Epidemiology of extended spectrum β-lactamase, AmpC and class A carbapenemases-producing organisms isolated at San Camillo Hospital of Treviso (Italy) between April 2012 and March 2014

The indiscriminate use of broad-spectrum cephalosporins of the last years has favoured the selection of extended spectrum β-lactamases (ESBLs), AmpC and class A carbapenemases (KPC)-producing <em>Enterobacteriaceae</em> strains, representing a real health emergency. At San Camillo Hospital of Treviso, Italy, between April 2012 and March 2014, we isolated 263 suspected ESBL-producing strains from various specimens, including urine (76.4%), wound swabs (9.9%), blood cultures (4.6%), vaginal swabs (2.7%), fragments of bone (1.5%) and other materials (4.9%). The majority of the isolated bacteria were represented by <em>Escherichia coli</em> (43.3%), followed by <em>Klebsiella pneumoniae</em> (34.2%), <em>Proteus mirabilis</em> (15.2%), <em>Enterobacter</em> spp. (3.8%), <em>Morganella morganii</em> (1.1%), <em>Serratia</em> spp. (0.8%), <em>Proteus vulgaris</em> (0.4%), <em>Citrobacter freudii</em> (0.4%), <em>Providencia</em> spp. (0.4%) and <em>Pseudomonas aeruginosa</em> (0.4%). Using confirmatory phenotypic tests, 89.4% of the isolated resulted ESBL producer, 15.3% of which were also AmpC-producers, 1.5% were ESBL negative and AmpC positive, 4.2% were ESBL negative and AmpC negative, and 4.9%, consisting solely of K.pneumoniae, were confirmed as KPC positive. ESBL-mediated resistance to cephalosporin is not always clearly evident using susceptibility testing performed by agar diffusion-disc or dilution methods, for this reason it is strictly recommended to use specific tests able to reveal important mechanisms of resistance. The optimal use of diagnostic tools in microbiology is necessary to fight the spreading of pathogens with multiple antibiotic resistance mechanisms and in order to avoid giving useless antibiotic therapies to the patients.