Improved medium for antimicrobial susceptibility testing of Haemophilus influenzae

Cefotaxime-non-susceptibility of Haemophilus influenzae induced by additional amino acid substitutions of G555E and Y557H in altered penicillin-binding protein 3

Cefotaxime-non-susceptible Haemophilus influenzae has rarely been isolated from clinical specimens. Although several reports have shown that amino acid (AA) alteration in penicillin-binding protein 3 (PBP3), encoded by the ftsI gene, reduces activity of cefotaxime, precise mechanisms conferring the non-susceptibility have been unclear. We analyzed the ftsI gene of two clinically isolated cefotaxime-non-susceptible H. influenzae strains, 16-11 and 20-07 (minimum inhibitory concentrations [MICs]: 16 and 8 μg/mL, respectively), and found that their deduced AA sequences of PBP3 included two AA substitutions of G555E and Y557H in addition to previously described AA alterations. To clarify whether the two additional substitutions are requisite for cefotaxime non-susceptibility, we produced transformants of Rd KW20 (cefotaxime MIC: ≤0.06 μg/mL) with the ftsI gene of 16-11. Cefotaxime MICs against transformants M1 and M2, of which deduced PBP3s were altered with that of 16-11 entirely and partially (only the N-terminal side up to the AA position 519), were 8 and 0.25 μg/mL, respectively. We also produced M2-555/7 through site-directed mutagenesis inducing additional substitutions of G555E and Y557H into the PBP3 of M2, against which cefotaxime MIC was 8 μg/mL. These findings show that the additional substitutions of G555E and Y557H in PBP3 with previously described alterations cause cefotaxime non-susceptibility. An additional substitution of either G555E or Y557H alone in altered PBP3 reduced cefotaxime activity but the elevation of MICs were within the category of susceptibility. To our knowledge, this is the first study clarifying a genetic factor in the PBP3 causing cefotaxime non-susceptibility among H. influenzae strains.

Meningitis due to ampicillin-and chloramphenicol-resistant Haemophilus influenzae type b in Canada. Case report and review

The first report of a case of ampicillin- and chloramphenicol-resistant Haemophilus influenzae type b invasive infection in Canada is described in a four-month-old male with meningitis. He was treated with cefotaxime 200 mg/kg/day divided every 6 h and dexamethasone 0.6 mg/kg/day divided every 6 h, eventually recovering after a complicated course. Follow-up at 21 months showed mild to moderate global developmental delay. While chloramphenicol resistance is rare in North America, a case of meningitis initially unresponsive to ampicillin and chloramphenicol must be considered suspect for resistance. Third generation cephalosporins should be used for resistant cases.

Evaluation of disk diffusion methods to detect low-level β-lactamase-negative ampicillin-resistant Haemophilus influenzae

We evaluated the efficacy of disk diffusion methods for detection of low-level β-lactamase-negative ampicillin-resistant (low-BLNAR) Haemophilus influenzae. Four hundred and seventy unselected, recent clinical isolates were tested with ampicillin (10 μg), cefaclor (30 μg) and cefuroxime (30 μg) on iso-Sensitest agar enriched with nicotinamide adenine dinucleotide (NAD) and horse blood [ST agar; Swedish Reference Group for Antibiotics (SRGA) guidelines], and on chocolate agar (in-house guidelines). Selected isolates (n = 147) were subjected to partial sequencing of the ftsI gene. Forty-seven strains (10.0%) were genotypically identified as low-BLNAR, which was confirmed by determination of minimal inhibitory concentration (MIC) using microbroth dilution method: only low level resistance to ampicillin was detected [MIC ≤1 μg/mL; MIC(50) = 0.5 μg/mL, implying susceptibility by Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antibiotic Susceptibility Testing (EUCAST) interpretative criteria]. The MIC of cefuroxime varied between 1 and 4 μg/mL (MIC(50) = 2 μg/mL), indicating susceptibility to cefuroxime by CLSI but not by EUCAST guidelines. Disk diffusion methods were able to discriminate low-BLNAR H. influenzae from the wild-type population with sensitivities ranging from 87% to 98% and specificities from 96% to 99%. Cefaclor was found to be superior to cefuroxime and ampicillin. Cefaclor zone diameter breakpoints of 30/29 and 23/22 mm are suggested for ST agar and chocolate agar, respectively.

In vitro activity of ampicillin, cefoperazone, their combinations with sulbactam and other antimicrobials: survey of Russian isolates

Methodological differences makes it difficult to compare results of antimicrobial susceptibility testing obtained in Russia and in other regions. During the period from October 1993 to May 1994 susceptibility of 1296 isolates of bacteria was investigated according to NCCLS standards by the broth microdilution method. The order of activity of antibiotics against Gram-negative bacteria based on percent of susceptible strains from common hospitals were: amikacin (98%) > ciprofloxacin (93%) = imipenem (93%) > cefoperazone/sulbactam (92%) > ceftazidime (89%) > ceftriaxone (81%) > cefotaxime (80%) > cefoperazone (77%) > gentamicin (71%) > ampicillin/sulbactam (51%) > cefazoline (45%) > ampicillin (25%). The order of activity against strains from teaching hospitals was similar but the percent of susceptible strains was 10-20% less for the majority of antibiotics. The susceptibility level of Gram-negative isolates from Moscow teaching hospitals is lower than from Northern America and Europe. Ampicillln/sulbactam and cefoperazone/sulbactam, as well as other cephalosporins, demonstrated high activity against methicillin-susceptible staphylococci and penicillin-susceptible pneumococci. B-lactams/beta-lactamase inhibitor combinations were active against 100% strains of anaerobic bacteria.

Low beta-lactamase-negative ampicillin-resistant Haemophilus influenzae strains are best detected by testing amoxicillin susceptibility by the broth microdilution method

Ampicillin resistance in Haemophilus influenzae due to alterations in penicillin-binding proteins (beta-lactamase negative ampicillin resistant [BLNAR]) is acquiring increasing clinical and epidemiological importance. BLNAR strains with low ampicillin MICs (0.5 to 4 microg/ml) represent the majority of this population in Europe and the United States, but separating them from susceptible isolates is challenging. To investigate the best method to identify low-BLNAR strains, we studied the antibiotic susceptibilities of 94 clinical isolates of H. influenzae by microdilution, Etest, and disk diffusion: 25 had no resistance mechanisms (gBLNAS), 34 had mutations in the ftsI gene only (gBLNAR), 20 were beta-lactamase producers only (gBLPAR), and 15 showed beta-lactamase production and mutations in the ftsI gene (gBLPACR). By current CLSI breakpoints, most gBLNAR isolates were ampicillin susceptible by microdilution (76.5%) or by Etest (88.2%). Most gBLNAR strains (79.4%) were nonsusceptible to amoxicillin (the most widely used community antibiotic in the United States and Europe) when tested by microdilution. By Etest, 15% of beta-lactamase-positive isolates were nonresistant to ampicillin or amoxicillin. The poorest agreement between Etest and microdilution results was for the gBLPAR isolates (25% for ampicillin, 15% for amoxicillin, and 10% for cefaclor). Low-strength disks of ampicillin and amoxicillin-clavulanic acid poorly identified low-BLNAR isolates and are not recommended as a screening method. We suggest new amoxicillin breakpoints for BLNAR isolates as follows: susceptible, MIC < or = 0.5 microg/ml (no resistance mechanisms; pharmacokinetic/pharmacodynamic [PK/PD] data favorable); intermediate, MICs = 1 to 2 microg/ml (resistance mechanisms present but PK/PD data favorable), and resistant, MICs > or = 4 microg/ml (resistance mechanisms present and PK/PD data unfavorable).

Antimycobacterial activity of bacteriocins and their complexes with liposomes

OBJECTIVES

Bacteriocins (Bcn) are natural peptides that are secreted by several taxonomically distant bacteria and exert bactericidal activity against other bacterial species. Their capacity to inhibit growth of virulent Mycobacterium tuberculosis H37Rv was evaluated in this study.

METHODS

Five different Bcn were isolated and purified from bacterial culture supernatants, their amino acid sequence was determined, and activity against mycobacteria assessed in three different models: in vitro mycobacterial cultures, in vitro infection of mouse macrophages and in vivo high-dose infection of inbred mice.

RESULTS

In the in vitro model, four out of five Bcn exhibited stronger antimycobacterial activity than equal concentrations of a widely used anti-TB antibiotic, rifampicin. These Bcn were non-toxic for mouse macrophages at a concentration of 0.1 mg/L (>MIC(90) of these compounds). Pure Bcn did not inhibit mycobacterial growth within murine macrophages when added at 0.01-0.1 mg/L, suggesting that at physiologically tolerable concentrations these molecules do not penetrate through the membrane of eukaryotic cells. However, when administered as a complex with phosphatidylcholine-cardiolipin liposomes, Bcn5 (selected as a model compound due to its cytotoxicity and antimycobacterial activity regular titration curves) demonstrated capacity both to inhibit intracellular growth of M. tuberculosis and to prolong survival of mice in an acute TB model.

CONCLUSIONS

Given that the mechanism of Bcn bactericidal activity differs from that of all commonly used antibiotics, their possible involvement in complex TB therapies deserves further study.

[Study of Haemophilus influenzae strains isolated at the Tunis children's hospital in the prevaccination era (1999-2002)]

OBJECTIVE

This study had for aim to define the pattern of Haemophilus influenzae infections in a Tunisian hospital during the prevaccination era. We determined serotypes, biotypes, and antibiotic susceptibility of H. influenzae strains.

DESIGN

187 H. influenzae strains were identified in various samples between 1999 and 2002.

RESULTS

Strains were isolated essentially from respiratory samples in 63.7% and cerebrospinal fluid in 21.4 %. The mean age of children with invasive infections was 16 months. All invasive strains belong to serotype b. Biotypes I, II and III were the most frequent (84.7%). Ampicillin resistance with betalactamase producing mechanism occurred in 26,7% of isolates, this type of resistance was more frequent among invasive strains (37.2%) than in non-invasive ones (22.8%). All betalactamase producing strains had amoxicillin MICs above 1 mg/l, these strains were susceptible to amoxicillin+clavulanate. Three strains were betalactamase negative ampicillin resistant with ampicillin MICs: 1.5, 3, and 4 mg/l. All strains were susceptible to cefotaxim with MICs < 0.19 mg/l. Antibiotic resistance concerned: chloramphenicol: 7.5%, tetracycline: 6.9% and trimethoprime-sulfamethoxazole: 13.9%. 8.1% of the strains were kanamicin resistant but concerned only betalactamase producing strains.

CONCLUSION

Before the introduction of a conjugate vaccine, all invasive infections in young children were caused by H. influenzae b strains.

Haemophilus influenzae carriage in children attending French day care centers: a molecular epidemiological study

The nasopharyngeal Haemophilus influenzae flora of healthy children under the age of 3 years attending day care centers in three distinct French geographic areas was analyzed by sampling during two periods, spring 1999 (May and June) and fall 1999 (November and December). The average carrier rate among 1,683 children was 40.9%. The prevalence of capsulated H. influenzae carriers was 0.4% for type f and 0.6% for type e. No type b strains were found among these children, of whom 98.5% had received one or more doses of anti-Haemophilus b vaccine. Among the strains, 44.5% were TEM-type beta-lactamase producers and nine (1.3%) were beta-lactamase-negative ampicillin-resistant strains. Pulsed-field gel electrophoresis restriction patterns showed a large diversity with 366 SmaI patterns from 663 strains. Among the strains isolated during a given period, 33% were isolated simultaneously in more than one area. In each area, depending on the sampling period, 68 to 72% of the strains had new pulsotypes and persistence of 28 to 32% of the strains was noted. For the 297 beta-lactamase-producing strains, 194 patterns were found. The genomic diversity of these strains was comparable to that of the whole set of strains and does not suggest a clonal diffusion. Among the beta-lactamase-producing strains isolated in November and December, depending on the area, 66 to 73% had new pulsotypes with persistence of only 27 to 33% of the strains. In any given geographic area, colonization by H. influenzae appears to be a dynamic process involving a high degree of genomic heterogeneity among the noncapsulated colonizing strains.

A novel glutathione transferase from Haemophilus influenzae which has high affinity towards antibiotics

Cytosolic glutathione transferase (GSTs) are a family of multi-functional proteins which catalyse the conjugation of glutathione (GSH) to a large variety of endogenous and exogenous electrophilic compounds. Much is known about cytosolic mammalian GSTs, however, the presence of GSTs in several aerobic and anaerobic micro-organisms has also been demonstrated. Several findings seem to suggest that bacterial GSTs are involved in processes of biodegradation of xenobiotics, including antibiotics. However, the function played by these enzymes in the bacterial cell still remains to be clarified. At present, it is ill-defined whether bacterial GST can be classified, as in the case of mammalian enzymes, into several distinct classes. Here we report the purification of a GST isoform from Haemophilus influenzae using GSH-affinity chromatography. The purified protein was characterised by immunological and kinetic properties different from other known GSTs. The dissociation constants of chloramphenicol, ampicillin, rifampicin and tetracycline to the purified enzyme were 0.62, 9.06, 4.08 and 1.77 microM, respectively, as determined by following the quenching of the protein intrinsic fluorescence. These values were much lower than those previously determined for the same drugs with other mammalian or bacterial GSTs. The present results indicate that the enzyme purified from H. influenzae is a novel GST isoform well distinguished from other known mammalian or bacterial GSTs.

Diversity of beta-lactam resistance-conferring amino acid substitutions in penicillin-binding protein 3 of Haemophilus influenzae

The sequences of the ftsI gene, encoding the transpeptidase domain of penicillin binding protein (PBP) 3A and/or PBP 3B, which are involved in septal peptidoglycan synthesis, were determined for 108 clinical strains of Haemophilus influenzae with reduced susceptibility to beta-lactam antibiotics with or without beta-lactamase production and were compared to those of the ampicillin-susceptible Rd strain and ampicillin-susceptible clinical isolates. The sequences have 18 different mutation patterns and were classified into two groups on the basis of amino acid substitutions deduced from the nucleotide sequences located between bp 960 and 1618 of the ftsI gene. In group I strains (n = 7), His-517 was substituted for Arg-517. In group II strains (n = 101), Lys-526 was substituted for Asn-526. In subgroup IIa (n = 5; H. influenzae ATCC 49247), the only observed substitution was Lys-526 for Asn-526; in subgroup IIb (n = 56), Val-502 was substituted for Ala-502 (n = 13), along with several other substitutions: Asn-350 for Asp-350 (n = 15), Asn-350 for Asp-350 and Glu-490 for Gly-490 (n = 14), and Asn-350 for Asp-350 and Ser-437 for Ala-437 (n = 5). In subgroup IIc (n = 25), Thr-502 was substituted for Ala-502. In subgroup IId, Val-449 was substituted for Ile-449 (n = 15). The MICs of beta-lactam antibiotics for the 108 strains were to 8 to 16 times the MICs for susceptible strains. The strains, isolated from both adults and children, were analyzed for genetic relationship by pulsed-field gel electrophoresis and by determination of ftsI sequence phylogeny. Both analyses revealed the lack of clonality and the heterogeneity of the strains, but some clusters suggest the spread and/or persistence of a limited number of strains of the same pulsotype and pattern of amino acid substitutions. Reduced susceptibility to beta-lactam, brought about by mutations of the ftsI gene, is becoming a frequent phenomenon, affecting both strains that produce beta-lactamase and those that do not. The level of resistance remains low but opens the way to greater resistance in the future.

Antimicrobial resistance trends in community-acquired respiratory tract pathogens in the Western Pacific Region and South Africa: report from the SENTRY antimicrobial surveillance program, (1998-1999) including an in vitro evaluation of BMS284756

From 1998 to 1999, a large number of community-acquired respiratory tract isolates of Streptococcus pneumoniae (n=566), Haemophilus influenzae (n=513) and Moraxella catarrhalis (n=228) were collected from 15 centres in Australia, Hong Kong, Japan, China, the Philippines, Singapore, South Africa and Taiwan through the SENTRY Antimicrobial Surveillance Program. Isolates were tested against 26 antimicrobial agents using the NCCLS-recommended methods. Overall, 40% of S. pneumoniae isolates were resistant to penicillin with 18% of strains having high-level resistance (MIC > or =2 mg/l). Rates of erythromycin and clindamycin resistance were 41 and 23%, respectively. Penicillin-resistant strains showed high rates of resistance to other antimicrobial agents: 96% to trimethoprim-sulphamethoxazole (TMP-SMX), 84% to tetracycline and 81% to erythromycin. A significant proportion of penicillin-susceptible strains was also resistant to erythromycin (21%), tetracycline (29%) and TMP-SMZ (26%). Small numbers of strains were resistant to levofloxacin (0.7%), trovafloxacin (0.4%) and grepafloxacin (1.3%) where as all strains remained uniformly susceptible to quinupristin/dalfopristin and BMS284756 (MIC(90), 0.06 mg/l), a new desfluoroquinolone. beta-lactamases were, produced by 20% H. influenzae isolates and only rare strains showed intrinsic resistance to amoxycillin. Other beta-lactam agents showed good activity with rates of resistance less than 2% and all isolates showed susceptibility to cefixime, ceftibuten, cefepime and cefotaxime. Rates of resistance to tetracycline and chloramphenicol were also relatively low at 3%. The majority (98%) of M. catarrhalis isolates was found to be beta-lactamase-positive and resistant to penicillins, however, resistance to erythromycin and tetracycline was also low at 1.8%. Both H. influenzae and M. catarrhalis isolates were uniformly susceptible to the new desfluoroquinolone and tested fluoroquinolones.

Identification of beta-lactamase-negative, ampicillin-resistant strains of Haemophilus influenzae with four methods and eight media

A challenge set of 143 non-beta-lactamase-producing strains of Haemophilus influenzae was tested for ampicillin susceptibility on two broth media and six agar media, using broth microdilution, agar dilution, disk diffusion, and E-test procedures. When beta-lactamase-negative, ampicillin-resistant (BLNAR) strains were defined as those for which the ampicillin MIC was > or = 4.0 microg/ml, 5 to 44% of our selected strains were BLNAR depending on the medium and/or test method used. If nonsusceptible strains for which ampicillin MICs were intermediate were included in the BLNAR category, 32 to 50% of our isolates would be considered BLNAR. These data emphasize the need for a standardized testing procedure and a universal definition of BLNAR strains before the clinical relevance of such strains can be evaluated. NCCLS dilution tests with haemophilus test medium broth or agar are preferred for testing ampicillin against H. influenzae.

Influence of variations in test methods on susceptibility of Haemophilus influenzae to ampicillin, azithromycin, clarithromycin, and telithromycin

The National Committee for Clinical Laboratory Standards standard broth microdilution method for testing the susceptibility of Haemophilus influenzae to ampicillin, azithromycin, clarithromycin, and telithromycin was evaluated by altering one variable at a time. Variables that were tested included age of colony for inoculum preparation, inoculum density, test medium, incubation atmosphere, and incubation time. For the macrolide, azalide, and ketolide agents, incubation in 5 to 7% CO(2) most significantly affected the MICs, producing nearly twofold increases for clarithromycin and telithromycin and a greater than threefold increase for azithromycin. For ampicillin, a 10-fold increase in inoculum density increased the geometric mean MICs for beta-lactamase-negative strains from 1. 50 to 2.45 microg/ml. In addition, 206 H. influenzae strains were tested for their susceptibilities to the same drugs by the broth microdilution tests in two media, as well as by agar dilution tests, disk diffusion tests, and Etests, on six different agar media. The three standard methods with Haemophilus test medium (HTM) compared favorably with each other except for a high minor discrepancy rate (27%) by the disk diffusion test with ampicillin and clarithromycin. Agar dilution test MICs on the five comparative media were generally higher than those on HTM agar but were only rarely more than one twofold concentration higher. Etest MICs of azithromycin and telithromycin were more than twofold higher than agar dilution and broth microdilution MICs on HTM; ampicillin Etest MICs were nearly twofold lower. The use of media other than HTM agar appears to have a minimal effect on susceptibility test results for the ketolide, azalide, or macrolide drugs that we tested against H. influenzae.

The bactericidal activity of levofloxacin against ampicillin-resistant and ampicillin-susceptible Haemophilus influenzae in comparison with ofloxacin, ciprofloxacin and sparfloxacin

The bactericidal activity of levofloxacin against four Haemophilus influenzae clinical isolates (two ampicillin-resistant and two susceptible) was compared with that of ofloxacin, ciprofloxacin and sparfloxacin at concentrations simulating the peak serum concentrations obtained with the recommended oral doses. Bactericidal activity was assessed using time-kill curves and minimum kill-time values. Both concentrations of levofloxacin rapidly killed all the study strains, with mean kill times of 4 h and no viable bacteria remaining after 18-h exposure. The bactericidal activities of levofloxacin, ofloxacin and sparfloxacin were similar. The minimum kill-times for both concentrations of ciprofloxacin were 28-35% longer than those of levofloxacin. These results support the use of levofloxacin for H. influenzae infections, including ampicillin-resistant strains.

Haemophilus influenzae and Moraxella catarrhalis from patients with community-acquired respiratory tract infections: antimicrobial susceptibility patterns from the SENTRY antimicrobial Surveillance Program (United States and Canada, 1997)

Between February and June of 1997, a large number of community-acquired respiratory tract isolates of Haemophilus influenzae (n = 1,077) and Moraxella catarrhalis (n = 503) from 27 U.S. and 7 Canadian medical centers were characterized as part of the SENTRY Antimicrobial Surveillance Program. Overall prevalences of beta-lactamase production were 33.5% in H. influenzae and 92.2% in M. catarrhalis with no differences noted between isolates recovered in the United States and those from Canada. Among a total of 21 different antimicrobial agents tested, including six cephalosporins, a beta-lactamase inhibitor combination, three macrolides, tetracycline, trimethoprim-sulfamethoxazole (TMP-SMX), rifampin, chloramphenicol, five fluoroquinolones, and quinupristin-dalfopristin, resistance rates of > 5% with H. influenzae were observed only with cefaclor (12.8%) and TMP-SMX (16.2%).

Synthesis and antibacterial activity of ketolides (6-O-methyl-3-oxoerythromycin derivatives): a new class of antibacterials highly potent against macrolide-resistant and -susceptible respiratory pathogens

In the search for new antibiotics active against macrolide-resistant pneumococci and Haemophilus influenzae, we synthesized a new class of 3-oxo-6-O-methylerythromycin derivatives, so-called "ketolides". A keto function was introduced in position 3 after removal of L-cladinose, a sugar which has long been thought essential. Further modifications of the macrolactone backbone allowed us to obtain three different series of 9-oxime, 11,12-carbamate, and 11, 12-hydrazonocarbamate ketolides. These compounds were found to be very active against penicillin/erythromycin-resistant pneumococci and noninducers of MLSB resistance. The 11,12-substituted ketolide 61 (HMR 3004) demonstrated a potent activity against multiresistant pneumococci associated with a well-balanced activity against all bacteria involved in respiratory infections including H. influenzae, Mycoplasma catarrhalis, group A streptococci, and atypical bacteria. In addition HMR 3004 displayed high therapeutic activity in animals infected by all major strains, irrespective of their resistance phenotype.

Clonal distribution of invasive Neisseria meningitidis isolates from the Norwegian county of Telemark, 1987 to 1995

Forty-two Neisseria meningitidis isolates were obtained from patients with meningococcal disease in the Norwegian county of Telemark (January 1987 to March 1995), and all were compared by PCR amplicon restriction endonuclease analysis (PCR-AREA) of the dhps gene, chromosomal DNA fingerprinting, and serological analysis. PCR-AREA divided the isolates into 11 classes, of which 4, comprising 15, 8, 6, and 2 isolates, were clonal while the remaining 8 classes were genetically heterogeneous or contained only 1 isolate. Three of the four clonal classes could be tentatively equated with recognized epidemic clones (ET5, ET37, and cluster A4) on the basis of their phenotypic characteristics, while the remaining clone appears to be new. There were significant differences in the geographical distribution of clones, with class 1 (ET5-like) isolates significantly overrepresented in rural parts of Telemark. Class 1 (ET5-like) isolates occurred throughout the study period and were dominant in 1987. Class 2 (ET37-like) isolates occurred from 1988 to 1992, and class 3 isolates (with no recognizable ET affinities) were found only in 1991 and 1992.

Comparison of broth microdilution method using Haemophilus test medium and agar dilution method for susceptibility testing of Eikenella corrodens

Susceptibility testing of Eikenella corrodens is usually performed by a Mueller-Hinton sheep blood agar dilution (AD) method. However, this method is impractical for testing only a few strains. We compared AD with the broth microdilution method using Haemophilus test medium (HTM) in order to determine the susceptibility of 36 clinical isolates of E. corrodens to eight antimicrobial agents. MICs obtained by the HTM method yielded 95.5 and 84% agreement (within 2 and 1 log2 dilutions, respectively) with those obtained by AD. The HTM method with incubation in CO2 for 48 h was highly reproducible and constitutes an easy alternative for antimicrobial susceptibility testing of E. corrodens.

Molecular epidemiology and phylogenetic analysis of Haemophilus parainfluenzae from chronic obstructive pulmonary disease exacerbations

This study was undertaken to characterize serial Haemophilus parainfluenzae strains from epidemiologically unrelated chronic obstructive pulmonary disease (COPD) patients and from healthy carriers. A comprehensive approach was used including different phenotypical and molecular typing methods: biotyping, antibiotyping, conventional ribotyping, pulsed field gel electrophoresis (PFGE) assay, and PCR-ribotyping. Conventional ribotyping and PFGE analysis were confirmed as excellent procedures to differentiate isolates of the same species and biotype. Conversely, in our study, PCR-ribotyping proved to be suitable for taxonomic purposes, unambiguously identifying H. parainfluenzae from H. influenzae but not discriminating strains at the intraspecific level for epidemiological typing. Phylogenetic analysis of restriction fragment length polymorphism (RFLP) data of sequences related to the rrn operon demonstrated that H. parainfluenzae strains associated to COPD are spread among many diverging lineages.

Laboratory issues in the detection and reporting of antibacterial resistance

The emergence of antimicrobial resistance among several common bacterial pathogens requires that clinical microbiology laboratories have the ability to promptly and accurately recognize resistance in patients' isolates. Laboratories have several options for performing routine susceptibility testing, including the broth microdilution procedure (with or without instrumentation for test reading), automated instrument systems that provide rapid results, antibiotic gradient diffusion, and disk diffusion procedures. In addition, there are definitive screening tests capable of recognizing resistance to drugs of choice among several common bacterial species based on single drug concentration tests or rapid spot tests. The likely emergence of still newer resistance mechanisms will provide a challenge to clinical microbiologists to devise accurate, yet cost-effective strategies for use in the future.

In vitro activity of the new ketolide HMR 3004 compared to an azalide and macrolides against Streptococcus pneumoniae and Haemophilus influenzae

The purpose of this study was to compare the in vitro activity of a new ketolide, HMR 3004 (RU64004), to that of three macrolides and one azalide against 608 Streptococcus pneumoniae and 202 Haemophilus influenzae. Macrolide-resistant pneumococci were susceptible to HMR 3004, even if they were resistant to clindamycin. Against Haemophilus influenzae, HMR 3004 and azithromycin were nearly identical in potency; the macrolides were 8- to 16-fold less active. HMR 3004 may be useful for treating respiratory tract infections if sufficient concentrations can be achieved at the local sites of infection.

Antibacterial activity of RU 64004 (HMR 3004), a novel ketolide derivative active against respiratory pathogens

The antibacterial activity of RU 64004, a new ketolide, was evaluated against more than 600 bacterial strains and was compared with those of various macrolides and pristinamycin. RU 64004 had good activity against multiresistant pneumococci, whether they were erythromycin A resistant or not, including penicillin-resistant strains. RU 64004 inhibited 90% of pneumococci resistant to erythromycin A and penicillin G at 0.6 and 0.15 microg/ml, respectively. Unlike macrolides, RU 64004 did not induce the phenotype of resistance to macrolides-lincosamides-streptogramin B. Its good antibacterial activity against multiresistant pneumococci ran in parallel with its well-balanced activity against all bacteria involved in respiratory infections (e.g., Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes). In contrast to all comparators (14- and 16-membered-ring macrolides and pristinamycin), RU 64004 displayed high therapeutic activity in animals infected with all major strains, irrespective of the phenotypes of the strains. The results suggest that RU 64004 has potential for use in the treatment of infections caused by respiratory pathogens including multiresistant pneumococci.

In vitro activity of BAY 12-8039, a novel 8-methoxyquinolone, compared to activities of six fluoroquinolones against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

The in vitro activity of a novel 8-methoxyquinolone, BAY 12-8039, against recent clinical isolates of Streptococcus pneumoniae (n = 404), Haemophilus influenzae (n = 330), and Moraxella catarrhalis (n = 250) was evaluated. Activity was compared to those of six other fluoroquinolones: ciprofloxacin, clinafloxacin, levofloxacin, ofloxacin, sparfloxacin and trovafloxacin. BAY 12-8039 and clinafloxacin had the highest levels of activity against S. pneumoniae, both with a MIC at which 90% of the isolates were inhibited (MIC90) of 0.06 microg/ml. Trovafloxacin and sparfloxacin were the next most active agents versus S. pneumoniae (MIC90s = 0.12 microg/ml). No differences in activity against penicillin-susceptible, -intermediate, or -resistant strains of S. pneumoniae were noted for any of the fluoroquinolones tested. MIC90s for the seven fluoroquinolones ranged from 0.008 to 0.06 microg/ml versus H. influenzae and from 0.008 to 0.12 microg/ml for M. catarrhalis. The MICs for two strains of S. pneumoniae and one strain of H. influenzae were noted to be higher than those for the general population of organisms for all of the fluoroquinolones tested. Finally, the activity of BAY 12-8039 versus S. pneumoniae was found to be diminished when MIC determinations were performed with incubation of agar dilution plates or broth microdilution trays in 5 to 7% CO2 versus ambient air.

In vitro and in vivo antibacterial activities of ER-35786, a new antipseudomonal carbapenem

ER-35786 is a new parenteral 1 beta-methyl carbapenem with a broad antibacterial spectrum and a potent antipseudomonal activity. It showed high in vitro activity, comparable to those of meropenem and a new carbapenem, BO-2727, against methicillin-susceptible Staphylococcus aureus and streptococci, with MICs at which 90% of strains tested are inhibited (MIC90S) of < or = 0.39 microgram/ml. Against methicillin-resistant S. aureus, ER-35786 was the most active among the compounds tested, yet its MIC90 was 12.5 micrograms/ml. Against members of the family Enterobacteriaceae, Moraxella catarrhalis, and Haemophilus influenzae, ER-35786 inhibited 90% of strains tested at a concentration of < or = 1.56 micrograms/ml. The MIC90 of ER-35786 for Pseudomonas aeruginosa was 3.13 micrograms/ml, and the compound was more active than meropenem. In addition, the activity of ER-35786 against imipenem-, meropenem-, cefclidin-, or ceftazidime-resistant P. aeruginosa was equal to or higher than that of the most active reference compound. The in vivo activity of ER-35786 was consistent with this in vitro activity. The in vivo activity of ER-35786 was highest for systemic infection models with methicillin-resistant S. aureus and beta-lactam-resistant P. aeruginosa strains. In acute pneumonia caused by P. aeruginosa, ER-35786 produced a greater reduction in the viable cell count in the lungs than did imipenem-cilastatin or meropenem.

A national collaborative study of the in vitro activity of oral cephalosporins and loracarbef (LY 163892). Australian Group for the Study of Antimicrobial Resistance (AGAR)

A national collaborative study involving the laboratories of 17 Australian hospitals examined the in vitro activity of loracarbef, cefaclor, cephalexin, amoxycillin and amoxycillin/clavulanate against 2661 recently isolated common bacterial pathogens. Loracarbef was the most active agent against Escherichia coli (MIC90 = 1 mg/l) and had activity comparable to other agents against Klebsiella pneumoniae and Proteus mirabilis. Like the oral cephalosporins, it had no activity against species of Enterobacter and Serratia. beta-lactamase-producing Staphylococcus aureus and Haemophilus influenzae were moderately sensitive to loracarbef (MIC90 = 8 mg/l for both species). Streptococcus pneumoniae was moderately sensitive to loracarbef (MIC90 = 2 mg/l) but strains which were insensitive to penicillin were often highly resistant.

Antibiotic resistance among clinical isolates of Haemophilus influenzae in the United States in 1994 and 1995 and detection of beta-lactamase-positive strains resistant to amoxicillin-clavulanate: results of a national multicenter surveillance study

A total of 1,537 clinical isolates of Haemophilus influenzae were recovered in 30 U.S. medical center laboratories between 1 November 1994 and 30 April 1995 and were characterized in a central laboratory with respect to serotype and beta-lactamase production and the in vitro activities of 15 oral antimicrobial agents. Overall, 36.4% of the isolates were found to produce beta-lactamase. The rank order of activity of six cephalosporins on the basis of MICs was cefixime > cefpodoxime > cefuroxime > loracarbef > or = cefaclor > cefprozil. On the basis of current National Committee for Clinical Laboratory Standards (NCCLS) breakpoints ages of isolates found to be resistant or intermediate to these agents were as follows: 0.1, 0.3, 6.4, 16.3, 18.3, and 29.8, respectively (National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, 4th ed. M7-A4, 1995). Azithromycin was, on a weight basis, the most potent of the macrolides tested in this study, followed by erythromycin and then clarithromycin. Azithromycin was typically fourfold more active than erythromycin, which was, in turn, slightly more active than clarithromycin. However, when compared on the basis of the frequency of resistance determined by using current NCCLS breakpoints, there was essentially no difference between azithromycin and clarithromycin, i.e., 0.5 and 1.9%, respectively (P = 0.086). Interpretive breakpoints for erythromycin MIC tests versus H. influenzae have not been developed. Resistance to other non- beta-lactam agents was variable, as follows: trimethoprim-sulfamethoxazole, 9.0%; chloramphenicol, 0.2%; tetracycline, 1.3%; and rifampin, 0.3%. Two conspicuous findings in this study were the identification of 39 strains H. influenzae that were beta-lactamase negative but ampicillin intermediate or resistant (BLNAR) and, even more surprisingly, 17 beta-lactamase-positive isolates that were resistant to amoxicillin-clavulanate (BLPACR). Strains of H. influenzae in the first group have heretofore been very uncommon; organisms in the second group have not previously been described in the literature. The percentages of all study isolates comprised of BLNAR and BLPACR organisms were 2.5 and 1.1, respectively. Overall resistance to ampicillin was thus 38.9%, and that to amoxicillin-clavulanate was 4.5%.

Nontypeable Haemophilus influenzae susceptibility: effect of inoculum size and beta-lactamase production

The activities of cefixime, cefpodoxime, cefprozil, cefuroxime, loracarbef, and amoxicillin/clavulanate against 72 clinical isolates of nontypeable Haemophilus influenzae were determined by using an agar dilution method. The effects of beta-lactamase production and bacterial inoculum size were investigated. All antimicrobials exhibited a significant inoculum effect, demonstrating the importance of accurately determining inoculum size in the performance of antimicrobial susceptibility testing of H. influenzae.

In vitro activity of sanfetrinem (GV104326), a new trinem antimicrobial agent, versus Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

Sanfetrinem, formerly GV104326, is a new trinem antimicrobial agent with extensive in vitro activity for a variety of different bacteria. The activity of sanfetrinem was determined using a broth microdilution MIC method versus a large number of clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis obtained in a recent 30-center United States surveillance study. The sanfetrinem MIC50 and MIC90 values for these three organism groups were 0.015 and 0.5 microgram/ml, 0.25, and 0.5 microgram/ml, and 0.015 and 0.03, respectively.

Comparison of the serum-supplemented Todd-Hewitt and the new Haemophilus test media for broth microdilution susceptibility testing of Streptococcus pneumoniae

Horse serum-supplemented Todd-Hewitt broth (STH) in use at Hôpital Ste-Justine for the last 12 years was compared to the recently proposed Haemophilus test medium (HTM), for broth microdilution susceptibility testing of Streptococcus pneumoniae. One hundred and twenty S. pneumoniae isolates from pediatric clinical specimens were used in this study. In general, the minimum inhibitory concentrations (MICs) in STH for 15 antimicrobial agents were quite comparable to those determined in HTM but tended to be higher. Drugs which generated MICs within +/- 1 log2 concentration differences in both media included penicillin, ampicillin, oxacillin, cefuroxime, cefotaxime, cefixime, clindamycin, chloramphenicol, trimethoprim-sulfamethoxazole, rifampin, ciprofloxacin and vancomycin. Cefaclor and tetracycline MICs tended to be > or = 2 log2 dilutions higher with STH for most of the isolates tested, while erythromycin MICs were often 2 log2 dilutions lower with STH than with HTM. Despite some differences in MICs noted above, few very major (0.4%), major (0.2%) and minor interpretive category errors (4.4%) were observed. The visual reading of the MICs for most of the 120 clinical isolates tested was generally easier in STH which was superior in supporting best the bacterial growth as detected by spectrophotometry. The risk of false susceptibility is thus decreased by using STH rather than HTM; furthermore, STH is free of the technical problems of the lysed horse blood Mueller-Hinton (LHB-MH) recommended by the NCCLS.

Brodimoprim: effects of subminimal inhibitory concentrations on virulence traits of respiratory and urinary tract pathogens, and on plasmid transfer and stability

The effects of brodimoprim, a new trimethoprim analogue, on several virulence traits of respiratory and urinary tract pathogens exposed to sub-lethal levels of the drug was studied. Adherence to tracheal epithelial cells was inhibited by brodimoprim in Klebsiella pneumoniae (41-67% reduction), Moraxella catarrhalis (87-90%) and Haemophilus influenzae (0-53%), while in Streptococcus pneumoniae binding was unaffected. With buccal epithelial cells the comparison between treated and control bacteria indicated statistically significant reduction in adherence with both S.pneumoniae and H.influenzae, (P < 0.015). With M.catarrhalis and Streptococcus pyogenes only marginal changes were detected (P > 0.05). Exoenzyme and capsule production were assessed in at least three isolates of diverse respiratory pathogens grown in the presence of sub-lethal levels of the new agent. The drug affected protease and beta-hemolysin (alpha-toxin) production in both oxacillin-susceptible and -resistant S.aureus. On the contrary, synthesis of lipase, DNase, coagulase, and beta-lactamase (S.aureus), pneumolysin (S.pneumoniae), streptolysin S, DNase, and protease (S.pyogenes), capsule (K.pneumoniae, H.influenzae and S.pneumoniae), and beta-lactamase (K.pneumoniae, H.influenzae and M.catarrhalis) were not inhibited by subminimal inhibitory concentrations (sub-MICs) of the drug. Finally, motility was blocked in urinary pathogens E.coli, P.mirabilis and P.aeruginosa, while in this latter microorganism pigment production was also affected. High molecular weight low-copy F'lac, and low molecular weight high-copy pHSG298 plasmids were eliminated from E.coli treated with sub-MIC concentrations of brodimoprim. The incidence and cured cells ranged from 9% for F'lac to 23% for pHSG298. F'lac transfer was also inhibited by the drug. When conjugation was carried out with bacteria exposed to brodimoprim (5XMIC), a reduction (50%) in the number of recombinants was noted in comparison to the control. The fact that brodimoprim interferes with the expression of some virulence traits, in particular with adherence, at sub-MIC levels may assist the drug in eradicating respiratory pathogens from the epithelial lining, thus diminishing the probability of reinfection.

The incidence of respiratory tract pathogens and antimicrobial susceptibilities of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella (Branhamella) catarrhalis isolated between 1990 and 1993

Using a quantitative culture of sputum, the incidence of pathogenic bacteria in respiratory infection in our laboratory between 1990 and 1993 were investigated. While Haemophilus influenzae, Streptococcus pneumoniae and Moraxella (Branhamella) catarrhalis were isolated at high rates (67-78%) from the specimens of outpatients throughout the study period, the incidence of S pneumoniae has increased gradually. The antimicrobial susceptibilities of these three pathogens were examined with the agar dilution method. A marked increase of penicillin (PC) resistant S. pneumoniae (MIC > or = 0.1 microgram/ml) was observed with a resistance rate of 2.1% in 1990 and 25% in 1993. Resistance to erythromycin (EM, MIC > or = 1.56 micrograms/ml) was 8.5% in 1990 but then increased to 34% in 1992. Most of the PC resistant isolates were resistant to multidrugs such as EM, minocycline and clindamycin. The MICs of all beta-lactams examined for S. pneumoniae increased along with the MICs of PC, though the level varied between drugs. The rates of beta-lactamase positive H. influenzae gradually decreased, being 14.3% in 1990 and 7.4% in 1993, whereas those of M. (B) catarrhalis were consistently high (> 90%) every year. In addition to beta-lactamase production, the emergence of strains of H. influenzae and M. (B) catarrhalis resistant to new quinolone drugs should be noted.

Comparison of five different susceptibility test methods for detecting antimicrobial agent resistance among Haemophilus influenzae isolates

The detection of antimicrobial agent resistance among ninety-eight Haemophilus influenzae isolates was assessed by six different antibiotic test methods: agar dilution on Mueller-Hinton agar supplemented with 5% lysed horse blood (MH-LHB), E-test using both Haemophilus test medium (HTM) agar and chocolate Mueller-Hinton (CMH) agar plates, Vitek Haemophilus susceptibility cards, and three overnight microdilution systems that included two commercial systems, Micro-Media and MicroScan, and the reference broth microdilution method using HTM broth. Agents tested in the study included ampicillin, amoxicillin/clavulanic acid (A/C), cefaclor, cefuroxime, cefotaxime, ceftriaxone, chloramphenicol, and trimethoprim/sulfamethoxazole. Both the reference HTM microbroth dilution method and agar dilution correctly classified all nine of the beta-lactamase negative ampicillin resistant (BLNAR) isolates. Each of the other test methods failed to detect one of the BLNAR strains, either because of growth failure (Micro-Media and MicroScan) or miscategorization of an isolate as susceptible (E-Test HTM, E-Test CMH, and Vitek). None of the test methods detected all six isolates identified as A/C resistant by HTM microbroth dilution. Of the remaining antimicrobials tested, ampicillin and cefuroxime yielded data that could be compared by all test methods. The very major, major, and minor errors for these two antimicrobials in comparison to the reference HTM microdilution method were as follows: Micro-Media (1.7%, 0%, and 4.8%); MicroScan (11.9%, 0%, and 8.1%); E-Test HTM (1.6%, 0%, and 2.0%); E-Test CMH (1.6%, 1.6%, and 4.6%); Vitek (8.1%, 0%, and 3.1%); and agar dilution on MH-LHB (0%, 0%, and 4.6%). Micro-Media and MicroScan panels failed to support the growth of 4.1% and 5.1% of the isolates, respectively.

Sulfonamide resistance in Neisseria meningitidis as defined by site-directed mutagenesis could have its origin in other species

Sulfonamide resistance in Neisseria meningitidis is mediated by altered forms of the chromosomal gene for the drug target enzyme dihydropteroate synthase. Sulfonamides have been used for decades both for prophylaxis and the treatment of meningococcal disease, and resistance is common. Two types of resistance determinants have been identified, and regions important for drug insusceptibility to the corresponding enzyme have been defined by site-directed mutagenesis. Both types of resistance traits have spread among strains of N. meningitidis of different serogroups and serotypes, and the large differences at the nucleotide level in a comparison of the resistance genes with the dhps genes of susceptible meningococci indicate the origin of one or maybe both types in other Neisseria species. One sulfonamide-sensitive strain of N. meningitidis was found to have a mosaic dhps gene with a central part identical to the corresponding part of a gonococcal strain. This observation supports the idea of an interspecies transfer of genetic material in Neisseria species as a mechanism for the development of chromosomally mediated resistance.

Multi-centre collaborative study for the in vitro evaluation of new macrolides dirithromycin and erythromycylamine. Australian Group for Antimicrobial Resistance (AGAR)

A national study was conducted to determine the in vitro activity of 2 newer macrolides, dirithromycin and erythromycylamine compared with that of erythromycin, tetracycline and penicillin. Nineteen major teaching hospitals participated in the study. Minimal Inhibitory Concentrations (MICs) were determined by agar dilution, mostly using Iso-Sensitest Agar and an inoculum of 10(4) cells per spot. 2284 clinically significant strains were isolated in late 1991 and early 1992, comprising 1736 Gram-positive cocci, 355 Haemophilus influenzae, 97 Moraxella catarrhalis, 32 Listeria monocytogenes, 25 Neisseria meningitidis and 39 Neisseria gonorrhoeae were tested. The study indicates that dirithromycin and erythromycylamine possess antibacterial activity equivalent to that of erythromycin against most Gram-positive cocci and M. catarrhalis. Strains resistant to erythromycin were also resistant to dirithromycin and to erythromycylamine. Tetracycline was as active as the macrolides against both penicillin-resistant and penicillin-susceptible strains of Staphylococcus aureus. Coagulase-negative penicillin-resistant staphylococci, compared with tetracycline, were relatively resistant to the macrolides. H. influenzae was less susceptible than the Gram-positive cocci.

Antimicrobial resistance in Haemophilus influenzae isolated from blood, cerebrospinal fluid, middle ear fluid and throat samples of children. A nationwide study in Finland in 1988-1990

A nation-wide survey of the prevalence of antimicrobial resistance in Haemophilus influenzae was conducted on isolates collected in 1988-90 from middle ear fluid (MEF), blood, or cerebrospinal fluid (CSF) in infected children or throat samples of healthy children. Altogether 885 strains were examined regarding capsular type b, beta-lactamase production and the minimal inhibitory concentration (MIC) of ampicillin, cefaclor, erythromycin, tetracycline, chloramphenicol, trimethoprim and trimethoprim-sulfamethoxazole for these strains was determined by the agar dilution method. 99% (578/585) of MEF isolates, 93% (112/121) of throat isolates, but only 6% (10/179) of blood/CSF isolates were not of type b (Hib). The rate of beta-lactamase production was 11.4% among Hib strains, 8.0% among non-type b MEF isolates, and 4.5% among non-type b throat isolates. No increase in the prevalence of beta-lactamase production in H. influenzae has taken place in Finland since the early 1980s. Resistance to ampicillin among strains that lacked beta-lactamase activity was rare (0.2%). Of the non-type b MEF and throat isolates, 5.9% and 2.7%, respectively, were resistant to trimethoprim and 3.6% and 2.7%, respectively, to trimethoprim-sulfamethoxazole. Resistance to other drugs was rare (< 2%) in all isolate groups.

In vitro activity of SCE-2787, a new cephalosporin with potent activity against Pseudomonas aeruginosa and members of the family Enterobacteriaceae

The in vitro activity of SCE-2787, 7-[(Z)-2-(5-amino-1,2,4-thiadiazol-3- yl)-2-methoxyiminoacetamido]-3-(1-imidazo[1,2-b]pyridazinium)methy l-3- cephem-4-carboxylate, was compared with those of ceftazidime, ceftriaxone, and imipenem against recent clinical isolates. SCE-2787 inhibited 50% of tested isolates of the family Enterobacteriaceae at < or = 0.25 micrograms/ml. SCE-2787 was equally active as or more active than ceftazidime and ceftriaxone against members of the Enterobacteriaceae, with the exception of Proteus vulgaris. The MIC of SCE-2787 at which 90% of the isolates of Pseudomonas aeruginosa were inhibited was 2 micrograms/ml, two- to fourfold lower than those of imipenem and ceftazidime, respectively. SCE-2787, like ceftazidime and imipenem, did not inhibit the majority of strains of Pseudomonas cepacia and Xanthomonas maltophilia. SCE-2787 inhibited beta-hemolytic streptococci at < or = 0.12 micrograms/ml, but it did not inhibit Enterococcus faecalis, Listeria monocytogenes, or the anaerobic species tested. Methicillin-resistant staphylococci required SCE-2787 MICs of > or = 16 micrograms/ml, whereas methicillin-susceptible staphylococci were inhibited by 2 micrograms/ml. No difference between the MICs and MBCs was noted, except for P. aeruginosa, for which there was a fourfold difference. SCE-2787 was active over a pH range of 6 to 8. The inoculum size of 10(5) to 10(7) CFU caused only a twofold change in the MIC for Escherichia coli and Staphylococcus aureus but a 4- to 16-fold change in Enterobacter cloacae and P. aeruginosa. beta-Lactamases from Bush groups 1, 2a, and 2b did not hydrolyze SCE-2787. There was significant hydrolysis of SCE-2787 by the beta-lactamases designated 2b', i.e., TEM-3, TEM-5, TEM-7, and TEM-9, and by the group 2d beta-lactamases. SCE-2787 had poor affinity for group 1 and group 2b enzymes and constitutively produced chromosomal beta-lactamases such as P-99 of Enterobacter cloacae and plasmid-mediated TEM-1 of E. coli. SCE-2787 has in vitro activity comparable to that of current parenteral cephalosporin and is more active against P. aeruginosa and S. aureus.

In vitro activity of the new fluoroquinolone CP-99,219

The in vitro activity of the new fluoroquinolone CP-99,219 [7-(3-azabicyclo[3.1.0]hexyl)naphthyridone] was compared with those of four other quinolones against 541 gram-negative, 283 gram-positive, and 70 anaerobic bacterial isolates. CP-99,219 inhibited 90% of many isolates in the family Enterobacteriaceae at a concentration of < or = 0.25 micrograms/ml (range, < 0.008 to 1 microgram/ml), an activity comparable to those of tosufloxacin and sparfloxacin and two times greater than that of temafloxacin. Ninety percent of the Proteus vulgaris, Providencia rettgeri, Providencia stuartii, and Serratia marcescens isolates were inhibited by 0.5 to 2 micrograms of CP-99,219 per ml. CP-99,219 inhibited 90% of the Pseudomonas aeruginosa and Haemophilus influenzae isolates at 1 and 0.015 micrograms/ml, respectively. The compound inhibited methicillin-susceptible Staphylococcus aureus at 0.06 micrograms/ml, whereas a ciprofloxacin concentration of 1 microgram/ml was required to inhibit these organisms. CP-99,219 inhibited 90% of methicillin-resistant S. aureus isolates at a concentration of < or = 4 micrograms/ml, while ciprofloxacin and temafloxacin had MICs against these isolates of > 16 micrograms/ml. Streptococci were inhibited by < or = 0.25 micrograms/ml, an activity comparable to that of tosufloxacin. CP-99,219 was eight times more active than ciprofloxacin against Streptococcus pneumoniae. Bacteroides species were inhibited by CP-99,219 at a concentration of 2 micrograms/ml, whereas inhibition of these species required 4- and 16-microgram/ml concentrations of tosufloxacin and ciprofloxacin, respectively. The MBCs of CP-99,219 ranged from two to four times the MICs, and inoculum size had a minimal effect on MIC. CP-99,219 was active against P. aeruginosa at pH 5.5, with only a fourfold increase in MIC compared with values obtained at pH 7.5. The addition of up to 9 mM Mg(2+) increased the MIC range from 0.03 to 0.06 microgram/ml to 0.12 to 0.5 microgram/ml. In view of its excellent in vitro activity against both gram-positive and gram-negative bacteria, CP-99,219 merits further study to determine it's clinical pharmacologic properties and potential for therapeutic use.

Disk diffusion versus broth microdilution susceptibility testing of Haemophilus species and Moraxella catarrhalis using seven oral antimicrobial agents: application of updated susceptibility guidelines of the National Committee for Clinical Laboratory Standards

Susceptibility testing of Haemophilus species and Moraxella catarrhalis is medium and inoculum dependent. Seven oral agents, ampicillin, amoxicillin-clavulanic acid, cefaclor, loracarbef, cefuroxime-axetil, cefixime, and erythromycin, were tested against 400 beta-lactamase-positive and -negative clinically significant respiratory strains of Haemophilus species and 100 strains of M. catarrhalis. Sources of the strains included teaching and regional hospitals and a private laboratory. All strains were tested by broth microdilution and disk diffusion in haemophilus test medium for Haemophilus species and Mueller-Hinton broth and agar for M. catarrhalis. Appropriate National Committee for Clinical Laboratory Standards (NCCLS) standards were followed. For Haemophilus species, by disk diffusion and broth microdilution, respectively, 27 and 27% of strains were resistant to ampicillin, 37 and 5% were resistant to erythromycin, 3 and 0.5% were resistant to cefaclor, 2 and 0.5% were resistant to loracarbef, and 0% were resistant to cefuroxime-axetil, cefixime, and amoxicillin-clavulanic acid. beta-Lactamase-negative ampicillin-resistant strains were not observed. Of M. catarrhalis strains, 56% were resistant to ampicillin by disk diffusion and 95% were resistant by broth microdilution. This species was susceptible to all other agents tested by either method. The disagreements between disk diffusion results and MICs for cefaclor, ampicillin, cefuroxime, and loracarbef that occurred with use of the 1990 NCCLS tables were resolved when the 1992 NCCLS tables were used.

Interpretive criteria for susceptibilities of Haemophilus influenzae to ampicillin, amoxicillin, and amoxicillin-clavulanic acid

One hundred fifty isolates of Haemophilus influenzae (including 30 beta-lactamase-positive strains and 23 beta-lactamase-negative, ampicillin-resistant strains) were tested for susceptibilities to ampicillin, amoxicillin, and amoxicillin-clavulanic acid (A/C) by the broth microdilution method in Haemophilus test medium (HTM) and in Mueller-Hinton medium with lysed horse blood and by the disk diffusion method on HTM agar. Our results support the use of HTM for susceptibility testing of H. influenzae but raise a number of questions regarding the interpretive criteria currently in use, particularly with respect to the fourfold difference in MIC susceptibility breakpoints for ampicillin and A/C and a resulting high proportion of A/C-susceptible beta-lactamase-negative, ampicillin-resistant strains.

In vitro activities of 12 orally administered antimicrobial agents against four species of bacterial respiratory pathogens from U.S. Medical Centers in 1992 and 1993

Clinical isolates of Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, and Moraxella catarrhalis were gathered from 19 different clinical laboratories throughout the continental United States. The in vitro activities of 12 orally administered antimicrobial agents were compared by broth microdilution tests with 3,151 bacterial isolates. Among 890 H. influenzae isolates, 30% were capable of producing beta-lactamase enzymes (12 to 41% in different medical centers). Most of the 619 beta-lactamase-negative H. influenzae strains were susceptible to ampicillicin (MIC, < or = 1.0 micrograms/ml): 5 strains were intermediate in susceptibility (MIC, 2.0 micrograms/ml) and 1 strain was ampilicillin resistant (MIC, 4.0 micrograms/ml). Ninety-two percent of 698 M. catarrhalis strains were beta-lactamase positive. Of 799 S. pneumoniae isolates, 15% were intermediate in susceptibility to penicillin and 7% were resistant to penicillin. The prevalence of penicillin-susceptible pneumococci in different institutions ranged from 63 to 95%. Only 1% of 764 S. pyogenes isolates were resistant to the macrolides, but 5% of S. pneumoniae isolates were macrolide resistant. Only 71% of 58 penicillin-resistant S. pneumoniae isolates were erythromycin susceptible, whereas 97% of the 622 penicillin-susceptible strains were erythromycin susceptible. Penicillin-resistant pneumococci were also relatively resistant to the cephalosporins and amoxicillin. Penicillin-susceptible pneumococci were susceptible to amoxicillin-clavulanic acid (MIC for 90% of isolates tested [MIC90], < or = 0.12/0.06 microgram/ml), cefixime (MIC90, 0.25 microgram/ml), cefuroxime axetil (MIC90, < or = 0.5 microgram/ml), cefprozil (MIC90, < or = 0.5 micrograms/ml), cefaclor (MIC90, 0.5 microgram/ml), and loracarbef (MIC90, 1.0 microgram/ml). Most strains of the other species remained susceptible to the study drugs other than amoxicillin.

Revised disk diffusion interpretive criteria for cefaclor, loracarbef, cefprozil and cefixime when testing Haemophilus influenzae on haemophilus test medium

The aim of the current five-center collaborative study was to reassess the interpretive criteria for cefaclor, loracarbef, cefprozil and cefixime previously adopted or proposed by the National Committee for Clinical Laboratory Standards (NCCLS) for disk diffusion susceptibility tests with Haemophilus influenzae on Haemophilus Test Medium (HTM) agar. MICs and zones of inhibition were determined using NCCLS methods, HTM and two collections of strains of Haemophilus influenzae. One group of strains consisted of 118 stock organisms taken largely from various recent U.S. antibiotic resistance surveillance studies. The emphasis in this selected group of organisms was on strains that were beta-lactamase negative but ampicillin resistant (BLNAR) by some other mechanism. The second collection of test organisms consisted of 50 recent clinical isolates of Haemophilus influenzae obtained from each of the five participating study centers. This group was considered representative of the type of Haemophilus influenzae currently recovered from clinical sources in the USA. Frequency distribution assessment and error-rate bounded analysis of scattergram comparisons of MICs and zone sizes were used to develop the following zone diameters interpretive for disk diffusion susceptibility tests with Haemophilus influenzae on HTM agar: cefaclor, > or = 20 mm (susceptible, S) and < or = 16 mm (resistant, R); loracarbef, > or = 19 mm (S) and < or = 15 mm (R); and cefprozil, > 18 mm (S) and < 14 mm (R). The respective MIC correlates for all three antimicrobial agents were < or = 8 micrograms/ml (S) and 32 micrograms/ml (R).(ABSTRACT TRUNCATED AT 250 WORDS)

Tentative criteria for confirming the in vitro susceptibilities of Haemophilus influenzae and Neisseria gonorrhoeae to two fluoroquinolones (sparfloxacin and levofloxacin), including quality control parameters

Sparfloxacin and levofloxacin were evaluated against 150 Haemophilus influenzae isolates and 149 Neisseria gonorrhoeae isolates in order to define susceptibility testing parameters. Sparfloxacin-susceptible H. influenzae strains were defined as those for which the MICs were < or = 0.25 microgram/ml and the zones were > or = 30 mm, and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.03 microgram/ml and the zones were > or = 39 mm (5-micrograms disks). Levofloxacin-susceptible strains of H. influenzae included those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 32 mm and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 37 mm (5-micrograms disks). Criteria for a resistant category cannot yet be defined for either quinolone. In multilaboratory studies with different lots of Haemophilus Test Medium, replicate tests with the standard control strain of H. influenzae (ATCC 49247) were evaluated. For sparfloxacin disk tests, the proposed zone size limits were 33 to 42 mm and broth microdilution MIC limits were 0.004 to 0.016 microgram/ml, whereas for levofloxacin tests, zone size limits were 32 to 41 mm and broth microdilution MIC limits were 0.008 to 0.03 microgram/ml. Other multilaboratory studies evaluated tests with supplemented GC agar and N. gonorrhoeae ATCC 49226; for both drugs, zone size limits were 44 to 52 mm and agar dilution MIC limits were 0.004 to 0.016 microgram/ml.

Isolation of moderately penicillin-susceptible strains of Neisseria meningitidis in Argentina

Four strains that were moderately susceptible to penicillin and/or ampicillin were found among 54 consecutive isolates of meningococci recovered from patients in one pediatric hospital in Argentina from October 1991 to December 1992. Disk diffusion tests performed with 2 U of penicillin failed to detect one strain. These findings suggest that attention should be paid to changes in the susceptibility patterns of meningococci in order to anticipate therapeutic failures in the future.