In vitro susceptibility testing of Haemophilus influenzae: review of new National Committee for Clinical Laboratory Standards recommendations

Doern, Gary V.

doi:10.1128/jcm.30.12.3035-3038.1992

Cited by 24 publications

(9 citation statements)

References 21 publications

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“…The results of the present study, however, showed that HTM prepared in-house at Mayo Clinic offered no advantage over HTM prepared by the two commercial sources, BBL and Remel, and in a general sense demonstrated, as we and others have previously (1, 2, 4-6, 11, 12) that disk diffusion testing of ampicillin against Haemophilus strains with HTM is an unreliable method. In a recent review, Doern (2) emphasized that the purpose of susceptibility testing of Haemophilus spp. must be carefully considered.…”

Section: Discussionmentioning

confidence: 99%

Comparison of in-house and commercially prepared haemophilus test media for disk diffusion testing of ampicillin against Haemophilus species

Laue¹,

Kohner²,

Cockerill³

1995

J Clin Microbiol

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The performance characteristics of two lots of Haemophilus Test Medium (HTM) prepared in-house at Mayo Clinic, one lot obtained from BBL (Cockeysville, Md.) and one lot obtained from Remel (Lenexa, Kans.), for disk diffusion susceptibility testing of ampicillin against 81 Haemophilus strains were assessed. Insufficient growth occurred in 2.5 to 13.6% of strains, depending on the HTM used, and was most frequent for ␤-lactamase-negative, ampicillin-resistant strains when they were tested with one lot of HTM prepared in-house. Results for all 14 ␤-lactamase-positive Haemophilus strains were in complete agreement for all lots of HTM when either 1990 or 1993 National Committee for Clinical Laboratory Standards (NCCLS) interpretive guidelines were followed. However, these ␤-lactamase-positive Haemophilus strains could be as precisely, but more rapidly, identified by the cefinase disk method. Results for 56 ␤-lactamase-negative, ampicillin-susceptible strains and 11 ␤-lactamase-negative, ampicillin-resistant strains varied significantly among all HTM lots tested and as to whether 1990 or 1993 NCCLS interpretive guidelines were followed. We conclude that in our hands disk diffusion testing with HTM prepared in-house or obtained from two commercial sources and following either 1990 or 1993 NCCLS guidelines is an unacceptable method for determining the susceptibilities of Haemophilus strains to ampicillin.

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Section: Discussionmentioning

confidence: 99%

Comparison of in-house and commercially prepared haemophilus test media for disk diffusion testing of ampicillin against Haemophilus species

Laue¹,

Kohner²,

Cockerill³

1995

J Clin Microbiol

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“…The MICs were lower in supplemented Shaedler's broth than in Haemophilus test medium (HTM) or Mueller-Hinton broth containing 3% lysed horse blood by the broth microdilution technique. The National Committee for Clinical Laboratory Standards (NCCLS) currently recommends that HTM be used for susceptibility testing of H. influenzae by the broth microdilution and disk diffusion methods to reduce the test variability associated with medium effects (4,10,11).…”

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confidence: 99%

Variability in susceptibilities of Haemophilus influenzae to clarithromycin and azithromycin due to medium pH

et al. 1997

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The National Committee for Clinical Laboratory Standards (NCCLS) methods for susceptibility testing of Haemophilus influenzae in Haemophilus test medium allow a pH range of 7.2 to 7.4. However, it is known that bacteria may appear to be less susceptible to macrolides at lower pHs. Forty-four strains of H. influenzae were tested for their susceptibilities to clarithromycin and azithromycin by the disk diffusion and broth microdilution methods. The isolates appeared to be less susceptible at pH 7.2 than at pH 7.4 by both methods. Clarithromycin was less active at pH 7.2 against 43% of the isolates by the disk diffusion method and against 52% of the isolates by the broth microdilution method. Similarly, azithromycin was less active at pH 7.2 against 41 and 45% of the isolates by the disk diffusion and broth microdilution methods, respectively. Forty-two isolates were classified as clarithromycin susceptible and all isolates were classified as azithromycin susceptible by the disk diffusion method, regardless of the medium pH. However, only 21 isolates were clarithromycin susceptible at pH 7.2 and 34 isolates were susceptible at pH 7.4 by the broth microdilution method, even though quality control results indicated valid testing at both pHs. This study indicated that the results of tests of the susceptibility of H. influenzae with clarithromycin and azithromycin are highly dependent on the pH of the medium. Test results and their interpretations varied even when the medium pH was within the NCCLSapproved range and, coupled with the current NCCLS breakpoint of 8 g/ml in the case of clarithromycin, may explain some of the observed discordances between the disk diffusion and broth microdilution methods. a Activity, MIC (in micrograms per milliliter) for the broth microdilution method and zone size (in millimeters) for the disk diffusion method. b P, paired t test comparing zone diameter at pH 7.2 to zone diameter at pH 7.4 for each strain. c P, Wilcoxon signed rank test comparing MIC at pH 7.2 to MIC at pH 7.4 for each strain. 1312NILIUS ET AL.

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“…HTM was adopted for DD testing because it had certain advantages over chocolatized Mueller-Hinton agar, including transparency and the ability to support DD testing of trimethoprim-sulfamethoxazole (chocolatized Mueller-Hinton agar contained large quantities of thymidine and thymidine analogs). HTM was also advantageous for both DD and broth dilution testing because of its low cost and its ability to adequately support the growth of H. influenzae (2,9). Nevertheless, problems with HTM have been reported, including its inability to support the growth of H. infiuenzae and provide consistency in susceptibility testing results (11).…”

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confidence: 99%

“…In June 1992, NCCLS realized that the HTM DD method could falsely categorize ,3-lactamase-negative, ampicillin-susceptible (BLNAS) H. influenzae strains as 3-lactamase-negative, ampicillin-resistant (BLNAR) strains. New interpretive criteria for zone diameters for DD testing were developed to alleviate this problem (2).…”

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confidence: 99%

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Comparison of agar dilution, broth dilution, and disk diffusion testing of ampicillin against Haemophilus species by using in-house and commercially prepared media

1994

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An evaluation to determine the optimal method for the in vitro susceptibility testing of Haemophilus strains to ampicillin was undertaken. In our hands, in-house-prepared Haemophilus Test Medium used by either the broth macrodilution or agar dilution method produced the most consistent results, especially for I-lactamasenegative, ampicillin-resistant H. influenzae strains.In 1985, the National Committee for Clinical Laboratory Standards (NCCLS) published disk diffusion (DD) and dilution susceptibility testing criteria for the in vitro susceptibility testing of Haemophilus influenzae (M2-A3 [12] and M7-A [13], respectively). These standards applied to the testing of ampicillin, amoxicillin-clavulanate, ampicillin-sulbactam, and chloramphenicol when H. infiuenzae was tested with chocolatized Mueller-Hinton agar for DD testing and Mueller-Hinton broth supplemented with lysed horse blood for dilution susceptibility testing.In January 1990, NCCLS published revised guidelines for H.influenzae DD and dilution susceptibility testing with Haemophilus Test Medium (HTM) (M2-A4 [14] and M7-A2 [15], respectively). HTM was adopted for DD testing because it had certain advantages over chocolatized Mueller-Hinton agar, including transparency and the ability to support DD testing of trimethoprim-sulfamethoxazole (chocolatized Mueller-Hinton agar contained large quantities of thymidine and thymidine analogs). HTM was also advantageous for both DD and broth dilution testing because of its low cost and its ability to adequately support the growth of H. influenzae (2,9). Nevertheless, problems with HTM have been reported, including its inability to support the growth of H. infiuenzae and provide consistency in susceptibility testing results (11). Interand intramanufacturer variabilities with batches of HTM (1, 3, 6, 7) as well as lot-to-lot and within-lot variabilities of HTM have also been reported (1, 3, 7). In June 1992, NCCLS realized that the HTM DD method could falsely categorize ,3-lactamase-negative, ampicillin-susceptible (BLNAS) H. influenzae strains as 3-lactamase-negative, ampicillin-resistant (BLNAR) strains. New interpretive criteria for zone diameters for DD testing were developed to alleviate this problem (2).We undertook a study to determine the optimal method for the in vitro susceptibility testing of H. influenzae strains to ampicillin. Specifically, we were interested in comparing the performance characteristics of agar dilution (AD) methods with HTM in comparison with those of our standard Mueller-Hinton agar supplemented with 1% hemoglobin and 1% IsoVitaleX (SMH). Furthermore, we wished to evaluate the * Corresponding author. broth dilution method using HTM and the DD method using HTM from two commercial sources (Remel and BBL). Finally, although current NCCLS guidelines do not specifically address other Haemophilus species, we included BLNAS Haemophilus parainfluenzae strains in our evaluation. These strains were previously characterized as ampicillin susceptible by our conventional SMH agar dilution technique...

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In vitro susceptibility testing of Haemophilus influenzae: review of new National Committee for Clinical Laboratory Standards recommendations

Cited by 24 publications

References 21 publications

Comparison of in-house and commercially prepared haemophilus test media for disk diffusion testing of ampicillin against Haemophilus species

Comparison of in-house and commercially prepared haemophilus test media for disk diffusion testing of ampicillin against Haemophilus species

Variability in susceptibilities of Haemophilus influenzae to clarithromycin and azithromycin due to medium pH

Comparison of agar dilution, broth dilution, and disk diffusion testing of ampicillin against Haemophilus species by using in-house and commercially prepared media

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