Clinical, Bacteriological, and Immunological Characterisation of Ampicillin-Resistant Hæmophilus Influenzæ Type B

Susceptibility to ampicillin and chloramphenicol in vitro has been determined for Haemophilus influenzae strains isolated from blood and/or cerebrospinal fluid cultures of patients admitted to two Atlanta hospitals from 1 January 1974 to 31 March 1975. Since the appearance of ampicillin-resistant strains of this organism in early 1974, chloramphenicol has been used in these hospitals as initial therapy for severe infection due to H. influenzae . Strains from five of 94 patients were resistant to ampicillin (minimum inhibitory concentration [MIC] ≥ 12.5 μg/ml), but all strains were susceptible to chloramphenicol (MIC < 2 μg/ml). The first 35 strains studied, including three resistant to ampicillin, were also tested for in vitro susceptibility to trimethoprim-sulfamethoxazole; all were highly susceptible (MIC ≤ 0.0312 μg of trimethoprim and 0.625 μg of sulfamethoxazole per ml).

Section: Discussionmentioning

confidence: 99%

Susceptibility of Haemophilus influenzae Isolates from Blood and Cerebrospinal Fluid to Ampicillin, Chloramphenicol, and Trimethoprim-Sulfamethoxazole

McGowan

Terry²,

Nahmias³

1976

“…The appearance of ampicillin-and chloramphenicol-resistant strains of Haemophilus influenzae (9,14) has stimulated interest in developing better techniques for assaying the antimicrobial susceptibility of these fastidious bacteria (5,6). Broth dilution assays, though commonly employed to measure both the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of antimicrobial agents, can be used to test the susceptibility of H. influenzae only if the medium is supplemented with hemin and nicotinamide adenine dinucleotide.…”

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confidence: 99%

Nitrate Reduction: New Method for Testing the Antibiotic Susceptibility of Haemophilus influenzae

Fleming

Fierer

1978

We have developed a new micro-broth-dilution assay for determining the antimicrobial susceptibility of Haemophilus influenzae. This assay is based on the ability of viable H. influenzae to reduce nitrates to nitrites. Bacterial viability is detected by a positive nitrite reaction rather than visible turbidity. The nitrate reduction assay was compared with a standard microassay using 51 isolates of H. influenzae and six beta-lactam antibiotics. Although there was good agreement between the two methods, the nitrate reduction assay was more sensitive in detecting viable bacteria, and so established a more accurate estimate of the minimal inhibitory concentration. The nitrate reduction assay offered the additional advantage that it could be used to determine the minimal bactericidal concentration without having to subculture the broth. Ampicillin, penicillin, and cefamandole were equally effective in vitro against susceptible strains (minimal inhibitory concentrations, 0.125 to 0.5 ,g/ml), whereas all three antibiotics were ineffective against two beta-lactamase-producing strains. Using the nitrate reduction assay, resistance to cefamandole was detectable with inoculum sizes ranging from 104 to 106 colony-forming units per ml, while the turbidity assay detected resistance only with the largest inoculum.The appearance of ampicillin-and chloramphenicol-resistant strains of Haemophilus influenzae (9, 14) has stimulated interest in developing better techniques for assaying the antimicrobial susceptibility of these fastidious bacteria (5, 6). Broth dilution assays, though commonly employed to measure both the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of antimicrobial agents, can be used to test the susceptibility of H. influenzae only if the medium is supplemented with hemin and nicotinamide adenine dinucleotide. Some broths will support the growth of H. influenzae, but even under good growth conditions turbidity may be difficult to detect (4, 7).We have developed a new assay procedure for testing the antimicrobial susceptibility of H. influenzae. The assay is based on the nitrate reductase activity of viable H. influenzae and the resultant production of nitrite (4, 16). Our method has the distinct advantage of increased reproducibility and accuracy, since the MIC is indicated by a color reaction, which is more easily detected than turbidity. This report includes a description of the assay and the results obtained with several beta-lactam antibiotics. MATERIALS AND METHODSBacteria. Fifty-one isolates of H. influenzae were tested. Thirty-nine isolates were smooth, nontypable H. influenzae recovered from sputum specimens submitted to the bacteriology laboratory, San Diego Veterans Administration Hospital. Ten isolates from various clinical specimens were classified serologically as type B and were ampicillin susceptible. Two strains were ampicillin-resistant, beta-lactamase-producing type B strains; one was obtained from Clyde Thornsberry, Center for Disease Control, Atlanta, Ga., ...

“…Co-trimoxazole was most active (<1% H. influenzae was resistant) when tested at an inoculum of 106 colony-forming units/ml on diagnostic susceptibility test agar with 5% lysed horse blood added. The majority of H. influenzae appeared resistant to co-trimoxazole with increases in the test inocula and/or when tested on brain heart infusion with Filde's, Levinthal's or "low-thymidine" Mueller-Hinton medium.The recognition of Haemophilus influenzae resistant to ampicillin has emphasized the importance of routine susceptibility testing of these bacteria in hospital laboratories (6,11,15). A study was undertaken to evaluate the comparative antimicrobial susceptibilities ofH.…”

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confidence: 99%

“…The recognition of Haemophilus influenzae resistant to ampicillin has emphasized the importance of routine susceptibility testing of these bacteria in hospital laboratories (6,11,15). A study was undertaken to evaluate the comparative antimicrobial susceptibilities ofH.…”

mentioning

confidence: 99%

Influences of Media and Inocula on the In Vitro Susceptibility of Haemophilus influenzae to Co-Trimoxazole, Ampicillin, Penicillin, and Chloramphenicol

Marks

Weinmaster²

1975

The effects of inocula and media on the activities of ampicillin, penicillin, chloramphenicol and co-trimoxazole against Haemophilus influenzae were examined in vitro. Two inocula and four media were tested by the disk diffusion, broth dilution, and agar dilution methods. Chloramphenicol activity versus H. influenzae was least affected by changes in inocula and media, whereas co-trimoxazole was most susceptible to these effects. Filde's and Levinthal's agar dilution tests were most satisfactory for ampicillin. Penicillin was less active on Levinthal's than on Filde's agar. Both ampicillin and penicillin were less active when tested against the higher inoculum. Co-trimoxazole was most active (<1% H. influenzae was resistant) when tested at an inoculum of 106 colony-forming units/ml on diagnostic susceptibility test agar with 5% lysed horse blood added. The majority of H. influenzae appeared resistant to co-trimoxazole with increases in the test inocula and/or when tested on brain heart infusion with Filde's, Levinthal's or "low-thymidine" Mueller-Hinton medium.The recognition of Haemophilus influenzae resistant to ampicillin has emphasized the importance of routine susceptibility testing of these bacteria in hospital laboratories (6,11,15). A study was undertaken to evaluate the comparative antimicrobial susceptibilities ofH. influenzae to four currently available antimicrobials and to determine the effects of inocula and media on these in vitro measurements. MATERIAL AND METHODSH. influenzae were identified by Gram stain, colonial morphology, and X-and V-factor growth requirements. Nitrate reduction and indole production tests were done on nontypable eye isolates (8). Typing was performed by the slide agglutination technique using commercial type-specific antisera (Difco) to H. influenzae.Strains were isolated from ill children seen at the Montreal Children's Hospital from 1 January to 31 October 1974 and were stored in pure culture in defibrinated horse blood at -70 C. The sources and respective number of H. influenzae studied were as follows: blood, 17; cerebrospinal fluid, 13; eye, 20; nose, 2; sputum, 3; throat, 7; pleural fluid, 2; ear, 1; nasopharynx, 5; wound, 2. Seventy-two isolates were tested for susceptibility to ampicillin, penicillin, chloramphenicol, and co-trimoxazole (trimethoprim [TMPl/sulfamethoxazole [SMZ]) by the disk diffusion, broth dilution, and agar dilution methods. Overnight cultures incubated at 37 C in Levinthal's broth were diluted to produce inocula of 106 and 108 colony-forming units (CFU)/ml, verified by colony counts. All tests were carried out using brain heart infusion (BHI; Difco), with 10% Filde's medium (Difco) added and Levinthal's medium prepared from defibrinated laked horse erythrocytes as described by McLinn et al. (10). In addition, cotrimoxazole agar dilution studies and all disk diffusion tests were performed on "low-thymidine" Mueller-Hinton agar (MH; Difco) with 5% defibrinated lysed horse blood plus 2.5 MLg of reduced betanicotinamide adenine dinucleotide (Sigma; ...