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Influence of growth medium on the in vitro activities of second- and third-generation cephalosporins against
Abstract:
The influence of culture medium of the MICs of eight cephalosporins for 45 strains of Streptococcus faecalis was investigated. The MICs of cephalothin, cefamandole, and cefoperazone were not substantially influenced by the type of culture medium used. In contrast, MICs of cefuroxime, ceftizoxime, cefotaxime, cefmenoxime, and ceftriaxone varied markedly with both the commercial brand and the blood content of the broth used. The use of Mueller-Hinton broths (from Oxoid Ltd., GIBCO Diagnostics, and Difco Laboratories) supplemented with 5% lysed sheep blood frequently resulted in MICs that were greater than or equal to 16 times lower than the MICs obtained with these same broths without blood. Similar, but less marked, patterns were observed when supplemented and unsupplemented brain heart infusion and Sceptor broths were used. The influence of the broth on MICs suggests a complex interaction between some cephalosporins, medium components, and organisms. The cephalosporins that were affected by media share an identical moiety at the 7-acyl position (cefuroxime is slightly different), but this structure is not shared by those cephalosporins that were not affected. This commonality in structure at the 7-acyl position may be partially responsible for the observed results.
Insights
Culture medium significantly impacts the minimum inhibitory concentrations (MICs) of certain cephalosporins for Streptococcus faecalis. Supplementing broths with blood reduced MICs for several cephalosporins, suggesting complex interactions.
Area of Science:
- Microbiology
- Pharmacology
- Clinical Chemistry
Background:
- The minimum inhibitory concentration (MIC) is crucial for determining antibiotic efficacy.
- Streptococcus faecalis is a significant pathogen, and its susceptibility to antibiotics can be influenced by various factors.
- Cephalosporins are a class of beta-lactam antibiotics widely used to treat bacterial infections.
Purpose of the Study:
- To investigate the influence of culture medium composition on the MICs of eight cephalosporins against Streptococcus faecalis.
- To identify which cephalosporins are most affected by variations in culture media.
- To explore potential reasons for observed differences in cephalosporin activity based on media components.
Main Methods:
- Tested MICs of eight cephalosporins for 45 strains of Streptococcus faecalis.
- Utilized various commercial culture media brands and assessed the impact of blood supplementation (5% lysed sheep blood).
- Compared MIC values obtained with different media formulations and blood content.
Main Results:
- MICs for cephalothin, cefamandole, and cefoperazone showed minimal variation across different media.
- MICs for cefuroxime, ceftizoxime, cefotaxime, cefmenoxime, and ceftriaxone varied significantly based on media brand and blood content.
- Supplementation with 5% lysed sheep blood in Mueller-Hinton broths often resulted in MICs that were at least 16 times lower for affected cephalosporins.
- Similar trends were observed with supplemented brain heart infusion and Sceptor broths, though less pronounced.
Conclusions:
- Culture medium composition, particularly blood content, significantly influences the in vitro activity of several cephalosporins against Streptococcus faecalis.
- The observed variability suggests complex interactions between specific cephalosporins, media components, and the bacteria.
- A shared structural moiety at the 7-acyl position in the affected cephalosporins may contribute to their differential response to media variations.