Isolation of Neisseria meningitidis strains with increase of penicillin minimal inhibitory concentrations

Moderately penicillin-resistant Neisseria meningitidis was responsible for an outbreak of meningococcal disease in Saskatoon, Saskatchewan, Canada in 1993. We tested fully susceptible and moderately resistant strains of N. meningitidis against ciprofloxacin, cefotaxime, ceftriaxone, chloramphenicol, penicillin, and rifampin. Eighteen percent of the isolates were moderately resistant to penicillin (MIC, >0.06 g/ml) whereas susceptibility was 100% for the other agents tested.Neisseria meningitidis with decreased susceptibility to penicillin (moderate resistance) was recognized in Spain in 1985 (9, 10) and subsequently in other countries (10) including Canada (8) and the United States (3, 4). In 1993, an outbreak of meningococcal disease occurred in Saskatoon, Saskatchewan, Canada, and the majority of the isolates (serogroup C, enzyme electrophoretic type 15) were found to have decreased susceptibility to penicillin (2). Pulsed-field gel electrophoresis showed that all isolates with decreased susceptibility had the same genomic fingerprints following digestion with any of three separate restriction enzymes and that the genomic fingerprints of isolates not showing decreased susceptibility were different.Ciprofloxacin is a 4-fluoroquinolone antimicrobial agent that has broad-spectrum activity against gram-positive and gram-negative bacteria. For N. meningitidis, MICs were reported to range from Ͻ0.002 to 0.012 g/ml (3). Previously, Pugsley et al. (6) and Renkonen et al. (7) evaluated ciprofloxacin for the treatment of nasopharyngeal carriage of N. meningitidis in studies that showed ciprofloxacin to be highly efficacious for this purpose. With the discovery of the Saskatoon isolates showing decreased susceptibility to penicillin, we were interested in determining if this change had any effects on the in vitro activity of ciprofloxacin. We undertook a study to investigate the in vitro activity of ciprofloxacin against N. meningitidis isolates that were either fully susceptible or showing reduced susceptibility to penicillin and compared the results with those for penicillin, cefotaxime, ceftriaxone, chloramphenicol, and rifampin.A total of 78 N. meningitidis isolates from three different geographical regions of Canada were tested: 30 from British Columbia, provided by J. A. Smith; 32 from Nova Scotia, provided by K. Forward and D. Haldane; and 16 from Saskatchewan. Ten of the isolates from Saskatchewan were identical by pulsed-field gel electrophoresis, and the MICs for these isolates ranged 0.12 to 0.25 g/ml. One of these ten isolates was included in testing to determine the susceptibility rates.The MICs of ciprofloxacin for N. meningitidis were determined by three separate methods: Microscan MIC Plus (Baxter Diagnostics, Inc., Deerfield, Ill.) type 2 panels, agar dilution, and E test (AB Biodisk, Solna, Sweden). The MICs of cefotaxime, ceftriaxone, chloramphenicol, penicillin, and rifampin were determined by using only the E test. The Microscan MIC panels were used according to the manufacturer's instructions, and i...

supporting

confidence: 92%

In vitro activities of ciprofloxacin, cefotaxime, ceftriaxone, chloramphenicol, and rifampin against fully susceptible and moderately penicillin-resistant Neisseria meningitidis

Blondeau

Yaschuk

1995

“…After describing a meningococcal isolate in 1985 with an MIC of penicillin of 0.2 ,ug/ml and nine isolates in 1986 with MICs of penicillin between 0.2 and 0.4 p,g/ml (0.4 and 5.3%, respectively, of strains isolated from patients and studied over the years), the percentages of moderately resistant strains (Penr) increased 7 and 20% during successive years (1987 to 1989) (12,14; J. A. Saez-Nieto, submitted for publication).…”

mentioning

confidence: 99%

Neisseria lactamica and Neisseria polysaccharea as possible sources of meningococcal beta-lactam resistance by genetic transformation

Sáez-Nieto

Luján

Martı́nez-Suárez

et al. 1990

We studied the susceptibilities of relatively penicillin G-resistant and -susceptible strains of Neisseria meningitidis, as well as Neisseria lactamica and Neisseria polysaccharea, to penicillin, ampicillin, and several cephalosporins. The MICs of penicillin, ampicillin, cephalothin, and cefuroxime for moderately resistant meningococci have increased two- to sixfold in relation to MICs for susceptible strains. For these strains of meningococci, N. lactamica, and N. polysaccharea, penicillin, ampicillin, cephalothin, and cefuroxime MICs for 50 and 90% of strains were similar. By genetic transformation of a penicillin-susceptible strain of N. meningitidis to low-level penicillin resistance with DNA from penicillin-resistant strains of N. meningitidis, N. lactamica, N. polysaccharea, and N. gonorrhoeae, isogenic strains with the same pattern of resistance to beta-lactams were obtained, suggesting that these commensal Neisseria spp. could be the source of meningococcal resistance genes.

“…Meningococci were considered moderately susceptible to penicillin and/or ampicillin when MICs of both antibiotics were 20.12 ,ug/ml and fully susceptible when MICs were .0.06 ,ug/ml (2,8,(11)(12)(13)(14)(15) …”

Section: Methodsmentioning

confidence: 99%

Discriminative criteria for Neisseria meningitidis isolates that are moderately susceptible to penicillin and ampicillin

Campos

Trujillo

Seuba

et al. 1992

The prevalence of Neisseria meningitidis isolates that are moderately susceptible to penicillin and ampicillin has increased very quickly in Spain; the current prevalences in our hospital are 48.4 and 55.6%, respectively. We studied the reliability of the disk diffusion method for discriminating between fully susceptible (MIC, .0.06 ,ug/ml) and moderately susceptible (MICs, 0.12 to 1.0 pg/ml) isolates. Thirty-eight isolates (12 Pens AmpS, 18 Penr Ampr, and 8 Pen' Ampr) were assayed by the disk diffusion and plate dilution methods by use of disks of 1, 2, 5, and 10 U of penicillin, 2 and 10 pg of ampicillin, and 1 pg of oxacillin on Mueller-Hinton agar with or without 5% sheep blood. Breakpoints were generated, and their discriminative values were determined with a collection of 195 meningococcal strains isolated consecutively from cerebrospinal fluid or blood. None of the strains produced 1-lactamase. Penicillin-and ampicillin-susceptible strains (MIC, <0.06 ,ug/ml) had oxacillin inhibition zones of >11 mm on blood agar. Moderate susceptibility to ampicillin and penicillin was suggested by an inhibition zone of < 10 mm around the 1-,ug oxacillin disk and an inhibition zone of .26 mm around the 2-U penicillin disk. We conclude that discrimination between fuly susceptible and moderately susceptible populations ofN. meningitidis can be accomplished by the disk diffusion method by use of Mueller-Hinton agar plus 5% sheep blood with the 1-,ug oxacillin disk (which is especially suited for screening methods) and the 2-U penicillin disk. The lack of an oxacillin inhibition zone indicates moderate susceptibility to either penicillin or ampicillin or both.Neisseria meningitidis isolates that are moderately susceptible to penicillin (MIC, 20.12 jg/ml) have been described in the last few years in Spain, England, and South Africa (1, 3, 11-13, 15, 16). Most of these isolates do not produce ,-lactamase, and modifications of the penicillinbinding proteins are believed to be a major mechanism of resistance (4, 5, 13). Current penicillin MICs for moderately susceptible isolates (0.12 to 1.0 ug/rml) are only 2-to 20-fold higher than that for the fully susceptible ones (.0.06 ,ug/ml) (8,(13)(14)(15).With regard to penicillin and ampicillin susceptibilities, three phenotypes have been described in N. meningitidis: susceptible to penicillin and ampicillin (Pens AmpS), moderately susceptible to both penicillin and ampicillin (Penr Ampr), and susceptible to penicillin and moderately susceptible to ampicillin (Pen' Ampr) (11, 14). The existence of Pen' Ampr strains (penicillin MIC, <0.06 ,ug/ml; ampicillin MIC, >0.12 ,ug/ml) is well documented (11,(13)(14)(15) moderately susceptible populations are of clinical and epidemiological interest. In the present study, we addressed the question of whether the three phenotypes mentioned above can be reliably discriminated by the disk susceptibility testing method. MATERIALS AND METHODSStrains. Identification of strains as N. meningitidis was carried out by standard bacteriological methods. ...