The chloramphenicol resistance genecmlAis disseminated on transferable plasmids that confer multiple-drug resistance in swineEscherichia coli

Abstract

A recent study of beta-hemolytic Escherichia coli isolated from diarrheic swine found that 53% were resistant to chloramphenicol, a drug that has been prohibited from use in food animals in the US since the mid-1980s. To identify the factors governing the persistence of chloramphenicol resistance in the absence of specific selection pressure, the location of the chloramphenicol resistance gene cmlA and its linkage to other resistance determinants were investigated. Southern blot analysis of plasmid DNA from 46 swine E. coli isolates indicated that cmlA was present on large plasmids greater than 100 kbp. Fifty-two percent of the isolates were able to transfer chloramphenicol resistance to an E. coli recipient at conjugation frequencies ranging from 10(-3) to 10(-8) per recipient. Antimicrobial susceptibility tests on transconjugant strains demonstrated that resistance to sulfamethoxazole, tetracycline, and kanamycin frequently transferred along with chloramphenicol resistance. The transconjugant strains possessed at least two distinct class 1 integrons that linked cmlA to both aminoglycoside resistance genes aadA1 and aadA2 and either to sul1 or to sul3 sulphonamide resistance genes. These results suggest that in the absence of specific chloramphenicol selection pressure, the cmlA gene is maintained by virtue of gene linkage to genes encoding resistance to antimicrobials that are currently approved for use in food animals.

Antimicrobial Resistance Genes in Salmonella enterica Isolates from Poultry and Swine in Thailand

“…In addition, having genes conferring resistance to multiple drugs was significantly associated with being multiresistance (p<0.01). Twenty-two percent of the Salmonella isolates were nega- aadA1 (6), aadA2 (6), aadB (6), bla TEM (6), cmlA (6), strA (2), strB (2), sul1 (3), sul2 (1), sul3 (6), tetA (6), tetB(2) AMP, CHP, SPC, STR, SUL, TET, TRI 11 (6.0) aadA1 (10), aadA2 (1), bla PSE-1 (5), bla TEM (9), cmlA (8), dfrA10 (1), dfrA12 (5), strA (9), strB (9), sul1 (6), sul2 (3), sul3 (9), tetA (8) tive to all the resistance genes tested, even through most of these isolates were resistant to at least one antimicrobial agent (data not shown).…”

“…The prevalence of chloramphenicol resistance and the existence of the chloramphenicol resistance gene (s) among E. coli isolates has been demonstrated [2,27] even through the antibiotic has been prohibited for using in domestic animals. This is in agreement of the results in our study, which the cmlA gene was found in the majority of chloramphenicol-resistant isolates.…”

“…In our previous study, the cmlA gene in 7 chloramphenicol-resistant Salmonella strains was shown to be part of gene cassettes in class 1 integrons with unusual 3' conserved segment linked to the qacH-sul3 domain and the common resistance genes in the gene cassettes included aadA1 and aadA2, and qacH [7]. This closegenetic linkage to other resistance genes could be a mechanism for maintenance and co-selection of chloramphenicol resistance in Salmonella in the absence of chloramphenicol selection pressure [2,27].…”

Prevalence and Antibiotic Susceptibility of Escherichia coli and Salmonella spp. isolated from milk of zero grazed cows in Arusha City

“…Some studies in Tanzania and Nigeria reported that, chloramphenicol is irrationally used in animals as evidenced by the presence of its residues in poultry and poultry products (Nonga et al, 2010;Darwish et al, 2013). However, it may be due to transfer of resistant genes as a result of cross contamination between humans, animals and the environment (Bischoff et al, 2005;Salehi and Bonab, 2006) or use of other antibiotics belonging to aphenicol group (Ruzauskas et al, 2009). The susceptibility pattern of E. coli from all the sampling sites is summarized in the Table 2.…”

A Cross Sectional Anthropo-Clinical Study on Antimicrobials Prescription Pattern in Goat Patients at Chittagong, Bangladesh

“…Most prescriptions contained either one single antimicrobial substance or a combination of two antimicrobials that complement each other (Regula et al, 2009). However, more than 500 prescriptions of a triple combination of sulphonamide, tetracycline and a macrolide were observed, which is likely to select for multidrug-resistant bacteria (Bischoff et al, 2005;Matter et al, 2007). Another study on prescription pattern in Switzerland shown the largest number of treatments with a dosage above two times the recommended maximum dose in sheep and goats, where group treatment is common (Regula et al, 2009).…”