Antibody response in patients with autoimmune inflammatory rheumatic disease after pneumococcal polysaccharide prime vaccination or revaccination.

OBJECTIVE: The aim of the study was to assess the pneumococcal antibody response in autoimmune inflammatory rheumatic disease (AIIRD) patients receiving 23-valent pneumococcal polysaccharide vaccine (PPV23) as a prime vaccination or revaccination. METHOD: Antibodies to 12 serotypes occurring in the commonly applied pneumococcal vaccines in Denmark were measured in AIIRD patients receiving biological disease-modifying anti-rheumatic drug (bDMARD) treatment for rheumatoid arthritis, spondyloarthritis, or psoriatic arthritis. Patients with a non-protective level of pneumococcal antibodies (geometric mean pneumococcal antibody level < 1 µg/mL) were invited to receive vaccination with PPV23 followed by control of antibody titre 3 months later. RESULTS: In total, 224 (74%) of 301 patients were included in the analyses, of whom 126 patients had previously received PPV23 vaccination. Post-vaccination antibody measurement revealed that only 80 patients (36%) achieved a protective level of antibodies. In a multivariable logistic regression analysis, significantly more patients without a previous PPV23 vaccination history achieved a protective antibody level compared with patients with a history of PPV23 vaccination less than 5 years ago (p = 0.005). This difference was not seen when comparing the former group with patients vaccinated 5 years ago or more. Methotrexate (MTX) treatment at the time of vaccination was associated with a non-protective antibody level (p < 0.001). CONCLUSION: Only 36% of patients with a non-protective antibody level achieved a protective level in response to pneumococcal vaccination. Pneumococcal vaccination within the last 5 years and MTX treatment at the time of vaccination were independently associated with a poor antibody response.

Associations between blood cultures after surgery for colorectal cancer and long-term oncological outcomes.

BACKGROUND: Systemic inflammation following curative surgery for colorectal cancer may be associated with increased risk of recurrence. [Correction added on 29 November 2019, after first online publication: text amended for accuracy.] This study investigated whether a clinically suspected infection, for which blood cultures were sent within 30 days after surgery for colorectal cancer, was associated with long-term oncological outcomes. METHODS: This register-based national cohort study included all Danish residents undergoing surgery with curative intent for colorectal cancer between January 2003 and December 2013. Patients who developed recurrence or died within 180 days after surgery were not included. Associations between blood cultures taken within 30 days after primary surgery and overall survival, disease-free survival and recurrence-free survival were analysed using Cox regression models adjusted for relevant clinical confounders, including demographic data, cancer stage, co-morbidity, blood transfusion, postoperative complications and adjuvant chemotherapy. RESULTS: The study included 21 349 patients, of whom 3390 (15·9 per cent) had blood cultures taken within 30 days after surgery. Median follow-up was 5·6 years. Patients who had blood cultures taken had an increased risk of all-cause mortality (hazard ratio (HR) 1·27, 95 per cent c.i. 1·20 to 1·35; P < 0·001), poorer disease-free survival (HR 1·22, 1·16 to 1·29; P < 0·001) and higher risk of recurrence (HR 1·15, 1·07 to 1·23; P < 0·001) than patients who did not have blood cultures taken. CONCLUSION: A clinically suspected infection requiring blood cultures within 30 days of surgery for colorectal cancer was associated with poorer oncological outcomes.

ANTECEDENTES: La inflamación sistémica en el cáncer colorrectal puede asociarse con un aumento del riesgo de recidiva. En este estudio se investigó si la sospecha clínica de infección, en la que se obtuvieron cultivos de sangre periférica durante los primeros 30 días de la cirugía por cáncer colorrectal, se asociaba con los resultados oncológicos a largo plazo. MÉTODOS: Se trata de un estudio de cohortes de un registro de una base de datos nacional, que incluyía todos los sujetos residentes en Dinamarca sometidos a cirugía por cáncer colorrectal con intención curativa desde enero de 2003 a diciembre de 2013. Los pacientes con recidiva o que fallecieron durante los primeros 180 días después de la cirugía fueron excluidos. Se estimaron las asociaciones entre los cultivos de sangre periférica efectuados en los primeros 30 días tras la cirugía primaria y la supervivencia global, supervivencia libre de enfermedad y supervivencia libre de recidiva mediante modelos de regresión de Cox, ajustados por variables clínicas confusoras relevantes (incluyendo datos demográficos, estadio del cáncer, comorbilidad, transfusión de sangre, complicaciones postoperatorias y quimioterapia adyuvante). RESULTADOS: El estudio incluyó 21.349 pacientes, de los cuales en 3.390 (16%) se habían obtenido cultivos de sangre periférica durante los primeros 30 días tras la cirugía. La mediana de seguimiento fue de 5,6 años. Los pacientes en los que se había obtenido cultivos de sangre periférica presentaron un riesgo aumentado de mortalidad por cualquier causa (cociente de riesgos instantáneos, hazard ratio, HR 1,27, i.c. del 95% 1,20-1,35; P < 0.0001), peor supervivencia libre de enfermedad (HR 1,22, i.c. del 95% 1,16-1,29; P < 0,0001) y mayor riesgo de recidiva (HR 1,15, i.c. del 95% 1,07-1,23; P < 0,0001) que los pacientes en los que no se habían obtenido cultivos. CONCLUSIÓN: La presencia de una infección sospechada clínicamente para la cual se requiere obtener cultivos de sangre periférica en los primeros 30 días tras cirugía por cancer colorrectal se asoció con peores resultados oncológicos.

Pneumococcal antibody protection in patients with autoimmune inflammatory rheumatic diseases with varying vaccination status.

Objectives: The aims of this cross-sectional study were to assess the pneumococcal antibody coverage in patients with autoimmune inflammatory rheumatic disease (AIRD) and to identify predictors associated with inadequate protective antibody levels. Method: Antibodies to 12 serotypes occurring in the commonly applied pneumococcal vaccines in Denmark were measured in AIRD patients with a diagnosis of rheumatoid arthritis, spondyloarthritis, or psoriatic arthritis attending the Department of Rheumatology at the North Denmark Regional Hospital. Immunization against pneumococcal infection was defined as a geometric mean level ≥ 1 µg antibodies/mL. Clinical information about vaccination status and disease/treatment history was retrieved from the medical file system. Results: Results of antibody measurement and vaccination status were available from 346 AIRD patients, of whom 200 (58%) were registered as receiving pneumococcal vaccination, whereas the remaining 146 patients (42%) were not. Of all 346 patients, only 61 (18%) were measured with an adequate level of protective antibodies (30% vs 1%, respectively). Methotrexate treatment at the time of vaccination and increasing age were identified as predictors of poor vaccination outcome in multiple logistic regression analysis. Conclusions: This post-vaccination study showed that less than one-fifth of the AIRD patients are adequately protected against pneumococcal infection, although the immunization programme had been implemented in more than half of the study population. Development of improved vaccination strategies is required to achieve a higher immunization coverage rate and more efficient lasting antibody response.

Biofilm production and antibiotic susceptibility of Staphylococcus epidermidis strains from Hidradenitis Suppurativa lesions.

BACKGROUND: An aberrant interaction between commensal skin bacteria and the host skin immune system is considered important in the pathogenesis of hidradenitis suppurativa (HS). OBJECTIVE: In this study, we investigated the antibiotic susceptibility and biofilm-forming capabilities of S. epidermidis strains isolated from HS patients. METHODS: Skin biopsies were taken from active HS lesions such as inflammatory nodules and/or sinuses and non-involved skin from 26 patients and cultured under optimal microbiological conditions for 24 h. Planktonic growth, biofilm production, antibiotic susceptibility and biofilm eradication by clindamycin, doxycycline, rifampicin and tetracycline were tested including a laboratory control strain of S. epidermidis for reference. RESULTS: Staphylococcus epidermidis was cultured in 16 of 26 HS patients (62%). In total 27 different S. epidermidis isolates were identified; 16 (59%) from non-involved skin and 11 (41%) from HS lesions. All bacterial strains showed planktonic growth. Twenty-four of 27 (89%) isolates were strong biofilm producers in vitro. The biofilm-forming capability varied amongst the strains from non-involved skin and lesional skin. Twenty-four strains had an intermediate to resistant antibiotic susceptibility to clindamycin (89%). Rifampicin was the most effective antibiotic at inhibiting planktonic growth and at eradication of biofilm (P < 0.05). CONCLUSION: We observed a slight increase in S. epidermidis virulence, characterized by resistance to commonly used antibiotics, increased biofilm production and resistance to biofilm eradication. In particular, the reduced sensitivity to tetracycline and clindamycin, two standard antibiotics in the treatment of HS, is alarming. Rifampicin, also important in HS treatment, showed the greatest efficacy at eradicating the biofilm at low MIC concentrations.

The microbiome of tunnels in hidradenitis suppurativa patients.

BACKGROUND: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease defined by recurrent nodules, tunnels and scarring involving the intertriginous regions. Recent next-generation sequencing (NGS) studies suggest genera such as Prevotella spp., Peptoniphilus spp. and Porphyromonas spp. are associated with chronic and early HS lesions. However, a systematic investigation of the bacterial microbiome in HS tunnels remains unexplored using NGS. OBJECTIVE: We aimed to investigate the bacterial composition of the luminal white gelatinous material found in HS tunnels using NGS. METHODS: An exploratory study of patients with diagnosis of HS (n = 32) with tunnels. The tunnels were present either in the groin (n = 17) or in the axilla (n = 15). During deroofing of the tunnels, a sterile E-swab was taken of the luminal gelatinous material. The samples were investigated using NGS targeting 16S ribosomal RNA. RESULTS: The skin microbiome was characterized in 32 HS patients. Overall, five microbiome types were identified: Porphyromonas spp. (type I), Corynebacterium spp., (type II), Staphylococcus spp. (type III), Prevotella spp. (type IV) and Acinetobacter spp (type V). Porphyromonas spp. (type I) and Prevotella spp. (IV) were the most frequent genera found the tunnels. CONCLUSION: This study points to a potential association between the presence of certain anaerobic bacteria (Porphyromonas spp., Prevotella spp.) and HS tunnels. It may be speculated that these two genera are associated with the pathogenesis in HS either as drivers or as biomarkers.

Moderate to severe hidradenitis suppurativa patients do not have an altered bacterial composition in peripheral blood compared to healthy controls.

BACKGROUND: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease defined by recurrent nodules, tunnels and scarring involving the intertriginous skin. Patients with HS often report an array of systemic symptoms such as fatigue and malaise. The aetiology of these symptoms remains unclear. Previously, various bacteria have been associated with mature HS lesions, and bacteraemia has been reported in patients with HS using traditional culturing methods. Thus, we hypothesized that a low-grade bacteraemia contributes to the symptomatology in patients with HS. OBJECTIVE: To explore the potential presence of bacteraemia in patients with HS and healthy controls. METHOD: A case-control study. Compositions of bacteria in the blood of 27 moderate to severe HS patients and 26 healthy controls were investigated using next-generation 16S ribosomal RNA gene sequencing (NGS) and routine anaerobic and aerobic blood culturing. None of the participants received any antibiotics (systemic or topical therapy) within 1 month prior to the study. HS patients with a recent flare were randomly selected by consecutive recruitment of eligible patients from the Department of Dermatology, Zealand University Hospital, Denmark. Healthy controls were recruited from the University of Copenhagen as well as from the healthcare staff. RESULTS: The different bacterial compositions were investigated using NGS and traditional anaerobic and aerobic blood culturing. Our NGS analysis provided a previously unreported characterization of the bacterial composition in peripheral blood from patients with HS and healthy controls. Overall, our data demonstrated that patients with HS do not have a different bacterial composition in their peripheral blood than healthy controls. CONCLUSION: The study suggests that the self-reported symptoms in HS such as malaise and fatigue may not be linked to bacteraemia.

A systematic review of Fusobacterium necrophorum-positive acute tonsillitis: prevalence, methods of detection, patient characteristics, and the usefulness of the Centor score.

The purpose of this study was to review the current evidence for an association between Fusobacterium necrophorum (FN) and acute tonsillitis (AT), to assess the prevalence of FN in AT, to identify the better FN detection method, and to characterize the clinical characteristics of FN-positive patients with uncomplicated AT. A systematic literature search was conducted in the PubMed, EMBASE, and SweMed+ databases for studies reporting on the recovery rates of FN in patients with AT. A total of 498 unique records were identified. Eleven studies were included in a qualitative synthesis and six studies were included in a meta-analysis. Considerable heterogeneity (I2 = 60 %) and risk of bias and confounders was found among the studies, though a subset of studies (prospective) had lower heterogeneity and higher study quality. FN was recovered significantly more frequently from patients (21.2 %) compared to healthy controls (7.6 %) (p < 0.001). FN recovery rates were similar between culture-based studies (20.3 %) and studies using polymerase chain reaction (PCR) methodology (22.2 %) (p = 0.462). The typical FN-positive AT patient was a smoking young (15-25 years) male presenting with tonsillar exudates and a Centor score of 2 or higher. A clear association between FN and AT was found. FN is likely to be a significant and prevalent pathogen in AT, especially in teenagers and young adults. However, no evidence for causality between FN and AT has been established and it is unexplored if timely antibiotic therapy directed against FN accelerates the resolution of symptoms and decreases the risk of complications.

Prevalence of tonsillar human papillomavirus infections in Denmark.

The incidence of tonsillar carcinomas associated with Human Papillomavirus (HPV) infection has increased dramatically over the last three decades. In fact, currently in Scandinavia, HPV-associated cases account for over 80 % of tonsillar carcinoma cases. Yet, the epidemiology and natural history of tonsillar HPV infections remains poorly characterized. Our aim was to characterize such infections in the Danish population in tumor-free tonsillar tissue. Unlike previous studies, we considered both palatine tonsils. We examined both tonsils from 80 patients with peritonsillar abscess (n = 25) or chronic tonsillar disease (n = 55). HPV was detected by nested PCR with PGMY 09/11 and GP5+/GP6+L1 consensus primers, and typed by sequencing. Samples were also analyzed using a higher-throughput method, the CLART HPV 2 Clinical Array Assay. The overall prevalence of HPV tonsillar infection was 1.25 % (1/80, 95 % CI 0.03-6.77 %) by nested PCR, and 0 % by CLART HPV2 Clinical Array. The HPV-positive patient was a 16-year-old female with recurrent tonsillitis and tonsillar hypertrophy. The type detected was HPV6. HPV was not detected in the contralateral tonsil of this patient. Compared to cervical HPV infections in Denmark, tonsillar HPV infections are 10- to 15-fold less frequent. In the HPV-positive patient in this study, HPV was detected in only one of the tonsils. This raises the possibility that prior studies may underestimate the prevalence of HPV infections, as they do not consider both palatine tonsils.

Antibody development to Fusobacterium necrophorum in patients with peritonsillar abscess.

A polymicrobial mixture of aerobic and anaerobic bacteria is commonly recovered from peritonsillar abscess (PTA) aspirates. Previous studies have suggested a role for Fusobacterium necrophorum (FN) in the development of PTA. The purpose of the current study was to explore whether anti-FN antibodies were produced in patients with PTA. We developed a novel immunofluorescence-based method to measure anti-FN antibody levels in acute and convalescent sera from 15 patients with PTA and 47 patients with chronic tonsillar conditions (controls) undergoing acute or elective tonsillectomy, respectively. Bacterial cultures were performed on tonsillar cores and surfaces, pus aspirates, and blood. An increase in anti-FN antibody levels (of at least doubling of the previous level) was observed in 8 of 11 (73 %) PTA patients with FN-positive pus aspirate cultures (FN-positive patients). In contrast, the four FN-negative PTA patients did not have an increase in anti-FN antibody levels (p = 0.026). The change in anti-FN antibody levels in FN-positive PTA patients was also significantly greater than that for FN-positive electively tonsillectomized patients (p = 0.0014) and all electively tonsillectomized patients (p < 0.001). Our results validate FN as a significant and prevalent pathogen in PTA. This finding has implications for the diagnostic work-up of PTA and may also have implications for the treatment of acute tonsillitis.

The role of viruses in the pathogenesis of peritonsillar abscess.

Peritonsillar abscess (PTA) is the most frequent complication of acute tonsillitis and a prevalent cause for acute admission to otorhinolaryngology departments. Our aim was to examine the role of viruses in the pathogenesis of PTA, as this has not previously been considered. We examined both palatine tonsils from 25 patients undergoing acute tonsillectomy for PTA, using PCR-based assays for herpes simplex virus-1 and -2 (HSV-1 and -2), adenovirus, Epstein-Barr virus (EBV), influenza A and B, and respiratory syncytial virus (RSV) A and B. We similarly examined tonsils from 55 patients undergoing elective tonsillectomy due to chronic tonsillar conditions. These patients served as a control group, as they did not have a clinically apparent infection at the time of surgery. Only HSV-1 (5/80, 6.3%), adenovirus (11/80, 13.8%), and EBV (71/80, 88.8%) were detected in our study population. There was no statistically significant difference in the frequency of these viruses across different diagnostic groups. Quantification of EBV load demonstrated no differences between the PTA and the elective tonsillectomy group, nor between the abscessed and non-abscessed tonsil of PTA patients. In summary, our data do not support a significant role for the examined viruses in the pathogenesis of PTA.

Significant pathogens in peritonsillar abscesses.

Peritonsillar abscesses (PTA) are polymicrobial infections, with a diverse aerobic and anaerobic flora. The aim of the present study is to compare bacteriologic culture results from patients with PTA to those from patients undergoing elective tonsillectomy (clinically non-infected tonsils), to better elucidate the pathogenic significance of various isolates. A prospective study was conducted on 36 PTA patients undergoing acute tonsillectomy and on 80 electively tonsillectomised patients. Fusobacterium necrophorum (FN) and Streptococcus group A (GAS) were isolated significantly more frequently from the tonsillar cores of PTA patients, from both the abscessed (p = 0.001 and p = 0.046, respectively) and non-abscessed sides (p < 0.001 and p = 0.046, respectively), than from the tonsillar cores of electively tonsillectomised patients. Our findings indicate that FN and GAS are the prominent pathogens in PTA. In patients with PTA, the incidence of FN and GAS isolated from the abscessed tonsil was the same as from the non-abscessed contralateral side, and the growth was comparable by a semi-quantitative approach. Our findings suggest that FN is also of pathogenic importance in acute tonsillitis, and that FN growth is not a subsequent phenomenon once an abscess has formed. Our findings further suggest that other factors influence the development of PTA.

Differentiation of Candida glabrata, C. nivariensis and C. bracarensis based on fragment length polymorphism of ITS1 and ITS2 and restriction fragment length polymorphism of ITS and D1/D2 regions in rDNA.

Different molecular methods for the discrimination of Candida glabrata, C. bracarensis and C. nivariensis were evaluated and the prevalence of these species among Danish blood isolates investigated. Control strains were used to determine fragment length polymorphism in the ITS1, ITS2, ITS1-5.8S-ITS2 regions and in the D1/D2 domain of 26S rDNA using primers designed for this study. A total of 133 blood isolates previously identified as C. glabrata were examined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and the peptide nucleic acid-fluorescent in situ hybridization (PNA-FISH) method. The size of ITS1 allowed differentiation between C. glabrata (483), C. nivariensis (361) and C. bracarensis (385), whereas the ITS2 region was of similar size in C. nivariensis (417) and C. glabrata (418). Sequence analysis of the ITS region suggested that many restriction enzymes were suitable for RFLP differentiation of the species. Enzymatic digestion of the D1/D2 domain with TatI produced unique band sizes for each of the three species. PCR-RFLP and PNA-FISH were in agreement for all of the isolates tested. None of the 133 Danish blood isolates were C. nivariensis or C. bracarensis. Fragment size polymorphism of ITS1 and RFLP of the D1/D2 domain or the ITS region are useful methods for the differentiation of the species within the C. glabrata group. C. bracarensis and C. nivariensis are rare among Danish C. glabrata blood isolates.

A prospective survey of Aspergillus spp. in respiratory tract samples: prevalence, clinical impact and antifungal susceptibility.

A three-month laboratory-based prospective survey was conducted at four major university hospitals covering one-third of the Danish population in order to determine the prevalence, significance, and susceptibility pattern of aspergilli in airway samples. Samples received in January-March 2007 for routine microbiologic investigation were examined for Aspergillus following routine procedures and with extended incubation (5 days). Identification was done by morphologic criteria and susceptibility testing using EUCAST method for azoles and amphotericin B E-test. Invasive aspergillosis (IA) was evaluated using modified EORTC/MSG criteria. A total of 11,368 airway samples were received. Growth of Aspergillus spp. was found in 129 and 151 patients using routine and extended incubation, respectively. Three patients had proven IA (2%), 11 probable (7%), four had allergic bronchopulmonary aspergillosis (ABPA) (3%), but the majority was colonised (88%). Underlying conditions were cystic fibrosis in 82 patients (55%), chronic obstructive pulmonary disease in 19 (13%) and haematological disorder in 11 (7%). Twenty-six patients (18%) were at intensive care unit and 69 (47%) received steroid treatment. Azole MICs were elevated for five isolates as follows (itraconazole, posaconazole, voriconazole MICs [mg/L]): two A. fumigatus isolates (>4; >4; 2 and >4; 0.125; 1), one A. lentulus isolate (2; 2; 0.5) and two A. terreus isolates (2; 2; 2 and 2; 0.125; 1). For four isolates the amphotericin B MIC was >1 µg/ml (3/112 A. fumigatus, 1/2 A. terreus). In conclusion, Aspergillus appears to be an important pathogen in Denmark. Elevated itraconazole MICs were detected in 4% of the isolates including a multi-azole resistant isolate.

Semi-national surveillance of fungaemia in Denmark 2004-2006: increasing incidence of fungaemia and numbers of isolates with reduced azole susceptibility.

A semi-national laboratory-based surveillance programme for fungaemia was initiated in 2003 that now covers c. 3.5 million inhabitants (64%) of the Danish population. In total, 1089 episodes of fungaemia were recorded during 2004-2006, corresponding to an annual incidence of 10.4/100 000 inhabitants. The annual number of episodes increased by 17% during the study period. Candida spp. accounted for 98% of the fungal pathogens. Although Candida albicans remained predominant, the proportion of C. albicans decreased from 66.1% in 2004 to 53.8% in 2006 (p <0.01), and varied considerably among participating departments, e.g., from 51.1% at a university hospital in Copenhagen to 67.6% in North Jutland County. Candida glabrata ranked second, and increased in proportion from 16.7% to 22.7% (p 0.04). Candida krusei was isolated rarely (4.1%), but the proportion doubled during the study period from 3.2% to 6.4% (p 0.06). MIC distributions of amphotericin B and caspofungin were in close agreement with the patterns predicted by species identification; however, decreased susceptibility to voriconazole, defined as an MIC of >1 mg/L, was detected in one (2.5%) C. glabrata isolate in 2004 and in 12 (14.0%) isolates in 2006 (p 0.03). Overall, the proportion of isolates with decreased susceptibility to fluconazole exceeded 30% in 2006. The incidence of fungaemia in Denmark was three-fold higher than that reported from other Nordic countries and is increasing. Decreased susceptibility to fluconazole is frequent, and a new trend towards C. glabrata isolates with elevated voriconazole MICs was observed.

Comparison of growth and susceptibility testing of pyrazinamide in different Bactec media using strains of the M. tuberculosis complex.

The aim of this study was to evaluate and compare growth and susceptibility testing of pyrazinamide (pza) in different Bactec media using 85 strains of the M. tuberculosis complex. Fifty-four were clinical isolates of M. tuberculosis, of which 34 strains were selected as they failed to grow in primary pza susceptibility testing. Fourteen were strains of M. bovis, 10 were different strains of M. bovis BCG, five were strains of M. africanum, and two were strains of M. microti. The following Bactec media were evaluated: (1) Bactec PZA test medium, (2) acidified Bactec 12B medium with pH reduced to 5.6, (3) acidified 12B medium supplemented with fresh egg yolk, (4) acidified 12B medium supplemented with a commercial egg yolk enrichment. Demonstration of pyrazinamidase activity was included for comparison. All strains of M. tuberculosis, M. microti and M. africanum were inhibited by pza at 100 micrograms/ml, and all strains of M. bovis and M. bovis BCG were found to be resistant to pza at 100 micrograms/ml. Bactec PZA test medium supported growth for all 85 strains tested. The two egg yolk-supplemented media supported growth in all strains except one strain of M. microti, and acidified but otherwise unsupplemented Bactec 12B medium supported growth in 64 strains (75%). A pza sensitivity test result could be obtained within one week in > 79% of strains. An overall correlation of 89% between susceptibility to pza and demonstration of pyrazinamidase activity was demonstrated.

Synergism and mechanism of subinhibitory concentration of streptomycin on Streptococcus faecalis.

The influence of various incubation conditions on synergism with cell wall-active agents combined with streptomycin was studied in a Streptococcus faecalis strain. It could be shown that both a synergistic increased killing effect and a synergistic prolongation of post-antibiotic effect (PAE) were not dependent on an active process, as they occurred both in an anaerobic atmosphere and when an electron transport inhibitor (sodium azide) was added to the media. Moreover, it was demonstrated that if a drug, alone or in combination with streptomycin, had a PAE, there was an increased susceptibility to a subinhibitory concentration of streptomycin (1/4xMIC) when added to a culture recovering from its PAE. These findings confirm the commonly held belief in a mechanistic mechanism of synergism: That cell wall-active agents modify in some way the cell-envelope, thereby enhancing aminoglycoside uptake and killing in Streptococcus faecalis.

Further studies on post-antibiotic effect and synergism in two strains of Streptococcus faecalis.

The differences in the synergistic potential for either killing effect or increase in duration of post-antibiotic effect (PAE) seen with various beta-lactam-aminoglycoside combinations in two strains of Streptococcus faecalis were further studied to examine this relationship in more detail. It was seen that a strain which produced a synergistic increase in recovery period (PAE greater than or equal to 0.5 h), comparing the beta-lactam antibiotics alone and when combined with streptomycin, showed increased sensitivity (greater than or equal to 1 log10 reduction in viable counts) to a subinhibitory concentration of streptomycin added to a culture recovering from the PAE; this was not demonstrated with a strain showing no increase in PAE when briefly exposed to a combination therapy, although its corresponding killing curve was clearly synergistic. Moreover, it was seen that the differences in the synergistic prolongation of recovery period when combining various aminoglycosides at 1/4 x MIC with ampicillin were consistent with the different duration of PAE with the particular aminoglycoside alone at the MIC.