Layer-by-layer coated hybrid nanoparticles with pH-sensitivity for drug delivery to treat acute lung infection.

Bacteria-induced acute lung infection (ALI) is a severe burden to human health, which could cause acute respiratory distress syndrome (ARDS) and kill the patient rapidly. Therefore, it is of great significance to develop effective nanomedicine and therapeutic approach to eliminate the invading bacteria in the lung and manage ALI. In this study, we design a layer-by-layer (LbL) liposome-polymer hybrid nanoparticle (HNP) with a pH-triggered drug release profile to deliver antibiotics for the eradication of bacteria to treat ALI. The liposome is prepared by the lipid film hydration method with a homogenous hydrodynamic diameter and low polydispersity index (PDI). The antibiotic spectinomycin is efficiently loaded into the liposomal core through the pH-gradient method. The pH-sensitive polycationic polymer poly(ß-amino ester) (PBAE) and polyanionic sodium alginate (NaAIg) layers are decorated on the surface of liposome in sequence via electrostatic interaction, resulting in spectinomycin-loaded layer-by-layer hybrid nanoparticles (denoted as Spe@HNPs) which have reasonable particle size, high stability, prolonged circulation time, and pH-triggered drug release profile. The in vitro results demonstrate that Spe@HNPs can efficiently induce the death of bacteria with low minimum inhibitory concentration (MIC) against Staphylococcus aureus (S. aureus) and drug-resistant MRSA BAA40 strains. The in vivo results reveal that Spe@HNPs can eradicate the invading MRSA BAA40 with improved antimicrobial efficacy and low side-effect for ALI treatment. This study not only reports a promising nanomedicine but also provides an effective method to prepare nanoplatforms for drug delivery and controlled release.

Development and Characterization of a Dry Powder Formulation for Anti-Tuberculosis Drug Spectinamide 1599.

PURPOSE: Human tuberculosis (TB) is a global health problem that causes nearly 2 million deaths per year. Anti-TB therapy exists, but it needs to be administered as a cocktail of antibiotics for six months. This lengthy therapy results in low patient compliance and is the main reason attributable to the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis. METHODS: One alternative approach is to combine anti-TB multidrug therapy with inhalational TB therapy. The aim of this work was to develop and characterize dry powder formulations of spectinamide 1599 and ensure in vitro and in vivo delivered dose reproducibility using custom dosators. RESULTS: Amorphous dry powders of spectinamide 1599 were successfully spray dried with mass median aerodynamic diameter (MMAD) = 2.32 ± 0.05 µm. The addition of L-leucine resulted in minor changes to the MMAD (1.69 ± 0.35 µm) but significantly improved the inhalable portion of spectinamide 1599 while maintaining amorphous qualities. Additionally, we were able to demonstrate reproducibility of dry powder administration in vitro and in vivo in mice. CONCLUSIONS: The corresponding systemic drug exposure data indicates dose-dependent exposure in vivo in mice after dry powder intrapulmonary aerosol delivery in the dose range 15.4 - 32.8 mg/kg.

Effect of Cessation of Ceftiofur and Substitution with Lincomycin-Spectinomycin on Extended-Spectrum-ß-Lactamase/AmpC Genes and Multidrug Resistance in Escherichia coli from a Canadian Broiler Production Pyramid.

Ceftiofur, a third-generation cephalosporin antimicrobial, was used in Canadian hatcheries for many years to prevent early mortality in chicks, leading to a high prevalence of cephalosporin resistance in Escherichia coli in chickens. Preventive use of ceftiofur in hatcheries ceased in 2014. We examined the effect of ceftiofur cessation (n = 40 flocks with ceftiofur and n = 28 flocks without antimicrobial at hatchery) and its replacement with an antimicrobial combination, lincomycin-spectinomycin (n = 32), at the hatchery on the proportion of samples with E. coli positive for extended-spectrum-ß-lactamase (ESBL) and AmpC ß-lactamase-related genes, and on the multidrug resistance profiles of ESBL/AmpC-positive E. coli in broilers and their associated breeders (n = 46 samples), at 1 year postcessation. For indicator E. coli from nonenriched media, a significant decrease postcessation in the proportion of samples harboring E. coli isolates positive for blaCMY-2 and/or blaCTX-M was observed. In contrast, following enrichment in medium containing ceftriaxone (1 mg/liter) to facilitate recovery of ESBL/AmpC ß-lactamase-producing E. coli colonies, both pre- and postcessation, 99% of the samples harbored E. coli positive for blaCMY-2 or blaCTX-M Among the 15 tested antimicrobial agents, flocks receiving lincomycin-spectinomycin after cessation of ceftiofur showed a significantly greater nonsusceptibility to aminoglycosides, folate inhibitors, phenicols, and tetracyclines and a greater proportion of possible extensively drug-resistant E. coli than those receiving ceftiofur or no antimicrobial at hatchery. This study clearly demonstrates an initial decrease in ESBL/AmpC-positive E. coli following the cessation of ceftiofur in the hatchery but an increase in antimicrobial non-ß-lactam resistance of ESBL/AmpC-positive E. coli following replacement with lincomycin-spectinomycin.IMPORTANCE Antimicrobial resistance is a global problem. The antimicrobial ceftiofur has been used worldwide for disease prevention in poultry production, resulting in a greatly increased resistance to this antimicrobial important in poultry and human medicine. Our study examined the impact of ceftiofur cessation and its replacement with the antimicrobial combination lincomycin-spectinomycin, a common practice in the industry. Our study demonstrated a decrease in ceftiofur resistance after the cessation of ceftiofur use, although the resistance genes remain ubiquitous in all phases of poultry production, showing that poultry remains a reservoir for ceftiofur resistance and requiring continued vigilance. We also observed a decrease in multidrug resistance involving different antimicrobial classes after cessation of ceftiofur but an increase following use of lincomycin-spectinomycin, indicating that this antimicrobial use should be questioned. Reduced resistance to ceftiofur in poultry may translate to better treatment efficacy, decreased morbidity/mortality, and enhanced food safety for humans.

Efficacy of Aminomethyl Spectinomycins against Complex Upper Respiratory Tract Bacterial Infections.

The most frequent ailment for which antibiotics are prescribed is otitis media (ear infections), which is most commonly caused by Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae Treatment of otitis media is complicated by the fact that the bacteria in the middle ear typically form biofilms, which can be recalcitrant to antibiotic treatment. Furthermore, bacterial respiratory infections can be greatly exacerbated by viral coinfection, which is particularly evidenced by the synergy between influenza and S. pneumoniae In this study, we sought to ascertain the in vivo efficacy of aminomethyl spectinomycin lead 1950, an effective antibacterial agent both in vitro and in vivo against Streptococcus pneumoniae in the context of complex respiratory infections and acute otitis media. A single dose of 1950 significantly reduced bacterial burden in the respiratory tract for all three pathogens, even when species were present in a coinfection model. Additionally, a single dose of 1950 effectively reduced pneumococcal acute otitis media from the middle ear. The agent 1950 also proved efficacious in the context of influenza-pneumococcal super infection. These data further support the development of this family of compounds as potential therapeutic agents against the common causes of complex upper respiratory tract infections and acute otitis media.

Comparative pharmacokinetics of spectinamide 1599 after subcutaneous and intrapulmonary aerosol administration in mice.

Spectinamides are a novel series of spectinomycin analogs being developed for the treatment of tuberculosis. Intrapulmonary aerosol (IPA) administration of lead spectinamide 1599 has previously been shown to be more efficacious than subcutaneous (SC) administration at comparable doses. The objective of the current study was to characterize the disposition of 1599 in plasma and lungs in mice in order to provide a potential rationale for the observed efficacy differences. 200 mg/kg of 1599 was administered to healthy BALB/c mice by SC injection or by IPA delivery. Plasma and major organs were collected at specified time points until 8 h after dosing. Drug concentrations were measured by LC-MS/MS and analyzed by noncompartmental pharmacokinetic analysis. 1599 demonstrated rapid absorption into plasma after IPA and SC administration, resulting in very similar plasma exposure for both routes. In contrast, drug exposure in the lungs was 48 times higher following IPA as compared to SC administration, which is highly desirable as the lungs are the main site of infection in pulmonary TB. The higher local exposure in the lungs is likely the basis for the increased efficacy after IPA compared to SC administration. Overall, this study supports the pulmonary route as a potential pathway for the treatment of tuberculosis with 1599.

Nonadherence to National Guidelines for Antibiotic Treatment of Uncomplicated Gonorrhea in China: Results From a Nationwide Survey.

BACKGROUND: Provider adherence to the national treatment guidelines for gonorrhea is critical to assuring effective treatment. It is also an important means of limiting antibiotic overuse, which can lead to development of resistant bacteria. The Chinese treatment guidelines recommend the monotherapy with ceftriaxone or spectinomycin in accordance with the World Health Organization guidelines for treatment of uncomplicated gonorrhea. We evaluated adherence to the guidelines among treatment providers in China. METHODS: The study was a nationwide cross-sectional study. In each of the 6 geographic regions in China, at least 1 province was selected. In each selected province, cities with elevated incidence of reported gonorrhea were purposively selected. Using a questionnaire, 2121 physicians recruited from 512 different categories and levels of health sectors from July to September 2017 were investigated. RESULTS: Of the participants, more than 99% diagnosed gonorrhea using one of the laboratory tests including Gram stain, culture, nucleic acid amplification test, or other tests. Culture was the predominant assay of the choice for the diagnosis. Of the 1890 physicians who provided information on prescription behaviors, 62.2% were not adherent to the regimens for treatment of uncomplicated gonorrhea recommended by the National Sexually Transmitted Disease (STD) Treatment Guidelines (National STD Guidelines). Physicians working in the areas located in Northern China (adjusted odds ratio [AOR], 3.06; 95% confidence intervals [CIs], 1.77-5.31), in general hospitals or departments of urology (AOR, 1.54; 95% CIs, 1.08-2.19), diagnosing more cases in the past 6 months (AOR, 1.82; 95% CIs, 1.25-2.67), or unfamiliar with the treatment regimens in the National STD Guidelines (AOR, 3.48; 95% CIs, 2.76-4.37) were significantly more likely to be nonadherent to the National STD Guidelines. CONCLUSIONS: It can be concluded from our study that nonadherence to the national guidelines and empirical treatment with high doses of ceftriaxone occurred frequently in China. Further studies on the impacts of the empirical treatment on antimicrobial resistance of gonorrhea are needed.

Antibiotics for treating gonorrhoea in pregnancy.

BACKGROUND: Gonorrhoea is a sexually transmitted infection that is caused by Neisseria gonorrhoeae, and is a major public health challenge today. N gonorrhoeae can be transmitted from the mother's genital tract to the newborn during birth, and can cause gonococcal ophthalmia neonatorum as well as systemic neonatal infections. It can also cause endometritis and pelvic sepsis in the mother. This review updates and replaces an earlier Cochrane Review on antibiotics for treating this infectious condition. OBJECTIVES: To assess the clinical effectiveness and harms of antibiotics for treating gonorrhoea in pregnant women. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 May 2017), LILACS database (1982 to April 5, 2017), the WHO International Clinical Trials Registry Platform (ICTRP; April 5, 2017), ClinicalTrials.gov (April 5, 2017), the ISRCTN Registry (April 5, 2017), and Epistemonikos (April 5, 2017). We also searched reference lists of all retrieved articles. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing the use of antibiotics for treating gonorrhoea in pregnancy. The antibiotics could have been used alone or in combination, were administered parenterally, orally, or both, and were compared with another antibiotic.We included RCTs regardless of their publication status (published, unpublished, published as an article, an abstract, or a letter), language, or country. We applied no limits on the length of follow-up.We excluded RCTs using a cluster- or cross-over design, or quasi-RCTs. DATA COLLECTION AND ANALYSIS: Three review authors independently assessed trials for inclusion and risk of bias, extracted data, and checked them for accuracy. MAIN RESULTS: We included two RCTs, that randomised 514 pregnant women (347 women analysed) at a mean gestational age of 22 weeks. Both trials were conducted in the outpatient department of the same two hospitals in the USA between 1993 and 2001, and had a follow-up of 14 days. One of the trials was sponsored by a drug company. We considered both trials to be at a high risk of bias.One trial compared ceftriaxone (125 mg, intramuscular) with cefixime (400 mg, oral); the other trial had three arms, and assessed ceftriaxone (250 mg, intramuscular) versus either amoxicillin (3 g, oral) plus probenecid (1 g, oral) or spectinomycin (2 g, intramuscular). We did not include the spectinomycin data because this medication is no longer produced. We were unable to conduct meta-analysis because the trials compared different medications.We found inconclusive evidence that there were clear differences in the cure of gonococcal infections (genital, extragenital, or both) between intramuscular ceftriaxone versus oral amoxicillin plus oral probenecid (risk ratio (RR) 1.07, 95% confidence interval (CI) 0.98 to 1.16; one RCT; 168 women; very low-quality evidence) or intramuscular ceftriaxone versus oral cefixime (RR 0.99, 95% CI 0.91 to 1.08; one RCT; 95 women; very low-quality evidence).Neither of the trials reported on two of this review's primary maternal outcomes: incidence of obstetric complications (miscarriage, premature rupture of membranes, preterm delivery, or fetal death), or disseminated gonococcal infection, or on the incidence of neonatorum ophthalmia in the neonates.One trial reported one case of vomiting in the oral amoxacillin plus probenecid group. Trials reported pain at the injection sites, but did not quantify it. Hyperberbilurrubinemia was more frequent in neonates whose mothers were exposed to ceftriaxone. There were no clear differences between groups for neonatal malformation. AUTHORS' CONCLUSIONS: This Cochrane Review found high levels of cure of gonococcal infections in pregnancy with the given antibiotic regimens. However, the evidence in this review is inconclusive as it does not support one particular regimen over another. This conclusion was based on very low-quality evidence (downgraded for poor trial design, imprecision) from two trials (involving 514 women), which we assessed to be at a high risk of bias for a number of domains. The harm profiles of the antibiotic regimes featured in this review remain unknown.High-quality RCTs are needed, with sufficient power to assess the clinical effectiveness and potential harms of antibiotics in pregnant women with gonorrhoea. These should be planned according to Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT),conducted following CONSORT recommendations, and based on Patient-Centered Outcomes Research Institute (PCORI) outcomes.

Time-kill curve analysis and pharmacodynamic modelling for in vitro evaluation of antimicrobials against Neisseria gonorrhoeae.

BACKGROUND: Gonorrhoea is a sexually transmitted infection caused by the Gram-negative bacterium Neisseria gonorrhoeae. Resistance to first-line empirical monotherapy has emerged, so robust methods are needed to evaluate the activity of existing and novel antimicrobials against the bacterium. Pharmacodynamic models describing the relationship between the concentration of antimicrobials and the minimum growth rate of the bacteria provide more detailed information than the MIC only. RESULTS: In this study, a novel standardised in vitro time-kill curve assay was developed. The assay was validated using five World Health Organization N. gonorrhoeae reference strains and a range of ciprofloxacin concentrations below and above the MIC. Then the activity of nine antimicrobials with different target mechanisms was examined against a highly antimicrobial susceptible clinical strain isolated in 1964. The experimental time-kill curves were analysed and quantified with a previously established pharmacodynamic model. First, the bacterial growth rates at each antimicrobial concentration were estimated with linear regression. Second, we fitted the model to the growth rates, resulting in four parameters that describe the pharmacodynamic properties of each antimicrobial. A gradual decrease of bactericidal effects from ciprofloxacin to spectinomycin and gentamicin was found. The beta-lactams ceftriaxone, cefixime and benzylpenicillin showed bactericidal and time-dependent properties. Chloramphenicol and tetracycline were purely bacteriostatic as they fully inhibited the growth but did not kill the bacteria. We also tested ciprofloxacin resistant strains and found higher pharmacodynamic MICs (zMIC) in the resistant strains and attenuated bactericidal effects at concentrations above the zMIC. CONCLUSIONS: N. gonorrhoeae time-kill curve experiments analysed with a pharmacodynamic model have potential for in vitro evaluation of new and existing antimicrobials. The pharmacodynamic parameters based on a wide range of concentrations below and above the MIC provide information that could support improving future dosing strategies to treat gonorrhoea.

WHO guidelines for the treatment of neisseria gonorrhoeae

Rationale for the guidelines: Since the publication of the WHO Guidelines for the management of sexually transmitted infections in 2003, changes in the epidemiology of STIs and advancements in prevention, diagnosis and treatment necessitate changes in STI management. There is an urgent need to update treatment recommendations for gonococcal infections to respond to changing antimicrobial resistance (AMR) patterns of N. gonorrhoeae. High-level resistance to previously recommended quinolones is widespread and decreased susceptibility to the extended-spectrum (third-generation) cephalosporins, another recommended first-line treatment in the 2003 guidelines, is increasing and several countries have reported treatment failures. These guidelines for the treatment of common infections caused by N. gonorrhoeae form one of several modules of guidelines for specific STIs. Other modules will focus on treatments for Chlamydia trachomatis (chlamydia), herpes simplex virus type 2 (HSV-2; genital herpes) and Treponema pallidum (syphilis). In addition, future work will provide guidance for syphilis screening and treatment of pregnant women, STI syndromic approach, clinical management, STI prevention, and treatments for other STIs. It is strongly recommended that countries take updated global guidance into account as they establish standardized national protocols, adapting this guidance to the local epidemiological situation and antimicrobial susceptibility data. The objectives of these guidelines are: to provide evidence-based guidance on treatment of infection with N. gonorrhoeae; and to support countries to update their national guidelines for treatment of gonococcal infection.

Pharmacokinetic profile of spectinomycin in rats.

Following intravenous (IV) administration, the pharmacokinetics of spectinomycin in rats was found to be on par with its profile in other mammalian species including humans with respect to its overall excretion and half-life at effective concentrations. This study, however, indicates that a small fraction of the spectinomycin dose is retained in peripheral tissues for a prolonged period of time at low concentrations.

Single-dose treatment of male patients with gonococcal urethritis using 2g spectinomycin: microbiological and clinical evaluations.

The microbiological and clinical efficacies of a single-dose treatment of 2g spectinomycin administered by intramuscular injection were studied in 365 male patients with gonococcal urethritis. A total of 210 patients (57.5%) could be evaluated, in 28 (13.3%) of whom Chlamydia trachomatis was detected in addition to Neisseria gonorrhoeae. A single dose of spectinomycin eradicated N. gonorrhoeae in 203 (96.7%) of the 210 patients. Among patients in whom N. gonorrhoeae was eradicated, pyuria and clinical symptoms, respectively, disappeared in 92.6% (162/175) and 98.9% (173/175) of patients without concomitant C. trachomatis and in 78.6% (22/28) and 71.4% (20/28) with C. trachomatis. Minimal inhibitory concentrations (MICs) were determined for four of seven N. gonorrhoeae strains isolated after spectinomycin treatment. MICs to spectinomycin for three of the four isolates were 16 microg/mL (defined as susceptible) and the MIC of the other isolate was 128 microg/mL, indicating resistance. The resistant isolate was a multidrug-resistant strain with resistance to ciprofloxacin, tetracycline, penicillin and cephalosporins, except for ceftriaxone. The results of this study indicate that a single-dose treatment using 2g spectinomycin is effective in treating patients with urethritis caused by N. gonorrhoeae, even in the era of multidrug-resistant N. gonorrhoeae.

[Acute urethritis caused by Neisseria meningitidis and Chlamydia trachomatis].

A 16-year-old heterosexual man presented to our hospital with a purulent urethral discharge and pain at voiding. These symptoms began seven days after oral-genital contact (fellatio) with his partner. A Gram-stained smear from the urethral discharge showed Gram-negative diplococci, and the antigen of Chlamydia trachomatis from urine was positive. We initially made a diagnosis of urethritis caused by Neisseria gonorrhoeae and C. trachomatis. However, N. meningitidis was isolated by culture. Clinicians should pay attention to the possibility of N. meningitidis infection in all cases resembling gonococcal urethritis.

Pharmacokinetics and bioavailability of spectinomycin after i.v., i.m., s.c. and oral administration in broiler chickens.

A pharmacokinetic and bioavailability study of spectinomycin was conducted in healthy broiler chickens following administration of a single (50 mg/kg bw) intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) dose and oral doses of 50 and 100 mg/kg bw. Following i.v. administration, the elimination half-life (t1/2beta), mean residence time (MRT), volume of distribution at steady-state (Vd(ss)), volume of distribution based on the terminal phase (Vd(z)) and total body clearance (ClB) were 1.46+/-1.10 h, 1.61+/-1.05 h, 0.26+/-0.009 L/kg, 0.34 (0.30-0.38) L/kg and 2.68+/-0.017 mL/min/kg respectively. After i.m. and s.c. dosing, the Cmax was 152.76+/-1.08 and 99.77+/-1.04 microg/mL, achieved at 0.25 (0.25-0.50) and 0.25 (0.25-1.00) h, the t1/2beta was 1.65+/-1.07 and 2.03+/-1.06 h and the absolute bioavailability (F) was 136.1% and 128.8% respectively. A significant difference in Cmax (5.13+/-0.10, 14.26+/-1.12 microg/mL), t1/2beta (3.74+/-1.07, 8.93+/-1.13 h) and ClB/F (22.69+/-0.018, 10.14+/-0.018 mL/min/kg) were found between the two oral doses (50 and 100 mg/kg bw respectively), but there were no differences in the tmax [2.00 (2.00-4.00), 2.00 (2.00-2.00) h] and Vd(z)/F [6.95 (6.34-9.06), 7.98 (4.75-10.62) L/kg). The absolute bioavailability (F) of spectinomycin was 11.8% and 26.4% after oral administration of 50 and 100 mg/kg bw respectively.

The effects of lincomycin-spectinomycin and sulfamethoxazole-trimethoprim on hyaluronidase activities and sperm characteristics of rams.

The effects of lincomycin-spectinomycin and sulfamethoxazole-trimethoprim combinations on the hyaluronidase enzyme of serum and semen and on sperm characteristics in rams were determined. Thirthy-two Akkaraman rams were used. The rams were randomly divided into four groups. Group A and group B were determined as control groups of group C (lincomycin-spectinomycin) and D (sulfamethoxazole-trimethoprim), respectively. Combinations of lincomycin-spectinomycin and sulfamethoxazole-trimethoprim were administered at doses of 15 mg.kg(-1) intramuscularly and 12 mg.kg(-1) body weights orally, respectively. Blood and semen samples were collected at 4, 12, 24, 48, 72, 192 and 384 hr. Semen hyaluronidase activities of rams in group C increased significantly (p<0.001, <0.05) compared with the control group at 24 and 48 hr, respectively. Semen hyaluronidase activities in group D rams also increased significantly (p<0.001) in comparison with the control group at all times except 72 and 384 hr. Serum hyaluronidase activities increased significantly (p<0.01, <0.001) at 24 and 48 hr after treatment of lincomycin-spectinomycin. Additionally, significant (p<0.05, <0.001) increases were detected in the serum hyaluronidase activities of group D at 48 and 72 hr, respectively. No significant correlation was found between serum and semen hyaluronidase activities. Furthermore, significant increases (p<0.05) were observed in the percentages of motile sperm in the rams of group C and D compared with the control groups. The values of sperm concentration and total number of sperm in group C and D rams decreased significantly (p<0.001) in comparison with control groups. No significant correlations were found between the semen hyaluronidase activities and sperm characteristics. In conclusion, these findings show that the combinations of lincomycin-spectinomycin and sulfamethoxazole-trimethoprim do not have any harmful effects on hyaluronidase activities and sperm motility. However, the use of both antibiotic combinations in breeding rams during the ramming season is not advisable due to the decrease of sperm concentration.

The effect of organic acids on the control of porcine post-weaning diarrhoea.

Post-weaning diarrhoea syndrome (PWDS) of piglets is caused mainly by Enterotoxigenic Escherichia coli (ETEC) strains. Six organic acids were tested for their efficacy in the control of PWDS, using a total of 384 weaned piglets, in eight groups, during a 28-day period. One group (negative control) was offered a diet free of antimicrobials, one group (positive control) was offered the same diet medicated with 44 p.p.m. of lincomycin and 44 p.p.m. spectinomycin (Lincospectin 22 premix, Upjohn), and six groups were offered feed supplemented with either 1.0 per cent propionic acid, 1.6 per cent lactic acid, 1.2 per cent formic acid, 1.2 per cent malic acid, 1.5 per cent citric acid or 1.5 per cent fumaric acid. Groups were compared with regard to the appearance of clinical signs, mortality, weight gain and feed conversion. All groups supplemented with organic acids had reduced incidence and severity of diarrhoea, and performed significantly better than the negative control group (P<0.05). At the end of the trial, ETEC strains were detected in the control group not receiving antibiotics but not in the treated group. Organic acids and especially lactic acid are a useful tool in controlling PWDS.

Efficacy of spectinomycin against Mycoplasma bovis induced pneumonia in conventionally reared calves.

Sixteen 3-week-old calves were intratracheally inoculated with Mycoplasma bovis. Follow-up consisted of regular bronchoalveolar lavages (BALs) and clinical examinations. Animals were slaughtered from 4 to 21 days after inoculation. Counts were made of the mycoplasmas and other bacteria systematically isolated from the BAL liquids and lung lobes after slaughter. On the 6th day, spectinomycin 20mg/kg was given intramuscularly in three repeated doses at 24h intervals to six randomly chosen calves. All animals had developed a persistent M. bovis infection with a maximum BAL count on the 6th day (start of treatment). Co-occuring Pasteurella multocida infection was found in most animals with a maximum rate on the 14th day. The extent of lung surface lesions varied widely (0-64%) but was greater in the later slaughtered calves. Average counts of M. bovis and P. multocida in the BAL liquids were lower in treated calves than in untreated ones but the difference was not statistically significant. However, M. bovis and P. multocida counts in the lungs of the treated group were significantly lower than in the untreated group (p=0.003 and 0.009, respectively).

Marking cell layers with spectinomycin provides a new tool for monitoring cell fate during leaf development.

Spectinomycin, an inhibitor of plastid protein synthesis, can be used to mark specific cell layers in the shoot meristem of Brassica napus. Pale yellow-green (YG) plants resulting from spectinomycin-treatment can be propagated indefinitely in vitro. Microscopic examination showed that YG-plants result from inactivation of plastids in the L2 and L3 layers and are composed of a pale green epidermis covering a white mesophyll layer. Epidermal cells of YG and normal green plants are similar and contain 10-20 small pale green plastids. YG plants are equivalent to periclinal chimeras with the important distinction that there is no genotypic difference between the white and green cell layers. Periclinal divisions of epidermal cells take place at all stages of leaf development to produce invaginations of green mesophyll located in sectors of widely varying sizes. A periclinal division rate of 1 in 3000-4000 anticlinal divisions for the adaxial epidermis, was 2-3-fold higher than that estimated for the abaxial epidermis. Analysis of white and green mesophyll showed that chloroplasts are essential for palisade cell differentiation and this requirement is cell-autonomous. Stable marking of cell lineages with spectinomycin is simple, rapid and reveals the requirement for functional plastids in cellular differentiation.