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[Expression of staphylococci resistance to oxacillin and cefalotin ]
Abstract:
The comportment to oxacillin (OXA) and cefalotin (CFT) of 32 strains of staphylococci - 18 Staphylococcus aureus and 14 coagulase-negative staphylococci (SCN) - was studied by three different methods, on three types of media, with or without 5 p. cent of NaCl and incubated at two temperatures (30 degree C-37 degree C). S. aureus showed always a cross-resistance to OXA and CFT. Three types were recognized : "susceptible" (S) and "high level resistant" (RO) types, whose comportment did not vary with culture conditions; "heterogenous resistant" type (RH) for which the OXA - resistance expression was better at 30 degree C and on salt medium. SCN did not always present a cross-resistance. In addition to S, RO and RH types, one strain showed a dissociated resistance to OXA and CFT, with a better expression at 30 degree C and on salt medium; one strain, which appeared to be susceptible by discs method, presented a resistant population level higher than that of the susceptible reference strain, whatever the culture conditions were.
Insights
Staphylococcus aureus strains exhibit consistent cross-resistance to oxacillin (OXA) and cefalotin (CFT). However, resistance expression in some strains varies with culture conditions, impacting antimicrobial susceptibility testing.
Area of Science:
- Microbiology
- Antimicrobial Resistance
Context:
- Investigates the antimicrobial susceptibility of Staphylococcus aureus and coagulase-negative staphylococci (SCN) to oxacillin (OXA) and cefalotin (CFT).
- Evaluates the influence of various culture conditions (media type, NaCl concentration, temperature) on resistance expression.
Purpose:
- To characterize the resistance patterns of staphylococcal strains to OXA and CFT.
- To identify factors influencing the expression of antimicrobial resistance in these bacteria.
Summary:
- Studied 32 staphylococcal strains (18 S. aureus, 14 SCN) using three methods, media types, with/without NaCl, and temperatures (30°C-37°C).
- S. aureus consistently showed cross-resistance to OXA and CFT, with three types identified: susceptible (S), high-level resistant (RO), and heterogeneously resistant (RH).
- RH strains showed enhanced OXA resistance at 30°C and on salt medium. SCN strains did not always exhibit cross-resistance, with some showing dissociated or underestimated resistance levels.
Impact:
- Highlights the importance of standardized culture conditions for accurate antimicrobial susceptibility testing of staphylococci.
- Identifies specific conditions that can unmask or alter resistance phenotypes, crucial for clinical interpretation and treatment strategies.