Comparative acitivity of ampicillin and cefuroxime against three types of Haemophilus influenzae

Animal Models for Drug Development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998), and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter describes the advantages, setups, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Effects of various test media on the activities of 21 antimicrobial agents against Haemophilus influenzae

As considerable variation in the antimicrobial susceptibility of Haemophilus influenzae has been reported, the effects of various test media on the susceptibility of H. influenzae were studied. MICs were determined by three laboratories for 21 antimicrobial agents against a panel of 100 selected isolates. Testing was performed using a reference NCCLS frozen broth microdilution method with Haemophilus test medium (HTM) broth and dried commercial MIC trays rehydrated with the following media: in-house and commercially prepared HTM broth, Mueller-Hinton broth with 2% lysed horse blood and NAD, IsoSensitest broth with 2% lysed horse blood and NAD, and IsoSensitest broth-based HTM. Overall, all results were very reproducible, with the MIC at which 50% of the isolates tested are inhibited (MIC(50)), MIC(90), and geometric mean MIC being within one doubling dilution by all six methods and at all three testing centers for 15 of the 21 agents tested. Interlaboratory differences were more marked than intralaboratory differences or differences among media. Cefprozil, cefaclor, and trimethoprim-sulfamethoxazole results differed the most, while results for ampicillin, amoxicillin-clavulanic acid, cefdinir, cefixime, ceftriaxone, and clarithromycin were the most reproducible. However, these variations in results caused considerable differences in susceptibility rates for agents for which NCCLS susceptible breakpoints were close to the geometric mean MIC, particularly for cefaclor and cefprozil. This was much less of a problem when pharmacokinetic-pharmacodynamic breakpoints were used. Reproducible susceptibility results were obtained for a wide range of agents against H. influenzae in three laboratories using a variety of media that support the growth of this fastidious species.

Susceptibilities of Streptococcus pneumoniae and Haemophilus influenzae to 10 oral antimicrobial agents based on pharmacodynamic parameters: 1997 U.S. Surveillance study

The susceptibilities of Streptococcus pneumoniae (1,476 strains) and untypeable Haemophilus influenzae (1,676 strains) to various oral beta-lactam, macrolide-azalide, and fluoroquinolone antimicrobial agents were determined by broth microdilution. Organisms were isolated from specimens obtained from outpatients in six geographic regions of the United States. MIC data were interpreted according to pharmacodynamically derived breakpoints applicable to the oral agents tested. Among H. influenzae strains, 41.6% were beta-lactamase positive. Virtually all H. influenzae strains were susceptible to amoxicillin-clavulanate (98%), cefixime (100%), and ciprofloxacin (100%), while 78% were susceptible to cefuroxime, 57% were susceptible to amoxicillin, 14% were susceptible to cefprozil, 9% were susceptible to loracarbef, 2% were susceptible to cefaclor, and 0% were susceptible to azithromycin and clarithromycin. Among S. pneumoniae isolates, 49.6% were penicillin susceptible, 17.9% were intermediate, and 32.5% were penicillin resistant, with penicillin MICs for 50 and 90% of the isolates tested of 0.12 and 4 microg/ml, respectively. Overall, 94% of S. pneumoniae isolates were susceptible to amoxicillin and amoxicillin-clavulanate, 69% were susceptible to azithromycin and clarithromycin, 63% were susceptible to cefprozil and cefuroxime, 52% were susceptible to cefixime, 22% were susceptible to cefaclor, and 11% were susceptible to loracarbef. Although ciprofloxacin has marginal activity against S. pneumoniae, no high-level fluoroquinolone-resistant strains were found. Significant cross-resistance was found between penicillin and macrolides-azalides among S. pneumoniae isolates, with 5% of the penicillin-susceptible strains being macrolide-azalide resistant, compared with 37% of the intermediate isolates and 66% of the resistant isolates. Resistance was highest in S. pneumoniae isolates from patients younger than 10 years of age, middle ear and paranasal sinus specimens, and the southern half of the United States. With the continuing rise in resistance, judicious use of oral antimicrobial agents is necessary in all age groups.

Evaluation of Haemophilus influenzae isolates with elevated MICs to amoxicillin/clavulanic acid

A 1994 to 1995 national Haemophilus influenzae surveillance study of 1910 strains showed that 13 strains (0.7%) were resistant to amoxicillin/clavulanic acid (MIC, > or = 8/4 micrograms/ml). These and other selected strains were investigated further in this study. Susceptibility of the surveillance study strains was determined with the commercial microdilution trays used in the original study and in triplicate with reference broth microdilution trays prepared by the investigators, as well as by Etest and disk diffusion. Amoxicillin/clavulanic acid resistance was confirmed for only one of the surveillance study strains. This strain produced double zones of growth with Etest and disk-diffusion methods, with the double zone containing spheroplasts. When the amoxicillin/clavulanic acid MICs of all beta-lactamase positive strains were compared, MIC results obtained with surveillance study trays and the Etest were one to two dilutions higher than MICs obtained with reference trays. The distribution and modal amoxicillin/clavulanic acid MICs of beta-lactamase-positive and -negative strains was essentially the same for a comparison group of strains using reference trays, in contrast to a fourfold higher modal MIC for beta-lactamase-positive strains using surveillance study reagents and strains. These differences in MICs could be attributed to variations in inoculum, the presence of spheroplasts, and/or a difference in potency of amoxicillin and/or clavulanic acid in the tray and Etest reagents used. Methods for assessing the adequacy of the clavulanic acid content are not adequate, amoxicillin control values and a beta-lactamase-positive H. influenzae control strain are required.

Ampicillin killing curve patterns for ampicillin-susceptible nontypeable Haemophilus influenzae strains by the agar dilution plate count method

Ampicillin killing curve patterns for 20 strains of ampicillin-susceptible nontypeable Haemophilus influenzae were determined by the agar dilution plate count method. The paradoxical effect was detected in the 24-h killing curve patterns for each strain. For the biphasic effect, minimum survivor percentages (maximum killing) occurred over a narrow range of ampicillin concentrations immediately above the MIC, with survivor percentages then rising rapidly to peak at approximately 1-log10-unit increment higher. The 24-h minimum survivor percentages for the 20 strains ranged from approximately 0.01% (rapid killing) to greater than 10% (slow killing). In comparison with the previous results for typeable strains, the present findings suggest that nontypeable stains are, on average, killed much more slowly. Based on the initial 24-h killing curve patterns for the 20 strains, 4 strains were selected as putative representatives of the range of bactericidal responses encountered. These strains were then studied to examine the reproducibility of the 24-h patterns and to determine sequential killing curves. These patterns were found to be reproducible and served to characterize the relative killing responses of the strains. In the sequential studies of three of the four strains, tiny colonies having the gross and microscopic characteristics of L-forms were found to be present on the agar dilution plate count plates prior to the application of penicillinase at 48 and 72 h. Such colonies reverted to vegetative forms within 24 to 48 h after application of penicillinase to the panels. Of particular interest was the observation that the paradoxical effect was manifested both by the L-form colonies and by the reverted vegetative colonies. The late development of L-forms was observed for both rapidly and slowly killed strains.

Haemophilus influenzae: antibiotic susceptibility

Ampicillin resistance was first reported among clinical isolates of Haemophilus influenzae in 1972. Reports of chloramphenicol resistance followed shortly thereafter. The principal mechanism of resistance to these two antibiotics is enzymatic. Although other mechanisms have been described, they are found in comparatively few strains. The genetic information for the inactivating enzymes is plasmid mediated and therefore readily transmissible to susceptible strains. Consequently, effective therapy for invasive disease caused by this pathogen has been seriously compromised. As antibiotic susceptibility became less predictable, in vitro testing became increasingly important. Unfortunately, the standardization of methods for laboratory testing has been slow and complicated by the fastidious nature of the organisms. This review traces the development of antibiotic resistance in H. influenzae, discusses the mechanisms which appear to be important in mediating resistance, explores newer antimicrobial agents which might be useful in the treatment of infection, and analyzes the various approaches to in vitro testing.

Influence of growth medium and supplement on growth of Haemophilus influenzae and on antibacterial activity of several antibiotics

In the present study, five non-beta-lactamase- and five beta-lactamase-producing strains of Haemophilus influenzae were used to determine whether three different growth media, Mueller-Hinton broth and agar, brain heart infusion broth and agar, and tryptic soy broth and agar, and their added supplements (0.2% hemin-0.1% IsoVitaleX, 1% hemin-1% IsoVitaleX, 2% sheep blood, 10% Fildes enrichment, 5% Fildes enrichment, 1% supplement B, 5% horse erythrocytes, and 2% hemoglobin-1% IsoVitaleX) would influence the growth rate of this microorganism and the antibacterial activity of eight antibiotics, including ampicillin, tetracycline, chloramphenicol, gentamicin, cefamandole, erythromycin, trimethoprim-sulfamethoxazole (TMP-SMX), and cefoperazone. The growth curve studies were carried out with an initial inoculum of 10(4) bacteria per ml, and MICs were determined with an inoculum of 5 X 10(5) microorganisms. Mueller-Hinton broth, brain heart infusion broth, and tryptic soy broth enriched with 5% Fildes resulted in a maximal growth of more than 10(8) CFU/ml at 24 h. When 10% Fildes or 2% sheep blood was added as enrichment to Mueller-Hinton broth, a considerable reduction in the growth rate of H. influenzae strains resulted (P less than 0.01). Significant variations in MICs (P less than 0.01) were observed with chloramphenicol, TMP-SMX, erythromycin, and cefoperazone when brain heart infusion agar, Mueller-Hinton agar, or tryptic soy agar was used. Chloramphenicol, gentamicin, erythromycin, and TMP-SMX were all affected by the different enrichments added to Mueller-Hinton agar. MICs were in general higher with 5% Fildes enrichment and lower with 1% supplement B. Cefoperazone was the only drug which exhibited a lower MIC in 5% Fildes enrichment for ampicillin-resistant H. influenzae strains.

Hemophilus influenzae pericarditis in two adults

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Effect of inoculum size and beta-lactamase production on in vitro activity of new cephalosporins against Haemophilus species

Sixty-three strains of Haemophilus species, 38 of which were beta-lactamase producers (37 H. influenzae type b, 1 H. parainfluenzae) and 25 of which were beta-lactamase negative (20 H. influenzae, 5 H. parainfluenzae), were tested for susceptibility to cefoxitin, moxalactam (LY127935) (Lilly), cefsulodin (CGP 7174 E, Ciba), and cefoperazone (T 1551, Pfizer). Cefsulodin was relatively inactive at both low and high inocula. LY127935 and cefoperazone displayed inoculum-dependent bactericidal activity. Cefoxitin displayed little inoculum effect against beta-lactamase-producing strains: 8 and 16 microgram/ml killed at least 90% of those tested at 10(4) and 10(6) colony-forming units per ml, respectively.

Use and interpretation of Schlichter's test on Haemophilus influenzae: relation of in vitro to in vivo results for cefamandole

When Haemophilus influenzae infections are treated by an antibiotic acting on the bacterial wall, the adequacy of antimicrobial therapy can be assessed by Schlichter's test. This test may be carried out using Mueller Hinton broth (or Mueller Hinton broth with 50% pooled serum and a supplement of Ca++ and Mg++) supplemented with Fildes' enrichment and an inoculum adjusted to the 0.5 McFarland turbidity standard diluted 200x. However, correct reading of end points can be obtained only by phase contrast microscopic examination, which allows the establishment of good correlation between the in vitro and in vivo findings. In patients with lung infections successfully treated with cefamandole, the presence of spheroplasts in samples derived from Schlichter's tests correlates well with clinical improvement and eradication of the pathogenic organism checked by transtracheal aspiration.

Cefuroxime: a review of its antibacterial activity, pharmacological properties and therapeutic use

Cefuroxime is a new semisynthetic cephalosporin for parenteral administration. It is resistant to destruction by beta-lactamases produced by staphylococci and most Gram-negative aerobic bacteria and is active against many bacteria resistant to cephalothin. Cefuroxime is the most active of the cephalosporins against gonococci and Haemophilus influenzae particularly against beta-lactamase producing strains. Given by intramuscular or intravenous injection cefuroxime is effective against a wide variety of infections caused by Gram-positive or Gram-negative aerobes, but has no effect against infections caused by Pseudomonas aeruginosa or B. fragilis. Cefuroxime is of value in the treatment of respiratory infections due to Haemophilus influenzae and Streptocococcus pneumoniae and is useful against cephalosporin-resistant Klebsiella and Enterobacter infections. Cefuroxime is an alternative to spectinomycin for the treatment of beta-lactamase producing Neisseria gonorrhoeae infections. It is generally well tolerated and appears not to be nephrotoxic when given alone at usual dosages.

Growth curves, microscopic morphology, and subcultures of beta-lactamase-positive and -negative Haemophilus influenzae under the influence of ampicillin and cefamandole

In contrast to the results obtained with ampicillin, the minimum inhibitory concentrations of cefamandole against Haemophilus influenzae were within the same range (0.5 to 1.5 mug/ml) whether or not the strains were beta-lactamase producers. The minimum bactericidal concentrations were somewhat higher for beta-lactamase-positive strains (6.4 mug/ml) than for negative strains (1.2 mug/ml). In a culture with high initial microbial density, monitored by recording optical densities, the addition of 10 mug of cefamandole per ml brought about rapid lysis of a beta-lactamase-negative strain. Observation of a beta-lactamase-positive strain revealed, in the early part of the growth curve, absence of lysis and an increase of biomass similar to that observed in a drug-free control curve. In contrast to the results obtained with ampicillin, the culture consisted uniformly of spherical forms, probably in the process of division, which were capable of generating colonies. When the microbial density exposed to cefamandole was increased still further, persistent bacillary forms were observed, and after 24 h hydrolysis had eliminated every trace of microbiologically active cefamandole.

Bronchopulmonary infection due to Branhamella catarrhalis: 11 cases assessed by transtracheal puncture

Transtracheal punctures were performed in 193 miners of anthracosilicotic coal who presented with an acute exacerbation of chronic bronchitis. The transtracheal aspirates were bacteriologically positive in 104 patients. Branhamella catarrhalis was isolated in 15 patients; 10 of these responded to chemotherapy, as shown by the resolution of all symptoms and the disappearance of the organism on a repeat transtracheal puncture performed 48 hours after the end of treatment. One ampicillin-treated patient, whose bronchial secretions yielded a beta-lactamase-producing B catarrhalis, showed no improvement. But subsequent treatment with cefuroxime was followed by clinical and bacteriological recovery. B catarrhalis probably acted as an opportunistic respiratory pathogen in these patients, who were probably compromised hosts in view of their clinical history. B catarrhalis normally responds to the penicillins commonly used for respiratory infections, but if treatment fails a transtracheal puncture is essential to identify the strain and determine an appropriate antibiotic.