Antibiotic resistance in Salmonella enterica subsp. enterica strains isolated in Poland from 1998 to 1999

Salmonella resistant to extended-spectrum cephalosporins: prevalence and epidemiology

Salmonella resistant to extended-spectrum cephalosporins (ESCs) have emerged worldwide since 1988. By 2004, 43 countries had reported this public health problem. Resistance was mediated by classical extended-spectrum beta-lactamases, plasmid-mediated cephalosporinases, and recently a class A carbapenemase. Of these, CMY-2 is the most widely disseminated enzyme. Salmonella enterica serotype Typhimurium and S. enterica serotype Enteritidis are the most common serovars associated with ESC resistance in human infections. Many outbreaks in humans have been reported, most often among children and neonates. ESC-resistant Salmonella is frequently recovered from animals and food, with poultry as primary food source, suggesting that humans are often infected by these routes.

Epidemiological characteristics of Salmonella Typhimurium isolated from animals and feed in Poland

Fifty-seven Salmonella Typhimurium strains isolated from poultry, swine and animal feed in Poland during the years 1979-1998 and 2000-2002 were analysed with conventional and molecular techniques. Antimicrobial resistance as well as multiresistance was found, respectively, in 80.1% and 56.1% of the isolates and most frequently among isolates from 2000-2002. Of several phage types noted, DT104 was prevalent among poultry, swine and feed isolates. DT104, U302 and non-typable strains had a multiple resistant profile (ACSSuT) due to the presence of class I integrons. Pulse-field gel electrophoresis of XbaI and BlnI digest showed high genomic similarity between the strains and confirmed clonal spread of S. Typhimurium infections. Plasmid profiling allowed further differentiation of the strains. We have, therefore, confirmed the appearance of S. Typhimurium DT104 showing genome integrated integron-mediated antimicrobial resistance in Poland. These findings are significant for public and animal health risks and document the dissemination of DT104 epidemic strains into new geographical regions.

Antibiotic resistance and class 1 integron patterns of non-typhoidal human Salmonella serotypes isolated in Hungary in 2002 and 2003

The antibiotic resistance profiles of 5178 Salmonella strains representing 19 non-typhoidal serotypes isolated from human salmonellosis cases in Hungary in 2002 and 2003 were analysed for resistance to 10 antibiotic agents. The most frequent resistances were to nalidixic acid (Nx), streptomycin (S), tetracycline (Tc), ampicillin (Amp) and chloramphenicol (Cm) (ranging from 27% to 13%). Forty-five percent of the Salmonella Typhimurium strains were multiple resistant and belonged mainly to the definitive phage types 104 and U302. A prevalence of 83-94% of strains of serotypes S. Infantis, S. Hadar and S. Virchow was observed with the NxSTc resistance pattern, sometimes complemented with other resistances. Multiple resistance was uncommon in S. Enteritidis; nevertheless, 20% of the strains, most of which belonged to phage type 4, were nalidixic acid resistant. One strain of S. Typhimurium was found to be resistant to ciprofloxacin. Four S. Typhimurium strains were resistant to cefotaxime and produced extended-spectrum beta-lactamase. Selected isolates were screened for the presence of class 1 integrons by polymerase chain reaction (PCR). Nucleotide sequencing of the PCR products revealed nine different variable regions. One resistance gene was identified in five variable regions (aadA1, aadA2, aadA23, dfrV and pse-1), and four variable regions carried two resistance gene cassettes (aadB-catB3, dhfrI-aadA, dfrA17-aadA5 and oxa-1-aadA1).

Trends in nalidixic acid resistance in nontyphoidal Salmonella isolated from 1999 to 2002: decreased susceptibility to 6 fluoroquinolones

We determined the resistance to nalidixic acid and 6 fluoroquinolones of 771 nontyphoidal Salmonella strains isolated from humans between 1999 and 2002. A total of 22 different serotypes were identified among the Salmonella isolates, the most common being Salmonella Enteritidis (79%) and Salmonella Derby (8%). Resistance to nalidixic acid increased from 38% in 1999 to 43% in 2002. This resistance was not homogeneous among the different serotypes, with the highest percentage of resistant isolates belonging to Salmonella Hadar (79%) followed by Salmonella Enteritidis (46%). Reduced ciprofloxacin susceptibility (minimal inhibitory concentrations [MICs] from 0.12 to 0.5 microg/mL) was observed in 300 (39%) Salmonella. In our study, the nalidixic acid-resistant strains had an MIC90 at least 4-fold higher than the susceptible ones for all the fluoroquinolones tested, thus showing that resistance to nalidixic acid is an indicator of low-level resistance to all fluoroquinolones.

Mechanism of resistance to several antimicrobial agents in Salmonella Clinical isolates causing traveler's diarrhea

The evolution of antimicrobial resistance in Salmonella isolates causing traveler's diarrhea (TD) and their mechanisms of resistance to several antimicrobial agents were analyzed. From 1995 to 2002, a total of 62 Salmonella strains were isolated from stools of patients with TD. The antimicrobial susceptibility to 12 antibiotics was determined, and the molecular mechanisms of resistance to several of them were detected as well. The highest levels of resistance were found against tetracycline and ampicillin (21 and 19%, respectively), followed by resistance to nalidixic acid (16%), which was mainly detected from 2000 onward. Molecular mechanisms of resistance were analyzed in 16 isolates. In these isolates, which were resistant to ampicillin, two genes encoding beta-lactamases were detected: oxa-1 (one isolate) and tem-like (seven isolates [in one strain concomitantly with a carb-2]). Resistance to tetracycline was mainly related to tetA (five cases) and to tetB and tetG (one case each). Resistance to chloramphenicol was related to the presence of the floR and cmlA genes and to chloramphenicol acetyltransferase activity in one case each. Different genes encoding dihydrofolate-reductases (dfrA1, dfrA12, dfrA14, and dfrA17) were detected in trimethoprim-resistant isolates. Resistance to nalidixic acid was related to the presence of mutations in the amino acid codons 83 or 87 of the gyrA gene. Further surveillance of the Salmonella spp. causing TD is needed to detect trends in their resistance to antimicrobial agents, as we have shown in our study with nalidixic acid. Moreover, such studies will lead to better treatment and strategies to prevent and limit their spread.

Expanded-spectrum cephalosporin resistance in non-typhoid Salmonella

Expanded-spectrum cephalosporins (ESCs) such as ceftriaxone, together with fluorinated quinolones, are the choice antibiotics in the treatment of invasive salmonella infections. Resistance to ESCs among non-typhoid salmonella has been recognised since the late 1980s. Currently, ESC-resistant salmonella strains are reported world-wide and in some areas their incidence is significant. Resistance is mainly due to acquisition of multi-resistant plasmids encoding a variety of extended-spectrum and AmpC-type beta-lactamases. The origins of ESC-resistant salmonellae are diverse. Exchange of resistance determinants between salmonellae and nosocomial enterobacteria seems to be frequent, at least in developing countries. Also, the use of newer beta-lactams in animal husbandry and veterinary medicine may have facilitated the spread of ESC-resistant salmonella strains in livestock.

Two different extended-spectrum beta-lactamases (ESBLs) in one of the first ESBL-producing salmonella isolates in Poland

Two extended-spectrum beta-lactamase (ESBL)-producing salmonella isolates, Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Typhimurium, were analyzed. Both isolates produced the CTX-M-3 ESBL; however, their bla(CTX-M-3) genes were located on different plasmids. The serovar Typhimurium isolate also expressed another ESBL, SHV-2a, and probably the two ESBL genes had been acquired independently by the strain.