IMPORTANCE When blood cultures are flagged as positive, they are incubated on solid media to produce enough biomass of the bacterium for identification and susceptibility testing. However, using only Choc is disadvantageous when the shortest incubation times to identification are strived for. When only one agar plate is used for short incubation of positive blood cultures, Choc may represent a compromise in terms of time to high-confidence identification by MALDI-TOF MS and the bacterial spectrum that is covered. However, the difference from results obtained with Choc was not statistically significant. The shortest median time to high-confidence identification (score of ≥2) was achieved on MAC for Gram-negative rods (2.0 h range, 1.9 to 4.2 h) and on CBA for Gram-positive cocci (4.0 h range, 1.9 to 25.0 h). A total of 187 blood cultures with Gram-positive cocci ( n = 124) and Gram-negative rods ( n = 63) were included in the final analysis. Exclusion criteria were (i) false-positive blood cultures, (ii) mixed cultures with different species, (iii) growth of anaerobes/fungi, and (iv) a total number of isolates of one group (i.e., Gram-positive/-negative cocci/rods) of <30. Positive aerobic/anaerobic blood cultures (2 drops = 50 μl) were incubated on CBA, Choc, MAC, and the required time of incubation to low-confidence identification (score of ≥1.7 to <2) and high-confidence identification (score of ≥2) by MALDI-TOF MS was measured. We therefore compared the time to species identification of blood cultures incubated on CBA, Choc, and MacConkey agar (MAC, for Gram-negative rods). Although Columbia blood agar (CBA) and chocolate agar (Choc) are widely used, a direct comparison of standard agars is lacking. range of the quinolone ciprofloxacin does not exceed 6 micrograms/ml.Short incubation of positive blood cultures on solid media is now increasingly applied to speed up species identification by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The minimal inhibitory concentrations (M.I.C.) of gentamicin, cephalothin, cefotaxime, ceftazidime ceftriaxone and sulfamethoxazole-trimethoprim do not exceed the range of 30 micrograms/ml. Low resistance is still seen in all above bacteria against ciprofloxacin and ofloxacin. Resistance frequencies of above 20% were found in Enterobacter and Pseudomonas for the newer antimicrobial agents such as: ceftriaxone, cefotaxime or ceftazidime. As for tobramycin, amikacin and mezlocillin, it is clear that the Gram negative bacteria have gained resistance to these drugs over recent years. In UPGNB, Klebsiella and Pseudomonas a significant increase in resistant isolates to cephalothin, gentamicin, sulfamethoxazole-trimethoprim and chloramphenicol was found. A significant rise in frequency of cephalothin and sulfamethoxazole-trimethoprim resistant E. coli was most predominant in both surveys in the internal wards while UPGNB were predominant in the geriatric-rehabilitation wards. coli, Urea positive Gram negative bacteria (UPGNB) Klebsiella, Enterobacter, Pseudomonas (in a decreasing order). The order of Gram negative frequencies was E. Gram negative rods accounted for 68% of the septicemia cases indicating a small increase since the former survey (61.2%). In addition, a comparison was made with a previous survey performed twelve years ago (1976-1978). This study reviews 2205 significant positive blood cultures from 534 patients treated at the Meir General Hospital during the period 1988-1990.
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