Quinolone antibiotics in therapy of experimental pneumococcal meningitis in rabbits

Using a rabbit model of pneumococcal meningitis, we compared the pharmacokinetics and bactericidal activities in cerebrospinal fluid (CSF) of older (ciprofloxacin, ofloxacin) and newer (levofloxacin, temafloxacin, CP-116,517, and Win 57273) quinolones with those of the beta-lactam ceftriaxone. All quinolones penetrated into the inflamed CSF better than ceftriaxone, and the speed of entry into CSF was closely related to their degrees of lipophilicity. At a dose of 10 mg/kg.h, which in the case of the quinolones already in use in clinical practice produced concentrations attainable in the sera and CSF of humans, ciprofloxacin had no antipneumococcal activity (delta log10 CFU/ml.h, +0.20 +/- 0.14). Ofloxacin (delta log10 CFU/ml.h, -0.13 +/- 0.12), temafloxacin (delta log10 CFU/ml.h, -0.19 +/- 0.18), and levofloxacin (delta log10 CFU/ml.h, -0.24 +/- 0.16) showed slow bactericidal activity (not significantly different from each other), while CP-116,517 (delta log10 CFU/ml.h, -0.59 +/- 0.21) and Win 57273 (delta log10 CFU/ml.h, -0.72 +/- 0.20) showed increased bactericidal activities in CSF that was comparable to that of ceftriaxone at 10 mg/kg.h (delta log10 CFU/ml.h, -0.80 +/- 0.17). These improved in vivo activities of the newer quinolones reflected their increased in vitro activities. All quinolones and ceftriaxone showed positive correlations between bactericidal rates in CSF and concentrations in CSF relative to their MBCs. Only when this ratio exceeded 10 did the antibiotics exhibit rapid bactericidal activities in CSF. In conclusion, in experimental pneumococcal meningitis the activities of new quinolones with improved antipneumococcal activities were comparable to that of ceftriaxone.

Rifampin for therapy of experimental pneumococcal meningitis in rabbits

Rifampin at a maximally effective dose was less active than ceftriaxone (both drugs at 10 mg/kg of body weight.h) in a rabbit model of pneumococcal meningitis (delta log10 CFU/ml.h, -0.40 +/- 0.13 versus -0.77 +/- 0.18; P < 0.01). The bactericidal activity of rifampin decreased at concentrations in cerebrospinal fluid greater than those that are clinically achievable, and use of rifampin in combination with ofloxacin had no synergistic or additive effect.

Pharmacodynamics of antibiotics in the therapy of meningitis: infection model observations

Detailed studies of pharmacodynamic principles relevant to the therapy of bacterial meningitis are difficult to perform in man, while the rabbit model of bacterial meningitis has proved to be extremely valuable and has led to insights that appear relevant for the treatment of humans. Most importantly in the light of the restricted penetration of antibiotics into the CSF, animal studies have shown that in meningitis there is a dose-response curve between the CSF concentrations achieved by antibiotics and their bactericidal activity. This appears to be true for all classes of antibiotics thus far examined, including the beta-lactams, which do not show such a dose-response behaviour in other infections. Only CSF concentrations that exceed the MBC of the infecting organism by at least 10-30-fold achieve consistent and rapid bactericidal activity. Such rapid bactericidal activity is a requirement for successful therapy with beta-lactams and can be impaired with certain antibiotics by the specific conditions in infected CSF (protein content; acidic pH; slow-growing bacteria). However, rapid antibiotic killing of the infecting organisms may not be without adverse effects either. Some antibiotics, particularly beta-lactams lead to the brisk liberation of bacterial cell wall components (e.g. endotoxin, in the case of Gram-negative organisms) which have an inflammatory effect on the host and can lead to a temporary deterioration of the disease. Dexamethasone, when administered with the antibiotic, can prevent some of the adverse effects of rapid bacterial lysis.

Influence of antibiotic dose, dosing interval, and duration of therapy on outcome in experimental pneumococcal meningitis in rabbits

We examined the influence of several pharmacokinetic parameters on cure rates in rabbits with experimental pneumococcal meningitis. When the duration of treatment was kept constant, cure rates improved as the individual dose of ampicillin was increased. On the other hand, when four doses of ampicillin at 60 mg/kg of body weight, producing peak concentrations in cerebrospinal fluid (CSF) of approximately 40 times the MBC, were administered at intervals of 24 instead of 4 h and the duration of therapy was thus prolonged from 12 to 72 h, cure rates also increased (85 versus 25%; P less than 0.01). These high cure rates were achieved even though bacterial titers in CSF 24 h after the first dose had reached levels similar to those present at the beginning of therapy. Cure in these animals was explained by the fact that the second ampicillin dose reduced bacterial titers in CSF significantly more than did the first dose (5.2 versus 2.5 log10 CFU/ml; P less than 0.02). The clinical relevance of these observations remains to be determined.

Pefloxacin therapy for experimental endocarditis caused by methicillin-susceptible or methicillin-resistant strains of Staphylococcus aureus

The therapeutic efficacy of pefloxacin in experimental endocarditis caused by methicillin-susceptible or methicillin-resistant Staphylococcus aureus was evaluated. In rabbits infected with a methicillin-susceptible strain, 4 days of pefloxacin therapy significantly reduced both the number of bacteria per gram of vegetation and the mortality rate compared with untreated controls, and pefloxacin was equivalent to cephalothin. Pefloxacin was also as effective as vancomycin in reducing vegetation titers and mortality rate in animals with endocarditis caused by a methicillin-resistant strain. These results suggest that pefloxacin may be an effective agent in the therapy of serious infections caused by either methicillin-susceptible or -resistant strains of S. aureus.

Influence of the developmental state of valvular lesions on the antimicrobial activity of cefotaxime in experimental enterococcal infections

Cefotaxime has little antimicrobial activity in vitro against most strains of enterococci, as measured by conventional MICs and MBCs. However, the MICs of cefotaxime against many enterococci are markedly reduced by the addition of serum to the test medium. To assess the relevance of this observation in vivo, we examined the efficacy of cefotaxime in experimental Streptococcus faecalis endocarditis. Since response to antimicrobial agents may vary with the degree of vegetation development, therapeutic efficacy was assessed both in rabbits with newly formed vegetations and in rabbits with well-developed endocardial lesions. Peak serum levels of cefotaxime (50.1 +/- 20.0 micrograms/ml) exceeded the MIC in medium supplemented with serum (4 micrograms/ml), but not in Mueller-Hinton broth alone (greater than 64 micrograms/ml). After 4 days of therapy, animals with newly formed lesions (therapy initiated 1 h after infection, transvalvular catheters removed) had lower mean vegetation bacterial titers than did untreated controls. Among animals with mature vegetations (therapy initiated 12 h after infection, catheters indwelling), the rate of mortality was significantly reduced by cefotaxime therapy. However, no difference in vegetation titers was observed. Thus, cefotaxime demonstrated antienterococcal activity within newly formed vegetations, but did not inhibit bacterial proliferation within well-established vegetations.

Antimicrobial activity of gentamicin in experimental enterococcal endocarditis

The in vitro activity of gentamicin was compared with its therapeutic efficacy in rabbits with Streptococcus faecalis endocarditis. The test strain was resistant to gentamicin as measured by MICs and MBCs determined in Mueller-Hinton broth alone or in broth supplemented with 50% rabbit serum. Gentamicin also failed to manifest anti-enterococcal activity when evaluated by time-kill studies in broth. However, the addition of serum to the medium did enhance the activity of gentamicin. In the therapy of experimental endocarditis, gentamicin used alone demonstrated anti-enterococcal activity equivalent to that of ampicillin used alone. Vegetation titers in animals treated with gentamicin alone were lower than those of untreated controls (P less than 0.01) and comparable to those in animals treated with ampicillin alone. Thus, gentamicin demonstrated anti-enterococcal activity in vivo despite the resistance observed in vitro, as measured by conventional assays to determine MICs and MBCs.

The influence of dosing schedules and cerebrospinal fluid bactericidal activity on the therapy of bacterial meningitis

Bacterial meningitis represents an infection in an area of impaired host defence. Optimal therapy of meningitis requires attaining bactericidal activity within cerebrospinal fluid (CSF). Studies in experimental animal models of meningitis suggest that maximal rates of bacterial killing in vivo and optimal cure rates are achieved when CSF antibiotic concentrations exceed the MBC of the test strain by greater than or equal to ten-fold. The results of clinical trials support this conclusion. In addition, a variable post-antibiotic effect occurs in-vivo after short periods of exposure to antimicrobial activity, thus maintaining therapeutic efficacy with intermittent dosage regimens. These basic principles of therapy are outlined in this review and serve as a basis for rational treatment regimens. For most antibiotics, the optimal dose, dosage interval, and duration of therapy for bacterial meningitis remain to be established.

Phage lytic enzyme Cpl-1 for antibacterial therapy in experimental pneumococcal meningitis

Treatment of bacterial meningitis caused by Streptococcus pneumoniae is increasingly difficult, because of emerging resistance to antibiotics. Recombinant Cpl-1, a phage lysin specific for S. pneumoniae, was evaluated for antimicrobial therapy in experimental pneumococcal meningitis using infant Wistar rats. A single intracisternal injection (20 mg/kg) of Cpl-1 resulted in a rapid (within 30 min) decrease in pneumococci in cerebrospinal fluid (CSF) by 3 orders of magnitude lasting for 2 h. Intraperitoneal administration of Cpl-1 (200 mg/kg) led to an antibacterial effect in CSF of 2 orders of magnitude for 3 h. Cpl-1 may hold promise as an alternative treatment option in pneumococcal meningitis.

Antimicrobial susceptibility of gram-positive udder pathogens from bovine mastitis milk in Switzerland

We evaluated the susceptibility of the gram-positive mastitis pathogens S. aureus, Str. uberis, Str. dysgalactiae, E. faecalis and L. garviae to antibiotics that are of epidemiological interest or are critically important for mastitis therapy and human medicine. Penicillin resistance was found to be most frequent in S. aureus, and nearly 5 % of the Str. uberis strains displayed a decreased susceptibility to this antibiotic. Resistance to aminoglycosides and macrolides was also detected in the strains tested. The detection of methicillin-resistant S. aureus (MRSA) and of a ciprofloxacin-resistant Str. dysgalactiae isolate corroborated the emergence of mastitis pathogens resistant to critically important antibiotics and underscores the importance of susceptibility testing prior to antibiotic therapy. The monitoring of antibiotic susceptibility patterns and antibiogram analyses are strongly recommended for targeted antimicrobial treatment and to avoid the unnecessary use of the latest generation of antibiotics.

Eluding antibiotic resistance: capitalizing on antimicrobial peptides interaction with the lipid bilayer

It is widely accepted that the emergence of drug-resistant pathogens is the result of the overuse and misuse of antibiotics. Infectious Disease Society of America, Center for Disease Control and World Health Organization continue to view, with concern, the lack of antibiotics in development, especially those against Gram-negative bacteria. Antimicrobial peptides (AMPs) have been proposed as an alternative to antibiotics due to their selective activity against microbes and minor ability to induce resistance. For example, the Food and Drug Administration approved Daptomycin (DAP) in 2003 for treatment of severe skin infections caused by susceptible Gram-positive organisms. Currently, there are 12 to 15 examples of modified natural and synthetic AMPs in clinical development. But most of these agents are against Gram-positive bacteria. Therefore, there is unmet medical need for antimicrobials used to treat infections caused by Gram-negative bacteria. In this study, we show that a pro-apoptotic peptide predominantly used in cancer therapy, (KLAKLAK)2, is an effective antimicrobial against Gram-negative laboratory strains and clinical isolates. Despite the therapeutic promise, AMPs development is hindered by their susceptibility to proteolysis. Here, we demonstrate that an all-D enantiomer of (KLAKLAK)2, resistant to proteolysis, retains its activity against Gram-negative pathogens. In addition, we have elucidated the specific site and mechanism of action of D(KLAKLAK)2 through a repertoire of whole-cell and membrane-model assays. Although it is considered that development of resistance does not represent an obstacle for AMPs clinical development, strains with decreased susceptibility to these compounds have been reported. Staphylococci resistance to DAP was observed soon after its approval for use and has been linked to alterations of the cell wall (CW) and cellular membrane (CM) properties. Immediately following staphylococcal resistance, Enterococci resistance to DAP was seen, yet the mechanism of resistance in enterococci remains unknown. Our findings demonstrate that, similar to S. aureus, development of DAP-resistance in a vancomycin-resistant E. faecalis isolate is associated with alterations of the CW and properties of the CM. However, the genes linked to these changes in enterococci appear to be different from those described in S. aureus.

Surveillance of antimicrobial resistance of Streptococcus pneumoniae and Haemophilus influenzae in children with pneumonia

In order to identify optimal therapy for children with bacterial pneumonia, Pakistan's ARI Program, in collaboration with the National Institute of Health (NIH), Islamabad, undertook a national surveillance of antimicrobial resistance in S. pneumoniae and H. influenzae. The project was carried out at selected urban and peripheral sites in 6 different regions of Pakistan, in 1991–92. Nasopharyngeal (NP) specimens and blood cultures were obtained from children with pneumonia diagnosed in the outpatient clinic of participating facilities. Organisms were isolated by local hospital laboratories and sent to NIH for confirmation, serotyping and antimicrobial susceptibility testing. Following were the aims of the study (i) to determine the antimicrobial resistance patterns of S. pneumoniae and H. influenzae in children aged 2–59 months; (ii) to determine the ability of selected laboratories to identify and effectively transport isolates of S. pneumoniae and H. influenzae cultured from nasopharyngeal and blood specimens; (iii) to validate the comparability of resistance patterns for nasopharyngeal and blood isolates of S. pneumoniae and H. influenzae from children with pneumonia; and (iv) to examine the effect of drug resistance and laboratory error on the cost of effectively treating children with ARI. ^ A total of 1293 children with ARI were included in the study: 969 (75%) from urban areas and 324 (25%) from rural parts of the country. Of 1293, there were 786 (61%) male and 507 (39%) female children. The resistance rate of S. pneumoniae to various antibiotics among the urban children with ARI was: TMP/SMX (62%); chloramphenicol (23%); penicillin (5%); tetracycline (16%); and ampicillin/amoxicillin (0%). The rates of resistance of H. influenzae were higher than S. pneumoniae: TMP/SMX (85%); chloramphenicol (62%); penicillin (59%); ampicillin/amoxicillin (46%); and tetracycline (100%). There were similar rates of resistance to each antimicrobial agent among isolates from the rural children. ^ Of a total 614 specimens that were tested for antimicrobial susceptibility, 432 (70.4%) were resistant to TMP/SMX and 93 (15.2%) were resistant to antimicrobial agents other than TMP/SMX viz. ampicillin/amoxicillin, chloramphenicol, penicillin, and tetracycline. ^ The sensitivity and positive predictive value of peripheral laboratories for H. influenzae were 99% and 65%, respectively. Similarly, the sensitivity and positive predictive value of peripheral laboratory tests compared to gold standard i.e. NIH laboratory, for S. pneumoniae were 99% and 54%, respectively. ^ The sensitivity and positive predictive value of nasopharyngeal specimens compared to blood cultures (gold standard), isolated by the peripheral laboratories, for H. influenzae were 88% and 11%, and for S. pneumoniae 92% and 39%, respectively. (Abstract shortened by UMI.)^

Antimicrobial susceptibility of canine Clostridium perfringens strains from Switzerland

Fifty Clostridium perfringens strains were isolated from individual dogs with acute diarrhoea that were not given antibiotics. Toxin types and minimal inhibitory concentrations of 15 antibiotics were determined for each of them. All strains harboured the alpha-toxin gene, 12 of them had both the alpha- and entero-toxin gene and 5 had both the alpha- and beta2-toxin gene. Eighteen percent of the isolates showed resistance to tetracycline and 54 % showed decreased susceptibility to metronidazole which is one of the most frequently used antibiotics in the treatment of canine diarrhoea. Apart from that, all isolates were susceptible to the remaining antibiotics tested. These findings lead to the conclusion that despite a general susceptibility to antibiotics in C. perfringens, resistance is developing in isolates from dogs. Therefore, careful identification of the pathogenic agent and antibiotic susceptibility testing should be performed prior to therapy in order to minimise further selection of antibiotic resistance.

Secondary analysis of effectivness of tinidazole-containing-quadruple eradication therapy in asymptomatic H. pylori infected children in El Paso

Helicobacter pylori infection is frequently acquired during childhood. This microorganism is known to cause gastritis, and duodenal ulcer in pediatric patients, however most children remain completely asymptomatic to the infection. Currently there is no consensus in favor of treatment of H. pylori infection in asymptomatic children. The firstline of treatment for this population is triple medication therapy including two antibacterial agents and one proton pump inhibitor for a 2 week duration course. Decreased eradication rate of less than 75% has been documented with the use of this first-line therapy but novel tinidazole-containing quadruple sequential therapies seem worth investigating. None of the previous studies on such therapy has been done in the United States of America. As part of an iron deficiency anemia study in asymptomatic H. pylori infected children of El Paso, Texas, we conducted a secondary data analysis of study data collected in this trial to assess the effectiveness of this tinidazole-containing sequential quadruple therapy compared to placebo on clearing the infection. Subjects were selected from a group of asymptomatic children identified through household visits to 11,365 randomly selected dwelling units. After obtaining parental consent and child assent a total of 1,821 children 3-10 years of age were screened and 235 were positive to a novel urine immunoglobulin class G antibodies test for H. pylori infection and confirmed as infected using a 13C urea breath test, using a hydrolysis urea rate >10 μg/min as cut-off value. Out of those, 119 study subjects had a complete physical exam and baseline blood work and were randomly allocated to four groups, two of which received active H. pylori eradication medication alone or in combination with iron, while the other two received iron only or placebo only. Follow up visits to their houses were done to assess compliance and occurrence of adverse events and at 45+ days post-treatment, a second urea breath test was performed to assess their infection status. The effectiveness was primarily assessed on intent to treat basis (i.e., according to their treatment allocation), and the proportion of those who cleared their infection using a cut-off value >10 μg/min of for urea hydrolysis rate, was the primary outcome. Also we conducted analysis on a per-protocol basis and according to the cytotoxin associated gene A product of the H. pylori infection status. Also we compared the rate of adverse events across the two arms. On intent-to-treat and per-protocol analyses, 44.3% and 52.9%, respectively, of the children receiving the novel quadruple sequential eradication cleared their infection compared to 12.2% and 15.4% in the arms receiving iron or placebo only, respectively. Such differences were statistically significant (p<0.001). The study medications were well accepted and safe. In conclusion, we found in this study population, of mostly asymptomatically H. pylori infected children, living in the US along the border with Mexico, that the quadruple sequential eradication therapy cleared the infection in only half of the children receiving this treatment. Research is needed to assess the antimicrobial susceptibility of the strains of H. pylori infecting this population to formulate more effective therapies. ^

THE SHORT- AND LONG-TERM EFFECTS OF A HANDBOOK ON THE ANTIMICROBIAL PRESCRIBING PATTERNS OF HOSPITAL PHYSICIANS

This study evaluates the effect of a specially designed, physician-oriented handbook of antimicrobial use on the prescribing patterns of a group of fifty doctors at a university hospital. Data were evaluated over a peroid of one-and-one-half years, before and after the distribution of the handbook. For the purposes of this study, antimicrobial therapy was classified: (1) inappropriate if it violated one of a number of recognized principles of antimicrobial therapy, (2) appropriate if it agreed with specific recommendations or alternatives given in the distributed reference handbook, and (3) acceptable if it was neither inappropriate nor appropriate as defined by the handbook. An initial survey of antimicrobial prescribing patterns was made. Five months later the handbook was distributed and a two-week orientation program, consisting of the distribution and promotion of the problem-oriented, pocket-size handbook of appropriate antimicrobial therapy, was conducted. The handbook, which was developed by the authors and reviewed and approved by a panel of infectious disease specialists, presented guidelines for appropriate and efficacious usage of antimicrobial agents as most currently accepted in common clinical infections. Subsequent surveys were then conducted two weeks, three months, and six months after distribution of the handbook. A statistically significant difference (p < 0.01) in antimicrobial prescribing patterns was noted between the survey conducted two weeks after the introduction of the handbook and the other surveys. In this survey, while therapy classified inappropriate decreased from 44% to 28%, therapy appropriate as recommended increased from 31% to 53%. The findings of this study demonstrate that the introduction and promotion of the handbook decreases abuse and increases proper use of antimicrobial therapy, although the effect is sustainable for only a short duration--no longer than three months. These results indicate the need for a vigorous, updated program to achieve and maintain current appropriate antibotic therapy in clinical medicine. ^