pH-dependent oxacillin tolerance of Staphylococcus aureus

Venglarcik, John; Blair, L L; Dunkle, Lisa M.

doi:10.1128/aac.23.2.232

Cited by 31 publications

(23 citation statements)

References 24 publications

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“…While the growth phase may not have a significant effect on MIC tests, as demonstrated by Barry et al (7) and Kim and Anthony (56), most investigators (48,56,70,75,108,114) have confirmed the importance of using log-phase growth for the inoculum for MBC tests. When stationary-phase growth is used, the number of surviving or "persisting" organisms tends to increase after 24 h of incubation, and therefore the MBC result may be artificially high.…”

Section: Introduction Introductionmentioning

confidence: 85%

“…The appearance of bacteriostatic or bactericidal activity is typically determined for each tube in the set, with the result indicating the optimal concentrations of each drug in combination for inhibitory and bactericidal effects. IN (59,67,78,85,99,104,114,120), the use of cation supplements (41,92,107,120), whether the culture is mixed or otherwise agitated during incubation (48,104,105,108,120), the growth phase of the inoculum (7,39,48,57,70,104,105,108,114,120), the pH of the medium (34,105,114,120), the use of serum (binding) proteins (92,120), the presence of complement (21,34,120), the elimination of antibiotic carryover during subculture (8,25,35,47,93,103,104,119,122), the final density of the bacterial inoculum …”

Section: Introduction Introductionmentioning

confidence: 99%

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Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance

1992

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Bactericidal testing has been used for several decades as a guide for antimicrobial therapy of serious infections. Such testing is most frequently performed when bactericidal antimicrobial agent therapy is considered necessary (such as when treating infectious endocarditis or infection in an immunocompromised host). It has also been used to ensure that the infecting organism is killed by (not tolerant to) usually bactericidal compounds. However, few data are available to support the role of such tests in direct patient care. Several important variables affect the reproducibility of the test results; however, proposed reference methods are now available for performing the MBC test. With minor modifications, these can provide a standardized approach for laboratories that need to perform them. Currently, little evidence is available to support the routine use of such testing for the care of individual patients. However, testing of new (investigational) antimicrobial agents can be beneficial in determining their potential to provide bactericidal antimicrobial activity during clinical use. New methods to assess bactericidal activity are being developed, but as yet none have been rigorously tested in patient care settings; further, for most of these methods, little information is available as to which technical parameters affect their results. In clinical laboratories, all bactericidal tests must be performed with rigorously standardized techniques and adequate controls, bearing in mind the limitations of the currently available test procedures.

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Section: Introduction Introductionmentioning

confidence: 85%

Section: Introduction Introductionmentioning

confidence: 99%

Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance

1992

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“…In contrast, S. mitis 1, although only slightly less susceptible than S. mitis 2 to the bactericidal effect of amoxicillin, never displayed a reduction of viable counts 419 VOL. 29,1986 on May 11, 2018 by guest http://aac.asm.org/ Downloaded from greater than 3 log10 (>99.9% killing) and therefore had a high MBC. Moreover, since 99.9% killing (delta log CFU, <3) was not achieved with either S. sanguis II or S. mitis 1, these two strains, which exhibited such different susceptibilities to amoxicillin, could both be considered tolerant when defined by the conventional MBC/MIC ratio.…”

Section: Resultsmentioning

confidence: 99%

Discrepancies between MBC and actual killing of viridans group streptococci by cell-wall-active antibiotics

Meylan¹,

Francioli²,

Glauser³

1986

Antimicrob Agents Chemother

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We determined the MBC of amoxicillin and vancomycin, two antibiotics advocated for treatment and prophylaxis of bacterial endocarditis, for 24 strains of viridans group streptococci isolated from patients with endocarditis. We found that the MIC of amoxicillin for all strains was <0.25 ,ug/ml and the MBC was either low (<0.5 ,ug/ml) in 6 nontolerant strains or high (>128 pg/ml) in 18 tolerant strains. The MIC of vancomycin for the 24 strains was '1 ,ug/ml, and the MBC was either low (<1 tig/ml) for 3 nontolerant strains or high (>128 pg/ml) for 21 tolerant strains. In addition to the MBC, we determined the actual reduction of the viable bacterial counts in each tube dilution after 24 h of incubation. This determination was made by subtracting the number of colonies observed on the subculture plate from the number of bacteria contained in the initial inoculum. For both antibiotics we found that the maximal reduction in viable counts was achieved at or very close to the MIC and did not increase with increasing antibiotic concentrations (up to 128 ,ug/ml). As expected, the six strains for which the amoxicillin MBC was <0.5 ,ug/ml and the three strains for which the vancomycin MBC was <1 ,ug/ml had a reduction of viable counts of more than 3 log10 (>99.9% killing). In contrast, among the strains defined as tolerant to amoxicillin and vancomycin, there were wide variations in the actual reduction of bacterial counts, ranging from 3 logl0 to <1 loglo. Therefore our observations suggest that the reduction of viable streptococcal counts reflects more accurately the bactericidal effect of amoxicillin and vancomycin than does the MBC, which artificially divides the strains into sensitive or tolerant strains.

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“…Evidence has gradually accumulated indicating a significant dependency of BDPC results, especially MBCs, on technical factor variations. It is not surprising that factors such as pH (18,38), temperature (30), type of medium (22,28,32), VOL. 28, 1985 on clinical isolates and allegedly oxacillin-tolerant reference strains, Taylor and associates (36) compared results obtained by the standard broth macrodilution BDPC method as outlined in the Manual of Clinical Microbiology with those of a carefully controlled procedure patterned along the lines recommended by Ishida and associates.…”

Section: Methodsmentioning

confidence: 99%