Kathy Katz

Inducible Clindamycin Resistance and Molecular Epidemiologic Trends of Pediatric Community-Acquired Methicillin-Resistant Staphylococcus aureus in Dallas, Texas

ABSTRACT Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection occurs commonly in children. Clindamycin resistance may be inducible or constitutive, and the rates of inducible resistance in CA-MRSA that could produce clindamycin treatment failures vary worldwide. The double-disk test was performed in 197 erythromycin-resistant and clindamycin-susceptible CA-MRSA strains from children in Dallas, Texas, from 1999 to 2002 to determine inducible clindamycin resistance. Resistance mechanisms were studied by PCR; epidemiologic trends were studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Inducible resistance was demonstrated in 28 (93% ±6%) of 30 tested isolates in 1999, 21 (64%, ±11%) of 33 in 2000, 12 (23% ±7%) of 52 in 2001, and 6 (7% ±3%) of 82 in 2002. All noninducible strains had the msr(A) gene. Among inducible resistant strains, 31 had erm(B), 24 had erm(C), and 12 had erm(A) genes. Two distinct pulsed types were the most prevalent; one of them was the most common pulsed type in 1999, whereas in 2002 a different pulsed type was prevalent. MLST analyses determined that ST-8 was the most common type, with 76% ±5% found in 2002. All but one of these clindamycin-susceptible, erythromycin-resistant ST-8 strains showed no induction of clindamycin resistance. We conclude that, among erythromycin-resistant, clindamycin-susceptible CA-MRSA strains isolated from children in Dallas, inducible methylase resistance became less common from 1999 to 2002 (P < 0.001). The phenotype of strains was associated with their sequence type. Our results demonstrate a clonal shift in CA-MRSA in Dallas children from 1999 to 2002.

Daptomycin therapy for invasive Gram-positive bacterial infections in children.

Background: Clinical improvement is often delayed among children with invasive infections caused by multidrug resistant Gram-positive bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) despite use of standard antimicrobial therapy. Daptomycin, a bactericidal lipopeptide antibiotic, may prove useful for treatment of these infections in children, but clinical experience is lacking. Methods: Retrospective review of medical records of hospitalized children who received daptomycin for treatment of invasive Gram-positive bacterial infections at Children’s Medical Center Dallas from December 2003 to March 2007. Bacterial isolates were tested for susceptibility to daptomycin and characterized by pulsed-field gel electrophoresis and polymerase chain reaction for staphylococcal cassette chromosome mec A. Results: Sixteen children (10 male; median age, 6.5 years) received daptomycin. Fifteen (94%) children had invasive staphylococcal disease (14, MRSA, of which 13 were community-associated; 1, methicillin-susceptible S. aureus), and 1 had urinary tract infection caused by VRE. Twelve children with disseminated staphylococcal disease had bacteremia for 2–10 days despite therapy with 2 or more of the following: vancomycin, clindamycin, rifampin, aminoglycoside, or linezolid. The addition of daptomycin resulted in bacteriologic cure in 6 of 7 evaluable patients with persistent bacteremia. No adverse events were attributed to daptomycin. Overall, 14 patients improved and were discharged home, and 2 died of complications of their underlying medical conditions. Conclusions: The majority of patients demonstrated clinical improvement after addition of daptomycin to conventional antimicrobial therapy. Further studies are needed to assess the pharmacokinetics, pharmacodynamics, safety, and effectiveness of daptomycin in infants and children.

Epidemiology and evolution of invasive pneumococcal disease caused by multidrug resistant serotypes of 19a in the 8 years after implementation of pneumococcal conjugate vaccine immunization in Dallas, Texas

Background: The heptavalent pneumococcal conjugate vaccine (PCV7) has significantly reduced vaccine-type invasive pneumococcal disease (IPD) in children. An increasing percentage of IPD cases are now caused by nonvaccine serotypes. The purpose of our observational study was to define the epidemiology of pneumococcal disease in Dallas, TX children for 8 years after implementation of PCV7 immunization. Methods: Streptococcus pneumoniae isolates from normally sterile sites were collected at Childrens Medical Center of Dallas from January 1, 1999 to December 31, 2008. Incidence of IPD was calculated using inpatient and emergency center admissions to Childrens Medical Center of Dallas as the denominator. Isolates were serotyped and penicillin and cefotaxime susceptibilities were determined. Serotype 19A isolates were further characterized by multilocus sequence typing. Results: Compared with the prevaccine period of 1999–2000, there was a significant reduction in the incidence of IPD from 2002 to 2008 (P < 0.05), although a significant increase in IPD incidence was observed from 2006 to 2008 (P = 0.038). The number of IPD cases caused by serotype 19A increased from 1999 to 2008 (P < 0.001). There were significant increases in penicillin and cefotaxime nonsusceptibile 19A isolates during this 10-year period (P < 0.001 and P = 0.004, respectively). The most common sequence type (ST) of the 19A isolates was ST-199 (42.7%). Clonal complex (cc-156) and cc-320 emerged in the period of 2005–2008 as penicillin and cefotaxime resistant 19A strains. Conclusions: In Dallas, PCV7 immunization reduced significantly the incidence of IPD caused by vaccine-type strains. A significant increase in IPD caused by serotype 19A was observed. The penicillin and cefotaxime nonsusceptible STs, not previously identified in Dallas, have recently become an important cause of IPD.

The Impact of Steroids Given with Macrolide Therapy on Experimental Mycoplasma pneumoniae Respiratory Infection

BACKGROUND Systemic steroids have been advocated in addition to antimicrobial therapy for severe Mycoplasma pneumoniae pneumonia. We evaluated the efficacy of clarithromycin, dexamethasone, and combination therapy for M. pneumoniae respiratory infection. METHODS Mice infected with M. pneumoniae were treated with clarithromycin, dexamethasone, combined clarithromycin/dexamethasone, or placebo daily; mice were evaluated at baseline and after 1, 3, and 6 days of therapy. Outcome variables included M. pneumoniae culture, lung histopathologic score (HPS), and bronchoalveolar lavage cytokine, chemokine, and growth factor concentrations. RESULTS Clarithromycin monotherapy resulted in the greatest reductions in M. pneumoniae concentrations. After 3 days of treatment, combination therapy significantly reduced lung HPS compared with placebo, clarithromycin, and dexamethasone alone, whereas, after 6 days of therapy, clarithromycin alone and combination therapy significantly reduced lung HPS compared with placebo. Concentrations of interleukin (IL)-12 p40, RANTES, macrophage chemotactic protein-1, and cytokine-induced neutrophil chemoattractant were significantly lower in mice treated with clarithromycin alone and/or combination therapy compared with dexamethasone alone and/or placebo; combination therapy resulted in a significantly greater reduction than clarithromycin alone for IL-12 p40 and RANTES. CONCLUSIONS Although monotherapy with clarithromycin had the greatest effect on reducing concentrations of M. pneumoniae, combination therapy had the greatest effect on decreasing levels of cytokines and chemokines as well as pulmonary histologic inflammation.

Effects of Large Dosages of Amoxicillin/Clavulanate or Azithromycin on Nasopharyngeal Carriage of Streptococcus pneumoniae, Haemophilus influenzae, Nonpneumococcal α-Hemolytic Streptococci, and Staphylococcus aureus in Children with Acute Otitis Media

Prior use of antibiotics is associated with carriage of resistant bacteria. Colonization by Streptococcus pneumoniae, Haemophilus influenzae, nonpneumococcal alpha-hemolytic streptococci (NPAHS), and Staphylococcus aureus was evaluated in children receiving antibiotic therapy for acute otitis media and in untreated, healthy control subjects. Children were randomly assigned to receive either amoxicillin/clavulanate (90 mg/kg per day) or azithromycin. Swabs were obtained before initiating therapy and again 2 weeks and 2 months after initiating therapy. We also obtained swabs from control subjects at the time of enrollment and 2 weeks and 2 months after enrollment. The decrease in the rate of carriage of S. pneumoniae and H. influenzae at 2 weeks was significant only in the amoxicillin/clavulanate group (P<.001 and P=.005, respectively). The rate of nasopharyngeal colonization with NPAHS among treated patients increased from 23% to 39% at 2 months (P=.01). This increase was similar for both treatment groups. These results suggest that the competitive balance between organisms is altered by antibiotic therapy.

Effects of Amoxicillin/Clavulanate or Azithromycin on Nasopharyngeal Carriage of Streptococcus pneumoniae and Haemophilus influenzae in Children with Acute Otitis Media

The effect of antibiotic therapy on nasopharyngeal colonization by Streptococcus pneumoniae and Haemophilus influenzae was evaluated in children diagnosed with acute otitis media. Children were randomly assigned to receive either amoxicillin/clavulanate or azithromycin therapy, and nasopharyngeal swabs were obtained for culture before and after starting therapy. Amoxicillin/clavulanate therapy eradicated or suppressed all strains of S. pneumoniae susceptible to penicillin, 75% of strains with intermediate resistance, and 40% of strains resistant to penicillin. Azithromycin therapy cleared two-thirds of azithromycin-susceptible strains of S. pneumoniae but none of azithromycin-nonsusceptible strains. Selection for antibiotic-resistant strains in individual children was not observed in children who received amoxicillin/clavulanate therapy but was observed in 2 children who received azithromycin therapy. Carriage of H. influenzae was also reduced by antimicrobial therapy but more so by amoxicillin/clavulanate. Antibiotic therapy does not directly increase the number of resistant strains in the population but, by eradicating susceptible strains, allows greater opportunity for carriage and spread of resistant strains.

Effect of clarithromycin on cytokines and chemokines in children with an acute exacerbation of recurrent wheezing: a double-blind, randomized, placebo-controlled trial

BACKGROUND Clarithromycin is postulated to possess immunomodulatory properties in addition to its antimicrobial activity. OBJECTIVE To evaluate the effect of clarithromycin on serum and nasopharyngeal cytokine and chemokine concentrations in children with an acute exacerbation of recurrent wheezing. METHODS Children with a history of recurrent wheezing or asthma and who presented with an acute exacerbation of wheezing were enrolled in a double-blind, randomized trial of clarithromycin vs placebo. Concentrations of tumor necrosis factor alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin-1beta (IL-1beta), IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, RANTES, eotaxin, macrophage inflammatory protein 1alpha, macrophage inflammatory protein 1beta, and monocyte chemoattractant protein 1 were measured in serum and/or nasopharyngeal aspirates before, during, and after therapy. Mycoplasma pneumoniae and Chlamydophila pneumoniae infection were evaluated for by polymerase chain reaction and serologic testing. RESULTS Nasopharyngeal concentrations of TNF-alpha, IL-1beta, and IL-10 were significantly and persistently lower in children treated with clarithromycin compared with placebo. There tended to be a greater effect of clarithromycin on nasopharyngeal cytokine concentrations in patients with evidence of M. pneumoniae or C. pneumoniae infection. No significant differences were detected in serum cytokines for children treated with clarithromycin compared with placebo. CONCLUSION Clarithromycin therapy reduces mucosal TNF-alpha, IL-1beta, and IL-10 concentrations in children with an acute exacerbation of recurrent wheezing.

Effect of dexamethasone on respiratory syncytial virus-induced lung inflammation in children: results of a randomized, placebo controlled clinical trial

Inflammatory mediators play a major role in the pathogenesis of respiratory syncytial virus (RSV) infection. The objective of this study was to evaluate the effect of i.v. dexamethasone on cytokine concentrations in tracheal aspirates (TA) of children with severe RSV disease and to correlate them with disease severity. Twenty‐five cytokines were measured in TA obtained from children <2 yr old intubated for severe RSV disease, and enrolled in a double‐blind study of i.v. dexamethasone (0.5 mg/kg; n = 22) vs. placebo (n = 19). Cytokine concentrations, measured at baseline and days 1 and 5 post‐randomization using a multiplex assay, were compared within both treatment groups and correlated with: (i) tracheal white blood cell counts, (ii) tracheal RSV loads by culture and (iii) parameters of disease severity, including number of days of requirement for mechanical ventilation, intensive care unit (ICU), and hospitalization. At baseline interleukin (IL)‐13 and IL‐15 concentrations were significantly higher in the dexamethasone treatment group. On day 1 post‐treatment, only MCP‐1, eotaxin and IL‐6 concentrations were significantly different but higher in the placebo group. On day 5: IL‐13, IL‐7, IL‐8 and MIP‐1α concentrations were higher in dexamethasone‐treated patients. In both groups MIP‐1β inversely correlated with the days of ventilator support; MIP‐1α, MIP‐1β and eotaxin inversely correlated with ICU days; and IL‐6 inversely correlated with hospitalization regardless of the treatment assigned. Systemic administration of dexamethasone did not have a consistent effect on TA concentrations of pro‐inflammatory cytokines. This may help explain, at least in part, the lack of clinical benefit of steroid treatment in children with severe RSV bronchiolitis.

Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in HIV-infected ambulatory patients.

Background:Estimates of the prevalence of colonization with methicillin-resistant Staphylococcus aureus (MRSA) vary in HIV-infected patients. Methods:HIV clinic patients were prospectively cultured. Bilateral nasal and axillary swabs were plated on BBL CHROMagar MRSA media. Molecular typing was done by pulse-field gel electrophoresis, and staphylococcal cassette chromosomemec typing was determined. A patient questionnaire was conducted to ascertain potential MRSA risk factors; medical records were reviewed. Results:Fifteen of 146 (10.3%) patients had MRSA nasal colonization; 1 also had axillary colonization. Twelve of 15 isolates were staphylococcal cassette chromosomemec type IV, and 8 of 14 were USA300 or USA400 genotype. MRSA colonization was associated with lower CD4 cell count, not receiving current or recent antibiotics, history of prior MRSA or methicillin-susceptible Staphylococcus aureus infection (P < 0.05 for all), and a trend toward history of hospitalization or emergency department visit in the past year (P = 0.064). Current use of trimethoprim-sulfamethoxazole was protective for colonization: 0 of 29 trimethoprim-sulfamethoxazole recipients were colonized versus 15 of 117 nonrecipients, P = 0.04. In a multivariate logistic regression model, prior infection with either methicillin-susceptible S. aureus (odds ratio = 32.4, 95% confidence interval 3.04 to 345.42) or MRSA (odds ratio = 9.71, 95% confidence interval 2.20 to 43.01), not receiving current or recent antibiotics (odds ratio = 0.026, 95% confidence interval 0.002 to 0.412), and lower CD4 count (odds ratio 0.996, 95% confidence interval 0.992 to 0.999) were associated with MRSA colonization. Discussion:The prevalence of MRSA nasal colonization was relatively high compared with prior studies; axillary colonization was rare. Prior staphylococcal infection (methicillin-susceptible S. aureus or MRSA), not receiving antibiotics, and lower CD4 count were associated with MRSA nasal colonization. Trimethoprim-sulfamethoxazole seemed to be protective of MRSA colonization.

Impact of Cethromycin (ABT-773) Therapy on Microbiological, Histologic, Immunologic, and Respiratory Indices in a Murine Model of Mycoplasma pneumoniae Lower Respiratory Infection

ABSTRACT Mycoplasma pneumoniae is a major etiologic agent of acute lower respiratory infections. We evaluated the antimicrobial and immunologic effects of cethromycin (ABT-773), a ketolide antibiotic, for the treatment of M. pneumoniae pneumonia in a mouse model. Eight-week-old BALB/c mice were inoculated intranasally once with 106 CFU of M. pneumoniae on day 0. Treatment was started 24 h after inoculation. Groups of mice were treated subcutaneously with cethromycin at 25 mg/kg of body weight or with placebo daily until sacrifice. Five to ten mice per group were evaluated at days 1, 4, 7, and 10 after inoculation. Outcome variables included bronchoalveolar lavage (BAL) for M. pneumoniae quantitative culture and cytokine and chemokine concentration determinations by enzyme-linked immunosorbent assay (tumor necrosis factor alpha [TNF-α], gamma interferon [IFN-γ], interleukin-1β [IL-1β], IL-2, IL-4, IL-12, granulocyte-macrophage colony-stimulating factor, IL-8, monocyte chemoattractant protein 1 [MCP-1], and macrophage inflammatory protein 1α [MIP-1α]), histopathologic score of the lungs (HPS), and pulmonary function tests (PFT) using whole-body, unrestrained plethysmography at the baseline and post-methacholine exposure as indicators of airway obstruction (AO) and airway hyperresponsiveness (AHR), respectively. The cethromycin-treated mice had a greater reduction in M. pneumoniae culture titers than placebo-treated mice, reaching statistical significance on days 7 and 10 (P < 0.05). HPS was significantly reduced in cethromycin-treated mice compared with placebo-treated mice on days 4, 7, and 10 (P < 0.05). Cytokine concentrations in BAL samples were reduced in mice that received cethromycin, and the differences were statistically significant for 7 of the 10 cytokines measured (TNF-α, IFN-γ, IL-1β, IL-8, IL-12, MCP-1, and MIP-1α) on day 4 (P < 0.05). PFT values were improved in the cethromycin-treated mice, with AO and AHR significantly reduced on day 4 (P < 0.05). In this mouse model, treatment with cethromycin significantly reduced M. pneumoniae culture titers in BAL samples, cytokine and chemokine concentrations in BAL samples, histologic inflammation in the lungs, and disease severity as defined by AO and AHR.