Chromogenic Cephalosporin Method Research Articles

Comparison of three different methods to detect the production of ?-lactamase enzyme by staphylococci

Production ?-lactamase enzyme is the most common and important mode of exhibiting resistance to ?-lactam antibiotics. Manifestation of this enzyme is difficult to demonstrate in routine antibiotic sensitivity testing. Sensitivity to penicillin is not sufficient to indicate whether this antibiotic should be used clinically and main factor compromising the clinical efficacy of these drugs is the production of ?-lactamase enzyme. Only feasible method for determination of ?-lactam resistance is to demonstrate the physical presence of enzyme. Three different methods (acidometric method, iodometric method and chromogenic cephalosporin method) are available for this. The objective of present study is to compare these 3 method to detect the production of ?-lactamase enzyme in staphylococci isolated from various clinical samples. Susceptibility to penicillin, oxacillin and vancomycin was also determined. Out of total 150 isolates, 114(76%) shows ?-lactamase production by chromogenic cephalosporin method, 110(73.3%) by iodometric method and 108(72%) by acidometric method. Penicillin and oxacillin resistance was 74.6% and 53.3% respectively. All isolates are sensitive to vancomycin. Out of three different methods used, chromogenic cephalosporin method is more sensitive (76%) than iodometric method (73.3%) and acidometric method (72%). Results also correlates with penicillin sensitivity in ABST except 2 isolates which shows ?-lactamase production by chromogenic cephalosporin method but remains penicillin sensitive in disc diffusion method. In case of agar diffusion tests, there is often insufficient ?-lactamase production from the test organism before an inhibitory concentration of antibiotic has diffused from the disc. Only ABST can lead to therapeutic failure sometimes.

Beta-lactamase production Haemophilus spp. and resistance to ampicillin in a general hospital in Porto Alegre city, RS, Brazil (2001-2005)

In a four-year period (July/2001-June/2005), 410 Haemophilus spp. isolates were studied. Those were isolated from sputum at Hospital Nossa Senhora da Conceição (NSC) in Porto Alegre city (RS). beta-lactamase enzyme was detected in 113 (27.6%) of isolates through chromogenic cephalosporin method. Fifty-eight (51.3%) of them showed sensibility to ampicillin through disc-diffusion method using Haemophilus Test Medium (HTM) by NCCLS criteria. In 297 (72.4%) isolates beta-lactamase was not detected by chromogenic cephalosporin method. Five (1.7%) of them were resistant and 1 (0.3%) intermediate to ampicillin using disc-diffusion method. The authors emphasized the importance of Haemophilus spp. resistance to ampicillin research in clinical laboratories routine and the use of more than one method for this analysis was proposed, due to different resistance mechanisms in Haemophilus spp.

Activities of beta-lactams against Acinetobacter genospecies as determined by agar dilution and E-test MIC methods.

The agar dilution MIC method was used to test activities of ticarcillin, ticarcillin-clavulanate, amoxicillin, amoxicillin-clavulanate, ampicillin, ampicillin-sulbactam, piperacillin, piperacillin-tazobactam, inhibitors alone, ceftazidime, and imipenem against 237 Acinetobacter genospecies. A total of 93.2% of strains were beta-lactamase positive by the chromogenic cephalosporin method. Overall, ampicillin-sulbactam was the most active combination against all strains (MIC at which 50% of the isolates are inhibited [MIC50] and MIC90, 4.0 and 32.0 microg/ml; 86.9% susceptible at < or = 16 microg/ml), followed by ticarcillin-clavulanate (16.0 and 128.0 microg/ml; 85.7% susceptible at < or = 64 microg/ml), piperacillin-tazobactam (16.0 and 128.0 microg/ml; 84.8% susceptible at < or = 64 microg/ml), and amoxicillin-clavulanate (16.0 and 64.0 microg/ml; 54.4% susceptible at < or =16 microg/ml). Ceftazidime and imipenem yielded MIC50s and MIC90s of 8.0 and 64.0 microg/ml (ceftazidime) and 0.5 and 1.0 microg/ml (imipenem), respectively; 71.3% of strains were susceptible to ceftazidime at < or = 16 microg/ml, and 99.2% were susceptible to imipenem at < or = 8 microg/ml. Sulbactam was the most active beta-lactamase inhibitor alone (MIC50 and MIC90, 2.0 and 16.0 microg/ml); clavulanate and tazobactam were less active (16.0 and 32.0 microg/ml for both compounds). Enhancement of beta-lactams by beta-lactamase inhibitors was not always seen in beta-lactamase-positive strains, and activity of combinations such as ampicillin-sulbactam was due to the inhibitor alone. Acinetobacter baumannii was the most resistant genospecies. By contrast, Acinetobacter haemolyticus, Acinetobacter calcoaceticus, Acinetobacter johnsonii, Acinetobacter junii, Acinetobacter radioresistens, and other non-Acinetobacter baumannii strains were more susceptible to all compounds tested. E-test MICs were within 1 dilution of agar dilution MICs in 38.4 to 89.6% of cases and within 2 dilutions in 61.6 to 98.6% of cases.

Influence of β-lactamase inhibitors on the activity of oxacillin against methicillin-resistant Staphylococcus aureus

We studied the in vitro susceptibility to oxacillin of 46 isolates of methicillin-resistant Staphylococcus aureus (MRSA) isolates with a minimum inhibitory concentration (MIC) >8 μg/ml of oxacillin, with and without adding clavulanic acid, sulbactam, or tazobactam in three different concentrations (2, 4, and 8 μg/ml). All 46 strains were found by the rapid chromogenic cephalosporin method to be β-lactamase producers. For those strains with low-level resistance (MIC of 16 or 32 μg/ml), the MICs of oxacillin decreased four- to 32-fold and two- to 32-fold after adding sulbactam and tazobactam, respectively. For those with high-level resistance (MIC of ⩾64 μg/ml), the MICs either did not change or decreased only two-fold after we added one of three β-lactamase inhibitors. The results suggest that β-lactamase production probably plays a role in resistance to oxacillin in those MRSA strains of low-level oxacillin resistance.

Susceptibility of urine isolates of Staphylococcus saprophyticus to antimicrobial agents

The minimum inhibitory concentrations (MICs) of 10 antimicrobial agents for 96 urinary isolates of Staphylococcus saprophyticus cultured from symptomatic females in the Western Australian general community are reported. All antimicrobial agents tested showed good activity, with the exceptions of norfloxacin (MIC90 8 mg/L) and ampicillin (MIC90 0.5 mg/L). Eighty-three of 96 isolates were susceptible to all antimicrobial agents tested. One isolate was resistant to both tetracycline and trimethoprim. The remainder were resistant to a single antimicrobial agent; 10 to tetracycline and 2 to trimethoprim. None of the isolates exhibited any detectable beta-lactamase activity when tested by the chromogenic cephalosporin method. Synergy between trimethoprim and sulphafurazole against Staph. saprophyticus was demonstrated in only 2 of 5 strains having an increased MIC of one or both of these agents.

Susceptibility of campylobacter jejuni to twenty-three antimicrobial agents

Twenty-three antimicrobial agents, including 4 new broadspectrum beta-lactam antibiotics were tested against 50 clinical isolates of Campylobacter jejuni. The activity of metabolites of metronidazole and tinidazole was also tested. Minimum inhibitory concentrations (MIC) were determined by agar dilution. beta-lactamase production was detected by a chromogenic cephalosporin method. All strains were susceptible to erythromycin, clindamycin, chloramphenicol, furazolidone, aminoglycosides (including gentamicin), cefotaxime and NF-thienamycin. All isolates were resistant to penicillin, cephalothin, cefoperazone, vancomycin, rifampicin and trimethoprim; beta-lactamase was detected in 2% of isolates. Some strains were resistant and others sensitive to the other drugs tested, which included ampicillin, moxalactum tetracycline, metronidazole and tinidazole. The 'hydroxy' metabolites of metronidazole and tinidazole were more active than the parent compounds.

A comparison of three rapid methods for the detection of beta-lactamase activity in Haemophilus influenzae.

Three methods for rapidly detecting beta-lactamase activity in Haemophilus influenzae are compared. The chromogenic cephalosporin method was found to be the most easily performed and the reagents could be stored for up to three weeks. The phenol red method was simple to perform but the iodometric method was more time consuming. All three tests gave identical results.