Characterization of Antibiotic Susceptibility Profiles of Extensively- and Pan-Drug Resistant Acinetobacter Baumannii Clinical Isolates

Acinetobacter baumannii is an opportunistic pathogen common in intensive care units (ICUs), particularly among immunocompromised individuals. Nosocomial A. baumannii infections have become increasingly problematic in recent years, as these bacteria rapidly acquire antibiotic resistance, leading to the emergence of multidrug, extensively drug and pan drug-resistant (MDR, XDR, and PDR, respectively) isolates. Recently, Cooper University Hospital (CUH) experienced a large increase in highly drug-resistant A. baumannii infections, which had a mortality rate of 60%. Oftentimes, physicians had to turn to combinations of drugs with no experimental verification or historically shelved antibiotics, such as the polymyxins, in a desperate attempt to save lives. This highlights the critical need for more research to identify new, effective treatment options for these difficult-to-treat infections. Here, we determined the susceptibility of 22 patient isolates from CUH against 22 standard-of-care drugs and three newly released antibiotics (eravacycline, omadacycline and plazomicin) by the standard broth microdilution technique. We found that the isolates in this collection were 70% XDR and 30% PDR, meaning there were few to no treatment options available. Overall, the collection was most susceptible to minocycline (77.3%), followed by rifampin (55%) and amikacin (40.9%). While official breakpoint data is not available from the Clinical Laboratory Standards Institute for the new tetracycline-class drugs, a number of strains had low minimum inhibitory concentrations (MICs) to eravacycline and omadacycline, suggesting that these new drugs may be effective in treatment of highly drug-resistant strains. The drug plazomicin was largely ineffective against these strains, with high MICs. We plan to explore novel combinations of eravacycline and omadacycline with the standard-of-care drugs and to search for synergistic combinatorial effects using checkerboard assays. This information can ultimately be used to design new Therapeutics against drug-resistant A. baumannii infections

Systemic Antimicrobial Therapy in Osteomyelitis

Appropriately designed antibiotic regimens are critical to the management of all stages of osteomyelitis, although goals of therapy may vary in different stages of infection. The most important consideration for antibiotic selection is spectrum of action. Route of administration by intravenous or oral route is less important than drug levels that are achievable at the site of infection. Outpatient parenteral therapy and use of oral agents has simplified delivery of long-term treatment regimens. There are few high-quality studies that compare specific treatment regimens or durations of therapy, and recommendations for drugs and duration of antibiotic therapy are based on expert opinion, case series, and extrapolations from animal models. Intravenous β-lactams are the treatment of choice for methicillin-susceptible Staphylococcus aureus, but there are also oral options available. Vancomycin has been the treatment of choice for methicillin-resistant Staphylococcus aureus osteomyelitis, but there are several newer parenteral and oral agents for treatment of methicillin-resistant Staphylococcus aureus including linezolid and daptomycin. Rifampin combined with other staphylococcal agents may increase cure rates, especially for device-associated infections. Oral fluoroquinolones and parenteral β-lactam agents can be used for treatment of gram-negative osteomyelitis, but increasing resistance has complicated management of these infections

Putative VanRS-Like Two-Component Regulatory System Associated with the Inducible Glycopeptide Resistance Cluster of Paenibacillus popilliae

Paenibacillus popilliae contains vanF encoding a putative d-Ala:d-lactate (d-Lac) ligase, VanF, as part of the vanY(F)Z(F)H(F)FX(F) cluster that is similar in structure to the enterococcal vanA and vanB clusters. Using growth curves, we demonstrated that vancomycin resistance in P. popilliae is inducible. Using degenerate oligonucleotides targeted at bacterial cell wall ligases, we identified a second ligase gene with features of a d-Ala:d-Ala ligase in both P. popilliae and the related, vancomycin-susceptible, Paenibacillus lentimorbus. The 3,380-bp region upstream of vanY(F)Z(F)H(F)FX(F) in P. popilliae ATCC 14706 was sequenced and found to contain genes encoding a putative two-component regulator, VanR(F)S(F), similar to VanRS but more closely related to a family of two-component regulators linked to VanY-like carboxypeptidases in several glycopeptide-susceptible Bacillus species. This upstream region also included a transposase similar to a transposase found in Bacillus halodurans and, in some strains, a 99-bp insertion of unknown function with 95% nucleotide identity to a portion of the Tn1546 transposase gene. Analysis of glycopeptide resistance-associated clusters from soil and/or insect-dwelling organisms may provide important clues to the molecular evolution of acquired glycopeptide resistance elements in human pathogens

Vancomycin-Dependent Enterococcus faecalis Clinical Isolates and Revertant Mutants

Three vancomycin-dependent clinical isolates of Enterococcus faecalis of the VanB type were studied by determining (i) the sequence of the ddl gene encoding the host d-Ala:d-Ala ligase and the vanS(B)-vanR(B) genes specifying the two-component regulatory system that activates transcription of the vanB operon, (ii) the level of expression of resistance genes by using dd-dipeptidase activity as a reporter, and (iii) the proportions of the peptidoglycan precursors synthesized. Each strain had a mutation in ddl leading to an amino acid substitution (D295 to V; T316 to I) or deletion (DAK251-253 to E) at invariant positions in d-Ala:d-Ala, d-Ala:d-Lac, and d-Ala:d-Ser ligases. These mutations resulted in impaired host d-Ala:d-Ala ligases since only precursors terminating in d-Ala-d-Lac were synthesized under vancomycin-inducing conditions. Two types of vancomycin-independent revertants of one isolate were obtained in vitro after growth in the absence of vancomycin: (i) vancomycin-resistant, teicoplanin-susceptible mutants had a 6-bp insertion in the host ddl gene, causing the E251-to-EYK change that restored d-Ala:d-Ala ligase activity, (ii) constitutive vancomycin-resistant, teicoplanin-resistant mutants had substitutions (S232 to F or E247 to K) in the vicinity of the autophosphorylation site of the VanS(B) sensor and produced exclusively precursors ending in d-Ala-d-Lac. Vancomycin- and teicoplanin-dependent mutants obtained by growth in the presence of teicoplanin had an 18-bp deletion in VanS(B), affecting residues 402 to 407 and overlapping the G2 ATP binding domain. The rapid emergence of vancomycin-independent revertants in vitro suggests that interruption of vancomycin therapy may not be sufficient to cure patients infected with vancomycin-dependent enterococci

Evaluating the Efficacy of Eravacycline and Omadacycline against Extensively Drug-Resistant <i>Acinetobacter baumannii</i> Patient Isolates

For decades, the spread of multidrug-resistant (MDR) Acinetobacter baumannii has been rampant in critically ill, hospitalized patients. Traditional antibiotic therapies against this pathogen have been failing, leading to rising concerns over management options for patients. Two new antibiotics, eravacycline and omadacycline, were introduced to the market and have shown promising results in the treatment of Gram-negative infections. Since these drugs are newly available, there is limited in vitro data about their effectiveness against MDR A. baumannii or even susceptible strains. Here, we examined the effectiveness of 22 standard-of-care antibiotics, eravacycline, and omadacycline against susceptible and extensively drug-resistant (XDR) A. baumannii patient isolates from Cooper University Hospital. Furthermore, we examined selected combinations of eravacycline or omadacycline with other antibiotics against an XDR strain. We demonstrated that this collection of strains is largely resistant to monotherapies of carbapenems, fluoroquinolones, folate pathway antagonists, cephalosporins, and most tetracyclines. While clinical breakpoint data are not available for eravacycline or omadacycline, based on minimum inhibitory concentrations, eravacycline was highly effective against these strains. The aminoglycoside amikacin alone and in combination with eravacycline or omadacycline yielded the most promising results. Our comprehensive characterization offers direction in the treatment of this deadly infection in hospitalized patients

Evaluating the Effectiveness of Hospital Antiseptics on Multidrug-Resistant Acinetobacter baumannii: Understanding the Relationship between Microbicide and Antibiotic Resistance

Acinetobacter baumannii hospital infections are difficult to treat due to the rapid emergence of multidrug-resistant (MDR) strains. In addition, A. baumannii can survive in numerous adverse environments, including in the presence of common hospital antiseptics. We hypothesized that in addition to accumulating drug resistance determinants, MDR A. baumannii strains also accumulate mutations that allow for greater microbicide tolerance when compared to pan-susceptible (PS) strains. To test this hypothesis, we compared the survival of five MDR and five PS patient isolates when exposed to bleach, ethanol, quaternary ammonium compounds, chlorhexidine gluconate, and povidone. We evaluated bacteria in a free-living planktonic state and under biofilm conditions. Each disinfectant eliminated 99.9% of planktonic bacteria, but this was not the case for bacterial biofilms. Next, we characterized strains for the presence of the known microbicide-resistance genes cepA, qacE&Delta;1, qacE, and qacA. MDR strains did not survive more than PS strains in the presence of microbicides, but microbicide-resistant strains had higher survival rates under some conditions. Interestingly, the PS strains were more likely to possess microbicide-resistance genes. Microbicide resistance remains an important topic in healthcare and may be independent of antimicrobial resistance. Hospitals should consider stricter isolation precautions that take pan-susceptible strains into account

A model for bringing TB expertise to HIV providers: Medical consultations to the CDC-funded Regional Tuberculosis Training and Medical Consultation Centers, 2013-2017.

BackgroundPersons living with human immunodeficiency virus (HIV) are at a greater risk of developing tuberculosis (TB) compared to people without HIV and of developing complications due to the complexity of TB/HIV coinfection management.MethodsDuring 2013-2017, the Centers for Disease Control and Prevention (CDC) funded 5 TB Regional Training and Medical Consultation Centers (RTMCCs) (now known as TB Centers of Excellence or COEs) to provide medical consultation to providers for TB disease and latent TB infection (LTBI), with data entered into a Medical Consultation Database (MCD). Descriptive analyses of TB/HIV-related consultations were conducted using SAS® software, version [9.4] to determine the distribution of year of consultation, medical setting and provider type, frequency of consultations regarding a pediatric (ResultsOf 14,586 consultations captured by the MCD in 2013-2017, 544 (4%) were categorized as TB/HIV-related, with 100 (18%) received in 2013, 129 (24%) in 2014, 104 (19%) in 2015, 117 (22%) in 2016, and 94 (17%) in 2017. Most TB/HIV consultations came from nurses (54%) or physicians (43%) and from local (65%) or state health departments (10%). Only 17 (3%) of HIV-related consultations involved pediatric cases. Off the 544 TB/HIV consultations, 347 (64%) concerned the appropriate treatment regimen for TB/HIV or LTBI/HIV for a patient on or not on antiretroviral therapy (ART).ConclusionsThe data support a clear and ongoing gap in areas of specialized HIV knowledge by TB experts that could be supplemented with proactive educational outreach. The specific categories of TB/HIV inquiries captured by this analysis are strategically informing future targeted training and educational activities planned by the CDC TB Centers of Excellence, as well as guiding HIV educational efforts at regional and national TB meetings