Cefazolin sodium microbiology

# Microbiology

## Mechanism of Action
Cefazolin is a bactericidal agent that acts by inhibition of bacterial cell wall synthesis.

## Mechanism of Resistance
Predominant mechanisms of bacterial resistance to cephalosporins include the presence of extended-spectrum beta-lactamases and enzymatic hydrolysis.

## Lists of Microorganisms
Cefazolin has been shown to be active against most isolates of the following microorganisms both in vitro and in clinical infections as described in the INDICATIONS AND USAGE (1) section.
- Staphylococcus aureus
- Staphylococcus epidermidis
- Streptococcus pyogenes
- Streptococcus agalactiae
- Streptococcus pneumoniae
Methicillin-resistant staphylococci are uniformly resistant to cefazolin,
Escherichia coli
Proteus mirabilis
Most isolates of indole positive Proteus (Proteus vulgaris), Enterobacter spp., Morganella morganii, Providencia rettgeri, Serratia spp. and Pseudomonas spp. are resistant to cefazolin.

## Susceptibility Test Methods
When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drug products used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug product for treatment.

### Dilution Techniques
Quantitative methods are used to determine minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standard test1,2 (broth and/or agar). The MIC values obtained should be interpreted according to criteria as provided in Table 4.

### Diffusion Techniques
Quantitative methods that require measurement of zone diameters provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be interpreted using a standard test method 2,3. This procedure uses paper disks impregnated with 30 mcg cefazolin to test the susceptibility of microorganisms to cefazolin. The disk diffusion interpretive criteria are provided in Table 4.
NOTE: S. pyogenes and S. agalactiae that have a penicillin MIC of 0.12 mcg/mL or disk diffusion zone diameters of 24 mm with a 10 mcg penicillin disk may be interpreted as susceptible to cefazolin. Non-meningitis isolates of S. pneumoniae that have a penicillin MIC of 0.06 mcg/mL may be interpreted as susceptible to cefazolin.
A report of Susceptible indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the infection site necessary to inhibit growth of the pathogen. A report of Intermediate indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug product is physiologically concentrated or in situations where a high dosage of the drug product can be used. This category also provides a buffer zone that prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of Resistant indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations usually achievable at the infection site; other therapy should be selected.
Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay and the techniques of the individual performing the test1,2,3. Standard cefazolin powder should provide the following MIC values noted in Table 5. For the diffusion technique using the 30 mcg disk, the criteria in Table 5 should be achieved.