title: Salt-supplemented medium for testing methicillin-resistant staphylococci with newer beta-lactams.
abstract: The addition of 2% NaCl to cation-supplemented Mueller-Hinton broth (CSMHB) was evaluated for microdilution testing of the susceptibility of staphylococci to five cephalosporins, imipenem, amoxicillin-clavulanate, and ticarcillin-clavulanate. With Staphylococcus aureus, NaCl improved the recognition of methicillin (oxacillin) resistance to cefamandole, imipenem, or ticarcillin-clavulanate. Resistance to amoxicillin-clavulanate was readily determined, irrespective of the presence of added salt. The addition of 2% NaCl to CSMHB did not significantly improve detection of resistance to any of the beta-lactams among coagulase-negative staphylococci. Since the addition of NaCl did not have significant adverse effects on tests with coagulase-negative staphylococci, the routine addition of 2% NaCl to oxacillin or methicillin tests with staphylococci may be justifiable on the basis of convenience or standardization. However, addition of NaCl to susceptibility tests of other beta-lactams does not consistently improve recognition of resistance among staphylococci and thus cannot be recommended for routine use.
authors.affiliation: Department of Pathology, University of Texas Health Science Center, San Antonio 78284-7751.
authors.forename: J H
authors.initials: JH
authors.lastname: Jorgensen
authors.forename: J S
authors.initials: JS
authors.lastname: Redding
authors.forename: L A
authors.initials: LA
authors.lastname: Maher
authors.forename: P E
authors.initials: PE
authors.lastname: Ramirez
mesh_terms: D000658:Amoxicillin / Q000494:pharmacology; D019980:Amoxicillin-Potassium Clavulanate Combination; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology; D002969:Clavulanic Acids / Q000494:pharmacology; D003470:Culture Media; D004359:Drug Therapy, Combination / Q000494:pharmacology; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008712:Methicillin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology; D010403:Penicillin Resistance; D012965:Sodium Chloride / Q000494:pharmacology; D013210:Staphylococcus / Q000187:drug effects*; D013211:Staphylococcus aureus / Q000187:drug effects*; D013982:Ticarcillin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D002969:Clavulanic Acids; D003470:Culture Media; D012965:Sodium Chloride; D015378:Imipenem; D019980:Amoxicillin-Potassium Clavulanate Combination; D000658:Amoxicillin; D013982:Ticarcillin; D008712:Methicillin; D010068:Oxacillin