Xylella fastidiosa subsp. fatidiosa is endemic in Costa Rica. Although the bacteria has great potential for disease and it is widespread throughout the country, a common feature is that symptoms of host infected plants tend to be asymptomatic or in worst scenarios show mild symptoms as reported for “crespera disease” in coffee. Another trait within this population is that isolates have shown broad genetic diversity, based on different typing techniques including MLST. Our recent efforts have focused on phenotypic characterization of isolated strains. We tested antibiotic susceptibility of X. fastidiosa subsp. fastidiosa to tetracycline, streptomycin, gentamicin, chloramphenicol, ciprofloxacin, and penicillin. Minimal Inhibition Concentration (MIC) (mg/ml) were generated using Etest® assay, a quantitative technique that has been used previously in slow growing bacteria including X. fastidiosa, with reproducible results, a difficult task to achieve using other susceptibility determination techniques. Results show an overall susceptibility of X. fastidiosa to most of the antibiotic tested; however, differences in MICs within isolates for each antibiotic should not be overlooked. To evaluate if endemic X. fastidiosa subsp. fastidiosa population is capable of infecting and causing sever disease in Nerium oleander as seen for X. fastidiosa subsp. pauca (ST53) also present in Costa Rica. Several isolates of X. fastidiosa subsp. fastidiosa representing different ST types, were assayed in a virulence test using Nerium oleander, 8 months after inoculation none of the tested isolates have induced evident symptoms of disease, bacteria were barely detected near the inoculation site after 6 months post inoculation, monitoring is still an ongoing task. This research was financially supported by funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 635646: POnTE (Pest Organisms Threatening Europe) and grant agreement No 727987: XF-ACTORS (Xylella fastidiosa active containment through a multidisciplinary oriented research strategy).