Prevalence of Ciprofloxacin Resistance Among Gram-Negative Bacilli at a Specialist Hospital in Saudi Arabia

Ahmad S Abstract: Background: Resistance to antimicrobials of different structural classes including fluoroquinolones has arisen in a multitude of bacterial species both in the community and the hospitals. This may complicate the therapeutic management of infections. Decreased susceptibility to fluoroquinolones arises mainly by singlestep mutations in the gyrA and parC genes, which encode the fluoroquinolones targets, the topoisomerase enzymes, conferring cross resistance to all fluoroquinolones. Accumulation of multiple mutations in several genes confers increasing level of resistance associated with clinical failure. However, even low level resistance can generate therapeutic failure. In 1998, some mobile elements with a potential for the horizontal transfer of the quinolone resistance genes were described. The loci which are responsible for this plasmid-mediated quinolone resistance, which have been designated as qnrA, qnrB and qnrS, have been identified in the Enterobacteriaceae species. Aim: To evaluate the susceptibility pattern of the isolates to various antibiotics and to know the prevalence rate of ciprofloxacin resistance in our hospital. Materials & Methods: A total of 916 gram-negative bacilli (GNB) were isolated from different clinical specimens over a period of nine months, were subjected to antibiotic susceptibility testing. Isolates with resistance or with a decreased susceptibility to ciprofloxacin (£20 mm) were then screened for their minimum inhibitory concentration (MIC) by using the E-test. Results: Out of 916 GNB, 321 (35%) isolates were resistant to ciprofloxacin. The MIC of these isolates ranged from 4 to >32?g/ml. Conclusion: The resistance rate to ciprofloxacin was 35% in our study. Most of the ciprofloxacin resistant isolates were from urinary tract infections (UTI). The ciprofloxacin resistance was also closely associated with multi-drug resistance, thus limiting the treatment options. Ciprofloxacin resistance can be used as a general surrogate marker of multidrug resistance, thus limiting the already restricted treatment options. The considerably high MIC values for ciprofloxacin in this study reflected the extent of the treatment problems for these resistant isolates and a need for the continuous evaluation of the commonly used antibiotics.


Introduction:
Fluoroquinolone antimicrobial drugs were a major therapeutic advance of the 1980s because they have 100-fold greater activity than their parent compound, nalidixic acid 1 .Unlike nalidixic acid, which is used only for urinary infections and occasionally shigellosis, the fluoroquinolones have a broad range of therapeutic indications and are given as prophylaxis, e.g., for in veterinary medicine fluoroquinolones are used as treatment and metaphylaxis but not as growth promoters.Early researchers thought that fluoroquinolone resistance was unlikely to evolve, largely because resistant Escherichia coli mutants are exceptionally difficult to select in vitro 2 and because plasmid-mediated quinolone resistance remained unknown even after 30 years of nalidixic acid usage.Nevertheless, mutational fluoro-quinolone resistance emerged readily in staphylococci and pseudomonads, which are inherently less susceptible than E. coli.More recently, fluoroquinolone resistance has emerged in E. coli and other Enterobacteriaceae, contingent on multiple mutations that diminish the affinity of its topoisomerase II and IV targets in varying ways reduce permeability, and up regulate efflux 3 .Plasmid-mediated quinolone resistance has been reported, but it is exceptional 4 .
Ciprofloxacin is a broad-spectrum antibiotic which is active against both gram-positive and gram-negative bacteria, which belongs to the fluoroquinolone class 5 .Bacterial resistance is a growing therapeutic problem, both in the community and the hospitals, involving all the antibiotics, which include fluoroquinolones.A decreased susceptibility to fluoro- .This study was undertaken to evaluate the susceptibility of GNB to various antibiotics and to know the prevalence rate of ciprofloxacin resistance in our hospital.

Materials and Methods:
A total of 916 gram-negative bacilli were isolated from different clinical specimens i.e., urine, pus, sputum, blood etc, received in the Microbiology Laboratory over a period of nine months were subjected to the study.Specimens were processed using different media like MacConkey's agar, Cystein Lactose Electrolyte Deficient (CLED) Agar, Sheep Blood Agar and Chocolate Agar.All isolates were identified using standard biochemical tests 9 .In addition commercially available biochemical kits, API 20E (Analytic Profile Index system, La Balme les Grottes, France) were also used for the identification of enteric pathogens.
Antibiotic sensitivity testing was performed using the disc diffusion method on 85 mm Mueller-Hinton agar (Oxoid) plates with agar depth of 4 mm.The bacterial suspension that was prepared for antibiotic sensitivity testing on Mueller-Hinton agar was adjusted to the recommended turbidities for all species 10 .
The Clinical Laboratory Standards Institute (CLSI) break points were used for interpretation of susceptibility patterns as sensitive or resistant 11 . Isolates with resistance or with decreased susceptibility to Ciprofloxacin (?20mm) were subjected to further study.This study design and protocol was approved by 'Research and Ethics Committee' of the institute.

E-Test
The resistance to ciprofloxacin was confirmed by breakpoint minimum inhibitory concentration (MIC in ?g/ml) by using E-test strips.The isolates with MIC value ?4 ?g/ml were defined as resistant isolates, as outlined by CLSI guidelines 11 .
Results:Escherichia coli (29.4%) was the most predominant isolate which was found among the GNB, followed by Klebsiella pneumoniae (26.2%)Pseudomonas aeruginosa (25.0%) and Proteus species (12.9%) as shown in Table I.

Table I: Total number of Gram-negative Bacilli isolated from different clinical specimens (n=916)
Out of 916 gram-negative bacilli, 321 (35%) isolates were resistant to ciprofloxacin.High rates of resistance were observed for Ampicillin and Amoxicillin-Clavulanic Acid, followed by Cephalothin, Trimethoprim-Sulphamethoxazole, and cefotaxime, while low levels of resistance were observed for nitrofurantoin, nalidixic acid, amikacin and norfloxacin, as shown in Table II The lowest level of resistance was observed for imipenem (4%).The resistance rate for ciprofloxacin was 35%.The MIC of ciprofloxacin for these isolates ranged from 4 to >32 ?g/ml (Table III).

Table III: MIC values of the resistant Gram Negative Bacilli to Ciprofloxacin (n=321)
The isolated bacteria showed wide differences in their susceptibility to ciprofloxacin.A high rate of resistance to ciprofloxacin was observed among Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter sps., and Proteus sps.followed by E. coli.

Discussion:
Evolution of reduced susceptibility to the quinolones is causing concern following rapidly rising rates of fluoroquinolone-resistant E. coli in many parts of the world 12 .The Surveillance Network database (http://www.mrlworld.com)shows resistance trends (with intermediate counted as resistant) in bloodstream isolates from 250 U.S. hospitals as follows: E. coli, 1.8% in 1996 and 4.3% in 1999; Klebsiella spp., 7.1% in 1996 and 6.7% in 1999; Enterobacter spp., 6.6% in 1996 and 6.5% in 1999; and P. mirabilis, 5.7% in 1996 and 12.7% in 1999.Much higher rates are reported from Barcelona, Spain, where 17% of E. coli isolates from community infections were ciprofloxacin resistant 13 , and India, where up to 50% of hospital E. coli are reported resistant 14 .High rates in E. coli may reflect contamination via the food chain: the Spanish study found quinolone-resistant E. coli in 90% of chicken feces and noted similar fecal carriage rates of resistant E. coli in children and adults.There is a small set of drugs commonly used to treat P. aeruginosa infection, including ciprofloxacin, tobramycin, gentamicin, ceftazidime, and imipenem.While P. aeruginosa has developed various levels of resistance to each of these, its response to ciprofloxacin is of particular interest because the drug is initially very effective, but P. aeruginosa rapidly acquires highlevel resistance, rendering the drug impotent.In clinical isolates, approximately 30% of strains now present high-level ciprofloxacin resistance 15 .
The resistance rate for ciprofloxacin was 35% in our study.Most of the ciprofloxacin resistant isolates were obtained from UTI samples.This may be because fluoroquinolones are preferred as the initial agents for empiric therapy in UTI, because of their excellent activity against the pathogens which are commonly encountered in UTI 16 .This emphasises the importance of the re-assessment of the antibiotics which are used in the empiric treatment of UTIs.Most of the isolates from UTIs were susceptible to nitrofurantoin, nalidixic acid, amikacin and imipenem.This was in agreement with the finding of a study reported by Astal ZE, 2005 17 .
These data suggest that nitrofurantoin can still be successfully used in the treatment of UTI.The ciprofloxacin resistance was also closely associated with multi-drug resistance, thus making the treatment options limited 18 .Ciprofloxacin resistance can be used as a general surrogate marker of multi-drug resistance.Hence, it severely limits the already restricted treatment options.This finding was in accordance with the finding of a study which was conducted by Paterson et al 19 .The high resistance pattern which was seen in our study was probably due to the inappropriate prescribing of antibiotics, lack of antibiotic policy and the poor infection control strategies.But the antibiotic history could not be properly elicited from the patients in this study.
Ciprofloxacin remains a potent antibiotic; but the slow accumulation of resistant Enterobacteriaceae is disturbing, not least because resistance is a class effect, affecting all fluoroquinolones.Ultimately, this resistance may be partly overcome by inhibiting the efflux pumps that contribute to the resistance but this strategy is still several years from fruition.In the interim, the best approach lies in the prudent use of fluoroquinolones in humans and animals, coupled with an emphasis on preventing patient-to-patient spread of resistant strains.
The antibiotic which showed maximum activity against most of the isolates was imipenem.Though carbapenems remain the final options for treating these infections, there is a possibility that the increasing use of carbapenems may lead to a rapid emergence of carbapenem resistance.

Conclusion:
The considerably high MIC values for ciprofloxacin in this study reflect the limited treatment options which are available for these resistant isolates and a need for the continuous evaluation of the commonly used antibiotics.Repeated surveillance, the formulation of an antibiotic policy, the prudent prescription of antibiotics and the recycling of antibiotics are the possible routes which can be used to curb the rapid emergence and the spread of these resistant isolates.

Table II : Antibiotic Susceptibility pattern of the isolates to various antibiotics (n=916)
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