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Cefazolin high-inoculum effect in methicillin-susceptible Staphylococcus aureus from South American hospitals

Sandra Rincón1, Jinnethe Reyes, Lina Paola Carvajal

  • 1Molecular Genetics and Antimicrobial Resistance Unit, Universidad El Bosque, Carrera 7B Bis No. 132-11, Bogotá, Colombia.

The Journal of Antimicrobial Chemotherapy
|June 25, 2013
PubMed
Abstract

Insights

The cefazolin inoculum effect (InE), a challenge in treating Staphylococcus aureus infections, is prevalent in South America. This effect, linked to beta-lactamase production, may compromise cefazolin treatment for deep-seated infections in Colombia and Ecuador.

Area of Science:

  • Infectious Diseases
  • Microbiology
  • Pharmacology

Background:

  • Cefazolin is a common treatment for methicillin-susceptible Staphylococcus aureus (MSSA) infections.
  • Clinical failures have been noted in high-inoculum infections caused by MSSA producing type A beta-lactamase.
  • The cefazolin inoculum effect (InE) is a phenomenon where higher bacterial concentrations reduce cefazolin susceptibility.

Purpose of the Study:

  • To determine the prevalence of the cefazolin inoculum effect (InE) in MSSA isolates from South American hospitals.
  • To investigate the association between InE and beta-lactamase production in MSSA.
  • To assess the potential impact of InE on cefazolin treatment efficacy in the region.

Main Methods:

  • Collected MSSA isolates from bloodstream and osteomyelitis infections across South American hospitals (2001-2008).
  • Determined cefazolin Minimum Inhibitory Concentrations (MICs) at standard (10^5 cfu/mL) and high (10^7 cfu/mL) inoculums.
  • Utilized Pulsed-Field Gel Electrophoresis (PFGE), Multilocus Sequence Typing (MLST), and blaZ sequencing for isolate characterization.

Main Results:

  • The overall prevalence of cefazolin InE was 36%, with higher rates in osteomyelitis (50%) than bloodstream infections (33%).
  • Ecuador (45%) and Colombia (63% in osteomyelitis) showed particularly high InE prevalence.
  • Prevalent beta-lactamases were Type A (66%) and Type C (31%), correlating with InE.

Conclusions:

  • A significant prevalence of cefazolin InE was observed in MSSA from Colombia and Ecuador, often associated with Type A beta-lactamase.
  • The findings suggest that cefazolin treatment for deep-seated MSSA infections in these countries may be less effective.
  • Further surveillance and consideration of alternative antibiotics are warranted for MSSA infections in high-InE prevalence areas.
Keywords:
bloodstream infectionsinoculum effectosteomyelitis

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