In vitro effect of subinhibitory concentrations of ceftazidime and meropenem on the serum sensitivity of Pseudomonas aeruginosa strains

The aim of this study was to determine the effect of subminimal inhibitory concentrations (subMICs) of ceftazidime, meropenem and gentamicin on the in vitro serum sensitivity of Pseudomonas aeruginosa strains isolated from a variety of isolation sites at two medical wards and an intensive care unit in a government university hospital in Croatia. A total of 20 serum-resistant P aeruginosa strains isolated from different clinical specimens were selected. Bacteria were exposed to 1/2, 1/4, 1/8, 1/16, and 1/32 x MIC of each antibiotic tested. Sensitivity of P. aeruginosa strains to bactericidal activity of normal human serum before and after bacterial exposure to subMICs was determined. Significant difference in serum sensitivity of the strains was observed after the bacteria were exposed to subMICs of ceftazidime and meropenem (p < 0.01), while the exposure to subMICs of gentamicin did not affect significantly the resistance of tested strains to the serum bactericidal activity. Comparing the number of serum-resistant strains before and after exposure to subMICs of antibiotics, statistically significant differences were determined (p < 0.01) after exposure of the strains to 1/2, 1/4, 1/8 and 1/16 x MIC of meropenem, and after exposure to 1/2, 1/4 and 1/8 x MIC of ceftazidime. SubMICs of ceftazidime and meropenem affected not only the resistance to serum bactericidal activity of bacteria, but also their morphology. The alterations in bacterial morphology caused by subMICs of ceftazidime and meropenem could be connected with consecutive bacterial serum sensitivity.     

Molecular epidemiology of penicillin resistantStreptococcus pneumoniae strains in Turkey. A multicenter study

A total of 539 isolates recovered from various clinical sites were collected from 13 hospitals from different regions of Turkey between 1999 and 2002. Susceptibility to penicillin and cefotaxime was determined by the E-test and the remaining antimicrobials were evaluated by disk diffusion tests. Penicillin resistant and intermediate isolates were serotyped and PFGE patterns were analysed. Overall 16 isolates (3%) were resistant to penicillin, and 143 (26.5%) were intermediate. Resistance and intermediate rates were 3.1% and 29.0% respectively in respiratory tract isolates. Multiple resistance (resistance to ≥3 antibiotics) occurred in 81.8% of the penicillin resistant isolates and the most frequent resistance phenotype was penicillin+trimethoprim/sulphamethoxazole (37.7%). Minimum inhibitory concentrations of cefotaxime were lower than 1 mg/ml for all the isolates. The highest rate of resistance was observed for trimethoprim/ sulphamethoxazole (26.6%) followed by doxycycline (12.6%). Resistance to erythromycin was 10.1%, clindamycin 9.9%, chloramphenicol 4.3%, ofloxacin 5.0% and levofloxacin 0.2%. There was no resistance to vancomycin. Resistant isolates belonged to serogroups 9, 23, and 6. The most frequent serogroups among intermediate isolates were 23, 19, 14, 1, 9, and 6. Five distinct PFGE patterns were observed among penicillin resistant isolates. There was no distinct clustering of specific PFGE patterns in the study centres. No correlation between serotypes, resistance and PFGE patterns was found. There seems to be genetic heterogeneity inStreptococccus pneumoniae isolates in Turkey.     

Susceptibility to selected antibiotics of Yersinia enterocolitica 03 strains, carrying and not carrying plasmid pYV

A total of 199 clinical strains of Yersinia enterocolitica serotype O3, biotype 4 were tested for their susceptibility to antibiotics (158 strains carried the virulence plasmid pYV and 41 strains did not). 114 isolates were tested by standard disk diffusion method for 21 antibiotics. Almost all tested strains were resistant to ampicillin and cefazolin and susceptible to amoxycillin/clavulanate, cefaclor, cefamandole, cefuroxime, cefotaxime, ceftriaxone, aztreonam, imipenem, gentamicin, amikacin, netilmicin, tetracycline, doxycycline, chloramphenicol, ciprofloxacin, sulphamethoxazole, co-trimoxazole, trimethoprim and furazolidone. In addition minimal inhibitory concentrations (MICs) of 15 antibiotics were determined by agar dilution method for all 199 strains (158 plasmid positive and 41 strains plasmid negative). Third-generation cephalosporins such as cefotaxime and ceftriaxone and a fluoroquinolone (ciprofloxacin) were the most active antimicrobial agents, tested followed by aztreonam, imipenem, trimethoprim, tetracycline, gentamicin, chloramphenicol, amoxycillin/clavulanate, cefaclor, cefuroxime, amikacin, furazolidone and sulphamethoxazole. The present study demonstrated a high susceptibility of clinical strains of Y. enterocolitica to most of the tested antibiotics. In general, there was no significant difference between susceptibility of virulence plasmid pYV positive and virulence plasmid negative strains to antibacterial agents.     

Coagulase-negative staphylococci in municipal waste

The total of 259 coagulase-negative staphylococci isolates gained from aerosols created during dumping and utilisation of municipal waste were investigated. Species and subspecies identification allowed to determine predominance of novobiocin-resistant species which primarily colonise rodents or other animals. However, about 30% of isolates were species originating from humans. Metabolic properties of the studied group of isolates were examined, as well as their sensitivity to a set of 8 commonly used antibiotics: amoxicillin, erythromycin, tetracycline, clindamycin, chloramphenicol, gentamicin, trimethoprim/sulfamethoxazole and ciprofloxacin. Many isolates resistant to erythromycin (19%), tetracycline (13%) and a considerably smaller group resistant to clindamycin (6.2%), chloramphenicol (2%) and trimethoprim/sulfamethoxazole (1%) were found. It appeared that processes of occurring at the time of dumping and utilisation of waste affect the prevalence of only some features. The examined metabolic features were found to be relatively stable and no changes were observed, which would indicate the tendency of adaptation to existence in the inanimate matter environment. Only isolates with active nitrate reductase were more frequently detected. The increase in frequency of occurrence of isolates resistant to tetracycline and chloramphenicol and simultaneous elimination of isolates resistant to other antibiotics were observed.     

Clinical Evaluation of Co-trimoxazole and Furazolidone in Treatment of Shigellosis in Children

Co-trimoxazole (trimethoprim—sulphamethoxazole) was compared with furazolidone in the treatment of shigellosis in two groups of 33 and 30 patients respectively. Those treated with co-trimoxazole recovered more quickly; none had shigellae in the faeces four days after the start of treatment, whereas in the group given furazolidone eight still had positive stool cultures seven days after treatment.The susceptibility of 104 shigella strains to seven antimicrobial agents was studied by plate dilution technique. All agents but tetracycline and chloramphenicol were found highly effective against most of the strains tested. All shigella isolates were resistant to sulphamethoxazole, and 63% were sensitive to trimethoprim. Potentiation of trimethoprim by sulphamethoxazole was shown in that all strains tested became sensitive to the combination of trimethoprim and sulphamethoxazole in a ratio of 1:20.     

Sensitivity of Haemophilus influenzae to Antibiotics

The use of many different antibiotics to treat chest infection has led us to test the sensitivity of 68 strains of Haemophilus influenzae to 15 different compounds. These included established compounds such as ampicillin and tetracycline and newer agents such as cephalosporins and clindamycin. The minimum inhibitory concentrations of the compounds for H. influenzae were then compared with blood levels attained after the usual dose regimens. There has been a significant increase in tetracycline resistance in the last few years, but all strains were sensitive to ampicillin, chloramphenicol, sulphamethoxazole, and trimethoprim, Several antibiotics were found to be microbiologically unsuitable for treating H. influenzae infections.     

Psychiatric care and politics.

The minimum inhibitory concentrations (MIC''s) of penicillin, ampicillin, tetracycline, erythromycin, spectinomycin and sulfadiazine were determined for 732 isolates of Neisseria gonorrhoeae collected in 1973-74. Comparison of the results of this survey with data from other Canadian studies showed that the percentage of isolates resistant to tetracycline had not changed since 1966, but that the percentage of erythromycin-resistant isolates had decreased. After an initial increase in 1966 the percentage of penicillin-resistant isolates stabilized. Spectinomycin-resistant isolates were not found. Positive correlations were observed between the MICs of the antibiotics tested; the highest positive correlations were between penicillin and ampicillin and between penicillin and tetracycline. A positive correlation was also noted between penicillin resistance and increasing spectinomycin MICs. Finally, a significant seasonal variation in MICs was found, the trend being towards increasing MICs during the summer.     

Susceptibility of Neisseria gonorrhoeae to seven antibiotics in vitro

One hundred consecutive isolates of N. gonorrhoeae were tested for susceptibility to penicillin, ampicillin, tetracycline, erythromycin, kanamycin, cephaloridine and cephalexin by an agar dilution method. Relative resistance to penicillin was frequent. For 39% of isolates the minimum inhibitory concentration (MIC) of penicillin was 0.05 U./ml. or less; in 55% the MIC was 0.5 to 2.0 U./ml. Ampicillin was slightly more active than penicillin G: all isolates were inhibited by 0.5μg./ml. or less. Resistance to tetracycline and erythromycin was frequent with MIC of 1 μg./ml. or greater observed in 32 and 24% of isolates respectively. The MIC of kanamycin for all gonococci was 8 μg./ml. or greater. Cephalexin was slightly more active than cephaloridine, though each drug exhibited a wide range of MIC values. Gonococcus isolates resistant to penicillin (MIC of 1.0 U./ml. or greater) tended to be resistant to the other antibiotics tested.     

Study of the L-transforming action on Brucella cells of tetracycline, streptomycin, rifampicin and their combinations with penicillin in in vitro experiments]

The in vitro study of the possible formation of L-forms of Brucella under the effect of tetracycline, streptomycin, rifampicin or their combinations with penicillin showed that passages of various Brucella species on media containing increasing concentrations of the antibiotics resulted in insignificant morphological changes in the cells. Passages of the same cultures on media containing combinations of the above antibiotics with penicillin resulted in more significant changes in the cell morphology, up to formation of spheroplasts. No L-transformation was observed under the experimental conditions.     

Molecular characterization of antibiotic resistance in clinical Salmonella typhi isolated in Ghana

Fifty-eight clinical Salmonella typhi strains isolated from patients suspected of suffering from typhoid fever were obtained at the Korle-Bu Teaching Hospital and the Noguchi Memorial Institute for Medical Research, both located in Ghana, Africa. Each isolate was examined for susceptibility to ampicillin, chloramphenicol, streptomycin, tetracycline, and trimethoprim/sulfamethoxazole by the disk diffusion assay. Five of the isolates were resistant to all five antibiotics while 10 isolates were resistant to ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole, which are considered 'first line' antibiotics in the treatment of typhoid fever. Thirty-four isolates were resistant to at least one of the antibiotics tested and 62% of these isolates possessed conjugable plasmids belonging to incompatibility group IncHI. Ninety percent of the conjugable plasmids conferred a multiple drug-resistant phenotype on the strains harboring them. Additionally, 14 strains contained plasmids that were transformable and six of them encoded multiple drug resistance. Our findings indicate that multiple drug resistance to the 'first line' antibiotics in S. typhi may be more prevalent in Africa than previously thought.     

Functional and safety aspects of Enterococci isolated from different Spanish foods

The incidence and diversity of enterococci in retail food samples of meat, dairy and vegetable origin was investigated. Enterococci were present, at concentrations of 10(1) to 10(4) CFU/g. Fifty selected isolates from food samples grouped in two separate clusters by RAPD analysis. Cluster G1 (72% of the isolates) contained the E. faecium CECT 410T type strain, and also showed a high degree of genetic diversity. Cluster G2 (28% of the isolates) contained the E. faecalis CECT 481T type strain and was genetically more homogeneous. Virulence traits (haemolysin, gelatinase or DNAse activities, or the presence of structural genes cylL, ace, asal and esp) were not detected. All isolates were sensitive to the antibiotics ampicillin, penicillin, gentamicin, streptomycin and chloramphenicol. A high pecentage of isolates were resistant to erythromycin and rifampicin. Many isolates showed intermediate sensitivity to several antibiotics (tetracycline, ciprofloxacin, levofloxacin, or quinupristin/dalfopristin). Vancomycin and teicoplanin resistance was detected in one strain, but vanA, vanB, vanC1, vanC2 or vanC3 genes were not detected. Many of the isolates showed functional properties of food or health relevance. Production of antimicrobial substances was detected in 17 of the isolates, and 14 of them carried structural genes for enterocins A, B and/or P.     

Intracellular production of Brucella L forms . II. Induction and survival of Brucella abortus L forms in tissue culture

Hatten, Betty A. (The University of Texas Southwestern Medical School, Dallas), and S. Edward Sulkin. Intracellular production of Brucella L forms. II. Induction and survival of Brucella abortus L forms in tissue culture. J. Bacteriol. 91:14-20. 1966.-Intracellular survival of altered brucellae, possibly L forms, was not greatly affected by penicillin or streptomycin in concentrations ranging from 5.0 to 40 mug/ml, but a combination of these two antibiotics (2.5 to 20 mug/ml each) reduced the number of positive L-form cultures. Tetracycline (2.0 mug/ml) decreased the number of positive L-form cultures at about the same rate as combinations of the higher concentrations of penicillin and streptomycin. Various concentrations of tetracycline (0.1 to 2.0 mug/ml) with 5.0 mug/ml of penicillin or streptomycin significantly reduced the number of positive L-form cultures. L forms were recovered for several days after elimination of bacteria from the cultures by all of the antibiotics tested. L-form production was not dependent upon the presence of antibiotics in the culture medium, but they were recovered in greater numbers when bacteria were still present in the hamster kidney cells. Addition of thallium acetate to infected cells (at varying intervals of time after infection) to control bacterial growth and conversion to the L phase during cellular disintegration decreased the number of positive L-form cultures obtained over a 10-day period. Comparison of the antibiotic sensitivity of bacteria recovered from infected tissue culture cells with the stock strain of Brucella abortus indicated that some resistance to penicillin and tetracycline had developed. A marked resistance to streptomycin was observed in those bacteria recovered from cells maintained in the presence of this antibiotic.     

Comparative Trial of Tetracycline,Chloramphenicol, and Trimethoprim Sulphamethoxazole in Eradication of Vibrio cholera El Tor

A comparison of tetracycline, chloramphenicol, and trimethoprim/sulphamethoxazole showed that all hasten the eradication of Vibrio cholerae from the stools of patients with cholera.A four-day period of tetracycline or trimethoprim/ sulphamethoxazole was adequate for eradicating V. cholerae from the stools of all patients, but three days, as suggested by the W.H.O. Expert Committee, was not. Four days of chloramphenicol therapy was sufficient for most patients, but a minority required up to seven days'' therapy.Purging produced reappearance of V. cholerae in the stools of one-eighth of the patients who had had three successive daily negative stool cultures; such patients are a potential danger to the population.     

Occurrence and antibiotic sensitivity of Enterobacteriaceae isolated from a group of Jordanian patients with community acquired urinary tract infections

The type and antibiotic sensitivity of urinary tract pathogens may differ in various communities. Of 207 isolates recovered from midstream urine specimens collected from a group of patients with community acquired urinary tract infections (UTI), 86% were species of Enterobacteriaceae. The most frequently recovered pathogens were Escherichia coli (82%), Klebsiella spp. (7.3%), Proteus spp. (6.2%), Enterobacter spp. (3.4%) and Citrobacter spp. (1.1%). High rates of resistance were found against ampicillin (95%), tetracycline (86%), carbenicillin (84%), trimethoprim/sulphamethoxazole (48%), and amoxycillin/clavulanic acid (45%). For the antibiotics tobramycin, aztreonam, ceftriaxone and gentamicin 7% of the isolates were resistant, while resistance varied from 9-18% for amikacin, ciprofloxacin, norfloxacin, nalidixic acid and cefuroxime. The incidence of UTI caused by Enterobacteriaceae was three times higher in females than in males, particularly in young and middle age groups (< or = 19 and 20-39 years).     

Molecular characterization of Salmonella weltevreden isolated from poultry: evidence of conjugal transfer of plasmid and antibiotic resistance

Ten strains of Salmonella weltevreden isolated from poultry sources were examined and found to contain plasmid DNA ranging in size from 1.8 to 68.5 MD. All isolates were susceptible to carbenicillin, cephalothin, ceftriazone, gentamicin, kanamycin and nalidixic acid, but resistance to bacitracin (100%), penicillin G (100%), rifampicin (100%), sulphamethoxazole (100%), cefuroxime (80%) and tetracycline (60%) was recorded. The 55 MD plasmid of strain SW5 determined resistance to penicillin G and tetracycline, which was transmissible to the E. coli K12 recipient at a frequency of 3.52 x 10(-5) transconjugants per input donor cell. The results of arbitrarily primed polymerase chain reaction (AP-PCR), using two 10-mer oligonucleotides and PCR-ribotyping to differentiate between the ten strains of S. weltevreden were compared. The strains were separated into ten different genome types by AP-PCR but were indistinguishable by PCR-ribotyping. These results suggest that poultry may constitute a reservoir for disseminating antibiotic resistance and that AP-PCR may be a valuable tool for epidemiological studies.     

Long-term antibiotic susceptibility pattern of strains of Neisseria gonorrhoeae isolated in Czechoslovakia in the years 1957-1982

Over the past 25 years a total of 7492 strains of Neisseria gonorrhoeae have been isolated in Czechoslovakia, mainly in Prague (64%). All these strains have been tested for susceptibility to the following antibiotics: penicillin G, ampicillin, tetracycline, spectinomycin, erythromycin, doxycycline, kanamycin, rifampin, chloramphenicol, gentamicin, cephalothin, cephaloridine, lincomycin and clindamycin. In addition, seven derivatives of newer antibiotics of penicillin and cephalosporin series were tested in 1981. The study showed that in 1957 the MIC of 0.03 units of penicillin per ml was effective against 95% of strains, but in 1981 only 37% of isolates were sensitive to this concentration. The first gonococcal strains with the MIC value of 4.0 units/ml to penicillin were detected in 1981. This tendency towards decreased gonococcal susceptibility to benzylpenicillin is alarming. Over the last eight years there have been described sporadic isolations of strains relatively resistant to tetracycline (MIC = 8.0 mg/l). The susceptibility to spectinomycin has been tested in over 4000 gonococcal strains, since 1967. The test showed that this antibiotic remained highly effective against the gonococcal infection with over 95% of gonococci with the MIC value of 16.0 mg/l. No fully spectinomycin resistant strains have been found. Penicillin G as well as spectinomycin and cefotaxim are still considered the antibiotics of the first choice in the treatment of gonorrhoea. The alternative antibiotics may include cefuroxim, chloramphenicol and, in cases of sensitive strains, tetracyclines.     

Macrolide resistance and <Emphasis Type="Italic">In Vitro</Emphasis> selection of resistance to antibiotics in <Emphasis Type="Italic">Lactobacillus</Emphasis> isolates

Spreading of resistance to antibiotics is of great concern due to the increasing rate of isolation of multiresistant pathogens. Since commensal bacteria may transfer determinants of resistance to pathogens, studies on development of resistance should include also lactobacilli. Resistance to macrolides, penicillins and tetracycline was determined in 40 isolates of Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus crispatus, and Lactobacillus casei isolated from faeces of apparently healthy volunteers. Frequency of mutation and changes in susceptibility after serial exposure to these antibiotics at concentrations of 4× and 8× MIC were evaluated in susceptible isolates. Acquired resistance was defined as an increment in MIC values of at least four times in respect to the pre-selection values. Resistance to macrolides and/or tetracycline was identified in 14 and 4 isolates, respectively. ermB gene and A2058G mutation in 23S rRNA were detected in macrolide resistant isolates. Frequencies of mutation of susceptible isolates (n=26) were lower for ampicillin and erythromycin than for tetracycline. Serial exposure to antibiotics led to selection of resistant mutants. However, acquired resistance was rather unstable and was lost after subcultures in antibiotic-free medium in most mutants. Resistance to erythromycin was associated to a A2058G mutation in 23S rRNA. In conclusion, results indicate that resistance to macrolides and tetracycline is present among intestinal lactobacilli. Decrease in susceptibility following serial exposure to antibiotics might occur in lactobacilli, in a strain- and antibiotic-dependent way. Since lactobacilli are often used as probiotics, their ability to acquire resistance should be evaluated for isolates candidate to be included in probiotics based products.     

Susceptibility of various purple and green sulfur bacteria to different antimicrobial agents

Abstract Several purple and green sulfur bacteria (genera Chromatium, Thiocapsa and Chlorobium ) were tested for their sensitivity to different antimicrobial agents by a disc diffusion assay, using thioacetamide as a source of hydrogen sulfide for plate growth. Chlorobium limicola strains were more sensitive to amoxicillin, erythromycin and nalidixic acid, whereas gentamicin and netilmicin were more active against the purple bacteria tested. None of the organisms were sensitive to oxacillin and trimethoprim + sulfamethoxazole. The critical concentrations at the edge of the inhibition zone were also calculated for three organisms and the antimicrobials colistin, mitomycin C, penicillin G, rifampicin, and streptomycin. The results obtained suggest that colistin, mitomycin C, penicillin G would provide selective conditions against the growth of Chlorobium limicola strains, while streptomycin and other aminoglycoside antibiotics would select against purple bacteria.     

Uterine Microbiology and Antimicrobial Susceptibility in Isolated Bacteria from Mares with Fertility Problems

Uterine microbiology and antimicrobial susceptibility was investigated in 239 mares with fertility problems in a prospective study in Sweden. Uterine swab samples were collected with double guarded swabs and transported overnight before being cultured. The Minimum Inhibitory Concentrations (MIC) was determined for a panel of antimicrobials. From 152 of the 239 mares at least one bacterial species was isolated, most frequently E. coli (104 isolates), β -haemolytic streptococci (31) and fungi (16). β -haemolytic streptococci were more frequently (p < 0.01) associated with clinical endometritis than with repeat breeding. The opposite was true for E. coli (p < 0.01). Among β -haemolytic streptococcal isolates some resistance was noted for 4 of 11 tested antibiotics, however, all isolates were susceptible to the widely used penicillin G. Among E. coli isolates enrofloxacin was the only of the 10 tested antibiotics for which no resistance was noted. Resistance was most commonly noted to cephalothin (39% of the isolates), streptomycin (22%), trimethoprim/sulphamethoxazole (15%) and ampicillin (11%). In conclusion, we show that both E. coli and β -haemolytic streptococci are frequently associated with fertility problems in mares and that antimicrobial resistance is a common feature of E. coli but also recognised for β -haemolytic streptococcal uterine isolates.