Comparative evaluation of etest for susceptibility testing Neisseria meningitidis with eight antimicrobial agents. An investigation using U.S. Food and Drug Administration regulatory criteria

Susceptibilities of invasive Neisseria meningitidis strains to agents used for prophylaxis and to penicillin G

BACKGROUND

The antimicrobial susceptibility of isolates of Neisseria meningitidis to agents used for chemoprophylaxis and to penicillin G was determined.

METHODS

Fifty N. meningitidis strains detected in Nova Scotia between 2004 and 2018 were included. The isolates were originally isolated from sites that might prompt chemoprophylaxis (27 blood, 18 cerebrospinal fluid [CSF], 3 CSF-blood, and 2 conjunctiva). Minimal inhibitory concentrations (MICs) were determined to azithromycin, ciprofloxacin, minocycline, rifampin, trimethoprim-sulfamethoxazole, and penicillin G, using a diffusion gradient strip on Mueller-Hinton agar with 5% sheep blood in 5% CO2 for 20-24 hours.

RESULTS

All isolates remained susceptible to azithromycin, ciprofloxacin, minocycline, and rifampin, but there was 26% resistance to trimethoprim-sulfamethoxazole. There was a rise in penicillin MIC of the isolates over the study period.

CONCLUSION

In our province, N. meningitidis isolates causing invasive infection remain susceptible to commonly used antimicrobial agents used for chemoprophylaxis. Significant resistance to trimethoprim-sulfamethoxazole is present and the degree of susceptibility to penicillin G is lessening.

Have South Australian isolates of Neisseria meningitidis become less susceptible to penicillin, rifampicin and other drugs? A study of strains isolated over three decades, 1971-1999

AIMS

To ascertain whether isolates of Neisseria meningitidis in South Australia (SA) have become less susceptible to antimicrobial agents. The patients studied were children and adults in SA with either meningococcal bacteraemia or meningitis or both.

METHODS

The susceptibility of meningococci to 11 antimicrobial agents, including sulphonamides, penicillin and rifampicin, was tested by agar dilution, and in the case of six of the drugs, by E test also.

RESULTS

Resistance to folate antagonists emerged in 1979 and became very common. Resistance peaked in 1995 at 76% of strains. Relative insusceptibility to penicillin was first encountered amongst strains isolated in 1985, and, while the incidence of such strains increased slightly, the overall incidence was low at 10 (5.2%) of 190 strains tested. Meningococci relatively insusceptible to rifampicin were encountered as early at 1971 and did not become more common. The incidence of such strains at 26 (13.7%) of 189 strains tested was higher than that for penicillin. For the 11-year period 1989-1999 of > or= 84 strains tested all were susceptible to ceftriaxone, chloramphenicol and ciprofloxacin; 98% were susceptible to azithromycin and 97% were susceptible to minocycline. Shifts in MIC values for these drugs were not detected.

CONCLUSIONS

Resistance was common to sulphonamides and co-trimoxazole, however >or=95% meningococci tested were susceptible to drugs commonly used in the treatment of meningococcal disease, including penicillin and ceftriaxone. Relative insusceptibility to rifampicin was more common but did not increase during the 29-year period. For all drugs tested, except rifampicin, there was good agreement between agar dilution and E test results.

Ceftriaxone: an update of its use in the management of community-acquired and nosocomial infections

Ceftriaxone is a parenteral third-generation cephalosporin with a long elimination half-life which permits once-daily administration. It has good activity against Streptococcus pneumoniae, methicillin-susceptible staphylococci, Haemophilus influenzae, Moraxella catarrhalis and Neisseria spp. Although active against Enterobacteriaceae, the recent spread of derepressed mutants which hyperproduce chromosomal beta-lactamases and extended-spectrum beta-lactamases has diminished the activity of all third-generation cephalosporins against these pathogens necessitating careful attention to sensitivity studies. Extensive data from randomised clinical trials confirm the efficacy of ceftriaxone in serious and difficult-to-treat community-acquired infections including meningitis, pneumonia and nonresponsive acute otitis media. Ceftriaxone also has efficacy in other community-acquired infections including uncomplicated gonorrhoea, acute pyelonephritis and various infections in children. In the nosocomial setting, extensive data also confirm the efficacy of ceftriaxone with or without an aminoglycoside in serious Gram-negative infections, pneumonia, spontaneous bacterial peritonitis and as surgical prophylaxis. Outpatient use of ceftriaxone, either as part of a step-down regimen or parenterally, is a distinguishing feature of the data gathered on the agent over the last decade. The review focuses on new applications of the drug and its use in infections in which the causative pathogens or their resistance patterns have changed over the past decade. Ceftriaxone has a good tolerability profile, the most common events being diarrhoea, nausea, vomiting, candidiasis and rash. Ceftriaxone may cause reversible biliary pseudolithiasis, notably at higher dosages of the drug (>/=2 g/day); however, the incidence of true lithiasis is <0.1%. Injection site discomfort or phlebitis can occur after intramuscular or intravenous administration.

CONCLUSIONS

As a result of its strong activity against S. pneumoniae, ceftriaxone holds an important place, either alone or as part of a combination regimen, in the treatment of invasive pneumococcal infections, including those with reduced beta-lactam susceptibility. Its once-daily administration schedule allows simplification of otherwise complex regimens in a hospital setting and has also contributed to its popularity as a parenteral agent in an ambulatory setting. These properties, together with a well characterised tolerability profile, mean that ceftriaxone is likely to retain its place as an important third-generation cephalosporin in the treatment of serious community-acquired and nosocomial infections.

Neisseria meningitidis with decreased susceptibility to penicillin: report from the SENTRY antimicrobial surveillance program, North America, 1998-99

The purpose of this study was to estimate the prevalence of Neisseria meningitidis with decreased susceptibility to penicillin (MIC, >0.06 microg/mL) in North America (NA). Antimicrobial susceptibility testing by Etest (AB BIODISK, Solna, Sweden) was performed on 53 invasive clinical isolates obtained from 11 SENTRY Antimicrobial Surveillance Program participants in NA (9 states, 2 provinces) during 1998-99. All strains were markedly susceptible to ciprofloxacin (MIC(90), 0.008 microg/mL) and cefotaxime (MIC(90), < or = 0.002 microg/mL). Only 54.7% were susceptible to trimethoprim-sulfamethoxazole (TMP/SMX) at < or = 0.5/9.5 microg/mL. One strain was resistant to rifampin (MIC, > 32 microg/mL) and 16 isolates (30.2%) were relatively resistant to penicillin with MICs ranging from 0.094 to 0.25 microg/mL. No beta-lactamase production was detected. The serogroup distribution was 40% Y, 28% B, 24% C, 2% W-135, and 6% of strains were nongroupable. The prevalence of N. meningitidis with decreased susceptibility to penicillin in NA appears higher than previous reports.

Medium compositions and culture conditions for the assay of fosfomycin susceptibility by Etest

The Etest (AB Biodisk, Solna, Sweden), a susceptibility testing method, was used for fosfomycin and was evaluated by comparison with the agar dilution method for 73 clinical isolates of Escherichia coli, including two resistant strains, and an optimal Etest method for fosfomycin was determined. Media and culture conditions greatly affected the minimum inhibitory concentrations (MICs) determined by the Etest for fosfomycin, as shown for the agar dilution methods. Our results showed that the most favorable conditions for the Etest for fosfomycin were with Mueller-Hinton agar (Becton-Dickinson Japan, Tokyo, Japan) under aerobic conditions. However, the MICs for the resistant strains were much higher than those determined by agar dilution methods, using Nutrient agar (Becton-Dickinson Japan) under anaerobic conditions. The addition of glucose-6-phosphate did not significantly affect the Etest results.

Unreliability of disc diffusion test for screening for reduced penicillin susceptibility in Neisseria meningitidis

The 2-U penicillin and microgram oxacillin discs proposed for screening meningococci for susceptibility to penicillin were evaluated by using MICs measured by the E test. The discs yielded unacceptably high frequencies of misclassification of susceptibility category and should be abandoned in favor of MIC estimations. An agreed breakpoint for reduced penicillin susceptibility in meningococci is needed for the E test.