RESUMEN
Human papillomaviruses (HPVs) are necessary, but not sufficient, for the development of cervical cancer (CC). Human beta-herpesviruses (beta-HHVs) have been suggested as possible cofactors in the oncogenesis of CC. In this cross-sectional study, the prevalence and possible association of cytomegalovirus (CMV), HHV-6 and -7 with HPV presence was investigated by quantitative real-time PCR assays in cervical samples obtained from 208 italian women. The two most common high-risk HPV types found were 31 and 16. Overall, the positive rates for CMV, HHV-6 and HHV-7 were 66%, 25%, and 6%, respectively. In particular, the prevalence of CMV was found to be extremely high irrespective of either the cytological category or HPV positivity. The prevalence of HHV-6 DNA was significantly higher in high-grade squamous intraepithelial lesions (HSIL) respect to normal women (P < 0.017); by contrast, the prevalence HHV-7 DNA was generally low and not associated with SIL. Copresence of CMV and HHV-6 DNA was found to be significantly higher in patients with SIL respect to normal women (P < 0.05). No correlation was demonstrated between the viral load of all three beta-HHVs and the different cytological stages or with the HPV presence. A few patients with severe disease however showed very high viral loads which for HHV-6 may be indicative of viral integration. In conclusion, this study suggests that CMV and HHV-7 alone are probably not implicated in the oncogenesis of CC whilst HHV-6 alone or together with CMV may contribute to the development of CC.
Asunto(s)
Transformación Celular Neoplásica , Infecciones por Citomegalovirus/epidemiología , Citomegalovirus/aislamiento & purificación , Infecciones por Herpesviridae/epidemiología , Herpesvirus Humano 7/aislamiento & purificación , Neoplasias del Cuello Uterino/virología , Animales , Transformación Celular Viral , Cuello del Útero/patología , Chlorocebus aethiops , Estudios Transversales , Citomegalovirus/patogenicidad , Infecciones por Citomegalovirus/virología , ADN Viral , Femenino , Infecciones por Herpesviridae/virología , Humanos , Reacción en Cadena de la Polimerasa , Neoplasias del Cuello Uterino/patología , Células VeroRESUMEN
The prevalence of the internalization-associated prtF1 gene was studied in 837 isolates of Streptococcus pyogenes obtained from 713 pediatric patients presenting with acute pharyngotonsillitis before and after antibiotic therapy. Its association with macrolide resistance and with bacteriological treatment failure was determined. The bacterial population isolated from baseline pharyngeal swabs showed an overall prtF1 positivity rate of 33%. A higher prtF1 positivity was found among erythromycin-resistant strains (45%) showing, however, marked differences between the inducible (iMLS), constitutive (cMLS), and efflux pump (M) resistance phenotypes. The prevalence was statistically higher (p < 0.001) in strains belonging to iMLS (84%) and cMLS (67%) phenotypes as compared to the M phenotype (15%). Interestingly, the prevalence of the prtF1 gene was significantly lower (p = 0.04) in strains belonging to M resistance phenotype as compared to erythromycin-susceptible strains (28%). Failed bacterial eradication was demonstrated in 124 patients. The prtF1 positivity rate remained unchanged in strains isolated before and after therapy in patients treated with macrolides (9/54). On the other hand, the positivity rate for the prtF1 gene was significantly higher (p = 0.015) in strains isolated after therapy with beta-lactams (21/70) as compared to baseline isolates (6/70), indicating a differential selection imposed on the organism by these agents. Finally, a high overall eradication rate (88%) of prtF1-positive isolates, belonging to both the erythromycin-susceptible and -resistant phenotypes, was demonstrated following macrolide treatment.
Asunto(s)
Adhesinas Bacterianas/genética , Antibacterianos/farmacología , Farmacorresistencia Bacteriana Múltiple , Faringitis/microbiología , Streptococcus pyogenes/genética , Tonsilitis/microbiología , Enfermedad Aguda , Antibacterianos/uso terapéutico , Niño , Eritromicina/farmacología , Eritromicina/uso terapéutico , Humanos , Pruebas de Sensibilidad Microbiana , Faringitis/tratamiento farmacológico , Reacción en Cadena de la Polimerasa , Streptococcus pyogenes/efectos de los fármacos , Streptococcus pyogenes/aislamiento & purificación , Tonsilitis/tratamiento farmacológico , Insuficiencia del Tratamiento , beta-Lactamas/farmacología , beta-Lactamas/uso terapéuticoRESUMEN
A total of 123 community paediatricians and 23 microbiology laboratories studied the clinical and bacteriological efficacy of treatment of group A streptococcal pharyngitis in Italy. Of 1065 patients, from whom Streptococcus pyogenes was isolated, 723 returned to follow up and of these 138 (19%) still had a positive throat culture. The erythromycin resistance (ER) rate was 23.7% with resistance phenotype distribution of: 31.7% constitutive (CR), 26.6% inducible (IR) and 41.7% efflux pump (M) resistance phenotype. All strains were susceptible to the beta-lactam agents tested. CR strains were highly resistant to all 14, 15 and 16 membered macrolides with the exception of rokitamycin which showed activity against 37.8% of isolates. All phenotype M and some IR isolates were susceptible to clindamycin, rokitamycin, josamycin and spiramycin; clarithromycin was active against a small percentage of strains belonging to the IR and M phenotype. Bacterial eradication was found in 85.5, 78.7 and 75.8% of the penicillin, macrolide and cephalosporin treated groups. Genotyping of strains showed that 8.7% of the 19% of cases classified as 'failed bacterial eradication' were due to recolonization with a different isolate, observed exclusively among beta-lactams treated patients. Clinical cure was achieved in a high percentage of cases, irrespective of the antibiotic prescribed, with the best clinical efficacy being found following therapy with amoxycillin and clarithromycin (90.9%).
Asunto(s)
Antibacterianos/uso terapéutico , Faringitis/tratamiento farmacológico , Faringe/microbiología , Infecciones Estreptocócicas/tratamiento farmacológico , Streptococcus pyogenes/efectos de los fármacos , Adolescente , Antibacterianos/farmacología , Niño , Preescolar , Farmacorresistencia Microbiana , Eritromicina/farmacología , Eritromicina/uso terapéutico , Humanos , Italia , Pruebas de Sensibilidad Microbiana , Penicilinas/farmacología , Penicilinas/uso terapéutico , Faringitis/microbiología , Infecciones Estreptocócicas/microbiología , Streptococcus pyogenes/aislamiento & purificaciónRESUMEN
To assess the spread of the new M phenotype, various erythromycin-resistant Streptococcus pyogenes strains from three Italian cities (Verona, Monza, Florence) were characterised. Each strain was analysed for the presence of genes ermAM and mefA, for the ability to accumulate radioactive erythromycin in the absence of sodium arsenate, for the protein T serological type, and for the DNA macrorestriction profile identified by means of pulsed-field gel electrophoresis. In a number of strains, the presence of the inducible ermAM gene was demonstrated; all these strains were negative in the efflux-pump detection assay, did not possess the mefA gene, and had similar restriction profiles. The strains with the efflux mechanism and mefA gene belonged to different serotypes. Of these, only one serotype, T4, was isolated in all three cities. The restriction profile analysis with SmaI and SfiI revealed a very close correlation between strains with the same serotype.
Asunto(s)
Antibacterianos/farmacología , Proteínas Bacterianas , Farmacorresistencia Microbiana/genética , Eritromicina/farmacología , Proteínas de la Membrana/genética , Metiltransferasas/genética , Streptococcus pyogenes , Técnicas de Tipificación Bacteriana , Electroforesis en Gel de Campo Pulsado , Humanos , Italia , Fenotipo , Reacción en Cadena de la Polimerasa , Serotipificación , Infecciones Estreptocócicas/microbiología , Streptococcus pyogenes/clasificación , Streptococcus pyogenes/efectos de los fármacos , Streptococcus pyogenes/genéticaRESUMEN
A retrospective analysis of susceptibility data available for Group A streptococcal isolates collected between January 1990 and January 1996 at the Hospital Microbiology Laboratory of Monza (North Italy), showed a sharp rise in the erythromycin resistance rates during the last 3 years. Streptococcus pyogenes resistant to erythromycin accounted for approximately 1% of strains isolated between 1990 and 1992; the percentage then rose from 5% in 1993 to almost 39% in 1995. In January 1996, the resistance rates peaked to 81%. A prospective controlled study performed between March and May of 1996 to determine the percentage of erythromycin-resistant Group A streptococci isolated in Monza from untreated children with acute pharyngo-tonsillitis, gave further confirmation of a high rate of erythromycin resistance (47%) in this area. Molecular characterization by T-serotyping and pulse-field gel electrophoresis analysis of 25 erythromycin-resistant Group A streptococcal isolates, showed a relatively high degree of heterogeneity among these strains, demonstrating that the increased resistance is not caused by the spread of a single clone.
Asunto(s)
Antibacterianos/farmacología , Eritromicina/farmacología , Faringitis/epidemiología , Faringitis/microbiología , Infecciones Estreptocócicas/epidemiología , Infecciones Estreptocócicas/microbiología , Streptococcus pyogenes/efectos de los fármacos , Tonsilitis/epidemiología , Tonsilitis/microbiología , Enfermedad Aguda , Antibacterianos/uso terapéutico , Niño , Preescolar , Farmacorresistencia Microbiana , Electroforesis en Gel de Poliacrilamida , Eritromicina/uso terapéutico , Femenino , Genes Bacterianos/genética , Humanos , Italia/epidemiología , Masculino , Pruebas de Sensibilidad Microbiana , Estudios Retrospectivos , Streptococcus pyogenes/genéticaRESUMEN
The in vitro efficacy of ceftriaxone plus amikacin combination against gram-positive and gram-negative bacteria, clinically isolated from patients affected by pneumonia in intensive care units, was compared to that of the 2 drugs used alone. The study was performed using a dynamic model in which the human kinetics of the drugs after intramuscular administration was simulated. The antibacterial activity was tested by determining the bacterial cell count (CFU/ml). Killing curves came out from plotting the log CFU/ml versus time. In the same way, ceftriaxone and amikacin concentrations were assayed by HPLC and fluorescence polarization immunoassay, respectively. The results show that ceftriaxone plus amikacin combination exert a high killing activity against all tested strains. The two antibiotics alone initially have a good killing activity but this is followed by bacterial regrowth for all tested isolates. This data supports the results of several clinical studies which have shown a good therapeutic efficacy of ceftriaxone plus amikacin combination in the treatment of severe infections caused by organisms intermediately sensitive to these drugs.
Asunto(s)
Quimioterapia Combinada/farmacología , Enterococcus faecalis/efectos de los fármacos , Pseudomonas aeruginosa/efectos de los fármacos , Staphylococcus/efectos de los fármacos , Amicacina/administración & dosificación , Amicacina/farmacología , Antibacterianos/administración & dosificación , Antibacterianos/farmacología , Ceftriaxona/administración & dosificación , Ceftriaxona/farmacología , Cefalosporinas/administración & dosificación , Cefalosporinas/farmacología , Esquema de Medicación , Humanos , Pruebas de Sensibilidad Microbiana , Modelos Biológicos , Neumonía Bacteriana/microbiologíaRESUMEN
The serum levels of flurithromycin ethylsuccinate achieved 30 min after a single oral dose of 375 mg were found to be equal or above the minimal inhibitory concentrations for sensitive strains, when administered to 12 healthy volunteers. The serum half-life was found to be approximately 4 h.
Asunto(s)
Eritromicina/análogos & derivados , Administración Oral , Adolescente , Adulto , Eritromicina/administración & dosificación , Eritromicina/sangre , Femenino , Semivida , Humanos , Masculino , Persona de Mediana EdadRESUMEN
The efficacy and safety of rufloxacin once daily was compared with that of ofloxacin b.i.d. for therapy of complicated cystitis and upper urinary tract infections. Eighty-three patients were randomly assigned to receive rufloxacin as a loading dose of 400 mg on the first day, followed by 200 mg s.i.d., and 80 received ofloxacin 300 mg b.i.d. Both agents were administered orally for a median duration of eight days. Bacterial elimination rates after treatment were 90% for rufloxacin and 81% for ofloxacin. Half of the treatment failures occurred in patients with infections caused by uropathogens that became either less sensitive or resistant to the quinolones being studied. At a two-week follow-up, recurrences had not occurred in any of the rufloxacin patients and had occurred in 17% of the ofloxacin patients. Minor adverse reactions were reported by 12 and 13 patients, respectively. Rufloxacin once daily is as effective as ofloxacin b.i.d. for the treatment of complicated cystitis and upper urinary tract infections.
Asunto(s)
Antiinfecciosos/uso terapéutico , Infecciones Bacterianas/tratamiento farmacológico , Cistitis/tratamiento farmacológico , Fluoroquinolonas , Ofloxacino/uso terapéutico , Quinolonas/uso terapéutico , Infecciones Urinarias/tratamiento farmacológico , Administración Oral , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Antiinfecciosos/administración & dosificación , Antiinfecciosos/efectos adversos , Infecciones Bacterianas/microbiología , Cistitis/microbiología , Esquema de Medicación , Femenino , Estudios de Seguimiento , Humanos , Masculino , Pruebas de Sensibilidad Microbiana , Persona de Mediana Edad , Ofloxacino/administración & dosificación , Ofloxacino/efectos adversos , Estudios Prospectivos , Quinolonas/administración & dosificación , Quinolonas/efectos adversos , Infecciones Urinarias/microbiologíaRESUMEN
Rufloxacin is a new broad-spectrum fluoroquinolone antibacterial agent. The pharmacokinetics and safety of rufloxacin were evaluated after repeated oral administration to healthy volunteers. The drug was administered once a day for 6 consecutive days following two different dose schedules. The first group of 11 subjects was given a loading dose of 300 mg on the first day and 150 mg on the subsequent 5 days. The second group of 12 subjects was given a loading dose of 400 mg and 200 mg for 5 days. Serum levels and urine concentrations of rufloxacin were determined by microbiological assay. A simultaneous fit of all data points for each subject was done according to a one-compartment open model. The drug was rapidly absorbed (absorption half-life 17 +/- 6 min in the 300 + 150 mg and 11 +/- 5 min in the 400 + 200 mg dose regimen group) and reached maximal serum concentrations (2.77 +/- 0.24 and 3.62 +/- 0.35 micrograms/ml) 4.2 +/- 0.4 and 4.0 +/- 0.9 h after the first administration. Steady-state serum concentrations (3.19 +/- 0.31 and 4.06 +/- 0.33 micrograms/ml) were reached in 3.7 +/- 0.7 and 4.5 +/- 0.4 days. Elimination half-lives were 29.5 +/- 2.4 and 36.0 +/- 2.8 h. Apparent volumes of distribution were 111 +/- 8 and 136 +/- 16 liters and apparent plasma clearances were 46 +/- 5 and 44 +/- 4 ml/min. Renal clearances were 18 +/- 3 and 17 +/- 2 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Antiinfecciosos/farmacocinética , Fluoroquinolonas , Quinolonas/farmacocinética , Administración Oral , Adulto , Antiinfecciosos/administración & dosificación , Esquema de Medicación , Semivida , Humanos , Masculino , Persona de Mediana Edad , Quinolonas/administración & dosificación , Quinolonas/sangre , Quinolonas/orinaRESUMEN
The in vitro activity of rufloxacin (MF 934), a new broad-spectrum fluoroquinolone, was tested against 1,032 gram-positive and gram-negative clinical isolates and compared to that of five other compounds of this class. All quinolones except for ciprofloxacin had limited activity against group A and B streptococci and pneumococci (MIC 90% of 4-64 mg/l) and no activity against enterococci. Most species of the enterobacteriaceae and staphylococci were found to be sensitive to rufloxacin (MIC 90% of 0.5-8 and 2-8 mg/l). Like the other quinolones except for ciprofloxacin, rufloxacin was not active against Pseudomonas aeruginosa. The antibacterial activity of rufloxacin was affected only minimally by an increase in the bacterial inoculum or by alterations in the pH of the medium. In spite of the relatively higher MICs of rufloxacin compared to those of the other quinolones, its favorable pharmacokinetic properties may account for its good clinical efficacy.
Asunto(s)
Antiinfecciosos , Bacterias/efectos de los fármacos , Fluoroquinolonas , Quinolonas/farmacología , Farmacorresistencia Microbiana , HumanosRESUMEN
The sera and the CSFs from 157 Multiple Sclerosis (MS) patients and 43 other neurological diseases (OND) cases have been evaluated for the presence of HTLVI antibodies. A commercial passive agglutination assay (PPA), an indirect fluorescence assay (IFA), and a Western Immunoblotting (WIB) performed in our laboratories have been employed. No OND samples showed HTLVI antibodies, while 14 sera and 1 CSF from MS patients resulted positive by PPA and 4 sera were positive with the IFA. When tested with WIB 6 MS sera showed a reactivity against one or more HTLVI proteins. Our results lead us to affirm that in a small number of MS patients, when sensitive tests are employed, it is possible to observe an antibody response toward proteins that share one or more epitope with HTLVI antigens.
Asunto(s)
Anticuerpos Anti-HTLV-I/sangre , Esclerosis Múltiple/inmunología , Enfermedades del Sistema Nervioso/inmunología , Anticuerpos Anti-HTLV-I/líquido cefalorraquídeo , HumanosRESUMEN
Cholera holotoxin produces both stimulation and inhibition of the growth of different cell populations. These opposite effects were both attributed to the enzymatic activity of the subunit A that activates adenylate cyclase, increasing the intracellular level of cAMP. We observed that the B subunit of cholera toxin produced by itself an inhibition of the 'in vitro' growth of two murine leukemia cell lines (L1210 limphoid leukemia and WEHI-3B myelomonocytic leukemia). The sensitivity of WEHI-3B cells towards cholera toxin was about 5000-times higher than that of the L1210 cells, whereas the two leukemias showed an identical sensitivity to the B subunit (IC50 = 5.10(-10) M for L1210 and 10(-10) M for WEHI-3B). The inhibition produced by the B subunit was neutralized by GM1 and in a minor degree by type II gangliosides. The two leukemias showed a remarkable difference in their gangliosides contents (L1210 cells contained GM1 (80.6%) and GM2 (19.4%), while WEHI-3B cells contained GM1 (28.2%), Fuc-GM1 (44.9%) and a band (26.9%) with a chromatographic mobility between GD1a and GD1b). The inhibition could be explained by a competitive mechanism between the B subunit and some autocrine factor binding GM1-containing receptors. Our data strengthen the suggestion to consider gangliosides as very important pleiotropic biomodulators.
Asunto(s)
Toxina del Cólera/farmacología , Leucemia L1210/patología , Leucemia Experimental/patología , Fragmentos de Péptidos/farmacología , Animales , División Celular/efectos de los fármacos , Factores Estimulantes de Colonias/farmacología , Femenino , Gangliósido G(M1)/análisis , Gangliósido G(M1)/farmacología , Gangliósidos/análisis , Gangliósidos/farmacología , Granulocitos/patología , Células Madre Hematopoyéticas/patología , Leucemia L1210/metabolismo , Leucemia Experimental/metabolismo , Macrófagos/patología , Ratones , Células Tumorales CultivadasAsunto(s)
Antibacterianos/farmacología , Factores Estimulantes de Colonias/biosíntesis , Fluoroquinolonas/farmacología , Activación de Macrófagos/efectos de los fármacos , Factores Estimulantes de Colonias/efectos de los fármacos , Humanos , Macrófagos/efectos de los fármacos , Macrófagos/fisiología , Ácido Nalidíxico/farmacologíaAsunto(s)
Fluoroquinolonas/farmacocinética , Quinolonas/farmacocinética , Administración Oral , Relación Dosis-Respuesta a Droga , Fluoroquinolonas/administración & dosificación , Fluoroquinolonas/sangre , Humanos , Tasa de Depuración Metabólica , Quinolonas/administración & dosificación , Quinolonas/sangre , Valores de ReferenciaAsunto(s)
Antiinfecciosos/farmacología , Enterobacter cloacae/efectos de los fármacos , Fluoroquinolonas/farmacología , Quinolonas/farmacología , Citrobacter freundii/efectos de los fármacos , Enterobacter cloacae/crecimiento & desarrollo , Escherichia coli/efectos de los fármacos , Escherichia coli/crecimiento & desarrollo , Pruebas de Sensibilidad Microbiana , Proteus/efectos de los fármacosRESUMEN
SQ 30836 is an orally absorbed salt of tigemonam, a new monobactam similar to aztreonam in structure and microbiologic properties. When assayed against 400 clinical isolates, tigemonam's activity was similar to that of aztreonam and carumonam. It was highly effective against Enterobacteriaceae but showed poor activity against gram-positive organisms. It inhibited 90% of Escherichia coli, Klebsiella, Shigella, Yersinia, Proteus, Providencia, and Morganella strains at 0.5 micrograms/mL or less, and all Salmonella and Hafnia strains at 1 micrograms/mL or less. Citrobacter, Enterobacter, and Serratia strains were less susceptible (minimum inhibitory concentrations [MIC30] of 2, 32, and 8 micrograms/mL respectively). The activity of the new compound against Enterobacteriaceae is comparable with and often higher than that of third-generation cephalosporins and oral comparison compounds. In contrast to aztreonam, tigemonam had minimal activity against Pseudomonas sp and glucose nonfermenting gram-negative bacteria. Data suggest that poor penetration through the outer membranes of Pseudomonas sp may be responsible for this failure. Tigemonam was stable to hydrolysis by plasmid-mediated and chromosomal beta-lactamases. It was more stable than aztreonam to hydrolysis by the Kl enzyme of Klebsiella and by the Proteus vulgaris beta-lactamase. Also, measurement of the IC50 (concentration of inhibitor able to reduce the activity of the enzyme by 59%) showed that tigemonam has less affinity than aztreonam for class I cephalosporinases. However, only levels of beta-lactamase, not hydrolysis rates or affinity, correlated to MICs of the two monobactams for the resistant Enterobacter and Citrobacter strains.
Asunto(s)
Bacterias Gramnegativas/efectos de los fármacos , Monobactamas/farmacología , beta-Lactamasas/farmacología , Interacciones Farmacológicas , Estabilidad de Medicamentos , Bacterias Gramnegativas/metabolismo , Hidrólisis , Pruebas de Sensibilidad Microbiana , Monobactamas/metabolismo , beta-Lactamasas/metabolismoRESUMEN
SQ 30836 is an orally absorbed salt of tigemonam, a new monobactam similar to aztreonam in structure and microbiologic properties. When assayed against 400 clinical isolates, tigemonam's activity was similar to that of aztreonam and carumonam. It was highly effective against Enterobacteriaceae but showed poor activity against gram-positive organisms. It inhibited 90% of Escherichia coli, Klebsiella, Shigella, Yersinia, Proteus, Providencia, and Morganella strains at 0.5µ/mL or less, and all Salmonella and Hafnia strains at 1 µg/mL or less. Citrobacter, Enterobacter, and Serratia strains were less susceptible (minimum inhibitory concentrations [MIC30] of 2, 32, and 8 µg/mL respectively). The activity of the new compound against Enterobacteriaceae is comparable with and often higher than that of third-generation cephalosporins and oral comparison compounds. In contrast to aztreonam, tigemonam had minimal activity against Pseudomonas sp and glucose nonfermenting gram-negative bacteria. Data suggest that poor penetration through the outer membranes of Pseudomonas sp may be responsible for this failure. Tigemonam was stable to hydrolysis by plasmid-mediated and chromosomal beta-lactamases. It was more stable than aztreonam to hydrolysis by the Kl enzyme of Klebsiella and by the Proteus vulgaris beta-lactamase. Also, measurement of the IC50 (concentration of inhibitor able to reduce the activity of the enzyme by 59%) showed that tigemonam has less affinity than aztreonam for class I cephalosporinases. However, only levels of beta-lactamase, not hydrolysis rates or affinity, correlated to MICs of the two monobactams for the resistant Enterobacter and Citrobacter strains.
RESUMEN
The in vitro activity of the novel monobactam carumonam (RO17-2301) was evaluated on 311 gram-negative clinical isolates in comparison to aztreonam, cefotaxime, ceftazidime, cefotetan and ceftriaxone. Carumonam showed an antibacterial potency equal to or higher than any other reference compound; in particular it was the most effective against Proteus indole positive and Klebsiella sp. Its antipseudomonal activity was comparable to that of ceftazidime and it showed, together with aztreonam, the highest activity against the Citrobacter, Enterobacter and Escherichia coli isolates. The minimal inhibitory concentrations performed on permeability altered organisms indicated that carumonam has a penetration rate comparable to aztreonam and higher than cefotetan and ceftriaxone. Carumonam demonstrated excellent stability to chromosomal and plasmid-mediated beta-lactamases and that correlated with its antibacterial activity against the producing strains and inoculum size effect.