Microbial resistance to antibiotics

Organisms that are normally sensitive to the action of an antibiotic may sometimes develop resistance or insensitivity to it. This, they may do through destroying the antibiotic or by retaining their growth even in the presence of the drug. Microbial resistance to antibiotics is now widespread and poses a serious clinical threat. Microorganisms develop resistance to antibiotics by any of the following mechanisms: selection, mutation, phage transduction, and transference while microbial resistance can either be inherent in the organism or acquired through the environment. Factors that have led to thecontinued occurrence of bacterial resistance to antimicrobial agents include: over prescription of antibiotics, use of under dose, prescribers’ irrational attitudes, patients’ demands, inappropriate advertisements and use of antibiotics in agriculture. Microbial resistance to antibiotics can thus beminimized through proper enlightenment, more rational antibiotic selection during treatment and proper legislation

Soil bacterial consortia and previous exposure enhance the biodegradation of sulfonamides from pig manure

Persistence or degradation of synthetic antibiotics in soil is crucial in assessing their environmental risks. Microbial catabolic activity in a sandy loamy soil with pig manure using C-12- and C-14-labelled sulfamethazine (SMZ) respirometry showed that SMZ was not readily degradable. But after 100 days, degradation in sulfadiazine-exposed manure was 9.2%, far greater than soil and organic manure (0.5% and 0.11%, respectively, p < 0.05). Abiotic degradation was not detected suggesting microbial catabolism as main degradation mechanism. Terminal restriction fragment length polymorphism showed biodiversity increases within 1 day of SMZ spiking and especially after 200 days, although some species plummeted. A clone library from the treatment with highest degradation showed that most bacteria belonged to alpha, beta and gamma classes of Proteobacteria, Firmicutes, Bacteroidetes and Acidobacteria. Proteobacteria (alpha, beta and gamma), Firmicutes and Bacteroidetes which were the most abundant classes on day 1 also decreased most following prolonged exposure. From the matrix showing the highest degradation rate, 17 SMZ-resistant isolates biodegraded low levels of (14) C-labelled SMZ when each species was incubated separately (0.2-1.5%) but biodegradation was enhanced when the four isolates with the highest biodegradation were incubated in a consortium (Bacillus licheniformis, Pseudomonas putida, Alcaligenes sp. and Aquamicrobium defluvium as per 16S rRNA gene sequencing), removing up to 7.8% of SMZ after 20 days. One of these species (B. licheniformis) was a known livestock and occasional human pathogen. Despite an environmental role of these species in sulfonamide bioremediation, the possibility of horizontal transfer of pathogenicity and resistance genes should caution against an indiscriminate use of these species as sulfonamide degraders