Early Pseudomonas aeruginosa infection in individuals with cystic fibrosis: is susceptibility testing justified?
OBJECTIVE
To test the presumption that Pseudomonas aeruginosa isolates responsible for initial lung infection in individuals with cystic fibrosis (CF) are invariably susceptible to antipseudomonal agents.


METHODS
Antibiotic susceptibility was determined (MIC and Etest) in two populations of P. aeruginosa associated with initial lung infection. Population 1: environmental isolates (n=78). Population 2: clinical isolates responsible for first infection in previously non-infected patients (85 isolates from 85 patients). Susceptibility or resistance was determined using current BSAC guidelines; ninth version (2009).


RESULTS
The majority (≥ 90%) of isolates in both bacterial populations were susceptible to the front-line antipseudomonal agents; colistin, ciprofloxacin, tobramycin, ceftazidime, amikacin and meropenem. Up to 10% of isolates were resistant to one or more antibiotics. A single isolate from each population would be defined as resistant to tobramycin based on a breakpoint (>128 mg/L) that has been suggested for use in patients receiving inhaled therapy.


CONCLUSIONS
The high prevalence of susceptibility found in P. aeruginosa isolates associated with initial infection contrasts with the high prevalence of resistance found in isolates from chronic CF lung infection. However, susceptibility in early isolates cannot be presumed. Until further data are obtained from clinically based studies, susceptibility tests should continue to be performed to assist the choice of antibiotics for treatment of early infection.
Macdonald
D
D
University of Edinburgh Medical School, Little France Crescent, Edinburgh EH16 4SB, UK.
Cuthbertson
L
L
Doherty
C
C
Campana
S
S
Ravenni
N
N
Taccetti
G
G
Govan
J R W
JR
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003550:Cystic Fibrosis / Q000150:complications*; D024881:Drug Resistance, Bacterial; D004783:Environmental Microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D018410:Pneumonia, Bacterial / Q000382:microbiology*; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification
D000900:Anti-Bacterial Agents