E. coli strains isolated from 5-day-old and 30-day-old healthy calves were tested for antibiotic resistance and H-factor mediated antibiotic resistance. An average of 1.6 antibiotic-resistant strains and 1.1 strains with transferable antibiotic resistance were isolated from each of the investigated calves. In comparison with the 30-day-old calves, the 5-day-old calves had significantly more strains with transferable antibiotic resistance (95.8 percent as against 63.4 percent). The R+ strains isolated from the younger calves transferred significantly more en bloc (43.5 percent as against 10.0 percent) and double plus multiple resistance (5292 percent as against 24.4 percent) than did those isolated from the older calves. The most common resistance was to sulphonamide and tetracycline and the most common transferred resistance was to sulphonamide.
A collection of 178 pneumococcal isolates found in Norway during the period 1987-1994 were tested for their susceptibility to benzylpenicillin, macrolides (azithromycin, clarithromycin, dirithromycin, erythromycin, roxithromycin, spiramycin), fluoroquinolones (ciprofloxacin, sparfloxacin), imipenem, chloramphenicol, and vancomycin by a standard agar dilution procedure. To benzylpenicillin, two strains (1%) showed resistance and 14 strains (8%) intermediate susceptibility. Towards erythromycin, eight strains (4%) showed resistance and four strains (2%) intermediate susceptibility. Cross-resistance was demonstrated among the macrolides. Among the fluoroquinolones, intermediate susceptibility occurred with 42% of the isolates for sparfioxacin and 90% for ciprofloxacin; to the latter 5.1% proved resistant. The sum of intermediate and highly resistant isolates was 53% for chloramphenicol. Both penicillin-resistant strains were isolated during the last 2 years of collection and came from patients of non-Norwegian ethnic background. Imported strains appeared over represented among the strains resistant to penicillin and macrolides. Only imipenem and vancomycin showed full susceptibility for all pneumococci tested. An over representation of serogroup 6 strains was apparent among the strains with intermediate susceptibility and high resistance to benzylpenicillin. It is apparent that high-level resistance has, not so far, become a difficult problem in Norway. Nevertheless, the situation requires monitoring of the resistance level, particularly in meningitis and septic patients, and certainly in patients who cntail a higher than usual possibility of acquiring pneumococci from pools of resistant strains outside Norway (visitors, immigrants and recent returness from abroad).
The emergence of ampicillin and chloramphenicol resistant Haemophilus influenzae type b in Denmark has created demands for alternative treatments of serious infections with H. influenzae. In this study 102 strains of H. influenzae recovered from cerebrospinal fluid (85) and blood (17) were tested for susceptibility to ampicillin, piperacillin, erythromycin, rifampicin, chloramphenicol, cefuroxime, cefotaxime, ceftazidime, ceftriaxone, moxalactam, aztreonam, and netilmicin by means of the agar dilution method. The majority (97%) was H. influenzae type b and of these strains 94% belonged to biotype I. Nine of the investigated strains were beta-lactamase producers. Ceftriaxone and cefotaxime were the most active agents (MIC90 less than or equal to 0.025 microliter/ml) followed by moxalactam and aztreonam (MIC90 = 0.1 microgram/ml). Except for ampicillin and piperacillin, the MIC was similar for beta-lactamase producers and non-producers. Several of the investigated antibiotics, especially some of the third generation cephalosporins, might constitute valid therapeutical alternatives to conventional drugs in the treatment of severe H. influenzae infections.
One hundred and nine strains of Haemophilus influenzae recovered from clinical specimens were examined for antibiotic sensitivity pattern and capsular types. All strains from blood cultures, cerebrospinal fluid and a joint aspirate were type b whereas most of the isolates were acapsular when recovered from other specimens viz. wound secretions (67%), maxillary sinus (75%), lower resp tract (86%), nasal cavity (90%). Out of the 109 strains 88 (81%) were non-typable, and 3.6% were beta-lactamase-producing, two of which were type e, one was type b and one was acapsular. Three beta-lactamase-producing strains were isolated from specimens from the respiratory tract and one from blood cultures. Beta-lactamase-producing strains including one chloramphenicol-resistant strain harboured similar plasmids, as judged by agarose gel electrophoresis. The strains showed quite a uniform sensitivity to antibacterial agents with the exception of sulphonamides to which the capsular strains, particularly type b strains, were less susceptible.
Collections of 589 human and 204 animal strains of Salmonella isolated in Ontario during the summer of1974 were examined for susceptibility to 12 antimicrobial agents. Many isolates were found to be resistant to both chloramphenicol (12.4% of the human and 38.2% of the animal sample) and ampicillin. The chloramphenicol resistance almost always occurred in strains which were also resistant to ampicillin and was usually due to a self-transmissible plasmid with a resistance pattern of CmKmSmTc (chloramphenicol, kanamycin, streptomycin, and tetracycline) or CmTc. Ampicillin resistance in these strains was mediated by a variety of plasmids with patterns ApSu (ampicillin and sulfa drugs) and ApSmSu, many of which were nonself-transmissible. Ampicillin resistance in chloramphenicol-sensitive strains was transferable from 21% of the strains, and it was associated with resistance patterns which were different from the self-transferable ampicillin patterns from the chloramphenicol-resistance strains.