Biochemical characteristics and susceptibility to antimicrobials of Paenibacillus larvae isolated in outbreaks of American Foulbrood of honey bees occurred in Italy and Argentina

MILITO M; GIACOMELLI A; FRANCO A; CAPRIOLI A; CERSINI A; PIZZARIELLO M; CORDARO G; BATTISTI A; SCHOLL F; BASSI S; CARRA E; DELLAIRA E; MACRÌ S; GENDE L; PIETROPAOLI M; FORMATO G

Congreso; Proceedings of the XXXXIII International Apicultural Congress.; 2013

A total of 29 isolates of Paenibacillus larvae obtained from American foulbrood outbreaks occurred between 2000 and 2011 in Italy (21 strains) and Argentina (8 strains) were examined for their biochemical characteristics (Api 50 CH and API 20 NE - Biomerieux) and susceptibility towards selected antimicrobials. All the isolates were confirmed by PCR and genotyped by rep-PCR using ERIC1R/ERIC2 primers.All isolates hydrolyzed gelatin, with the exception of one from Argentina; most isolates (86.2%) reduced nitrates to nitrites. Isolates were also positive to : 5-potassium ketogluconate (100%), D-trehalose (20.7%), N-acetylglucosamine (20.7%), D-glucose (10.3%), D-ribose (10.3%), D-tagatose (10.3%), D-arabinose (3.4%), glycerol (3.4%), D-lactose (3.4%) and D-maltose (3.4%). Api CH50 and API 20 NE do not seem the most appropriate method for Paenibacillus larvae identification, even thou few specific reactions could play a great role for it.As for antimicrobial susceptibility, isolates were tested by using agar disk diffusion method towards tetracycline, sulfonamide, gentamicin, trimethoprim, sulfamethoxazole, clindamycin, enrofloxacin, ampicillin, amoxicillin-clavulanic acid, erythromycin, cephalothin and kanamycin. The tests were performed according to CLSI M31-A3 standard. Resistance to sulfonamides was detected in 2 out of 8 isolates from Argentina (25%) and in 1 out of 21 Italian isolates (4.8%). All isolates resulted susceptible to the other antimicrobials tested and interpreted according to the CLSI standard and available literature (Alippi et al., 2007). Although all isolates showed susceptibility to tetracycline when results were interpreted by the above standard (clinical breakpoints), 2 out of 8 isolates from Argentina (25%) and 1 out of 21 isolates from Italy (4.8%) showed a reduction of the inhibition diameter which merits further investigation