Sensitivity testing and concentration dependent killing (cdk) in mucoid-producing pseudomonas aeruginosa (mpa)

ABSTRACT 1021 _Pulmonary: Cystic Fibrosis Poster Symposium, Tuesday, 5/4_ BACKGROUND: MPa are a major cause of morbidity and mortality in persons with cystic fibrosis. Treatment of MPa

consists of combined β-lactam and aminoglycoside (AG) antibiotics, guided by sensitivity tests. Experiments have shown that AG-MPa interactions decrease AG effectiveness and cause variations

in minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) depending on the testing method. Also, bactericidal effects of AG increase with higher concentration

of AG (CDK), although this has not been well-established for MPa. OBJECTIVE: To determine whether MPa demonstrate CDK when exposed to T and to determine if there are discrepancies between

different methods of determining MIC for MPa. MATERIALS & METHODS: 5 strains of MPa isolated from patients with CF and a reference strain (ATCC27853) were studied. Strains were incubated

in cation-supplemented Mueller-Hinton Broth (MHB) then plated and re-incubated. MICs to T were determined from these plated specimens using the MicroScan WalkAway-96 or tube macrodilution

following National Committee for Clinical Laboratory Standards. After incubation, aliquots from macrodilution tubes without turbidity were plated and incubated for MBC determination, defined

as the lowest dilution that showed 99.9% titer reduction. For time-kill determination, strains were incubated overnight in MHB then diluted and incubated 1 hour to achieve logarithmic

growth. 5 to 8 log10/ml were added to T at 10 µg/ml and 25 µ/ml. Every hour for 8 hours, quantitative titers were determined by 1:10 serial dilution. Linear regression was done using

least-squares method of log10/ml vs time plot. RESULTS: MIC and MBC are presented in µg/ml. CDK is presented as rate of titer reduction (log10) per hour: a positive value signifies net

growth. Results are presented below. (Table) CONCLUSIONS: MIC and MBC determination for MPa is dependent on the method used. The rate of MPa killing is significantly slower for comparably

sensitive strains when compared to the ATCC27853 reference strain. For MPa strains with an MBC below the exposed concentration, a faster rate of titer reduction is seen with exposure to

increased concentration of T suggesting that higher concentrations of T can overcome the inhibitory effects of MPa. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Pediatric Infectious

Diseases, University of California San Francisco California, San Francisco, CA K A Slavin & Jay H Tureen Authors * K A Slavin View author publications You can also search for this author

inPubMed Google Scholar * Jay H Tureen View author publications You can also search for this author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS

ARTICLE CITE THIS ARTICLE Slavin, K., Tureen, J. Sensitivity Testing and Concentration Dependent Killing (CDK) in Mucoid-Producing _Pseudomonas aeruginosa_ (MPa). _Pediatr Res_ 45, 175

(1999). https://doi.org/10.1203/00006450-199904020-01038 Download citation * Issue Date: 01 April 1999 * DOI: https://doi.org/10.1203/00006450-199904020-01038 SHARE THIS ARTICLE Anyone you

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