Differentiation between Pseudomonas and Stenotrophomonas Species Isolated from Fish Using Molecular and MALDI-TOF Method

For the purpose of precise antibiotic susceptibility testing it is necessary to clearly distinguish Pseudomonas and Stenotrophomonas genera, considering acquired resistance of Pseudomonas species, as well as the intrinsic resistance of Stenotrophomonas species. This is why in the identification of the 51 isolates originated from fish, the following methods were used: standard PCR, 16S rRNA gene sequencing, and MALDI-TOF.

The results of the standard PCR test, 16S rRNA gene sequencing and MALDI-TOF analysis confirmed 35 strains to belong to the Pseudomonas genus. Standard PCR test and VITEK MS device confirmed that 10 strains belong to Stenotrophomonas maltophilia species.

Three strains were positive in both standard PCR tests for Pseudomonas and Stenotrpohomonas. 16S rRNA gene sequencing identified these 3 strains to be 99% Pseudomonas sp. and 99% Stenotrophomonas sp. VITEK MS first identified these three strains as 99% Stenotrophomonas, and in the repeated identification it identified them as 99% Pseudomonas. MALDI TOF/TOF 4800 Plus device identified these strains as Stenotrophomonas.

Three strains were negative in both standard PCR tests for Pseudomonas and Stenotrpohomonas. 16S rRNA gene sequencing identified these 3 strains to be 99% Pseudomonas sp. and 99% Stenotrophomonas sp. VITEK MS first identified these three strains as 99% Stenotrophomonas, and in the repeated identification it identified them as 99% Pseudomonas. MALDI TOF/TOF 4800 Plus device identified these strains as Stenotrophomonas.

Although modern test methods that have very high specificity (PCR, 16S rRNA gene sequencing, MALDI TOF) were used in this study, precise differentiation between Pseudomonas and Stenotrophomonas species for 6 isolates could not be reached using the above mentioned methods.