Biomedical subjects

M C Negri

Publications and source records attributed to M C Negri.

21 records · Page 2Linked to original sources

PubMed1995

New extended-spectrum TEM-type beta-lactamase from Salmonella enterica subsp. enterica isolated in a nosocomial outbreak.

A new extended-spectrum beta-lactamase was detected in a lactose-positive Salmonella enterica subsp. enterica strain that caused a nosocomial outbreak involving eight patients in a pediatric cardiology unit. This strain showed high levels of resistance to ceftazidime and aztreonam and relatively low levels of resistance to cefotaxime and ceftriaxone. Resistance was associated with a conjugative plasmid of 59 kb, which encoded a new beta-lactamase with an isoelectric point of 5.9 that strongly hydrolyzed ceftazidime and to a much lesser extent hydrolyzed cefotaxime. The enzyme activity was inhibited by clavulanate. The corresponding bla gene was cloned and sequenced. The deduced amino acid sequence showed three significant amino acid replacements with respect to the TEM-1 sequence: Arg-164-->His, Glu-240-->Lys, and Thr-265-->Met. This combination is unique among extended-spectrum beta-lactamases and served to characterize the new enzyme, TEM-27.

Amino Acid Sequence↗

PubMed1994

In vitro selective antibiotic concentrations of beta-lactams for penicillin-resistant Streptococcus pneumoniae populations.

Therapeutic regimens containing beta-lactam antibiotics are selecting penicillin-resistant Streptococcus pneumoniae populations all over the world. The selective pressure after 4 h of exposure to different concentrations of amoxicillin, cefixime, cefuroxime, and cefotaxime for low-level or high-level penicillin-resistant S. pneumoniae was evaluated in an in vitro model with mixed populations with penicillin susceptibilities of 0.015, 0.5, 1, and 2 micrograms/ml. The antibiotic concentration selecting for low-level resistance strongly reduced the susceptible population. Increasing antibiotic concentrations tended to decrease the total proportion of penicillin-resistant bacteria because of reduced numbers of the low-level-resistant population. The antibiotic concentration selecting for high-level resistance produced fewer resistant populations, but most of the organisms selected represented high-level resistance. In general, amoxicillin was a good selector for the low-level-resistant population and a poor selector for high-level resistance; cefuroxime and cefotaxime were poor selectors for low-level resistance and better selectors than amoxicillin for high-level penicillin resistance. Cefixime was the best selector of low-level penicillin resistance. When only resistant populations were mixed, the strains with high-level resistance were selected even at low antibiotic concentrations. Determination of the effects of selective antibiotic concentrations on mixed cultures of bacteria expressing different antibiotic resistance levels may help researchers to understand the ecology and epidemiology of penicillin-resistant S. pneumoniae populations.

Amoxicillin↗

PubMedDate not supplied

In vitro activity of cefpirome compared with other third generation cephalosporins against nosocomial isolates in Argentina.

The in vitro activity of cefpirome was evaluated against strains that showed conflicting results for third generation cephalosporins. Against isolates with derepressed inducible chromosomal cephalosporinase (n = 40) cefpirome was the sole cephalosporin with an MIC90 in the susceptible range; Klebsiella spp. with plasmid-mediated beta-lactamases (broad spectrum SHV-2 or SHV-2 type) (n = 40) remained most susceptible to ceftizoxime and cefpirome; against aminoglycoside-resistant Pseudomonas aeruginosa (n = 50), cefpirome was as active as ceftazidime and cefoperazone; against oxacillin-susceptible and oxacillin-resistant Staphylococcus spp., (n = 40), cefpirome was more active than other third generation cephalosporins but killing was inadequate against both oxacillin-resistant staphylococci and enterococci.

Argentina↗