Animal and Human Multidrug-Resistant, Cephalosporin-Resistant Salmonella Isolates Expressing a Plasmid-Mediated CMY-2 AmpC β-Lactamase

Abstract

Salmonella spp. are important food-borne pathogens that are demonstrating increasing antimicrobial resistance rates in isolates obtained from food animals and humans. In this study, 10 multidrug-resistant, cephalosporin-resistant Salmonella isolates from bovine, porcine, and human sources from a single geographic region were identified. All isolates demonstrated resistance to cephamycins and extended-spectrum cephalosporins as well as tetracycline, chloramphenicol, streptomycin, and sulfisoxazole. Molecular epidemiological analyses revealed eight distinct chromosomal DNA patterns, suggesting that clonal spread could not entirely explain the distribution of this antimicrobial resistance phenotype. However, all isolates encoded an AmpC-like ␤-lactamase, CMY-2. Eight isolates contained a large nonconjugative plasmid that could transform Escherichia coli. Transformants coexpressed cephalosporin, tetracycline, chloramphenicol, streptomycin, and sulfisoxazole resistances. Plasmid DNA revealed highly related restriction fragments though plasmids appeared to have undergone some evolution over time. Multidrug-resistant, cephalosporin-resistant Salmonella spp. present significant therapeutic problems in animal and human health care and raise further questions about the association between antimicrobial resistance, antibiotic use in animals, and transfer of multidrug-resistant Salmonella spp. between animals and man.Salmonella spp. are important zoonotic pathogens in humans and animals. In the United States it is estimated that over 1.4 million cases of salmonellosis occur each year, 95% of which are the result of food-borne transmission (28). Large outbreaks have been associated with ingestion of poultry, meat, and milk and other dairy products (6). Although the majority of infections result in asymptomatic or self-limited diarrheal illness, severe, life-threatening bacteremias and other deep-seated infections do occur, particularly in immunocompromised hosts, neonates, and the elderly (7,14).

Resistance profile to antimicrobials of Salmonella spp. isolated from human infections

“…A contributing factor for resistance dissemination observed in certain Salmonella serotypes has been the unnecessary use of antimicrobials for self limited gastroenteritis treatment. It has been suggested that these treatments be reserved only for extraintestinal salmonellosis and in cases of child gastroenteritis or elderly and immune suppressed patients where antibioticotherapy is fundamental to control these diseases (Winokur et al, 2000;Prats et al, 2000). Regarding antimicrobials resistance of enteric pathogens, the most worrying factor has been the increase of multiresistance dissemination of S. typhimurium and also, on a smaller scale, by other serotypes due to the use of these antimicrobials in animal feeding for prophylaxis and growth promotion.…”

“…No S. enteritidis strain with this resistance mechanism was isolated in this study. A second resistance mechanism has recently been detected mainly in Typhimurium serotype, concerned to a Beta Lactamase type Amp-C mediated by plasmid, conferring additional resistance to cefamicines (Winokur et al 2000). In the present study, our strains of S. typhimurium and S. enterica subspecies enterica serotype 4,5,12:i:-presented a multiresistance pattern and among these resistance patterns were detected from first to fourth generation cefalophorines, such as cephalotin (1 st generation); cefoxitin (2 nd generation); cefotaxime and ceftriaxone (3 rd generation); cefepime (4 th generation), and also to the monobactamic aztreonam.…”

“…Food, such as egg, meat, milk and other dairy products, are the commonest source of salmonella for humans (Winokur et al, 2000). The Salmonella genus belongs to the Enterobacteriacea family, according to current taxonomy, and consists of two species: S. enterica and S. bongori.…”

Multi-drug-resistant Gram-negative bacteria

“…CMY-2 type of resistance was commonly described in Salmonella and E. coli isolated from food-producing animals 5,6 . CMY-2 producing E. coli is also relatively common in humans and nearly as common as ESBL.…”

Development of a Polymerase Chain Reaction Assay for the Detection of Antibiotic Resistance Genes in Community DNA

“…These genes confer resistance to the cephalosporin class of antibiotics, and of particular concern, the third-generation cephalosporins such as ceftriaxone, cefotaxime, and ceftiofur. 45 These genes are typically located on plasmids. The second focus was the flo gene, which confers resistance to florfenicol and chloramphenicol.…”