Outpatient Parenteral Antibiotic Therapy in Older Adults.

Outpatient parenteral antimicrobial therapy (OPAT) for older adults is a complex process that involves multiple stakeholders and care coordination, but it is a useful and patient-centered tool with opportunities for the treatment of complicated infections, improved patient satisfaction, and reduced health-care costs. Older age should not be an exclusion for OPAT but rather prompt the OPAT provider to thoroughly evaluate candidacy and safety. Amid the on-going COVID-19 pandemic, innovations in OPAT are needed to shepherd OPAT care into a more patient-centered, thoughtful practice, whereas minimizing harm to older patients from unnecessary health-care exposure and thus health-care associated infections.

Antibiotic-Resistant Infections and Treatment Challenges in the Immunocompromised Host: An Update.

This article reviews antibiotic resistance and treatment of bacterial infections in the growing number of patients who are immunocompromised: solid organ transplant recipients, the neutropenic host, and persons with human immunodeficiency virus and AIDS. Specific mechanisms of resistance in both gram-negative and gram-positive bacteria, as well as newer treatment options are addressed elsewhere and are only briefly discussed in the context of the immunocompromised host.

Ibrutinib Therapy and Mycobacterium chelonae Skin and Soft Tissue Infection.

Ibrutinib is an irreversible inhibitor of Bruton's tyrosine kinase approved for the treatment of B-cell malignancies. There is growing concern about the risk of opportunistic infections following ibrutinib therapy. Herein, we describe the first case of Mycobacterium chelonae skin and soft tissue infection in a patient receiving ibrutinib and recount the challenges in treating this infection.

Bulgecin A as a ß-lactam enhancer for carbapenem-resistant Pseudomonas aeruginosa and carbapenem-resistant Acinetobacter baumannii clinical isolates containing various resistance mechanisms.

Genetic screening of Pseudomonas aeruginosa (PSDA) and Acinetobacter baumannii (ACB) reveals genes that confer increased susceptibility to ß-lactams when disrupted, suggesting novel drug targets. One such target is lytic transglycosylase. Bulgecin A (BlgA) is a natural product of Pseudomonas mesoacidophila and a lytic transglycosolase inhibitor that works synergistically with ß-lactams targeting PBP3 for Enterobacteriaceae. BlgA also weakly inhibits di-Zn2+ metallo-ß-lactamases like L1 of Stenotrophomonas maltophilia. We hypothesized that because of its unique mechanism of action, BlgA could restore susceptibility to carbapenems in carbapenem-resistant PSDA (CR-PSDA) and carbapenem-resistant ACB, as well as ACB resistant to sulbactam. A BlgA-containing extract was prepared using a previously published protocol. CR-PSDA clinical isolates demonstrating a variety of carbapenem resistance mechanisms (VIM-2 carbapenemases, efflux mechanisms, and AmpC producer expression) were characterized with agar dilution minimum inhibitory concentration (MIC) testing and polymerase chain reaction. Growth curves using these strains were prepared using meropenem, BlgA extract, and meropenem plus BlgA extract. A concentrated Blg A extract combined with low concentrations of meropenem, was able to inhibit the growth of clinical strains of CR-PSDA for strains that had meropenem MICs ≥8 mg/L by agar dilution, and a clinical strain of an OXA-24 producing ACB that had a meropenem MIC >32 mg/L and intermediate ampicillin/sulbactam susceptibility. Similar experiments were conducted on a TEM-1 producing ACB strain resistant to sulbactam. BlgA with ampicillin/sulbactam inhibited the growth of this organism. As in Enterobacteriaceae, BlgA appears to restore the efficacy of meropenem in suppressing the growth of CR-PSDA and carbapenem-resistant ACB strains with a variety of common carbapenem resistance mechanisms. BlgA extract also inhibits VIM-2 ß-lactamase in vitro. BlgA may prove to be an exciting adjunctive compound to extend the life of carbapenems against these vexing pathogens.

An unusual case of underlying rilpivirine resistance in an antiretroviral-naïve man with AIDS.

Primary resistance mutations to second generation HIV non-nucleoside reverse transcriptase inhibitors are rare in HIV-infected persons in the US (estimated at 1.8%). We report an antiretroviral treatment (ART)-naïve patient with acquired immunodeficiency syndrome (AIDS) (CD4 cell count 20 cells/mm3, viral load 8439 copies/mL), who was infected with HIV-1 sub-type B virus containing a reverse transcriptase mutation, E138A, associated with rilpivirine resistance. Subsequently, he was initiated on a single tablet ART regimen containing an integrase inhibitor and developed immune reconstitution inflammatory syndrome (IRIS), presenting as Mycobacterium avium cervical adenitis. The patient went on to develop rifamycin-induced neutropenia during treatment of his opportunistic infection but later recovered his counts, and remains well on an integrase-based HIV regimen. His case illustrates the growing importance of archived resistance mutations including the less common E138A mutation, as well as the risk and rapid occurrence of IRIS in AIDS patients initiated on integrase inhibitors.

Profile of ceftolozane/tazobactam and its potential in the treatment of complicated intra-abdominal infections.

Drug-resistant pathogens have gained a foothold especially in the most vulnerable patient populations, hospitalized and immunocompromised individuals. Furthermore, extended-spectrum ß-lactamase and carbapenemase-producing organisms are finding their way even into the community, with patients presenting to the hospital with established colonization and infection with resistant Enterobacteriaceae in particular. Recently, a novel antipseudomonal cephalosporin in combination with an established Class A ß-lactamase inhibitor, ceftolozane/tazobactam has been approved by the FDA for use in the treatment of complicated urinary tract infections and complicated intra-abdominal infections. Ceftolozane is a uniquely potent antipseudomonal cephalosporin because of its high affinity for the penicillin-binding proteins of Pseudomonas aeruginosa, its low affinity for the intrinsic Class C ß-lactamases of P. aeruginosa, its ability to enter P. aeruginosa through the outer membrane without the utilization of OprD protein, and the fact that it is not a substrate of the often upregulated MexAB/OprM efflux system of P. aeruginosa. The biological chemistry, pharmacokinetics/pharmacodynamics, microbiologic spectrum, and clinical trials that led to the approval of ceftolozane is reviewed. A discussion regarding its potential role in the treatment of complicated intra-abdominal infections and other infectious disease syndromes associated with drug-resistant pathogens follows.

A rare case of immune reconstitution inflammatory syndrome presenting as secondary syphilis.

Immune reconstitution syndrome has rarely been reported in the context of syphilis infection. We report a patient with AIDS (CD4 42 cells/mm(3), viral load 344,000 cp/ml), treated previously for secondary syphilis and started on an integrase inhibitor-based single-tablet antiretroviral treatment regimen. After four weeks of antiretroviral treatment, he presented with non-tender, non-blanching erythematous nodules on his chest, an elevated rapid plasma reagin (1:1024) and immune reconstitution (CD4 154 cells/mm(3), HIV-RNA 130 cp/ml). A detailed workup to exclude opportunistic infections including secondary and neurosyphilis was performed. The patient was continued on antiretroviral treatment and treated empirically for neurosyphilis given cerebrospinal lymphocytosis and dermatopathology suggesting treponemal antigen-driven B-cell hyperplasia. We favour a diagnosis of immune reconstitution in association with prior syphilis infection attributable to rapid and potent immune restoration afforded by integrase inhibitors.

Effect of asparagine substitutions in the YXN loop of a class C ß-lactamase of Acinetobacter baumannii on substrate and inhibitor kinetics.

Class C cephalosporinases are a growing threat, and inhibitors of these enzymes are currently unavailable. Studies exploring the YXN loop asparagine in the Escherichia coli AmpC, P99, and CMY-2 enzymes have suggested that interactions between C6' or C7' substituents on penicillins or cephalosporins and this Asn are important in determining substrate specificity and enzymatic stability. We sought to characterize the YXN loop asparagine in the clinically important ADC-7 class C ß-lactamase of Acinetobacter baumannii. Mutagenesis at the N148 position in ADC-7 yields functional mutants (N152G, -S, -T, -Q, -A, and -C) that retain cephalosporinase activity. Using standard assays, we show that N148G, -S, and -T variants possess good catalytic activity toward cefoxitin and ceftaroline but that cefepime is a poor substrate. Because N152 variants of CMY-2, another class C ß-lactamase, are more readily inhibited by tazobactam due to higher rates of inactivation, we also tested if the N148 substitutions in ADC-7 would affect inactivation by sulfone inhibitors, sulbactam and tazobactam, class A ß-lactamase, and A. baumannii penicillin-binding protein (PBP) inhibitors with in vitro activity against ADC-7. The 50% inhibitory concentrations (IC50s) for tazobactam and sulbactam were improved, with 7-fold and 2-fold reductions, respectively, for the N148S variant. A homology model of the N148S ADC-7 enzyme in a Michaelis-Menten complex with tazobactam showed a loss of interaction between N148 and the sulfone moiety of the inhibitor. We postulate that this may result in more-rapid secondary ring opening of the inhibitor, as the unbound sulfone is an excellent leaving group, leading to more-rapid formation of the stable linearized inhibitor.

N152G, -S, and -T substitutions in CMY-2 ß-lactamase increase catalytic efficiency for cefoxitin and inactivation rates for tazobactam.

Class C cephalosporinases are a growing threat, and clinical inhibitors of these enzymes are currently unavailable. Previous studies have explored the role of Asn152 in the Escherichia coli AmpC and P99 enzymes and have suggested that interactions between C-6' or C-7' substituents on penicillins or cephalosporins and Asn152 are important in determining substrate specificity and enzymatic stability. We sought to characterize the role of Asn152 in the clinically important CMY-2 cephalosporinase with substrates and inhibitors. Mutagenesis of CMY-2 at position 152 yields functional mutants (N152G, -S, and -T) that exhibit improved penicillinase activity and retain cephamycinase activity. We also tested whether the position 152 substitutions would affect the inactivation kinetics of tazobactam, a class A ß-lactamase inhibitor with in vitro activity against CMY-2. Using standard assays, we showed that the N152G, -S, and -T variants possessed increased catalytic activity against cefoxitin compared to the wild type. The 50% inhibitory concentration (IC50) for tazobactam improved dramatically, with an 18-fold reduction for the N152S mutant due to higher rates of enzyme inactivation. Modeling studies have shown active-site expansion due to interactions between Y150 and S152 in the apoenzyme and the Michaelis-Menten complex with tazobactam. Substitutions at N152 might become clinically important as new class C ß-lactamase inhibitors are developed.

Early insights into the interactions of different ß-lactam antibiotics and ß-lactamase inhibitors against soluble forms of Acinetobacter baumannii PBP1a and Acinetobacter sp. PBP3.

Acinetobacter baumannii is an increasingly problematic pathogen in United States hospitals. Antibiotics that can treat A. baumannii are becoming more limited. Little is known about the contributions of penicillin binding proteins (PBPs), the target of ß-lactam antibiotics, to ß-lactam-sulbactam susceptibility and ß-lactam resistance in A. baumannii. Decreased expression of PBPs as well as loss of binding of ß-lactams to PBPs was previously shown to promote ß-lactam resistance in A. baumannii. Using an in vitro assay with a reporter ß-lactam, Bocillin, we determined that the 50% inhibitory concentrations (IC(50)s) for PBP1a from A. baumannii and PBP3 from Acinetobacter sp. ranged from 1 to 5 µM for a series of ß-lactams. In contrast, PBP3 demonstrated a narrower range of IC(50)s against ß-lactamase inhibitors than PBP1a (ranges, 4 to 5 versus 8 to 144 µM, respectively). A molecular model with ampicillin and sulbactam positioned in the active site of PBP3 reveals that both compounds interact similarly with residues Thr526, Thr528, and Ser390. Accepting that many interactions with cell wall targets are possible with the ampicillin-sulbactam combination, the low IC(50)s of ampicillin and sulbactam for PBP3 may contribute to understanding why this combination is effective against A. baumannii. Unraveling the contribution of PBPs to ß-lactam susceptibility and resistance brings us one step closer to identifying which PBPs are the best targets for novel ß-lactams.

Substitutions at position 105 in SHV family ß-lactamases decrease catalytic efficiency and cause inhibitor resistance.

Ambler position 105 in class A ß-lactamases is implicated in resistance to clavulanic acid, although no clinical isolates with mutations at this site have been reported. We hypothesized that Y105 is important in resistance to clavulanic acid because changes in positioning of the inhibitor for ring oxygen protonation could occur. In addition, resistance to bicyclic 6-methylidene penems, which are interesting structural probes that inhibit all classes of serine ß-lactamases with nanomolar affinity, might emerge with substitutions at position 105, especially with nonaromatic substitutions. All 19 variants of SHV-1 with variations at position 105 were prepared. Antimicrobial susceptibility testing showed that Escherichia coli DH10B expressing Y105 variants retained activity against ampicillin, except for the Y105L variant, which was susceptible to all ß-lactams, similar to the case for the host control strain. Several variants had elevated MICs to ampicillin-clavulanate. However, all the variants remained susceptible to piperacillin in combination with a penem inhibitor (MIC, ≤2/4 mg/liter). The Y105E, -F, -M, and -R variants demonstrated reduced catalytic efficiency toward ampicillin compared to the wild-type (WT) enzyme, which was caused by increased K(m). Clavulanic acid and penem K(i) values were also increased for some of the variants, especially Y105E. Mutagenesis at position 105 in SHV yields mutants resistant to clavulanate with reduced catalytic efficiency for ampicillin and nitrocefin, similar to the case for the class A carbapenemase KPC-2. Our modeling analyses suggest that resistance is due to oxyanion hole distortion. Susceptibility to a penem inhibitor is retained although affinity is decreased, especially for the Y105E variant. Residue 105 is important to consider when designing new inhibitors.

The importance of the trans-enamine intermediate as a ß-lactamase inhibition strategy probed in inhibitor-resistant SHV ß-lactamase variants.

The ability of bacteria to express inhibitor-resistant (IR) ß-lactamases is stimulating the development of novel inhibitors of these enzymes. The 2'ß-glutaroxypenicillinate sulfone, SA2-13, was previously designed to enhance the stabilization of the deacylation-refractory, trans-enamine inhibitory intermediate. To test whether this mode of inhibition can overcome different IR mutations, we determined the binding mode of SA2-13 through X-ray crystallography, obtaining co-crystals of the inhibitor-protein complex by soaking crystals of the IR sulfhydryl variable (SHV) ß-lactamase variants S130G and M69V with the inhibitor. The 1.45 Å crystal structure of the S130G SHV:SA2-13 complex reveals that SA2-13 is still able to form the stable trans-enamine intermediate similar to the wild-type complex structure, yet with its carboxyl linker shifted deeper into the active site in the space vacated by the S130G mutation. In contrast, data from crystals of the M69V SHV:SA2-13 complex at 1.3 Å did not reveal clear inhibitor density indicating that this IR variant disfavors the trans-enamine conformation, likely due to a subtle shift in A237.

Penicillin sulfone inhibitors of class D beta-lactamases.

OXA beta-lactamases are largely responsible for beta-lactam resistance in Acinetobacter spp. and Pseudomonas aeruginosa, two of the most difficult-to-treat nosocomial pathogens. In general, the beta-lactamase inhibitors used in clinical practice (clavulanic acid, sulbactam, and tazobactam) demonstrate poor activity against class D beta-lactamases. To overcome this challenge, we explored the abilities of beta-lactamase inhibitors of the C-2- and C-3-substituted penicillin and cephalosporin sulfone families against OXA-1, extended-spectrum (OXA-10, OXA-14, and OXA-17), and carbapenemase-type (OXA-24/40) class D beta-lactamases. Three C-2-substituted penicillin sulfone compounds (JDB/LN-1-255, JDB/LN-III-26, and JDB/ASR-II-292) showed low K(i) values for the OXA-1 beta-lactamase (0.70 +/- 0.14 --> 1.60 +/- 0.30 microM) and demonstrated significant K(i) improvements compared to the C-3-substituted cephalosporin sulfone (JDB/DVR-II-214), tazobactam, and clavulanic acid. The C-2-substituted penicillin sulfones JDB/ASR-II-292 and JDB/LN-1-255 also demonstrated low K(i)s for the OXA-10, -14, -17, and -24/40 beta-lactamases (0.20 +/- 0.04 --> 17 +/- 4 microM). Furthermore, JDB/LN-1-255 displayed stoichiometric inactivation of OXA-1 (the turnover number, i.e., the partitioning of the initial enzyme inhibitor complex between hydrolysis and enzyme inactivation [t(n)] = 0) and t(n)s ranging from 5 to 8 for the other OXA enzymes. Using mass spectroscopy to study the intermediates in the inactivation pathway, we determined that JDB/LN-1-255 inhibited OXA beta-lactamases by forming covalent adducts that do not fragment. On the basis of the substrate and inhibitor kinetics of OXA-1, we constructed a model showing that the C-3 carboxylate of JDB/LN-1-255 interacts with Ser115 and Thr213, the R-2 group at C-2 fits between the space created by the long B9 and B10 beta strands, and stabilizing hydrophobic interactions are formed between the pyridyl ring of JDB/LN-1-255 and Val116 and Leu161. By exploiting conserved structural and mechanistic features, JDB/LN-1-255 is a promising lead compound in the quest for effective inhibitors of OXA-type beta-lactamases.

Enhancing resistance to cephalosporins in class C beta-lactamases: impact of Gly214Glu in CMY-2.

The biochemical properties of CMY-32, a class C enzyme possessing a single-amino acid substitution in the Omega loop (Gly214Glu), were compared to those of the parent enzyme, CMY-2, a widespread class C beta-lactamase. In parallel with our microbiological characterization, the Gly214Glu substitution in CMY-32 reduced catalytic efficiency (k(cat)/K(m)) by 50-70% against "good" substrates (i.e., cephalothin) while increasing k(cat)/K(m) against "poor" substrates (i.e., cefotaxime). Additionally, CMY-32 was more susceptible to inactivation by sulfone beta-lactamase inhibitors (i.e., sulbactam and tazobactam) than CMY-2. Timed electrospray ionization mass spectrometry (ESI-MS) analysis of the reaction of CMY-2 and CMY-32 with different substrates and inhibitors suggested that both beta-lactamases formed similar intermediates during catalysis and inactivation. We next showed that the carbapenems (imipenem, meropenem, and doripenem) form long-lived acyl-enzyme intermediates and present evidence that there is beta-lactamase-catalyzed elimination of the C(6) hydroxyethyl substituent. Furthermore, we discovered that the monobactam aztreonam and BAL29880, a new beta-lactamase inhibitor of the monobactam class, inactivate CMY-2 and CMY-32 by forming an acyl-enzyme intermediate that undergoes elimination of SO(3)(2-). Molecular modeling and dynamics simulations suggest that the Omega loop is more constrained in CMY-32 than CMY-2. Our model also proposes that Gln120 adopts a novel conformation in the active site while new interactions form between Glu214 and Tyr221, thus explaining the increased level of cefotaxime hydrolysis. When it is docked in the active site, we observe that BAL29880 exploits contacts with highly conserved residues Lys67 and Asn152 in CMY-2 and CMY-32. These findings highlight (i) the impact of single-amino acid substitutions on protein evolution in clinically important AmpC enzymes and (ii) the novel insights into the mechanisms by which carbapenems and monobactams interact with CMY-2 and CMY-32 beta-lactamases.

SAME is different: a case report and literature review of Staphylococcus aureus metastatic endophthalmitis.

We present a case of methicillin-sensitive Staphylococcus aureus metastatic endophthalmitis (SAME) that developed from a bacteremia. We compare this to a literature review of similar cases and report unique characteristics of SAME. We discuss important considerations in the work-up and treatment of endogenous endophthalmitis.