Campylobacter susceptibility testing

Campylobacter susceptibility testing

Most Campylobacter infections are self-limiting but antimicrobial treatment (e.g., macrolides, fluoroquinolones) is necessary in severe or prolonged cases. Susceptibility testing continues to play a critical role in guiding therapy and epidemiological monitoring of resistance. The methods of choice for Campylobacter recommended by the Clinical and Laboratory Standards Institute (CLSI) are agar dilution and broth microdilution, while a disk diffusion method was recently standardized by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Macrolides, quinolones, and tetracyclines are among the common antimicrobials recommended for testing. Molecular determination of Campylobacter resistance via DNA sequencing or PCR-based methods has been performed. High levels of resistance to tetracycline and ciprofloxacin are frequently reported by many national surveillance programs, but resistance to erythromycin and gentamicin in Campylobacter jejuni remains low. Nonetheless, variations in susceptibility observed over timeunderscore the need for continued public health monitoring of Campylobacter resistance from humans, animals, and food.

Testing conditions

· Disk diffusion (EUCAST standardised disk diffusion method) Medium: Mueller-Hinton agar + 5% defibrinated horse blood and 20 mg/L β-NAD (MH-F).

· Inoculum: McFarland 0.5

· Incubation: Microaerobic environment, 41±1ºC, 24h. Isolates with insufficient growth after 24h incubation are re-incubated immediately and inhibition zones read after a total of 40-48h incubation.

· Reading: Read zone edges as the point showing no growth viewed from the front of the plate with the lid removed and with reflected light.

· Quality control: Campylobacter jejuni ATCC 33560

Break points(EUCAST 2018)

Antimicrobial agents	Disc content (µg)	Zone diameter break points		MIC break points
Antimicrobial agents	Disc content (µg)	S ≥	R≤	S ≥	R≥
Erythromycin	15	C.Jejuni 20 C.Coli 24	20 24	4 8	4 8
Ciprofloxacin	5	26	26	0.5	0.5
Tetracycline	30	30	30	2	2

Erythromycin can be used to determine susceptibility to azithromycin (CLSI and EUCAST) and clarithromycin (CLSI, EUCAST)and tetracycline can be used to determine susceptibility to doxycycline (EUCAST).

References

Antimicrobial resistance in Campylobacter: Susceptibility testing methods and resistance trends Beilei Ge a,⁎, Fei Wang a,b, Maria Sjölund-Karlsson c, Patrick F. McDermott
European Committee on Antimicrobial Susceptibility Testing Breakpoint tables for interpretation of MICs and zone diameters.

Contributed by Irim Iftikhar