Need for annual surveillance of antimicrobial resistance in Streptococcus pneumoniae in the United States: 2-year longitudinal analysis.

Although changing patterns in antimicrobial resistance in Streptococcus pneumoniae have prompted several surveillance initiatives in recent years, the frequency with which these studies are needed has not been addressed. To approach this issue, the extent to which resistance patterns change over a 1-year period was examined. In this study we analyzed S. pneumoniae antimicrobial susceptibility results produced in our laboratory with isolates obtained over 2 consecutive years (1997-1998 and 1998-1999) from the same 96 institutions distributed throughout the United States. Comparison of results revealed increases in resistant percentages for all antimicrobial agents studied except vancomycin. For four of the agents tested (penicillin, cefuroxime, trimethoprim-sulfamethoxazole, and levofloxacin), the increases were statistically significant (P < 0.05). Resistance to the fluoroquinolone remained low in both years (0.1 and 0.6%, respectively); in contrast, resistance to macrolides was consistently greater than 20%, and resistance to trimethoprim-sulfamethoxazole increased from 13.3 to 27.3%. Multidrug resistance, concurrent resistance to three or more antimicrobials of different chemical classes, also increased significantly between years, from 5.9 to 11%. The most prevalent phenotype was resistance to penicillin, azithromycin (representative macrolide), and trimethoprim-sulfamethoxazole. Multidrug-resistant phenotypes that included fluoroquinolone resistance were uncommon; however, two phenotypes that included fluoroquinolone resistance not found in 1997-1998 were encountered in 1998-1999. This longitudinal surveillance study of resistance in S. pneumoniae revealed that significant changes do occur in just a single year and supports the need for surveillance at least on an annual basis, if not continuously.

Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance.

Given the propensity for Enterobacteriaceae and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Enterobacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae except Providencia spp. (

Resistance surveillance of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis isolated in the United States, 1997-1998.

A national antimicrobial resistance surveillance study was conducted from December 1997 to May 1998 to determine the prevalence of antimicrobial resistance in 6620 clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. In this centralized study, which involved 163 institutions located in 43 states, we determined MICs for representatives of five antimicrobial classes: beta-lactams (penicillin, co-amoxiclav, cefuroxime, ceftriaxone), macrolides (azithromycin, clarithromycin), co-trimoxazole, glycopeptides (vancomycin) and fluoroquinolones (levofloxacin). In most S. pneumoniae isolates, all antimicrobials were to be found active, but amongst penicillin-resistant isolates (MICs > or = 2 mg/L), resistance to other beta-lactams, macrolides and co-trimoxazole was common. For vancomycin and levofloxacin, however, activity was not associated with penicillin resistance. The prevalence of penicillin-nonsusceptible (intermediate and resistant) pneumococci was highest in the South Atlantic (44%) and East South Central (43%) regions and lowest in the Mid-Atlantic (28%) and New England (28%) regions. Resistance to beta-lactams, macrolides and co-trimoxazole was more commonly found amongst respiratory isolates than blood isolates and in strains from patients < or = 12 years old than from older patients. beta-lactamase, which was detected in 33% of H. influenzae and 92% of M. catarrhalis strains, did not affect the activity of the beta-lactams under study other than ampicillin. Certain agents, such as vancomycin and the fluoroquinolones, remain highly active, and well-designed surveillance systems that monitor MIC distributions would be needed to detect a potential for reduced susceptibility. In addition, surveillance programmes should be designed to collect information about associated resistance as well as differences in prevalence associated with region, specimen source and patient age.

Molecular characterization of penicillin-resistant Streptococcus pneumoniae isolates causing respiratory disease in the United States.

Three hundred twenty-eight (328) penicillin-resistant Streptococcus pneumoniae isolates collected in 39 states of the United States between October, 1996, and March, 1997, from (mostly adult) patients with respiratory disease were characterized by microbiological, serological, and molecular fingerprinting techniques, including determination of chromosomal macrorestriction pattern with pulsed-field gel electrophoresis (PFGE) and hybridization with DNA probes specific for various antibiotic resistance genes. The overwhelming majority of the isolates were in five serogroups (23, 6, 19, 9, 14). All isolates had penicillin MIC values of at least 2 microg/ml, but the collection also included isolates with MIC values as high as 16 microg/ml. Virtually all isolates (96.6%) were resistant to trimethoprim/sulfamethoxazole (SXT) and many isolates were also resistant to chloramphenicol (43%), tetracycline (55%), and erythromycin (65%). Resistance to levofloxacin was extremely rare. The molecular fingerprinting methods showed that a surprisingly large proportion (167 out of 328, or 50.9%) of the isolates belonged to two international epidemic clones of S. pneumoniae: clone A (127, or 38.7%) with properties indistinguishable from that of the 23F multiresistant "Spanish/USA" clone widely spread in Europe, Asia, Latin America, and South Africa, and clone B (40, or 12.2%) belonging to the "French" serogroup 9/14 clone widely spread in Europe and South America. Virtually all members of clone A were also resistant to chloramphenicol (cat+), tetracycline (tetM+), and SXT, and about 75% were also resistant to erythromycin (mefE+ or ermB+). Close to 30% (39 out of 127) of the clone A isolates expressed anomalous serotypes (primarily serotypes 19 and 14, and nontypable) and most likely represented spontaneous capsular transformants. Most of the 40 isolates (35/40) belonging to clone B expressed serotype 9, with five of the isolates expressing serotypes 14 or 19, or were nontypable. All members of this clone were resistant to penicillin and SXT with only occasional isolates showing resistance to macrolides, tetracycline, and chloramphenicol. The combination of microbiological tests and DNA hybridizations also allowed the identification of unusual strains, for instance, isolates that reacted with the tetM or mefE DNA probes without showing phenotypic antibiotic resistance, an isolate showing phenotypic macrolide resistance without hybridizing with either the ermB or mefE DNA probes, or isolates that hybridized with both of these DNA probes. In addition to clones A and B, another large portion of the S. pneumoniae isolates (112 of 328, or 34.1%) was represented by eight clusters, each with a unique PFGE type. These clusters, together with the clone A and clone B isolates, made up 85% of all the penicillin-resistant isolates identified in this survey in the United States. Both international clones and the unique clusters showed wide geographic dispersal: Clone A was present in 30 of the 39 states and clone B in 18. The data suggest that the major mode of spread of penicillin-resistant pneumococci in the United States is by clonal expansion and that the most significant components (clones A and B) have been imported into the United States from abroad.

Surveillance of antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the United States in 1996-1997 respiratory season. The Laboratory Investigator Group.

A U.S. surveillance study of antimicrobial resistance in respiratory tract pathogens in the respiratory season (1996-1997) is reported that included 11,368 isolates from 434 institutions in 45 states and the District of Columbia. beta-lactamase was produced by 33.4% of Haemophilus influenzae and 92.7% of Moraxella catarrhalis. Of the 9,190 Streptococcus pneumoniae isolates tested, 33.5% were not susceptible to penicillin (MIC > or = 0.12 microgram/mL), with 13.6% having high-level resistance (MICs > 1 microgram/mL). For H. influenzae, the most active antimicrobials (based on percent of strains susceptible) were levofloxacin (100%) and ceftriaxone (99.9%); the least active were ampicillin (67.2%) and clarithromycin (58.1%). For M. catarrhalis, the most active drugs were amoxicillin-clavulanate, ceftriaxone, and levofloxacin (100%); the least active was ampicillin. The order of the activity of the drugs against S. pneumoniae were levofloxacin (97.3%) > ceftriaxone (87.1%) > amoxicillin-clavulanate (81.7%) = clarithromycin (80.9%) > cefuroxime (74.5%) > penicillin (66.5%). The activity of the beta-lactams and clarithromycin against isolates of S. pneumoniae was closely associated with the resistance to penicillin. Levofloxacin was more active against S. pneumoniae overall, because it exhibited no cross-resistance. These data indicate that the incidence of beta-lactamase production in H. influenzae (33.4%) and M. catarrhalis (92.7%) is similar to other recent studies, and that the incidence of penicillin-intermediate and -resistant S. pneumoniae is increasing, particularly the high-level penicillin-resistant (MICs > 1 microgram/mL) strains, which were often multi-resistant.

Possible physiological functions of penicillin-binding proteins in Staphylococcus aureus.

There are four penicillin-binding proteins (PBPs) in Staphylococcus aureus, of which PBPs 2 and 3 are essential. Cefotaxime binds selectively to PBP 2, and cephalexin binds to PBP 3, each at its respective MIC. The morphology of S. aureus strains grown in the presence of the two antibiotics was examined by phase-contrast and scanning electron microscopy. Exposure of the cells to cefotaxime at concentrations at which it bound selectively to PBP 2 resulted in the extrusion of cytoplasm and cell lysis, whereas exposure to cephalexin at concentrations at which it bound exclusively to PBP 3 resulted in cell enlargement and the cessation of septation. The latter morphological response was very similar to that produced by norfloxacin. The results suggest that in S. aureus, PBP 2 may be the primary peptidoglycan transpeptidase, and PBP 3 may be involved in septation.

Morphologic changes produced by amdinocillin alone and in combination with beta-lactam antibiotics: in vitro and in vivo.

Scanning electron microscopy was used to study the morphologic effects of amdinocillin (mecillinam) when combined with several beta-lactam antibiotics in vitro (Escherichia coli, three isolates; Klebsiella pneumoniae, one isolate) and also in vivo (E. coli, one isolate). Ovoid forms were found in the cultures of E. coli and K. pneumoniae following in vitro exposure to amdinocillin. This characteristic in vitro effect was also produced in the amdinocillin-treated E. coli-infected mouse. Varying degrees of filament formation were seen both in vitro and in vivo with the other beta-lactam antibiotics tested. The in vitro combination of amdinocillin with the beta-lactam antibiotics produced morphologic effects on E. coli and K. pneumoniae (enhanced cell distortion and lysis) not seen with the individual agents at the doses tested. Amdinocillin was synergistic with ampicillin, carbenicillin, and cephalothin in mice challenged with E. coli 736; scanning electron microscopy of bacteria from peritoneal lavages of mice treated with these synergistic combinations indicated that the organisms were more enlarged and distorted than those from animals receiving the individual agents. The enhanced morphologic effect observed in vivo was in agreement with the in vitro effect. Viable counts of bacteria recovered from mice treated with ampicillin plus amdinocillin were appreciably less than those from mice treated with each agent alone. The morphologic results from the scanning electron microscopy study point to a synergistic or enhanced effect of amdinocillin in combination with beta-lactam antibiotics and are in accord with prior reports of the synergistic effects of amdinocillin.