Clinical Manifestations and Molecular Characterization of Pertactin-Deficient and Pertactin-Producing Bordetella pertussis in Children, Philadelphia 2007-2014.

BACKGROUND: Bordetella pertussis strains lacking expression of pertactin, a bacterial adhesin and vaccine target, are emerging. There are limited data on disease manifestations of mutant strains in children. We sought to compare clinical manifestations of pertactin-deficient and pertactin-producing B. pertussis infection in infants and describe corresponding molecular characteristics. METHODS: Molecular characterization of archived B. pertussis isolates (collected January 2007 to March 2014) included Western blot analysis, pulsed-field gel electrophoresis (PFGE), polymerase chain reaction, and pertactin gene sequencing. Medical record review compared epidemiologic and clinical courses of pertactin-producing and pertactin-deficient B. pertussis infections. RESULTS: Sixty of 72 B. pertussis isolates were viable for analysis. Within the cohort of infants, the median age was 95 days, 90% received ≤1 dose of vaccine, and 72% were hospitalized. Pertactin deficiency was first noted in 2008, and its prevalence increased over time (68% overall prevalence). There were no statistically significant differences in presenting symptoms or signs, hospitalization, intensive care, respiratory support, or laboratory results related to pertactin expression. Illness length was shorter in pertactin-deficient group (mean difference, 3.2 days; P = .04); no difference was noted in the subgroup of infants <4 months old. Molecular analyses identified 11 PFGE profiles (Centers for Disease Control and Prevention profile No. 002 predominant, 47%). In 41 pertactin-deficient strains, sequencing identified 2 stop codon and 3 IS481 locations disrupting the prn gene. Mutations and nucleotide positions were not unique to PFGE type, nor were they clustered in time. CONCLUSIONS: In this cohort of predominantly unimmunized infants, clinical disease did not differ between infection with pertactin-deficient and those with pertactin-producing B. pertussis. Molecular analyses demonstrated remarkable PFGE strain diversity, with multiple mechanisms and molecular sites of pertactin inactivation.

Synergistic activity of ceftobiprole and vancomycin in a rat model of infective endocarditis caused by methicillin-resistant and glycopeptide-intermediate Staphylococcus aureus.

The therapeutic activity of ceftobiprole medocaril, the prodrug of ceftobiprole, was compared to that of vancomycin, daptomycin, and the combination of a subtherapeutic dose of ceftobiprole and vancomycin in a rat model of infective endocarditis due to methicillin-resistant Staphylococcus aureus (MRSA) (ATCC 43300) or glycopeptide-intermediate Staphylococcus aureus (GISA) (NRS4 and HIP 5836) strains. The minimum bactericidal concentrations of ceftobiprole, vancomycin, and daptomycin at bacterial cell densities similar to those encountered in the cardiac vegetation in the rat endocarditis model were 2, >64, and 8 µg/ml, respectively, for MRSA ATCC 43300 and 4, >64, and 8 µg/ml, respectively, for the GISA strain. Ceftobiprole medocaril administered in doses of 100 mg/kg of body weight given intravenously (i.v.) twice a day (BID) every 8 h (q8h) (equivalent to a human therapeutic dose of ceftobiprole [500 mg given three times a day [TID]) was the most effective monotherapy, eradicating nearly 5 log(10) CFU/g MRSA or 6 log(10) CFU/g GISA organisms from the cardiac vegetation and had the highest incidence of sterile vegetation compared to the other monotherapies in the endocarditis model. In in vitro time-kill studies, synergistic effects were observed with ceftobiprole and vancomycin on MRSA and GISA strains, and in vivo synergy was noted with combinations of subtherapeutic doses of these agents for the same strains. Additionally, sterile vegetations were achieved in 33 and 60%, respectively, of the animals infected with MRSA ATCC 43300 or GISA NRS4 receiving ceftobiprole-vancomycin combination therapy. In summary, ceftobiprole was efficacious both as monotherapy and in combination with vancomycin in treating MRSA and GISA infections in a rat infective endocarditis model and warrants further evaluation.

Antistaphylococcal activities of the new fluoroquinolone JNJ-Q2.

The new broad-spectrum fluoroquinolone JNJ-Q2 displays in vitro activity against Gram-negative and Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and ciprofloxacin-resistant MRSA isolates. Tested with isogenic methicillin-susceptible S. aureus (MSSA) and MRSA strains bearing quinolone-resistant target mutations, JNJ-Q2 displayed MICs ≤ 0.12 µg/ml, values 16- to 32-fold lower than those determined for moxifloxacin. Overexpression of the NorA efflux pump did not impact JNJ-Q2 MICs. Inhibition of S. aureus DNA gyrase and DNA topoisomerase IV enzymes demonstrated that JNJ-Q2 was more potent than comparators against wild-type enzymes and enzymes carrying quinolone-resistant amino acid substitutions, and JNJ-Q2 displayed equipotent activity against both enzymes. In serial-passage studies comparing resistance selection in parallel MRSA cultures by ciprofloxacin and JNJ-Q2, ciprofloxacin readily selected for mutants displaying MIC values of 128 to 512 µg/ml, which were observed within 18 to 24 days of passage. In contrast, cultures passaged in the presence of JNJ-Q2 displayed MICs ≤ 1 µg/ml for a minimum of 27 days of serial passage. A mutant displaying a JNJ-Q2 MIC of 4 µg/ml was not observed until after 33 days of passage. Mutant characterization revealed that ciprofloxacin-passaged cultures with MICs of 256 to 512 µg/ml carried only 2 or 3 quinolone resistance-determining region (QRDR) mutations. Cultures passaged with JNJ-Q2 selection for up to 51 days displayed MICs of 1 to 64 µg/ml and carried between 4 and 9 target mutations. Established in vitro biofilms of wild-type or ciprofloxacin-resistant MRSA exposed to JNJ-Q2 displayed greater decreases in bacterial counts (7 days of exposure produced 4.5 to >7 log(10) CFU decreases) than biofilms exposed to ciprofloxacin, moxifloxacin, rifampin, or vancomycin.

Hydrolysis and inhibition profiles of beta-lactamases from molecular classes A to D with doripenem, imipenem, and meropenem.

The stability of doripenem to hydrolysis by beta-lactamases from molecular classes A to D was compared to the stability for imipenem and meropenem. Doripenem was stable to hydrolysis by extended-spectrum beta-lactamases and AmpC type beta-lactamases and demonstrated high affinity for the AmpC enzymes. For the serine carbapenemases SME-3 and KPC-2 and metallo-beta-lactamases IMP-1 and VIM-2, doripenem hydrolysis was generally 2- to 150-fold slower than imipenem hydrolysis. SPM-1 hydrolyzed meropenem and doripenem fourfold faster than imipenem.

Differential selection of single-step AmpC or efflux mutants of Pseudomonas aeruginosa by using cefepime, ceftazidime, or ceftobiprole.

Single-step Pseudomonas aeruginosa mutants, selected with ceftobiprole, ceftazidime, or cefepime, were generated at frequencies of 10(-6) to <10(-9) at two and four times the MIC. The chromosomal AmpC ß-lactamase activity was increased in all ceftazidime-selected mutants. Mutants selected with cefepime either increased AmpC activity or upregulated expression of the mexXY efflux genes. Mutants selected with ceftobiprole did not overexpress AmpC; 90% of these produced elevated levels of mexXY RNA, indicating that increased efflux, not AmpC derepression, is the predominant response to ceftobiprole during first-step mutations in P. aeruginosa.

Impact of different carbapenems and regimens of administration on resistance emergence for three isogenic Pseudomonas aeruginosa strains with differing mechanisms of resistance.

We compared drugs (imipenem and doripenem), doses (500 mg and 1 g), and infusion times (0.5 and 1.0 [imipenem], 1.0 and 4.0 h [doripenem]) in our hollow-fiber model, examining cell kill and resistance suppression for three isogenic strains of Pseudomonas aeruginosa PAO1. The experiments ran for 10 days. Serial samples were taken for total organism and resistant subpopulation counts. Drug concentrations were determined by high-pressure liquid chromatography-tandem mass spectrometry (LC/MS/MS). Free time above the MIC (time > MIC) was calculated using ADAPT II. Time to resistance emergence was examined with Cox modeling. Cell kill and resistance emergence differences were explained, in the main, by differences in potency (MIC) between doripenem and imipenem. Prolonged infusion increased free drug time > MIC and improved cell kill. For resistance suppression, the 1-g, 4-h infusion was able to completely suppress resistance for the full period of observation for the wild-type isolate. For the mutants, control was ultimately lost, but in all cases, this was the best regimen. Doripenem gave longer free time > MIC than imipenem and, therefore, better cell kill and resistance suppression. For the wild-type organism, the 1-g, 4-h infusion regimen is preferred. For organisms with resistance mutations, larger doses or addition of a second drug should be studied.

New variant of CTX-M-type extended-spectrum beta-lactamases, CTX-M-71, with a Gly238Cys substitution in a Klebsiella pneumoniae isolate from Bulgaria.

A single Klebsiella pneumoniae strain isolated in a Bulgarian hospital was found to produce CTX-M-71, a new CTX-M variant characterized by one amino acid substitution from glycine to cysteine at position 238 in comparison to CTX-M-15. This exchange decreased the hydrolytic activity of the beta-lactamase for cefotaxime, ceftazidime, and cefepime.

Effect of MexXY overexpression on ceftobiprole susceptibility in Pseudomonas aeruginosa.

Ceftobiprole, an anti-methicillin-resistant Staphylococcus aureus broad-spectrum cephalosporin, has activity (MIC for 50% of strains tested, < or =4 microg/ml) against many Pseudomonas aeruginosa strains. A common mechanism of P. aeruginosa resistance to beta-lactams, including cefepime and ceftazidime, is efflux via increased expression of Mex pumps, especially MexAB. MexXY has differential substrate specificity, recognizing cefepime but not ceftazidime. In ceftobiprole clinical studies, paired isolates of P. aeruginosa from four subjects demonstrated ceftobiprole MICs of 2 to 4 microg/ml at baseline but 16 microg/ml posttreatment, unrelated to beta-lactamase levels. Within each pair, the level of mexXY RNA, but not mexAB, mexCD, and mexEF, increased by an average of 50-fold from baseline to posttreatment isolates. Sequencing of the negative regulatory gene mexZ indicated that each posttreatment isolate contained a mutation not present at baseline. mexXY expression as a primary ceftobiprole and cefepime resistance mechanism was further examined in isogenic pairs by using cloned mexXY and mexZ. Expression of cloned mexXY in strain PAO1 or in a baseline isolate increased the ceftobiprole MIC to that for the posttreatment isolate. In contrast, in posttreatment isolates, lowering mexXY expression via introduction of cloned mexZ decreased the ceftobiprole MIC to that for the baseline isolates. Similar changes were observed for cefepime. A spontaneous mutant selectively overexpressing mexXY displayed a fourfold elevation in its ceftobiprole MIC, while overexpression of mexAB, -CD, and -EF had a minimal effect. These data indicate that ceftobiprole, like cefepime, is an atypical beta-lactam that is a substrate for the MexXY efflux pump in P. aeruginosa.

Increasing FIM2/3 antigen-content improves efficacy of Bordetella pertussis vaccines in mice in vivo without altering vaccine-induced human reactogenicity biomarkers in vitro.

Current acellular-pertussis (aP) vaccines appear inadequate for long-term pertussis control because of short-lived efficacy and the increasing prevalence of pertactin-negative isolates which may negatively impact vaccine efficacy. In this study, we added fimbriae (FIM)2 and FIM3 protein to licensed 2-, 3- or 5-component aP vaccines (Pentavac®, Boostrix®, Adacel®, respectively) to assess whether an aP vaccine with enhanced FIM content demonstrates enhanced efficacy. Vaccine-induced protection was assessed in an intranasal mouse challenge model. In addition, potential reactogenicity was measured by biomarkers in a human whole blood assay (WBA) in vitro and benchmarked the responses against licensed whole cell pertussis (wP) and aP vaccines including Easyfive®, Pentavac® and Pentacel®. The results show that commercial vaccines demonstrated reduced efficacy against pertactin-negative versus pertactin-positive strains. However, addition of higher amounts of FIM2/3 to aP vaccines reduced lung colonization and increased vaccine efficacy against a pertactin-negative strain in a dose-dependent manner. Improvements in efficacy were similar for FIM2 and FIM3-expressing strains. Increasing the amount of FIM2/3 proteins in aP formulations did not alter vaccine-induced biomarkers of potential reactogenicity including prostaglandin E2, cytokines and chemokines in human newborn cord and adult peripheral blood tested in vitro. These results suggest that increasing the quantity of FIM proteins in current pertussis vaccine formulations may further enhance vaccine efficacy against B. pertussis infection without increasing the reactogenicity of the vaccine.

VIM-15 and VIM-16, two new VIM-2-like metallo-beta-lactamases in Pseudomonas aeruginosa isolates from Bulgaria and Germany.

Two Pseudomonas aeruginosa urine isolates from Bulgaria and Germany produced two new VIM-2 variants. VIM-15 had one amino acid substitution (Tyr218Phe) which caused a significant increase in hydrolytic efficiency. The substitution Ser54Leu, characterizing VIM-16, showed no influence on enzyme activity. Both genes were part of class I integrons located in the chromosome.

Molecular correlation for the treatment outcomes in bloodstream infections caused by Escherichia coli and Klebsiella pneumoniae with reduced susceptibility to ceftazidime.

Data are limited on outcomes of treatment with extended-spectrum cephalosporins (ESCs) for infections caused by Enterobacteriaceae that produce extended-spectrum beta-lactamases (ESBLs). This study describes the largest treatment experience of a nonoutbreak series of bloodstream infections caused by strains of Escherichia coli (23 episodes) and Klebsiella pneumoniae (13 episodes) with a ceftazidime minimal inhibitory concentration of > or =2 microg/mL. E. coli isolates produced a greater variety of beta-lactamase types than did K. pneumoniae isolates, among which ESBL production was predominant. Five ESBL types were identified: TEM-12, TEM-71, TEM-6, SHV-12, and SHV-5. Most patients were treated empirically with an ESC-based regimen. A favorable response to treatment with a nonceftazidime ESC was observed when the causative pathogen produced either TEM-6 or TEM-12; ceftazidime treatment was associated with failure of therapy in all patients. Despite the limited clinical success, ESCs are currently not recommended for the treatment of serious infections caused by ESBL-producing strains.

The mouse intranasal challenge model for potency testing of whole-cell pertussis vaccines.

INTRODUCTION: A mouse intracerebral challenge model is used for potency testing of whole-cell pertussis (wP) vaccines. We investigated the use of a mouse nasopharyngeal challenge model, which better reflects the clinical features of pertussis disease, to differentiate between efficacy of wP vaccines. METHODS: Efficacy of three wP vaccines (Quinvaxem(®), Easyfive(®) and Pentavac(®)) was tested in the nasopharyngeal challenge model. Mice were vaccinated at 4 and 7 weeks and challenged with Bordetella pertussis at 9 weeks. Vaccine efficacy was determined based on CFU in the lungs 5 days after challenge. RESULTS: The mouse nasopharyngeal challenge model has the capacity to differentiate between the efficacy of whole cell pertussis vaccines. CONCLUSION: The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. Whether this model directly correlates with clinical vaccine efficacy requires further investigations. The mouse nasopharyngeal challenge model could be considered as a potency and release assay for wP vaccines.

Assessment of the combination of doripenem plus a fluoroquinolone against non-susceptible Acinetobacter baumannii isolates from nosocomial pneumonia patients.

Carbapenem- and fluoroquinolone-non-susceptible Acinetobacter baumannii were obtained from four nosocomial pneumonia patients who were clinically cured following combination therapy with doripenem/levofloxacin or ciprofloxacin. In vitro synergy of doripenem/levofloxacin or ciprofloxacin was evaluated using time-kill analysis. In vivo synergy was tested using a mouse lethal infection model. In time-kill studies, doripenem and levofloxacin were both bactericidal when tested at Cmax; at ½Cmax, the combination showed synergy up to 8 hours. Ciprofloxacin, alone or combined with doripenem, was not bactericidal. For mouse septicemia, doripenem (100 mg/kg) was ≥90% effective in preventing death in all four isolates. Levofloxacin (200 mg/kg) was 73% effective, and ciprofloxacin (35 mg/kg) was ineffective in preventing death. At lower drug concentrations, increased efficacy was observed for doripenem/levofloxacin, but not for doripenem/ciprofloxacin. Overall, the results suggest that a doripenem/levofloxacin combination may have clinical utility in treating some non-susceptible A. baumannii infections.

Detection systems for carbapenemase gene identification should include the SME serine carbapenemase.

Carbapenemase detection has become a major problem in hospitals that encounter outbreaks of infections caused by carbapenem-resistant Gram-negative bacteria. Rapid detection systems have been reported using multiplex PCR analyses and DNA microarray assays. Major carbapenemases that are detected by these systems include the KPC and OXA serine carbapenemases, and the IMP, VIM and NDM families of metallo-ß-lactamases. However, increasing numbers of the SME serine carbapenemase are being reported from Serratia marcescens, especially from North and South America. These organisms differ from many of the other carbapenemase-producing pathogens in that they are generally susceptible to the expanded-spectrum cephalosporins ceftazidime and cefepime while retaining resistance to almost all other ß-lactam antibiotics. Thus, multiplex PCR assays or DNA microarray testing of carbapenem-resistant S. marcescens isolates should include analyses for production of the SME carbapenemase. Confirmation of the presence of this enzyme may provide reassurance that oxyimino-cephalosporins can be considered for treatment of infections caused by these carbapenem-resistant pathogens.

Multidrug resistance among Acinetobacter spp. in the USA and activity profile of key agents: results from CAPITAL Surveillance 2010.

Multidrug resistance among Acinetobacter spp. leaves few effective antibiotic options for treatment. To monitor antibiotic resistance in Acinetobacter spp., the US CAPITAL 2010 Surveillance data were evaluated by patient demographics, specimen source, and hospital ward. Isolates (N=514) were collected from 65 sites across the USA and Puerto Rico. Isolates were centrally tested for susceptibility to carbapenems and key antimicrobials by broth microdilution. Colistin was the most effective agent tested, with 95% susceptibility. The overall susceptibility of Acinetobacter spp. was low (39% for piperacillin/tazobactam, 41% for levofloxacin, 45% for ceftazidime, 47-51% for the carbapenems, and 58% for tobramycin). Multidrug resistance (MDR), defined as resistance to ≥3 antimicrobial agent groups, was detected in 54% of the isolates. MDR isolates were most common among elderly patients (65%), lower respiratory tract isolates (62%), and inpatient/intensive care unit isolates (54-58%). These data update trends in the distribution and prevalence of the MDR phenotype in Acinetobacter spp.

Carbapenemases: the versatile beta-lactamases.

Carbapenemases are beta-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these beta-lactamases may cause serious infections in which the carbapenemase activity renders many beta-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D beta-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-beta-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type beta-lactamases frequently detected in Acinetobacter baumannii. The metallo-beta-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of beta-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

Interactions of ceftobiprole with beta-lactamases from molecular classes A to D.

The interactions of ceftobiprole with purified beta-lactamases from molecular classes A, B, C, and D were determined and compared with those of benzylpenicillin, cephaloridine, cefepime, and ceftazidime. Enzymes were selected from functional groups 1, 2a, 2b, 2be, 2d, 2e, and 3 to represent beta-lactamases from organisms within the antibacterial spectrum of ceftobiprole. Ceftobiprole was refractory to hydrolysis by the common staphylococcal PC1 beta-lactamase, the class A TEM-1 beta-lactamase, and the class C AmpC beta-lactamase but was labile to hydrolysis by class B, class D, and class A extended-spectrum beta-lactamases. Cefepime and ceftazidime followed similar patterns. In most cases, the hydrolytic stability of a substrate correlated with the MIC for the producing organism. Ceftobiprole and cefepime generally had lower MICs than ceftazidime for AmpC-producing organisms, particularly AmpC-overexpressing Enterobacter cloacae organisms. However, all three cephalosporins were hydrolyzed very slowly by AmpC cephalosporinases, suggesting that factors other than beta-lactamase stability contribute to lower ceftobiprole and cefepime MICs against many members of the family Enterobacteriaceae.

Novel carbapenem-hydrolyzing oxacillinase OXA-62 from Pandoraea pnomenusa.

Pandoraea spp. are gram-negative, glucose nonfermenting rods detectable in blood cultures and sputa of cystic fibrosis patients. They are resistant to various antibiotic groups, with imipenem being the only active beta-lactam. We isolated an imipenem-resistant (MIC, 64 microg/ml) Pandoraea pnomenusa strain from a cystic fibrosis patient. Cloning and sequencing identified two beta-lactamases of Bush group 2d, namely, the known OXA-33, located on an integron, and the novel carbapenem-hydrolyzing oxacillinase OXA-62. OXA-62 is only distantly related to other oxacillinases (OXA-50 being closest with 43% amino acid identity). It hydrolyzes penicillins, oxacillin, imipenem, and meropenem but not expanded-spectrum cephalosporins. The blaOXA-62 gene is chromosome located. No transposable elements were found in its genetic neighborhood. With OXA-62-specific primers, blaOXA-62 could be identified in all P. pnomenusa strains and appears to be species specific. This additional mechanism of carbapenem resistance further complicates the treatment of infections caused by P. pnomenusa.