Comparative efficacies of ciprofloxacin, ampicillin and chloramphenicol in treatment of experimental Haemophilus influenzae pneumonia

An experimental murine model of bacteraemic Haemophilus influenzae pneumonia was used to evaluate the therapeutic efficacy of ciprofloxacin, as compared with ampicillin and chloramphenicol. An ampicillin-sensitive (AS) and an ampicillin-resistant (AR) challenge strain were employed. Ciprofloxacin treatment produced intrapulmonary killing of H. influenzae which was superior to that achieved with ampicillin (P less than 0.001, both strains) and chloramphenicol (P less than 0.001, strain AS; P less than 0.005, strain AR). Likewise, survival from strain AS pneumonia was 61% in the ciprofloxacin-treated animals, as compared with 43% for the chloramphenicol-treated, and 22% for the ampicillin-treated groups. We conclude that ciprofloxacin may be an effective agent in treating pneumonia caused by either ampicillin-sensitive or ampicillin-resistant strains of H. influenzae.     

Comparative evaluation of ciprofloxacin, enoxacin, and ofloxacin in experimental Pseudomonas aeruginosa pneumonia.

The therapeutic activity of ciprofloxacin, enoxacin, and ofloxacin was evaluated in guinea pigs with acute and chronic experimental Pseudomonas aeruginosa pneumonia. Intratracheal instillations of P. aeruginosa resulted in fatal pneumonia in all untreated animals within 36 h. Among treatment groups (80 mg/kg [body weight] per day), cumulative survival rates were: 47%, ciprofloxacin; 55%, enoxacin; and 42%, ofloxacin. These rates were not significantly different. Intrapulmonary killing of P. aeruginosa was equivalent 3 h after a single dose of ciprofloxacin or ofloxacin (20 mg/kg) or enoxacin (40 mg/kg). The combination of ciprofloxacin with azlocillin, ceftazidime, or tobramycin did not increase the efficacy of intrapulmonary killing of P. aeruginosa over that of ciprofloxacin alone. A chronic, nonfatal bronchopneumonia was induced in guinea pigs by intratracheal instillation of microscopic agar beads impregnated with a mucoid strain of P. aeruginosa. Compared with no treatment, ciprofloxacin and enoxacin produced greater than or equal to 99.9% intrapulmonary killing, and ofloxacin sterilized the lungs completely, after 4 days of treatment. In no quinolone-treated animal did resistant strains of P. aeruginosa emerge during 4-day treatment periods. In further studies with the chronic model, oral and parenteral ciprofloxacin treatment were found to be equivalent in efficacy. We conclude that several quinolone derivatives may be effective for the treatment of P. aeruginosa pneumonia and that combinations of quinolones with beta-lactams or aminoglycosides may not increase efficacy against P. aeruginosa pneumonia.     

Comparison of cotrimoxazole, ampicillin, and chloramphenicol in treatment of experimental Haemophilus influenzae type B meningitis.

To evaluate cotrimoxazole in the treatment of bacterial meningitis, we compared its action with that of ampicillin and chloramphenicol in experimental Haemophilus influenzae type b meningitis. Both trimethoprim and sulfamethoxazole penetrated well into the cerebrospinal fluid of infected rabbits, reaching 40 and 26%, respectively, of their simultaneous serum levels. Levels measured 30 and 60 min after intravenous injection exceeded the minimum inhibitory concentration of this combination for H. influenzae by 10- to 100-fold. The mean ratio of trimethoprim to sulfamethoxazole in cerebrospinal fluid was 1:22. Cotrimoxazole was as effective as ampicillin in therapy of beta-lactamase-negative H. influenzae meningitis and as effective as chloramphenicol for a beta-lactamase positive strain. These findings corroborate favorable preliminary clinical experience reported by others and indicate that cotrimoxazole deserves further study in the therapy of bacterial meningitis.     

Comparative susceptibilities of ampicillin and chloramphenicol resistant Haemophilus influenzae to fifteen antibiotics

Eighty-three isolates of ampicillin and chloramphenicol resistant Haemophilus influenzae were tested for susceptibility to fifteen antibiotics by the agar dilution method. Fifty-four were from paediatric patients with H. influenzae disease and 29 from nasopharyngeal carriers (pre-school children). Twenty-five strains belonged to serotype b, one to serotype a, one to serotype c and the rest were non-typable. All strains produced beta-lactamase and inactivated chloramphenicol in a rapid bioassay, suggesting the production of chloramphenicol-acetyltransferase. The most active drugs were ceftriaxone, cefotaxime, latamoxef, aztreonam and desacetyl-cefotaxime (MIC90: 0.03, 0.06, 0.12, 0.25 and 0.25 mg/l, respectively). Cefuroxime, rifampicin and imipenem (MIC90 1 mg/l), and the combination of amoxycillin and clavulanic acid (MIC90 2:1 mg/l), also showed good activity. Cefaclor, erythromycin, tetracycline, trimethoprim, sulfamethoxazole and cotrimoxazole were the least active of the drugs studied. The excellent in-vitro activity of the new beta-lactam agents against H. influenzae resistant to ampicillin and chloramphenicol offers a therapeutic alternative in the treatment of serious infections caused by these micro-organisms.     

Evaluation of ceftazidime, ampicillin and chloramphenicol in experimental Haemophilus influenzae type b meningitis

In an infant rat model of Haemophilus influenzae, type b meningitis, where treatment was given 24 and 48 h after infection, the dose of ceftazidime required to eradicate the infection from the CSF of half the animals (CD50) ranged from less than 0.15-1.5 mg/kg/dose. The accompanying blood infections were marginally less responsive to therapy with CD50 values ranging from 0.5-3.9 mg/kg/dose. Comparable data for ampicillin were 12.5-40 mg/kg/dose and 20- greater than 200 mg/kg/dose for the CSF and blood infections while those for chloramphenicol were 18- greater than 100 mg/kg/dose and 22- greater than 100 mg/kg/dose for the CSF and blood infections respectively. Investigation of the relative rates of kill in vivo showed that all three drugs rapidly reduced the bacterial numbers to minimal levels. However, whereas ceftazidime completely eradicated the infection, chloramphenicol, and to a lesser extent, ampicillin-treated rats experienced substantial relapsing. Ceftazidime penetrated into the CSF of infected and uninfected rats slightly better than ampicillin--7.3% compared to 4.0% of the corresponding blood levels respectively. These results indicate that ceftazidime is significantly more active in the infant rat model of H. influenzae, type b meningitis than ampicillin or chloramphenicol.     

Combined action of chloramphenicol and ampicillin on chloramphenicol-resistant Haemophilus influenzae.

Previous studies have demonstrated high, concentration-dependent serum protein binding of cefonicid. To determine the in vivo pharmacokinetic significance of these observations, the pharmacokinetics of both total and unbound (non-protein-bound) cefonicid was studied in six volunteers after a single intravenous dose of 30 mg/kg. Saturable serum protein binding was observed in vivo; the mean +/- standard deviation free fraction of cefonicid was 17.6 +/- 6.1% immediately after administration and declined to a constant value of approximately 2% as total serum concentrations fell below 100 micrograms/ml. This nonlinear binding was associated with a pronounced decline in unbound serum cefonicid concentrations during the first 3 h after administration, with low or undetectable unbound drug concentrations by 12 h. Renal clearance of total cefonicid averaged 21.1 ml/min per kg and did not vary with time; in contrast, the mean +/- standard deviation unbound cefonicid renal clearance increased from 5.7 +/- 2.1 to 10.8 +/- 1.6 ml/min per kg with time (P less than 0.02). This study may partially explain the poor results obtained with single daily dosing of cefonicid in endocarditis. Dosage regimens of certain antimicrobial agents with high, saturable serum protein binding and extensive renal tubular secretion may be most appropriately designed based on unbound drug pharmacokinetics.     

Ketolide treatment of Haemophilus influenzae experimental pneumonia

The MICs of HMR 3004 and HMR 3647 at which 90% of beta-lactamase-producing Haemophilus influenzae isolates were inhibited were 4 and 2 micrograms/ml, respectively. Both HMR 3004 and HMR 3647 were active against beta-lactamase-producing H. influenzae in a murine model of experimental pneumonia. As assessed by pulmonary clearance of H. influenzae, HMR 3004 was more effective (P < 0.05) than was azithromycin, ciprofloxacin, clarithromycin, erythromycin A, pristinamycin, or HMR 3647 in this model.     

In vitro interactions between rifampin and ampicillin or chloramphenicol against Haemophilus influenzae.

Twenty clinical isolates of Haemophilus influenzae type b were used to determine the in vitro interactions of rifampin with ampicillin or chloramphenicol. Potential interactions of the drugs were evaluated by calculating the fractional inhibitory concentration index and fractional bactericidal concentration index for each strain after treatments with the drugs alone and in combination. There was no evidence of synergy or antagonisms between ampicillin and rifampin or between chloramphenicol and rifampin. With ampicillin-susceptible H. influenzae type b strains, an additive effect was observed with seven strains, and an indifferent effect was observed with three strains. Similarly, with chloramphenicol-susceptible H. influenzae type b strains, an additive effect was observed with eight strains, and an indifferent effect was observed with two strains.     

Activities of newer beta-lactam antibiotics against ampicillin, chloramphenicol, or multiply-resistant Haemophilus influenzae

The susceptibilities of singly or multiply-resistant clinical isolates of Haemophilus influenzae were determined by agar dilution to aztreonam, imipenem, and six third-generation cephalosporins. These included selected isolates that were resistant to ampicillin only, chloramphenicol only, and four isolates that were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. All of the isolates were highly susceptible to these newer beta-lactam antibiotics. Isolates resistant to trimethoprim-sulfamethoxazole and/or chloramphenicol had susceptibilities similar to those of strains resistant only to ampicillin. Ceftriaxone, ceftizoxime, and cefotaxime were the most active of the study antibiotics (MIC90 = 0.004-0.016 micrograms/ml), and were also bactericidal at concentrations no more than twice the minimum inhibitory concentration (MIC). Minimum inhibitory concentrations of cefoperazone increased dramatically with only a 10-fold increase in inoculum size of beta-lactamase producing strains, while MICs of the other new agents were not significantly affected by elevation of the inoculum. These new antibiotics appear to be promising candidates for therapy of infections due to resistant H. influenzae.     

Characterization of non-beta-lactamase-mediated ampicillin resistance in Haemophilus influenzae.

Ampicillin resistance in Haemophilus influenzae is most often due to the plasmid-mediated production of TEM beta-lactamase. We studied four strains with high-level ampicillin resistance (MIC of 32 micrograms/ml with an inoculum of 10(5) CFU on solid media) which did not produce detectable beta-lactamase activity with two different detection methods. Two of the four strains contained extrachromosomal DNA by agarose gel electrophoresis. Conjugation failed to transfer ampicillin resistance; in contrast, transformation yielded ampicillin-resistant transformants in three of the four strains. These transformants did not contain detectable extrachromosomal DNA. In addition, mobilization of the resistance determinant by transformation to, or conjugation with, recombination-deficient strains was unsuccessful. DNA-DNA hybridization experiments revealed no homology of the DNA of these strains with two R plasmids (one coding for ampicillin resistance, the other for chloramphenicol and tetracycline resistance). We conclude that the genetic basis of the non-beta-lactamase ampicillin resistance in these strains appears to be chromosomally mediated. We investigated the mechanism of resistance in these strains. Enzymatic modification of penicillin was not detected by autoradiography of a thin-layer chromatogram of cell sonic extracts of three ampicillin-resistant transformant strains incubated with [14C]penicillin. To assess changes in permeability of the cell envelope, a plasmid coding for beta-lactamase was conjugated into these strains, and the hydrolysis of penicillin by intact cells and cell sonic extracts was compared. Only one of three transformant strains had significantly diminished permeability. Outer membrane proteins of these strains analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed apparent differences in comparison with the isogenic ampicillin-susceptible recipient strain. Autofluorography of a sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Sarkosyl-solubilized crude membrane (the putative inner membranes) from these ampicillin-resistant transformant strains incubated with [3H]penicillin compared with the isogenic ampicillin-susceptible recipient strain revealed reduced binding to PBP 3 and 6, 3 and 4, or 4. In addition, affinity binding studies revealed decreased affinity of PBP 4 for ampicillin of all four transformants tested. We conclude that the major mechanism of resistance in these strains is altered penicillin-binding proteins; however, other mechanisms, including permeability, may also play a role.     

Comparative activity of mezlocillin, penicillin, ampicillin, carbenicillin, and ticarcillin against gram-positive bacteria and Haemophilus influenzae.

The in vitro activity of mezlocillin was compared to penicillin G, ampicillin, carbenicillin, and ticarcillin in tests with 195 gram-positive bacteria and 20 Haemophilus influenzae. Against gram-positive isolates excluding enterococci, penicillin was the most active drug, followed by ampicillin, mezlocillin, carbenicillin, and ticarcillin. Ampicillin was the most active of the five drugs against enterococci, whereas mezlocillin was the most active drug against 14 strains of ampicillin-susceptible H. influenzae.     

Rapid detection of chloramphenicol resistance in Haemophilus influenzae.

We compared a rigid (1-h) screening method for the detection of chloramphenicol acetyltransferase (CAT) activity with the standard spectrophotometric CAT assay to determine whether CAT-mediated chloramphenicol resistance in Haemophilus influenzae could be determined upon primary isolation. Of 58 H. influenzae cell sonicates, 28 had detectable CAT activity when the chloramphenicol-dependent production of free coenzyme A from acetyl coenzyme A was measured spectrophotometrically (standard method). These 28 strains were identified as producing CAT by the rapid method which uses lysed cell suspensions and a color change to detect CAT. The remaining 30 strains did not have CAT activity detectable by either method. This 1-h test for CAT should prove to be useful for the early presumptive identification of chloramphenicol resistance in H. influenzae.     

In vitro susceptibility of 104 clinical isolates of Haemophilus influenzae to moxalactam (LY127935), ampicillin, chloramphenicol, and ticarcillin.

A total of 104 strains of Haemophilus influenzae isolated from pediatric patients over a 1-year period were tested for susceptibility to moxalactam (LY127935), ampicillin, chloramphenicol, and ticarcillin. Of these strains, 30 produced beta-lactamase. LY127935 inhibited 99% of the strains at a concentration of 0.125 microgram/ml; the remaining strain was inhibited by this antibiotic at 0.25 microgram/ml. beta-Lactamase-producing strains were inhibited by ampicillin at greater than or equal to 2 microgram/ml. beta-Lactamase-negative strains were all inhibited by ampicillin at less than or equal to 1 microgram/ml, except for one nontypable strain which required 2 microgram of ampicillin per ml for inhibition. All strains were susceptible to chloramphenicol at less than or equal to 4 microgram/ml. beta-Lactamase-producing strains were less susceptible (geometric mean = 4.702 microgram/ml) to ticarcillin than were strains which did not produce beta-lactamase (geometric mean = 0.331 microgram/ml). LY127935 susceptibility was not influenced by increasing inoculum size, as ws ampicillin susceptibility. Combinations of LY127935 and chloramphenicol or ampicillin were not antagonistic in vitro.     

Penicillin-binding proteins and ampicillin resistance in Haemophilus influenzae

Ampicillin-resistant, non-beta-lactamase-producing isolates of Haemophilus influenzae contain a variety of penicillin-binding protein (PBP) patterns that differ from the single pattern of eight PBPs characteristic of susceptible strains. During genetic transformation of resistance, only some of the anomalies in PBP pattern were transformed, specifically those relating to the penicillin-binding capacities of PBPs 4 (Mr of 62,000) and 5 (Mr of 59,000) and, in some transformations, PBP 3 (Mr of 71,000). Comparison of the binding of penicillin by PBPs 4 and 5 of three resistant transformants (derived with DNA from different donors) revealed a decrease in the rate of PBP acylation and no appreciable change in the rate of deacylation as compared to the susceptible recipient. Thus, rapid turnover of these PBPs does not play a role. Retransformation studies confirm that altered PBPs 3, 4, and 5 are associated with resistance and suggest that these PBPs are major targets for the beta-lactam antibiotics in H. influenzae.     

Quantitative PCR assay to evaluate ampicillin, ofloxacin, and doxycycline for treatment of experimental leptospirosis

The susceptibility of Leptospira interrogans serovar icterohaemorrhagiae strain Verdun to selected antibiotics used in medical practice (ampicillin, doxycycline, and ofloxacin) was evaluated in a Syrian hamster model, to determine the efficacy of these antibiotics during the course of the disease. A quantitative PCR assay was used to monitor the density of leptospires in blood and in target organs (liver, kidney, lung, heart, and spleen). Our results demonstrated the ability of ampicillin at a high dose (100 mg/kg of body weight) to clear leptospires from the host, except from kidneys and heart, where 10(2) leptospires/g remained at day 6. Ofloxacin (30 mg/kg) was unable to clear bacteria from blood or kidneys. With doxycycline (10 mg/kg), the clearance of leptospires occurred in 2 days in all the target organs studied, with the exception of liver, which required 3 days. Our data demonstrate the value of monitoring the kinetics of experimental leptospiral infection in order to accurately evaluate the efficacy of antibiotics. We have demonstrated the potential value of doxycycline for the treatment of leptospirosis cases, except in circumstances where it is contraindicated. This experimental model could be used to define better therapeutic strategies for human leptospirosis, by testing associations or new formulations of antibiotics.     

Synergistic action of ampicillin and nafcillin against ampicillin-resistant Haemophilus influenzae.

Six strains of ampicillin-resistant Haemophilus influenzae type b were studied in vitro for synergy between ampicillin and nafcillin. The minimal inhibitory concentrations for these strains with 10(4) colony-forming units per ml were 6.25 to 12.5 microgram of ampicillin per ml and 6.25 to 25 microgram of nafcillin per ml. Studies with these agents demonstrated synergism against all six strains of H. influenzae type b. Most strains were inhibited by 0.78 microgram of nafcillin plus 0.78 microgram of ampicillin per ml. A child with osteomyelitis caused by H. influenzae type b was successfully treated with a combination of ampicillin and nafcillin. These data suggest that further studies assessing the synergistic effect of this drug combination against H. influenzae type b are warranted.     

Limited in vitro activity of cefamandole against 100 beta-lactamase- and non-beta-lactamase-producing Haemophilus influenzae strains: comparison of moxalactam, chloramphenicol, and ampicillin.

In the present study, the minimal inhibitory concentrations and minimal bactericidal concentrations of moxalactam, cefamandole lithium, ampicillin, and chloramphenicol were determined, both in broth and on solid medium, against 75 non-beta-lactamase-producing and 25 beta-lactamase-producing strains of Haemophilus influenzae. Most of the 75 strains were inhibited or killed by 2 microgram or less of ampicillin, chloramphenicol, or moxalactam per ml, but cefamandole exhibited poor bactericidal activity against 11 non-beta-lactamase-producing strains, of which 9 were non-type B H. influenzae. Most of the 25 beta-lactamase-producing H. influenzae were resistant to 128 microgram of ampicillin per ml. Both moxalactam and chloramphenicol, which had minimal inhibitory concentrations of less than 0.25 and 2 microgram/ml, respectively, were more active than cefamandole, which had a minimal inhibitory concentration ranging from 2 to greater than or equal to 128 microgram/ml.     

流感嗜血杆菌氨苄西林耐药基因研究

目的明确我院分离的流感嗜血杆菌（H1）氨苄西林耐药的基因。方法用E试验测定我院上呼吸道感染患儿鼻咽部分离300株HI对氨苄西林耐药情况；以Nitrocdin纸片检测β内酰胺酶；PCR扩增及序列分析确定产酶株的基因型。结果32株氨苄西林耐药株均产β内酰胺酶，占总菌株数11％（32／300），PCR检测出TEM-131株，ROB-11株。结论产β内酰胺酶是H1对氨苄西林耐药的重要机制，TEM-1型是β内酰胺酶主要基因型，ROB-1型β内酰胺酶也首次被检出，值得关注和长期监测。