The accuracy of antimicrobial susceptibility data submitted by microbiology laboratories to national and international surveillance systems has been debated for a number of years. To assess the accuracy of data submitted to the World Health Organization by users of the WHONET software, the Centers for Disease Control and Prevention distributed six bacterial isolates representing key antimicrobial-resistance phenotypes to approximately 130 laboratories, all but one of which were outside of the United States, for antimicrobial susceptibility testing as part of the World Health Organization's External Quality Assurance System for Antimicrobial Susceptibility Testing. Each laboratory also was asked to submit 10 consecutive quality control values for several key organism-drug combinations. Most laboratories were able to detect methicillin (oxacillin) resistance in Staphylococcus aureus, high-level vancomycin resistance in Enterococcus faecium, and resistance to extended-spectrum cephalosporins in Klebsiella pneumoniae. Many laboratories, particularly those using disk diffusion tests, had difficulty in recognizing reduced susceptibility to penicillin in an isolate of Streptococcus pneumoniae. The most difficult phenotype for laboratories to detect was reduced susceptibility to vancomycin in an isolate of Staphylococcus epidermidis. The proficiency testing challenge also included a request for biochemical identification of a gram-negative bacillus, which most laboratories recognized as Enterobacter cloacae. Although only a small subset of laboratories have submitted their quality control data, it is clear that many of these laboratories generate disk diffusion results for oxacillin when testing S. aureus ATCC 25923 and S. pneumoniae ATCC 49619 that are outside of the acceptable quality control range. The narrow quality control range for vancomycin also proved to be a challenge for many of the laboratories submitting data; approximately 27% of results were out of range. Thus, it is important to establish the proficiency of laboratories submitting data to surveillance systems in which the organisms are tested locally, particularly for penicillin resistance in pneumococci and glycopeptide resistance in staphylococci.Resistance to a variety of antimicrobial agents is emerging in bacterial pathogens throughout the world (8,21,50). Increases in the prevalence of penicillin resistance in Streptococcus pneumoniae (13,36,39,47), methicillin resistance in Staphylococcus aureus (1, 3, 38), vancomycin resistance in enterococci (5, 9, 16, 28), extended-spectrum ␤-lactamase-production in enteric gram-negative bacilli (2, 18, 37), and fluoroquinolone resistance in Neisseria gonorrhoeae (17) are just a few examples of the rising problem of resistance documented by both national and international surveillance systems in the past few years. The antimicrobial susceptibility testing data collected by the various surveillance systems are generated in several different fashions. In some systems, bacterial isolates are sent to a central labo...

We determined the patterns of antimicrobial susceptibility of 65 isolates of Bacillus anthracis (50 historical and 15 recent U.S. clinical isolates) to nine antimicrobial agents using the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution reference method. The results for the 50 historical B. anthracis isolates obtained by the broth microdilution method were compared to those generated by the Etest agar gradient diffusion method. One isolate of B. anthracis was ␤-lactamase positive and resistant to penicillin (MIC, 128 g/ml); a second isolate, which was ␤-lactamase negative, was borderline penicillin resistant, with the penicillin MICs for the isolate varying from 0.12 to 0.25 g/ml; and the remainder of the isolates were ␤-lactamase negative and penicillin susceptible (MICs, <0.12 g/ml). Approximately 78% of the isolates showed reduced susceptibility to ceftriaxone (MICs, >16 g/ml). All B. anthracis isolates were susceptible to chloramphenicol (MICs, <8 g/ml), ciprofloxacin (MICs, < 1 g/ml), clindamycin (MICs, <0.5 g/ml), rifampin (MICs, <0.5 g/ml), tetracycline (MICs, <0.06 g/ml), and vancomycin (MICs, <2 g/ml) by use of NCCLS breakpoints for staphylococci. All 15 recent B. anthracis isolates from the United States were susceptible to penicillin, doxycycline, and ciprofloxacin. By use of the susceptibility breakpoint for staphylococci of <0.5 g/ml, 97% of the B. anthracis isolates tested would have been categorized as intermediate to erythromycin. No statistically significant difference was found between the results of broth microdilution testing and the results of the Etest method for any of the antimicrobial agents tested; however, the results for penicillin obtained by the Etest were 1 to 9 dilutions lower than those obtained by the broth microdilution method. The differences in the penicillin MICs by the Etest method and the difficulties of reading the Etest results through the glass of a biological safety cabinet may limit the utility of this alternate susceptibility testing method for B. anthracis isolates.

Extended-spectrum β-lactamases (ESBLs) are enzymes produced in some gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. They are most common inKlebsiella spp. and Escherichia coli but are present in a variety of Enterobacteriaceae. Resistance mediated by these enzymes can be difficult to detect depending on the antimicrobial agents tested. AmpC β-lactamases are related to the chromosomal enzymes of Enterobacter andCitrobacter spp. and also mediate resistance to extended-spectrum cephalosporins and aztreonam in addition to cephamycins, such as cefoxitin. Unlike ESBLs, however, AmpC β-lactamases are not inhibited by clavulanic acid or other similar compounds. To assess the abilities of various antimicrobial susceptibility testing methods to detect ESBLs, we sent three ESBL-producing organisms, one AmpC-producing organism, and a control strain that was susceptible to extended-spectrum cephalosporins to 38 laboratories in Connecticut for testing. Eight (21.0%) of 38 labs failed to detect extended-spectrum cephalosporin or aztreonam resistance in any of the ESBL- or AmpC-producing isolates. Errors were encountered with both automated and disk diffusion methods. Conversely, seven (18.4%) labs categorized at least some of the four resistant isolates as potential ESBL producers and reported the results with the extended-spectrum cephalosporins and aztreonam as resistant as suggested by current National Committee for Clinical Laboratory Standards (NCCLS) guidelines. The percentage of laboratories that failed to detect resistance in the ESBL or AmpC isolates ranged from 23.7 to 31.6% depending on the type of enzyme present in the test organism. This survey suggests that many laboratories have difficulty detecting resistance in ESBL and AmpC-producing organisms and may be unaware of the NCCLS guidelines on modifying susceptibility testing reports for ESBL-producing strains.

Objective: The aim of this study was to identify potential bacterial isolates and their antimicrobial susceptibility pattern among patients who visited eye clinic of Gondar university hospital. Results: From year of January 2009 to January 2019 a total of 319 eye discharge specimens were submitted for microbiological analysis, of which 133(41.7%) were culture positive. A total of 42(31.6%) Gram negatives and 91(68.4%) Gram-positive bacteria were isolated. Among isolated Gram-negative bacterial species, Klebsiella spp was the most predominant, 42.9% followed by E. coli 26.2%. Among isolated Gram-positive pathogenic bacterial species, S. aureus was the most prevalent, 59.5% followed by S. pyogenes , 8% and S. pneumoniae , 5.5%. Most of the bacterial isolates were resistant to cotrimoxazole, 81.6%, amoxicillin, 78.7%, tetracycline,76.2%, and ampicillin 75.9%. About 47.4 % of bacterial isolates showed multi drug resistance to three or more classes of antimicrobials. Antimicrobials like: ampicillin, amoxicillin, ceftriaxone, ciprofloxacin, and norfloxacin exhibited year to year increment of resistance (p<0.0001).