. coli-expressed recombinant gG1 and gG2 proteins as diagnostic antigens and demonstrated the MBP fusion system to be a simple and effective method of producing adequate amounts of low-cost, easily purified gG antigens.