CTX-M-127 with I176F mutations found in bacteria isolates from Bangladeshi circulating banknotes

Extended-spectrum beta-lactamase (ESBL)-producing organisms are widely recognized as clinically relevant causes of difficult-to-treat infections. CTX-M has formed a rapidly growing family distributed worldwide among a wide range of clinical bacteria, particularly members of Enterobacteriaceae. Circulating banknotes, exchanged daily among people, pose a potential vehicle for transmitting multidrug resistance. We screened for ESBL-carrying bacteria in the present study and reported CTX-M mutations in Bangladesh's banknotes. We sequenced the genes and performed homology modeling using the Swiss model with CTX-M-15 (4HBT) as a template. Then, we performed molecular docking of mecillinam with the template and the generated model using Autodock 4.2 (Release 4.2.6). After docking, we visually inspected the complexes built using Autodock tools for polar contacts and pi-pi interactions in PyMOL 2.5.4. Our partially sequenced blaCTX-M was related to blaCTX-M-10 and blaCTX-M-15. We observed multiple single-nucleotide substitution mutations, i.e., G613T (silent mutation), A626T (I176F), and A503G (N135D). Homology modeling showed high similarity when the model was superimposed over the template. The orientation of Asn (135) in the template and Asp (135) in the model does not show a significant difference. Likewise, Ile (176) in the template and Phe (176) in the model offer the same orientation. Our generated model could bind to Lys237, Ser240, and Asp135 residues with the lowest binding energy on docking. Our predicted binding of the mecillinam to the mutated D-135 residue in the model indicates contributions and supports previous reports proposing CTX-M-15 to CTX-M-127 mutational conversion on the mecillinum resistance phenotype.

(p)ppGpp modifies RNAP function to confer β-lactam resistance in a peptidoglycan-independent manner

(p)ppGpp is a nucleotide alarmone that controls bacterial response to nutrient deprivation. Since elevated (p)ppGpp levels confer mecillinam resistance and are essential for broad-spectrum β-lactam resistance as mediated by the β-lactam-insensitive transpeptidase YcbB (LdtD), we hypothesized that (p)ppGpp might affect cell wall peptidoglycan metabolism. Here we report that (p)ppGpp-dependent β-lactam resistance does not rely on any modification of peptidoglycan metabolism, as established by analysis of Escherichia coli peptidoglycan structure using high-resolution mass spectrometry. Amino acid substitutions in the β or β' RNA polymerase (RNAP) subunits, alone or in combination with the CRISPR interference-mediated downregulation of three of seven ribosomal RNA operons, were sufficient for resistance, although β-lactams have no known impact on the RNAP or ribosomes. This implies that modifications of RNAP and ribosome functions are critical to prevent downstream effects of the inactivation of peptidoglycan transpeptidases by β-lactams.

Phage-induced bacterial morphological changes reveal a phage-derived antimicrobial affecting cell wall integrity

In a looming post-antibiotic era, antibiotic alternatives have become key players in the combat against pathogens. Although recent advances in genomic research allow scientists to fully explore an organism's genome in the search for novel antibacterial molecules, laborious work is still needed in order to dissect each individual gene product for its antibacterial activity. Here, we exploited phage-induced bacterial morphological changes as anchors to explore and discover a potential phage-derived antimicrobial embedded in the phage genome. We found that, upon vibriophage KVP40 infection, Vibrio parahaemolyticus exhibited morphological changes similar to those observed when treated with mecillinam, a cell wall synthesis inhibitor, suggesting the mechanism of pre-killing that KVP40 exerts inside the bacterial cell upon sieging the host. Genome analysis revealed that, of all the annotated gene products in the KVP40 genome that are involved in cell wall degradation, lytic transglycosylase (LT) is of particular interest for subsequent functional studies. A single-cell morphological analysis revealed that heterologous expression of wild-type KVP40-LT induced similar bacterial morphological changes to those treated with the whole phage or mecillinam, prior to cell burst. On the contrary, neither the morphology nor the viability of the bacteria expressing signal-peptide truncated- or catalytic mutant E80A- KVP40-LT was affected, suggesting the necessity of these domains for the antibacterial activities. Altogether, this research paves the way for the future development of the discovery of phage-derived antimicrobials that is guided through phage-induced morphological changes.

Mecillinam: A Possible Alternative Option for Non-Complicated Urinary Tract Infections Treatment Caused by Enterobacterales

N/a.

Clavulanate combinations with mecillinam, cefixime or cefpodoxime against ESBL-producing Enterobacterales frequently associated with blaOXA-1 in a paediatric population with febrile urinary tract infections

OBJECTIVES

Oral treatment of febrile urinary tract infections (FUTIs) can be impaired by MDR Enterobacterales often combining ESBL and inhibitor-resistant genes. We studied the impact of β-lactamases and Enterobacterales' genotypes on the cefixime, cefpodoxime and mecillinam ± amoxicillin/clavulanate MICs.

MATERIALS AND METHODS

In this multicentric study, we included 251 previously whole-genome-sequenced ESBL-producing Enterobacterales, isolated in French children with FUTIs. The MICs of cefixime, cefpodoxime, mecillinam alone and combined with amoxicillin/clavulanate were determined and analysed with respect to genomic data. We focused especially on the isolates' ST and their type of β-lactamases. Clinical outcomes of patients who received cefixime + amoxicillin/clavulanate were also analysed.

RESULTS

All isolates were cefixime and cefpodoxime resistant. Disparities depending on blaCTX-M variants were observed for cefixime. The addition of amoxicillin/clavulanate restored susceptibility for cefixime and cefpodoxime in 97.2% (MIC50/90 of 0.38/0.75 mg/L) and 55.4% (MIC50/90 of 1/2 mg/L) of isolates, respectively, whatever the ST, the blaCTX-M variants or the association with inhibitor-resistant β-lactamases (34.2%). All isolates were susceptible to mecillinam + amoxicillin/clavulanate with MIC50/90 of 0.19/0.25 mg/L, respectively. Neither therapeutic failure nor any subsequent positive control urine culture were reported for patients who received cefixime + amoxicillin/clavulanate as an oral relay therapy (n = 54).

CONCLUSIONS

Despite the frequent association of ESBL genes with inhibitor-resistant β-lactamases, the cefixime + amoxicillin/clavulanate MICs remain low. The in vivo efficacy of this combination was satisfying even when first-line treatment was ineffective. Considering the MIC distributions and pharmacokinetic parameters, mecillinam + amoxicillin/clavulanate should also be an alternative to consider when treating FUTIs in children.

Analysis of the effect of ppGpp on the ftsQAZ operon in Escherichia coli

Escherichia coli loses its rod shape by inactivation of PBP2 (penicillin-binding protein 2), target of the beta-lactam mecillinam. Under these conditions, cell division is blocked in rich medium. Division in the absence of PBP2 activity is restored (and resistance to mecillinam is conferred) when the three cell division proteins FtsQ, FtsA and FtsZ are overproduced, but not when only one or two of them are overproduced. Division in the absence of PBP2 activity is also restored by a doubling in the ppGpp pool, as in the argS201 mutant. However, the nucleotide ppGpp, a transcriptional regulator of many operons, does not govern any of the five promoters of the ftsQAZoperon, as shown by S1 mapping of ftsQAZ mRNA 5' ends in exponentially growing wild-type cells in the mecillinam-resistant argS201 mutant (intermediate ppGpp level) or during the stringent response elicited by isoleucine starvation (high ppGpp level). Furthermore, the concentration of FtsZ protein is not increased in exponentially growing mecillinam-resistant argS201 cells. These results show that the ftsQAZ operon is not the ppGpp target responsible for mecillinam resistance. We are currently trying to identify those targets that, at intermediate ppGpp levels, allow cells to divide as spheres in the absence of PBP2.

Penicillin-binding protein 2 inactivation in Escherichia coli results in cell division inhibition, which is relieved by FtsZ overexpression

Aminoacyl-tRNA synthetase mutants of Escherichia coli are resistant to amdinocillin (mecillinam), a beta-lactam antibiotic which specifically binds penicillin-binding protein 2 (PBP2) and prevents cell wall elongation with concomitant cell death. The leuS(Ts) strain, in which leucyl-tRNA synthetase is temperature sensitive, was resistant to amdinocillin at 37 degrees C because of an increased guanosine 5'-diphosphate 3'-diphosphate (ppGpp) pool resulting from partial induction of the stringent response, but it was sensitive to amdinocillin at 25 degrees C. We constructed a leuS(Ts) delta (rodA-pbpA)::Kmr strain, in which the PBP2 structural gene is deleted. This strain grew as spherical cells at 37 degrees C but was not viable at 25 degrees C. After a shift from 37 to 25 degrees C, the ppGpp pool decreased and cell division was inhibited; the cells slowly carried out a single division, increased considerably in volume, and gradually lost viability. The cell division inhibition was reversible when the ppGpp pool increased at high temperature, but reversion required de novo protein synthesis, possibly of septation proteins. The multicopy plasmid pZAQ, overproducing the septation proteins FtsZ, FtsA, and FtsQ, conferred amdinocillin resistance on a wild-type strain and suppressed the cell division inhibition in the leuS(Ts) delta (rodA-pbpA)::Kmr strain at 25 degrees C. The plasmid pAQ, in which the ftsZ gene is inactivated, did not confer amdinocillin resistance. These results lead us to hypothesize that the nucleotide ppGpp activates ftsZ expression and thus couples cell division to protein synthesis.

Round-cell mutants of Salmonella typhimurium produced by transposition mutagenesis: lethality of rodA and mre mutations

Thirty-three insertions of transposon Tn10 delta 16 delta 17 into genes involved in the control of rod cell shape were isolated in Salmonella typhimurium by the characteristic glossy appearance of colonies composed of spherical cells. Genetic tests demonstrated that 25 (76%) were insertions in the rodA gene, 7 (21%) were mre mutants, and 1 (3%) was a divD mutant. No insertion in the pbpA gene were found. Insertions in cell shape genes only appeared when strains displaying resistance to mecillinam (not caused by beta-lactamase production) were employed. Neither rodA nor mre insertions could be transduced to wild-type strains but they were normally accepted by mecillinam-resistant derivatives and by cya and crp mutants, which, unlike the corresponding Escherichia coli strains, did not display resistance to mecillinam. On the other hand, the divD insertion could be efficiently transduced to any strain. It is concluded that the rodA, mre, and divD genes are involved in the control of rod cell shape but, in addition, the RodA and Mre products perform some function(s) that is essential for wild-type cells but dispensable for some mecillinam-resistant strains, and for cya and crp mutants.

Penicillin-binding protein 2 is essential in wild-type Escherichia coli but not in lov or cya mutants

Penicillin-binding protein 2 (PBP2), target of the beta-lactam mecillinam, is required for rod morphology and cell wall elongation in Escherichia coli. A new temperature-sensitive PBP2 allele and an in vitro-constructed insertion deletion allele were shown to be lethal in wild-type strains, establishing that the activity of this protein is essential. Mutations in the lov or cya genes, conferring mecillinam resistance, compensated for the deleterious effect of the absence of PBP2. The resulting double mutants grew as spheres. In a cya mutant lacking PBP2, the restoration of a Cya+ phenotype by addition of cyclic AMP caused lethality and a block in cell division. These results show that in wild-type cells, PBP2 is essential for growth and division.

Critical evaluation of amdinocillin disk susceptibility tests correlated with agar dilution tests

Tests with 10-micrograms amdinocillin disks were performed in parallel with agar dilution tests and three different ranges of inoculum density. A resistance breakpoint of less than or equal to 13 mm and an intermediate category of 14 to 16 mm are recommended. Susceptible strains provided zones greater than or equal to 17 mm in diameter, but many appeared to be resistant by the agar dilution methods if the inoculum exceeded 10(4) CFU per spot.

The X-ray structural investigation of 6-(n,n-1,6-hexyleneformamidine)-penicillanic acid (mecillinam)

A new type of 6-formamidinepenicillanic acid in which the omega-nitrogen atom is involved in the azaheptane ring (mecillinam) having a strong selective activity against Gram-negative bacteria strains has been investigated by the X-ray single-crystal diffraction methods using crystals in the solvated state. The conformation of penam part as well as of the amidine group is discussed. Two independent molecules of mecillinam found in the asymmetric unit of the crystal cell differ from each other in their detailed conformations. The problem of the stability of the compound has been discussed also.