Clinical perspectives on penicillin tolerance

Image-Based Dynamic Phenotyping Reveals Genetic Determinants of Filamentation-Mediated β-Lactam Tolerance

Antibiotic tolerance characterized by slow killing of bacteria in response to a drug can lead to treatment failure and promote the emergence of resistance. β-lactam antibiotics inhibit cell wall growth in bacteria and many of them cause filamentation followed by cell lysis. Hence delayed cell lysis can lead to β-lactam tolerance. Systematic discovery of genetic factors that affect β-lactam killing kinetics has not been performed before due to challenges in high-throughput, dynamic analysis of viability of filamented cells during bactericidal action. We implemented a high-throughput time-resolved microscopy approach in a gene deletion library of Escherichia coli to monitor the response of mutants to the β-lactam cephalexin. Changes in frequency of lysed and intact cells due to the antibiotic action uncovered several strains with atypical lysis kinetics. Filamentation confers tolerance because antibiotic removal before lysis leads to recovery through numerous concurrent divisions of filamented cells. Filamentation-mediated tolerance was not associated with resistance, and therefore this phenotype is not discernible through most antibiotic susceptibility methods. We find that deletion of Tol-Pal proteins TolQ, TolR, or Pal but not TolA, TolB, or CpoB leads to rapid killing by β-lactams. We also show that the timing of cell wall degradation determines the lysis and killing kinetics after β-lactam treatment. Altogether, this study uncovers numerous genetic determinants of hitherto unappreciated filamentation-mediated β-lactam tolerance and support the growing call for considering antibiotic tolerance in clinical evaluation of pathogens. More generally, the microscopy screening methodology described here can easily be adapted to study lysis in large numbers of strains.

High-throughput time-resolved morphology screening in bacteria reveals phenotypic responses to antibiotics

Image-based high-throughput screening strategies for quantifying morphological phenotypes have proven widely successful. Here we describe a combined experimental and multivariate image analysis approach for systematic large-scale phenotyping of morphological dynamics in bacteria. Using off-the-shelf components and software, we established a workflow for high-throughput time-resolved microscopy. We then screened the single-gene deletion collection of Escherichia coli for antibiotic-induced morphological changes. Using single-cell quantitative descriptors and supervised classification methods, we measured how different cell morphologies developed over time for all strains in response to the β-lactam antibiotic cefsulodin. 191 strains exhibit significant variations under antibiotic treatment. Phenotypic clustering provided insights into processes that alter the antibiotic response. Mutants with stable bulges show delayed lysis, contributing to antibiotic tolerance. Lipopolysaccharides play a crucial role in bulge stability. This study demonstrates how multiparametric phenotyping by high-throughput time-resolved imaging and computer-aided cell classification can be used for comprehensively studying dynamic morphological transitions in bacteria.

Clinical significance of tolerant strains of streptococci in adults with infective endocarditis

OBJECTIVES

To compare the characteristics of patients with endocarditis due to tolerant and non-tolerant Streptococcus strains.

PATIENTS AND METHODS

A retrospective nine-year study was conducted in a single tertiary-care hospital. The study included 24 cases of streptococcal endocarditis with known beta-lactam minimal inhibitory and bactericidal concentrations.

RESULTS

Ten of the 24 patients concerned were infected with tolerant streptococcal strains, and 14 with non-tolerant strains. Bacterial tolerance was not associated with higher mortality or increased frequency of surgery. Fewer patients infected with tolerant than non-tolerant strains had serum bactericidal titers reaching success-predictive levels, and more of these experienced failure of initial antibiotic treatment and needed longer treatment.

CONCLUSIONS

The results of this study strongly suggest that penicillin tolerance of the streptococci responsible for endocarditis has a clinical impact. Consequently, pending a larger prospective study addressing the problem of tolerance, it is clinically relevant to determine the minimal inhibitory and bactericidal penicillin concentrations for all streptococcal isolates causing endocarditis.

Identification and molecular analysis of PcsB, a protein required for cell wall separation of group B streptococcus

Group B streptococcus (GBS) is the leading cause of bacterial sepsis and meningitis in neonates. N-terminal sequencing of major proteins in the culture supernatant of a clinical isolate of GBS identified a protein of about 50 kDa which could be detected in all of 27 clinical isolates tested. The corresponding gene, designated pcsB, was isolated from a GBS cosmid library and subsequently sequenced. The deduced PcsB polypeptide consists of 447 amino acid residues (M(r), 46,754), carries a potential N-terminal signal peptide sequence of 25 amino acids, and shows significant similarity to open reading frames of unknown function from different organisms and to the murein hydrolase P45 from Listeria monocytogenes. Northern blot analysis revealed a monocistronic transcriptional organization for pcsB in GBS. Insertional inactivation of pcsB in the genome of GBS resulted in mutant strain Sep1 exhibiting a drastically reduced growth rate compared to the parental GBS strain and showing an increased susceptibility to osmotic pressure and to various antibiotics. Electron microscopic analysis of GBS mutant Sep1 revealed growth in clumps, cell separation in several planes, and multiple division septa within single cells. These data suggest a pivotal role of PcsB for cell division and antibiotic tolerance of GBS.

Prophylaxis for neonatal group B streptococcus infections

For the past two decades, group B streptococcus (GBS) has been the pathogen most frequently isolated from neonates with invasive bacterial disease. This is a review of the relevant aspects of microbiology, epidemiology, and clinical manifestations and a summary of the major studies of prevention strategies that led to the development of the 1996 consensus guidelines for prevention of perinatal GBS disease. There is now sufficient experience to know that > or = 80% of cases of early onset GBS disease can be prevented when a protocol for intrapartum chemoprophylaxis with either penicillin or ampicillin is implemented consistently within a delivery population. Present controversies revolve around the choice between a universal screening-based strategy versus a risk factor-based strategy, optimal management of the neonate born to a mother who received intrapartum antimicrobial prophylaxis, and effective methods to ensure implementation. The present guidelines will likely be refined as additional experience is gained.

A double-blind, multicenter comparative study of two regimens of clindamycin hydrochloride in the treatment of patients with acute streptococcal tonsillitis/pharyngitis

In a double-blind, prospective, randomized, multicenter study, 164 patients with a clinical and bacteriologic diagnosis of acute streptococcal tonsillitis/pharyngitis were enrolled to compare the efficacy and safety of two regimens of clindamycin. A rapid identification test of Group A beta-hemolytic streptococci (GABHS) was used to initiate the therapy; however, a positive tonsillar/pharyngeal culture was required at pretreatment to determine if the patient was assessable. Another culture was repeated at least 2 days after the 10 days of drug therapy. From 164 patients enrolled (mean age, 27.7 years; range, 14 to 60 years), 141 were assessable for efficacy; 22 patients were excluded because they did not have a positive culture at pretreatment and 1 patient did not complete the study due to a side effect (rash). All patients were included in the safety analysis. Patients received either clindamycin hydrochloride capsules 150 mg four times per day (QID) or clindamycin hydrochloride capsules 300 mg two times per day (BID) and placebo capsules BID for 10 days. There were no significant differences between groups in terms of demographics, medical history, and evolution of symptoms. The clinical efficacy rate in the two groups at day 12 was as follows: QID group--cured, 64 (92.8%) of 69 patients; improved, 5 (7.2%) of 69 patients; BID group--cured, 67 (93.1%) of 72 patients; improved, 5 (6.9%) of 72 patients. There were no significant differences between the groups. Both regimens were well tolerated with only 1 patient in the QID group who did not complete the therapy due to a rash.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of cefuroxime axetil suspension compared with that of penicillin V suspension in children with group A streptococcal pharyngitis

The bacteriological and clinical efficacies of cefuroxime axetil suspension (20 mg/kg of body weight per day in two divided doses) were compared with those of penicillin V suspension (50 mg/kg/day in three divided doses) in a multicenter, randomized, evaluator-blinded study. Children aged 2 to 13 years with clinical signs and symptoms of acute pharyngitis and a positive throat culture for group A beta-hemolytic streptococci (GABHS) were eligible. Patients were assessed and samples from the throat for culture were obtained at the time of diagnosis, 3 to 7 days after the initiation of treatment, and 4 to 8 days and 19 to 25 days after the completion of 10 days of therapy. Of the 385 evaluable patients, GABHS were eradicated from 244 of 259 (94.2%) cefuroxime-treated patients and 106 of 126 (84.1%) penicillin-treated patients (P = 0.001). Complete resolution of the signs and symptoms present at the time of diagnosis was achieved in 238 of 259 (91.9%) cefuroxime-treated patients and 102 of 126 (81.0%) penicillin-treated patients (P = 0.001). Potential drug-related adverse events were reported in 7.0 and 3.2% of the cefuroxime- and penicillin-treated patients, respectively (P = 0.078). In the present study, cefuroxime axetil suspension given twice daily resulted in significantly greater bacteriological and clinical efficacies than those of penicillin V suspension given three times daily to pediatric patients with acute pharyngitis and a positive throat culture for GABHS.

Distribution, antibiotic susceptibility and tolerance of bacterial isolates in culture-positive cases of endocarditis in The Netherlands

During a two-year period data were collected nationwide in The Netherlands on 438 episodes of bacterial endocarditis (BE) in 432 patients. Of the strains isolated in these patients 419 were available for analysis. Of these, 326 were isolated in native valve endocarditis (NVE) and 93 in prosthetic valve endocarditis (PVE). Viridans streptococci, staphylococci and enterococci together constituted 87% of the isolates. More than 46% of the viridans streptococci consisted of Streptococcus sanguis. Enterococcus faecalis and Staphylococcus aureus were the predominant species in the late form of PVE. The majority of the viridans streptococci and haemolytic streptococci were highly susceptible to penicillin. Five of 35 strains of coagulase negative staphylococci were resistant to methicillin. Eleven percent of a random sample of the streptococci collected were tolerant to penicillin. After repeated exposure to a concentration gradient of an appropriate beta-lactam antibiotic, this figure increased to 49%. Of the staphylococci, 5-6% of the strains were tolerant before induction and 16-20% after induction. Of the Enterococcus strains (n = 40), 12.5% showed high-level resistance to one or more aminoglycoside.

Degree and stability of tolerance to penicillin in Streptococcus pyogenes

The degree of antibiotic tolerance may be assessed by determining the tolerance percentage of a bacterial strain, defined as the surviving fraction of an inoculum that has been exposed for 24 hours to a high concentration of a beta-lactam antibiotic. In 61 clinical isolates of Streptococcus pyogenes, tolerance percentages ranged from 0 to 0.43. From the slopes of the killing curves it can be deduced that killing starts to be delayed at a tolerance percentage of 0.1. Although a tolerance percentage exceeding 0.1 was observed in 41.4% of the strains, the incidence of clinically relevant forms of tolerance is expected to occur in a smaller fraction of the strains. Tolerance percentages of two strains stored at 20 degrees C, 4 degrees C or -70 degrees C (tolerance percentages 0.43 and 0.36) decreased to 0.03 or less in six weeks. Tolerance percentages could be completely restored in these strains, but not in sensitive strains, by successive selection for this property on penicillin gradients of increasing concentration. In four strains isolated from a family outbreak, identical levels of tolerance percentage could be selected for with the same technique.