In vitro and in vivo antibacterial activities of omadacycline, a novel aminomethylcycline.

Omadacycline is the first intravenous and oral 9-aminomethylcycline in clinical development for use against multiple infectious diseases including acute bacterial skin and skin structure infections (ABSSSI), community-acquired bacterial pneumonia (CABP), and urinary tract infections (UTI). The comparative in vitro activity of omadacycline was determined against a broad panel of Gram-positive clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Lancefield groups A and B beta-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae (PRSP), and Haemophilus influenzae (H. influenzae). The omadacycline MIC90s for MRSA, VRE, and beta-hemolytic streptococci were 1.0 µg/ml, 0.25 µg/ml, and 0.5 µg/ml, respectively, and the omadacycline MIC90s for PRSP and H. influenzae were 0.25 µg/ml and 2.0 µg/ml, respectively. Omadacycline was active against organisms demonstrating the two major mechanisms of resistance, ribosomal protection and active tetracycline efflux. In vivo efficacy of omadacycline was demonstrated using an intraperitoneal infection model in mice. A single intravenous dose of omadacycline exhibited efficacy against Streptococcus pneumoniae, Escherichia coli, and Staphylococcus aureus, including tet(M) and tet(K) efflux-containing strains and MRSA strains. The 50% effective doses (ED50s) for Streptococcus pneumoniae obtained ranged from 0.45 mg/kg to 3.39 mg/kg, the ED50s for Staphylococcus aureus obtained ranged from 0.30 mg/kg to 1.74 mg/kg, and the ED50 for Escherichia coli was 2.02 mg/kg. These results demonstrate potent in vivo efficacy including activity against strains containing common resistance determinants. Omadacycline demonstrated in vitro activity against a broad range of Gram-positive and select Gram-negative pathogens, including resistance determinant-containing strains, and this activity translated to potent efficacy in vivo.

Enhancement of neonatal innate defense: effects of adding an N-terminal recombinant fragment of bactericidal/permeability-increasing protein on growth and tumor necrosis factor-inducing activity of gram-negative bacteria tested in neonatal cord blood ex vivo.

Innate defense against microbial infection requires the action of neutrophils, which have cytoplasmic granules replete with antibiotic proteins and peptides. Bactericidal/permeability-increasing protein (BPI) is found in the primary granules of adult neutrophils, has a high affinity for lipopolysaccharides (or "endotoxins"), and exerts selective cytotoxic, antiendotoxic, and opsonic activity against gram-negative bacteria. We have previously reported that neutrophils derived from newborn cord blood are deficient in BPI (O. Levy et al., Pediatrics 104:1327-1333, 1999). The relative deficiency in BPI of newborns raised the possibility that supplementing the levels of BPI in plasma might enhance newborn antibacterial defense. Here we determined the effects of addition of recombinant 21-kDa N-terminal BPI fragment (rBPI(21)) on the growth and tumor necrosis factor (TNF)-inducing activity of representative gram-negative clinical isolates. Bacteria were tested in citrated newborn cord blood or adult peripheral blood. Bacterial viability was assessed by plating assay, and TNF-alpha release was measured by enzyme-linked immunosorbent assay. Whereas adult blood limited the growth of all isolates except Klebsiella pneumoniae, cord blood also allowed logarithmic growth of Escherichia coli K1/r and Citrobacter koseri. Bacteria varied in their susceptibility to rBPI(21)'s bactericidal action: E. coli K1/r was relatively susceptible (50% inhibitory concentration [IC(50)], approximately 10 nM), C. koseri was intermediate (IC(50), approximately 1,000 nM), Klebsiella pneumoniae was resistant (IC(50), approximately 10,000 nM), and Enterobacter cloacae and Serratia marcescens were highly resistant (IC(50), >10,000 nM). All isolates were potent inducers of TNF-alpha activity in both adult and newborn cord blood. In contrast to its variable antibacterial activity, rBPI(21) consistently inhibited the TNF-inducing activity of all strains tested (IC(50), 1 to 1,000 nM). The antibacterial effects of rBPI(21) were additive with those of a combination of conventional antibiotics typically used to treat bacteremic newborns (ampicillin and gentamicin). Whereas ampicillin and gentamicin demonstrated little inhibition of bacterially induced TNF release, addition of rBPI(21) either alone or together with ampicillin and gentamicin profoundly inhibited release of this cytokine. Thus, supplementing newborn cord blood with rBPI(21) potently inhibited the TNF-inducing activity of a variety of gram-negative bacterial clinical pathogens and, in some cases, enhanced bactericidal activity. These results suggest that administration of rBPI(21) may be of clinical benefit to neonates suffering from gram-negative bacterial infection and/or endotoxemia.

Time to detection of positive cultures in 28- to 90-day-old febrile infants.

OBJECTIVE: To determine the time to detection of positive blood, urine, and cerebrospinal fluid (CSF) cultures among febrile 28- to 90-day-old infants. STUDY DESIGN: Retrospective cohort of consecutive 28- to 90-day-old infants presenting with a temperature of >/=38 degrees C to an urban pediatric emergency department. Positive cultures and times to detection were noted. Patients were categorized as being at high risk for serious bacterial illness (SBI) based on clinical and laboratory criteria. RESULTS: Of the 3166 febrile infants seen in the emergency department during the study, 2733 had blood (86%), 2517 had urine (80%), and 2361 had CSF (75%) specimens obtained for culture, and 2190 had all 3 cultures (69%) sent. There were 224 positive cultures in 214 patients; of these, 191 had all 3 cultures (89%) sent. Subsequent analyses were confined to those who had all 3 cultures sent. The detected rate of SBI was 8.7% (191/2190). There were 28 positive blood cultures (1. 3%), 165 positive urine cultures (7.5%), and 8 positive CSF cultures (.4%). Median time to detection of positive cultures was 16 hours for blood, 16 hours for urine, and 18 hours for CSF. Four blood cultures (.1%), 20 urine cultures (.9%), and 0 CSF cultures were noted to have growth of a pathogen >24 hours after the specimen was obtained. All 4 blood cultures and 17 of 20 urine cultures with growth noted after 24 hours occurred among high-risk patients. CONCLUSIONS: The risk of identifying SBI after 24 hours is 1.1% among all 28- to 90-day-old febrile infants and.3% in low-risk infants.

False resistance to imipenem with a microdilution susceptibility testing system.

Routine monitoring of antibiotic resistance at Children's Hospital, Boston, detected a dramatic increase in the prevalence of imipenem-resistant strains of Pseudomonas aeruginosa. Further studies documented that false resistance to imipenem was due, in part, to the loss of imipenem potency in customized MIC microdilution trays supplied by Sensititre Ltd. (West Sussex, United Kingdom). Recognition of the problem was delayed by use of the quality control standard recommended by the manufacturer, which were higher and broader than those suggested by the National Committee for Clinical Laboratory Standards.

Performance of a solid phase enzyme immunoassay for detection of group A streptococci in a pediatric office laboratory as refereed by a hospital laboratory.

We evaluated the performance of a new rapid solid phase enzyme immunoassay, SUDS Group A Strep (MUREX Corp., Norcross, GA) for the detection of Group A beta-hemolytic streptococci in a pediatric office practice. Duplicate throat swabs were obtained from 341 children with pharyngitis. One swab was used in the SUDS test and the other was cultured in the office laboratory. Office SUDS and culture (sheep blood agar plate, aerobic 24-hour incubation) were compared with culture using reference techniques (sheep blood agar plate, anaerobic 48-hour incubation) in a hospital laboratory. Compared with hospital laboratory culture, the sensitivity of office SUDS (73.8%) was superior to that of office culture (66.6%) at P = 0.05. Specificities were 93.1 and 98.6%, respectively; positive predictive values were 86.1 and 96.6%; and negative predictive values were 85.9 and 83.5%. The sensitivity and specificity of SUDS compared with office culture were 88.5 and 87.8%, respectively, but would have been 93 and 94% had hemolyzed media not been used on several occasions in the office culture procedure. We conclude that SUDS Group A Strep was significantly more sensitive than throat cultures as performed in a typical pediatric practice although the performance of office cultures could have been improved by standard quality control techniques.

Impact of rapid antigen tests for group A streptococcal pharyngitis on physician use of antibiotics and throat cultures.

Using case scenarios and an interview guided by a decision tree diagram, the clinical strategies of 150 physicians (50 private pediatricians, 50 health maintenance organization pediatricians and 50 pediatric residents) were assessed for the management of pharyngitis under three conditions: (1) no rapid antigen detection test available for diagnosing Group A streptococcal disease; (2) antigen test result available in 20 minutes; and (3) antigen test result available in 4 hours. The sensitivity of the antigen test was designated as 0.95 if the growth of rare or few Group A streptococci on throat culture was discounted and 0.82 if any growth was considered significant, and the specificity was set at 0.98. In a standardized pediatric case with a prior probability of Group A streptococcal disease of 0.58, 84% of clinicians would order a 20-minute test and 39% would order a 4-hour test. The 20-minute test would reduce throat culture use by 54%, reduce the proportion of patients exposed to antibiotics from 86% to 65% and reduce total antibiotic treatment days by 13.8%. Effects would be less pronounced for a low probability case or if results of antigen testing were not available for 4 hours. Provided a test with a documented high sensitivity and specificity were used, a rapid antigen test with results promptly available would substantially reduce throat culture use and unnecessary antibiotic exposures in children with a moderate prior probability of streptococcal disease.

Comparison of a new, rapid enzyme-linked immunosorbent assay with latex particle agglutination for the detection of Haemophilus influenzae type b infections.

A new, rapid enzyme-linked immunosorbent assay (ELISA) for the detection of polyribosylribitol phosphate of Haemophilus influenzae type b was compared with a commercially available latex particle agglutination (LPA) system (Bactigen; Wampole Laboratories, Cranbury, N.J.). By adding specimens and the anti-polyribosylribitol phosphate immunoglobulin-enzyme conjugate to the solid phase in a single step, it was possible to complete the ELISA procedure in 30 min. The ELISA was capable of detecting 0.3 ng of polyribosylribitol phosphate per ml in cerebrospinal fluid, 0.6 ng/ml in urine, and 1.2 ng/ml in serum; the in vitro sensitivity of LPA in these body fluids was 0.6, 0.3, and 0.3 ng/ml, respectively. Both procedures detected polyribosylribitol phosphate in specimens from 25 patients with bacteriologically confirmed H. influenzae type b infections. The specificity of ELISA appeared to be superior to that of LPA. ELISA was positive in only one of seven patients who had a positive LPA test and a clinical illness that was not compatible with haemophilus infection. Moreover, five patients with bacteriologically confirmed infections due to other pathogens (Streptococcus pneumoniae type 14 [two patients], Neisseria meningitidis group C, Escherichia coli K100, and Staphylococcus aureus) had false-positive LPA tests; only two (E. coli and S. aureus) were positive by ELISA. A total of 108 samples from 61 patients who had no evidence of haemophilus infections were negative by both procedures. The ELISA is a rapid, sensitive, and specific alternative to LPA for the detection of haemophilus polyribosylribitol phosphate.

Osteomyelitis caused by Capnocytophaga ochracea.

A 13-year-old boy is reported with osteomyelitis of the greater trochanter caused by a facultative anaerobic organism (Capnocytophaga ochracea) not known to cause infections in normal immunocompetent individuals, nor implicated in bone or joint infections even in compromised hosts. There remains a need to consider unusual organisms and to obtain accurate bacteriologic data in all cases of osteomyelitis.

Mucoid Escherichia coli in cystic fibrosis.

Patients with cystic fibrosis commonly harbor in their lungs strains of Pseudomonas aeruginosa that have a mucoid coating considered virtually pathognomonic for the disease. We found that strains of Escherichia coli with a morphologically similar mucoid coating were present in the respiratory tracts of eight (11.8 per cent) of 68 patients with cystic fibrosis whose sputum cultures yielded Esch. coli, as compared with none of 89 patients without cystic fibrosis who had Esch. coli in sputum. Mucoid strains of Esch. coli were also recovered from the stools of five (11.1 per cent) of 45 patients with cystic fibrosis, as compared with one (0.7 per cent) of 150 patients without cystic fibrosis. The mucoid substances purified from Esch. coli were biochemically and antigenically distinct from those of P. aeruginosa. We conclude that the respiratory tract in cystic fibrosis offers an environment conducive to the production of a mucoid coating not only by P. aeruginosa but by other gram-negative bacilli as well.

Changes in intestinal flora of farm personnel after introduction of a tetracycline-supplemented feed on a farm.

A prospective study was undertaken to determine whether feeding farm animals antibiotics in feed caused changes in the intestinal bacterial flora of farm dwellers and their neighbors. Chickens were fed tetracycline-supplemented feed (tet-feed), and, as expected, within one week their intestinal flora contained almost entirely tetracycline-resistant organisms. Increased numbers of resistant intestinal bacteria also appeared, but more slowly, in farm members, but not their neighbors. Within five and six months, 31.3 per cent of weekly fecal samples from farm dwellers contained greater than 80 per cent tetracycline-resistant bacteria as compared to 6.8 per cent of the samples from the neighbors (P less than 0.001). Seven of the 11 farm members, but only three of the 24 neighbors, had two or more fecal samples containing greater than 80 per cent tetracycline-resistant coliforms (P less than 0.01). These resistant bacteria contained transferable plasmids conferring multiple antibiotic resistances. Selective pressure by tet-feed for antibiotic-resistant bacteria in chickens extends to human beings in contact with chickens and the feed.