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PubMed1997

Genetic instability and its possible evolutionary implications on the chromosomal structure of Streptomyces.

Recent progress in the understanding of the chromosomal rearrangements in Streptomyces has allowed us to envisage the possible involvement of genetic instability in the evolution of the chromosomal structure. The characterization of recombinational events in the terminal parts of the S ambofaciens chromosome, as well as the observation by other groups that linear plasmids and chromosomes are able to interact, would provide an explanation for the very high levels of polymorphism seen in the terminal inverted repeats of different strains of Streptomyces.

Chromosomes, Bacterial↗
PubMed1999

Evolution of the X-specific block embedded in the human Xq21.3/Yp11.1 homology region.

The region Xq21.3/Yp11.1 represents the largest segment of homology between the sex chromosomes in humans, though no recombination occurs in male meiosis. It presumably arose as a transposition from the X to the Y chromosome; the present-day organization in the latter chromosome indicates a paracentric inversion that disrupted its continuity. Moreover, an X-specific block (defined by the marker DXS214) is embedded in the region. Previously, no hypotheses about the length, origin, or evolution of this X-specific segment have been proposed. Here we report on the refinement of the size and the sequence of the distal boundary of the X-specific block. Furthermore, we have tracked by FISH experiments the evolution of this region in primates. This further clarifies the multistep mechanism of origin for the XY homology region, by demonstrating that the X-specific block was deleted from the Y chromosome after the initial transfer from the X chromosome.

Animals↗
PubMed1999

Evolution of the linear DNA replicons of the Borrelia spirochetes.

Members of the spirochete genus Borrelia carry numerous linear DNA replicons with covalently closed hairpin telomeres. The genome of one member of this genus, B. burgdorferi B31, has now been completely characterized and contains a linear chromosome, twelve linear plasmids and nine circular extra-chromosomal elements. The phylogenetic position of the Borrelia spirochetes strongly suggests that a progenitor with circular replicons acquired the ability to replicate linear DNA molecules.

Base Sequence↗
PubMed1996

Crystal structure of the 2[4Fe-4S] ferredoxin from Chromatium vinosum: evolutionary and mechanistic inferences for [3/4Fe-4S] ferredoxins.

The crystal structure of the 2[4Fe-4S] ferredoxin from Chromatium vinosum has been solved by molecular replacement using data recorded with synchrotron radiation. The crystals were hexagonal prisms that showed a strong tendency to develop into long tubes. The hexagonal prisms diffracted to 2.1 A resolution at best, and a structural model for C. vinosum ferredoxin has been built with a final R of 19.2%. The N-terminal domain coordinates the two [4Fe-4S] clusters in a fold that is almost identical to that of other known ferredoxins. However, the structure has two unique features. One is a six-residue insertion between two ligands of one cluster forming a two-turn external loop; this short loop changes the conformation of the Cys 40 ligand compared to other ferredoxins and hampers the building of one NH...S H-bond to one of the inorganic sulfurs. The other remarkable structural element is a 3.5-turn alpha-helix at the C-terminus that covers one side of the same cluster and is linked to the cluster-binding domain by a six-residue external chain segment. The charge distribution is highly asymmetric over the molecule. The structure of C. vinosum ferredoxin strongly suggests divergent evolution for bacterial [3/4Fe-4S] ferredoxins from a common ancestral cluster-binding core. The unexpected slow intramolecular electron transfer rate between the clusters in C. vinosum ferredoxin, compared to other similar proteins, may be attributed to the unusual electronic properties of one of the clusters arising from localized changes in its vicinity rather than to a global structural rearrangement.

Amino Acid Sequence↗
PubMed2006

Detailed genomic analysis of the Wbeta and gamma phages infecting Bacillus anthracis: implications for evolution of environmental fitness and antibiotic resistance.

Phage-mediated lysis has been an essential laboratory tool for rapidly identifying Bacillus anthracis for more than 40 years, relying on the gamma phage derivative of a Bacillus cereus prophage called W. The complete genomic sequences of the temperate W phage, referred to as Wbeta, and its lytic variant gamma were determined and found to encode 53 open reading frames each, spanning 40,864 bp and 37,373 bp, respectively. Direct comparison of the genomes showed that gamma evolved through mutations at key loci controlling host recognition, lysogenic growth, and possibly host phenotypic modification. Included are a cluster of point mutations at the gp14 tail fiber locus of gamma, encoding a protein that, when fused to green fluorescent protein, binds specifically to B. anthracis. A large 2,003-bp deletion was also identified at the gamma lysogeny module, explaining its shift from a temperate to a lytic lifestyle. Finally, evidence of recombination was observed at a dicistronic Wbeta locus, encoding putative bacterial cell surface-modifying proteins, replaced in gamma with a locus, likely obtained from a B. anthracis prophage, encoding demonstrable fosfomycin resistance. Reverse transcriptase PCR analysis confirmed strong induction at the dicistronic Wbeta locus and at four other phage loci in B. anthracis and/or B. cereus lysogens. In all, this study represents the first genomic and functional description of two historically important phages and is part of a broader investigation into contributions of phage to the B. anthracis life cycle. Initial findings suggest that lysogeny of B. anthracis promotes ecological adaptation, rather than virulence, as with other gram-positive pathogens.

Amino Acid Sequence↗
PubMed2025

Understanding Mycobacterium tuberculosis through its genomic diversity and evolution.

Pathogen evolution and genomic diversity are shaped by specific host immune pressures and therapeutic interventions. Analysis of the extant genomes of circulating strains of Mycobacterium tuberculosis, a leading cause of infectious mortality that has co-evolved with humans for thousands of years, can provide new insights into host-pathogen interactions that underlie specific aspects of pathogenesis and onward transmission. With the explosion in the number of fully sequenced M. tuberculosis strains that are now paired with detailed clinical data, there are new opportunities to understand the evolutionary basis for and consequences of M. tuberculosis strain diversity. This review examines mechanistic findings that have emerged from pairing whole genome sequencing data and evolutionary analysis with functional dissection of specific bacterial variants. These include improved understanding of secreted effectors that modulate the properties and migratory behavior of infected macrophages as well as bacterial genetic alterations important for survival within hypoxic microenvironments. Genomic, evolutionary, and functional analyses across diverse M. tuberculosis strains will identify prominent bacterial adaptations to their human hosts and shape our understanding of TB disease biology and the host immune response.

Mycobacterium tuberculosis↗
PubMed2026

Collateral sensitivity-harnessing microbial vulnerabilities as a solution to antimicrobial resistance.

Bacteria exhibit an evolutionary trade-off through their development of collateral sensitivity (CS) which allows them to resist one antibiotic while becoming more vulnerable to another. This vulnerability offers a compelling therapeutic opportunity by selecting against resistant isolates. Laboratory evolution studies, genome sequencing, deep mutagenesis and use of artificial intelligence and machine learning can design the bespoke strategy against multi-drug-resistant bacteria. This review discusses about recent studies that are rationally designed to harness this evolutionary trade-off for the development of alternative antimicrobial strategies. The translational barriers to the clinical implementation of CS are addressed and evidence-based design principles for optimization of CS-guided therapy are discussed.

Bacteria↗
PubMed1997

Current patterns and evolution of antibiotic resistance among bacterial pathogens involved in acute otitis media.

Penicillin resistance among Streptococcus pneumoniae is becoming a global problem. Different evolutionary phases in the development of resistance can be differentiated according to the local distribution of bacterial strains with different levels of penicillin resistance: susceptible, early phase, low-level resistance phase, multipopulational phase, high-level resistance phase and very high-level resistance phase. These phases evolve in different periods (cryptic, penetration period, evolutionary period and stationary period) which describe the presumed natural history of the resistant organisms. The selective effect of the antibiotic usage depends on the amount and type of the drug, and also on the evolutionary period dominating the geographic area where the antibiotic is used. Macrolide resistance is also a growing problem, probably proportional to the amount of drug used. In the case of beta-lactams, 'more is different' strategies may be useful to control clinically low-level resistant strains with aminopenicillins, and could slow the evolution to higher rates of resistance in some areas; nevertheless, surveillance of the evolution of high-level resistance is mandatory. In Haemophilus influenzae, the proportion of beta-lactamase-positive strains is also very high, frequently over 25% of cases; in all cases the combination amoxycillin---clavulanate restores the susceptible phenotype. In this case, surveillance should be focused on the increase in non-beta-lactamase-mediated penicillin resistance and fluoroquinolone resistance, or in the potential evolution towards extended-spectrum beta-lactamases.

Journal Article↗
PubMed2002

Origin and evolution of eukaryotic apoptosis: the bacterial connection.

The availability of numerous complete genome sequences of prokaryotes and several eukaryotic genome sequences provides for new insights into the origin of unique functional systems of the eukaryotes. Several key enzymes of the apoptotic machinery, including the paracaspase and metacaspase families of the caspase-like protease superfamily, apoptotic ATPases and NACHT family NTPases, and mitochondrial HtrA-like proteases, have diverse homologs in bacteria, but not in archaea. Phylogenetic analysis strongly suggests a mitochondrial origin for metacaspases and the HtrA-like proteases, whereas acquisition from Actinomycetes appears to be the most likely scenario for AP-ATPases. The homologs of apoptotic proteins are particularly abundant and diverse in bacteria that undergo complex development, such as Actinomycetes, Cyanobacteria and alpha-proteobacteria, the latter being progenitors of the mitochondria. In these bacteria, the apoptosis-related domains typically form multidomain proteins, which are known or inferred to participate in signal transduction and regulation of gene expression. Some of these bacterial multidomain proteins contain fusions between apoptosis-related domains, such as AP-ATPase fused with a metacaspase or a TIR domain. Thus, bacterial homologs of eukaryotic apoptotic machinery components might functionally and physically interact with each other as parts of signaling pathways that remain to be investigated. An emerging scenario of the origin of the eukaryotic apoptotic system involves acquisition of several central apoptotic effectors as a consequence of mitochondrial endosymbiosis and probably also as a result of subsequent, additional horizontal gene transfer events, which was followed by recruitment of newly emerging eukaryotic domains as adaptors.

Animals↗
PubMed1994

The crystal structure of pertussis toxin.

BACKGROUND: Pertussis toxin is an exotoxin of the A-B class produced by Bordetella pertussis. The holotoxin comprises 952 residues forming six subunits (five different sequences, S1-S5). It plays an important role in the development of protective immunity to whooping cough, and is an essential component of new acellular vaccines. It is also widely used as a biochemical tool to ADP-ribosylate GTP-binding proteins in the study of signal transduction. RESULTS: The crystal structure of pertussis toxin has been determined at 2.9 A resolution. The catalytic A-subunit (S1) shares structural homology with other ADP-ribosylating bacterial toxins, although differences in the carboxy-terminal portion explain its unique activation mechanism. Despite its heterogeneous subunit composition, the structure of the cell-binding B-oligomer (S2, S3, two copies of S4, and S5) resembles the symmetrical B-pentamers of the cholera toxin and Shiga toxin families, but it interacts differently with the A-subunit. The structural similarity is all the more surprising given that there is almost no sequence homology between B-subunits of the different toxins. Two peripheral domains that are unique to the pertussis toxin B-oligomer show unexpected structural homology with a calcium-dependent eukaryotic lectin, and reveal possible receptor-binding sites. CONCLUSION: The structure provides insight into the pathogenic mechanisms of pertussis toxin and the evolution of bacterial toxins. Knowledge of the tertiary structure of the active site forms a rational basis for elimination of catalytic activity in recombinant molecules for vaccine use.

Amino Acid Sequence↗
PubMed2002

[Antibiotic prophylaxis in surgery: news and controversies].

Preoperative administration of antibiotics to prevent possible post-surgical infections represents a cornerstone of modern medicine. Although the general principles of surgical prophylaxis have been quite clearly defined during the last few decades, advenaces in surgical techniques, the changes in bacterial ecology in hospital, the spread of bacterial resistance and the substantial increase in the surgical population at risk, suggest that several aspects of surgical prophylaxis should be reviewed and new controlled studies should be carried on. The American guidelines for surgical prophylaxis, worked out recently by the CDC, have not modified their general structure, and have strongly influenced the protocols and the prescriptive behaviour of other countries, including Italy. The following points suggest that these guidelines are probably no longer adeguate for the situation in question: evidence from several sources would extend the advisability of antibiotic prophylaxis to other clean surgeries; the current classification of surgical procedures does not consider the "new" population of risk patients; the duration of prophylaxis and its role in preventing post-surgical infections "at a distance" infections has not been carefully defined; the evolution of bacterial epidemiology and bacterial resistance and the contemporary availability of new antibiotics has moved the fear of a post-antibiotic era In the clinical practice, according to these considerations and whilst awaiting the results of new clinical trials, in some cases and for some at risk patients it would appear justified to use third generation cephalosporins and especially ceftriaxone that, because of its peculiar pharmacokinetcs characteristics, guarantees with a single dose the same efficacy of three doses of other cephalosporins.

Anti-Bacterial Agents↗
PubMed2005

Evolution of antibiotic resistance by human and bacterial niche construction.

Antibiotic treatment by humans generates strong viability selection for antibiotic-resistant bacterial strains. The frequency of host antibiotic use often determines the strength of this selection, and changing patterns of antibiotic use can generate many types of behaviors in the population dynamics of resistant and sensitive bacterial populations. In this paper, we present a simple model of hosts dimorphic for their tendency to use/avoid antibiotics and bacterial pathogens dimorphic in their resistance/sensitivity to antibiotic treatment. When a constant fraction of hosts uses antibiotics, the two bacterial strain populations can coexist unless host use-frequency is above a critical value; this critical value is derived as the ratio of the fitness cost of resistance to the fitness cost of undergoing treatment. When strain frequencies can affect host behavior, the dynamics may be analyzed in the light of niche construction. We consider three models underlying changing host behavior: conformism, the avoidance of long infections, and adherence to the advice of public health officials. In the latter two, we find that the pathogen can have quite a strong effect on host behavior. In particular, if antibiotic use is discouraged when resistance levels are high, we observe a classic niche-construction phenomenon of maintaining strain polymorphism even in parameter regions where it would not be expected.

Anti-Bacterial Agents↗
PubMed2026

Nonantibiotic-driven evolution reveals rare but predictable routes to broad antibiotic resistance.

Many medications not prescribed to treat infectious diseases have antibacterial activity at physiologically relevant concentrations, raising the risk that chronic administration of such nonantibiotics may inadvertently select for resistance in the host microbiome. However, how frequently such exposures select for adaptations that impact broad drug resistance, including to antibiotics, remains unclear. Here, we systematically evolved Escherichia coli under exposure to 40 antibiotics and nonantibiotics and profiled the cross-resistance of the drug-adapted strains to 21 antibiotics representing all major classes. Our measurements revealed that most drug-adapted strains did not become multidrug resistant. However, five nonantibiotics and three antibiotics emerged as exceptions and were repeatedly selected for broad antibiotic resistance. Whole-genome sequencing of all 168 evolved strains revealed that changes in the regulation of efflux pumps repeatedly underlay broad drug resistance and converged into two key regulatory genes, acrR and lon. Our work suggests that although inadvertent antibiotic cross-resistance is rare, specific nonantibiotics can still potentially pose a risk for the emergence of multidrug resistance.IMPORTANCEMany medications not typically prescribed to treat infectious diseases have potent antimicrobial activity at physiological concentrations. This anti-bacterial activity raises concern that long-term administration of such nonantibiotics might unintentionally select for multidrug resistance, including resistance to antibiotics. Using Escherichia coli, we show that in most cases, these nonantibiotics do not broadly select for resistance to antibiotics in vitro. However, we identified five nonantibiotics that repeatedly selected for resistance to multiple antibiotics through a shared mechanism of action-upregulation of the multidrug efflux pump AcrAB-TolC. These findings highlight that while the overall risk is low, certain nonantibiotics may still contribute to the emergence of multidrug resistance. Identifying these high-risk drugs can help guide safer prescribing practices and inform strategies to limit the spread of antibiotic resistance.

Escherichia coli↗
PubMed2005

Community-acquired pneumonia in children.

PURPOSE OF REVIEW: This review highlights recent developments in the diagnosis, etiology, therapy, and prevention of community-acquired pneumonia in children. RECENT FINDINGS: Sensitive new diagnostic methods have increased the detection rate of the causative agent up to 94%. Streptococcus pneumoniae is the most prevalent bacterial pathogen in all ages. Polymerase chain reaction is a rapid and sensitive method for the detection of Chlamydia pneumoniae and Mycoplasma pneumoniae, which have gained greater importance in recent years. During the period covered by this review, two new agents causing pneumonia were extensively studied. Human metapneumonovirus detected in young children is a leading cause of respiratory disease during the first years of life. A novel coronavirus was identified as the causative agent of severe respiratory syndrome, a new respiratory illness that affects adults and children. One multicenter trial concluded that nonsevere pneumonia can be treated with a short course of oral amoxicillin and a multicenter international study showed that children with severe pneumonia have similar outcomes whether treated with oral amoxicillin or parenteral penicillin, but more data are needed to demonstrate the safety and efficacy of such regimens. SUMMARY: The continued evolution of bacterial resistance highlights the need for appropriate use of antibacterials. Improved diagnostic techniques will aid the treatment of children with community-acquired pneumonia. Aggressive vaccination with the pneumococcal conjugate vaccine and other available vaccines as well as the development of new vaccines will aid the prevention of respiratory disease in children.

Adolescent↗
PubMed2002

Evolution of multiresistance in nontyphoid salmonella serovars from 1984 to 1998 in Argentina.

Molecular evolution of multiresistance in nontyphoid Salmonella spp. was investigated with 155 isolates obtained in Argentina from 1984 to 1998. In 74 isolates obtained from 1984 to 1988 resistance was associated with the presence of Tn3, Tn9, class I (In0) and II (Tn7) integrons, and the aac(3)-IIa gene. Extended-spectrum cephalosporin (ESC) resistance in Salmonella spp. emerged in 1989, and 81 isolates resistant to at least one ESC and one aminoglycoside were collected thereafter. Among these, two patterns of antimicrobial resistance mechanisms were found: from 1989 to 1992, resistance was related to the spreading of Tn1331 and bla(CTX-M-2), in addition to the persistence of In0 and Tn7. From 1993 to 1998, several integrons were added to the first pattern and three integron groups (IG), namely, IG1 (38% of the isolates), IG2 (51%), and IG3 (11%), were identified. At least two beta-lactamase genes were detected in 65% of the isolates (after 1989) by PCR analysis. Furthermore, five beta-lactamase genes, bla(CTX-M-(2)), bla(OXA-9), bla(OXA-2), bla(TEM-1), and bla(PER-2), were found in two isolates. The bla(CTX-M-2) gene was found in several complex sulI-type integrons with different rearrays within the variable region of class I integrons, suggesting evolution of these integrons in nontyphoid Salmonella. In conclusion, progressive acquisition and accumulation of plasmid-mediated resistance determinants occurred from 1984 to 1998 in nontyphoid Salmonella isolates of the most prevalent serovars from Argentina. It is suggested that antimicrobial resistance mechanisms in these bacteria may have been the consequence of plasmid exchange between Salmonella enterica serovar Typhimurium and Escherichia coli or Shigella flexneri and/or spreading of mobile elements from the nosocomial environment.

Argentina↗
PubMed2002

Asymmetric directional mutation pressures in bacteria.

BACKGROUND: When there are no strand-specific biases in mutation and selection rates (that is, in the substitution rates) between the two strands of DNA, the average nucleotide composition is theoretically expected to be A = T and G = C within each strand. Deviations from these equalities are therefore evidence for an asymmetry in selection and/or mutation between the two strands. By focusing on weakly selected regions that could be oriented with respect to replication in 43 out of 51 completely sequenced bacterial chromosomes, we have been able to detect asymmetric directional mutation pressures. RESULTS: Most of the 43 chromosomes were found to be relatively enriched in G over C and T over A, and slightly depleted in G+C, in their weakly selected positions (intergenic regions and third codon positions) in the leading strand compared with the lagging strand. Deviations from A = T and G = C were highly correlated between third codon positions and intergenic regions, with a lower degree of deviation in intergenic regions, and were not correlated with overall genomic G+C content. CONCLUSIONS: During the course of bacterial chromosome evolution, the effects of asymmetric directional mutation pressures are commonly observed in weakly selected positions. The degree of deviation from equality is highly variable among species, and within species is higher in third codon positions than in intergenic regions. The orientation of these effects is almost universal and is compatible in most cases with the hypothesis of an excess of cytosine deamination in the single-stranded state during DNA replication. However, the variation in G+C content between species is influenced by factors other than asymmetric mutation pressure.

AT Rich Sequence↗
PubMed2005

Sequence comparisons of plasmids pBJS-O of Spiroplasma citri and pSKU146 of S. kunkelii: implications for plasmid evolution.

BACKGROUND: Spiroplasma citri BR3-3X and S. kunkelii CR2-3X cause serious diseases worldwide on citrus and maize species, respectively. S. citri BR3-3X harbors a plasmid, pBJS-Original (pBJS-O), that encodes the spiroplasma adhesion related protein 1 (SARP1), a protein implicated in binding of the pathogen to cells of its leafhopper vector, Circulifer tenellus. The S. kunkelii CR2-3X plasmid, pSKU146, encodes a homolog of SARP1, Sk-ARP1. Due to the close phylogenetic relationship of the two pathogens, we hypothesized that the two plasmids are closely related as well. RESULTS: The nucleotide sequence of pBJS-O was determined and compared to the sequences of a plasmid from BR3-T (pBJS-T), which is a multiply passaged leafhopper transmissible derivative of BR3-3X, and to known plasmid sequences including that of pSKU146. In addition to arp1, the 13,374 bp pBJS-O sequence putatively contains nine genes, recognized as open reading frames (ORFs). Several pBJS-O ORFs have homologs on pSKU146. However, the sequences flanking soj-like genes on both plasmids were found to be more distant from one another than sequences in any other region. Further, unlike pSKU146, pBJS-O lacks the conserved oriT region characteristic of the IncP group of bacterial plasmids. We were unable to identify a region in pBJS-O resembling a known plasmid origin of transfer. In regions where sequence was available for the plasmid from both BR3-3X and BR3-T, the pBJS-T sequence had a 0.4 kb deletion relative to its progenitor, pBJS-O. Southern blot hybridization of extrachromosomal DNA from various S. citri strains and spiroplasma species to an arp-specific probe and a probe made from the entire plasmid DNA of BR3-3X revealed limited conservation of both sequences in the genus Spiroplasma. Finally, we also report the presence on the BR3-3X chromosome of arp2, an S. citri homolog of arp1 that encodes the predicted protein SARP2. The C-terminal domain of SARP2 is homologous to that of SARP1, but its N-terminal domain is distinct. CONCLUSION: Our data suggest that pBJS is a novel S. citri plasmid that does not belong to any known plasmid incompatibility group. The differences between pBJS-O and pSKU146 suggest that one or more events of recombination have contributed to the divergence of the plasmids of the two sister Spiroplasma species; the plasmid from S. citri itself has diverged slightly during the derivation of S. citri BR3-T from BR3-3X. Our data also show that pBJS-O encodes the putative adhesin SARP1. The presence of traE and mob on pBJS-O suggests a role for the plasmid in spiroplasmal conjugation.

Adhesins, Bacterial↗
PubMedDate not supplied

The emergence of bacterial resistance and its influence on empiric therapy.

The discovery of antimicrobial agents had a major impact on the rate of survival from infections. However, the changing patterns of antimicrobial resistance caused a demand for new antibacterial agents. Within a few years of the introduction of penicillin, the majority of staphylococci were resistant to that drug. In the 1960s the production of the semisynthetic penicillins provided an answer to the problem of staphylococcal resistance. In the early 1960s most Escherichia coli were susceptible to the new beta-lactam antibiotic ampicillin; by the end of that decade, plasmid-mediated beta-lactamase resistance was found in 30%-50% of hospital-acquired E. coli. Use of certain agents resulted in the selection of bacteria, such as Klebsiella, that are intrinsically resistant to ampicillin. The original cephalosporins were stable to beta-lactamase, but the use of these agents was in part responsible for the appearance of infections due to Enterobacter species, Citrobacter species, and Pseudomonas aeruginosa. These bacteria, as well as Serratia, were resistant to many of the available beta-lactam agents. Aminoglycosides initially provided excellent activity against most of the facultative gram-negative bacteria. However, the widespread dissemination of the genes that cause production of the aminoglycoside-inactivating enzymes altered the use of those agents. Clearly, the evolution of bacterial resistance has altered the prescribing patterns for antimicrobial agents. Knowledge that beta-lactam resistance to ampicillin or cephalothin is prevalent is causing physicians to select as empiric therapy either a combination of two or more agents or agents to which resistance is uncommon. The new cephalosporins offer a broad spectrum of anti-bacterial activity coupled with low toxicity. However, physicians must closely follow the changing ecology of bacteria when these agents are used, because cephalosporins can also select bacteria resistant to themselves and thereby abolish their value as empiric therapy.

Aminoglycosides↗