Genetic regulation of penicillinase synthesis in Gram-positive bacteria

Beta-lactam resistance and the effectiveness of antimicrobial peptides against KPC-producing bacteria

Bacterial resistance is a problem that is giving serious cause for concern because bacterial strains such as Acinetobacter baumannii and Pseudomonas aeruginosa are difficult to treat and highly opportunistic. These bacteria easily acquire resistance genes even from other species, which confers greater persistence and tolerance towards conventional antibiotics. These bacteria have the highest death rate in hospitalized intensive care patients, so strong measures must be taken. In this review, we focus on the use of antimicrobial peptides (AMPs) as an alternative to traditional drugs, due to their rapid action and lower risk of generating resistance by microorganisms. We also present an overview of beta-lactams and explicitly explain the activity of AMPs against carbapenemase-producing bacteria as potential alternative agents for infection control.

Systems biology approach to functionally assess the Clostridioides difficile pangenome reveals genetic diversity with discriminatory power

SignificanceClostridioides difficile infections are the most common source of hospital-acquired infections and are responsible for an extensive burden on the health care system. Strains of the C. difficile species comprise diverse lineages and demonstrate genome variability, with advantageous trait acquisition driving the emergence of endemic lineages. Here, we present a systems biology analysis of C. difficile that evaluates strain-specific genotypes and phenotypes to investigate the overall diversity of the species. We develop a strain typing method based on similarity of accessory genomes to identify and contextualize genetic loci capable of discriminating between strain groups.

Lanza V, Rodríguez-Beltrán J, Galán JC, San Millán A, Cantón R, Coque TM. Evolutionary Pathways and Trajectories in Antibiotic Resistance

Evolution is the hallmark of life. Descriptions of the evolution of microorganisms have provided a wealth of information, but knowledge regarding "what happened" has precluded a deeper understanding of "how" evolution has proceeded, as in the case of antimicrobial resistance. The difficulty in answering the "how" question lies in the multihierarchical dimensions of evolutionary processes, nested in complex networks, encompassing all units of selection, from genes to communities and ecosystems. At the simplest ontological level (as resistance genes), evolution proceeds by random (mutation and drift) and directional (natural selection) processes; however, sequential pathways of adaptive variation can occasionally be observed, and under fixed circumstances (particular fitness landscapes), evolution is predictable. At the highest level (such as that of plasmids, clones, species, microbiotas), the systems' degrees of freedom increase dramatically, related to the variable dispersal, fragmentation, relatedness, or coalescence of bacterial populations, depending on heterogeneous and changing niches and selective gradients in complex environments. Evolutionary trajectories of antibiotic resistance find their way in these changing landscapes subjected to random variations, becoming highly entropic and therefore unpredictable. However, experimental, phylogenetic, and ecogenetic analyses reveal preferential frequented paths (highways) where antibiotic resistance flows and propagates, allowing some understanding of evolutionary dynamics, modeling and designing interventions. Studies on antibiotic resistance have an applied aspect in improving individual health, One Health, and Global Health, as well as an academic value for understanding evolution. Most importantly, they have a heuristic significance as a model to reduce the negative influence of anthropogenic effects on the environment.

Altered production of penicillin-binding protein 2a can affect phenotypic expression of methicillin resistance in Staphylococcus aureus

Altered production of penicillin-binding protein 2a (PBP 2a) may affect the phenotypic expression of resistance in methicillin-resistant Staphylococcus aureus (MRSA). COL, an MRSA strain that constitutively produces PBP 2a, was transformed with a recombinant plasmid containing the two beta-lactamase regulatory genes, blaI and blaR1, with either the beta-lactamase gene, blaZ, or a truncated blaZ. Both of the transformed MRSA strains now produced an inducible PBP 2a, and the MICs of nafcillin, methicillin, and imipenem for these strains were similar to those for the parental strain. A mutation in blaR1 that resulted in the complete repression of PBP 2a production altered the phenotypic expression of methicillin resistance in that strain, as evidenced by efficiency-of-plating experiments. Rather than being homogeneously resistant like COL, the blaR1 mutant strain now appeared to have a small resistant subpopulation. Gene products that regulate PBP 2a production may contribute to the organism's expression of methicillin resistance, but additional chromosomally located factors are required.

blaI and blaR1 regulate beta-lactamase and PBP 2a production in methicillin-resistant Staphylococcus aureus

For Staphylococcus aureus, it is hypothesized that two genes located upstream of the beta-lactamase gene, blaZ, are required for the inducible expression of beta-lactamase. blaR1 is predicted to encode a signal-transducing membrane protein, and blaI is predicted to encode a repressor protein. These same two genes may also regulate the production of penicillin-binding protein 2a (PBP 2a), a protein essential for expression of methicillin resistance. To confirm that these two genes encode products that can control both beta-lactamase and PBP 2a production, blaI, blaR1, and blaZ with a 150-nucleotide deletion at the 3' end were subcloned from a 30-kb staphylococcal beta-lactamase plasmid and three beta-lactamase-negative strains of methicillin-resistant S. aureus were transformed with the recombinant plasmid containing that insert. The production of PBP 2a and a nonfunctional beta-lactamase was detected by fluorography and by immunoblots with polyclonal antisera directed against each of the proteins. Whereas the parent strains did not produce beta-lactamase and constitutively produced PBP 2a, PBP 2a and a truncated beta-lactamase were now inducible in the transformants. Therefore, two plasmid-derived genes regulate the production of both PBP 2a and beta-lactamase.

Nucleotide sequence of the beta-lactamase gene from Enterococcus faecalis HH22 and its similarity to staphylococcal beta-lactamase genes

The nucleotide sequence of the constitutively produced beta-lactamase (Bla) gene from Enterococcus faecalis HH22 was shown to be identical to the published sequences of three of four staphylococcal type A beta-lactamase genes; more differences were seen with the genes for staphylococcal type C and D enzymes. One hundred forty nucleotides upstream of the beta-lactamase start codon were determined for an inducible staphylococcal beta-lactamase and were identical to those of the constitutively expressed enterococcal gene, indicating that the changes resulting in constitutive expression are not due to changes in the promoter or operator region. Moreover, complementation studies indicated that production of the enterococcal enzyme could be repressed. The genes for the enterococcal Bla and an inducible staphylococcal Bla were each cloned into a shuttle vector and transformed into enterococcal and staphylococcal recipients. The major difference between the backgrounds of the two hosts was that more enzyme was produced by the staphylococcal host, regardless of the source of the gene. The location of the enzyme was found to be host dependent, since each cloned gene generated extracellular (free) enzyme in the staphylococcus and cell-bound enzyme in the enterococcus. On the basis of the identities of the enterococcal Bla and several staphylococcal Bla sequences, these data suggest the recent spread of beta-lactamase to enterococci and also suggest the loss of a functional repressor.

Cloning and expression of the imipenem-hydrolyzing beta-lactamase operon from Pseudomonas maltophilia in Escherichia coli

The L-1 penicillinase structural gene, blaS, from Pseudomonas maltophilia has been cloned into the vector pACYC184. The pMON01 recombinant plasmid selected by ampicillin resistance carried a 2.6-kilobase Sau3A fragment of P. maltophilia DNA and was confirmed to express L-1 beta-lactamase by comparative isoelectric focusing. A detailed physical map was constructed, and the blaS structural gene was localized with a 17-mer oligonucleotide mixed probe encoding the L-1 N-terminal amino acid sequence. Induction studies confirmed constitutive expression. Isolation of a complete beta-lactamase operon was attempted by construction of a P. maltophilia genomic library into phage lambda 2001. A recombinant phage was selected by DNA hybridization, and the 13.4-kilobase DNA insert was physically mapped and subcloned into plasmid vectors. Expression and L-1 beta-lactamase synthesis were studied in Escherichia coli.

Nature of monocyclic beta-lactam antibiotic Nocardicin A to beta-lactamases

Nocardicin A is the antibiotic which was first found to possess a monocyclic beta-lactam ring. This antibiotic was inactivated by the cleavage of its beta-lactam ring. The direct spectrophotometric assay was applied to measure the rate of enzymatic hydrolysis of Nocardicin A. Nocardicin A was highly stable to both chromosomal and plasmid-mediated beta-lactamases. Of the nine beta-lactam antibiotics including cefoxitin and cefuroxime, Nocardicin A was the most stable to the beta-lactamases tested excluding those from Klebsiella oxytoca and Proteus vulgaris. The latter broad-spectrum beta-lactamases hydrolyzed Nocardicin A rather intensively. Extreme stability of Nocardicin A to beta-lactamases was suggested to be due to the combination of its low affinity to the enzymes and stabilization of its monocyclic beta-lactam ring. Nocardicin A was shown to have inducing ability toward beta-lactamases.

Role of beta-lactamase in expression of resistance by methicillin-resistant Staphylococcus aureus

Of 27 unique clinical isolates of methicillin-resistant Staphylococcus aureus, only 4 were homogeneously resistant, and all 4 produced little or no beta-lactamase. Among heterogeneously resistant strains, those most resistant to beta-lactam antibiotics produced the most beta-lactamase. Similar genes may regulate production of the low-affinity penicillin-binding protein and beta-lactamase.

Antimicrobial resistance of Staphylococcus aureus: genetic basis

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Molecular hybridization versus isoelectric focusing to determine TEM-type beta-lactamases in gram-negative bacteria

Isoelectric focusing and molecular hybridization with a TEM DNA probe were used to screen for TEM beta-lactamase in 328 bacterial isolates representing 11 gram-negative genera. The TEM enzyme was detected in 50% of isolates, and nine additional types of beta-lactamase could be identified in 36.9% of isolates. The TEM gene was detected in 53.6% of isolates. The results obtained by both methods were concordant in 92.7% of the entire sample. In situ colony hybridization with a specific probe therefore appears to be a convenient method to screen rapidly for the presence of homologous genetic sequences among a large number of isolates. Positive hybridization was observed for 16 isolates in which no TEM beta-lactamase was detected by isoelectric focusing. The significance of this hybridization remains to be determined.

Nucleotide sequence of the penicillinase repressor gene penI of Bacillus licheniformis and regulation of penP and penI by the repressor

Bacillus licheniformis penicillinase genes, penP and penI, are coded on a 4.2-kilobase EcoRI fragment of pTTE21 (T. Imanaka, T. Tanaka, H. Tsunekawa, and S. Aiba, J. Bacteriol. 147:776-186, 1981). The EcoRI fragment was subcloned in a low-copy-number plasmid pTB522 in Bacillus subtilis. B. subtilis carrying the recombinant plasmid pPTB60 (Tcr penP+ penI+) was chemically mutagenized. Of about 150,000 colonies, two penI(Ts) mutant plasmids, pPTB60D13 and pPTB60E24, were screened by the plate assay at 30 and 48 degrees C for penicillinase. By constructing recombinant plasmids between wild-type and mutant plasmids, the mutation points were shown to be located in a 1.7-kilobase EcoRI-PstI fragment. The EcoRI-PstI fragments of the wild-type plasmid and two mutant plasmids were sequenced. A large open reading frame, composed of 384 bases and 128 amino acid residues (molecular weight, 14,983), was found. Since the mutation points were located at different positions in the protein coding region (Ala to Val for pPTB60D13 and Pro to Leu for pPTB60E24), the coding region was concluded to be the penI gene. A Shine-Dalgarno sequence was found 7 bases upstream from the translation start site (ATG). A probable promoter sequence which is very similar to the consensus sequence was also found upstream of the penP promoter, but in the opposite direction. A consensus twofold symmetric sequence (AAAGTATTA CATATGTAAGNTTT) which might have been used as a repressor binding region was found downstream and in the midst of the penP promoter and also downstream of the penI promoter. The regulation of penP and penI by the repressor is discussed.

Transcriptional analysis of beta-lactamase regulation in Bacillus licheniformis

The expression of the blaP gene for the beta-lactamase of Bacillus licheniformis was examined by transcriptional analyses. Radiolabeled probes containing the blaP gene or various regions 3' or 5' to it were used to analyze RNA samples prepared from induced and uninduced cultures of wild-type and mutant B. licheniformis strains. The level of blaP mRNA was low in uninduced wild-type cells. At 37 degrees C, blaP mRNA levels reached a maximum 1 h after induction while rising up to 180-fold and then declined, but remained severalfold above the uninduced level for several hours. The rate of beta-lactamase synthesis was roughly proportional to the levels of blaP mRNA in both wild-type and mutant strains, indicating that regulation of beta-lactamase formation occurs primarily at the level of transcription. Turnover of blaP mRNA in the presence of rifampin was rapid, giving a blaP mRNA half-life of about 2 min. Yet, high levels of blaP mRNA were maintained for at least 1 h after removal of free inducer. Three blaP mRNAs of 1.2, 2.9, and 3.4 kilobases were produced from the blaP promoter. The most abundant made up about 97% of all blaP transcripts and was also the smallest, ending at a transcriptional terminator located about 60 bases 3' to the blaP structural gene. Variables such as incubation temperature, cytotoxicity of inducer, and type of strain had essentially no effect on the ratio of large blaP mRNA to total blaP mRNA. The 2.9- and 3.4-kilobase blaP mRNAs identify potential locations of genetically linked regulators of beta-lactamase synthesis.