Efficacy of silver nanoparticles against multidrug resistant clinical Staphylococcus aureus isolates from Nigeria

Multidrug resistant (MDR) S. aureus infections continue to account for excess mortality in hospital and community settings and constitute a rising global health problem. However, data on the efficacy and mechanism of actions of alternative solutions like silver nanoparticles in developing countries are lacking. This study investigated anti-staphylococcal activity of silver nanoparticles (AgNP) against local strains from Nigeria. A total 119 clinical isolates of S. aureus from five Nigerian laboratories categorized as MRSA (n = 52) and MSSA (n = 67) by PCR were studied. The MIC of AgNP produced by chemical reduction method and characterized by surface plasmon resonance absorbance and size equivalence by scanning electron microscopy was determined by microbroth dilution method. Its effect on protease activity and plasmids were also investigated. Baseline characteristics of the isolates revealed MDR phenotype of the isolates, carriage of diverse plasmids (15-32 kb) among the MDR MSSA, and mean extracellular protease activity of 24.8-55.7 U/mL. The chemically synthesized AgNP had a peak absorbance at 400 nm with a size equivalence of 4.58 nm. The MICs of AgNP against the isolates were 4.7 μg/mL and 4.9 μg/mL, respectively, for MRSA and MSSA (P > 0.05). The bactericidal effect of AgNP at 2.5-5 μg/mL on the MSSA and MRSA isolates was observed at 2.7-5.5 h post exposure in vitro. Further analysis revealed plasmid eviction in the MDR MSSA isolates exposed to 5 μg/mL AgNP and dose-dependent reduction in extracellular protease activity by 84.6-93.1%. Hemolysis of human erythrocytes by AgNP was not observed at the MIC range. Conclusion: This study revealed safety and efficacy of AgNP against clinical MDR S. aureus isolates from Nigeria, using plasmid eviction and protease inhibition as mechanisms of action.

Occurrence of extended-spectrum and AmpC β-lactamases in multiple drug resistant Salmonella isolates from clinical samples in Lagos, Nigeria

PURPOSE

Salmonella spp. are important foodborne pathogens exhibiting increasing resistance to antimicrobial drugs. Resistance to broad-spectrum β-lactams, mediated by extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase enzymes is fast spreading and has had negative impacts on the clinical outcomes, particularly on third-generation cephalosporins. This study investigated the carriage of AmpC gene among multidrug-resistant Salmonella spp. from Lagos, Nigeria.

METHODS

Forty Salmonella spp. from clinical samples (S. typhi = 13; S. typhimurium = 10; S. enteritidis = 8; S. choleraesuis = 5; S. paratyphi = 4) were subjected to in vitro susceptibility test by disk diffusion methods. Isolates that were resistant to cefoxitin and third-generation cephalosporins were screened for ESBL (Double Disk Synergy Test Method) and AmpC enzyme (AmpC disk test) production. Detection of AmpC fox gene was carried out by polymerase chain reaction.

RESULTS

Thirty-two (80%) of the Salmonella isolates were cefoxitin resistant. Plasmid-mediated AmpC β-lactamase and ESBL enzymes were recorded in 10/40 (25%) and 16/40 (40%) of the Salmonella isolates, respectively. Specifically, 16/40 (40%) of the Salmonella isolates possessed 380 bp AmpC fox gene, with the highest occurrence found in S. typhi strains (43.8%) followed by S. typhimurium (25%). There was no AmpC fox gene detected in S. paratyphi strains. Interestingly, coproduction of enzymes occurred in some of the isolates, raising fears of resistance to a multitude of antibiotics in the treatment of bacterial infections.

CONCLUSION

Emergence of AmpC β-lactamase-producing Salmonella isolates in our environment was recorded for the first time, raising concern on increased antibiotic resistance among strains of Salmonella serovars in Lagos. Further genotypic study of the isolates could answer the questions on strain sources, clonal relatedness, and mechanism of spread.

Multidrug resistance in Salmonella enterica serovar typhi isolated from patients with typhoid fever complications in Lagos, Nigeria

OBJECTIVE

The aim of this study was to determine the prevalence of Salmonella enterica serovar typhi in patients with pyrexia of unknown origin (PUO), and antimicrobial resistance in strains isolated from patients with S. typhi in Lagos, Nigeria.

STUDY DESIGN

In total, 103 patients were included in this study, subdivided into two categories. Category A comprised 74 patients presenting with PUO, and Category B comprised 29 patients harbouring S. typhi who did not respond to initial treatment.

METHODS

Blood samples were cultured for bacterial isolates and identified by standard procedures. Susceptibility testing was performed according to the National Committee for Clinical Laboratory Standards. Plasmid DNA extraction was performed using the alkaline lysis method with Escherichia coli v517 used as the standard. Conjugation and transformation experiments were performed using standard methods. For the latter, E. coli K12 HB 101 (ara-14, galK2, hsd 520, lacyl, leu, mtl-1, Pro A2, rec A13, rps L20, sup E44, thii xyl-5) was used as the recipient and plasmid PBR 322 was used as the positive control.

RESULTS

The prevalence of S. typhi in PUO was 16.2% (12/74). In all, 25 of 41 (61.0%) cases were multidrug resistant (MDR) with phenotypic-resistant patterns: ACoCT, ACTCeS, ACTCoCe and ACTS were commonly encountered among the strains. Interestingly, four of the strains harbouring similar plasmid DNA were isolated from patients with hepatosplenomegaly, and a strain harbouring a large transferable plasmid of 81.2MDa was isolated from a psychosis patient.

CONCLUSIONS

Our study confirmed the circulation of MDR S. typhi in Lagos, Nigeria. Periodic review of antibiotics used in hospitals is essential as the efficacies of chloramphenicol, ampicillin and cotrimoxazole are now doubtful. Ciprofloxacin and ofloxacin are effective drugs for treatment of typhoid fever, but with current trends of drug abuse in Nigeria, resistance is likely to develop. These results, therefore, provide an early warning signal for the prudent use of fluoroquinolone antimicrobials to preserve their usefulness.

Screening of some medicinal plants used in south-west Nigerian traditional medicine for anti-Salmonella typhi activity

Ten Nigerian medicinal plants used traditionally for the treatment of several ailments of both microbial and non-microbial origins were tested on multi-drug resistant S. typhi (MDR) strains of which six of them were active. The results revealed that both the aqueous and ethanol extracts of Terminalia avicennioides, Momordica balsamina, Combretum paniculatum and Trema guineensis were effective on the MDR-S. typhi strains with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranging from 9.60 to 14 mcg/ml and 24 to 33 mcg/ml, respectively. Whereas, only the aqueous extracts of Morinda lucida and Ocimum gratissimum were found to be active against this pathogen with MIC and MBC values of 9.60 and 24 mcg/ml for M. lucida, 40 and 55 mcg/ml for O. gratissimum, respectively. There was no statistical significant difference (P > 0.05) between the activity of each plant extract and the decoctions prepared from them. All the six active plants showed positive reactions to alkaloids, tannins, flavonoids and anthraquinones but in variable degrees. All but M. balsamina, indicated the presence of saponin.

Prevalence of multi-drug resistant Salmonella typhi among clinically diagnosed typhoid fever patients in Lagos, Nigeria

A total of 635 clinically diagnosed typhoid fever patients were bled from three different health institutions in the metropolis of Lagos, Nigeria over a period of 15 months, May 1997 to July 1998. Out of the total blood cultured, 101 (15.9%) isolates of Salmonella species were isolated of which 68 (67.3%) were S. typhi, 17 (16.8%) and 16 (15.8%) were S. paratyphi A. and S. arizonae respectively. The overall isolation rate of S. typhi among patients is 10.7%, with most isolates 45.9% found among the severely-ill young adults, age group 16-30 years. All isolates were subjected to anti-microbial susceptibility testing using 12 different antibiotics: chloramphenicol, ampicillin, cotrimoxazole, gentamicin, colistin sulfate, nalidixic acid, nitrofurantoin, cefotaxime, tetracycline, streptomycin, ofloxacin and ciprofloxacin. All the S. typhi and S. paratyphi A isolates showed resistance to two or more of the 10 of 12 antibiotics tested particularly the 3-first-line antibiotics commonly used (chloramphenicol, ampicillin and cotrimoxazole) in the treatment of typhoid fever in Nigeria. No isolate showed resistance to ofloxacin and ciprofloxacin, however, nalidixic acid and gentamicin showed a moderate and appreciable inhibition to most of our isolates.

Escherichia coli in patients with acute gastroenteritis in Lagos, Nigeria

Over a period of 12 months, a total of 852 stool samples from patients (both children and adults) with acute diarrhoeal diseases attending some public and government recognised health institutions in Lagos metropolis were screened for diarrhoeagenic bacterial agents. One hundred and eighty two bacterial isolates were found out of which 83 (45.6%) were Escherichia coli, 38 (20.9%) Shigella spp, 31 (17%) Salmonella spp, 16 (8.8%) Klebsiella spp, eight (4.4%) Aeromonas spp, while there were only six (3.3%) isolates for Plesiomonas spp. Of the 83 isolates for E. coli group, 49 (59%) were enteropathogenic (EPEC), 17 (20.5%) enterotoxigenic (ETEC), 10 (12.1%) enteroinvasive (EIEC) and seven (8.4%) enterohaemorrhagic (EHEC). The EPEC strains particularly serotype 055, were mostly encountered in children aged over five years. On the other hand, EIEC and ETEC strains were found mainly in adults while EHEC O157: H7 strains occurred in all the age groups studied. This study further stresses the important role of EIEC and ETEC in acute diarrhoeal diseases and the possible implication of EHEC in acute gastroenteritis, especially in children in Lagos, Nigeria.