A conserved active site PenA β-lactamase Ambler motif specific for Burkholderia pseudomallei/B. mallei is likely responsible for intrinsic amoxicillin-clavulanic acid sensitivity and facilitates a simple diagnostic PCR assay for melioidosis

Burkholderia pseudomallei is a soil- and water-dwelling Gram-negative bacterium that causes melioidosis in humans and animals. Amoxicillin-clavulanic acid (AMC) susceptibility has been hailed as an integral part of the screening algorithm for identification of B. pseudomallei, but the molecular basis for the inherent AMC susceptibility of this bacterium remains undefined. This study showed that B. pseudomallei (and the closely-related B. mallei) wild-type strains are the only Burkholderia spp. that contain a ⁷⁰STSK⁷³ PenA Ambler motif. This motif was present in >99.5% of 1820 analysed B. pseudomallei strains and 100% of 83 analysed B. mallei strains, and is proposed as the likely cause for their inherent AMC sensitivity. The authors developed a polymerase chain reaction (PCR) assay that specifically amplifies the penA⁷⁰ST(S/F)K⁷³-containing region from B. pseudomallei and B. mallei, but not from the remaining B. pseudomallei complex species or the ⁷⁰STFK⁷³ region from the closely-related penB of B. cepacia complex species. The abundance and purity of the 193-bp PCR fragment from putative B. pseudomallei isolates from clinical and environmental samples is likely sufficient for reliable confirmation of the presence of B. pseudomallei. The PCR assay is designed to be especially suited for use in resource-constrained areas. While not further explored in this study, the assay may allow diagnosis of putative B. mallei in culture isolates from animal and human samples.

Insights into structure and activity relationship of clinically mutated PER1 and PER2 class A β-lactamase enzymes

PER1 and PER2 are among the class A β-lactamase enzymes, which have evolved clinically to form antibiotic resistance and have significantly expanded their spectrum of activity. Hence, there is a need to study the clinical mutation responsible for such β-lactamase mediated antibiotic resistance. Alterations in catalytic centre and Ω-loop structure could be the cause of antibiotic resistance in these β-lactamase enzymes. Structural and functional alterations are caused due to mutations on or near the catalytic centre, which results in active site plasticity and are responsible for its expanded spectrum of activity in these class A β-lactamase enzymes. Multiple sequence alignment, structure, kinetic, molecular docking, MMGBSA and molecular dynamic simulation comparisons were done on 38 clinically mutated and wild class A β-lactamase enzymes. This work shows that PER1 and PER2 enzymes contains most unique mutations and have altered Ω-loop structure, which could be responsible for altering the structure-activity relationship and extending the spectrum of activity of these enzymes. Alterations in molecular docking, MMGBSA, kinetic values reveals the modification in the binding and activity of these clinically mutated enzymes with antibiotics. Further, the cause of these alterations can be revealed by active site interactions and H-bonding pattern of these enzymes with antibiotics. Met69Gln, Glu104Thr, Tyr105Trp, Met129His, Pro167Ala, Glu168Gln, Asn170His, Ile173Asp and Asp176Gln mutations were uniquely found in PER1 and PER2 enzymes. These mutations occurs at catalytic important residues and results in altered interactions with β-lactam antibiotics. Hence, these mutations could be responsible for altering the structure-activity of PER1 and PER2 enzymes.

Regulation of Class A β-Lactamase CzoA by CzoR and IscR in Comamonas testosteroni S44

A genomic analysis of Comamonas testosteroni S44 revealed a gene that encodes a LysR family transcriptional regulator (here named czoR, czo for cefazolin) located upstream of a putative class A β-lactamase encoding gene (here named czoA). A putative DNA-binding motif of the Fe-S cluster assembly regulator IscR was identified in the czoR-czoA intergenic region. Real-time RT-PCR and lacZ fusion expression assays indicated that transcription of czoA and czoR were induced by multiple β-lactams. CzoA expressed in Escherichia coli was shown to contribute to susceptibility to a wide range of β-lactams judged from minimum inhibitory concentrations. In vitro enzymatic assays showed that CzoA hydrolyzed seven β-lactams, including benzylpenicillin, ampicillin, cefalexin, cefazolin, cefuroxime, ceftriaxone, and cefepime. Deletion of either iscR or czoR increased susceptibility to cefalexin and cefazolin, while complemented strains restored their wild-type susceptibility levels. Electrophoretic mobility shift assays (EMSA) demonstrated that CzoR and IscR bind to different sites of the czoR-czoA intergenic region. Precise CzoR- and IscR-binding sites were confirmed via DNase I footprinting or short fragment EMSA. When cefalexin or cefazolin was added to cultures, czoR deletion completely inhibited czoA expression but did not affect iscR transcription, while iscR deletion decreased the expressions of both czoR and czoA. These results reveal that CzoR positively affects the expression of czoA with its own expression upregulated by IscR.

Emergence of sequence type 252 Enterobacter cloacae producing GES-5 carbapenemase in a Czech hospital

ST252 Enterobacter cloacae, producing GES-5 carbapenemase, was isolated in a Czech hospital. bla_GES-5 was part of a novel class 1 integron, In1406, which also included a new allele of the aadA15 gene cassette. In1406 was located on a ColE2-like plasmid, pEcl-35771cz (6953bp).

A one-step multiplex PCR to identify Klebsiella pneumoniae, Klebsiella variicola, and Klebsiella quasipneumoniae in the clinical routine

Klebsiella pneumoniae, Klebsiella variicola and Klebsiella quasipneumoniae are difficult to differentiate phenotypically, leading to misinterpretation of their infection prevalence. We propose a multiplex PCR for bla_SHV, bla_LEN and bla_OKP and their flanking gene (deoR). Since this scheme focuses only on chromosomal genes, it will be feasible for Klebsiella identification in the clinical routine.