Characterization of Escherichia coli virulence genes, pathotypes and antibiotic resistance properties in diarrheic calves in Iran

BACKGROUND: Calf diarrhea is a major economic concern in bovine industry all around the world. This study was carried out in order to investigate distribution of virulence genes, pathotypes, serogroups and antibiotic resistance properties of Escherichia coli isolated from diarrheic calves. RESULTS: Totally, 76.45% of 824 diarrheic fecal samples collected from Isfahan, Chaharmahal, Fars and Khuzestan provinces, Iran were positive for E. coli and all of them were also positive for cnf2, hlyA, cdtIII, f17c, lt, st, stx1, eae, ehly, stx2 and cnf1 virulence genes. Chaharmahal had the highest prevalence of STEC (84.61%), while Isfahan had the lowest (71.95%). E. coli serogroups had the highest frequency in 1-7 days old calves and winter season. Distribution of ETEC, EHEC, AEEC and NTEC pathotypes among E. coli isolates were 28.41%, 5.07%, 29.52% and 3.49%, respectively. Statistical analyses were significant for presence of bacteria between various seasons and ages. All isolates had the high resistance to penicillin (100%), streptomycin (98.25%) and tetracycline (98.09%) antibiotics. The most commonly detected resistance genes were aadA1, sul1, aac[3]-IV, CITM, and dfrA1. The most prevalent serogroup among STEC was O26. CONCLUSIONS: Our findings should raise awareness about antibiotic resistance in diarrheic calves in Iran. Clinicians should exercise caution when prescribing antibiotics.

Intraspecies transfer of a chloramphenicol-resistance plasmid of staphylococcal origin.

BACKGROUND & OBJECTIVES: The emergence of antibiotic-resistant bacteria is a phenomenon of concern to the clinician as well as to the pharmaceutical industry, because it is the major cause of failure in the treatment of infectious diseases. The genetic exchange of plasmids containing antibiotic resistant determinants (R-plasmids) between organisms of the same or different species is believed to play a crucial role in the evolution of antibiotic resistant bacteria. Staphylococcus aureus is well known for its multi-drug resistance (MDR). This work was undertaken to study the intraspecies transfer of a chloramphenicol (C) resistance staphylococcal R-plasmid among different clinical isolates of S. aureus. METHODS: From a MDR S. aureus MC524 strain, a small plasmid pMC524/MBM was isolated. Lysostaphin lysis and sucrose mediated detergent lysis were used for plasmid preparation. Agarose gel electrophoresis, transformation experiments, Southern blotting and hybridization were done. Restriction endonuclease (RE) digestions were performed. RESULTS: pMC524/MBM, which codes for C resistance could be transferred into some C sensitive clinical strains of S. aureus. The size and the RE digestion patterns of the plasmids isolated from the S. aureus transformants were identical to those of pMC524/MBM. INTERPRETATION & CONCLUSION: These results suggest that pMC524/MBM, without any modification is capable of transferring, maintaining, replicating and expressing itself in different clinical strains of S. aureus and hence may be responsible for the spread of C resistance.

Plasmid mediated multidrug resistance in Salmonella typhi.

Between September 1989 and February 1991, strains of S. typhi showing multiple drug resistance were isolated from blood cultures of patients with typhoid fever. A total of 283 isolates were obtained over a period of 18 months. Forty four (11%) of these isolates were resistant to chloramphenicol, ampicillin, co-trimoxazole and tetracycline, the first three being drugs currently used in treating typhoid fever. Forty of the 44 multi-resistant strains tested showed transfer of resistance 'en block' to recipient Escherichia coli K 12 (J62-2). All 44 multi-resistant strains were sensitive to ciprofloxacin and ofloxacin. Since the resistance is plasmid-mediated, the problem is likely to get aggravated.