Biochemical characterization of a novel extended-spectrum beta-lactamase from Pseudomonas aeruginosa 802

Dissemination and genetic support of broad-spectrum beta-lactam-resistant Escherichia coli strain isolated from two Tunisian hospitals during 2004-2012

BACKGROUND

The dissemination of extended-spectrum β-lactamase (ESBL)-producing bacteria presented a great concern worldwide. Gram-negative organisms such as Escherichia coli and Klebsiella pneumoniae are the most frequently isolated pathogens responsible for nosocomial infections.

OBJECTIVES

The aim of this study was to investigate and to follow the emergence of resistance and the characterization of Extended-Spectrum Beta-Lactamases (ESBL) among broad-spectrum beta-lactam-Escherichia coli clinical isolates recovered from the military hospital and Habib Thameur hospital in Tunisia.

METHODS

A total of 113 E.coli isolates obtained during the period 2004 through 2012 showed a significant degree of multi-resistance. Among these strains, the double-disk synergy test confirmed the ESBL phenotype in 46 isolates. These included 32(70%) strains from Hospital A and 14(30%) from Hospital B.

RESULTS

The ESBL was identified as CTX-M-15. The ESBL resistance was transferred by a 60 kb plasmid CTXM-15-producing isolates were unrelated according to the PFGE analysis and characterization of the regions surrounding the blaCTX-M-15 showed the ISEcp1 elements located in the upstream region of the bla gene and 20 of them truncated by IS26.

CONCLUSION

ESBL producing E. coli strains are a serious threat in the community in Tunisia and we should take into consideration any possible spread of such epidemiological resistance.

Multidrug-resistant phenotype and isolation of a novel SHV- beta-Lactamase variant in a clinical isolate of Enterobacter cloacae

Background

ESBL-producing bacteria are a clinical problem in the management of diseases caused by these pathogens. Worldwide, systemic infections with BL enzymes are evolving by mutations from classical bla genes in an intensified manner and they continue to be transferred across species.

Results

E.cloacae BF1417 isolate and its transconjugants gave positive results with the DDST, suggesting the presence of ESBL. Sequence analysis revealed a bla_SHV-ESBL-type gene that differs from the gene encoding SHV-1 by five point mutations resulting in three amino acid substitutions in the coding region: C123R, I282T and L286P. This novel SHV-type enzyme was designated SHV-128. The conjugation tests and plasmid characterization showed that the bla_SHV-128 is located on a conjugative plasmid IncFII type. Expression studies demonstrated that the above mutations participated in drug resistance, hydrolysis of extended spectrum β-lactam and the change of the isoelectric point of the protein.

Conclusion

These findings underscore the diversity by which antibiotic resistance can arise and the evolutionary potential of the clinically important ESBL enzymes. In addition, this study highlights the need for systematic surveillance of ESBL-mediated resistance as well as in clinical areas and communities.

Cloning and sequencing of the class A β-lactamase gene (blaTEM-15) located on a chromosomal Tn801 transposon

Escherichia coli CA0210 was identified in a stool culture of a 03-month-neonate in Tunisia. This strain was resistant to beta-lactams, including ureidopenicillins, ticarcillin-clavulanic acid, cefpirome, ceftazidime, and cefotaxime, but it remained susceptible to imipenem and cefoxitin. The beta-lactam-hydrolyzing beta-lactamase gene of E. coli CA0210 and the upstream and downstream regions were cloned, sequenced, and expressed in E. coli DH5alpha. These resistances were carried by a 1080-bp chromosomal gene that encoded a beta-lactamase with a pI of 6.3. Cloning and sequencing experiments showed that the corresponding blaTEM-15 gene was part of a chromosomally located Tn801 transposon.

First characterization in Tunisia of a TEM-15, extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolate

Klebsiella pneumoniae CH0905 strain exhibiting high-level cefotaxime resistance was isolated from a stool culture in the intensive care unit. The resistance gene responsible was shown to be located on a conjugative 60-kb plasmid designated pCH0905. The minimum inhibitory concentration (MIC) values for cefotaxime and ceftazidime of the original isolate and the transconjugates were 256 mug/ml. Isoelectric focusing of a protein preparation from the K. pneumoniae strain showed beta-lactamases with the pI values of 7.6 and 6.3. A 1,080-bp fragment amplified with PCR was cloned into the pGEM-T Easy vector. The nucleotide sequence of the complete 1,080 bp was determined. Sequence analysis revealed that the bla(TEM) gene of pCH0905 differed from bla(TEM-1) by two mutations, leading to the following amino acid substitutions: the glutamic acid residue at position 104 by lysine and the glycine residue at position 238 by serine (Ambler numbering). The association of these two mutations was described previously in TEM-15 beta-lactamase, but this is the first detection of this enzyme in Tunisia.

Cefotaxime and ceftazidime-resistant Escherichia coli isolate producing TEM-15 beta-lactamase from a Tunisian hospital

A clinical isolate of Escherichia coli LBT04 was found to have a high-level resistance to broad-spectrum beta-lactams. Analysis of this strain by the disk diffusion test revealed synergies between clavulanic acid and ceftazidime, cefotaxime. Clavulanic acid decreased the MICs of ceftazidime, cefotaxime, and ceftriaxone, which suggested that LBT04 produced an extended-spectrum beta-lactamase. These resistances were carried by a 1080-bp chromosomal gene that encoded a beta-lactamase with a pI of 6.3. Cloning and sequencing experiments showed that this beta-lactamase revealed identity with the bla(TEM-1) gene encoding the TEM-1 beta-lactamase, except for a replacement of the Glu residue at position 104 by Lys, and of the Gly residue at position 238 by Ser. These two mutations were encountered in TEM-15 beta-lactamase, but this is the first description of this enzyme in the E. coli species in Tunisian hospitals.

A novel extended-spectrum TEM-type beta-lactamase, TEM-138, from Salmonella enterica serovar Infantis

A novel natural TEM beta-lactamase with extended-spectrum activity, TEM-138, was identified in a ceftazidime-resistant clinical isolate of Salmonella enterica serovar Infantis. Compared to TEM-1, TEM-138 contains the following mutations: E104K, N175I, and G238S. The bla(TEM-138) gene was located on a 50-kb transferable plasmid. Expression studies with Escherichia coli revealed efficient ceftazidimase and cefotaximase activities for TEM-138.

Involvement of SHV-12 and SHV-2a encoding plasmids in outbreaks of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a Tunisian neonatal ward

Previous genotypic investigations of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae recovered in a Tunisian neonatal ward revealed the spread of two epidemic strains and a high number of genetically unrelated isolates. The aim of the present study was to determine the role of the dissemination of self-transferrable plasmids harboring bla genes in the outbreaks experienced by the ward. The 49 previously identified clinical isolates of ESBL-producing K. pneumoniae were examined for relationships between their enzymes and plasmids. Analysis of crude extracts by isoelectric focusing showed four beta-lactamase-activities at pI 8.2, 7.6, 6, and 5.4. Clinical isolates contained large plasmids that could be transferred by conjugation and transformation conferring resistance to expanded-spectrum cephalosporins. DNA amplification and sequencing were performed to confirm the identities of transferred beta-lactamases. Nucleotide sequence analysis of SHV-specific PCR products from six isolates identified two bla(SHV) genes corresponding to SHV derived ESBLs, SHV-12 and SHV-2a. PstI digestion of plasmid DNA from transformants revealed six restriction patterns. The occurrence of the prevalent plasmid pattern in both epidemic strains and unrelated isolates indicated that diffusion and endemic persistence of the bla(SHV-ESBL) genes in the ward were due to concomitant spread of epidemic strains and plasmid dissemination among unrelated strains.