Azithromycin resistance in Escherichia coli and Salmonella from food-producing animals and meat in Europe.

OBJECTIVES To characterize the genetic basis of azithromycin resistance in Escherichia coli and Salmonella collected within the EU harmonized antimicrobial resistance (AMR) surveillance programme in 2014-18 and the Danish AMR surveillance programme in 2016-19. METHODS WGS data of 1007 E. coli [165 azithromycin resistant (MIC > 16 mg/L)] and 269 Salmonella [29 azithromycin resistant (MIC > 16 mg/L)] were screened for acquired macrolide resistance genes and mutations in rplDV, 23S rRNA and acrB genes using ResFinder v4.0, AMRFinder Plus and custom scripts. Genotype-phenotype concordance was determined for all isolates. Transferability of mef(C)-mph(G)-carrying plasmids was assessed by conjugation experiments. RESULTS mph(A), mph(B), mef(B), erm(B) and mef(C)-mph(G) were detected in E. coli and Salmonella, whereas erm(C), erm(42), ere(A) and mph(E)-msr(E) were detected in E. coli only. The presence of macrolide resistance genes, alone or in combination, was concordant with the azithromycin-resistant phenotype in 69% of isolates. Distinct mph(A) operon structures were observed in azithromycin-susceptible (n = 50) and -resistant (n = 136) isolates. mef(C)-mph(G) were detected in porcine and bovine E. coli and in porcine Salmonella enterica serovar Derby and Salmonella enterica 1,4, [5],12:i:-, flanked downstream by ISCR2 or TnAs1 and associated with IncIγ and IncFII plasmids. CONCLUSIONS Diverse azithromycin resistance genes were detected in E. coli and Salmonella from food-producing animals and meat in Europe. Azithromycin resistance genes mef(C)-mph(G) and erm(42) appear to be emerging primarily in porcine E. coli isolates. The identification of distinct mph(A) operon structures in susceptible and resistant isolates increases the predictive power of WGS-based methods for in silico detection of azithromycin resistance in Enterobacterales

Antimicrobial resistance patterns to beta-lactams of gram-positive cocci isolated from bovine mastitis in Lithuania

The aim of the study was to isolate gram-positive cocci from cows with mastitis and to determine their resistance to beta-lactamic antibiotics. Eight hundred and nine strains were isolated and identified as staphylococci (n=516), streptococci (n=199) and enterococci (n=94) from sub-clinical and clinical cases of bovine mastitis in Lithuania. The most common causative agents of udder disease included: S. epidermidis (n=176), S. aureus (n=176), S. agalactiae (n=134), S. hyicus (136) and E. hirae (n=68). Isolates were analysed for antimicrobial resistance to penicillin, ampicillin, amoxicillin, cephalothin, cephalexin, amoxicillin + clavulanate. The susceptibility patterns were analysed using the agar disk diffusion method. S. aureus showed the highest level of resistance to amoxicillin (81.3%), penicillin (76.7%) and ampicillin (78.4%). The corresponding values for CNS strains were 59.7%, 59.7% and 50.6% against penicillin, ampicillin and amoxicillin respectively. Streptococci were the most frequently resistant to amoxicillin (29.3%), and enterococci to penicillin (27%), amoxicillin (27.5%) and amoxicillin/clavulanic acid (23.8%). The resistance of all tested mastitis pathogens to aminopenicillins and penicillin highly correlated (r=0.83). Compared with other antibiotics, amoxicillin and clavulanic acid combination tended to be more effective (p<0.05) against all tested bacteria in vitro. However, S. aureus, in 38.1% of cases, was resistant to this combination of antimicrobials. This study demonstrates that S. epidermidis, S. aureus, S. hyicus, S. agalactiae and E. hirae remain the most frequent mastitis causative agents on Lithuanian cattle farms. The highest resistance in vitro to penicillins was demonstrated by S. aureus, S. hyicus and S. intermedius. Resistance to cephalosporins remains low, irrespective of bacterial species of gram-positive cocci